JP6878052B2 - Rolling bearing with seal - Google Patents

Description

The present invention relates to a rolling bearing with a seal, and relates to a rolling bearing with a seal used in a transmission mounted on a vehicle such as an automobile or various construction machines.

Foreign matter such as gear wear debris is mixed in the transmission. This foreign matter causes premature peeling of the rolling surface of the bearing. For this reason, the sealing member prevents foreign matter from entering the internal space of the bearing and prevents premature peeling of the rolling surface.

A general sealing member has a sealing lip made of a rubber material or the like. The bearing component that rotates in the circumferential direction with respect to the seal member is formed with a sliding surface that slides into contact with the seal lip. Since the seal lip and the sliding surface slide into contact with each other over the entire circumference, the bearing torque increases due to the drag resistance (seal torque) of the seal lip.

In order to suppress such an increase in bearing torque, Patent Document 1 provides a protrusion on the sliding portion of the seal lip, and oil penetrates into the sliding portion due to the wedge film effect to prevent the seal member and the sliding surface. It has been proposed to reduce the torque by putting it in a fluid lubricating oil state.

Further, if there is more oil than necessary for lubrication inside the bearing, the stirring resistance increases, which also causes an increase in the bearing torque. However, in the above-mentioned Patent Document 1, the case where more oil than necessary enters the inside of the bearing is not considered.

International Publication No. 2016/143786

An object of the present invention is to provide a rolling bearing with a seal in which the stirring resistance does not increase even when more oil than necessary enters the bearing.

In order to solve the above-mentioned problems, the present invention presents an outer ring, an inner ring, an outer diameter portion fitted into a pair of seal fitting grooves provided at both ends of the inner diameter surface of the outer ring, and an outer diameter portion facing the inner ring. A seal member having an inner diameter portion including a seal lip is provided, and an oil passage communicating the inside of the bearing and the outside of the bearing is formed between the seal lip and the inner ring, and the seal member of at least one of the seal members is said to have an oil passage. An oil relief groove that communicates the inside of the bearing and the outside of the bearing is formed on the outer diameter side.

Further, the oil relief grooves may be arranged at equal intervals over the entire circumference of the outer diameter portion in the circumferential direction. Further, the oil relief groove can be provided obliquely with respect to the axial direction. Then, the oil relief groove can be provided in an arc shape when viewed from the axial direction.

Further, the seal lip is in sliding contact with the sliding surface of the inner ring, a plurality of protrusions are provided on the sliding portion of the seal lip, and the oil passage is configured to be formed between the plurality of protrusions. be able to.

Further, the outer diameter portion may be formed of a rubber material.

As described above, in the rolling bearing with a seal, the oil relief groove that communicates the inside of the bearing and the outside of the bearing is formed on the outer diameter side of at least one of the seal members, so that the inside of the bearing is unnecessarily. The lubricating oil that has entered can be discharged from the oil relief groove to the outside of the bearing, and an increase in stirring resistance can be prevented.

It is a perspective view of the state in which a part of the outer ring of the rolling bearing with a seal which concerns on embodiment of this invention is cut out, and the cage is omitted. It is a side view of the rolling bearing with a seal which concerns on embodiment of this invention in a state where a part of the outer ring is cut out, and the cage is omitted. It is a vertical sectional front view which shows a part of the rolling bearing with a seal which concerns on embodiment of this invention in an enlarged manner. It is sectional drawing which enlarges and shows the seal member part of the rolling bearing with a seal which concerns on embodiment of this invention. It is sectional drawing which enlarges and shows the inward lip of the rolling bearing with a seal which concerns on embodiment of this invention, and the sliding surface portion of an inner ring. It is a perspective view which shows the seal member used in embodiment of this invention. It is a front view which shows the seal member used in embodiment of this invention. It is a schematic cross-sectional view which shows the seal member used in embodiment of this invention in an enlarged manner. It is sectional drawing which enlarges and shows the seal member part of the rolling bearing with a seal which concerns on other embodiment of this invention. It is the schematic which shows the example which used the rolling bearing with a seal which concerns on embodiment of this invention in a transmission.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIGS. 1 to 3, the rolling bearing 1 with a seal (hereinafter, also simply referred to as a rolling bearing) 1 includes an outer ring 2, an inner ring 3, and a raceway groove 4 formed on the inner diameter surface of the outer ring 2. It is composed of a plurality of balls 6 incorporated between the raceway grooves 5 formed on the outer diameter surface of the inner ring 3 and a cage 7 for holding the balls 6. That is, the rolling bearing 1 of this embodiment is a ball bearing.

Hereinafter, the direction along the bearing central axis of the rolling bearing 1 is referred to as an axial direction, and the direction orthogonal to the axial direction is referred to as a radial direction. The circumferential direction around the center axis of the bearing is called the circumferential direction.

Lubricating oil is supplied to the inside of the annular bearing formed by the outer ring 2 and the inner ring 3 by an appropriate means such as grease or an oil bath.

The rolling bearing 1 with a seal according to the embodiment of the present invention is used, for example, in a transmission of an automobile. FIG. 10 is a schematic view showing an example incorporated in a transmission of an automobile. The figure is an example of an automatic transmission. The outer rings 2 of the rolling bearings 1 and 1 with seals are fitted to both ends of the case 23 in the axial direction, and both ends of the main shaft 24 are rotatably supported by the inner rings 3 of the bearings 1 and 1. A counter shaft 25 is provided in the case 23 in parallel with the main shaft 24. The counter shaft 25 has a gear portion that meshes with the gear portion of the main shaft 24, and is rotatably supported by the case 23 via a bearing.

The rolling bearing 1 with a seal according to the embodiment of the present invention is used for bearings of differentials, constant velocity joints, propeller shafts, turbochargers, machine tools, etc., in addition to vehicle transmissions, and is attached to these rotating shafts.

As described above, the inner ring 3 is attached to the main shaft 24 (see FIG. 10) and rotates integrally with the main shaft 24. The outer ring 2 is attached to the case 23 (see FIG. 10).

A pair of seal fitting grooves 8 are formed on the inner diameter surface of the outer ring 2 at both ends in the axial direction, while the outer diameter surface of the inner ring 3 faces the pair of seal fitting grooves 8 in the radial direction. A seal groove 9 is formed at the position.

The outer diameter portion 11 of the rubber seal member 10 is fitted in each of the pair of seal fitting grooves 8 formed in the outer ring 2. The seal member 10 includes a core metal 10b and a rubber portion 10a that covers the core metal 10b. Specifically, the rubber portion 10a covers the entire core metal 10b excluding the axial inner side surface of the core metal 10b. The rubber portion 10a is made of a rubber having excellent oil resistance and heat resistance, such as nitrile rubber, heat-resistant nitrile rubber, hydrogenated nitrile rubber, acrylic rubber, and fluororubber.

The seal member 10 separates the inside of the bearing from the outside of the bearing. On the outer side of the seal member 10 as a boundary, there are foreign substances such as gear wear powder, clutch wear powder, and minute quarrying, depending on where the rolling bearing 1 is incorporated. Such powdery foreign matter reaches the vicinity of the rolling bearing 1 due to the flow of lubricating oil or atmosphere. The seal member 10 prevents foreign matter from entering the bearing from the outside of the bearing.

As described above, the seal member 10 has an outer diameter portion 11 that is press-fitted into the seal fitting groove 8, a radial seal lip 13 that faces outward on the inner peripheral side, and an axial seal lip 14 that faces inward. .. The seal member 10 is attached to the outer ring 2 by press-fitting the outer diameter portion 11 into the seal fitting groove 8.

As shown in FIGS. 3 and 4, the radial seal lip 13 of the seal member 10 elastically contacts the sliding surface 31 formed of a small-diameter cylindrical surface formed outward in the axial direction of the seal groove 9, while being axial. The tip of the seal lip 14 is in elastic contact with the sliding surface 32 on the inner surface of the seal groove 9. A tightening allowance is formed in the radial direction between the radial seal lip 13 and the sliding surface 31, and a tightening allowance is formed in the axial direction on the sliding surface 32 on the inner surface of the axial seal lip 14 and the seal groove 9. Due to these tightening margins, rubber-like elastic deformation occurs, and the bearing space is sealed.

The contact surface of the radial seal lip 13 with respect to the sliding surface 31 is provided with minute protrusions 15 over the entire surface, and the contact surface of the inner surface of the seal groove 9 of the axial seal lip 14 with respect to the sliding surface 32 is also provided. A minute protrusion 17 is provided over the entire surface.

As shown in FIGS. 4 to 8, the radial seal lip 13 has a protrusion 15 having a protrusion height in the direction orthogonal to the sliding surface 31, that is, in the normal direction perpendicular to the tangent line in contact with the sliding surface 31. .. Since the sliding surface 31 has a cylindrical surface shape centered on the bearing center axis, the direction orthogonal to this corresponds to the radial direction. The protrusion 15 is formed over the entire range from the tip of the radial seal lip 13 to the sliding surface 31 so as to face the sliding surface 31 in the radial direction. Oil passages 16 that communicate with each other are formed on both sides of the protrusion 15 that contacts the sliding surface 31.

As shown in FIGS. 4 and 6 to 8, the axial seal lip 14 is arranged in the direction orthogonal to the sliding surface 32 on the inner surface of the seal groove 9, that is, in the normal direction perpendicular to the tangent line in contact with the sliding surface 32. It has a protrusion 17 having a protrusion height. Since the sliding surface 32 has a mortar shape centered on the bearing central axis, the direction orthogonal to the sliding surface 32 is a direction inclined by a predetermined angle from the axial direction. The protrusion 17 is formed over the entire range from the tip of the axial seal lip 14 to the sliding surface 32 in the axial direction. Oil passages 18 that communicate with each other are formed on both sides of the protrusion 17 that contacts the sliding surface 32.

The inside of the bearing and the outside of the bearing are communicated with each other by the oil passage 16 and the oil passage 18.

The protrusions 15 of the radial seal lip 13 are arranged at uniform intervals over the entire circumference in the circumferential direction. Therefore, the oil passages 16 are also generated at uniform intervals over the entire circumference in the circumferential direction. The protrusions 15 are dispersedly arranged over the entire circumference, and the radial seal lip 13 makes sliding contact with the sliding surface 31 at the protrusions 15. Further, the protrusions 17 of the axial seal lip 14 are arranged at uniform intervals over the entire circumference in the circumferential direction. Therefore, the oil passages 18 are also generated at uniform intervals over the entire circumference in the circumferential direction. The protrusions 17 are dispersedly arranged over the entire circumference, and the axial seal lip 14 makes sliding contact with the sliding surface 32 at the protrusions 17.

The oil passage 16 has a groove shape substantially along the sliding surface 31 and communicates with the seal groove 9 inside the bearing and the external space, and the oil passage 18 communicates with the seal groove 9 and the inside of the bearing. In the case of an oil bath or a splash, as shown by the broken line arrow A in FIG. 4, the lubricating oil reaches the inside of the bearing from the outside through the oil passages 16 and 18, and is sent to the outer ring 2 side by centrifugal force. ..

FIG. 5 shows an enlarged cross section of the vicinity of the radial seal lip 13 of the seal member 10. This cross section shows a gap in the direction orthogonal to the sliding surface between the radial seal lip 13 and the sliding surface 31.

As shown in FIG. 5, the protrusion 15 is substantially deformed by the tension force generated by the elastic deformation of the radial seal lip 13 based on the tightening allowance between the radial seal lip 13 and the sliding surface 31 and the hydraulic pressure of the lubricating oil. Is prevented from occurring.

The radial seal lip 13 has a tip that defines the inner diameter of the radial seal lip 13 in a natural state. The protrusion 15 extends to the tip of the radial seal lip 13 and is formed over the entire range having a radial tightening allowance with the sliding surface 31.

The protrusions 15 are arranged at regular intervals d in the circumferential direction. Considering the appearance of the radial seal lip 13 when viewed from the axial direction, a plurality of protrusions 15 appear in a radial pattern arranged in the circumferential direction at a constant pitch angle θ corresponding to the interval d. The radiation center is on the central axis of the seal member 10 (not shown).

Since each protrusion 15 is present near the tip of the radial seal lip 13, the radial seal lip 13 is in sliding contact with the sliding surface 31 at each protrusion 15, and an oil passage 16 is formed between the protrusions 15 and 15.

The protrusion 15 has an R shape that gradually approaches the sliding surface from both ends in the circumferential direction w toward the center in the circumferential direction. This R shape is given over the entire length of the protrusion 15 in the radial direction. Therefore, the region where the protrusion 15 and the sliding surface 31 come into contact with each other exists in the center of the protrusion 15 in the circumferential direction.

When the sliding surface 31 rotates relative to the radial seal lip 13 in the direction of arrow A, the lubricating oil in the oil passage 16 is drawn into the wedge-shaped gap between the protrusion 15 and the sliding surface 31. Since the wedge angle in the wedge-shaped gap described above gradually decreases from the oil passage 16 on the wide side where the lubricating oil to be drawn is present toward the narrow side, the protrusion 15 and the sliding surface 31 are in sliding contact with each other in a linear shape. The closer to the area, the stronger the wedge effect. Therefore, the oil pressure of the oil film in the linear region can be increased more effectively, the protrusion 15 can be completely separated from the sliding surface 31, and the oil film in the linear region can be thickly formed, and the protrusion 15 and the slide can be formed. It becomes easy to change the lubrication state between the moving surface 31 and the moving surface 31 to the fluid lubrication state.

Here, if there is an oil film that completely separates the protrusion 15 and the sliding surface 31, the fluid lubrication state is achieved in which the sliding surface 31 slides without direct contact with the protrusion 15. By maintaining such an oil film between each protrusion 15 and the sliding surface 31, the fluid lubrication state can be established between the radial seal lip 13 and the sliding surface 31.

As shown in FIGS. 7 and 8, as in the radial seal lip 13, the protrusion 17 is formed over the entire range from the tip of the axial seal lip 14 to the sliding surface 32 in the axial direction. Oil passages 18 that communicate with each other are formed on both sides of the protrusion 17 that contacts the sliding surface 32. Similar to the protrusion 15 of the radial seal lip 13, the protrusions 17 are also arranged in the circumferential direction at regular intervals, and a plurality of protrusions 17 are formed in a radial pattern in which the plurality of protrusions 17 are arranged in the circumferential direction at a constant pitch angle corresponding to the spacing. ing. The radiation center is on the central axis of the seal member 10 (not shown).

Since each protrusion 17 is present near the tip of the axial seal lip 14, the protrusion 17 makes sliding contact with the sliding surface 32, and an oil passage 18 is formed between the protrusions 17 and 17. Like the protrusion 15 of the radial seal lip 13, this protrusion 17 also has an R shape that gradually approaches the sliding surface from both ends in the circumferential direction toward the center in the circumferential direction, and this R shape has the overall length of the protrusion 17 in the radial direction. It may be formed over.

In this way, by providing the protrusion 17 at the tip of the axial seal lip 14, the fluid lubrication state can be established between the axial seal lip 14 and the sliding surface 32 of the seal groove 9 in the same manner as the radial seal lip 13. it can.

As described above, in the case of an oil bath or a splash, as shown by the broken arrow A in FIG. 4, the lubricating oil is drawn from the outside of the bearing through the oil passages 16 and 18 into the inside of the bearing, and the radial seal is provided. Both the lip 13 and the axial seal lip 14 are in a fluid lubricated state, and the seal torque can be reduced.

The rolling bearing 1 with a seal in this embodiment is assumed to be used in a vehicle transmission. Lubricating the rolling bearings with seals existing in the transmission of the vehicle is performed by a method such as splashing, an oil bath, or nozzle injection. Therefore, lubricating oil is present around the seal lip of the seal member fixed to the rolling bearing with a seal. The lubricating oil to be refueled is also commonly used in other lubricating parts such as gears existing in the transmission. The lubricating oil is circulated by an oil pump and filtered by an oil filter provided in the circulation path.

As described in Patent Document 1, when lubricating oil filtered by an oil filter is supplied to a bearing with a seal used for supporting a rotating part of a drive system such as a vehicle transmission or a differential gear, the particle size As long as the sealing member 10 prevents large foreign matter exceeding 50 μm from entering the inside of the bearing, even if foreign matter having a particle size of 50 μm or less contained in the lubricating oil is allowed to enter the inside of the bearing, there is a problem in bearing life. Does not wake up. According to the research of the applicant of the present application, if the heights of the protrusions 15 and 17 are set to 0.07 mm or less, a narrow gap (including an oil passage) where foreign matter having a particle size of more than 50 μm cannot easily pass is sealed with the seal lip. It was found that it can be generated between the sliding surfaces. Therefore, the size of the oil passage 16 formed in the radial seal lip 13 and the oil passage 18 formed in the axial seal lip 14 in this embodiment may be 70 μm or less.

In this embodiment, the heights h of the protrusions 15 and 17 are set to 0.07 mm or less, specifically 0.05 mm. This height h is a value at the highest position in the range where it can come into contact with the sliding surface 31 or 32 by design. This position is also where the tightening allowance set between the protrusions 15 and 17 and the sliding surface is maximized. Since the amount of deformation of the protrusions during bearing operation can be ignored, the gap (including the oil passage) in the direction orthogonal to the sliding surface between the seal lip 13 (14) and the sliding surface 31 (32) slides. The height corresponds to the height h of the protrusions 15 and 17 at the narrowest point in the direction orthogonal to the surface, and does not substantially exceed 0.05 mm. Therefore, even if the external lubricating oil contains a foreign substance having a particle size of more than 50 μm, it is considered that the foreign substance does not pass through the oil passages 16 and 18 substantially.

Assuming that the wear debris that causes early breakage of the rolling bearing 1 with a seal is a foreign substance having a particle size of more than 0.3 mm, the protrusion heights of the protrusions 15 and 17 may be set to 0.3 mm or less. Further, in order to improve the oil permeability of the oil passages 16 and 18, the protrusion height of the protrusions 15 and 17 may be 0.05 mm or more. The protrusion heights of the protrusions 15 and 17 may be appropriately selected from the viewpoint of oil permeability of the oil passages 16 and 18 and prevention of the passage of foreign matter.

As described above, the lubricating oil is drawn into the bearing from the outside through the oil passages 16 and 18 by the oil bath or the splashing, as shown by the arrow A of the broken line in FIG. Due to the inflow of the lubricating oil, the seal lips 13 and 14 and the sliding surfaces 31 and 32 are in a fluid lubricated state, and low torque can be achieved. However, if the lubricating oil enters the bearing more than necessary, the stirring resistance increases. Lubricating oil that has once entered the inside of the bearing is sent to the outer ring 2 side by centrifugal force and stays on the outer ring 2 side.

Therefore, in this embodiment, an oil relief groove 12 that communicates the inside of the bearing and the outside of the bearing is formed on the outer peripheral surface side of the outer diameter portion 11 of the seal member 10. As shown in FIGS. 6 and 7, a plurality of oil relief grooves 12 are provided in the outer diameter portion 11 at equal intervals over the entire circumference in the circumferential direction. The oil relief grooves 12 may be provided at unequal intervals. The oil relief groove 12 is formed so that the inner peripheral side of the seal member 10 is deep and shallow toward the outer peripheral side. In this embodiment, the lubricating oil sent to the outer ring side by centrifugal force is discharged from the oil relief groove 12 to the outside of the bearing as shown by the arrow B in FIG. By providing a plurality of oil relief grooves 12 on the outer diameter portion 11 side in this way, the lubricating oil that has flowed in more than necessary is discharged, the lubricating oil is suppressed from staying on the outer ring side, and the stirring resistance is increased. Suppress doing.

As shown in FIGS. 2 and 6, the oil relief groove 12 is provided obliquely with respect to the axial direction so that the lubricating oil sent to the outer ring 2 side by centrifugal force can be easily released. , The oil relief groove 12 is formed in an arc shape.

The width of the oil relief groove 12 is formed so as to be wide on the inner side of the bearing and narrower toward the outer side of the bearing. By changing the width of the oil relief groove 12 in this way, the lubricating oil can be easily discharged to the outside of the bearing, and the inflow of foreign matter into the bearing can be suppressed.

Then, as shown in FIG. 4, when the outer diameter portion 11 of the seal member 10 is fitted and attached to the seal fitting hole 8, an oil relief groove located between the outer ring 2 of the bearing and the seal member 10 is formed. It is preferable that the radial distance g of 12 is 0.05 mm or more and 0.3 mm or less. The oil relief groove 12 is mainly used for discharging the lubricating oil, but when the lubricating oil reaches the oil relief groove 12 from the outside of the bearing when the rotating shaft is not rotating, the oil relief groove 12 is used. Lubricating oil flows into the bearing from 12. Since lubricating oil for initial lubrication is required when shifting from non-rotation to rotation, it is possible to improve the shortage of lubricating oil during initial operation by entering the lubricating oil from the oil relief groove 12 during non-rotation. it can. However, it is not preferable that foreign matter enters together with the lubricating oil. Therefore, in order to prevent foreign matter from entering through the oil escape groove 12, the oil escape groove 12 facing the outer ring 2 side is considered to have oil permeability and the mixture of foreign matter in the same manner as the protrusions 15 and 17 of the seal lips 13 and 14 described above. The depth is shallower and the width is narrower from the inner peripheral side to the outer peripheral side of the outer diameter portion 11 so as to be 0.05 mm or more and 0.3 mm or less.

In the above embodiment, the radial seal lip 13 of the seal member 10 elastically contacts the sliding surface 31 formed of a small-diameter cylindrical surface formed on the outer side of the seal groove 9 in the axial direction, while the axial seal lip 14 The tip of the seal groove 9 is in elastic contact with the sliding surface 32 on the inner surface of the seal groove 9. In the seal member 10 shown in another embodiment shown in FIG. 9, the seal lip 19 provided on the inner ring 3 side is a non-contact type seal member that does not come into contact with the outer diameter surface of the inner ring 3. An oil passage is formed between the seal lip 19 and the outer diameter surface of the inner ring 3, and as shown by the arrow A, the lubricating oil flows into the bearing and the lubricating oil sent to the outer ring side by centrifugal force is indicated by the arrow B. As shown in the above, the oil is discharged from the oil relief groove 12 to the outside of the bearing. In this way, the lubricating oil that has flowed in more than necessary is discharged, the lubricating oil is suppressed from staying on the outer ring side, and the stirring resistance is suppressed from increasing.

In the above-described embodiment, the seal member 10 is formed of the core metal 10b and the rubber portion 10a covering the core metal 10b, but a metal seal plate in which the seal member 10 is formed of a metal plate may also be used. A cut groove may be formed in the outer diameter portion to be fitted to the bearing fitting portion of the metal seal plate so as to discharge the lubricating oil.

Further, in the above-described embodiment, the oil escape groove 12 is provided in the outer diameter portion 11 of the pair of seal members 10, but it may be provided only in one of the seal members 10.

The present invention is not limited to the above-described embodiments, and it goes without saying that the present invention can be carried out in various forms without departing from the gist of the present invention. Indicated by the scope of, and further include the equal meaning described in the claims, and all modifications within the scope.

1: Rolling bearing with seal 2: Outer ring 3: Inner ring 4: Raceway groove 5: Raceway groove 6: Ball 7: Cage 8: Seal fitting groove 9: Seal groove 10: Seal member 10a: Rubber part 10b: Core metal 11: Outer diameter portion 12: Oil relief groove 13: Radial seal lip 14: Axial seal lip 15: Protrusion 16: Oil passage 17: Projection 18: Oil passage 19: Seal lip 31: Sliding surface 32: Sliding surface

Claims (6)

A seal member having an outer ring, an inner ring, an outer diameter portion fitted into a pair of seal fitting grooves provided at both ends of the inner diameter surface of the outer ring, and an inner diameter portion including a seal lip facing the inner ring. , With
An oil passage communicating the inside of the bearing and the outside of the bearing is formed between the seal lip and the inner ring.
An oil relief groove that communicates the inside of the bearing and the outside of the bearing is formed on the outer diameter side of at least one of the sealing members .
A rolling bearing with a seal, characterized in that the width of the oil relief groove is formed so as to widen the inner side of the bearing and narrow it toward the outer side of the bearing. The rolling bearing with a seal according to claim 1, wherein the oil relief grooves are arranged at equal intervals over the entire circumference of the outer diameter portion in the circumferential direction. The rolling bearing with a seal according to claim 2, wherein the oil relief groove is provided obliquely with respect to the axial direction. The rolling bearing with a seal according to claim 3, wherein the oil relief groove is provided in an arc shape when viewed from the axial direction. The seal lip is in sliding contact with the sliding surface of the inner ring,
A plurality of protrusions are provided on the sliding portion of the seal lip.
The rolling bearing with a seal according to any one of claims 1 to 4, wherein the oil passage is formed between the plurality of protrusions. The rolling bearing with a seal according to any one of claims 1 to 5, wherein the outer diameter portion is made of a rubber material.

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