JP2009242893A - Holder for rolling bearing and its surface treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a holder for a rolling bearing which copes with the high speed rotation and high additional capacity of the rolling bearing, has high fatigue strength and less abrasion loss, and to provide its surface treatment method. <P>SOLUTION: A base material for a press holder for a self aligning rolling bearing is manufactured by the press forming from a cold-rolled steel plate SPCC or a hot-rolled steel plate SPHD, and subjected to the primary heat treatment, the secondary heat treatment, and the cooling treatment. The primary heat treatment is the gas nitriding at the temperature of 400-590°C. The secondary heat treatment is the treatment of keeping the plate at the temperature of 590-700°C while restricting the plate in a straightening die. The cooling treatment is the quenching treatment by the water cooling or the like. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steel cage incorporated in a rolling bearing and a surface treatment method thereof.

Conventionally, a high-strength brass machined cage that is excellent in strength is often used for a rolling bearing on which a load acts. However, high-strength brass is self-lubricating and excellent in slidability and wear resistance, but is expensive. Therefore, a high-strength brass machined cage has a problem of high material cost. In addition, since it is processed by milling, the processing cost is high and the material yield is low. Therefore, the high-strength brass machined cage has been limited to special applications.
Therefore, in recent years, it has been manufactured from cold-rolled steel plates typified by SPCC materials and hot-rolled steel plates typified by SPHD materials by optimizing the cage design to reduce costs and improve cage strength. A pressed press holder is used.

  In general, SPCC material is inferior in sliding property and wear resistance compared to high-strength brass. Therefore, when the lubrication conditions are severe, the contact portion between the rolling element and the cage pocket, the guide surface of the cage and the race wheel Wear may significantly progress at the contact area with the material, and rotation accuracy may be reduced. In the worst case, seizure may occur and damage may occur. Therefore, the cage made of SPCC material or SPHD material is subjected to soft nitriding treatment represented by salt bath nitriding treatment or gas soft nitriding treatment, and a hard nitride layer made of a compound of iron and nitrogen is held in the cage. Efforts have been made to improve wear resistance by forming on the surface.

  For example, in Patent Document 1, a deep groove ball bearing is punched by nitriding from an Al-killed steel plate having a low carbon copper content of 0.12% C or less and a Ti content of 0.0015% or less. A technique for making a cage is disclosed. Thereby, since Ti content in steel is controlled, there is no embrittlement of the internal part of a steel plate at the time of a tuftride treatment, the toughness of a cage is secured, and the fracture strength is increased.

Further, Patent Document 2 discloses a gas nitriding method including a fluorination treatment in which the oxide on the surface of the cage is replaced with a metal fluoride film before the nitriding treatment. Thereby, it is possible to quickly obtain a uniform nitride layer on the steel surface.
Patent Document 3 discloses the production of a rolling bearing cage in which a steel material formed into a predetermined shape is subjected to nitriding treatment, then quenched from a temperature of 680 to 750 ° C., and subjected to subzero treatment after quenching. A method is disclosed. According to this manufacturing method, since quenching is performed after nitriding, a cage having excellent fatigue strength can be manufactured.
JP-A-6-49623 Japanese Patent Laid-Open No. 10-2336 JP 2007-107077 A

  2. Description of the Related Art In recent years, the function of a cage has been advanced, and the shape of a press cage has become complicated in order to provide a guide function and a function for controlling the posture of a needle roller. Therefore, in a cage that has been subjected to salt bath nitriding as described in Patent Document 1, an excessively repetitive stress is applied to a specific part of the cage depending on the rotation condition, which may cause breakage of the cage. . This is because the salt bath does not spread sufficiently and uneven nitriding occurs, and the thinned portion of the nitride layer becomes the starting point of destruction.

Further, in Patent Document 2, it is difficult to obtain a hard nitrided layer to the deep part, and there is a possibility that the strength of the cage material is insufficient.
In recent years, the use of rolling bearings has become more and more severe due to the multi-stage A / T aimed at reducing fuel consumption of automobiles. Therefore, a cage that can cope with high-speed rotation and high added capacity of rolling bearings. Is desired. In addition, since extremely high dimensional accuracy is required, it is necessary to suppress deformation as much as possible.

In addition, as in Patent Document 3, when the quenching is performed after the temperature is maintained at 680 to 750 ° C. in the second heat treatment, the decomposition and diffusion of the nitride film may progress and the wear resistance may be lowered. Moreover, although it can hold | maintain at 750 degrees C or less, a thermal stress can be reduced, However, Since hardening is performed, a deformation | transformation cannot be avoided. Since the cage requires extremely high dimensional accuracy, it is necessary to suppress deformation as much as possible.
Accordingly, the present invention has been made paying attention to the above-mentioned problems, and its purpose is to meet the demands for high-speed rotation and high added capacity of rolling bearings, high fatigue strength, and low wear amount for rolling bearings. An object of the present invention is to provide a cage and a surface treatment method thereof.

A surface treatment method for a rolling bearing cage according to claim 1 of the present invention is a gas nitriding treatment at a temperature of 400 to 590 ° C. with respect to the surface of a base material of a rolling bearing cage formed by press forming a steel material. It is characterized in that a primary heat treatment is performed, followed by a secondary heat treatment that is constrained to a correction die and maintained at a temperature of 590 to 700 ° C., and thereafter a cooling treatment for rapid cooling is performed.
A surface treatment method for a rolling bearing cage according to claim 2 of the present invention is the surface treatment method for a rolling bearing cage according to claim 1, wherein the surface of the base material of the rolling bearing cage after press molding is used. After the fluorination treatment, the gas nitriding treatment is performed.

The rolling bearing retainer according to claim 3 of the present invention is a primary heat treatment in which a gas nitriding treatment is performed at a temperature of 400 to 590 ° C. after the surface of the rolling bearing retainer formed by press forming a steel material is fluorinated. After that, it is obtained by performing a secondary heat treatment that is constrained to a straightening mold and is maintained at a temperature of 590 to 700 ° C., and then performing a cooling treatment for rapid cooling.
By performing a primary heat treatment by gas nitriding treatment on the surface of the base material of the rolling bearing cage, a nitrided layer is formed on the surface, so that the surface hardness is increased and the wear resistance is improved. If the surface of the base material of the rolling bearing cage is subjected to a fluorination treatment before the gas nitriding treatment, the effect is further improved. Further, in the secondary heat treatment, the cage is held at a temperature of 590 to 700 ° C. in a state in which the cage is restrained with a straightening mold, and then rapidly cooled, and a structure containing bainite or martensite is formed in the nitride layer, thereby achieving high accuracy. A cage having wear resistance and high fatigue strength can be produced. Here, there is no restriction | limiting in particular if the said correction | amendment type | mold is a shape which maintains the shape of the holder | retainer before secondary heat processing, According to the objective, it selects suitably.

  According to the present invention, a cage for a rolling bearing having high fatigue strength and low wear is obtained.

An embodiment of a surface treatment method for a rolling bearing cage and a rolling bearing cage according to the present invention will be described below with reference to the drawings.
When nitriding is applied to a low carbon steel plate typified by SPCC material or SPHD material, nitrogen and iron react on the steel surface, and nitrogen atoms diffuse into the steel. _A hard nitride layer made of a compound of iron and nitrogen such as ₂ N, Fe ₃ N, or Fe ₄ N is formed. The hardness of the nitrided layer measured by the Vickers hardness tester is generally HV400 or more, and the hardness is increased as compared with the cage base material before nitriding. Further, in a steel rolling bearing cage formed with a nitride layer, the metal contact between the rolling element and the cage or the metal contact between the sliding guide surface and the cage is caused by the nitride layer. Therefore, wear resistance and seizure resistance are improved.

Then, the surface treatment method of the rolling bearing retainer according to the present invention includes a fluorination treatment and a primary heat treatment on the surface of the retainer base material 1 formed by press-forming the steel shown in FIGS. 1 (a) and (b). Second heat treatment and cooling treatment are performed.
The fluorination treatment is a treatment in which the oxide present on the surface of the cage base material is replaced with a fluoride film. Prior to nitridation of the cage base material, first, while heating the cage base material in the furnace, in this state, a fluorine compound or a gas containing fluorine is introduced into the furnace, and the surface of the cage base material is When the contact is made, the activated fluorine atoms destroy and remove the inorganic and organic contaminants adhering to the surface of the cage base material, purify the surface, and the fluorine atoms react with the oxide film. It changes to a fluoride film, and the surface of the cage base material is covered and protected by the fluoride film.

  The primary heat treatment is a nitriding treatment performed on a fluorinated steel at a temperature of 400 to 590 ° C. using ammonia gas as a nitriding medium. By performing the nitriding treatment by the primary heat treatment, a nitride layer is formed on the surface, so that the surface hardness is increased and the wear resistance is improved. If the temperature in the primary heat treatment is less than 400 ° C., a good nitride film cannot be obtained, and if it exceeds 590 ° C., it exceeds the A1 transformation point of the cage base material, resulting in heat treatment deformation and high dimensional accuracy. Can't get.

  The secondary heat treatment is a treatment in which the cage base material subjected to the primary heat treatment is held at a temperature of 590 to 700 ° C. by constraining the retainer base material to a straightening mold. The cooling process is a process of rapidly cooling the cage base material subjected to the secondary heat treatment. By heating and holding at 590 to 700 ° C. in the secondary heat treatment to form austenite and then rapidly cooling, a structure containing bainite or martensite is formed in the nitride layer, so that the fatigue strength is improved. Here, since it exceeds the A1 transformation point at 590 ° C. or higher, warping or the like may occur due to quenching deformation, and high dimensional accuracy may not be obtained. Therefore, high dimensional accuracy can be obtained by performing heating and cooling in a state where the cage is corrected with a correction die.

The straightening mold is not particularly limited as long as it retains the shape of the cage before the secondary heat treatment, and is appropriately selected according to the purpose. FIG. 2 is a cross-sectional view showing a configuration when the base material of the rolling bearing cage is restrained by a straightening die in the secondary heat treatment. As shown in FIG. 2, warping or the like is reduced by restraining the cage with the correction die 2.
If the temperature in the secondary heat treatment is lower than 590 ° C., the A1 transformation point is not exceeded, and the structure becomes ferrite, and high hardness cannot be obtained. If the temperature in the secondary heat treatment exceeds 700 ° C., decomposition and diffusion in the nitride layer proceed, and sufficient wear resistance cannot be obtained. A preferable secondary heat treatment temperature is 600 to 670 ° C. Further, the cooling rate in the cooling treatment is preferably 50 ° C./s or more. If the cooling rate is less than 50 ° C./s, the deep portion of the cage base material may not be sufficiently cured, and sufficient fatigue strength may not be obtained.

The steel materials to be press-formed are C: 0.08 to 0.20 mass%, Si: 0.30 mass% or less, Mn: 0.05 to 1.0 mass%, P: 0.03 mass% or less. S: 0.05% by mass or less, Al: 0.01-0.1% by mass, and the balance is preferably composed of Fe and inevitable impurities.
The reason for limiting the numerical values of the above-mentioned components is as follows.

[C: 0.08 to 0.20 mass%]
C is an element necessary for ensuring the strength. When the carbon content is less than 0.08% by mass, sufficient strength cannot be obtained. Moreover, when carbon content exceeds 0.20 mass%, the workability of a cage | basket material will fall.
[Si: 0.30 mass% or less]
Si is an element necessary for deoxidation, and if it exceeds 0.30% by mass, workability deteriorates.

[Mn: 0.05 to 1.0% by mass]
Mn is an element necessary for deoxidation / desulfurization, and if it is less than 0.05% by mass, deoxidation is insufficient and the amount of nonmetallic inclusions is increased. Moreover, when it exceeds 1.0% mass, toughness will fall.
[P: 0.03 mass% or less]
P is a harmful impurity element inevitably mixed in the steel, and its upper limit is 0.03% by mass.

[S: 0.05% by mass or less]
S is a harmful impurity element inevitably mixed in the steel, and its upper limit is 0.05 mass%.
[Al: 0.01 to 0.1% by mass]
Al is an element necessary for improving the nitriding characteristics, particularly for improving the surface hardness and for suppressing the coarsening of crystal grains, and needs to be contained in an amount of 0.01% by mass or more. Moreover, when it exceeds 0.1 mass%, toughness will fall.

(Example)
Hereinafter, the present invention will be described with reference to more specific examples.
A steel material containing the components shown in Table 1 was press-molded to produce a base material for a rolling bearing cage. The surface of the base material was fluorinated at 350 ° C. Then, based on the processing conditions shown in Table 2, after performing a primary heat treatment (nitriding treatment) in a heating furnace, the furnace was cooled. Then, based on the process conditions shown in Table 2, it heated and hold | maintained in the heating furnace in the state which restrained the cage | basket with the correction type | mold as secondary heat processing. Then, water cooling was performed as a cooling process, and the rolling bearing cages of Examples 1 to 4 and Comparative Examples 1 to 7 were obtained.

Next, the fatigue strength of the rolling bearing cages of Examples 1 to 4 and Comparative Examples 1 to 7 was evaluated. That is, the fatigue strength test was performed on the end faces of the rolling bearing cages of Examples 1 to 4 and Comparative Examples 1 to 7, and the fatigue strength ratio was determined with the fatigue strength of Example 1 being 1, and this was evaluated. . In the fatigue strength test, stress is repeatedly applied at 20 Hz to the end faces of the rolling bearing cages of Examples 1 to 4 and Comparative Examples 1 to 7, and the number of repetitions until the rolling bearing cage is cracked is measured. The fatigue strength when the number of repetitions was 1 × 10 ⁷ cycles was determined. The results of the fatigue strength ratio are shown in Table 2.

Next, the abrasion resistance of the cages of Examples 1 to 4 and Comparative Examples 1 to 7 was evaluated. That is, the cage was assembled in a self-aligning roller bearing (nominal number 22211) and a high-speed rotation test was conducted, and the wear situation of the cage after the rotation test was evaluated by mass change. The conditions of the rotation test are as follows.
・ Load: 15415N
・ Rotation speed: 6750 min
-Lubrication conditions: Grease lubrication-Test time: 24 hours Table 2 shows the wear amount ratio of the cage. The wear amount ratio of the cage is a relative value when the wear amount of the cage of Example 1 is 1.
As shown in Table 2, good evaluation results could be obtained for Examples 1 to 4 that satisfy the requirements of the present invention.

  On the other hand, since Comparative Examples 1 and 2 were processed at a temperature lower than the processing temperature defined in the primary heat treatment and the secondary heat treatment, higher fatigue strength than that in Example 1 could not be obtained. In particular, Comparative Example 1 treated at a low temperature in the primary heat treatment also had low wear resistance. Moreover, since the comparative example 3 processed at the temperature higher than the processing temperature prescribed | regulated in primary heat processing and secondary heat processing, it was not able to obtain abrasion resistance higher than Example 1. FIG. In Comparative Example 5, the secondary heat treatment was not rapid cooling as the cooling treatment, and the furnace cooling was performed at a cooling rate that was significantly slower than 50 ° C./s, so that higher fatigue strength than that of Example 1 was obtained. I couldn't. Moreover, since the comparative example 6 did not perform secondary heat processing, the fatigue strength higher than Example 1 was not able to be obtained. Moreover, since the comparative example 7 performed salt bath nitriding instead of gas nitriding in the primary heat treatment, it was not possible to obtain higher fatigue strength and wear resistance than in the first embodiment. Furthermore, since Comparative Example 4 was processed at a temperature higher than the processing temperature specified in the secondary heat treatment, the heat treatment was deformed and a fatigue test could not be performed.

  In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, after nitriding by primary heat treatment, secondary heat treatment may be performed without cooling, and cooling treatment may be performed after holding for a certain period of time. This cooling process may be water cooling or oil cooling. In addition, the primary heat treatment may be performed by gas nitriding in a state where the cage is restrained by a straightening mold. The straightening mold used at this time is not particularly limited as long as it retains the shape of the cage before the primary heat treatment, and is appropriately selected depending on the purpose. In addition, the cooling process may be performed in a state where the cage is constrained by a correction die. Moreover, the kind of steel which comprises a cage is not specifically limited, You may manufacture a cage using materials other than a cold rolled steel plate and a hot rolled steel plate. Further, the manufacturing method of the cage is not particularly limited, and is not limited to the press cage and may be a machined cage. Furthermore, the rolling bearing retainer according to the present invention can be applied to various types of rolling bearings. For example, radial roller bearings such as spherical roller bearings, deep groove ball bearings, angular contact ball bearings, self-aligning ball bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, thrust ball bearings, thrust roller bearings This is a thrust type rolling bearing.

  The cage for rolling bearings of the present invention is suitable for rolling bearings used in automobiles, general industrial machines, machine tools, steel machines and the like.

It is a schematic diagram explaining the structure of the base material of the cage for rolling bearings before heat processing. It is sectional drawing which shows a structure when the base material of the cage for rolling bearings is restrained with the correction type | mold in secondary heat processing.

Explanation of symbols

1 Base material of cage for rolling bearing 2 Straightening type

Claims (3)

  The surface of the base material of the rolling bearing retainer formed by press forming the steel material is subjected to a primary heat treatment in which gas nitriding treatment is performed at a temperature of 400 to 590 ° C., and then constrained to a correction die to be 590 to 700 ° C. A surface treatment method for a rolling bearing retainer, characterized in that a secondary heat treatment is performed to maintain the temperature, followed by a cooling treatment for rapid cooling.   The surface treatment method for a rolling bearing cage according to claim 1, wherein the gas nitriding treatment is performed after the surface of the base material of the rolling bearing cage after press forming is fluorinated.   After the surface of a rolling bearing cage formed by press forming a steel material is subjected to fluorination treatment, primary heat treatment is performed by performing gas nitriding treatment at a temperature of 400 to 590 ° C., and then constrained to a correction die to be 590 to 700 ° C. A rolling bearing retainer obtained by performing a secondary heat treatment to be maintained at a temperature of 1, and then performing a cooling treatment for rapid cooling.

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