Screw element having axially asymmetrical screw profile having at least two construction points located within screw profile

Abstract

To provide a screw element which has an axially asymmetrical screw cross-sectional profile which has at least two construction points located within the screw cross-sectional profile.SOLUTION: In an extruding molding machine having two drive shafts which rotate in the same direction and at the same speed in order to process or produce a plastic material as an extruded molding object. screw elements, relating to the arrangement of the two identical or different screw elements, are located opposite each other as a pair on the two drive shafts. The extruding molding machine is equipped with the two screw elements located opposite each other as a pair on the two drive shafts, and being identical or different, and each having an axially asymmetrical screw cross-sectional profile which has at least two construction points located within the screw cross-sectional profile.SELECTED DRAWING: Figure 6b

Description

Technical Field

[0001] The present invention relates to a screw element having a screw cross-sectional profile with at least two plotting points present within a non-axisymmetric screw cross-sectional profile. The screw element according to the present invention is suitable for use in an extruder having two drive shafts that rotate in the same direction and at the same speed for processing or producing a plastic material in the form of an extruded product. The present invention also relates to the arrangement of two identical or different screw elements according to the present invention in an extruder having two drive shafts that rotate in the same direction and at the same speed, wherein the screw elements according to the present invention are paired and positioned opposite each other on the two drive shafts. The present invention further relates to an extruder comprising two identical or different screw elements according to the present invention and having two drive shafts that rotate in the same direction and at the same speed, wherein the screw elements according to the present invention are paired and positioned opposite each other on the two drive shafts. Furthermore, the present invention further relates to the use of the screw element according to the present invention for processing or producing a plastic material.

Background Art

[0002] In an arrangement of two identical or different screw elements according to the present invention in an extruder having two drive shafts that rotate in the same direction and at the same speed, wherein the screw elements according to the present invention are paired and positioned opposite each other on the two drive shafts, the screw elements according to the present invention that are paired and positioned opposite each other on the two drive shafts partially, rather than completely, clean each other.

[0003] The screw elements according to the present invention are also suitable for use in an extruder having three or more drive shafts, for example, an extruder having four or more or five or more drive shafts, or an annular extruder having eight to sixteen, particularly twelve drive shafts arranged annularly with respect to each other, which is known. In this regard, the same or different screw elements according to the present invention are arranged on the drive shafts in numbers corresponding to the number of drive shafts of each extruder, opposite to each other.

[0004] An arrangement of three or more identical or different screw elements according to the present invention in an extruder having three or more drive shafts rotating in the same direction and at the same speed, wherein the screw elements according to the present invention are paired and located opposite to each other on three or more drive shafts, and even if the screw elements according to the present invention paired and located opposite to each other on three or more drive shafts partially clean each other rather than completely.

[0005] The screw cross-sectional profile is hereinafter also simply referred to as the screw profile. In the context of the present invention, a drafting point is understood to mean a point at which at least one arc of the screw profile is drafted and which is the center of this at least one arc. In this regard, the center of the arc represents a point that is the center of the circle of which the relevant arc is a part.

[0006] The term "arc" means that the arc is not only a point on the screw profile, but also has at least two points with different and non-zero angular intervals from each other, and all points of the arc have the same center and the same radius, and the arc is a part of a circular line belonging to a sector. The angular interval is hereinafter also referred to as the central angle.

[0007] Two arcs directly adjacent to a specific arc are on the one hand, the arc directly preceding the specific arc, and on the other hand, the arc directly following the specific arc.

[0008] Adjacent arcs have a common contact point. If the screw profile can be differentiated at this contact point, the two arcs with this common contact point have different radii. This is because if these two arcs had the same radius instead, the two arcs could combine to form a larger arc. If the screw profile cannot be differentiated at this contact point, the two arcs with this common contact point can have different radii or the same radius.

[0009] The drive shaft of an extruder equipped with a screw element is hereinafter also referred to as the screw shaft, regardless of whether the screw element pertains to the present invention or the prior art.

[0010] Screw elements suitable for use in an extruder having two drive shafts rotating in the same direction and at the same speed for processing or producing a plastic material in the form of an extruded product have been known for many years. For example, Non-Patent Document 1 provides a detailed and appropriate overview of the prior art regarding such screw elements and extruders. An "extruder" is hereinafter also referred to as a "lathe".

[0011] In the case of screw elements according to the prior art, the problems that occur frequently individually or concurrently are as follows. - The mixing action is inappropriate. - A non-uniform force distribution occurs between the inner wall of the housing of the extruder and the thread lands of these screw elements, particularly between the inner wall of the housing and the screw thread land closest to the housing. - The angle of the screw thread land closest to the housing cannot be freely selected. -When the extruder is partially filled, a uniform distribution of the extrudate is not guaranteed. By "partially filled" it is to be understood in particular that in a part of the extruder, the actual throughput of the extrudate is lower than the maximum throughput possible through this part without pressure build-up, preferably at least 10% lower, particularly preferably at least 20% lower, very particularly preferably 25% to 75% lower. -In recent years, the screw profile has not been based on a standard screw profile such as the Erdmenger screw profile, and as a result, the drafting cost and the manufacturing cost have been increasing.

[0012] Figure 5 of Patent Document 1 discloses an Erdmenger screw profile, and the centers (83, 83') of the Erdmenger screw profile are not the same as the rotation axes (84, 84') or the housing bores. Such a screw profile is called eccentric. The three-start Erdmenger screw profile disclosed in Figure 5 of Patent Document 1 is eccentrically positioned such that exactly one screw thread land 80 (or 80') forms a symmetric and narrow gap with respect to the inner wall of the housing, while the other two thread lands form the same but significantly larger gaps with respect to the inner wall of the housing. This type of positioning results in a non-uniform gap between the screw thread land 80 (or 80') and the housing, and as a result, a non-uniform force distribution occurs.

[0013] Also, the two-start and three-start Erdmenger screw profiles disclosed in Patent Document 1 have only one thread land tip. That is, the Erdmenger screw profile has a thread land angle of 0 degrees. Such a thread land tip is mechanically unstable. Similarly, an eccentrically positioned two-start thread land Erdmenger screw profile having a thread land angle greater than 0 degrees also has a non-uniform gap between the screw thread land and the housing, and as a result, a non-uniform force distribution occurs. -has a non-uniform gap between the screw thread land and the housing, and as a result, a non-uniform force distribution occurs.

[0014] Similarly, Patent Document 2 discloses a screw element with three eccentric threads. All the screw thread lands of this screw element have a thread land angle of 0 degrees, and thus it is mechanically unstable.

[0015] Patent Document 3 discloses screw elements with three and four eccentric threads. All the screw thread lands of this screw element have a thread land angle of 0 degrees, and thus it is mechanically unstable.

[0016] Patent Document 4 discloses a screw element whose cross-sectional contour is eccentrically offset with respect to the center of the housing bore and the rotation center of the conveying shaft. When the contours of the screw elements are arranged opposite to each other on the conveying shaft, they completely wear against each other. In this arrangement, the intention is to improve product quality and reduce the torque load peak on the support shaft, and thus essentially improve the cost-effectiveness of the extruder. Similarly here, due to this positioning similar to Patent Document 1, a non-uniform gap is generated between the screw thread land and the housing, and as a result, a non-uniform force distribution occurs. Furthermore, as a result of the screw element self-cleaning without limitation, the mass transfer is relatively poor. That is, only an inappropriate mixing action is achieved.

[0017] Patent Document 5 discloses a screw element having at least two threads, wherein the first thread land cleans the inner wall of the extruder housing with a small gap, and the second thread land cleans the inner wall of the extruder housing with a relatively large gap. In this arrangement, the intention is to provide a multi-screw extruder that can self-clean without limitation and significantly and effectively improve product quality. Since the screw element can self-clean without limitation, as a result, the mass transfer is relatively poor. That is, only an inappropriate mixing action is achieved.

[0018] As a result, even if the screw element according to Patent Document 4 or Patent Document 5 is used, it is not possible to satisfactorily solve the above problems.

[0019] What has been described above for Patent Document 5 also applies to Patent Documents 6 and 7 in the same manner.

[0020] Figures 6 to 8 of Patent Document 8 disclose a screw element with two threads, and the thread lands of this screw element have a radius that deviates significantly from the radius of the inner wall of the housing by more than the housing gap. Even with this configuration similar to Patent Document 1, a non-uniform gap is generated between the screw thread lands and the housing, resulting in a non-uniform force distribution. Regarding the screw element disclosed in Figure 9 of Patent Document 8, the same applies as what has been described above for Patent Document 5. In Figure 7 of Patent Document 8, the thread land has a thread land angle of 0 degrees. As further explained above, such a thread land tip is mechanically unstable.

Prior Art Documents

Patent Documents

[0021]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Non-Patent Documents

[0022]

Non-Patent Document 1

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0023] Therefore, an object of the present invention is to provide a screw element capable of solving the above-described problems.

[0024] In particular, an object of the present invention is to provide a screw element that enables the following when used in an extruder having two or more drive shafts. - Improving the mixing action. - Ensuring a uniform force distribution between the single or plural thread lands of the screw element and the inner wall of the housing of the extruder. - Handling the extruded product more carefully. - Ensuring a uniform distribution of the extruded product when the extruder is partially filled. In this regard, the single or plural thread lands of the screw element according to the present invention should be mechanically stable.

MEANS FOR SOLVING THE PROBLEM

[0025] The above object is achieved by a screw element having the features of the main claim.

[0026] In particular, the above object is a screw element having a number Z of grooves, suitable for a twin-shaft threading machine, the twin-shaft threading machine being Two screw shafts SW1 and SW2 rotating in the same direction and at the same speed, wherein the rotation axis D1 of the screw shaft SW1 and the rotation axis D2 of the screw shaft SW2 are separated by an axial distance a, two screw shafts SW1 and SW2, Two circular housing bores penetrating each other, each of the housing bores having the same housing inner radius rg and bore centers M1 and M2 of the housing bores separated by a distance equal to the axial distance a, and the bore centers M1 and M2 of the housing bores coinciding with the centers of the cross-sections of the respective rotation axes D1 and D2 of the screw shafts SW1 and SW2, two circular housing bores, having, The screw element is a screw profile, (1) forming a closed convex curve, (2) composed only of arcs with a radius of a or less in the axial direction, and directly adjacent arcs having different radii, (3) having a first plotting point K1 existing within the screw profile, (4) not axisymmetric with respect to the plotting point K1, (5) composed of at least 4, preferably 4 to 25, particularly preferably 4 to 17 arcs, (6) having a second plotting point K2 existing within the screw profile and not coinciding with the plotting point K1, (7) not point-symmetric or axisymmetric with respect to the plotting point K2, (8) coinciding with one of the bore centers M1 or M2 and having a rotation point DP existing on the path from the plotting point K1 to the plotting point K2, (9) having exactly one major thread land HK, the major thread land HK being formed from only one arc, the center of this arc being the plotting point K2, and the major thread land HK and the contact points of the two arcs directly adjacent to the major thread land HK being the set of points on the screw profile farthest from the plotting point K2, (10) having at least one groove, one groove being formed from only one respective arc whose center is the plotting point K1, one groove being an arc having a radius equal to the core radius ri, and two arcs directly adjacent to each one groove being at a greater distance from the plotting point K1 than the arc of this groove, except for their respective common contact points, (11) having a plurality of flanks, the flanks being regions of a screw profile that are arcs having a center that is neither the plotting point K1 nor the plotting point K2, (12) the groove being separated from the closest point of the main thread land HK by at least one arc that is a flank, achieved by a screw element having a screw profile.

[0027] Here, the number Z of grooves is understood to mean the number of grooves in the screw profile. The number Z of grooves is a natural number of 1 or more. The number Z of grooves is preferably a natural number from 1 to 4, and 2 grooves are particularly preferred.

[0028] According to the present invention, preferably, the screw profile according to the present invention is not point-symmetrical with respect to the plotting point K1, or is point-symmetrical, and preferably, the screw profile according to the present invention is not point-symmetrical with respect to the plotting point K1.

[0029] The arc forming the main thread land HK preferably has a central angle greater than 0 degrees, and the arc forming the main thread land HK preferably has a central angle from 1 degree to 179 degrees. As a result, when the screw element is used as intended, the main thread land HK, which is generally exposed to the greatest mechanical load, has a high mechanical stability compared to the prior art.

[0030] According to the present invention, the number of arcs of the screw profile according to the present invention is preferably equal to the number Z of grooves multiplied by 4, or equal to the number of grooves multiplied by 4 and then added by 1, that is, the screw profile according to the present invention is - when the number Z of grooves = 1, preferably composed of exactly 4 arcs, or exactly 5 arcs, and particularly preferably composed of exactly 5 arcs, - When the number of grooves Z = 2, it is preferably composed of exactly 8 arcs, or exactly 9 arcs, and particularly preferably composed of exactly 9 arcs. - When the number of grooves Z = 3, it is preferably composed of exactly 12 arcs, or exactly 13 arcs, and particularly preferably composed of exactly 13 arcs. - When the number of grooves Z = 4, it is preferably composed of exactly 16 arcs, or exactly 17 arcs, and particularly preferably composed of exactly 17 arcs.

[0031] According to the present invention, the second plotting point K2 of the screw profile according to the present invention preferably exists in a circle having the plotting point K1 as the center and the core radius ri as the radius, and the core radius ri is the radius corresponding to the minimum distance from the plotting point K1 and a point on the screw profile.

[0032] According to the present invention, it is particularly preferable that the second plotting point K2 of the screw profile according to the present invention exists in a circle having the plotting point K1 as the center and a radius that is at most 30%, very particularly preferably at most 20%, of the core radius ri.

[0033] Thereby, when the screw element is being used as intended, a situation is achieved in which it has high mechanical stability compared to the prior art. Also, this makes it possible to handle the extruded product more carefully compared to the prior art.

[0034] The rotation point DP of the screw element according to the present invention preferably exists closer to the plotting point K2 than to the plotting point K1, and particularly preferably, the rotation point DP exists on the plotting point K2.

[0035] The radius rHK of the arc of the major thread land HK preferably corresponds to the housing inner radius rg minus the major thread land gap c_HK. The major thread land gap c_HK is greater than 0 in this case. Here, the major thread land gap c_HK is preferably 0.1% to 3.2% of the housing inner radius rg, preferably 0.2% to 2.6%, particularly preferably 0.3% to 2.0%, and very particularly preferably approximately 0.8% to 1.4%. It is particularly preferable that the major thread land gap c_HK is constant throughout the entire major thread land HK. In this way, a shear gap with a constant distance is formed between the major thread land HK and the inner wall of the housing.

[0036] The arc forming the groove preferably - When the number of grooves Z = 1, it has a central angle of 90 degrees to 150 degrees, preferably 95 degrees to 140 degrees, and particularly preferably 100 degrees to 130 degrees. - When the number of grooves Z = 2, each has a central angle of 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, and particularly preferably 15 degrees to 30 degrees. The central angles of the grooves can be the same or different, but it is preferable that they are the same. - When the number of grooves Z = 3, each has a central angle of 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, and particularly preferably 9 degrees to 18 degrees. The central angles of the grooves can be the same or different, but it is preferable that they are the same. - When the number of grooves Z = 4, each has a central angle of 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, and particularly preferably 6 degrees to 12 degrees. The central angles of the grooves can be the same or different, but it is preferable that they are the same.

[0037] The screw profile according to the present invention has a third plotting point K3. The screw profile is not axisymmetric or point - symmetric with respect to the plotting point K3. The plotting point K3 is a point having the same distance from the plotting point K1 as the plotting point K2. The plotting points K1, K2, and K3 are on a straight line and K1, K2, and K3 are not the same.

[0038] The screw profile according to the present invention can have a single secondary thread land or a plurality of secondary thread lands NK i =NK 1 ~NK n and each secondary thread land NK i is formed from only one arc, and the center of the arc is the plotting point K1, or the plotting point K2, or the plotting point K3. The subscripts i and n represent natural numbers. The subscript n designates the number of secondary thread lands NK 1 ~NK n . The number of thread lands NK 1 ~NK n is preferably equal to the number Z of grooves.

[0039] When the screw profile according to the present invention has at least one secondary thread land NK i , the groove is separated from the closest point of the secondary thread land NK by at least one arc that is a flank. As already explained above, since the groove is separated from the closest point of the main thread land NK by at least one arc that is a flank, when the screw profile according to the present invention has at least one secondary thread land NK i , the groove is separated not only from the closest point of the main thread land NK by at least one arc that is a flank, but also from the closest point of the secondary thread land NK i by at least one arc that is a flank. i This also applies.

[0040] The arc forming the secondary thread land NK i preferably has a central angle greater than 0 degrees, and the arc forming the secondary thread land NK i preferably has a central angle of 1 degree to 179 degrees. As a result, when the screw element is used as intended, the secondary thread land NK i that is generally subjected to the next largest mechanical load after the main thread land HK has high mechanical stability compared to the prior art.

[0041] The secondary thread land NK iwhile forming, and for arcs where neither of two directly adjacent arcs is the major thread crest land HK in this case, particularly preferably, - when the number of grooves Z = 2, a central angle of 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, particularly preferably 15 degrees to 30 degrees, - when the number of grooves Z = 3, a central angle of 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, particularly preferably 9 degrees to 18 degrees, - when the number of grooves Z = 4, a central angle of 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, particularly preferably 6 degrees to 12 degrees, having, and for a plurality of minor thread crest lands NK 1 ~NK n in the case of, the central angles of the minor thread crest lands NK 1 ~NK n can be the same or different.

[0042] For the minor thread crest land NK i while forming, and for an arc where one of two directly adjacent arcs is the major thread crest land HK in this case, particularly preferably, - when the number of grooves Z = 1, a central angle greater than 0 degrees and up to 140 degrees, preferably 5 degrees to 110 degrees, particularly preferably greater than 10 degrees and up to 80 degrees, - when the number of grooves Z = 2, respectively, a central angle greater than 0 degrees and up to 45 degrees, preferably 5 degrees to 30 degrees, particularly preferably greater than 10 degrees and up to 15 degrees, - when the number of grooves Z = 3, respectively, a central angle greater than 0 degrees and up to 27 degrees, preferably 2 degrees to 18 degrees, particularly preferably 4 degrees to 9 degrees, - when the number of grooves Z = 4, respectively, a central angle greater than 0 degrees and up to 18 degrees, preferably 1 degree to 12 degrees, particularly preferably 2 degrees to 6 degrees, having, and for a plurality of minor thread crest lands NK 1 ~NK n in the case of, the central angles of the minor thread crest lands NK 1 ~NK n can be the same or different.

[0043] One or more secondary thread flanks NK that can have the screw profile according to the invention i =NK 1 ~NK n The following further applies thereto. - For one secondary thread flank NK i The two arcs directly adjacent to each other are, when the center of the arc forming the secondary thread flank NK i is the construction point K1, except for each common contact point with the secondary thread flank NK i at a smaller distance from the construction point K1, or, when the center of the arc forming the secondary thread flank NK i is the construction point K2, at a smaller distance from the construction point K2, or, when the center of the arc forming the secondary thread flank NK i is the construction point K3, at a smaller distance from the construction point K3. - For the secondary thread flank NK i when the center of the arc forming it is the construction point K2, the arc forming the secondary thread flank NK i is at a smaller distance from the construction point K2 than the main thread flank HK.

[0044] The arc forming the main thread flank HK preferably contacts the arc forming the secondary thread flank NK i and the arc of the secondary thread flank NK i has as its center the construction point K1 and a radius rNK corresponding to the housing inner radius rg minus the secondary thread flank clearance c_NK.

[0045] For the arcs that form the main thread flank HK and where neither of the two directly adjacent arcs is an arc of the secondary thread flank NK i it is preferably - In the case where the number of grooves Z = 1, a central angle of 90° to 150°, preferably a central angle of 95° to 140° and particularly preferably a central angle of 100° to 130° - When the number of grooves Z = 2, the central angle is 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, particularly preferably 15 degrees to 30 degrees. - When the number of grooves Z = 3, the central angle is 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, particularly preferably 9 degrees to 18 degrees. - When the number of grooves Z = 4, the central angle is 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, particularly preferably 6 degrees to 12 degrees. It has.

[0046] While forming the main thread crest land HK, one of the two directly adjacent arcs is the secondary thread crest land NK i The arc that is is preferably - When the number of grooves Z = 1, the central angle is 10 degrees to 150 degrees, preferably 30 degrees to 140 degrees, particularly preferably 50 degrees to 130 degrees. - When the number of grooves Z = 2, the central angle is 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, particularly preferably 15 degrees to 30 degrees. - When the number of grooves Z = 3, the central angle is 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, particularly preferably 9 degrees to 18 degrees. - When the number of grooves Z = 4, the central angle is 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, particularly preferably 6 degrees to 12 degrees. It has.

[0047] In particular, the two interior angles between the arc of the main thread crest land HK and the arc that directly precedes the arc of the main thread crest land HK and has a common contact point with the arc of the main thread crest land HK, and the arc that directly follows the arc of the main thread crest land HK and has a common contact point with the arc of the main thread crest land HK are 130 degrees to 180 degrees, preferably 135 degrees to 180 degrees, particularly preferably 140 degrees to 180 degrees. In this regard, these two interior angles can be the same or different, but it is preferable that they are different.

[0048] Regarding the present invention, the interior angle between two directly adjacent arcs is the angle that exists between the tangents of the relevant arcs within the screw profile, and the tangents pass through the common contact point of the relevant arcs.

[0049] Furthermore, in particular, the arc of the minor thread land NK i and the arc that directly precedes the arc of the minor thread land NK i and has a common contact point with the arc of the minor thread land NK i and the arc that directly follows the arc of the minor thread land NK i and has a common contact point with the arc of the minor thread land NK i The two interior angles between both arcs are 130 degrees to 180 degrees, preferably 135 degrees to 180 degrees, particularly preferably 140 degrees to 180 degrees. In this regard, these two interior angles can be the same or different.

[0050] Most particularly, all of the interior angles between two directly adjacent arcs of the screw profile according to the present invention are 130 degrees to 180 degrees, preferably 135 degrees to 180 degrees, particularly preferably 140 degrees to 180 degrees.

[0051] Thereby, when the screw element is being used as intended, a situation is further achieved where it has higher mechanical stability compared to the prior art. Also, thereby, it becomes possible to handle the extruded product more carefully compared to the prior art.

[0052] Frank preferably has a radius corresponding to the axial distance a. More preferably, the arc forming Frank does not have a center at the plotting point K1, the plotting point K2, or the plotting point K3.

[0053] More preferably, the distance from the plotting point K1 to the plotting point K2 is 0.2% to 20% of the inner radius rg of the housing, preferably 0.4% to 15%, particularly preferably 0.6% to 10%, and very particularly preferably 0.8% to 5%.

[0054] More preferably, in the case of the screw profile according to the present invention, - When the number of grooves Z = 1, the smaller angle between the angle bisector of the groove and the line connecting K1 and K2 is from 0 degrees to 90 degrees, preferably from 45 degrees to 70 degrees, and particularly preferably approximately 55 degrees. - When the number of grooves Z = 2, the smaller angle between the angle bisector of the groove (the arc points of the groove on the angle bisector are separated from the closest point of the major thread land HK by the smaller curve length) and the line connecting K1 and K2 is from 110 degrees to 160 degrees, preferably from 125 degrees to 145 degrees, and particularly preferably approximately 135 degrees. - When the number of grooves Z = 3, the smaller angle between the angle bisector of the groove (the arc points of the groove on the angle bisector are separated from the closest point of the major thread land HK by the smaller curve length) and the line connecting K1 and K2 is from 130 degrees to 170 degrees, preferably from 140 degrees to 160 degrees, and particularly preferably approximately 150 degrees. - When the number of grooves Z = 4, the smaller angle between the angle bisector of the groove (the arc points of the groove on the angle bisector are separated from the closest point of the major thread land HK by the smaller curve length) and the line connecting K1 and K2 is from 140 degrees to 175 degrees, preferably from 150 degrees to 165 degrees, and particularly preferably approximately 157.5 degrees.

[0055] The following is obtained from the above. - The distance from the construction point K1 to the major thread land HK at each point of the major thread land HK is greater than the core radius, and thus this distance is also greater than the distance between the groove and the construction point K1. - The distance from the construction point K2 to the major thread land HK at each point of the major thread land HK is less than or equal to the inner radius rg of the housing. - The associated minor thread land NK i The distance from the construction point K1 to each minor thread land NK i at each point is greater than the core radius, and thus this distance is also greater than the distance between the groove and the construction point K1. - The major thread land HK and the minor thread land NK i can be directly adjacent to each other and have a common contact point.

[0056] The screw element according to the invention enables the following when used in an extruder having two or more drive shafts. - Improving the mixing action. - Ensuring a uniform force distribution between the single or multiple thread lands of the screw element and the inner wall of the housing of the extruder. - Handling the extruded product more carefully. - Ensuring a uniform distribution of the extruded product when the extruder is partially filled. In this case, the screw element, in particular the main thread land HK, and, if present, the secondary thread land NK i or the secondary thread land NK 1 ~NK n , and most particularly the main thread land HK, has a high mechanical stability compared to the prior art.

[0057] This is surprising. Because, as already explained above, in an extruder having two drive shafts rotating in the same direction and at the same speed, in the arrangement of two identical or different screw elements according to the invention, where the screw elements according to the invention are paired and located opposite each other on the two drive shafts, the screw elements according to the invention paired and located opposite each other on the two drive shafts do not completely but partially clean each other. The same applies, as explained above, to the arrangement of three or more identical or different screw elements according to the invention in an extruder having three or more drive shafts rotating in the same direction and at the same speed, where the screw elements according to the invention are paired and located opposite each other on each of the three or more drive shafts.

[0058] So far, it has been assumed that screw elements that completely clean each other are necessary for achieving the objective.

[0059] However, surprisingly, by using the screw element according to the invention, - A better mixing action due to the extrudate flowing back into the area of the screw element that has not been self-cleaned, and - A uniform force distribution due to a shear gap having a constant distance between the major thread land HK and the inner wall of the housing, and - A more uniform distribution of the plastic material in the case of partial filling due to the extrudate flowing back into the area of the screw element that has not been self-cleaned, and have been found to be achieved. This further enables the extrudate to be handled more carefully compared to the prior art.

[0060] When used in a threading machine, the major thread land HK of the screw element according to the invention shortens the flow channel formed such that a uniform flow gap is formed along the inner wall of the housing. As a result, the force distribution becomes uniform.

[0061] The screw element according to the invention is suitable for being arranged and operated in pairs in a threading machine having two drive shafts having another screw element according to the invention that rotates in the same direction and at the same speed and having the same or different screw profiles and the same or different arrangements of the rotation points on the other screw shaft, and it is preferred that the screw element according to the invention having the same screw profile is used. The screw element according to the invention is similarly suitable for use in a threading machine having three or more drive shafts that rotate in the same direction and at the same speed.

[0062] The screw element according to the invention can be in the form of a conveying element, a kneading element or a mixing element, and preferably can be in the form of a conveying element or a kneading element.

[0063] Accordingly, the present invention also relates to the arrangement of two identical or different screw elements according to the present invention in an extruder having two drive shafts rotating in the same direction and at the same speed, and the screw elements according to the present invention are paired on the two drive shafts and are located opposite to each other. Correspondingly, the present invention also relates to the arrangement of three or more identical or different screw elements according to the present invention in an extruder having three or more drive shafts rotating in the same direction and at the same speed, and the screw elements according to the present invention are paired on each of the three or more drive shafts and are located opposite to each other.

[0064] Furthermore, the present invention further relates to an extruder comprising two identical or different screw elements according to the present invention and having two drive shafts rotating in the same direction and at the same speed, and the screw elements according to the present invention are paired on the two drive shafts and are located opposite to each other. Correspondingly, the present invention further relates to an extruder comprising three or more identical or different screw elements according to the present invention and having three or more drive shafts rotating in the same direction and at the same speed, and the screw elements according to the present invention are paired on each of the three or more drive shafts and are located opposite to each other.

[0065] The screw profile according to the present invention can be drawn from a reference screw profile in a simple manner. This reference screw profile is preferably a screw profile according to the prior art, and particularly preferably is the one known as the Erdmenger profile (see pages 249 to 253 of Non-Patent Document 1).

[0066] In this regard, the following applies. · The core radius ri, the number of grooves Z, and the outer radius ra of the screw profile according to the present invention correspond to the core radius ri, the number of grooves Z, and the outer radius ra of the reference screw profile, and the plotting point K1 of the screw profile according to the present invention is the same as the plotting point K1 of the reference profile. · The outer radius rfra of the reference screw profile is 0.2% to 10% smaller than the housing inner radius rg, preferably 0.4% to 7.5% smaller, particularly preferably 0.6% to 5% smaller, and very particularly preferably 0.8% to 2.5% smaller. · Two similar reference profiles of the reference screw profile ○ When one of the reference screw profiles has a reference distance fra corresponding to the axial distance a, and ○ When the reference screw profiles rotate at the same speed in the same rotational direction at their respective reference rotation points, the reference rotation point 1 (rfDP1) and the reference rotation point 2 (rfDP2). Pair up and clean each other precisely.

[0067] Therefore, for such a reference screw profile, the second plotting point K2 is inserted as described above, and, as appropriate, the third plotting point K3 is also inserted as described above. Proceeding from this plotting point K2, and also from the plotting point K3 if it exists, at least one additional arc is inserted into the screw profile, and this at least one additional arc intersects at least one arc already existing in the reference screw profile, and the portion of at least one already existing arc "cut off" by the at least one additional arc is replaced by the at least one additional arc.

[0068] The present invention further relates to the use of the screw element according to the invention for processing or producing plastic materials.

[0069] Regarding the present invention, the plastic material is understood to mean the following. Suspensions, pastes, glass melts, unfired ceramics, metal melts, plastics, plastic melts or solutions, polymer melts or solutions, elastomers, rubber melts or solutions.

[0070] It is preferable to use plastics, polymer solutions or polymer melts, particularly preferably thermoplastic polymers. The thermoplastic polymers to be used are preferably selected from the group consisting of polycarbonate, polyamide, polyester, particularly polybutylene terephthalate and polyethylene terephthalate, polylactide, polyether, thermoplastic polyurethane, polyacetal, fluoropolymer, particularly polyvinylidene fluoride, polyethersulfone, polyolefin, particularly polyethylene and polypropylene, polyimide, polyacrylate, particularly poly(methyl)methacrylate, polyphenylene oxide, polyphenylene sulfide, polyether ketone, polyaryl ether ketone, styrene polymer, particularly polystyrene, styrene copolymer, particularly styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer, and polyvinyl chloride. Similarly preferably used are those known as blends of the exemplified polymers, and those skilled in the art understand that they are combinations of two or more polymers. Particularly preferred are polycarbonate and mixtures containing polycarbonate, and very particularly preferred is polycarbonate, which can be obtained, for example, by an interfacial process or a melt transesterification process. It is obtained by a melt transesterification process.

[0071] Other preferred feed materials are rubbers. The rubbers to be used are preferably at least one selected from the group consisting of styrene-butadiene rubber, natural rubber, butadiene rubber, isoprene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, butadiene-acrylonitrile rubber, hydrogenated nitrile rubber, butyl rubber, halobutyl rubber, chloroprene rubber, ethylene-vinyl acetate rubber, polyurethane rubber, thermoplastic polyurethane, gutta-percha, acrylate rubber, fluorinated rubber, silicone rubber, vulcanized rubber, and chlorosulfonated polyethylene rubber. Of course, combinations of two or more of the exemplified rubbers, or combinations of one or more rubbers and one or more plastics are also possible.

[0072] These thermoplastics and elastomers can be used in their pure form, or especially as mixtures with fillers or reinforcing agents such as glass fibers, as mixtures with each other or with other polymers, or as mixtures with conventional polymer additives.

[0073] In a preferred embodiment, the additive is added to the plastic material, especially to the polymer melt and mixtures of polymer melts. This additive can be added to the extruder in solid, liquid or solution form together with the polymer, or otherwise at least part or all of the additive is supplied via a side stream.

[0074] The additive can impart various properties to the polymer. This additive can be, for example, a colorant, pigment, processing aid, filler, antioxidant, strengthening agent, UV absorber and light stabilizer, metal deactivator, peroxide scavenger, basic stabilizer, nucleating agent, benzofuran and indolinone having a stabilizing or antioxidant effect, release agent, flame retardant additive, antistatic agent, dye, and melt stabilizer. Examples of these include carbon black, glass fibers, clay, mica, graphite fibers, titanium dioxide, carbon fibers, carbon nanotubes, ionic liquids, and natural fibers.

[0075] Hereinafter, the present invention will be described in more detail by way of example with reference to the drawings, but the present invention is not limited thereto. All the drawings were drawn using a computer program.

[0076] For the purpose of creating or describing a screw profile or screw element, dimensionless features are used to simplify the compatibility (transferability) of screw elements of different sizes or to an extruder. It is appropriate to use properties. For example, as a reference variable for geometric variables such as length, radius, or gap, the axial distance a is suitable. This is because this variable in the extruder cannot change. For the dimensionless axial distance A, A = a / a = 1 holds. The dimensionless housing inner radius RG is calculated as RG = rg / a, where rg is the housing inner radius. For the dimensionless screw outer radius RA of the screw profile, RA = ra / a, where ra is the screw outer radius. The dimensionless core radius RI of the screw profile is calculated as RI = ri / a, where ri is the core radius. The dimensionless gap C between the screw thread land and the housing is calculated as C = c / a, where c is the gap of the screw thread land with respect to the housing. The corresponding dimensionless gap of the main thread land HK is represented by C_HK, and the corresponding dimensionless gap of the secondary thread land NK i is represented by C_NK. For the dimensionless radius R, correspondingly, R = r / a holds.

[0077] In the figure, all the geometric variables on the right side of each drawing are used in dimensionless form. All angles are recorded in radians or degrees.

Brief Description of the Drawings

[0078]

Figure 1a

Figure 1b

Figure 2a

Figure 2b

Figure 3a

Figure 3b

Figure 4a

Figure 4b

Figure 5a

Figure 5b

Figure 6a

Figure 6b

Figure 7a

Figure 7b

Figure 8a

Figure 8b

Figure 9a

Figure 9b

Figure 10a

Figure 10b

Figure 11a1

Figure 11a2

Figure 11b1

Figure 11b2

Figure 12a1

Figure 12a2

Figure 12b1

Figure 12b2

Figure 13a1

Figure 13a2

Figure 13b1

Figure 13b2

Figure 14a1

Figure 14a2

Figure 14b1

Figure 14b2

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

DETAILED DESCRIPTION OF THE INVENTION

[0079] Figures 1 to 14 basically have the same structure, which will be described in more detail later. Each of the drawings has a drawing point K1, which is also the origin of the x / y coordinate system. In addition to the drawing point K1, the drawing may also have a drawing point K2, and further may have a drawing point K3. The arcs of the screw profile are identified by thick solid lines with their respective numbers given. The arcs are numbered continuously counterclockwise, i.e., in the mathematically positive direction. In this regard, when an arc is translated horizontally in the mathematically positive direction, the starting point of this arc is the first point of the arc, and the ending point is the last point of the arc. The centers of the arcs are represented by small circles. The centers of the arcs are connected by thin solid lines to both the starting point and the ending point of the related arc. The dimensionless screw outer radius RA is characterized by a thin dashed line, and the numerical value of the outer radius RA is recorded as the four significant digits in the lower right of the figure. The dimensionless housing inner radius RG is characterized by a thin solid line, and the numerical value of the inner radius RG is similarly recorded as the four significant digits in the lower right of the figure. On the right side of the drawing, for each arc, the related dimensionless radius R, the related central angle α, the related dimensionless x coordinate Mx of the arc center M, the related dimensionless y coordinate My of the arc center M, the related dimensionless x coordinate Ax of the starting point AP of the arc, and the related dimensionless y coordinate Ay of the starting point AP of the arc are recorded as four significant digits in each case. This information clearly defines the screw profile. Further, in each of these drawings, the dimensionless screw outer radius RA and the dimensionless housing inner radius RG are recorded.

[0080] In each of Figures 15 to 18, the dimensionless housing inner radius RG is recorded, and in Figure 20, the dimensionless reference housing inner radius RFRG and the dimensionless reference screw outer radius RFRA are recorded.

[0081] In each of FIGS. 15 and 17, for the screw profiles on both the left and right sides, the arcs are numbered continuously in a mathematically positive manner. In each of FIGS. 16 and 18, for the left screw profile, the arcs are numbered continuously in a mathematically positive manner, and for the right screw profile, they are numbered continuously in a mathematically negative manner.

[0082] FIG. 1a: FIG. 1a shows a screw profile with the number of grooves Z = 1 according to the prior art. The dimensionless screw outer radius is RA = 0.61. The dimensionless housing inner radius is RG = 0.66. The plotting point K1 is at the center M1 of the housing bore and thus at the associated rotation point DP1.

[0083] This embodiment is disadvantageous because the gap between the housing and the screw thread land (arc 2) is large, resulting in poor cleaning of the housing.

[0084] FIG. 1b: The screw profile in FIG. 1b was obtained by displacing the screw profile in FIG. 1a. This displacement was carried out such that the end point of arc 2 corresponding to the start point of arc 3, the plotting point K1, and the plotting point K2 lie on a straight line. The plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The end point of arc 2 corresponding to the start point of arc 3 lies on the dimensionless screw outer radius RA. The dimensionless screw outer radius is RA = 0.65. The dimensionless housing inner radius is RG = 0.66.

[0085] Compared with the embodiment according to FIG. 1a, this embodiment has a narrow gap between the housing and the end point of arc 2, and as a result, the cleaning of the housing is good. However, in this embodiment, the gap between the housing and the screw thread land (arc 2) is not constant, and as a result, it is disadvantageous in that a converging channel or a diverging channel is brought about between the housing and the screw thread land (arc 2) depending on the direction of rotation. When the screw profile rotates clockwise around the drafting point K2, the polymer mass is pressed into the converging channel between the housing and the screw thread land (arc 2), and as a result, a large compressive force that can move the screw element far enough from the rotation point DP1 so that the screw element contacts the housing and / or directly adjacent screw elements acts on the screw element, which leads to mechanical wear of the screw element.

[0086] FIG. 2a: FIG. 2a shows a closed screw profile according to the invention having a number of grooves Z = 1 and consisting of five arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The dimensionless gap of the secondary thread land NK i (arc 2) is C_NK = 0.05.

[0087] The screw profile is present at the center M1 of the housing bore and thus has a drafting point K1 that is present at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the drafting point K1. The drafting point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.8186 ≈ 46.9 degrees. Arc 2 is the secondary thread land NK iThis is because the two directly adjacent arcs 1 and 2a have a smaller distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 1.9217 ≈ 110.1 degrees. Arc 4 represents a groove. This is because the two directly adjacent arcs 1 and 3 have a larger distance from the plotting point K1 except for the common contact point.

[0088] The screw profile does not coincide with the plotting point K1, exists within the screw profile, and further has a plotting point K2 that exists within a circle whose center is the plotting point K1 and whose dimensionless radius is the same as the dimensionless core radius RI. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K2. The plotting point K2 is the center of arc 2a. Arc 2a has a dimensionless radius R_2a = 0.65, which is slightly smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_2a = 1.0799 ≈ 61.9 degrees. Arc 2a represents the main thread land HK. This is because the two directly adjacent arcs 2 and 3 have a smaller distance from the plotting point K2 except for the common contact point.

[0089] The distance between the plotting point K2 and the plotting point K1 is approximately 0.1 21 times that of the dimensionless housing inner radius RG. The smaller angle between the angular bisector of the groove (arc 4) and the line connecting K1 and K2 is 55.1 degrees. The plotting point K1, the plotting point K2, and the center of arc 1 exist on one line.

[0090] Arcs 1 and 3 represent flanks. The dimensionless radii R_1 and R_3 of the two arcs 1 and 3 are respectively R_1 = R_3 = 1.00. The centers of these two arcs are not the same as the plotting points K1 and K2 in each case.

[0091] The main thread land HK (arc 2a) and the secondary thread land NK i (arc 2) are in contact with each other. The main thread land HK and the secondary thread land NK iare each separated from the groove by Frank.

[0092] Figure 2b: The screw profile in Figure 2b was obtained by displacing the screw profile of Figure 2a. This displacement was carried out such that the plotting point K2 lies at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. The arc 2a has a dimensionless radius R_2a = 0.65, which is the same as the dimensionless screw outer radius RA. The dimensionless clearance of the main screw thread land HK (arc 2a) with respect to the housing is C_HK = 0.01. The plotting point K1, the plotting point K2, and the center of the arc 1 lie on one line.

[0093] This embodiment is advantageous because it has a constant narrow gap between the housing and the main screw thread land HK (arc 2a), resulting in good cleaning of the housing. Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the main screw thread land HK (arc 2) is substantially smaller than the length in the embodiment according to Figure 1b. Thus, when rotating clockwise, a converging channel is created between the housing and the main screw thread land HK (arc 2a), and when rotating counterclockwise, a diverging channel is created.

[0094] Figure 3a: Figure 3a shows a closed screw profile according to the invention having a groove number Z = 1 and consisting of five arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The dimensionless clearance of the secondary screw thread land NK i (arc 2) with respect to the housing is C_NK = 0.05.

[0095] The screw profile is located at the center M1 of the housing bore and thus has a construction point K1 that lies at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the construction point K1. The construction point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.6946 ≈ 39.8 degrees. Arc 2 represents the secondary thread land NK i because the two directly adjacent arcs 1 and 2a have a smaller distance to the construction point K1 except for the common contact point. The construction point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 1.9217 ≈ 110.1 degrees. Arc 4 represents the groove because the two directly adjacent arcs 1 and 3 have a larger distance to the construction point K1 except for the common contact point.

[0096] The screw profile does not coincide with the construction point K1, exists within the screw profile, and further has a construction point K2 that lies within a circle whose center is the construction point K1 and whose dimensionless radius is the dimensionless core radius RI. The screw profile is not axisymmetric or point-symmetric with respect to the construction point K2. The construction point K2 is the center of arc 2a. Arc 2a has a dimensionless radius R_2a = 0.65, which is somewhat smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_2a = 1.1594 ≈ 66.4 degrees. Arc 2a represents the primary thread land HK because the two directly adjacent arcs 2 and 3 have a smaller distance to the construction point K2 except for the common contact point.

[0097] The distance between the construction point K2 and the construction point K1 is approximately 0.091 times the housing inner radius RG. The smaller angle between the angular bisector of the groove and the line connecting K1 and K2 is 35.0 degrees. The line between the construction point K1 and the center of arc 1 and the line between the construction point K2 and the starting point of arc 3 are approximately parallel.

[0098] Arcs 1 and 3 represent flanks. The radii of the two arcs are, respectively, R_1 = R_3 = 1.00. The centers of these two arcs are not the same as the construction points K1 and K2 in each case.

[0099] The major thread land HK (arc 2a) and the minor thread land NK i (arc 2) are in contact with each other. The major thread land and the minor thread land NK i are separated from the groove by the flanks, respectively.

[0100] Figure 3b: The screw profile in Figure 3b is obtained by displacing the screw profile in Figure 3a. This displacement was performed such that the construction point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. Arc 2a has a dimensionless radius R_2a = 0.65, which is equal to the dimensionless screw outer radius RA. The dimensionless clearance of the major thread land HK (arc 2a) with respect to the housing is C_HK = 0.01.

[0101] This embodiment is advantageous because it has a constant narrow gap between the housing and the major thread land HK (arc 2a), resulting in good cleaning of the housing. Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the minor thread land NK i (arc 2) is substantially smaller than the length in the embodiment according to Figure 1b. Thus, when rotating clockwise, a converging channel is created between the housing and the major thread land HK (arc 2a), and when rotating counterclockwise, a diverging channel is created.

[0102] Figure 4a: Figure 4a shows a closed screw profile according to the present invention having a groove number Z = 1 and consisting of five arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The minor thread land NK with respect to the housing iThe dimensionless gap of (arc 2) is C_NK = 0.05. Here, the center of arc 1 is the same as the starting point of arc 3.

[0103] The screw profile exists at the center M1 of the housing bore and thus has a plotting point K1 that exists at the associated rotation point DP1. The screw profile is not axisymmetric or point - symmetric with respect to the plotting point K1. The plotting point K1 is the center of arc 2. Arc 2 has a radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.5238 ≒ 30.0 degrees. Arc 2 represents the secondary thread land NK i because the two directly adjacent arcs 1 and 2a have a smaller distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 1.9217 ≒ 110.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 1 and 3 have a larger distance to the plotting point K1 except for the common contact point.

[0104] The screw profile does not coincide with the plotting point K1, exists within the screw profile, and furthermore has a plotting point K2 that exists within a circle whose center is the plotting point K1 and whose dimensionless radius is the core radius RI. The screw profile is not axisymmetric or point - symmetric with respect to the plotting point K2. The plotting point K2 is the center of arc 2a. Arc 2a has a dimensionless radius R_2a = 0.65, which is somewhat smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_2a = 1.2966 ≒ 74.3 degrees. Arc 2a represents the primary thread land HK because the two directly adjacent arcs 2 and 3 have a smaller distance to the plotting point K2 except for the common contact point.

[0105] The distance between the plotting point K2 and the plotting point K1 is approximately 0.077 times the dimensionless housing inner radius RG. The smaller angle between the angular bisector of the groove and the line connecting K1 and K2 is 15.0 degrees. The size and position of arc 3 remain unchanged compared to Figure 1a.

[0106] Arcs 1 and 3 represent flanks. The dimensionless radii of the two arcs are, respectively, R_1 = R_3 = 1.00. The centers of these two arcs are not the same as the plotting points K1 and K2 in each case.

[0107] The major thread land HK (arc 2a) and the minor thread land NK i (arc 2) are in contact with each other. The major thread land HK and the minor thread land NK i are separated from the groove by flanks respectively.

[0108] Figure 4b: The screw profile in Figure 4b was obtained by displacing the screw profile in Figure 4a. This displacement was performed so that the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. Arc 2a has a radius R_2a = 0.65, which is the same as the dimensionless screw outer radius RA. The dimensionless clearance of the major thread land HK (arc 2a) with respect to the housing is C_HK = 0.01. The center of circle 1 corresponds to the starting point of circle 3.

[0109] This embodiment has a constant narrow gap between the housing and the major thread land HK (arc 2a), and as a result, it is advantageous because the housing can be cleaned well. Also, this embodiment is advantageous because the length of the converging channel or diverging channel (depending on the direction of rotation) between the housing and the minor thread land NK i (arc 2) is substantially smaller than the length in the embodiment according to Figure 1b. Therefore, when rotating clockwise, a converging channel is formed between the housing and the major thread land HK (arc 2a), and when rotating counterclockwise, a diverging channel is formed.

[0110] Figure 5a: Figure 5a shows a screw profile according to the prior art with the number of grooves Z = 2. The dimensionless screw outer radius is RA = 0.61. The dimensionless housing inner radius is RG = 0.66. The plotting point K1 is located at the center M1 of the housing bore and thus at the associated rotation point DP1.

[0111] This embodiment is disadvantageous because the gaps between the housing and the first thread land (arc 2) and also between the housing and the second thread land (arc 6) are large, resulting in poor cleaning of the housing.

[0112] Figure 5b: The screw profile in Figure 5b was obtained by displacing the screw profile of Figure 5a. This displacement was performed such that the smaller angle between the angular bisector of arc 8 and the line connecting the plotting point K1 and the plotting point K2 is 135 degrees. The plotting point K2 is located at the center M1 of the housing bore and thus at the associated rotation point DP1. The end point of arc 6 corresponding to the starting point of arc 7 is located on the dimensionless screw outer radius RA. The dimensionless screw outer radius is RA = 0.65. The dimensionless housing inner radius is RG = 0.66.

[0113] Compared to the embodiment according to Figure 5a, this embodiment has a narrow gap between the housing and the end point of arc 6, resulting in good cleaning of the housing. However, this embodiment is disadvantageous in that the gap between the housing and the second thread land (arc 6) is not constant, resulting in a converging channel or a diverging channel between the housing and the second thread land (arc 6) depending on the direction of rotation. When the screw profile rotates clockwise around the plotting point K2, the polymer mass is pressed into the converging channel between the housing and the second thread land (arc 6), and as a result, a large compressive force acts on the screw element that can move the screw element far enough from the rotation point DP1 so as to contact the housing and / or directly adjacent screw elements, which leads to mechanical wear of the screw element.

[0114] Figure 6a: Figure 6a shows a closed screw profile according to the present invention, having a number of grooves Z = 2 and consisting of 9 arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The first secondary thread crest land NK 1 (arc 2) and the second secondary thread crest land NK 2 (arc 6) have a dimensionless gap of C_NK = 0.05 each.

[0115] The screw profile is centered at the center M1 of the housing bore and thus has a plotting point K1 that lies at the associated rotation point DP1. The screw profile is not axisymmetric or point symmetric with respect to the plotting point K1. The plotting point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.3509 ≈ 20.1 degrees. Arc 2 represents the secondary thread crest land NK i because the two directly adjacent arcs 1 and 3 have a smaller distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 6. Arc 6 has a radius R_6 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_6 = 0.0001 ≈ 0.006 degrees. Arc 6 represents the secondary thread crest land NK i because the two directly adjacent arcs 5 and 6a have a smaller distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.3509 ≈ 20.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 3 and 5 have a larger distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 8. Arc 8 has a radius R_8 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.3509 ≈ 20.1 degrees. Arc 8 represents a groove because the two directly adjacent arcs 1 and 7 have a larger distance from the plotting point K1 except for the common contact point.

[0116] The screw profile does not coincide with the plotting point K1, exists within the screw profile, and further has a plotting point K2 that is centered at the plotting point K1 and exists within a circle whose radius is the dimensionless core radius. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K2. The plotting point K2 is the center of the arc 6a. The arc 6a has a dimensionless radius R_6a = 0.65, which is somewhat smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_6a = 0.3618 ≒ 20.7 degrees. The arc 6a represents the main thread land HK. This is because the two directly adjacent arcs 6 and 7 have a smaller distance from the plotting point K2 except for the common contact point.

[0117] The distance between the plotting point K2 and the plotting point K1 is approximately 0.100 times the dimensionless housing inner radius RG. The smaller angle between the angular bisector of the groove (the arc points of the groove that exist on the angular bisector of the groove are separated from the closest point of the main thread land HK by the smaller curve length) and the line connecting K1 and K2 is 135.0 degrees.

[0118] The arcs 1, 3, 5, and 7 represent flanks. The dimensionless radii of the four arcs are respectively R_1 = R_3 = R_5 = R_7 = 1.00. The centers of these four arcs are not the same as the plotting points K1 and K2 in each case.

[0119] The main thread land HK (arc 6a) and the second secondary thread land NK 2 (arc 6) are in contact with each other. The main thread land HK, the first secondary thread land NK 1 (arc 2) and the second secondary thread land NK 2 (arc 6) are separated from the groove by flanks respectively.

[0120] Figure 6b: The screw profile in Figure 6b was obtained by displacing the screw profile of Figure 6a. This displacement was performed such that the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. The arc 6a has a dimensionless radius R_6a = 0.65, which is the same as the dimensionless screw outer radius RA. The dimensionless gap of the main screw thread land HK (arc 6a) with respect to the housing is C_HK = 0.01.

[0121] This embodiment is advantageous because it has a constant narrow gap between the housing and the main screw thread land HK (arc 6a), and as a result, the cleaning of the housing is good. Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the secondary screw thread land NK i (arc 6) is substantially equal to zero as opposed to Figure 5b. Thus, when rotating clockwise, a converging channel is created between the housing and the main screw thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is created.

[0122] Figure 7a: Figure 7a shows a closed screw profile according to the present invention having a number of grooves Z = 2 and consisting of 9 arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The dimensionless gaps of the first secondary screw thread land NK 1 (arc 2) and the second secondary screw thread land NK 2 (arc 6) with respect to the housing are each C_NK = 0.05.

[0123] The screw profile is located at the center M1 of the housing bore and thus has a plotting point K1 that is located at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K1. The plotting point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.3509 ≈ 20.1 degrees. Arc 2 represents the secondary thread land NK i because the two directly adjacent arcs 1 and 3 have a smaller distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 6. Arc 6 has a dimensionless radius R_6 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_6 = 0.0837 ≈ 4.8 degrees. Arc 6 represents the secondary thread land NK i because the two directly adjacent arcs 5 and 6a have a smaller distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.3509 ≈ 20.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 3 and 5 have a larger distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 8. Arc 8 has a dimensionless radius R_8 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.3509 ≈ 20.1 degrees. Arc 8 represents a groove because the two directly adjacent arcs 1 and 7 have a larger distance to the plotting point K1 except for the common contact point.

[0124] The screw profile does not coincide with the plotting point K1, exists within the screw profile, and further has a plotting point K2 that exists within a circle whose center is the plotting point K1 and whose radius is the dimensionless core radius RI. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K2. The plotting point K2 is the center of the arc 6a. The arc 6a has a dimensionless radius R_6a = 0.65, which is somewhat smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_6a = 0.2731 ≒ 15.6 degrees. The arc 6a represents the major thread land HK. This is because the two directly adjacent arcs 6 and 7 have a smaller distance from the plotting point K2 except for the common contact point.

[0125] The distance between the plotting point K2 and the plotting point K1 is approximately 0.091 times the dimensionless housing inner radius RG. The smaller angle between the groove angle bisector (the arc points of the groove that exist on the groove angle bisector and are separated from the closest point of the major thread land HK by the smaller curve length) and the line connecting K1 and K2 is 135.0 degrees.

[0126] The arcs 1, 3, 5, and 7 represent flanks. The radii of the four arcs are respectively R_1 = R_3 = R_5 = R_7 = 1.00. The centers of these four arcs are not the same as the plotting points K1 and K2 in each case.

[0127] The major thread land HK (arc 6a) and the second minor thread land NK 2 (arc 6) are in contact with each other. The major thread land HK, the first minor thread land NK 1 (arc 2) and the second minor thread land NK 2 (arc 6) are separated from the groove by the flanks respectively.

[0128] Figure 7b: The screw profile in Figure 7b was obtained by displacing the screw profile of Figure 7a. This displacement was carried out such that the plotting point K2 was present at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. The arc 6a has a dimensionless radius R_6a = 0.65, which is the same as the dimensionless screw outer radius RA. The dimensionless clearance of the main screw thread land HK (arc 6a) with respect to the housing is C_HK = 0.01.

[0129] This embodiment is advantageous because it has a constant narrow gap between the housing and the main screw thread land HK (arc 6a), and as a result, the housing can be cleaned well. Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the secondary screw thread land NK i (arc 6) is substantially smaller than the length in the embodiment according to Figure 5b. Thus, when rotating clockwise, a converging channel is formed between the housing and the main screw thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is formed.

[0130] Figure 8a: Figure 8a shows a closed screw profile according to the invention having a number of grooves Z = 2 and consisting of 9 arcs. The housing inner radius is RG = 0.61. The dimensionless screw outer radius is RA = 0.58. The dimensionless clearances of the first secondary screw thread land NK 1 (arc 2) and the second secondary screw thread land NK 2 (arc 6) with respect to the housing are each C_NK = 0.03.

[0131] The screw profile is located at the center M1 of the housing bore and thus has a plotting point K1 that is located at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K1. The plotting point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.58, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.5079 ≈ 29.1 degrees. Arc 2 represents the secondary thread land NK i because the two directly adjacent arcs 1 and 3 have a smaller distance from the plotting point K1 except at the common contact point. The plotting point K1 is the center of arc 6. Arc 6 has a dimensionless radius R_6 = 0.58, which is the same as the screw outer radius RA. The central angle is α_6 = 0.0320 ≈ 1.9 degrees. Arc 6 represents the secondary thread land NK because the two directly adjacent arcs 5 and 6a have a smaller distance from the plotting point K1 except at the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.42, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.5079 ≈ 29.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 3 and 5 have a larger distance from the plotting point K1 except at the common contact point. The plotting point K1 is the center of arc 8. Arc 8 has a dimensionless radius R_8 = 0.42, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.5079 ≈ 29.1 degrees. Arc 8 represents a groove because the two directly adjacent arcs 1 and 7 have a larger distance from the plotting point K1 except at the common contact point. i because the two directly adjacent arcs 5 and 6a have a smaller distance from the plotting point K1 except at the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.42, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.5079 ≈ 29.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 3 and 5 have a larger distance from the plotting point K1 except at the common contact point. The plotting point K1 is the center of arc 8. Arc 8 has a dimensionless radius R_8 = 0.42, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.5079 ≈ 29.1 degrees. Arc 8 represents a groove because the two directly adjacent arcs 1 and 7 have a larger distance from the plotting point K1 except at the common contact point.

[0132] The screw profile does not coincide with the plotting point K1, exists within the screw profile, and further has a plotting point K2 that lies within a circle whose center is the plotting point K1 and whose dimensionless radius is the dimensionless core radius RI. The screw profile is neither axisymmetric nor point-symmetric with respect to the plotting point K2. The plotting point K2 is the center of the circular arc 6a. The circular arc 6a has a dimensionless radius R_6a = 0.60, which is somewhat smaller than the housing inner radius RG = 0.61. The central angle is α_6a = 0.4895 ≒ 28.0 degrees. The circular arc 6a represents the main thread land HK. This is because the two directly adjacent circular arcs 6 and 7 are at a smaller distance from the plotting point K2 except at the common contact point.

[0133] The distance between the plotting point K2 and the plotting point K1 is approximately 0.055 times the housing inner radius RG. The smaller angle between the angular bisector of the groove (the arc points of the groove that lie on the angular bisector of the groove are separated from the closest point of the main thread land HK by the smaller curve length) and the line connecting K1 and K2 is 135.0 degrees.

[0134] The circular arcs 1, 3, 5, and 7 represent flanks. The dimensionless radii of the four circular arcs are each R_1 = R_3 = R_5 = R_7 = 1.00. The centers of these four circular arcs are not the same as the plotting points K1 and K2 in each case.

[0135] The main thread land HK (circular arc 6a) and the second secondary thread land NK 2 (circular arc 6) are in contact with each other. The main thread land HK, the first secondary thread land NK 1 (circular arc 2) and the second secondary thread land NK 2 (circular arc 6) are each separated from the groove by a flank.

[0136] Figure 8b: The screw profile in Figure 8b was obtained by displacing the screw profile of Figure 8a. This displacement was carried out such that the plotting point K2 lies at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.61. The dimensionless screw outer radius is RA = 0.60. The arc 6a has a dimensionless radius R_6a = 0.60, which is the same as the dimensionless screw outer radius RA. The dimensionless clearance of the main screw thread land HK (arc 6a) with respect to the housing is C_HK = 0.01.

[0137] This embodiment has a constant narrow gap between the housing and the main screw thread land HK (arc 6a), and as a result, it is advantageous because the housing can be cleaned well. Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the secondary screw thread land NK i (arc 6) is substantially smaller than the length in the embodiment according to Figure 5b. Thus, when rotating clockwise, a converging channel is formed between the housing and the main screw thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is formed.

[0138] Figure 9a: Figure 9a shows a closed screw profile according to the present invention having a number of grooves Z = 2 and consisting of 10 arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The dimensionless clearances of the first secondary screw thread land NK 1 (arc 2) and the second secondary screw thread land NK 2 (arc 6) with respect to the housing are each C_NK = 0.05.

[0139] The screw profile is located at the center M1 of the housing bore and thus has a plotting point K1 that is located at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K1. The plotting point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.0550 ≒ 3.2 degrees. Arc 2 represents the secondary thread land NK i because the two directly adjacent arcs 2a and 3 have a smaller distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 6. Arc 6 has a dimensionless radius R_6 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_6 = 0.0837 ≒ 4.8 degrees. Arc 6 represents the secondary thread land NK i because the two directly adjacent arcs 5 and 6a have a smaller distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.3509 ≒ 20.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 3 and 5 have a larger distance to the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 8. Arc 8 has a radius R_8 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.3509 ≒ 20.1 degrees. Arc 8 represents a groove because the two directly adjacent arcs 1 and 7 have a larger distance to the plotting point K1 except for the common contact point.

[0140] The screw profile does not coincide with the plotting point K1, is located within the screw profile, and further has a plotting point K2 that is located within a circle whose center is the plotting point K1 and whose dimensionless radius is the dimensionless core radius RI. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K2. The plotting point K2 is the center of arc 2a. Arc 2a has a dimensionless radius R_2a = 0.564, which is smaller than the dimensionless screw outer radius RA = 0.61. The central angle is α_2a = 0.3577 ≒ 20.5 degrees. Arc 2a represents the secondary thread land NKi This is because for two directly adjacent arcs 1 and 2, the distance to the construction point K2 is smaller except for the common contact point, while for arc 6a, the distance to the construction point K2 is larger. The construction point K2 is the center of arc 6a. Arc 6a has a dimensionless radius R_6a = 0.65, which is slightly smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_6a = 0.2731 ≒ 15.6 degrees. Arc 6a represents the main thread land HK. This is because for two directly adjacent arcs 6 and 7, the distance to the construction point K2 is smaller except for the common contact point, and for arc 2a, the distance to the construction point K2 is smaller.

[0141] The distance between the construction point K2 and the construction point K1 is approximately 0.091 times the dimensionless housing inner radius RG. The smaller angle between the groove angular bisector (the arc points of the groove on the groove angular bisector are separated from the closest point of the main thread land HK by the smaller curve length) and the line connecting K1 and K2 is 135.0 degrees.

[0142] Arcs 1, 3, 5, and 7 represent flanks. The dimensionless radii of the four arcs are respectively R_1 = R_3 = R_5 = R_7 = 1.00. The centers of these four arcs are not the same as the construction points K1 and K2 in each case.

[0143] The main thread land HK (arc 6a) and the second secondary thread land NK 2 (arc 6) are in contact with each other. The main thread land HK, the first secondary thread land NK 1 (arc 2) and the second secondary thread land NK 2 (arc 6) are separated from the groove by the flanks respectively.

[0144] Figure 9b: The screw profile in Figure 9b was obtained by displacing the screw profile of Figure 9a. This displacement was performed such that the plotting point K2 is present at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. The arc 6a has a dimensionless radius R_6a = 0.65, which is equal to the dimensionless screw outer radius RA. The dimensionless clearance of the main screw thread land HK (arc 6a) with respect to the housing is C_HK = 0.01.

[0145] This embodiment has a constant narrow clearance between the housing and the main screw thread land HK (arc 6a), and as a result, it is advantageous because the housing can be cleaned well. This embodiment is further advantageous because it has a constant clearance between the housing and the first secondary screw thread land NK 1 (arc 2a). Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the secondary screw thread lands NK (arc 2) and the second secondary screw thread land NK 2 (arc 6) is substantially smaller than the length in the embodiment according to Figure 5b. Therefore, when rotating clockwise, a converging channel is formed between the housing and the main screw thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is formed.

[0146] Figure 10a: Figure 10a shows a closed screw profile according to the present invention having a number of grooves Z = 2 and consisting of 10 arcs. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.61. The clearances of the first secondary screw thread land NK 1 (arc 2) and the second secondary screw thread land NK 2 (arc 6) with respect to the housing are each C_NK = 0.05.

[0147] The screw profile is located at the center M1 of the housing bore and thus has a construction point K1 that lies on the associated rotation point DP1. The screw profile is point-symmetrical with respect to the construction point K1. The construction point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.0837 ≈ 4.8 degrees. Arc 2 represents the secondary thread land NK i because the two directly adjacent arcs 2a and 3 have a smaller distance from the construction point K1 except for the common contact point. The construction point K1 is the center of arc 6. Arc 6 has a dimensionless radius R_6 = 0.61, which is the same as the dimensionless screw outer radius RA. The central angle is α_6 = 0.0837 ≈ 4.8 degrees. Arc 6 represents the secondary thread land NK 2 because the two directly adjacent arcs 5 and 6a have a smaller distance from the construction point K1 except for the common contact point. The construction point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.3509 ≈ 20.1 degrees. Arc 4 represents a groove because the two directly adjacent arcs 3 and 5 have a larger distance from the construction point K1 except for the common contact point. The construction point K1 is the center of arc 8. Arc 8 has a dimensionless radius R_8 = 0.39, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.3509 ≈ 20.1 degrees. Arc 8 represents a groove because the two directly adjacent arcs 1 and 7 have a larger distance from the construction point K1 except for the common contact point.

[0148] The screw profile does not coincide with the construction point K1, is located within the screw profile, and further has a construction point K2 that lies within a circle whose center is the construction point K1 and whose dimensionless radius is the dimensionless core radius RI. The screw profile is axis-symmetrical or point-symmetrical with respect to the construction point K2 It is not symmetric. The plotting point K2 is the center of the arc 6a. The arc 6a has a dimensionless radius R_6a = 0.65, which is somewhat smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_6a = 0.2731 ≒ 15.6 degrees. The arc 6a represents the main thread land HK. Because the two directly adjacent arcs 6 and 7 have a smaller distance to the plotting point K2 except for the common contact point.

[0149] The screw profile has a plotting point K3 that has the same distance to the plotting point K1 as the plotting point K2. The plotting points K1, K2, and K3 are on a straight line, and K1, K2, and K3 are not the same. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K3. The plotting point K3 is the center of the arc 2a. The arc 2a has a dimensionless radius R_2a = 0.65, which is somewhat smaller than the dimensionless housing inner radius RG = 0.66. The central angle is α_2a = 0.2731 ≒ 15.6 degrees. The arc 2a represents the secondary thread land NK 3 Because the two directly adjacent arcs 2 and 3 have a smaller distance to the plotting point K3 except for the common contact point.

[0150] The distance between the plotting point K2 and the plotting point K1 is approximately 0.091 times the dimensionless housing inner radius RG. The smaller angle between the angular bisector of the groove (the arc points of the groove that exist on the angular bisector of the groove are separated from the closest point of the main thread land HK by the smaller curve length) and the line connecting K1 and K2 is 135.0 degrees.

[0151] The arcs 1, 3, 5, and 7 represent flanks. The dimensionless radii of the four arcs are respectively R_1 = R_3 = R_5 = R_7 = 1.00. The centers of these four arcs are not the same as the plotting points K1 and K2 in each case.

[0152] The main thread land HK (arc 6a) and the second secondary thread land NK 2 (arc 6) are in contact with each other. The main thread land HK, the first secondary thread land NK 1 (arc 2) and the second secondary thread land NK 2(Arc 6) is separated from the groove by Frank respectively.

[0153] The screw profile is point-symmetric rather than axis-symmetric with respect to the plotting point K1. In this way, the screw profile can be plotted particularly easily.

[0154] Figure 10b: The screw profile in Figure 10b is obtained by displacing the screw profile in Figure 10a. This displacement was performed such that the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.66. The dimensionless screw outer radius is RA = 0.65. Arc 6a has a dimensionless radius R_6a = 0.65, which is the same as the dimensionless screw outer radius RA. The dimensionless clearance of the main screw thread land (arc 6a) with respect to the housing is C_HK = 0.01.

[0155] This embodiment is advantageous because it has a constant narrow gap between the housing and the main screw thread land (arc 6a), and as a result, the housing can be cleaned well. Also, this embodiment is advantageous because the length of the converging channel or diverging channel (depending on the direction of rotation) between the housing and the main screw thread land (arc 6) is substantially smaller than the length in the embodiment according to Figure 5b. Therefore, when rotating clockwise, a converging channel is formed between the housing and the main screw thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is formed.

[0156] Figure 11a: Figure 11a1 shows a screw profile with the number of grooves Z = 3 according to the prior art, and Figure 11a2 shows an enlarged detailed view around arc 6 of Figure 11a1. The dimensionless screw outer radius is RA = 0.54. The dimensionless housing inner radius is RG = 0.584 is. The plotting point K1 is at the center M1 of the housing bore and thus at the associated rotation point DP1.

[0157] This embodiment is disadvantageous because the gaps between the housing and the first thread land (arc 2), and also between the housing and the second thread land (arc 6), and also between the housing and the third thread land (arc 10) are large, resulting in poor cleaning of the housing.

[0158] Figure 11b: The screw profile in Figure 11b1 was obtained by displacing the screw profile of Figure 11a1. Figure 11b2 shows an enlarged detailed view around arc 6 of Figure 11b1. The displacement was performed such that the smaller angle between the angular bisector of arc 8 and the line connecting the plotting points K1 and K2 is 150 degrees. The plotting point K2 is located at the center M1 of the housing bore and thus at the associated rotation point DP1. The end point of arc 6 corresponding to the start point of arc 7 is located on the dimensionless screw outer radius RA, and the start point of arc 6 is not located on the dimensionless screw outer radius RA. The dimensionless screw outer radius is RA = 0.58. The dimensionless housing inner radius is RG = 0.584.

[0159] Compared with the embodiment according to Figure 11a1, this embodiment has a narrow gap between the housing and the end point of arc 6, and as a result, the cleaning of the housing is good. However, this embodiment is disadvantageous in that the gap between the housing and the second thread land (arc 6) is not constant, and as a result, a converging channel or a diverging channel is brought about between the housing and the second thread land (arc 6) depending on the direction of rotation. Thus, when rotating clockwise, a converging channel is created between the housing and the main thread land HK (arc 6), and when rotating counterclockwise, a diverging channel is created.

[0160] Figure 12a: Figure 12a1 shows a closed screw profile according to the invention having a number of grooves Z = 3 and consisting of 13 arcs, and Figure 12a2 shows an enlarged detailed view around arcs 6 and 6a of Figure 12a1. The dimensionless housing inner radius is RG = 0.584. The dimensionless screw outer radius is RA = 0.54. The first secondary thread land NK with respect to the housing 1(Arc 2), the second secondary thread land NK 2 (Arc 6) and the third secondary thread land NK 3 The dimensionless gaps of (Arc 10) are each C_NK = 0.044

[0161] The screw profile exists at the center M1 of the housing bore and thus has a plotting point K1 that exists at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K1. The plotting point K1 is the center of arc 2. Arc 2 has a dimensionless radius R_2 = 0.54, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.2726 ≈ 15.6 degrees. Arc 2 represents the secondary thread land NK 1 because the two directly adjacent arcs 1 and 3 have a smaller distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 6. Arc 6 has a dimensionless radius R_6 = 0.54, which is the same as the dimensionless screw outer radius RA. The central angle is α_6 = 0.0501 ≈ 2.9 degrees. Arc 6 represents the secondary thread land NK 2 because the two directly adjacent arcs 5 and 6a have a smaller distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 10. Arc 10 has a dimensionless radius R_10 = 0.54, which is the same as the dimensionless screw outer radius RA. The central angle is α_10 = 0.2726 ≈ 15.6 degrees. Arc 10 represents the secondary thread land NK 3 because the two directly adjacent arcs 9 and 11 have a smaller distance from the plotting point K1 except for the common contact point. The plotting point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.46, which is the same as the dimensionless core radius RI. The central angle is α_4 = 0.2726 ≈ 15.6 degrees. Arc 4 represents a groove. Because the two directly adjacent arcs This is because 3 and 5 are at a greater distance from the construction point K1 except for the common contact point. The construction point K1 is the center of the arc 8. The arc 8 has a radius R_8 = 0.46, which is the same as the dimensionless core radius RI. The central angle is α_8 = 0.2726 ≈ 15.6 degrees. The arc 8 represents a groove. This is because the two directly adjacent arcs 7 and 9 are at a greater distance from the construction point K1 except for the common contact point. The construction point K1 is the center of the arc 12. The arc 12 has a radius R_12 = 0.46, which is the same as the dimensionless core radius RI. The central angle is α_12 = 0.2726 ≈ 15.6 degrees. The arc 12 represents a groove. This is because the two directly adjacent arcs 1 and 11 are at a greater distance from the construction point K1 except for the common contact point.

[0162] The screw profile does not coincide with the construction point K1, exists within the screw profile, and further has a construction point K2 that exists within a circle whose center is the construction point K1 and whose dimensionless radius is the dimensionless core radius RI. The screw profile is not axisymmetric or point-symmetric with respect to the construction point K2. The construction point K2 is the center of the arc 6a. The arc 6a has a dimensionless radius R_6a = 0.58, which is somewhat smaller than the dimensionless housing inner radius RG = 0.584. The central angle is α_6a = 0.2282 ≈ 13.1 degrees. The arc 6a represents the major screw thread land HK. This is because the two directly adjacent arcs 6 and 7 are at a smaller distance from the construction point K2 except for the common contact point.

[0163] The distance between the construction point K2 and the construction point K1 is approximately 0.073 times the housing inner radius RG. The smaller angle between the angular bisector of the groove (the arc points of the groove that exist on the angular bisector of the groove are separated from the closest point of the major screw thread land HK by the smaller curve length) and the line connecting K1 and K2 is 150.0 degrees.

[0164] Arcs 1, 3, 5, 7, 9, and 11 represent flats. The dimensionless radii of the six arcs are, respectively, R_1 = R_3 = R_5 = R_7 = R_9 = R_11 = 1.00. The centers of these six arcs are not the same as the plotting points K1 and K2 in each case.

[0165] The major thread land HK (arc 6a) and the minor thread land NK 2 (arc 6) are in contact with each other. The major thread land HK (arc 6a), the first minor thread land NK 1 (arc 2), the second minor thread land NK 2 (arc 6), and the third minor thread land NK 3 (arc 10) are separated from the groove by flats, respectively.

[0166] Figure 12b: The screw profile in Figure 12b1 is obtained by displacing the screw profile of Figure 12a1. Figure 12b2 shows an enlarged detailed view around arcs 6 and 6a of Figure 12b1. The displacement was performed such that the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The inner radius of the housing is RG = 0.584. The dimensionless outer radius of the screw is RA = 0.58. Arc 6a has a dimensionless radius R_6a = 0.58, which is the same as the dimensionless outer radius RA of the screw. The dimensionless clearance of the major thread land HK (arc 6a) with respect to the housing is C_HK = 0.004.

[0167] This embodiment is advantageous because it has a constant narrow clearance between the housing and the major thread land HK (arc 6a), resulting in good cleaning of the housing. Also, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the major thread land (arc 6) is substantially smaller than the length in the embodiment according to Figure 11b. Thus, when rotating clockwise, a converging channel is formed between the housing and the major thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is formed.

[0168] Figure 13a: Figure 13a1 shows a screw profile according to the prior art having a number of grooves Z = 4, and Figure 13a2 shows an enlarged detailed view around the arc 6 of Figure 13a1. The dimensionless screw outer radius is RA = 0.52. The dimensionless housing inner radius is RG = 0.554. The plotting point K1 is located at the center M1 of the housing bore and thus at the associated rotation point DP1.

[0169] This embodiment is disadvantageous because the gaps between the housing and the first thread land (arc 2), and also between the housing and the second thread land (arc 6), and also between the housing and the third thread land (arc 10), and also between the housing and the fourth thread land (arc 14) are large, resulting in poor cleaning of the housing.

[0170] Figure 13b: The screw profile in Figure 13b1 was obtained by displacing the screw profile of Figure 13a1. Figure 13b2 shows an enlarged detailed view around the arc 6 of Figure 13b1. The displacement was carried out such that the smaller angle between the angular bisector of arc 8 and the line connecting the plotting point K1 and the plotting point K2 is 157.5 degrees. The plotting point K2 is located at the center M1 of the housing bore and thus at the associated rotation point DP1. The end point of arc 6 corresponding to the start point of arc 7 is located on the dimensionless screw outer radius RA, and the start point of arc 6 is not located on the dimensionless screw outer radius RA. The dimensionless screw outer radius is RA = 0.55. The dimensionless housing inner radius is RG = 0.554.

[0171] Compared with the embodiment according to FIG. 13a1, this embodiment has a narrow gap between the housing and the end point of the arc 6, and as a result, the cleaning of the housing is good. However, in this embodiment, the gap between the housing and the second thread land (arc 6) is not constant, and as a result, it is disadvantageous in that a converging channel or a diverging channel is brought about between the housing and the second thread land (arc 6) depending on the direction of rotation. Therefore, when rotating clockwise, a converging channel is formed between the housing and the main thread land HK (arc 6), and when rotating counterclockwise, a diverging channel is formed.

[0172] FIG. 14a: FIG. 14a1 shows a closed screw profile according to the present invention having a number of grooves Z = 4 and consisting of 17 arcs. FIG. 14a2 shows an enlarged detailed view around the arcs 6 and 6a of FIG. 14a1. The dimensionless housing inner radius is RG = 0.554. The screw outer radius is RA = 0.52. The gap between the housing and the first secondary thread land NK 1 (arc 2), the second secondary thread land NK 2 (arc 6), the third secondary thread land NK 3 (arc 10) and the fourth secondary thread land NK 4 (arc 14) is C_NK = 0.034 respectively.

[0173] The screw profile exists at the center M1 of the housing bore, and thus has a plotting point K1 that exists at the associated rotation point DP1. The screw profile is not axisymmetric or point-symmetric with respect to the plotting point K1. The plotting point K1 is the center of the arc 2. The arc 2 has a dimensionless radius R_2 = 0.52, which is the same as the dimensionless screw outer radius RA. The central angle is α_2 = 0.2289 ≒ 13.1 degrees. The arc 2 is the secondary thread land NK 1represents this. This is because for the two directly adjacent arcs 1 and 3, the distance to the construction point K1 is smaller except for the common contact point. The construction point K1 is the center of arc 6. Arc 6 has a dimensionless radius R_6 = 0.52, which is the same as the dimensionless screw outer radius RA. The central angle is α_6 = 0.0381 ≒ 2.2 degrees. Arc 6 represents the secondary thread land NK 2 represents this. This is because for the two directly adjacent arcs 5 and 6a, the distance to the construction point K1 is smaller except for the common contact point. The construction point K1 is the center of arc 10. Arc 10 has a dimensionless radius R_10 = 0.52, which is the same as the dimensionless screw outer radius RA. The central angle is α_10 = 0.2289 ≒ 13.1 degrees. Arc 10 represents the secondary thread land NK 3 represents this. Why because for the two directly adjacent arcs 9 and 11, the distance to the construction point K1 is smaller except for the common contact point. The construction point K1 is the center of arc 14. Arc 14 has a dimensionless radius R_14 = 0.52, which is the same as the dimensionless screw outer radius RA. The central angle is α_14 = 0.2289 ≒ 13.1 degrees. Arc 14 represents the secondary thread land NK 4This is because the two directly adjacent arcs 13 and 15 have a smaller distance to the construction point K1 except for the common contact point. The construction point K1 is the center of arc 4. Arc 4 has a dimensionless radius R_4 = 0.48, which is the same as the dimensionless core radius. The central angle is α_4 = 0.2289 ≈ 13.1 degrees. Arc 4 represents a groove. This is because the two directly adjacent arcs 3 and 5 have a larger distance to the construction point K1 except for the common contact point. The construction point K1 is the center of arc 8. Arc 8 has a dimensionless radius R_8 = 0.48, which is the same as the dimensionless core radius. The central angle is α_8 = 0.2289 ≈ 13.1 degrees. Arc 8 represents a groove. This is because the two directly adjacent arcs 7 and 9 have a larger distance to the construction point K1 except for the common contact point. The construction point K1 is the center of arc 12. Arc 12 has a dimensionless radius R_12 = 0.48, which is the same as the dimensionless core radius. The central angle is α_12 = 0.2289 ≈ 13.1 degrees. Arc 12 represents a groove. This is because the two directly adjacent arcs 11 and 13 have a larger distance to the construction point K1 except for the common contact point. The construction point K1 is the center of arc 16. Arc 16 has a dimensionless radius R_16 = 0.48, which is the same as the dimensionless core radius. The central angle is α_16 = 0.2289 ≈ 13.1 degrees. Arc 16 represents a groove. This is because the two directly adjacent arcs 1 and 15 have a larger distance to the construction point K1 except for the common contact point.

[0174] The screw profile does not coincide with the construction point K1, exists within the screw profile, and further has a construction point K2 that is within a circle whose center is the construction point K1 and whose dimensionless radius is the dimensionless core radius. The screw profile is not axisymmetric or point-symmetric with respect to the construction point K2. The construction point K2 is the center of arc 6a. Arc 6a has a dimensionless radius R_6a = 0.55, which is slightly smaller than the dimensionless housing inner radius RG = 0.554. The central angle is α_6a = 0.01950 ≈ 11.2 degrees. Arc 6a represents the main screw thread land HK. This is because the two directly adjacent arcs 6 and 7 have a smaller distance to the construction point K2 except for the common contact point.

[0175] The dimensionless distance between the plotting point K2 and the plotting point K1 is approximately 0.051 times the dimensionless housing inner radius RG. The smaller angle between the angular bisector of the groove (the arc points of the groove that exist on the angular bisector of the groove are separated from the nearest point of the major screw thread land HK by the smaller curve length) and the line connecting K1 and K2 is 157.5 degrees.

[0176] Arcs 1, 3, 5, 7, 9, 11, 13, and 15 represent flanks. The dimensionless radii of the eight arcs are respectively R_1 = R_3 = R_5 = R_7 = R_9 = R_11 = R_13 = R_15 = 1.00. The centers of these eight arcs are not the same as the plotting points K1 and K2 in each case.

[0177] The major screw thread land HK (arc 6a) and the second minor screw thread land NK 2 (arc 6) are in contact with each other. The major screw thread land HK, the first minor screw thread land NK 1 (arc 2), the second minor screw thread land NK 2 (arc 6), the third minor screw thread land NK 3 (arc 10) and the fourth minor screw thread land NK 4 (arc 14) are each separated from the groove by a flank.

[0178] Figure 14b: The screw profile in Figure 14b1 was obtained by displacing the screw profile of Figure 14a. Figure 14b2 shows an enlarged detailed view around arcs 6 and 6a of Figure 14b1. The displacement was performed such that the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1. The dimensionless housing inner radius is RG = 0.554. The dimensionless screw outer radius is RA = 0.55. Arc 6a has a dimensionless radius R_6a = 0.55, which is the same as the dimensionless screw outer radius RA. The dimensionless clearance of the major screw thread land HK (arc 6a) with respect to the housing is C_HK = 0.004.

[0179] This embodiment is advantageous because there is a constant narrow gap between the housing and the major thread land HK (arc 6a), and as a result, the housing can be cleaned well. Further, this embodiment is advantageous because the length of the converging or diverging channel (depending on the direction of rotation) between the housing and the major thread land (arc 6) is substantially smaller than the length in the embodiment according to FIG. 13b. Thus, when rotating clockwise, a converging channel is created between the housing and the major thread land HK (arc 6a), and when rotating counterclockwise, a diverging channel is created.

[0180] Figs. 1 to 14 show screw profiles having a number of grooves Z from 1 to 4, and in these screw profiles, the dimensionless screw outer radius RA has different discrete values. The screw element according to the invention is not limited to these discrete values of the screw outer radius. A screw profile having one groove or two grooves can have a dimensionless screw outer radius in the range of RA = 0.57 to RA = 0.67, preferably in the range of RA = 0.59 to RA = 0.65, when the construction point K1 is present at the center M1 of the housing bore and thus at the associated rotation point DP1. A screw profile having three grooves can have a screw outer radius in the range of RA = 0.515 to RA = 0.56, preferably in the range of RA = 0.525 to RA = 0.55, when the construction point K1 is present at the center M1 of the housing bore and thus at the associated rotation point DP1. A screw profile having four grooves can have a screw outer radius in the range of RA = 0.51 to RA = 0.535, preferably in the range of RA = 0.515 to RA = 0.53, when the construction point K1 is present at the center M1 of the housing bore and thus at the associated rotation point DP1.

[0181] When the plotting point K1 is at the center M1 of the housing bore and thus at the associated rotation point DP1, the dimensionless screw outer radius RA is 0.2% to 10% smaller than the dimensionless housing inner radius RG, preferably 0.4% to 7.5% smaller, particularly preferably 0.6% to 5% smaller, and very particularly preferably approximately 0.8% to 2.5% smaller. That is, when the plotting point K1 is at the center M1 of the housing bore and thus at the associated rotation point DP1, the dimensionless clearance C_NK between the secondary thread flank land NK i and the housing is 0.2% to 10% of the dimensionless housing inner radius RG, preferably 0.4% to 7.5%, particularly preferably 0.6% to 5%, and very particularly preferably approximately 0.8% to 2.5%. For a plurality of secondary thread flank lands NK 1 ~NK n these secondary thread flank lands can have the same or different dimensionless clearances C_NK.

[0182] When the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1, the dimensionless screw outer radius RA is 0.1% to 3.2% smaller than the dimensionless housing inner radius RG, preferably 0.2% to 2.6% smaller, particularly preferably 0.3% to 2.0% smaller, and very particularly preferably approximately 0.4% to 1.4% smaller. That is, when the plotting point K2 is at the center M1 of the housing bore and thus at the associated rotation point DP1, the dimensionless clearance C_HK between the primary thread flank land HK and the housing is 0.1% to 3.2% of the dimensionless housing inner radius RG, preferably 0.2% to 2.6%, particularly preferably 0.3% to 2.0%, and very particularly preferably approximately 0.4% to 1.4%.

[0183] The distance from the plotting point K1 to the plotting point K2, and the angular bisector of the groove (the arc point of the groove that exists on the angular bisector of the groove and is the point closest to the primary thread flank land HK according to the smaller curve length separated therefrom), the smaller angle between the line connecting K1 and K2 allows the position of the major thread land HK and the size of its central angle, and thus the screw profile or the screw element having this screw profile, to be adapted to the machining task in the twin - shaft threading machine. Thus, for example, in the case of the profile according to FIG. 6a, the above - mentioned distance (0.1 times the inner radius of the housing), and the angle bisector of the groove (the arc points of the groove existing on the angle bisector of the groove are separated from the closest point of the major thread land HK by the smaller curve length) and the smaller angle (135 degrees) between the line connecting K1 and K2 are selected such that the arc 6 is almost non - existent. In FIG. 7a, the distance between K1 and K2 is reduced to 0.091 times the inner radius of the housing, as a result, the central angle of the arc 6 increases and the central angle of the arc 6a representing the major thread land HK decreases. In FIG. 6a, if the distance between K1 and K2 is increased to be greater than 0.1 times the inner radius of the housing, the arc 6 will completely disappear from the screw profile. In this case, it is necessary to confirm the intersection point between the arcs 5 and 6a so that the central angles of the arcs 5 and 6a can be determined. The same applies to the case of a screw profile having the number of grooves Z = 3 or the number of grooves Z = 4.

[0184] The secondary thread land NK formed from an arc whose center is the plotting point K2 or the plotting point K3 i When the screw profile has it, the position of the plotting point K2 or the plotting point K3, and the secondary thread land NK i By the radius of the arc forming the secondary thread land NK i can be adapted to the machining task in the twin - shaft threading machine. In FIG. 9a, the arc 2a whose center is the plotting point K2 is the corresponding secondary thread land NK iis formed. In FIG. 9a, when the radius of arc 2a is decreased, the central angle of arc 2a increases. When the radius of arc 2a is small enough, arc 2 will completely disappear from the screw profile. In this case, it is necessary to confirm the intersection between arc 2a and 3 so that the central angles of arc 2a and 3 can be obtained. In FIG. 10a, arc 2a whose center is the drafting point K3 forms the corresponding secondary thread land NK i is formed. In FIG. 10a, when the radius of arc 2a is decreased, the central angle of arc 2a increases. When the radius of arc 2a is small enough, arc 2 will completely disappear from the screw profile. In this case, it is necessary to confirm the intersection between arc 1 and 2a so that the central angles of arc 1 and 2a can be obtained.

[0185] FIGS. 1 to 14 show screw profiles having groove numbers Z = 1 to Z = 4. In these screw profiles, the distance between drafting points K1 and K2 has different discrete values. The screw element according to the present invention is not limited to these discrete values. The distance from drafting point K1 to drafting point K2 is 0.2% to 20%, preferably 0.4% to 15%, particularly preferably 0.6% to 10%, and very particularly preferably 0.8% to 5% of the dimensionless housing inner radius RG.

[0186] Figures 1 to 14 show screw profiles having the number of grooves Z = 1 to Z = 4. In these screw profiles, the smaller angle between the angular bisector of the groove (the arc points of the groove existing on the angular bisector of the groove are separated from the closest point of the major screw thread land HK by the smaller curve length) and the line connecting K1 and K2 has different discrete values. The screw element according to the present invention is not limited to these discrete values. When the number of grooves Z = 1, the smaller angle between the angular bisector of the groove and the line connecting K1 and K2 is in the range of 0 degrees to 90 degrees, preferably in the range of 45 degrees to 70 degrees, and particularly preferably approximately 55 degrees. When the number of grooves Z = 2, the smaller angle between the angular bisector of the groove (the arc points of the groove existing on the angular bisector of the groove are separated from the closest point of the major screw thread land HK by the smaller curve length) and the line connecting K1 and K2 is in the range of 110 degrees to 160 degrees, preferably in the range of 125 degrees to 145 degrees, and particularly preferably approximately 135 degrees. When the number of grooves Z = 3, the smaller angle between the angular bisector of the groove (the arc points of the groove existing on the angular bisector of the groove are separated from the closest point of the major screw thread land HK by the smaller curve length) and the line connecting K1 and K2 is in the range of 130 degrees to 170 degrees, preferably in the range of 140 degrees to 160 degrees, and particularly preferably approximately 150 degrees. When the number of grooves Z = 4, the smaller angle between the angular bisector of the groove (the arc points of the groove existing on the angular bisector of the groove are separated from the closest point of the major screw thread land HK by the smaller curve length) and the line connecting K1 and K2 is in the range of 140 degrees to 175 degrees, preferably in the range of 150 degrees to 165 degrees, and particularly preferably approximately 157.5 degrees.

[0187] Figures 1 to 14 show screw profiles having a number of grooves Z = 1 to Z = 4. In these screw profiles, the central angles of the arcs forming the grooves have different discrete values. The screw element according to the present invention is not limited to these discrete values. When the number of grooves Z = 1, the arc forming the groove has a central angle of 90 degrees to 150 degrees, preferably 95 degrees to 140 degrees, and particularly preferably 100 degrees to 130 degrees. When the number of grooves Z = 2, the arcs forming the grooves each have a central angle of 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, and particularly preferably 15 degrees to 30 degrees. When the number of grooves Z = 3, the arcs forming the grooves each have a central angle of 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, and particularly preferably 9 degrees to 18 degrees. When the number of grooves Z = 4, the arcs forming the grooves each have a central angle of 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, and particularly preferably 6 degrees to 12 degrees.

[0188] Figures 1 to 14 show screw profiles having a number of grooves Z = 1 to Z = 4. In these screw profiles, the central angles of the arcs forming the main screw thread land HK have different discrete values. The screw element according to the present invention is not limited to these discrete values. In the first situation, for example, one of two adjacent arcs of the main screw thread land HK may be the secondary screw thread land NK i In the second situation, for example, both of the two directly adjacent arcs of the main screw thread land HK are the secondary screw thread land NK iIt may not be the case. When the number of grooves Z = 1, in the first situation, the arc forming the main thread land HK has a central angle of 10 degrees to 150 degrees, preferably 30 degrees to 140 degrees, particularly preferably 50 degrees to 130 degrees. When the number of grooves Z = 1, in the second situation, the arc forming the main thread land HK has a central angle of 90 degrees to 150 degrees, preferably 95 degrees to 140 degrees, particularly preferably 100 degrees to 130 degrees. When the number of grooves is 2, in the first situation, the arc forming the main thread land HK has a central angle of 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, particularly preferably 15 degrees to 30 degrees. When the number of grooves is 2, in the second situation, the arc forming the main thread land HK has a central angle of 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, particularly preferably 15 degrees to 30 degrees. When the number of grooves is 3, in the first situation, the arc forming the main thread land HK has a central angle of 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, particularly preferably 9 degrees to 18 degrees. When the number of grooves is 3, in the second situation, the arc forming the main thread land HK has a central angle of 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, particularly preferably 9 degrees to 18 degrees. When the number of grooves is 4, in the first situation, the arc forming the main thread land HK has a central angle of 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, particularly preferably 6 degrees to 12 degrees. When the number of grooves is 4, in the second situation, the arc forming the main thread land HK has a central angle of 2 degrees to 20 degrees, preferably 4 degrees to 16 degrees, particularly preferably 6 degrees to 12 degrees.

[0189] Figures 1 to 14 show screw profiles having the number of grooves Z = 1 to Z = 4. In these screw profiles, the central angles of the arcs forming the secondary thread lands NK 1 ~NK n have different discrete values. The screw element according to the present invention is not limited to these discrete values. In the first situation, for example, one of the two directly adjacent arcs of the secondary thread land NK i may be the main thread land HK. In the second situation, for example, the secondary thread land NKi Two directly adjacent arcs may not both be the major thread land HK. In the case where the number of grooves Z = 1, in the first situation, the minor thread land NK i is formed by an arc having a central angle greater than 0 degrees and up to 140 degrees, preferably greater than 0 degrees and up to 110 degrees, particularly preferably greater than 0 degrees and up to 80 degrees. In the case where the number of grooves Z = 2, in the first situation, the minor thread land NK i is formed i by an arc having a central angle greater than 0 degrees and up to 45 degrees, preferably greater than 0 degrees and up to 30 degrees, particularly preferably greater than 0 degrees and up to 15 degrees. In the case where the number of grooves Z = 2, in the second situation, the minor thread land NK i is formed i by an arc having a central angle of 5 degrees to 50 degrees, preferably 10 degrees to 40 degrees, particularly preferably 15 degrees to 30 degrees. In the case where the number of grooves Z = 3, in the first situation, the minor thread land NK i is formed i by an arc having a central angle greater than 0 degrees and up to 27 degrees, preferably greater than 0 degrees and up to 18 degrees, particularly preferably greater than 0 degrees and up to 9 degrees. In the case where the number of grooves Z = 3, in the second situation, the minor thread land NK i is formed i by an arc having a central angle of 3 degrees to 30 degrees, preferably 6 degrees to 24 degrees, particularly preferably 9 degrees to 18 degrees. In the case where the number of grooves Z = 4, in the first situation, the minor thread land NK i is formed i by an arc having a central angle greater than 0 degrees and up to 18 degrees, preferably greater than 0 degrees and up to 12 degrees, particularly preferably greater than 0 degrees and up to 6 degrees. In the case where the number of grooves Z = 4, in the second situation, the minor thread land NK i is formed

[0190] Figure 15 shows the screw profile according to the present invention having the number of grooves Z = 1 in FIG. 2b as a pair of two identical screw profiles. Figure 15 is obtained by copying the arcs 1, 2, 2a, 3, and 4 of the housing and the screw profile in FIG. 2b and displacing these copies in the positive x-axis direction by an axial distance. The copied and displaced arcs are given the symbols 1', 2', 2a', 3', and 4'. The arc 2a of the left screw profile is not washed by the right screw profile. The arc 2a' of the right screw profile is not washed by the left screw profile. The self-cleaning of the screw profile is not completely achieved.

[0191] Figure 16 shows the screw profile according to the present invention having the number of grooves Z = 2 in FIG. 6b as a pair of two identical screw profiles. Figure 16 is obtained by copying the housing in FIG. 6b and displacing it in the positive x-axis direction by an axial distance, copying the arcs 1, 2, 3, 4, 5, 6, 6a, 7, and 8 of the screw profile in FIG. 6b, inverting the copied arcs at point K2 with respect to the x-axis, rotating them 90 degrees clockwise at point K2, and displacing these copies in the positive x-axis direction by an axial distance. The copied and displaced arcs are given the symbols 1', 2', 3', 4', 5', 6', 6a', 7', and 8'. The arc 6a of the left screw profile is not washed by the right screw profile. The arc 6a' of the right screw profile is not washed by the left screw profile. The self-cleaning of the screw profile is not completely achieved.

[0192] Figure 17 shows the screw profile according to the invention having the number of grooves Z = 3 of Figure 12b as a pair of two identical screw profiles. Figure 17 is obtained by copying the arcs 1, 2, 3, 4, 5, 6, 6a, 7, 8, 9, 10, 11 and 12 of the housing and the screw profile of Figure 12b and displacing these copies by an axial distance in the positive x-axis direction. The copied and displaced arcs are given the symbols 1', 2', 3', 4', 5', 6', 6a', 7', 8', 9', 10', 11' and 12'. The arc 6a of the left screw profile is not washed by the right screw profile. The arc 6a' of the right screw profile is not washed by the left screw profile. The self-cleaning of the screw profile is not completely achieved.

[0193] Figure 18 shows the screw profile according to the invention having the number of grooves Z = 4 of Figure 14b as a pair of two identical screw profiles. Figure 18 is obtained by copying the housing of Figure 14b, displacing it by an axial distance in the positive x-axis direction, copying the arcs 1, 2, 3, 4, 5, 6, 6a, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16 of the screw profile of Figure 14b, inverting the copied arcs at point K2 with respect to the x-axis, rotating them clockwise by 135 degrees at point K2, and displacing these copies by an axial distance in the positive x-axis direction. The copied and displaced arcs are given the symbols 1', 2', 3', 4', 5', 6', 6a', 7', 8', 9', 10', 11', 12', 13', 14', 15' and 16'. The arc 6a of the left screw profile is not washed by the right screw profile. The arc 6a' of the right screw profile is not washed by the left screw profile. The self-cleaning of the screw profile is not completely achieved.

[0194] Figure 19 shows the screw profile according to the invention of FIG. 16 in the form of a pair of conveying elements having rotation axes D1 and D2. The rotation axes D1 and D2 are separated from each other by a dimensionless axial distance A and are located at the same height on the drive shafts AW1 and AW2. The dimensionless housing inner radius is RG = 0.66 and the dimensionless screw outer radius is RA = 0.65. The dimensionless gap between the main screw thread land HK of the conveying element and the inner wall of the housing is C_HK = 0.01. The dimensionless length of the conveying element is 1.2 times the dimensionless axial distance A. The dimensionless pitch of the conveying element is T = 1.2, where the dimensionless pitch is understood to mean the axial length required for the rotation of the screw profile divided by the angle of 6.2832 = 360 degrees and the axial distance a. The housing is shown by hatching the left and right of the two conveying elements. Also shown on the surfaces of the two conveying elements are possible calculation grids that can be used to calculate the flow in twin-screw extruders and multi-screw extruders. Regarding the press fit between the drive shaft AW, such as the drive shaft AW1 or the drive shaft AW2, and the screw element, tongue-and-groove systems, or a mechanism of a plurality of interlocking teeth can be used. The mechanism of a plurality of interlocking teeth may be configured as trapezoidal, or may be wavy and either symmetric or asymmetric.

[0195] As an alternative, the screw profile according to the invention of FIG. 16 may also be used in the form of a pair of kneading elements or a pair of mixing elements.

[0196] As is known (see, for example, pages 227 to 248 of Non-Patent Document 1), the conveying element is distinguished in that the screw profile has an axially continuous helical twist and a continuous part. In this case, the conveying element may be on the right side or the left side. The pitch of the conveying element preferably falls within the range of 0.1 times to 10 times the axial distance, and the axial length of the conveying element preferably falls within the range of 0.1 times to 10 times the axial distance.

[0197] The kneading elements are distinguished in that, as is known (see, for example, pages 227 to 248 of Non-Patent Document 1), the screw profile is in the form of a kneading disk and is continuous in an axially offset form. The kneading disk may be located on the right side, on the left side, or in a neutral position. The axial distance of the kneading disk preferably falls within the range of 0.05 times to 10 times the axial distance. The axial distance between two adjacent kneading disks preferably falls within the range of 0.002 times to 0.1 times the axial distance.

[0198] As is known (see, for example, pages 227 to 248 of Non-Patent Document 1), the mixing element is formed by a conveying element having an opening in the screw thread land. The mixing element may be on the right side or on the left side. The pitch of the mixing element preferably falls within the range of 0.1 times to 10 times the axial distance, and the axial length of the element preferably falls within the range of 0.1 times to 10 times the axial distance. The opening preferably has the form of a U-shaped or V-shaped groove, and this groove is preferably arranged opposite to the conveying direction or parallel to the axial direction.

[0199] A series of screw elements consisting of conveying elements and / or kneading elements and / or mixing elements on the drive shaft AW is called a screw configuration. All the screw elements on the drive shaft AW and the drive shaft AW itself together form a screw shaft SW. The first drive shaft is represented by AW1, and the first screw shaft is represented by SW1. The second drive shaft is represented by AW2, and the second screw shaft is represented by SW2.

[0200] The screw profile according to the present invention can be obtained particularly easily from a reference profile that is axially symmetric with respect to the plotting point K1. Such an axially symmetric reference profile is characterized as follows. · The dimensionless core radius RG, the number of grooves Z, and the dimensionless outer radius RA of such an axially symmetric reference profile correspond to the dimensionless core radius RG, the number of grooves Z, and the dimensionless outer radius RA of the screw profile according to the present invention. ·The plotting point K1 of such an axisymmetric reference contour is the same as the plotting point K1 of the screw contour according to the present invention, ·When the number Z of grooves is odd, such an axisymmetric reference contour is axisymmetric with respect to the x-axis or the y-axis, ·When the number Z of grooves is even, such an axisymmetric reference contour is axisymmetric with respect to the x-axis and the y-axis, ·Two similar axisymmetric reference contours, ○When these axisymmetric reference contours have a reference distance RFA corresponding to the axial distance A, and, ○When the number Z of grooves is odd, when these axisymmetric reference contours do not rotate relative to each other at their respective reference rotation axes RFD1 and RFD2, ○When the number Z of grooves is even, when these axisymmetric reference contours rotate relative to each other by an angle of π / Z = 180 degrees / Z at their respective reference rotation axes RFD1 and RFD2, ○When these axisymmetric reference contours rotate at the same speed in the same rotation direction at their respective reference rotation axes RFD1 and RFD2, pair up and clean each other precisely.

[0201] Therefore, - Fig. 1a shows a reference contour that is axisymmetric with respect to the plotting point K1 and has a groove number Z = 1 for the screw contour according to the present invention according to Fig. 2a, Fig. 3a or Fig. 4a. - Fig. 5a shows a reference contour that is axisymmetric with respect to the plotting point K1 and has a groove number Z = 2 for the screw contour according to the present invention according to Fig. 6a, Fig. 7a, Fig. 9a or Fig. 10a. - Fig. 11a shows a reference contour that is axisymmetric with respect to the plotting point K1 and has a groove number Z = 3 for the screw contour according to the present invention according to Fig. 12a. - Fig. 13a shows a reference contour that is axisymmetric with respect to the plotting point K1 and has a groove number Z = 4 for the screw contour according to the present invention according to Fig. 14a. - Figure 5a shows a reference contour that is axisymmetric with respect to the plotting point K1 for the screw contour according to the present invention and has a number of grooves Z = 2. The arcs 1 to 5, arc 8, and the plotting point K1 are identical respectively. Therefore, the dimensionless core radius RI, the number of grooves Z, and the dimensionless outer radius RA of the axisymmetric reference contour and the screw contour according to the present invention are of the same size in each case. Therefore, furthermore, the rotation point of the axisymmetric reference contour and the rotation point of the screw contour according to the present invention will correspond.

[0202] For example, in order to convert the reference contour according to FIG. 5a, which is axisymmetric with respect to the plotting point K1, into the screw contour according to the present invention according to FIG. 7a, the arc 6a representing the major thread land HK must be inserted into the axisymmetric reference contour between arcs 6 and 7, and correspondingly, it is necessary to adapt arcs 6 and 7. The radius of arc 6a is selected to be the same as that obtained by subtracting the dimensionless housing inner radius RG = 0.66 by the dimensionless gap C_HK = 0.01. The center of arc 6a exists at the plotting point K2. The position of the plotting point K2 is such that the smaller angle between the angular bisector of the groove (the arc point of the groove existing on the angular bisector of the groove is separated from the closest point of the major thread land HK by the smaller curve length) and the line connecting K1 and K2 is 135.0 degrees, and the distance between the plotting points K1 and K2 is equal to 0.06. The new end point of arc 6 is generated from the intersection of arc 6a and the original arc 6. The starting point of arc 6a is the same as the end point of arc 6. The new starting point of point 7 on the circle is generated from the intersection of arc 6a and the original arc 7. The end point of arc 6a is the same as the starting point of arc 7. With the currently known starting points, end points, and centers of arcs 6, 6a, and 7, it becomes possible to calculate the respective central angles.

[0203] Figure 20 shows a pair of reference contours having a number of grooves Z = 2. The reference contour of the left shaft that is axisymmetric with respect to the plotting point K1 corresponds to the axisymmetric contour according to FIG. 5a. The reference contour of the right shaft represents a copy of the reference contour of the left shaft and is therefore also axisymmetric, · This copy is inverted with respect to the x-axis, ·At the origin of the x / y coordinate system, it is rotated clockwise by an angle of π / 2 = 180 / 2 = 90 degrees, ·It is displaced in the positive x-axis direction by the dimensionless reference axis direction distance RFA corresponding to the dimensionless axis direction distance A. By this procedure, the arc 1 of the reference contour of the left shaft that is axisymmetric with respect to the plotting point K1 is converted into the arc 1' of the axisymmetric reference contour of the right shaft. The same applies to arcs 2 to 8, thereby generating arcs 2' to 8'. The plotting point K1 is identical to the reference rotation point RFD1. The plotting point K1' displaced by the reference axis direction distance in the positive x-direction is identical to the reference rotation point RFD2. When the axial reference contour rotates at the same speed in the same rotation direction about their respective reference rotation axes RFD1 and RFD2, the axisymmetric reference contours of the left shaft and the right shaft pair up and clean each other.

[0204] In FIG. 20, the reference screw outer radius RFRA is the same as the reference housing inner radius RFRG = 0.61. The reference screw outer radius RFRA is smaller than the housing inner radius RG by 0.2% to 10%, preferably by 0.4% to 7.5%, particularly preferably by 0.6% to 5%, and very particularly preferably by 0.8% to 2.5%.

[0205] At a given dimensionless axis direction distance A corresponding to the dimensionless reference axis direction distance RFA, the reference contour can be easily plotted according to the method disclosed on pages 95 to 109 of Non-Patent Document 1.

Claims

1. A screw element having a number Z of grooves, It is suitable for a twin shaft screw machine, which has Two screw shafts SW1 and SW2 rotating in the same direction and at the same speed, the rotation axis D1 of the screw shaft SW1 and the rotation axis D2 of the screw shaft SW2 being separated by an axial distance a; two mutually penetrating circular housing bores, each of which has the same inner housing radius rg and bore centers M1 and M2 of the housing bores spaced apart by a distance equal to the axial distance a, the bore centers M1 and M2 of the housing bores coinciding with the centers of cross sections of the rotation axes D1 and D2 of the screw shafts SW1 and SW2, respectively; having The screw elements are screw profiles, (1) Form a closed convex line; (2) the circular arc is made up of only arcs whose radii are equal to or less than the axial distance a, and directly adjacent arcs have different radii; (3) A first construction point K1 is present within the screw profile; (4) It is not axially symmetrical with respect to the drawing point K1, (5) Consisting of at least four circular arcs; (6) A second construction point K2 that does not coincide with the construction point K1 and exists within the screw profile, (7) The drawing point K2 is not point-symmetric or axially symmetric, (8) A rotation point DP coincides with one of the bore centers M1 and M2 and exists on a path from the drawing point K1 to the drawing point K2, (9) There is exactly one main thread land HK, which is formed from only one circular arc, the center of which is the drawing point K2, and the points of contact between the main thread land HK and the two circular arcs directly adjacent to the main thread land HK are the pair of points of the screw profile farthest from the drawing point K2; (10) having at least one groove, each groove being formed from only one respective arc having a center at said drawing point K1, each groove being an arc having a radius equal to said core radius ri, and each of two arcs directly adjacent to a groove being at a greater distance from said drawing point K1 than said arc of said groove, except for said respective common tangent points; (11) A region of the screw profile having a plurality of flanks, the flanks being circular arcs having centers which are neither the drawing point K1 nor the drawing point K2; (12) the groove is separated from the nearest point of the main thread land HK by at least one circular arc that is a flank; A screw element having a screw profile.

2. The screw element according to claim 1, wherein the arc forming the main thread land HK has a central angle greater than 0 degrees, preferably between 1 degree and 179 degrees.

3. The screw element according to claim 1 or 2, wherein the screw element is not point-symmetric or point-symmetric with respect to the drawing point K1, preferably the screw element is not point-symmetric with respect to the drawing point K1.

4. The number of arcs of the screw profile is equal to the number of grooves Z multiplied by 4 or equal to the number of grooves multiplied by 4 and added by 1, preferably the screw profile of the screw element has If the number of grooves Z=1, then the grooves are made up of exactly 4 circular arcs or exactly 5 circular arcs, particularly preferably exactly 5 circular arcs, For a number of grooves Z=2, the grooves are made up of exactly 8 circular arcs or exactly 9 circular arcs, preferably exactly 9 circular arcs, if the number of grooves Z=3, then it is composed of exactly 12 circular arcs or exactly 13 circular arcs, preferably exactly 13 circular arcs, 4. A screw element according to claim 1, which is preferably made up of exactly 16 circular arcs or exactly 17 circular arcs, preferably made up of exactly 17 circular arcs, for a number of grooves Z=4.

5. The screw element according to any one of claims 1 to 4, wherein the second construction point K2 of the screw profile lies within a circle having the construction point K1 as its center and the core radius ri as its radius.

6. The screw element according to any one of claims 1 to 5, wherein the rotation point DP of the screw element according to the present invention is preferably closer to the drawing point K2 than to the drawing point K1, and preferably the rotation point DP is on the drawing point K2.

7. The screw element according to any one of claims 1 to 6, wherein the arc radius rHK of the main thread land HK corresponds to the housing inner radius rg minus the main thread land clearance c_HK.

8. The arcs forming the groove are When the number of grooves Z=1, the groove has a central angle of 90° to 150°, preferably a central angle of 95° to 140°, particularly preferably a central angle of 100° to 130°, In the case of a number of grooves Z=2, each has a central angle of 5° to 50°, preferably a central angle of 10° to 40°, particularly preferably a central angle of 15° to 30°, the central angles of the grooves being the same or different, In the case of a number of grooves Z=3, each has a central angle of 3° to 30°, preferably a central angle of 6° to 24°, particularly preferably a central angle of 9° to 18°, the central angles of the grooves being the same or different, 8. The screw element according to claim 1, having a central angle of 2 degrees to 20 degrees, preferably a central angle of 4 degrees to 16 degrees, particularly preferably a central angle of 6 degrees to 12 degrees, for a number of grooves Z=4.

9. The screw element according to any one of claims 1 to 8, wherein the screw profile has a third drawing point K3, the screw profile is not axially symmetric or point symmetric with respect to the drawing point K3, the drawing point K3 is a point having the same distance from the drawing point K1 as the drawing point K2, the drawing points K1, K2 and K3 are on a straight line, and K1, K2 and K3 are not identical.

10. The screw profile may have a single secondary thread land NK or multiple secondary thread lands NK １ ~ N.K. ｎ Each secondary thread land NK ｉ is formed from only one circular arc, and the center of the circular arc is the drawing point K1, the drawing point K2, or the drawing point K3.

11. At least one arc is formed on the flank of the secondary thread land NK ｉ The screw element according to any one of claims 1 to 10, wherein the grooves are separated from the nearest point of

12. The rotation point DP of the screw profile is the drawing point K2. Item 12. The screw element according to any one of items 1 to 11.

13. The screw element according to any one of claims 1 to 12, which is suitable for being placed and operated on the screw machine in a pair with another screw element having the same or a different screw profile and the same or a different arrangement of the rotation point on the other screw shaft, preferably two identical screw elements according to any one of claims 1 to 12 are used.

14. the core radius ri, the number of grooves Z, and the outer radius ra of a screw profile correspond to the core radius ri, the number of grooves Z, and the outer radius ra of a reference screw profile, The plotting point K1 of the screw profile is the same as the plotting point K1 of the reference profile, the nominal outer screw radius rfra is smaller than the inner housing radius rg by 0.2% to 10%, preferably by 0.4% to 7.5%, particularly preferably by 0.6% to 5%, very particularly preferably by 0.8% to 2.5%, Two similar reference contours are the reference profile has a reference distance rfa corresponding to the axial distance a; and If the reference profile rotates at the same speed and in the same direction of rotation at its respective reference rotation points rfDP1 and rfDP2, Screw elements according to any one of claims 1 to 13, which come in pairs for precise cleaning of each other.

15. 15. An extruder having two or more drive shafts rotating in the same direction and at the same speed, the extruder comprising two or more identical or different screw elements according to any one of claims 1 to 14.

16. Use of a screw element according to any one of claims 1 to 14 for processing or producing plastic materials.

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