Polygonal shaft for extruder screw

Abstract

The invention relates to an apparatus (1) for extruding plastics material, comprising a housing (2) in which a process chamber (3) is formed and a first screw shaft (4) which has a first longitudinal axis (5), wherein: the first screw shaft (4) is mounted in the housing (2) inside the process chamber (3), the first screw shaft (4) comprising a first shaft shank (6) and a first screw element (7) which can be slid onto and taken off of the first shaft shank (6); in a first normal plane (8) of the first longitudinal axis (5), the first shaft shank (6) has a first cross section (9) in the form of a polygonal profile; and the first screw element (7) has a first mounting region (10) which has a complementary shape to the polygonal profile of the first cross section (9).

Description

[0001] POLYGON SHAFT FOR EXTRULATOR SHELL

[0002] The invention relates to a device for plastics processing with a housing having a process chamber formed therein and a first screw shaft received in the process chamber, wherein the screw shaft has a first shaft with a polygon profile and a first screw element with a first receiving area whose shape is complementary to the polygon profile.

[0003] From WO 2006 045 412 A2, an extruder with multiple screw shafts is known, wherein individual screw segments are coupled to a shaft by means of a profiled shaft connection for torque and speed transmission. Such profiled shaft connections, and in particular the splined shaft connection disclosed in the prior art, have the disadvantage that stress peaks occur, especially in the notch root of a respective groove, which negatively affect the fatigue strength of these machine elements and thus the economic efficiency of a system with such machine elements.

[0004] The object of the present invention was to overcome the disadvantages of the prior art and to provide a device by means of which the economic efficiency of plastics processing is improved, while at the same time improving operational reliability by positively influencing fatigue strength.

[0005] This task is solved by a device according to the claims.

[0006] The device according to the invention for the continuous processing and / or manufacturing of plastics, in particular for the extrusion of plastic material, comprises a housing with a process chamber formed therein and a first screw shaft with a first longitudinal axis, wherein the first screw shaft is received in the housing within the process chamber, wherein the first screw shaft comprises a first shaft and a first screw element that can be slid onto and removed from the first shaft, wherein the first shaft has a first cross-section designed as a polygon profile in a first normal plane of the first longitudinal axis, wherein the first screw element has a first receiving area whose shape is complementary to the polygon profile of the first cross-section, so that the first screw element can be coupled to the first shaft in a way that transmits speed and torque.In the context of the device according to the invention, a shaft is understood to be a machine element whose axial length in the direction of the first longitudinal axis is a multiple of its mean diameter. The primary function of such a shaft is to transmit torque and rotational speed, which can be introduced by a drive coupled to the shaft, to the worm gear element. Simultaneously, the worm gear element is supported on the shaft by the specific design of the shaft with a polygonal profile.

[0007] The first receiving area can be understood as a design of the inner surface of the first worm element, which is shaped to be complementary to the first cross-section, taking into account a corresponding fit, so that the first worm element can be slid onto and removed from the first shaft. Thus, both the first cross-section and the cross-section of the inner surface are designed as polygon profiles. The first shaft in question can also be referred to as a polygon shaft.

[0008] In the context of the device according to the invention, a polygon profile is understood to mean a polygonal shape of the outer contour of the cross-section of the shaft. Thus, the radially outer surface of the shaft has a polygonal cross-sectional shape, so the shaft could also be referred to as a polygon shaft. Similarly, the cross-section of the inner surface of the worm element has a polygonal cross-section, since the receiving area is shaped to be complementary to the first cross-section of the polygon shaft.

[0009] In the context of the invention, a screw element is understood to be a machine element that has, in its radially outer region, a screw contour or a similar contour for extruding, conveying, processing, comminuting, or mixing plastic material, in operative connection with the housing surrounding this screw element and / or a further screw shaft. Typically, such a screw element is coupled to the shaft by means of a profiled shaft connection, such as a splined shaft connection, in a torque- and speed-transmitting manner. Particularly in a screw extruder, a high torque is transmitted via the shaft to process the plastic material to be extruded.Since the screw element is coupled to the shaft via a polygonal profile, transmitting torque and speed, the stress concentration effect of this coupling is significantly reduced compared to a conventional coupling, such as a splined shaft connection. This allows the shaft and the corresponding screw element to have a smaller diameter and wall thickness, respectively, compared to a known extruder screw design. This results in material and cost savings in both the manufacturing of the extruder screw and the housing. Furthermore, the reduced stress concentration improves fatigue strength.

[0010] A further advantage of the device according to the invention is that the coupling of the shaft and worm gear element by means of a polygon profile as a positive-locking connection is self-centering, since a polygon profile has a symmetrical shape, which reduces vibrations of the device according to the invention and also improves its operational strength. At the same time, impact loads during operation of the device according to the invention result in reduced stress peaks compared to the use of a conventional splined shaft. This also means that the replaceability of the worm gear element is simplified or improved, since no wedging effect or jamming of the components can occur between the worm gear element and the shaft.

[0011] Furthermore, it can be advantageous to accommodate a second screw shaft with a second longitudinal axis within the process chamber. This second screw shaft comprises a second shaft with a second cross-section formed as a polygonal profile in a second normal plane of the second longitudinal axis, and a second screw element with a second receiving area whose shape is complementary to the polygonal profile of the second cross-section. This allows the second screw element to be coupled to the second shaft for speed and torque transmission. All subsequently described useful measures, alternative designs, or extensions are applicable to both a simple extruder with a single first screw shaft and a twin-screw extruder with two screw shafts, i.e., a first screw shaft and a second screw shaft.However, in the following description, some useful extensions are only described for the first screw shaft, although each of these useful extensions is also applicable to a second screw shaft of a twin-screw extruder.

[0012] Since both the first and second shafts of such a twin-screw extruder now have a polygonal profile, or are designed as polygonal shafts, the advantageous effect arises that the corresponding screw elements can each have more extended screw profiles in the radial direction. This is because the notch effect is reduced compared to known couplings using profiled shaft connections, and thus a polygonal shaft can have a smaller mean diameter. As a result, more complex screw geometries for the screw profiles of the individual screw elements can be implemented and the device can continue to operate reliably and with long service lives. In particular, the reduced stress peaks resulting from the polygonal profile design of the shafts mean that tightly meshing screw geometries of two interconnected screw shafts in a twin-screw extruder can be used with exceptional robustness and operational reliability.

[0013] Especially in a conically tapered twin-screw extruder, the use of polygon shafts or polygon shanks, i.e., shafts with a polygonal profile, offers significant advantages. A conically tapered twin-screw extruder is defined as one in which the first screw shaft has a first longitudinal axis and the second screw shaft has a second longitudinal axis, with the first and second longitudinal axes intersecting each other or at least intersecting in a projection onto a plane. Specifically, the longitudinal axes can form an angle with each other within a range of 0.5° to 5°.Due to the convergence of the screw longitudinal axes in conjunction with the taper of the screw shafts themselves, the screw segments in the plasticizing zone and / or in an end region of such a conically tapered twin-screw extruder have a relatively small mean outer diameter. To nevertheless achieve the required service life, the prior art often forms the plasticizing zone or end region, such as a final extrusion section, of the screw shafts as a single unit with the shaft. Thus, the end region is fixed, while the remaining sections of the screw shaft can still be fitted with slide-on screw segments. This disadvantage can be avoided by using a polygonal shaft according to the invention. A polygonal shaft exhibits a significantly lower notch effect than the splined shafts conventionally used in extruders.This allows a polygonal shaft to be used even in sections with a small average outer diameter, such as the end section, to accommodate the screw segments. Therefore, the screw geometry can be changed even in the end section by replacing the screw segments. This results in a cost advantage compared to manufacturing a shaft with an integral section of the screw geometry in the end section.

[0014] Consequently, the screw segments can be made of different materials than the associated shaft, which is not technically feasible or at least not economically viable with a shaft where the screw geometry is an integral part of the plasticizing zone or end area. This significantly increases the flexibility of a twin-screw extruder in terms of the different materials that can be processed.

[0015] Furthermore, it may be provided that the polygon profile and the recording area are designed as a P3G profile according to DIN 32711 or as a P4C profile according to DIN 32712.

[0016] Provided the polygon profile is designed according to a common standard, this has the advantage that explosive forces on the screw element are limited within a safety range due to high local surface pressures. In conjunction with an extruder, a further advantage arises from material savings compared to conventional profile shaft connections. Furthermore, manufacturing a polygon profile according to a common standard, even for a shaft shaft, offers the advantage that established non-circular turning processes can be applied, resulting in cost savings. In addition, the screw element can be designed to comprise several screw segments that can be arranged in series along the longitudinal axis.

[0017] An advantage of this design is that, due to the reduced longitudinal extent of each screw element resulting from its division along the longitudinal axis, the multiple screw elements can be more easily removed from or slid onto the shaft. In conjunction with the polygonal profile, a further advantage arises: the multiple screw elements exhibit less radial play relative to each other along the longitudinal axis. This allows the mass flow rate of the individual sections, which follow one another along the longitudinal axis, to be maintained more effectively, thus improving the processing of free-flowing materials using the extruder.

[0018] It is also advantageous to have a design in which the screw segments are designed to be flat and free of positive locking couplings at axially opposite end sections.

[0019] This prevents the screw segments from becoming wedged together during operation of the device, which facilitates easy disassembly.

[0020] According to further training, it is possible that the first shaft and / or the second shaft is tapered in the direction of the longitudinal axis, especially in the direction of the conveying direction of the extruder or the twin screw extruder.

[0021] This causes the screw segments or screw element to clamp onto the shaft during operation of the device due to the axial force exerted during extrusion. This also results in the self-centering of the screw segments or screw element. Thus, a robust and simple design measure allows for backlash-free mounting of the screw segments or screw element to the shaft. The screw element of an extruder screw is often pushed onto the shaft, with one end of the shaft bearing against a flank to fix the screw element in an axial position. The screw element can then be secured against this stop at the opposite end. This can be achieved, for example, with a screw-on nut.In any case, a worm gear element must be secured axially against axial disengagement with as little play as possible to the shaft. By providing a tapered shaft, the axial force necessarily required by a locking element can be further reduced, or the stop required for axial locking can be eliminated or at least reduced.

[0022] Furthermore, it may be advantageous if a screw segment has a clearance with respect to the respective associated shaft, so that the screw segment has two contact surfaces for contact with the associated shaft, wherein the contact surfaces are designed as a subsection of the receiving area.

[0023] This allows the clamping or jamming of a screw segment on the shaft to be influenced in such a way that a screw segment can be lifted from the shaft more easily than if the screw segment had a continuous contact surface with the contacting component on the shaft.

[0024] Furthermore, it may be provided that the respective shaft has a surface with depressions, dimples, indentations, grooves, slots or similar area-specific indentations formed in it.

[0025] In particular, it can be provided that the grooves are formed parallel to the first longitudinal axis in the shaft, with the longitudinal grooves being arranged distributed over a circumference of the shaft.

[0026] In particular, it may be provided that the longitudinal grooves are formed by means of a tool perpendicular to the

[0027] The longitudinally aligned bores are fluidically coupled to a central bore within the shaft shaft. This allows a solvent, particularly glycol, to be introduced into the grooves through the central bore.

[0028] This simplifies the removal of the screw element or screw segments. Simultaneously, the surface depressions, particularly those created during removal of the screw element or screw segments, can trap contaminants or impurities, such as those caused by plastic seepage from the device's process chamber, thus facilitating removal and reducing clamping.

[0029] Furthermore, it may be provided that the respective shaft shaft comprises a central bore and a radial opening with the central bore, so that a fluid can be introduced via the central bore and, in the assembled state of the respective shaft shaft with the respective associated screw element, can be introduced or pressed in between the shaft shaft and the associated screw element.

[0030] The fluid can be a solvent capable of dissolving plastics, allowing contaminants that have entered the area between the shaft and screw elements from the process chamber to be dissolved, thus improving the removableness of the screw element from the shaft. The same applies analogously if the screw element comprises multiple screw segments.

[0031] Alternatively, the fluid can also be hydraulic oil, whereby jams between the shaft and the worm element can be resolved by injecting the hydraulic oil, thus improving the removableness of the worm element from the shaft. The same applies analogously if the worm element comprises several worm segments.

[0032] Alternatively, a temperature-controlled fluid can be introduced through the central bore and the radial opening to temper the screw shaft or to easily regulate the temperature as required during extrusion processes. This tempering can also be used to cool or heat the screw shaft components at different rates, thereby increasing or decreasing the clamping force between them.

[0033] To better understand the invention, it is explained in more detail with reference to the following figures.

[0034] They each show, in a highly simplified, schematic representation:

[0035] Fig. 1 ... a device for extruding plastic material;

[0036] Fig. 2 ... a sectional view of a snail segment;

[0037] It should be noted at the outset that in the differently described embodiments, identical parts are provided with the same reference numerals or component designations, and the disclosures contained in the entire description can be applied analogously to identical parts with the same reference numerals or component designations. Furthermore, the positional designations chosen in the description, such as top, bottom, side, etc., refer to the figure directly described and illustrated, and these positional designations must be applied analogously to the new position if the position changes.

[0038] Figure 1 shows a highly simplified, schematic representation of a device 1 for extruding plastic material. The device 1 comprises a housing 2 with a process chamber 3 formed therein, the housing 2 being shown in section in Figure 1. Furthermore, Figure 1 shows a cross-section AA through the device 1 shown alongside, where the same component designations and reference numerals are used for identical parts as in the adjacent representation of the device 1. Figure 1, including the section view, should be viewed and understood in conjunction with the following figure description.

[0039] In addition to the housing 2 with the process chamber 3 formed therein, the device 1, which can also be commonly referred to as an extrusion device or extruder, further comprises a first screw shaft 4 with a first longitudinal axis 5, wherein the first screw shaft 4 is received in the housing 2 within the process chamber 3.

[0040] The first screw shaft 4 comprises a first shaft 6 and a first screw element 7 that can be slid onto and removed from the first shaft 6. The first screw element 7 has a screw geometry in its radially outer diameter region with respect to the first longitudinal axis 5, by means of which plastic can be extruded during operation of the device 1.

[0041] The device 1 is characterized in that the first shaft 6 has a first cross-section 9, designed as a polygonal profile, in a first normal plane 8 of the first longitudinal axis 5, wherein the first worm element 7 has a first receiving area 10 that is form-complementary to the polygonal profile of the first cross-section 9. The first receiving area 10 can be understood as a configuration of the inner surface 11 of the first worm element 7 that is form-complementary to the first cross-section 9, taking into account a corresponding fit, so that the first worm element 7 can be slid onto and removed from the first shaft 6. Thus, both the first cross-section 9 and the cross-section of the inner surface 11 are designed as polygonal profiles. The first shaft 6 in question can also be referred to as a polygonal shaft.

[0042] In an alternative and advantageous embodiment of the device 1, it can also be provided that a second screw shaft with a second longitudinal axis is accommodated within the process chamber 3, wherein the second screw shaft comprises a second shaft with a second cross-section formed as a polygonal profile in a second normal plane 8 of the second longitudinal axis, and a second screw element with a second receiving area whose shape is complementary to the polygonal profile of the second cross-section. The second screw shaft can therefore be designed identically to the first screw shaft with respect to its shaft. Thus, a twin-screw extruder, in particular a conically tapered twin-screw extruder, can be designed in which both screw shafts each have a polygonal shaft, i.e., the first screw shaft has a first polygonal shaft and the second screw shaft has a second polygonal shaft.

[0043] This design is not apparent from the sectional view in Fig. 1. However, this design generally offers a number of advantages, which were discussed in the introductory section.

[0044] In general, it can be advantageous if the polygon profile and its associated receiving area 10 are manufactured according to a standard. In particular, the polygon profile and its associated receiving area 10 can be designed as a P3G profile according to DIN 32711 or as a P4C profile according to DIN 32712. This applies to both the first screw shaft 4 and the second screw shaft of a possible embodiment of a twin-screw extruder, whereby both the first polygon shaft and the second polygon shaft can each have a polygon profile according to a common standard.

[0045] The first worm element 7 of the first worm shaft 4 and / or the second worm element of the second worm shaft can each be composed of several worm segments 12 that can be arranged in series along the first longitudinal axis 5 or along the second longitudinal axis, respectively. It can be provided that the worm segments 12 are planar and free of any form-fitting couplings at axially opposite end sections. Thus, a worm segment 12 can have a planar surface at each axially opposite distal end, so that two adjacent worm segments 12, which are successively pushed onto, for example, the first shaft 6, are positioned with their respective planar surfaces abutting and in contact with each other.

[0046] In an advantageous embodiment, which is not shown in Fig. 1, the first shaft 6 can further be designed to taper in the direction of the longitudinal axis 5, particularly in the direction of conveying. This can be provided analogously for the second shaft of a twin-screw extruder. The conveying direction of the device or extruder also determines the direction of action of the axial force during extruder operation. The tapering in the direction of conveying allows the axial force to be absorbed more effectively during extruder operation.

[0047] Figure 2 shows a highly simplified, schematic cross-sectional view of a screw segment 12. Again, the same component designations and reference numerals are used for identical components as in Figure 1 described above. As can be seen in Figure 2, a screw segment 12 can have a relief 13 in a central region, so that the screw segment 12 has two contact surfaces 15 for contact with the shaft 6. The two contact surfaces 15 thus form the inner surface 11 or a part of the inner surface 11, which is shaped to be complementary to the polygon profile of the first shaft 6 or the second shaft 6. It may also be provided that a surface 14 of the first shaft 6 and / or the second shaft 6 has depressions formed therein, such as hollows, dimples, indentations, or grooves.

[0048] It may also be provided that the shaft 6 and / or the second shaft each comprise a central bore 16 and a radial opening 17 with the central bore 16, so that a fluid can be introduced via the central bore 16 and, in the assembled state of the first shaft 6 with the first screw element 7 or in the assembled state of the second shaft 6 with the second screw element, can be introduced or pressed in between the respective shaft 6 and the associated screw element.

[0049] In this context, it can also be provided that grooves 18 are formed in the shaft 6 extending from its surface 14, wherein the grooves 18 are formed longitudinally parallel to the first longitudinal axis 5 in the shaft 6, and wherein the longitudinal grooves 18 are arranged distributed over the circumference of the shaft 6. It can be provided that the grooves 18 are fluidically coupled to the central bore 16 by means of radial openings 17, so that a solvent can be introduced into the grooves 18 through the central bore 16.

[0050] The exemplary embodiments show possible embodiment variants, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiment variants, but rather various combinations of the individual embodiment variants are also possible and this possibility of variation lies within the skill of the person skilled in this technical field due to the teaching on technical action by the present invention.

[0051] The scope of protection is defined by the claims. However, the description and drawings must be consulted for the interpretation of the claims. Individual features or combinations of features from the different embodiments shown and described can, in themselves, represent independent inventive solutions. The problem underlying these independent inventive solutions can be found in the description. All references to value ranges in this description are to be understood as encompassing any and all sub-ranges thereof. For example, the reference 1 to 10 is to be understood as including all sub-ranges, starting from the lower limit 1 and the upper limit 10. That is, all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g., 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0052] Finally, for the sake of clarity, it should be noted that, for a better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced in size.

[0053] Reference numeral list

[0054] device

[0055] Housing

[0056] Trial Chamber

[0057] First wave of snails

[0058] First longitudinal axis

[0059] First wave shaft

[0060] First snail element

[0061] Normal plane

[0062] First cross-section

[0063] First reception area

[0064] Inner surface

[0065] snail segment

[0066] exemption

[0067] surface

[0068] Site area

[0069] Drilling

[0070] breakthrough

[0071] Nut

Claims

Patent claims 1. Device (1) for extruding plastic material, comprising a housing (2) with a process chamber (3) formed therein and a first screw shaft (4) with a first longitudinal axis (5), wherein the first screw shaft (4) is received in the housing (2) within the process chamber (3), wherein the first screw shaft (4) comprises a first shaft (6) and a first screw element (7) that can be slid onto and removed from the first shaft (6), characterized in that the first shaft (6) has a first cross-section (9) formed as a polygon profile in a first normal plane (8) of the first longitudinal axis (5), wherein the first screw element (7) has a first receiving area (10) that is complementary in shape to the polygon profile of the first cross-section (9).

2. Device (1) according to claim 1, characterized in that a second screw shaft with a second longitudinal axis is received within the process chamber (3), wherein the second screw shaft comprises a second shaft shaft with a second cross-section formed as a polygon profile in a second normal plane of the second longitudinal axis and a second screw element with a second receiving area that is complementary in shape to the polygon profile of the second cross-section.

3. Device (1) according to one of the preceding claims, characterized in that the polygon profile and the receiving area (10) are designed as a P3G profile according to DIN 32711 or as a P4C profile according to DIN 32712.

4. Device (1) according to one of the preceding claims, characterized in that the screw element (7) comprises several screw segments (12) which can be arranged one after the other in the direction of the first longitudinal axis (5).

5. Device (1) according to claim 4, characterized in that the screw segments (12) are designed to be planar and free of positive locking couplings at axially opposite end sections.

6. Device (1) according to one of the preceding claims, characterized in that the shaft (6) is tapered in the direction of the longitudinal axis (5), in particular in the direction of the conveying direction.

7. Device (1) according to claim 4, characterized in that a screw segment (12) has a clearance (13) with respect to the shaft (6) such that the screw segment (12) has two contact surfaces (15) for contact with the shaft (6).

8. Device (1) according to one of the preceding claims, characterized in that the shaft (6) has a surface (14) with depressions, dimples, indentations, grooves, slots (18) or similar partial indentations formed therein.

9. Device (1) according to claim 8, characterized in that the grooves (18) are formed extending longitudinally parallel to the first longitudinal axis (5) in the shaft (6), wherein the longitudinally extending grooves (18) are arranged distributed over a circumference of the shaft (6).

10. Device (1) according to one of the preceding claims, characterized in that the shaft (6) comprises a central bore (16) and a radial opening (17) with the central bore (16), so that a fluid can be introduced via the central bore (16) and, in the assembled state of the shaft (6) with the screw element (7), can be introduced or pressed in between the shaft (6) and the screw element (7).

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