Screw section

Abstract

Provided is a screw section capable of alleviating stress concentration at both ends in the circumferential direction of a groove bottom surface while suppressing a reduction in wall thickness at the groove bottom of a spline groove. The screw section (162) constitutes a screw shaft for an extruder by a combination of a shaft body (161) fitted with a spline, and is provided with a female spline hole having a plurality of spline grooves (162a). Each of the plurality of spline grooves (162a) is surrounded by a groove side surface (162b), a groove bottom surface (162c), and a recessed surface (162d). The recessed surface (162d) is configured from a smooth concave curved surface, is connected to both end portions of the groove bottom surface (162c) in the circumferential direction and to the end portion of the groove side surface (162b) on the outside in the radial direction, and is configured so as to be recessed on both sides on the outside in the radial direction and on the outside in the circumferential direction so as to be separated from the male spline (161a).

Description

Technical Field

[0001] This utility model relates to screw sections for extruders. Background Technology

[0002] In screw-type extruders, there are cases where a screw shaft is used, comprising a shaft body and multiple screw segments fitted into that shaft body (e.g., Patent Document 1). In the screw shaft consisting of the shaft body and multiple screw segments, an external spline is provided on the shaft body, and a spline groove is provided on each screw segment to engage with the external spline. By adopting such a structure, the rotational driving force input to the shaft body is transmitted to each screw segment without slippage.

[0003] In a screw shaft employing the spline fitting structure described above, stress concentration occurs at the corner of the circumferential end of the spline groove bottom surface due to the transmission of driving force from the shaft body to the screw section. This stress concentration at the corner of the spline groove can potentially lead to cracks at that corner.

[0004] Patent document 2 discloses a structure for mitigating stress concentration at the corners of the spline grooves in a screw section. (Using...) Figure 10 The structure disclosed in Patent Document 2 will be described.

[0005] like Figure 10 As shown, the screw shaft in Patent Document 2 is formed by spline engagement between a shaft body 961 with an external spline 961a and a screw segment 962 with a spline groove 962a. The spline groove 962a of the screw segment 962 includes a groove side surface 962b opposite to the tooth surface 961b of the external spline 961a and a groove bottom surface 962c opposite to the large diameter surface 961c of the external spline 961a, separated by a gap G, and is surrounded by a groove side surface 962b.

[0006] In the spline groove 962a, recessed grooves 962d are respectively provided at the two circumferential corners of the groove bottom surface 962c, facing radially outward. For example... Figure 10 As shown in the enlarged portion, a concave portion 962e with a radius of curvature R9 is formed on the bottom side of the recess 962d.

[0007] In Patent Document 2, by providing a recessed groove 962d with a concave portion 962e at the bottom of the spline groove 962a, the stress concentration factor can be reduced.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2005-22091

[0011] Patent document 2: Japanese Patent Application Publication No. 09-32813. Utility Model Content

[0012] Problem to be solved by the Invention

[0013] However, in the case where the structure disclosed in the above-described Patent Document 2 is adopted, there is a case where stress concentration is not sufficiently mitigated in a case where the rotational resistance received from the mixing target object is large.

[0014] As a countermeasure to sufficiently achieve mitigation of stress concentration also in a case where the rotational resistance received from the mixing target object is large, it is also possible to consider increasing the radius of curvature R9 of the concave portion 962e, but in this case, the depth of the retreat groove 962d becomes deeper, and the wall thickness F of the screw segment 962 at this portion becomes thinner. If the wall thickness F at the bottom of the retreat groove 962d becomes thinner like this, the strength of the screw segment 962 is instead reduced, and deformation, cracking, or the like can occur.

[0015] The present Invention has been made in order to solve the above-described problem, and has an object to provide a screw segment capable of mitigating stress concentration at both circumferential ends of a groove bottom surface while suppressing thinning of the wall thickness at the groove bottom of a spline groove.

[0016] Means for solving the problem

[0017] The screw segment according to the technical solution of the present Invention constitutes a screw shaft for an extruder in combination with a shaft body into which splines are fitted, and has an internal spline hole having a plurality of spline grooves. In a cross section in a direction orthogonal to the axis of the aforementioned screw shaft, the aforementioned plurality of spline grooves are each surrounded by a groove side surface, a groove bottom surface, and a recessed surface to constitute. The aforementioned groove side surface opposes a tooth surface of an external spline of the aforementioned shaft body. The aforementioned groove bottom surface opposes a large-diameter surface of the aforementioned external spline with a gap therebetween. The aforementioned recessed surface is constituted by a smooth curved surface of a concave shape, and is connected to both ends in the circumferential direction of the aforementioned groove bottom surface and to ends on the radially outer side of the aforementioned groove side surface, and is constituted so as to be recessed toward both the radially outer side and the circumferentially outer side in a manner to be apart from the aforementioned external spline.

[0018] The recessed surface of the screw segment according to the above-described technical solution is constituted by a smooth curved surface in a manner to be recessed toward both the radially outer side and the circumferentially outer side. In this way, in the screw segment in which the recessed surface is constituted by a smooth curved surface in a manner to be recessed toward both the radially outer side and the circumferentially outer side, the recessed surface is positioned approximately at an imaginary intersection point on an extension line of the groove bottom surface and the groove side surface, on the outer side of the imaginary intersection point. Therefore, unlike the case where the retreat groove 962d is formed in a manner to be recessed only toward the radially outer side like the screw segment of the above-described Patent Document 2, it is possible to suppress thinning of the wall thickness at the groove bottom of the spline groove also in the case where the recessed surface having a large radius of curvature is formed. Thus, the aforementioned screw segment can mitigate stress concentration at both circumferential ends of the groove bottom surface while suppressing thinning of the wall thickness at the groove bottom of the spline groove.

[0019] In the screw segment according to the above technical solution, the concave surface can also be connected to the groove bottom surface and the groove side surface in a state of angularly protruding at the connection site, respectively.

[0020] In the screw segment according to the above technical solution, the concave surface is connected to the groove bottom surface and the groove side surface in a state of angularly protruding at the connection site (a state of edge standing up), respectively, without passing through other surfaces (tapered surfaces, curved surfaces). That is, in the above screw segment, chamfering processing or R processing is not performed on the connection site of the concave surface to the groove bottom surface and the groove side surface, respectively. Thus, the above screw segment can realize reduction of manufacturing cost corresponding to no chamfering processing or the like.

[0021] Another technical solution of the present application is a screw segment that is combined with a shaft body engaged with a spline to form a screw shaft for an extruder, and has an internal spline hole having a plurality of spline grooves. In a cross section orthogonal to an axis of the screw shaft, the plurality of spline grooves are each surrounded by a groove side surface, a groove bottom surface, and a concave surface. The groove side surface faces the tooth surface of an external spline of the shaft body. The groove bottom surface faces the large-diameter surface of the external spline with a gap therebetween. The concave surface is formed of a curved surface of a smooth concave shape, and is connected to both ends in a circumferential direction of the groove bottom surface and to ends on a radially outer side of the groove side surface, and is recessed toward the circumferential outer side away from the external spline.

[0022] The concave surface of the screw segment according to the above technical solution is formed to be recessed toward the circumferential outer side, and is provided in a structure not recessed toward the radially outer side. Thus, unlike a case where the retreat groove 962d is formed in a manner of being recessed only toward the radially outer side as in the screw segment of the above Patent Document 2, in a case where the concave surface is formed to have a large radius of curvature, the wall thickness at the groove bottom of the spline groove is not thinned. Thus, the above screw segment can alleviate stress concentration at both ends in the circumferential direction of the groove bottom surface while suppressing thinning of the wall thickness at the groove bottom of the spline groove.

[0023] In the screw segment according to the above technical solution, the concave surface can also be connected to the groove side surface in a state of angularly protruding at the connection site, respectively.

[0024] The concave surface of the screw segment according to the above technical solution is connected to the groove side surface in a state of angularly protruding at the connection site (a state of edge standing up) without sandwiching other surfaces (tapered surfaces, curved surfaces) therebetween. That is, in the above screw segment, chamfering processing or R processing is not performed on the connection site of the concave surface to the groove side surface. Thus, the above screw segment can realize reduction of manufacturing cost corresponding to no chamfering processing or the like.

[0025] Effects of the present application

[0026] The screw segment according to the above-described aspects can be a screw segment that suppresses thinning of the wall thickness at the bottom of the spline groove while mitigating stress concentration at the circumferential ends of the groove bottom. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a side view showing an extruder provided with the screw segment according to the first embodiment.

[0028] Figure 2 is a side view showing the structure of the screw shaft.

[0029] Figure 3 is a cross-sectional view showing the cross section of the screw shaft.

[0030] Figure 4 is a cross-sectional view showing the cross-sectional shape of the spline groove.

[0031] Figure 5 is an enlarged cross-sectional view showing the A portion of Figure 4

[0032] Figure 6 is a cross-sectional view showing the structure of the shaft body fitted with the screw segment according to the modified example 1.

[0033] Figure 7 (a) is a cross-sectional view showing the structure of the screw segment according to the modified example 2, Figure 7 (b) is a cross-sectional view showing the structure of the screw segment according to the modified example 3.

[0034] Figure 8 is a cross-sectional view showing the structure of the screw segment according to the second embodiment.

[0035] Figure 9 is an enlarged cross-sectional view showing the D portion of Figure 8

[0036] Figure 10 is a cross-sectional view showing the structure of the screw segment according to the related art. DETAILED DESCRIPTION

[0037] [First Embodiment]

[0038] 1. Extruder 1

[0039] The extruder 1 provided with the screw segment 162 according to the present embodiment is a machine for mixing and extruding a material such as resin, and is a twin-screw extruder, for example. The screw segment 162 according to the present embodiment is used in the extruder 1. Figure 1 The extruder 1 will be described.

[0040] As shown in FIG. 1, the extruder 1 according to the present embodiment is a twin-screw extruder including a barrel 2, a screw shaft 3, and a screw segment 162. Figure 1 ​​As shown, the extruder 1 includes a drive motor 11, a reducer 12, a cylinder 13, a connecting box 14, a storage tank 15, and a pair of screw shafts 16. The drive motor 11 generates rotational driving force. The reducer 12 reduces the rotation input from the drive motor 11 and generates torque corresponding to the reduction ratio.

[0041] The connecting box 14 connects the reducer 12 to the cylinder 13. A pair of screw shafts 16 are housed in parallel within the cylinder 13. Each pair of screw shafts 16 consists of a spline-fitted shaft body 161 and multiple screw segments 162. Furthermore, in Figure 1 The diagram only shows one of the pair of screw shafts 16, but the other two are shown in the figure. Figure 1 The screw shaft 16 is arranged in a direction orthogonal to the paper. However, it is also possible to make a single-screw extruder 1 that houses only one screw shaft 16 inside the cylinder 13.

[0042] The material storage device 15 is used to feed materials and is located on the cylinder 13 at a distance close to the connection with the connecting box 14.

[0043] 2. A pair of 16mm screw shafts

[0044] use Figure 2 The structure of each of the pair of screw shafts 16 will be described. Additionally, in Figure 2 The diagram only shows a portion of the multiple screw segments 162 that are splinedly engaged with shaft 161. Furthermore, in... Figure 2 The diagram only shows one of the two screw shafts 16, but the other screw shaft 16 has the same structure.

[0045] like Figure 2 As shown, the shaft 161 has a plurality of external splines 161a on its outer peripheral surface, which are formed in such a way that they protrude radially outward and extend along the axis Ax16 of the screw shaft 16.

[0046] Multiple screw segments 162 each have an internal spline hole 162g that engages with the external spline 161a. As described later, the internal spline hole 162g has multiple spline grooves.

[0047] 3. External spline 161a and internal spline hole 162g

[0048] use Figure 3 and Figure 4 The cross-sectional structure of the external spline 161a and the internal spline hole 162g is described.

[0049] like Figure 3 As shown, the shaft 161 has multiple external splines 161a on its outer periphery. The external splines 161a are formed to protrude radially outwards from the shaft center Ax16. Figure 4As shown, each external spline 161a has tooth surfaces 161b provided on both sides in the circumferential direction and a large-diameter surface 161c constituting a top surface on the radially outer side. In this embodiment, the tooth profile of the tooth surface 161b is constituted by a prescribed involute curve.

[0050] The screw segment 162 has a plurality of spline grooves 162a for spline engagement with the external spline 161a in the inner peripheral portion of the internal spline hole 162g. Each spline groove 162a has a groove side surface 162b opposed to the tooth surface 161b of the external spline 161a, a groove bottom surface 162c opposed to the large-diameter surface 161c of the external spline 161a with a gap G in the radial direction, and a recessed surface 162d formed so as to be recessed in the radial and circumferential directions outward from the corner 161d of the external spline 161a. In addition, the tooth profile of the groove side surface 162b is constituted by a prescribed involute curve, like the tooth surface 161b of the external spline 161a.

[0051] The recessed surface 162d is connected to the end portion of the groove bottom surface 162c (boundary portion 162e) at a portion on the inner side in the circumferential direction than the corner 161d of the external spline 161a, and is connected to the end portion of the groove side surface 162b (boundary portion 162f) at a portion on the inner side in the radial direction than the corner 161d of the external spline 161a. The recessed surface 162d is constituted by a curved surface of a smooth concave shape.

[0052] 4. Detailed shape of recessed surface 162d

[0053] Use Figure 5 The detailed shape of the recessed surface 162d will be described. In addition, Figure 5 is an enlarged view of the A portion of Figure 4 .

[0054] In the cross section shown in Figure 5 , in this embodiment, as an example, the recessed surface 162d is formed by one R of the curvature radius R1. The center Pc of the curvature of the recessed surface 162d is provided at a position that is separated by a distance B1 radially inward from the groove bottom surface 162c.

[0055] The curvature radius R1 is set to be larger than the distance B1. The distance B1 is set to be larger than the gap G.

[0056] Further, in the case where the shaft body 161 rotates and the tooth surface 161b comes into contact with the groove side surface 162b (in the case where the gap B2 = 0), the distance B3 of the corner 161d of the external spline 161a from the circumferential direction of the recessed surface 162d is also not "0" but is prescribed in a shape in which a gap remains. That is, the recessed surface 162d is formed so as to satisfy the relationship B3 > B2.

[0057] Further, the recessed surface 162d is connected to the groove bottom surface 162c and the groove side surface 162b each at a cornered state (edge-stand state) at each boundary portion 162e, 162f as a connecting portion. In other words, at each boundary portion 162e, 162f, the recessed surface 162d is directly connected to the groove bottom surface 162c and the groove side surface 162b each in a state where chamfer processing, R processing is performed.

[0058] 5. Effects

[0059] The recessed surface 162d of the screw segment 162 according to the present embodiment is composed of a smooth curved surface in a range from the groove bottom surface 162c to the groove side surface 162b, and is configured to satisfy the relationship of R1 > B1 and B3 > B2. That is, the recessed surface 162d of the screw segment 162 is composed of a smooth curved surface that is recessed toward both the radial outer side and the circumferential outer side. In the screw segment 162 in which the recessed surface 162d is composed of a smooth curved surface that is recessed toward both the radial outer side and the circumferential outer side, the recessed surface 162d is positioned approximately at the imaginary intersection point on the outer side of the imaginary intersection point on the extension line of the groove bottom surface 162c and the groove side surface 162b. Therefore, unlike the case where the retreat groove 962d is formed in a manner of being recessed only toward the radial outer side as in the screw segment of the above-described Patent Document 2, the wall thickness at the groove bottom of the spline groove 162a can be suppressed from being thinned even in the case where the recessed surface 162d having a large radius of curvature R1 is formed. Thus, the screw segment 162 can suppress the stress concentration at both ends in the circumferential direction of the groove bottom surface 162c while mitigating the wall thickness at the groove bottom of the spline groove 162a from being thinned.

[0060] Further, the recessed surface 162d of the screw segment 162 is connected to the groove bottom surface 162c and the groove side surface 162b each at a cornered state (edge-stand state) at each boundary portion 162e, 162f as a connecting portion. In other words, at each boundary portion 162e, 162f, the recessed surface 162d is directly connected to the groove bottom surface 162c and the groove side surface 162b each in a state where chamfer processing, R processing is performed.

[0061] [Modified Example 1]

[0062] Use Figure 6 The structure of the screw segment 162 and the surrounding structure according to Modified Example 1 will be described. In addition, the shape of the external spline 161a on the shaft body 161 of the present modified example is different from that of the above-described First Embodiment, and the remaining structure including the structure of the screw segment 162 is the same as that of the above-described First Embodiment.

[0063] As Figure 6As shown, the corner portion of the external spline 161a is chamfered. Specifically, at the corner portion of the external spline 161a, a tapered surface 161e composed of a bevel is formed. The tapered surface 161e is formed so as to be farther from the recessed surface 162d of the spline groove 162a than the imaginary intersection point Pv of the large-diameter surface 161c and the tooth surface 161b.

[0064] The tapered surface 161e is connected to the circumferential end of the large-diameter surface 161c (boundary portion 161f) and to the radial end of the tooth surface 161b (boundary portion 161g). The position of the boundary portion 161g is preferably the same position as the boundary portion 162f in the radial direction or a position farther outward in the radial direction than the boundary portion 162f. This is because the corner portion of the external spline 161a is reliably prevented from abutting against the recessed surface 162d of the spline groove 162a when the shaft body 161 rotates, and the tooth surface 161b can be brought into abutment with the groove side surface 162b to ensure a large abutment area.

[0065] This modified example has the same structure as the above-described first embodiment except that the corner portion of the external spline 161a of the shaft body 161 is chamfered. Thus, the same effects as the above-described first embodiment can be achieved in this modified example as well.

[0066] [Modified Example 2]

[0067] Use Figure 7 (a) The structure of the screw segment 162 relating to Modified Example 2 will be described. In addition, the shape of the recessed surface 162d of the screw segment 162 relating to this modified example is different from that of the above-described first embodiment, and the other structures are the same.

[0068] As shown in (a), in the screw segment 162 relating to this modified example, the recessed surface 162d has an elliptical arc shape. However, in this modified example, the recessed surface 162d can also have a long circular arc shape. Figure 7

[0069] This modified example has the same structure as the above-described first embodiment except that the recessed surface 162d has an elliptical arc shape. Thus, the same effects as the above-described first embodiment can be achieved in this modified example as well.

[0070] [Modified Example 3]

[0071] Use Figure 7 (b) The structure of the screw segment 162 relating to Modified Example 3 will be described. In addition, the shape of the recessed surface 162d of the screw segment 162 relating to this modified example is different from that of the above-described first embodiment, and the other structures are the same.

[0072] As shown in (b), in the screw segment 162 relating to this modified example, the recessed surface 162d has a long circular arc shape. However, in this modified example, the recessed surface 162d can also have an elliptical arc shape. Figure 7 ​(b) As shown, in the screw segment 162 relating to this modification example, the recessed surface 162d is composed of a plurality of circular arcs C1 to C3 that are contiguous with each other. Also, in this modification example, the recessed surface 162d is composed of three circular arcs C1 to C3 as an example, but the recessed surface 162d can also be composed of two circular arcs that are contiguous with each other, or the recessed surface 162d can also be composed of four or more circular arcs that are contiguous with each other.

[0073] This modification example has the same structure as the above-described first embodiment except for the point that the recessed surface 162d is composed of three circular arcs C1 to C3. Thus, the same effects as the above-described first embodiment can also be achieved in this modification example.

[0074] [Second Embodiment]

[0075] Use Figure 8 and Figure 9 The structure of the screw segment 162 relating to the second embodiment will be described. Also, the screw segment 162 relating to this embodiment has a different shape of the recessed surface 162d from the above-described first embodiment, and has the same other structure.

[0076] As shown in Figs. 17 and 18, the screw segment 162 has, in each spline groove 162a, a recessed surface 162d that is recessed in the circumferential direction in such a manner as to depart outward from the corner portion 161d of the external spline 161a. Here, the screw segment 162 relating to this embodiment differs from the above-described first embodiment in that the recessed surface 162d is configured to be recessed only toward the circumferential direction outward, and not toward the radial direction outward. Figure 8 Figure 9 As shown, the screw segment 162 has, in each spline groove 162a, a recessed surface 162d that is recessed in the circumferential direction in such a manner as to depart outward from the corner portion 161d of the external spline 161a. Here, the screw segment 162 relating to this embodiment differs from the above-described first embodiment in that the recessed surface 162d is configured to be recessed only toward the circumferential direction outward, and not toward the radial direction outward.

[0077] The recessed surface 162d is connected (boundary portion 162e) to the end portion of the groove bottom surface 162c at a portion that is on the inner side in the circumferential direction from the corner portion 161d of the external spline 161a, and is connected (boundary portion 162f) to the end portion of the groove side surface 162b at a portion that is on the inner side in the radial direction from the corner portion 161d of the external spline 161a. The recessed surface 162d is composed of a curved surface of a concave shape that is contiguous with the groove bottom surface 162c and is smooth.

[0078] In this embodiment, the recessed surface 162d is formed by one R of the curvature radius R2 as an example. The center Pc of the curvature of the recessed surface 162d is disposed at a position that departs by a distance E1 inward in the radial direction from the groove bottom surface 162c. The distance E1 is set to be larger than the gap G.

[0079] Further, the curvature radius R2 is set to be equal to the distance E1. Thus, the recessed surface 162d is contiguous with the groove bottom surface 162c at the boundary portion 162e.

[0080] ​Further, the distance E3 between the corner portion 161d of the external spline 161a and the circumferential direction of the recessed surface 162d is not "0" but is defined by a shape in which a gap remains, in a case where the shaft body 161 rotates and the tooth surface 161b is in abutment with the groove side surface 162b (in a case where the gap E2 = 0).

[0081] Further, at the boundary portion 162f of the recessed surface 162d and the groove side surface 162b, the recessed surface 162d is connected to the groove side surface 162b without other surfaces (tapered surfaces, curved surfaces) being interposed therebetween in a state in which the recessed surface 162d intersects the groove side surface 162b. In other words, at the boundary portion 162f, the recessed surface 162d and the groove side surface 162b are directly connected in a manner in which an edge stands up.

[0082] The screw segment 162 according to the present embodiment is configured such that the recessed surface 162d is recessed toward the outer side in the circumferential direction, and is provided in a structure in which the recessed surface 162d is not recessed toward the outer side in the radial direction. Therefore, unlike a case in which the retreat groove 962d is formed in a manner in which it is recessed toward the outer side in the radial direction, as in the screw segment of Patent Document 2 described above, in a case in which the recessed surface 162d having a large radius of curvature R2 is formed, the wall thickness does not become thin at the groove bottom of the spline groove 162a. Thus, the screw segment 162 can alleviate stress concentration at both ends in the circumferential direction of the groove bottom surface 162c while suppressing the wall thickness from becoming thin at the groove bottom of the spline groove 162a.

[0083] Further, the recessed surface 162d is connected to the groove side surface 162b in a state in which the corner portion 162f stands out (in a state in which an edge stands up) at the connection portion (boundary portion 162f). That is, in the screw segment 162, chamfering processing, R processing is not performed on the boundary portion 162f of the recessed surface 162d and the groove side surface 162b. Thus, the screw segment 162 can achieve a reduction in manufacturing cost in response to not performing chamfering processing or the like.

[0084] In addition, the same modifications 1 to 3 as described above can also be applied to the screw segment 162 according to the present embodiment.

[0085] The embodiments and modifications disclosed this time are illustrative in all respects and are not intended to be restrictive. The present application is not limited to the above-described embodiments and modifications, and various changes, improvements, and the like can be made within the scope of the gist thereof. For example, in the above-described first and second embodiments and modifications 1 to 3, the screw segment 162 used in the twin-screw extruder 1 is described as an example, but the screw segment 162 used in a single-screw extruder in which only one screw shaft 16 is housed in the barrel 13 can also be applied in the present application.

[0086] Explanation of Reference Signs

[0087] 1 extruder

[0088] 16 screw shaft

[0089] 161 shaft body

[0090] 161a external spline

[0091] 161b tooth surface

[0092] 161c large diameter surface

[0093] 162 screw segment

[0094] 162a spline groove

[0095] 162b groove side surface

[0096] 162c groove bottom surface

[0097] 162d concave surface

[0098] 162g internal spline hole

Claims

1. A screw section, which, when combined with a shaft body that engages with a spline, constitutes a screw shaft for an extruder, and has an internal spline hole with multiple spline grooves, characterized in that, In a cross-section orthogonal to the axis of the aforementioned screw shaft, the aforementioned plurality of spline grooves are respectively surrounded by the following surfaces: The side of the groove faces the tooth surface of the external spline of the aforementioned shaft; The bottom surface of the groove is positioned opposite the large-diameter surface of the aforementioned external spline, separated by a gap; and The recessed surface is formed by a smooth concave curved surface and is connected to the two circumferential ends of the bottom surface of the aforementioned groove and the radially outer ends of the side surface of the aforementioned groove. It is configured to be recessed toward the radially outer and circumferentially outer sides in a manner that is away from the aforementioned external spline.

2. The screw section as described in claim 1, characterized in that, The aforementioned recessed surface is connected to the aforementioned groove bottom surface and the aforementioned groove side surface in a state of angular protrusion at the connection part.

3. A screw section, which, when combined with a shaft body that engages with a spline, constitutes a screw shaft for an extruder, and has an internal spline hole with multiple spline grooves, characterized in that... In a cross-section orthogonal to the axis of the aforementioned screw shaft, the aforementioned plurality of spline grooves are respectively surrounded by the following surfaces: The side of the groove faces the tooth surface of the external spline of the aforementioned shaft; The bottom surface of the groove is positioned opposite the large-diameter surface of the aforementioned external spline, separated by a gap; and The recessed surface is formed by a smooth concave curved surface and is connected to the two circumferential ends of the bottom surface of the aforementioned groove and the radially outer ends of the side surface of the aforementioned groove, and is configured to be recessed circumferentially outward relative to the aforementioned external spline.

4. The screw section as described in claim 3, characterized in that, The aforementioned concave surface is connected to the aforementioned groove side surface in a state where it protrudes at an angle at the connection point.

Images