JP2008095926A - Thrust needle roller bearing and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining a raceway member excellent in wear resistance of a raceway surface with the raceway member subjected to a less warped amount in a manufacturing method of a raceway member having a platy portion of a thrust needle roller bearing. <P>SOLUTION: After nitriding, quench hardening is applied at a heat holding temperature 680 to 750 °C, and next a sub-zero process is applied. As a result, on an inner raceway surface 1a and an outer raceway surface 2a, formed is a hardened layer with a superficial layer hardness of 700 Hv or more, an effectively hardened layer depth of 0.10 mm or more, and a most superficial layer's nitrogen content of 1.0 by mass% or more. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thrust needle roller bearing and a method for manufacturing the same.

  The following Patent Document 1 describes a needle roller bearing that supports a shaft of a compressor for a car air conditioner. Needle roller bearings for this application operate under a wide range of conditions, from high speed to low speed, and from no load to heavy load, and because a large amount of lubricant cannot be supplied from the outside, lubricity Is used under very harsh conditions because it is difficult to ensure.

In particular, thrust needle roller bearings are more prone to wear and surface roughness because they are more slippery than other thrust bearings or radial type rolling bearings.
In recent years, alternative chlorofluorocarbons such as HFC (hydrofluorocarbon) -134a, CO ₂ (carbon dioxide), and the like have been used as refrigerants for compressors, but these refrigerants have poor self-lubricating properties. In addition, since only a very small amount of lubricating oil can be added to the refrigerant, it is increasingly difficult to ensure lubricity.

  Thrust needle roller bearings often use plate-like raceway members, but such raceway members are likely to be deformed such as warpage during quenching. As a method for suppressing this deformation, there is a method of performing quenching or tempering in a state of being pressed with a mold. Patent Document 2 below describes a method of quenching by pressing the mold as a quenching medium while pressing the mold. Since this method requires special equipment, the manufacturing cost increases.

In addition, as a method of manufacturing the raceway member of the thrust needle roller bearing so as to be able to withstand severe usage conditions, for example, using SUJ2 or SK5 as a material and performing a carburizing process at a heating and holding temperature of about 840 to 950 ° C. Alternatively, after carbonitriding, quenching is performed at a heating holding temperature of about 840 to 860 ° C., and then tempering is performed at a temperature of about 160 to 200 ° C., so that the hardness of the surface layer portion is HRC 60 or more and retained austenite A method of adjusting the amount to 15 to 40% by mass is mentioned.
JP 2005-76780 A JP-A-2005-113186

However, since the plate-like track member obtained by the above-described method is greatly warped, it is necessary to correct the deformation using the special equipment as described above.
An object of the present invention is to provide a method for producing a raceway member having a plate-like portion of a thrust needle roller bearing, in which a raceway member having excellent wear resistance on a raceway surface is obtained with a small amount of warpage. It is.

  In order to solve the above-described problems, the present invention provides a thrust needle provided with first and second race members having plate-like portions and a plurality of needle rollers disposed between the race members so as to roll freely. In the method of manufacturing the raceway member of the tapered roller bearing, a material made of steel having a carbon content of 0.3% by mass or more and 1.2% by mass or less is processed into a predetermined shape, and thereafter, 550 to 590 ° C. Nitriding treatment is performed, followed by quenching at a heating holding temperature of 680 to 750 ° C., followed by subzero treatment, so that the hardness of the surface layer portion (for example, the range from the surface to 50 μm) is Hv 700 or more effective. Form a hardened layer having a hardened layer depth (for example, a depth of Hv500) of 0.10 mm or more and a nitrogen content of the outermost part (for example, a range from the surface to 1 μm) of 1.0% by mass or more. Thrust needle roller bearing A method for manufacturing the raceway member is provided.

According to this method, by using a material made of steel having a carbon content of 0.3% by mass or more and 1.2% by mass or less, and performing nitriding treatment at 550 to 590 ° C. below the austenite transformation point, the race member A nitrogen diffusion layer is formed in the surface layer portion of the raceway surface in a state in which the dimensional change is suppressed.
Examples of the steel material used include high-carbon chromium bearing steel type 2 (SUJ2) defined by “JIS G 4805”, SC materials such as S45C, S55C, and S70C, and SCR materials such as SCR440.
In addition, by setting the heating and holding temperature of quenching to 680 to 750 ° C., the nitrogen diffusion layer is sufficiently austenitic transformed to obtain a hardness of the surface layer portion of Hv 700 or more and an effective hardened layer depth of 0.1 mm or more. The dimensional change of the track member is suppressed. When the quenching temperature exceeds 750 ° C., the effect of suppressing the dimensional change of the raceway member becomes insufficient.

In addition, since nitrogen significantly lowers the Ms point, a large amount of retained austenite exists in the nitrogen diffusion layer after quenching, but this is reduced by applying a sub-zero treatment after quenching to ensure sufficient quenching hardness. . The sub-zero treatment is preferably performed at −80 ° C. or lower in order to obtain sufficient quenching hardness.
Moreover, the required abrasion resistance is obtained by making the hardness of the surface layer part (for example, the range from the surface to 50 micrometers) of the hardened layer formed in a track surface Hv700 or more.
Moreover, a required peeling lifetime is obtained by making the effective hardened layer depth (for example, depth which becomes Hv500) of the hardened layer formed in a track surface into 0.10 mm or more.

In addition, nitrogen existing in the outermost surface portion of the hardened layer formed on the raceway surface (for example, a range from the surface to 1 μm) exists as a nitride or carbonitride, and has the effect of significantly improving the friction and wear characteristics. Since it has the effect of lowering the austenite transformation point, the quenching temperature can be lowered.
By setting the nitrogen content to 1.0% by mass or more, the quenching temperature can be set to 750 ° C. or lower (a temperature at which a change in the dimensions of the raceway member can be suppressed). Moreover, in order to prevent an excessive fall of Ms point and to ensure sufficient quenching hardness, it is preferable to make this nitrogen content into 7.0 mass% or less.

  Since the raceway member having the plate-like portion of the thrust needle roller bearing obtained by the method of the present invention has excellent wear resistance of the raceway surface and is obtained in a state with a small amount of warpage, it is a method using special equipment. There is no need to correct the deformation.

Hereinafter, embodiments of the present invention will be described.
The thrust needle roller bearing shown in FIG. 1 was produced by the following method.
This thrust needle roller bearing is composed of a first race member 1, a second race member 2, needle rollers 3 and a cage 4. The first track member 1 is composed of a cylindrical portion 11 in which a shaft is fitted and a disc-shaped track portion 12, and a contact surface 1a of the track portion 12 with the needle roller 3 corresponds to an inner ring raceway surface. The second track member 2 is a disc, and has a circular hole 21 into which the cylindrical portion 11 of the first track member 1 is loosely fitted. The contact surface 2a of the second track plate 2 with the needle rollers 3 corresponds to the outer ring raceway surface.

The dimensions of this thrust needle roller bearing are: inner diameter: 40 mm, outer diameter: 60 mm, height (dimension in the axial direction): 5 mm, PCD: 49 mm, needle roller diameter: 3 mm, needle roller length : 6 mm. The thickness of the first track member 1 is 1 mm, and the thickness of the second track member 2 is 1 mm.
The first race member 1 was manufactured by forming a cylindrical portion 11 by pressing a material made of SUJ2 and performing barrel processing, and then performing different heat treatments for each sample as shown in Table 1 below. Further, finish polishing was performed after the heat treatment.

The second track member 2 was manufactured by cutting a disk-shaped material made of SUJ2 and then polishing, and then performing different heat treatments for each sample as shown in Table 1 below. Further, finish polishing was performed after the heat treatment.
The needle roller 3 was produced by the following method. First, a rod-shaped material made of SUJ2 is cut into the shape of the needle roller 3, and a carbonitriding process is performed in an atmosphere of Rx gas + enrich gas + ammonia at 840 to 900 ° C. for 2 to 3 hours. Next, after heating and holding at 840 to 860 ° C. within 1 hour, quenching with oil cooling is performed. Next, tempering is performed at 160 to 200 ° C. for 1.5 to 2 hours. By this heat treatment, the hardness of the surface layer portion is set to Hv 700 or more. Next, finish polishing is performed.
The cage 4 was produced by pressing a steel plate.

The heat treatment method for the first track member 1 and the second track member 2 is as follows.
[Sample Nos. 1-3]
First, gas nitriding is performed in ammonia gas at 550 to 590 ° C. for 20 to 30 hours. Next, quenching is performed by oil cooling after holding at 750 ° C. for 30 minutes to 1 hour. Subsequently, it is cooled to −80 ° C. or −196 ° C., kept at that temperature for 30 minutes to 1 hour, returned to room temperature, and then tempered at 160 to 180 ° C. for 1.5 to 2 hours.

[Sample Nos. 4 to 11]
First, gas soft nitriding is performed in a mixed gas atmosphere of Rx gas and ammonia gas at 550 to 590 ° C. for 1 to 3 hours. Next, quenching is performed by oil cooling after holding at each temperature of 670 to 800 ° C. for 30 minutes to 1 hour. Subsequently, it is cooled to −80 ° C. or −196 ° C., kept at that temperature for 30 minutes to 1 hour, returned to room temperature, and then tempered at 160 to 180 ° C. for 1.5 to 2 hours.
[Sample Nos. 12-13]
First, carbonitriding is performed in an atmosphere of Rx gas + enrich gas + ammonia at 840 to 900 ° C. for 2 to 3 hours. Next, after heating and holding at 840 to 860 ° C. within 1 hour, quenching with oil cooling is performed. Next, tempering is performed at 180 to 200 ° C. for 1.5 to 2 hours.

  About the 1st track member 1 of sample Nos. 1-13 obtained in this way, and the track surfaces 1a and 2a of the 2nd track member 2, the nitrogen content of the range (uppermost part) from the surface to 1 micrometer [N] was measured by quantitative analysis using EPMA. In addition, using a micro Vickers hardness tester, the hardness of the cross section is measured from the surface in the depth direction, and from the result, the hardness (Hv) at a position of 50 μm from the surface and the depth at which Hv500 is obtained (Effective hardened layer depth) was measured. The results are also shown in Table 1 below.

Moreover, the curvature amount of the 2nd track member 2 of sample No. 1-13 was calculated | required with the following method. The height of one part of the rolling surface was measured circumferentially using a dial gauge, and the difference between the highest part and the lowest part was defined as the “warp amount”. Then, the relative value of the warpage amount of each sample was calculated with the warpage amount of No. 13 as “1”. The results are also shown in Table 1 below.
In addition, the first needle member 1 and the second race member 2 for each sample, and the same needle roller 3 and the retainer 4 are used for all samples, and a thrust needle roller bearing is assembled and subjected to a rotation tester. The first track member 1 was rotated under the following conditions. However, in No. 12 and No. 13 where the warpage was large, the relative value of the warpage amount of the second race member 2 was set to “0.3 or less by performing tempering after quenching while pressing with a die (press temper). ”Was used.

Then, after rotating for 24 hours, it was examined whether or not the raceway surface 2a of the second raceway member 2 was worn or peeled off. The results are also shown in Table 1 below. This result indicates that wear is a level that can be visually confirmed, “large”, a level that can be confirmed with a microscope is “small”, and a level that cannot be confirmed using a microscope is “no”. It was shown in 1. For peeling, “Yes” or “No” was determined by observation with a microscope.
<Rotational test conditions>
Contact pressure: 2GPa
Rotational speed: 3000min ^-1
Lubricating oil: white kerosene

In Table 1, the part outside the scope of the present invention is underlined.
As can be seen from Table 1, the thrust needle roller bearings Nos. 1-2, 4-8 corresponding to the examples of the present invention are not only worn and peeled in the durability test, Compared to the thrust needle roller bearing, the amount of warpage was “½” or less, so no correction was required. On the other hand, the thrust needle roller bearings Nos. 3 and 9 to 13 corresponding to the comparative examples of the present invention were defective in either the result of the durability test or the amount of warpage.

It is sectional drawing which shows the shape of the thrust needle roller bearing produced in embodiment.

Explanation of symbols

1 First track member (inner ring)
1a Inner ring raceway surface 2 Second raceway member (outer ring)
2a Outer ring raceway surface 3 Needle rollers 4 Cage

Claims (2)

A thrust needle roller bearing comprising a first and second race member having a plate-like portion and a plurality of needle rollers arranged to roll between the race members. There,
After processing the raw material which consists of steel whose carbon content rate is 0.3 mass% or more and 1.2 mass% or less into a predetermined shape, nitriding treatment is performed at 550 to 590 ° C., and then the heating and holding temperature is 680 to 750 ° C. By applying quenching and then sub-zero treatment, the surface of the raceway surface has a hardness Hv of 700 or more, an effective hardened layer depth of 0.10 mm or more, and a nitrogen content of the outermost part of 1.0% by mass or more. A method for manufacturing a raceway member of a thrust needle roller bearing, wherein a hardened layer is formed. Manufactured by the method of claim 1,
The nitrogen content of the outermost part is 1.0% by mass or more,
The hardness of the surface layer part is Hv700 or more,
A thrust needle roller bearing comprising first and second race members on which a hardened layer having an effective hardened layer depth of 0.10 mm or more is formed.

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