GEAR SPINDLE AND OIL SEAL USED THEREIN

Abstract

In a gear spindle, outer cylinder gear sections (11) are each integrally formed on an inner peripheral surface of a spindle outer cylinder and inner cylinder gear sections (14) are each integrally formed on an outer peripheral surface of a spindle inner cylinder (13). An oil seal (27) that seals in the lubricating oil (20) for each of the aforementioned gear sections includes, a seal body (29) having a channel-shaped cross section and interposed in the peripheral gap between the inner peripheral surface of the spindle outer cylinder and the outer peripheral surface of the spindle inner cylinder (13), and a seal mounting member (30) that includes a band, a spring, or the like that tightens and fixes the seal body to the outer peripheral surface of the spindle inner cylinder (13) to allow expansion of the seal body in the axial direction in the aforementioned peripheral gap.

Claims

1. An oil seal used in a gear spindle including an outer-cylinder portion with a gear portion carved on an inner peripheral surface thereof and an inner cylinder portion with a gear portion carved on an outer peripheral surface thereof, the gear spindle configured to rotate with the gear portions meshing with each other, the oil seal configured to seal a lubricating oil for the gear portions, the oil seal comprising: a seal body interposed in a peripheral gap between the inner peripheral surface of the outer cylinder portion and the outer peripheral surface of the inner cylinder portion, and a seal attachment member configured to fix the seal body to the outer peripheral surface of the inner cylinder portion, wherein the seal body has an outer ring portion in surface contact with the inner peripheral surface of the outer cylinder portion, an inner ring portion in surface contact with the outer peripheral surface of the inner cylinder portion, and an intermediate ring portion connecting the outer ring portion and the inner ring portion to each other, the intermediate ring portion having a shape recessed to the lubricating oil side, and the outer ring portion is formed to extend from an end portion of the intermediate ring portion to both sides in an axial direction.

2. The oil seal according to claim 1, wherein a reinforcement ring to give rigidity to the outer ring portion is embedded in the outer ring portion.

3. The oil seal according to claim 2, wherein the reinforcement ring is divided into multiple pieces in a width direction of the outer ring portion.

4. The oil seal according to claim 3, wherein the end portion of the intermediate ring portion connected to the outer ring portion is arranged between the divided pieces of the reinforcement ring.

5. The oil seal according to claim 1, wherein the at least one of end portions of the outer ring portion in the width direction is formed in a wedge shape, and the outer ring portion is retained by a wedge-shaped retention member coinciding in shape with the wedge shape of the end portion of the outer ring portion.

6. The oil seal according to claim 1, wherein the intermediate ring portion forms a U shape having a single large arc.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a sectional view of a main portion of a gear spindle showing Embodiment 1 of the present invention.

[0031] FIG. 2 is a sectional view of a main portion of a gear spindle showing Embodiment 2 of the present invention.

[0032] FIG. 3 is a sectional view of an oil seal portion showing Embodiment 3 of the present invention.

[0033] FIG. 4 is a sectional view of an oil seal portion showing Embodiment 4 of the present invention.

[0034] FIG. 5 is a sectional view of a main portion of a gear spindle showing Embodiment 5 of the present invention.

[0035] FIG. 6 is a sectional view of a main portion of a gear spindle according to a conventional example.

MODE FOR CARRYING OUT THE INVENTION

[0036] Embodiments of a gear spindle and an oil seal used therein are described in detail below using the drawings.

Embodiment 1

[0037] FIG. 1 is a sectional view of a main portion of a gear spindle showing Embodiment 1 of the present invention.

[0038] As shown in FIG. 1, a large-diameter cylindrical portion (constituting part of an outer cylinder portion) 10a is formed in one (right) half portion of a spindle outer cylinder 10, and a fit hole 10c is formed in the other (left) half portion of the spindle outer cylinder 10, the fit hole 10c being separated from the large-diameter cylindrical portion 10a by a center-portion partition wall.

[0039] An outer cylinder gear portion (internal teeth) 11 is integrally formed on an axially-middle portion of the large-diameter cylindrical portion 10a. A spindle of a work roll of a rolling mill (not shown) can be fitted into the fit hole 10c such that the spindle can be attached and detached (inserted and removed) and cannot be rotated. A base end portion of an outer-cylinder pivot 12 is fitted into a hole 10b in the center-portion partition wall of the outer cylinder.

[0040] One (left) end portion of a spindle inner cylinder (inner cylinder portion) 13 configured to be rotated by a drive shaft (device) (not shown) is inserted into the large-diameter cylindrical portion 10a, and an inner cylinder gear portion (outer teeth) 14 integrally formed on an axial end of the spindle inner cylinder 13 meshes with the outer cylinder gear portion 11 in such a manner as to be slidable axially. The shaft axis of the spindle inner cylinder 13 is slanted by a slant angle relative to the shaft axis of the spindle outer cylinder 10.

[0041] A tip portion of the outer-cylinder pivot 12 is loosely fit into a cylinder hole 13a of the spindle inner cylinder 13, and an inner-cylinder pivot 15 is housed in the cylinder hole 13a of the spindle inner cylinder 13 while being in spherical contact with the outer-cylinder pivot 12 and biased by a helical compression spring 16 toward the outer-cylinder pivot 12. Thus, the spindle outer cylinder 10 is constantly biased toward the work roll side to maintain their fitted state. Reference numeral 17 in FIG. 1 is a stopper configured to prevent the inner-cylinder pivot 15 from coming off.

[0042] In the large-diameter cylindrical portion 10a of the spindle outer cylinder 10, an oil-supply-side oil chamber 18 and a seal-side oil chamber 19 are defined with a portion of the outer cylinder gear portion 11 and the inner cylinder gear portion 14 being a border therebetween. Lubricating oil 20 is supplied into the oil-supply-side oil chamber 18 through a cylinder hole (not shown) of the spindle outer cylinder 10.

[0043] A halved stopper ring 23 is attached to an opening-end portion of the large-diameter cylindrical portion 10a via a flanged, cylindrical coupling cover (constituting part of the outer cylinder portion) 22 which is coupled to an end surface of the large-diameter cylindrical portion 10a with multiple bolts 21. The stopper ring 23 restricts an axial travel distance B (mm) of the spindle outer cylinder 10 during roll change. Reference numeral 24 is a seal member such as an O-ring.

[0044] The axial travel distance B (mm) of the spindle outer cylinder 10 is set within the following formula:

B<(D/2)sin +A

(A is for example 5), where

[0045] D is the outer diameter (mm) of the spindle inner cylinder 13 at the inner cylinder gear portion 14, is a maximum slant angle (deg), and A is a constant (mm) determined considering an error in machining of components of the gear spindle, an error in assemblage of the components, and an oscillatory displacement due to rotation.

[0046] A flanged, cylindrical seal case (constituting part of the outer cylinder portion) 25 is connected to (the end surface of) the coupling cover 22 by a spigot joint, and an oil seal 27 is interposed, via a seal plate 26, in a peripheral gap between the inner peripheral surface of the seal case 25 and the outer peripheral surface of the spindle inner cylinder 13 (see an outer diameter D.sub.0 (mm) (D.sub.0<D) of an oil seal attachment portion in FIG. 1), the oil seal 27 being made of a rubber or the like and configured to seal the lubricating oil 20 in the oil-supply-side oil chamber 18 and the seal-side oil chamber 19. The seal case 25 and the seal plate 26 are together fastened to the end surface of the coupling cover 22 with multiple bolts 28. The seal plate 26 may be an integral component or a halved component.

[0047] The oil seal 27 includes a seal body 29 interposed in the aforementioned peripheral gap and a seal attachment member 30 configured to tighten the seal body 29 securely to the outer peripheral surface of the spindle inner cylinder 13 such that the seal body 29 can expand inside the aforementioned peripheral gap. In the example shown in FIG. 1, the oil seal 27 includes: the seal body 29 having a channel-shaped cross section and having an outer ring portion 29a which comes into contact with the inner peripheral surface of the seal case 25 and has high rigidity, an inner ring portion 29b which comes into contact with the outer peripheral surface of the spindle inner cylinder 13 and has rigidity lower than that of the outer ring portion 29a, and an intermediate ring portion 29c which connects the outer ring portion 29a and the inner ring portion 29b to each other and has excellent flexibility; and the seal attachment member 30 formed of a highly-rigid spring and configured to attach the inner ring portion 29b to the spindle inner cylinder 13. The outer ring portion 29a thus configured is pressed against the inner peripheral surface of the seal case 25 due to an internal pressure of the lubricating oil 20 generated by rotation. Thus, the outer ring portion 29a provided for the purpose of preventing leakage of the lubricating oil 20 can satisfy its function with a simple structure, and is suitable for a small-diameter spindle having a small space.

[0048] The seal attachment member 30 is placed on a side having the lubricating oil 20, and a predetermined gap is set between an inner-peripheral plate portion (seal-neighboring component) of the seal plate 26 and the intermediate ring portion 29c. Thus, even if the centrifugal force of the lubricating oil 20 generated during rotation of the gear spindle causes the intermediate ring portion 29c of the seal body 29 to expand axially to an opposite side to the side having the lubricating oil 20, the intermediate ring portion 29c does not interfere (come into contact) with not only the seal attachment member 30 but also the inner-peripheral plate portion of the seal plate 26. Further, the inner ring portion 29b configured as above is pressed against the outer peripheral surface of the spindle inner cylinder 13 due to an internal pressure of the lubricating oil 20 generated by rotation. Thus, the seal attachment member 30 provided for the purpose of fixing the inner ring portion 29b to the outer peripheral surface of the spindle inner cylinder 13 and preventing leakage of the lubricating oil 20 can satisfy its function with a compact and simple structure, and is suitable for a small-diameter spindle having a small space.

[0049] The outer diameter D.sub.0 (mm) of the oil seal attachment portion of the spindle inner cylinder 13 is set to be smaller than the diameters of portions located on both sides of the oil seal attachment portion in the axial direction, namely, the outer diameter D (mm) of the spindle inner cylinder 13 at the inner cylinder gear portion 14 and an outer diameter D.sub.1 (mm) of a portion of the spindle inner cylinder 13 on the drive-shaft side. When the oil seal 27 is to be attached, the seal body 29 (exactly, the intermediate ring portion 29c and the inner ring portion 29b) diametrically extends and contracts to enable the attachment of the oil seal 27.

[0050] The inner ring portion 29b is given low rigidity so as to be expandable. Since adequate sealability between the inner ring portion 29b and the spindle inner cylinder 13 cannot be offered with such an inner ring portion 29b only, sealability is ensured by fixing the inner ring portion 29b to the outer peripheral surface of the spindle inner cylinder 13 by use of the highly-rigid seal attachment member 30 which is a separate component from the seal body 29.

[0051] Further, the outer ring portion 29a is required to provide high sealability between the outer ring portion 29a and the seal case 25, and therefore to have high rigidity. The inner ring portion 29b is required to provide high sealability between the inner ring portion 29b and the spindle inner cylinder 13 and to diametrically extend and contract so that the oil seal 27 can be attached after passing beyond both end portions of the spindle inner cylinder 13. Further, the intermediate ring portion 29c is required to have strength to overcome the internal pressure, to have flexibility to follow the slant of the spindle inner cylinder 13, and to diametrically extend and contract so that the oil seal 27 can be attached after passing beyond both end portions of the spindle inner cylinder 13. As described, each portion of the oil seal has its own requirements, and therefore has to be designed taking those requirements into consideration.

[0052] An assembly procedure for the oil seal 27 is briefly described. First, the seal plate 26 and the seal case 25 are sequentially inserted into the spindle inner cylinder 13. Next, the oil seal 27 is attached to the spindle inner cylinder 13 by diametrically extending and contracting the oil seal 27 and passing beyond the inner cylinder gear portion 14, and is tightened securely and fixed with the seal attachment member 30. Next, the coupling cover 22 is inserted into the spindle inner cylinder 13, and then the spindle inner cylinder 13 is inserted into the spindle outer cylinder 10. Next, the halved stopper ring 23 is attached to the coupling cover 22, and then the coupling cover 22 is attached to the spindle outer cylinder 10. Next, the seal case 25 is attached to the coupling cover 22 by passing beyond the oil seal 27, and then the seal plate 26 is attached to the seal case 25.

[0053] With such a configuration, rotary torque of the drive shaft is transmitted at same velocity from the spindle inner cylinder 13 slanted at the slant angle to the spindle outer cylinder 10 via the inner cylinder gear portion 14 and the outer cylinder gear portion 11 meshing therewith. The work roll is thus rotated. Meanwhile, the meshing portion of the inner cylinder gear portion 14 and the outer cylinder gear portion 11 is lubricated with the lubricating oil 20 over their entire peripheries to undergo less wear and generate less heat.

[0054] In this embodiment, the spindle outer cylinder 10 (exactly, the large-diameter cylindrical portion 10a) has the outer cylinder gear portion 11 formed integrally with the inner peripheral surface thereof, and the spindle inner cylinder 13 has the inner cylinder gear portion 14 formed integrally with the outer peripheral surface thereof. Thus, the gear spindle has surely adequate strength and high torque transmission capacity.

[0055] Moreover, the seal body 29 of the oil seal 27 is interposed compactly in the peripheral gap between the inner peripheral surface of the seal case 25 and the outer peripheral surface of the spindle inner cylinder 13, and the seal body 29 is attached by use of the seal attachment member 30 such that the seal body 29 can expand inside the aforementioned peripheral gap. This can ensure the sealability of and prevent damage of the oil seal 27 during operation at high rotational speed.

[0056] To be more specific, since the inner ring portion 29b of the seal body 29 is tightened securely and fixed to the spindle inner cylinder 13 by use of the seal attachment member 30 having high rigidity, the spindle inner cylinder 13 can offer adequate sealability even during operation at high rotational speed in which the spindle inner cylinder 13 is slanted at the slant angle .

[0057] Further, the seal attachment member 30 is placed on the side having the lubricating oil 20, and the predetermined gap is set between the inner-peripheral plate portion of the seal plate 26 and the intermediate ring portion 29c. Thus, even if the centrifugal force of the lubricating oil 20 generated during operation at high rotational speed causes the intermediate ring portion 29c of the seal body 29 to expand axially as described above, the intermediate ring portion 29c does not interfere (come into contact) with not only the seal attachment member 30 but also the inner-peripheral plate portion of the seal plate 26. Thus, damage of the seal body 29 can be avoided.

[0058] Moreover, the stopper ring 23 whose position is determined by the formula described earlier restricts the axial travel distance B (mm) of the spindle outer cylinder 10 during roll change to a minimum and prevents abnormal expansion of the intermediate ring portion 29c due to an increase in the internal pressure of the seal-side oil chamber 19. Thus, prevention of damage of the seal body 29 is further fostered. Moreover, the intermediate ring portion 29c of the seal body 29 can be reduced in thickness because the increase in the internal pressure of the seal-side oil chamber 19 is suppressed.

[0059] In other words, the reduction in the thickness of the intermediate ring portion 29c can give high flexibility to the intermediate ring portion 29c, and therefore the oil seal 27 can easily pass beyond the inner cylinder gear portion 14 of the spindle inner cylinder 13 by the diametrical extension and contraction of the seal body 29. This further improves assemblability.

[0060] As a result, the gear spindle can be reduced in diameter, allowing a special steel made of a hard material (such as a stainless steel) to be rolled with high productivity and high product quality.

Embodiment 2

[0061] FIG. 2 is a sectional view of a main portion of a gear spindle showing Embodiment 2 of the present invention.

[0062] In this embodiment, an oil seal 27 is a modified seal 27 of Embodiment 1 above such that the intermediate ring portion 29c of a seal body 29A is formed in a U shape with a single large arc and formed to be thin and long as much as possible, and that a reinforcement ring 31 is embedded in an outer ring portion 29a. In addition, an annular groove 13b that receives an annular protruding portion 29d formed in an inner ring portion 29b for positioning of the seal attachment member 30 is formed in an outer peripheral surface of the spindle inner cylinder 13, and a solid band is used as the seal attachment member 30. Other configurations are the same as Embodiment 1 except for the above points. Thus, components and portions that are the same as those in FIG. 1 are denoted by the same reference numerals as those used in FIG. 1, and are not described again here.

[0063] This configuration offers the following advantages in addition to similar operation and advantageous effects achieved by Embodiment 1. Specifically, since the intermediate ring portion 29c is formed in a U shape with a single large arc, seal-generating stress is lessened. If multiple small arc-shaped seals are employed, more stress is generated by the seals, shortening the lifetime. In addition, forming the intermediate ring portion 29c to be thin and long as much as possible increases the flexibility of an oil seal 27 and thus improves assemblability. On the other hand, embedding the reinforcement ring 31 in the outer ring portion 29a improves the sealability of the oil seal 27 by avoiding degradation of the rigidity of the outer ring portion 29a (the degradation of the rigidity occurs because the outer ring portion 29a has to be thin due to limitation of its attachment space caused by forming the intermediate ring portion 29c in an U shape with a single larger arc).

Embodiment 3

[0064] FIG. 3 is a sectional view of an oil seal portion showing Embodiment 3 of the present invention.

[0065] In this embodiment, an oil seal 27 is a modified oil seal 27 of Embodiment 2 above such that multiple (for example two as shown in Fig.) reinforcement rings 31a, 31b are embedded in the outer ring portion 29a, the reinforcement rings 31a, 31b being divided in a width direction (the axial direction of the gear spindle). Other configurations are the same as Embodiment 2. Thus, components and portions that are the same as those in FIG. 2 are denoted by the same reference numerals as those used in FIG. 2, and are not described again here.

[0066] According to this configuration, the following advantages are offered in addition to similar operation and advantageous effects offered by Embodiment 2. Specifically, embedding the reinforcement rings 31a, 31b ensures rigidity of the outer ring portion 29a, and because no reinforcement ring is provided in the outer ring portion 29a at the base portion of the intermediate ring portion 29c, stress at this portion can be mitigated (flexibility increases). Thus, the sealability of the oil seal 27 at its outer ring portion 29a can be ensured. To be more specific, if the stress in the outer ring portion 29a at the base portion of the intermediate ring portion 29c is high, the strength of the oil seal 27 may lower. This embodiment can avoid such a problem.

Embodiment 4

[0067] FIG. 4 is a sectional view of an oil seal portion showing Embodiment 4 of the present invention.

[0068] In this embodiment, an oil seal 27 is a modified seal 27 of Embodiment 2 above such that, instead of embedding the reinforcement ring 31 (see FIG. 2) in the outer ring portion 29a, at least one (both in the example shown) of end portions of the outer ring portion 29a in the width direction (the axial direction of the gear spindle) is formed in a wedge shape, and the outer ring portion 29a is sandwiched by a wedge-shaped retainer (wedge-shaped retention member) 32 and a seal plate 26 having a wedge-shaped portion (wedge-shaped retention member) 26a, the wedge-shaped retention members corresponding to the wedge shape of the corresponding end portion of the outer ring portion 29a. Other configurations are the same as Embodiment 2. Thus, components and portions that are the same as those in FIG. 2 are denoted by the same reference numerals as those used in FIG. 2, and are not described again here.

[0069] This configuration offers the following advantages in addition to similar operation and advantageous effects offered by Embodiment 2. Specifically, since the reinforcement ring 31 (see FIG. 2) is not embedded in the outer ring portion 29a, the low rigidity of the entire oil seal 27 allows the oil seal 27 to diametrically extend and contract before the oil seal 27 is attached, and thus improves the assemblability. On the other hand, adequate sealability is attained after the oil seal 27 is attached because the outer ring portion 29a is sandwiched by the wedge-shaped retainer 32 and the seal plate 26 having the wedge-shaped portion 26a.

Embodiment 5

[0070] FIG. 5 is a sectional view of a main portion of a gear spindle showing Embodiment 5 of the present invention.

[0071] In this embodiment, the outer diameter D.sub.0 of the oil seal attachment portion of Embodiment 1 is set to be larger than a diameter D.sub.2 of the base of an inner cylinder gear portion 14, and the oil seal portion employs a structure slightly modified from the structure in Embodiment 4. Specifically, the outer ring portion 29a whose both end portions in the width direction are formed in a wedge shape is sandwiched by the seal case 25 having a wedge-shaped portion (wedge-shaped retention member) 25a and a seal plate 26 having the wedge-shaped portion 26a, without using the wedge-shaped retainer 32 (see FIG. 4) employed in the oil seal portion of Embodiment 4. In addition, a highly rigid spring or solid band is used as the seal attachment member 30. Further, the helical compression spring 16 (see FIG. 1) in Embodiment 1 is not used, and the lubricating oil 20 supplied into the oil-supply-side oil chamber 18 through a cylinder hole (not shown) provided in the outer cylinder 10 is actively supplied to the seal-side oil chamber 19 through multiple communication holes 13c formed in the spindle inner cylinder 13. Other configurations are the same as Embodiment 1. Thus, components and portions that are the same as those in FIG. 1 are denoted by the same reference numerals as those used in FIG. 1, and are not described again here.

[0072] In a case where the specifications of an inner cylinder gear portion 14 (the outer diameter D of an spindle inner cylinder 13 at the inner cylinder gear portion 14) are determined, the diameter D.sub.2 of the base of the inner cylinder gear portion 14 is limited and cannot be set to a value larger than a certain value for reasons of machining of the gear portion. However, according to this embodiment, the following advantages can be offered in addition to similar operation and advantageous effects offered by Embodiments 1 and 4. Specifically, by setting the outer diameter D.sub.0 of the oil seal attachment portion to be independently of the diameter D.sub.2 of the base of the inner cylinder gear portion 14, the difference between the outer diameter D of the spindle inner cylinder 13 at the inner cylinder gear portion 14 and the outer diameter D.sub.0 of the oil seal attachment portion can be set to be as small as possible. Thus, diametrical extension and contraction needed in attachment of the oil seal 27 can be made small, which can improve the assemblability even more.

[0073] Generally, if the difference between an inner diameter D.sub.3 of the outer ring portion 29a and an outer diameter D.sub.4 of the inner ring portion 29b is large with the outer diameter D.sub.0 of the oil seal attachment portion being constant, the seal's inner-pressure strength lowers due to the internal pressure of the lubricating oil 20 caused by rotation. However, the strength of seal deformation due to the slant of the spindle inner cylinder 13 improves. Thus, when the outer diameter D.sub.0 of the oil seal attachment portion is set in view of the assemblability and strength of the oil seal, independently of the diameter D.sub.2 of the base of the inner cylinder gear portion 14 as in this embodiment, the optimum dimensions can be set for the oil seal 27 according to use conditions, independently of the diameter D.sub.2 of the base of the inner cylinder gear portion 14.

[0074] It goes without saying that the present invention is not limited to the embodiments described above, and can be variously modified in the shape of the oil seal and the like without departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

[0075] The gear spindle and the oil seal used therein according to the present invention are suitable for use in a drive device for a work roll in a rolling mill or the like.

EXPLANATION OF REFERENCE NUMERALS

[0076] 10 spindle outer cylinder [0077] 10a large-diameter cylindrical portion (outer cylinder portion) [0078] 10b communication hole [0079] 10c fit hole [0080] 11 outer cylinder gear portion (internal teeth) [0081] 12 outer-cylinder pivot [0082] 13, 13, 13 spindle inner cylinder (inner cylinder portion) [0083] 13a cylinder hole [0084] 13b annular groove for positioning [0085] 13c communication hole [0086] 14, 14 inner cylinder gear portion (external teeth) [0087] 15 inner-cylinder pivot [0088] 16 helical compression spring [0089] 17 stopper [0090] 18 oil-supply-side oil chamber [0091] 19 seal-side oil chamber [0092] 20 lubricating oil [0093] 21 bolt [0094] 22 coupling cover (outer cylinder portion) [0095] 23 stopper ring [0096] 24 seal member [0097] 25 seal case (outer cylinder portion) [0098] 25a wedge-shaped portion (wedge-shaped retention member) [0099] 26, 26, 26 seal plate [0100] 26a, 26a wedge-shaped portion (wedge-shaped retention member) [0101] 27, 27, 27, 27 oil seal [0102] 28 bolt [0103] 29, 29A, 29B, 29C, 29D seal body [0104] 29a outer ring portion [0105] 29b inner ring portion [0106] 29c intermediate ring portion [0107] 30 seal attachment member [0108] 31, 31a, 31b reinforcement ring [0109] 32 wedge-shaped retainer (wedge-shaped retention member) [0110] A constant [0111] B axial travel distance of spindle outer cylinder 10 [0112] D outer diameter of spindle inner cylinder 13 at inner cylinder gear portion 14 [0113] D.sub.0 outer diameter of oil seal attachment portion [0114] D.sub.1 outer diameter of spindle inner cylinder 13 at a portion on the drive-shaft side [0115] D.sub.2 diameter of the base of inner cylinder gear portion 14 [0116] D.sub.3 inner diameter of outer ring portion 29a [0117] D.sub.4 outer diameter of inner ring portion 29b [0118] slant angle