JP2000199524A - Rolling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve silence and durability against impact and vibration in transportation and fretting while the equipment is being operated and eliminate the problems of impact resistance and pre-load dropping in a hybrid bearings. SOLUTION: At least one of an external member, internal member and roller body of a rolling device such as a rolling bearing is made of steel, and a nitriding layer of Hv800 or more or desirably Hv900 or more is given to the one made of steel, and the surface is finished to 0.1 μmRa or less in surface roughness. In addition, the diameter of nitriding particles containing Cr, Mo, V, Nb, W, Ti, Al, Si, etc., is made smaller, and the hardness at a depth of 2%Da (means 2% of diameter) is made Hv653 or more. The thickness of the nitriding compound layer on the surface of the rolling body is made 3 μm or more and 2%Da or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing including a ball bearing incorporated in a machine tool, a food machine, a hard disk drive (HDD), a video tape recorder (VTR), a digital audio tape recorder (DAT), and the like. The present invention relates to rolling devices such as a linear guide, a ball guide, a ball screw, etc., in particular, to enhance their functions and improve durability.

[0002]

2. Description of the Related Art Rolling devices such as rolling bearings include:
As its constituent parts, an outer member and an inner member are provided, and a rolling element that rolls while being in contact with both of them is included. The rolling element is included while the outer and inner members and the rolling element are in contact with each other. The moving surface is called a rolling surface. Also, the outer member is
In the case of a rolling bearing, the outer ring, in the case of a linear guide, a slider or a guide rail, in the case of a ball screw, a nut is shown, and in the case of a rolling bearing, the inner ring or shaft, and in the case of a linear guide. Guide rail or slider,
In the case of a ball screw, the screw shaft is shown. Therefore, the rolling surface of the outer member refers to the raceway surface of the outer ring in the case of a rolling bearing, the raceway groove of a slider or guide rail in the case of a linear guide, and the thread groove of a nut in the case of a ball screw. The rolling surface of the inner member refers to the raceway surface of the inner race in the case of a rolling bearing, the raceway groove of a guide rail or a slider in the case of a linear guide, and the thread groove of a screw shaft in the case of a ball screw.

Generally, rolling devices such as rolling bearings include balls or rollers as rolling elements, outer members and inner members as outer rings, inner rings, shafts, sliders, guide rails, and the like.
As materials for nuts, screw shafts, etc., SUJ2 of Japanese Industrial Standards is mainly used for bearing steel, SUS440C or 13Cr-based martensitic stainless steel of Japanese Industrial Standard for stainless steel, and Japan for case-hardened steel. A steel material equivalent to the industrial standard SCR420 is used. Also,
Since such rolling bearings and other rolling devices are used by repeatedly receiving shear stress and slip under high surface pressure on the above-mentioned rolling surface, the rolling fatigue life to withstand the shear stress and the abrasion resistance to slip. To ensure that
The bearing steel is quenched and tempered, and the case hardened steel is quenched and tempered after carburizing or carbonitriding in the austenitic region of Ac1 or more to have a hardness of HRC 58 to 64.

[0004]

Among rolling bearings, in particular, in ball bearings used for information equipment such as HDDs and VTRs or fan motors, there is a demand for reduction of torque, sound, noise, and the like. Because it is very severe, it is finished with extremely high precision. Materials such as SUJ2, which is a high carbon chromium bearing steel, or SUS440C, which is a martensitic stainless steel, or 0.7C-13Cr stainless steel, are often used as bearing materials for these materials. Quenching and tempering are performed to obtain abrasion resistance, and the hardness of the race is HRC 58-64.
It has been. Except in special cases, the rolling elements are often basically made of the same material as the raceway or one of the outer and inner rings.

[0005] Conventionally, SUJ2 has often been used as a material for forming these bearings, but rust often poses a problem, and stainless steel is often used. However, conventional stainless steels such as SUS440C produce coarse eutectic carbides during the solidification process,
Because it is present even after the heat treatment, it is inferior to SUJ2 in quietness, and there are some limits to the application of the bearing that requires relatively quietness.

Accordingly, the present inventors have conducted intensive studies and, as disclosed in Japanese Patent Application Laid-Open No. 9-287053, prevented the formation of coarse eutectic carbides as in conventional stainless steel, and We have developed a stainless steel for bearings that has both quietness and corrosion resistance. However, in recent years, the increased portability due to the miniaturization of equipment has increased the chances of falling during transportation and being exposed to vibration during transportation, and the rolling surface of the ball bearing incorporated in the equipment has fretting damage. The performance of the device may be degraded, and there is an increasing demand for further improvement in durability. In other words, when an impact load is applied to equipment, especially in small ball bearings, the contact ellipse is small, so even a relatively small impact load causes permanent deformation of the raceway surface, which causes sound deterioration and uneven rotation torque. And the like, and the performance of the device incorporating the ball bearing is degraded. This problem is thought to occur due to the low yield stress of soft components such as retained austenite inherent in steel,
In order to maintain the hardness required for ball bearings and reduce residual austenite, SUJ2 is quenched and then subjected to sub-zero treatment or tempered at a relatively high temperature of about 220 to 240 ° C. In addition, measures are taken to prevent acoustic degradation and the like due to impact load. However, no countermeasures have been taken so far in terms of materials with respect to fretting caused by vibration or operation of equipment.

[0007] In addition, the use environment of machine tools and other rolling bearings has been increasing, and the temperature and speed have been increasing.
In addition to the rolling fatigue life, properties such as heat resistance and seizure resistance have become very important. Rolling devices such as linear guides and ball screws are no exception.
Sliding is more likely to occur than ball bearings, and in addition, it is often used at minute swings or at very low speeds.Therefore, the lubrication state on the rolling surface tends to be poor. There is also a problem that the gaps between the moving body, the outer member, and the inner member are increased, and as a result, the preload is released early and, for example, precise positioning of the machine cannot be performed.

The present invention has been developed to solve the above-mentioned problems, and an object of the present invention is to provide a rolling device which is excellent in not only fatigue life but also various characteristics such as fretting durability, abrasion resistance and seizure resistance. It is the purpose.

[0009]

In order to solve the above-mentioned problems, for example, in ball bearings, the use of ceramics such as silicon nitride for the rolling elements has been increasing (hereinafter, rolling using ceramics for the rolling elements). The bearing is called a hybrid bearing). Ceramics are expensive, but if only rolling elements are used, the increase in cost can be minimized.At the same time, by using rolling elements as ceramics, adhesive wear on the contact surface is suppressed, and Such characteristics are greatly improved. However, even in hybrid bearings, the cost ratio of the rolling elements is not only very large, but also the elastic coefficient and linear expansion coefficient are significantly different from steel, so for example, ball bearings for information equipment with high demand for quietness However, when an impact load is applied to the bearing, indentations are formed on the raceway and the sound is likely to deteriorate, and from the viewpoint of fatigue life, the surface pressure increases and the life tends to decrease. Along with this, there is a different problem that the preload changes to cause a torque fluctuation, and in a severe case, the rigidity is significantly impaired.

The present inventors basically utilize the characteristics of steel as it is, and form an appropriate modified layer only on the surface of the components of the rolling device, so that not only fatigue life but also fretting durability, Investigations were made to see if various properties such as wear resistance and seizure resistance could be improved. The surface modification method includes a vapor deposition method such as a PVD method or a CVD method or a plating method. The modified film obtained by these methods is a so-called deposited one and has excellent slidability. It is extremely difficult to form a uniform modified layer on the surface, and as a rolling member subjected to high shear stress, there is a possibility that the interface strength between the base material and the film is insufficient and the film may easily fall off. And there is a problem of lack of reliability.

Therefore, the present inventors examined the applicability of a nitriding treatment, which is a diffusion modifying treatment. The nitriding treatment includes salt bath nitriding, gas nitriding, and ion nitriding, and has been used as a surface treatment method for machine parts for a long time, but is basically performed for the purpose of imparting slidability. Therefore, there are few cases in which the present invention is applied to rolling parts such as rolling bearings which receive high shear stress.

For example, in Japanese Patent Application Laid-Open No. Hei 10-131970, one of the components made of general bearing steel is subjected to a nitriding treatment to improve corrosion resistance and to reduce the average particle diameter of nitride in the surface layer to 1 μm or less. Rolling bearings that improve seizure resistance and are suitable for auxiliary equipment such as water pumps of automobile engines have been proposed, but this publication only describes the surface of the nitrided layer, and the rolling life is not sufficiently considered. is there. For example, if a nitride layer is formed on the surface,
Since the substrate will be tempered at a very high temperature,
The hardness is greatly reduced. Rolling bearings and other rolling devices are subject to high shear stress, and if the base is not sufficiently strong, the nitrided layer on the surface is easily damaged, resulting in a reduction in fatigue life. In addition, since the surface roughness is not specified only by limiting the size of the nitride particles formed on the surface, a ball bearing for information equipment that requires a rough surface and quietness as it is simply nitrided It cannot be used at all.

Thus, in the rolling device according to the present invention, a rolling element is provided between the outer member and the inner member, and the rolling element contacts the outer member and the inner member while rolling. In the moving rolling device, at least one of the outer member and the inner member and the rolling element is made of bearing steel, and has a nitrided layer of Hv800 or more, preferably Hv900 or more on the surface of the finished product, and At least the rolling surface has a surface roughness of 0.1
It is characterized in that it is finish-processed to a value of μmRa or less.

Further, Cr, Mo, V, Nb, W, Ti,
A steel containing at least one or more of Al and Si in a total content of 2% or more and 25% or less is used as a base material and 2% Da (diameter of 2%).
% Means that the hardness at the depth is at least Hv653 or more. When a nitrided layer is formed on the rolling element surface, the nitrided layer is composed of a compound layer and a diffusion layer, and the thickness of the compound layer is desirably 3 μm or more and 2% Da or less.

In the case where the rolling device is a ball bearing, the ball bearing is composed of an outer ring and an inner ring and a plurality of rolling elements, or a ball bearing composed of an outer ring, a shaft and a plurality of rolling elements. At least one of the constituent parts except the rolling element is made of bearing steel having an HRC of 58 or more and having a retained austenite of 4% or less, and the rolling element is made of steel and has a surface layer having a surface hardened layer of Hv900 or more. It is desirable to have.

The critical significance will be described below. [Materials] As bearing steel used as base metal, in addition to high carbon chromium bearing steel, carburized steel, heat-resistant steel, stainless steel,
Alloy tool steel, high-speed tool steel, chromium steel, chromium molybdenum steel, or the like is used, and a nitride layer of Hv800 or more, preferably Hv900 or more is formed on the surface layer. Preferably, the total content of at least one of Cr, Mo, V, Nb, W, Ti, Al and Si is 2% or more, preferably 5% or more.
% And 25% or less, when a nitrided layer is provided on the surface of the steel, fine nitrides containing these elements are precipitated on the nitrided layer, resulting in fretting durability, seizure resistance,
The wear resistance is improved. In addition, the nitriding treatment is usually 400 to
Since it is performed at a relatively high processing temperature of about 600 ° C.,
If the base material does not have sufficient heat resistance, the strength of the base supporting the nitrided layer is insufficient and the surface nitrided layer is easily damaged.
Therefore, the hardness at the depth of 2% Da, which is also the maximum shear stress position, is at least Hv653 or more. Specifically, the heat resistance is improved by adding the alloy element,
Alternatively, a nitride layer (diffusion layer) is provided deeper. Further, heat resistance may be ensured by performing carburizing or carbonitriding before nitriding. Further, martensitic stainless steel or high-speed tool steel is more preferable because it has sufficient heat resistance and can maintain sufficient hardness even after nitriding. Further, when the nitriding temperature is high, the heat resistance of the base material is insufficient and the base may not have sufficient hardness in some cases. Therefore, the nitriding temperature is preferably 500 ° C or lower, more preferably 460 ° C. The following is assumed. [Surface Roughness] The surface roughness after nitriding treatment was 0.5
Since it is as large as about 2.0 μmRa, it cannot be applied to a ball bearing for information equipment or a ball bearing for various fan motors that require quietness as it is. In addition, in order to reduce the reliability of the device because the nitride or oxide particles on the surface fall off during rolling, it is necessary that at least the rolling surface be finished after nitriding. Also, when the roughness is large, the aggressiveness to the counterpart material on the rolling surface tends to increase, and for example, the life tends to be short under boundary lubrication. Therefore, in order to avoid these problems and draw out sufficient characteristics, at least the rolling contact surface is 0.1 μm.
m or less. [Regarding that the nitrided layer is composed of a compound layer and a diffusion layer, and the thickness of the compound layer is not less than 3 μm and not more than 2% Da] Since the nitrided layer generally consists of a compound layer and a diffusion layer, the coating film and the base material And strong adhesion, making it difficult to peel off. However, if a large shear stress is applied at a position deeper than the nitrided layer, as in a rolling bearing, the problem of peeling will also be involved.
As described above, it is necessary to consider the hardness of the base. Further, compound _{layer, (Fe, Cr) 2,} 3or4 N, CrN, C
It is made of a dense nitride such as r ₂ N, Mo ₂ N, VN, etc., and has excellent surface characteristics. In addition, when the thickness of the compound layer increases, not only does the processing cost increase,
The physical properties of steel are impaired. For example, impact resistance of a ball bearing for information equipment is reduced. Therefore, in consideration of reliability, the thickness of the compound layer is preferably 3 μm or more and 2% Da or less. [Regarding Material of Bearing Ring Constituting Ball Bearing] The bearing steel constituting the ball bearing is defined by S described in JIS G 4805.
Not only UJ2, but SUS440C and 0.7C-
It shows general steel used for bearings, such as 13Cr stainless steel or M50 or carburized steel. However, ball bearings are often fixed to the housing or shaft with an adhesive, and if rust-preventive oil is attached, the adhesive strength is reduced, or the rust-preventive oil reacts with this to cause rust. And further outgas is generated, which adheres to, for example, the surface of the hard disk and
Because there are problems such as lowering the reliability of the DD device,
It is often completely degreased, and stainless steel is preferred in terms of equipment reliability. However, a conventional high carbon martensitic stainless steel such as SUS440C contains a large number of coarse eutectic carbides, and thus is inferior to SUJ2 in terms of quietness of the bearing. Therefore, it is desirable to use a material that is excellent in quietness and corrosion resistance and satisfies the following specifications for the race.

C is an element that improves the hardness after quenching and tempering by converting the matrix into martensite to increase the strength, but the smaller the better, the better the corrosion resistance. When added in a large amount, Cr forms coarse eutectic carbide during steelmaking, and as a result, not only is the Cr concentration in the matrix insufficient but sufficient corrosion resistance cannot be obtained, but also the rolling life and quietness are reduced. Therefore, the carbon content is set to 0.5% by weight or less.

N has the effect of strengthening martensite and improving pitting corrosion resistance in the same manner as C.
In order to suppress the formation of hypoeutectic carbides, 0.05% by weight or more, preferably 0.08% by weight or more is added. But,
If an attempt is made to add a large amount of nitrogen, under the atmospheric pressure, bubbles are generated in the coagulation process and a large amount of pores are introduced into the ingot, thereby impairing the soundness of the material. Therefore, the content of N is less than 0.2% by weight. Preferably, the content is 0.18% by weight or less.

Further, the hardness after sufficient quenching and tempering (HR
(C58 or more), and the total content of C + N is required to be 0.45% by weight or more in order to avoid damage due to fatigue and wear. Mn is a necessary element as a deoxidizing agent in steel making and is added in an amount of 0.1% by weight or more. However, when added in a large amount, not only decreases forgeability and machinability but also causes a large amount of retained austenite after quenching. Generated and the silence tends to deteriorate due to the impact load. Therefore, Mn is 1.0% by weight.
Or less, preferably 0.5% by weight or less.

Further, Si needs to be 0.1% by weight or more as a deoxidizing agent at the time of steel making like Mn. Further, it is an element effective for increasing the tempering softening resistance and improving the rolling fatigue life. However, if added in a large amount, the toughness and the workability are reduced, so the upper limit was made 1.0% by weight or less. In addition, Cr
Is the most necessary element to impart corrosion resistance to steel,
If it is less than 0% by weight, good corrosion resistance cannot be obtained. When the Cr content is increased, the corrosion resistance is improved. However, when added more than necessary, δ ferrite is formed and becomes brittle, Ms (martensite transformation start temperature) is reduced, and a large amount of retained austenite is formed. Therefore, the hardness may be reduced, so the content is set to 16.0% by weight or less. However,
Preferably, it is 11.5% by weight or more and 13.5% by weight or less. Further, the relationship with the C content is C% ≦ −0.05Cr%
If +1.41 is not satisfied, coarse eutectic carbides are formed, and both silence and corrosion resistance are reduced.

Retained austenite is soft and has a low yield stress. When bearings are worn out or subjected to a slight impact load, extremely small permanent deformation occurs at a contact portion with a rolling element, causing acoustic deterioration. Therefore, the content is set to 4% or less, preferably 2% or less. [Regarding Rolling Elements of Ball Bearings] Rolling elements used in the ball bearings are protected by grease, lubricating oil and the like, so that corrosion resistance hardly causes a problem. Therefore, in order to improve durability such as fretting resistance. A nitride layer of Hv900 or more is provided on the surface. Thereby, surface wear is suppressed and durability is dramatically improved. In addition, the provision of the nitride layer tends to suppress not only damage to itself but also damage to a mating member that comes into contact with the nitride layer, so that fretting resistance can be significantly improved. In addition, by providing the rolling element with a nitride layer, ball flaws during assembly are extremely reduced, which is also effective in reducing the defective rate.

Generally, the nitriding treatment is carried out at a temperature in the range of 400 ° C. to 600 ° C., preferably 400 ° C. to 480 ° C., but after the nitriding treatment, the core may be softened by tempering and the hardness may be significantly reduced. . Usually, after the nitriding treatment, a compound layer is formed on the surface, and a deeper portion has a diffusion hardened layer by diffusion of nitrogen. Since the nitriding treatment has this diffusion hardened layer, the adhesion between the film and the base material is strong, and the nitriding treatment is difficult to peel. However, when the bearing is operated and receives a large shear force at the maximum shear stress position deeper than the nitrided layer, if the part does not have sufficient strength, it causes plastic deformation and damage of the surface hardened layer. There is fear. Therefore, it is necessary that the material used for the rolling element has a sufficient hardness to withstand the shear stress even after the nitriding treatment. Specifically, using martensitic stainless steel, high-speed tool steel or alloy tool steel,
HRC 58 or more at 2% Da depth from the surface,
Alternatively, the core hardness is HRC 58 or more after the nitriding treatment.

[0023]

Embodiments of the present invention will be described below. First, a two-cylinder wear test shown in FIG.
A wear test of the test materials shown in Table 1 is performed.

[0024]

[Table 1]

In this two-cylinder abrasion test, a test material is mounted on a pair of upper and lower cylinders 10 which are opposed to each other and rotated at a low speed in opposite directions while contacting each other while applying a load P from above. The wear amount of the test piece was determined. In preparing the test pieces, the test pieces were first processed into a predetermined shape, then quenched and hardened, and subjected to a grinding finish. Further, a nitriding treatment was performed under any of the following conditions. Condition 1: Fluorination treatment at 300 to 380 ° C. × 1 hour (90% N ₂ −1)
0% NF ₃ mixed gas), then 400-480 ° C × 24-4
8 hours of nitriding (50% N ₂ -50% NH ₃ mixed gas) Condition 2: 480-560 ° C. × 3-8 hours of nitriding (50% N ₂ −
50% NH ₃ mixed gas) Condition 3: nitrocarburizing treatment (salt bath nitriding mainly composed of cyanate (KCNO and NaCNO)) for 3 to 8 hours at 480 to 560 ° C. This is an example of a case where a nitriding treatment is performed.Since the surface oxide layer that inhibits nitriding is removed by the cleaning action of the fluorine-based gas, a uniform nitride layer can be formed at a lower temperature. This is a particularly effective technique. Condition 2 is an example of conventional gas nitriding, and Condition 3 is an example of soft nitriding (tufftrid). The test was carried out on the as-nitrided (black scale) and the finish-finished one. The quality of the finished product and the test results are shown in Table 2 below. Table 2 shows the average value of the wear amount of a pair of cylindrical test pieces vertically opposed to each other. The surface hardness used was an average value obtained by measuring the number of samples n = 10 times with a load of 100 g. Further, the thickness of the compound layer is determined by observing the sample number n = 10 times with an optical microscope after etching with a picral or ferric chloride / hydrochloric acid solution, and clearly observing the compound layer from the boundary between the surface nitrided layer and the base. Find the thickness,
The average value is described.

The conditions for the wear test are as follows. (Two-cylinder abrasion test) Load: 50 kgf Revolution: 10 rpm Slip rate: 10% Lubrication: Mineral oil Test time: 100 hours Test temperature: normal temperature

[0027]

[Table 2]

As is clear from Table 2, Examples A-1 to A-8 satisfying the above-mentioned conditions of the present invention are comparative examples A
It has much better wear resistance than -9 to A-13. On the other hand, Comparative Example A-9 is an example in which nitriding treatment was performed on SUJ2, and although the abrasion resistance was slightly improved as compared with Comparative Example A-13 without nitriding treatment,
Neither the surface hardness nor the surface roughness satisfies the above conditions, and it can be seen that the effect is small as compared with the examples. Comparative Examples A-10 and A-11 are examples in which SUJ2 is subjected to a finishing treatment after nitriding treatment, but only a small amount of the compound layer is formed. As a result, the above conditions were not satisfied in terms of the surface hardness and the thickness of the compound layer, and the result was slightly inferior to that of Comparative Example A-9. However, since the diffusion layer is present, the effect is somewhat confirmed on the abrasion resistance as compared with Comparative Example A-13. Also, there is little difference in the nitriding process, that is, the difference due to the difference in the nitriding condition.

Next, a life test was performed using a ball rod life tester shown in FIG. In general, the life of a bearing in the market often results in damage to the material from the surface due to poor lubrication and the like, leading to destruction. Therefore, S10 (40 ° C.-10 cst), which is a low-viscosity oil, is used as the lubricating oil, and a rolling element made of SUJ2 balls with a roughness of 0.27 μmRa by barrel processing is used. The test was performed such that the oil film parameter Λ to be performed was 1 or less, that is, a boundary lubrication state. Table 3 below shows the quality of the finished product and the evaluation results of the prepared test pieces. In addition,
The hardness at a 2% Da depth in Table 3 was obtained by measuring the Vickers hardness under a load of 500 g and measuring the number of samples n = 10 times, and described the average value.

[0030] ^{_{Λ = hm / (σ 1 2}} + σ 2 2) 1/2 ......... (1) hm: minimum oil film thickness sigma _1: Ball surface roughness sigma _2: Rod surface roughness (ball rod life test) Test piece: φ26 mm × 80 mm, 27/32 inch ball Rotation speed: 7,800 rpm Surface pressure: 45 kgf / mm ² Lubricating oil: S10

[0031]

[Table 3]

From Table 3, it can be seen that Example B satisfying the above conditions was used.
It can be seen that -1 to B-5 all have a longer life than Comparative Examples B-6 to B-11. On the other hand, Comparative Examples B-6 and B-8 are examples in which a nitride layer was formed on the surface of SUJ2, but the surface hardness did not satisfy the above-described conditions, and Comparative Example B-8 Since the surface roughness is still black and does not satisfy the above conditions, the surface damage is remarkable as compared with each of the examples. In addition, the hardness at a depth of 2% Da is not sufficient, so that the life is short. In Comparative Example B-7, the surface damage was slight, but the hardness at a depth of 2% Da was not sufficient, and as a result, the life was short. Comparative Example B-9
No finish processing was performed after the nitriding treatment, the surface condition was poor, and peeling occurred starting from the surface, resulting in a short life. Further, Comparative Example B-10 is an example of SUJ2, but is not subjected to nitriding treatment, and has a remarkable surface damage and a short life.
Comparative Example B-11 is an example in which SUS302 was subjected to a nitriding treatment. Although the surface damage was slight, 2% D
a) The hardness was short, and the life was short. As described above, Examples in which the surface hardness and the hardness at a depth of 2% Da satisfy the above conditions are excellent in terms of rolling fatigue.

Table 4 shows the results of evaluation of seizure resistance. The evaluation was carried out by a four-ball type baking limit test shown in FIG. 3. Using a SUJ2 ball on the fixed side, the load was changed under oil bath lubrication (jet oil II) at a constant rotation speed of 6000 rpm, and the baking limit load was determined. That is, the PV value was determined. Table 4
Examples C-1 to C-5 satisfying all the above conditions
Is superior in seizure resistance as compared with each comparative example. On the other hand, Comparative Example C-8 having an insufficient surface hardness and a large surface roughness while maintaining the black scale, Comparative Example C-9 having a large surface roughness while maintaining the black scale,
Comparative Example C not subjected to nitriding treatment and having insufficient surface hardness
-10 is inferior to each example in abrasion resistance.

[0034]

[Table 4]

Next, the results of evaluation using a ball bearing for information equipment as an example are shown below. The evaluation was performed using a ball bearing 695 (JIS
No.), and in consideration of cost, a nitride layer was provided only on the rolling element surface. For the race, use SUJ2,
After quenching, it was tempered at 220 to 240 ° C. for 2 hours to reduce retained austenite to 4% or less. A plastic cage was used for the cage, and a mineral oil grease was used for lubrication of the bearing.

First, after forming a coarse sphere using the materials described in Table 1 above, quenching and hardening, grinding to a target size, nitriding treatment, and lapping are further performed.
mm rolling element, grade 3 described in JIS B 1501
(G3) Finish processing was performed with high precision as described above. In addition, if the finish processing is performed with high precision before the nitriding treatment, the roughness and shape collapse due to the nitriding treatment are small, and it is possible to manufacture with a little reduction in the lap finishing margin. Even if the accuracy is about G100, for example, sphericity 2.5μ
In the case of finishing with high precision of m and surface roughness of 0.125 Ra, the margin of lap finishing is several μm to ten and several μm, whichever is sufficient, so whichever may be performed first. That is, the former is preferable when the thickness of the nitride layer is not sufficient, and the latter is preferable when the thickness of the nitride layer is sufficient.

Table 5 shows the quality of the finished product of the rolling element produced by this method. Among them, the surface hardness is 5 μm below the surface.
The average value obtained by measuring the hardness of the position at a load of 50 g and the number of samples n = 10 was used. Further, the thickness of the compound layer is determined by observing the sample number n = 10 times with an optical microscope after etching with a picral or ferric chloride / hydrochloric acid solution, and clearly observing the compound layer from the boundary between the surface nitrided layer and the base. The thickness was determined, and the average value was described. The hardness at a depth of 2% Da was determined by measuring the Vickers hardness under a load of 50 g with the number of samples n =
The measurement was performed ten times, and the average value was described. The surface roughness was measured using a Talysurf 6-type ball unit manufactured by Taylor Hobson Co., and the number of samples was measured n = 10 times, and the average value was described.

The function evaluation of the bearing includes the initial sound evaluation,
Sound durability evaluation, fretting durability evaluation, and impact resistance evaluation were performed. The evaluation results are shown in Table 5 above. The initial sound evaluation was performed by measuring the sound pressure when the ball bearing was operated at a preload of 1.2 kgf and a rotation speed of 1800 rpm. The results are shown as ratios when the measured average value of Comparative Example D-12 as a bearing is set to 1.

The acoustic durability was evaluated with a preload of 1.2 kg.
f, after rotating at 7,200 rpm at a temperature of 70 ° C. for 500 hours, again applying a preload of 1.2 kgf and a rotating speed of 18
The evaluation was performed by measuring the sound pressure at 00 rpm, and similarly, the average value obtained by measuring the number of samples n = 10 was obtained, and the average value of Comparative Example D-12, which is a SUJ2 bearing, was shown as a ratio when the average value was set to 1. Was.

The evaluation of fretting durability was carried out by measuring the number of samples n = 10 times under the following conditions, and again applying a preload of 1.2.
The sound pressure was measured at kgf and a rotation speed of 1800 rpm, and an average value obtained by measuring the number of samples n = 10 was determined. The average value of Comparative Example D-12, which is a bearing made of SUJ2, was shown as a ratio when the average value was set to 1. The impact resistance was evaluated for ball bearings at 1.2k.
gf, 5 kgf, and thereafter, an axial load is applied in the order of 0.5 kgf, and the sound pressure is 30 mG compared to that before the test.
The rise was defined as the impact resistance load, and the impact resistance load of Comparative Example D-12, which is a SUJ2 bearing, was set to 0, and the load reduced therefrom was described. (Evaluation of fretting durability) Preload: 1.2 kgf Oscillation condition: 2 °, 27 Hz Oscillation frequency: 300,000 times

[0041]

[Table 5]

As is clear from Table 5, all of Examples D-1 to D-8 satisfying the above conditions have Hv90 on the surface.
It has a nitride layer of 0 or more, and is remarkably excellent in various characteristics. In contrast, Comparative Examples D-9 and D-10
Is because the nitrided layer formed on the rolling element surface is very thick and the thickness is larger than 2% Da, so that the physical properties inherent in steel are impaired, and the impact resistance is lower than that of each of the examples. Inferior results were obtained. Comparative Example D-11 is an example in which SUJ2 was subjected to nitriding treatment. However, the surface hardness was lower than the above conditions, and there was almost no compound layer. Inferior. Comparative Example D-12
Is an example of a conventional SUJ2 steel ball, but is insufficient in acoustic durability and fretting durability as described above. Further, Comparative Examples D-13 and D-14 are examples in which a ball that has been subjected to nitriding treatment is incorporated. However, since the surface roughness is low and the diameter difference is large, the initial sound is very large. Was omitted. Comparative Example D-15
Shows an example of a hybrid bearing using ceramic spheres (Si ₃ N ₄ ) for reference, but it has very good acoustic durability and fretting durability, but very poor impact resistance. I have.

Next, the above-mentioned Example D-5 and Comparative Example D-1
Table 2 shows the results obtained by calculating the influence of the difference in the linear expansion coefficient of D-15 on the preload by using the linear expansion coefficient of the base material. The hub material is assumed to be ferritic stainless steel (10.4 × 10 ⁻⁶ / ° C.), the preload at 20 ° C. is 0.8 kgf, and the residual radial gap is 16.5 μm.
m was calculated in the range of 0 ° C to 70 ° C.

[0044]

[Table 6]

As is clear from Table 6, in the embodiment in which steel was used as the base material and only the surface was modified, the effect of temperature on the preload was small, and the SUJ2 was also reduced in rigidity due to preload loss. As in Comparative Example D-12 of the bearing made, it is very excellent. On the other hand, ceramic sphere (Si ₃ N ₄ )
In Comparative Example D-15, which is a hybrid bearing using the same, the preload loss was completely generated at 70 ° C.

Next, the results of evaluating the durability of the ball screw which is a direct acting component are shown below. Evaluation is screw shaft 2
An abrasion test was performed using a ball screw device having a lead of 0 mm and a lead of 4 mm. Also in this case, in consideration of the cost, the evaluation was performed by providing a nitride layer only on the rolling elements. In addition, rolling elements C-1 to C10 described in Table 4 were used as the rolling elements,
The screw shaft and the nut used were JIS steel type SCM420H that had been quenched and tempered. The test conditions are as follows. (Ball screw durability test) Initial preload: 490 N (no external load applied) For rotation speed: 1 rpm (ultra low speed) Lubricant: Mineral oil-based grease (base oil viscosity at 40 ° C: 3
7cst) The evaluation was performed under the conditions of the test in the first half of the test.
km durability test, and the preload dynamic torque remaining rate after the test before and after the test (percentage of torque reduced by fluctuation of preload due to wear when the initial preload torque is 100%) This was performed by comparing the degree of progress. Table 7 shows the test results.

[0047]

[Table 7]

As is clear from Table 7, Examples E-1 to E-5 all show very good abrasion resistance because cohesive wear with the mating material is less likely to occur. In contrast,
In Comparative Examples E-8 and E-9, the surface roughness was very large, and preload loss occurred relatively early due to abrasive wear. Comparative Example E-10 is an example in which the SUJ2 steel ball was incorporated. However, since there was no nitrided layer, wear progressed quickly and the preload dynamic torque residual ratio was the smallest.

Next, Table 8 shows the evaluation results of the quality when the heat treatment quality of the bearing race is changed, and the evaluation results of the fretting durability and impact resistance. The rolling elements include D-
5 was used. The race was made of SUJ2. The hardness of the race and the amount of retained austenite (γR) were determined by maintaining the heat treatment temperature at 830 to 870 ° C. for 30 minutes and then quenching.
Various adjustments were made by performing tempering at 80 to 240 ° C. Examples F-1 to F-3 in the table are cases where the sub-zero treatment was performed, and F-6 to F- which are comparative examples in the table.
8 is an example when the sub-zero process is not performed. Further, F-1 in the table is the same as D-5 described in Table 5 above. The impact resistance test was carried out under the same conditions as above,
Each sound pressure was measured at a load where the sound pressure of Example F-1 was increased by 10 mG as compared with before the test, and the sound pressure of Example F-1 was measured.
(F-1 is assumed to be 1.0). Also,
The fretting durability test was carried out under the same conditions and the same evaluation method as those described above, and the results were shown as ratios when Example F-1 was 1.0.

[0050]

[Table 8]

As is evident from Table 8, the higher the amount of retained austenite, the lower the impact resistance.
In particular, when the amount of retained austenite exceeds 4%, this is remarkable, and it can be confirmed that the impact resistance of the examples is excellent. However, when the amount of retained austenite is reduced, the hardness tends to be low, and the fretting durability tends to be slightly inferior. Therefore, in the table, SU
Addition of 1% of Mo to J2 increases the tempering resistance, and the orbital ring is made of material "X" in which the amount of retained austenite is 4% or less, which are shown as Examples F-4 and F-5. Was. The heat treatment was performed under the same conditions as in Examples F-1 to F-3. As is clear from the table, Examples F-4 and F-
5 has high hardness and a small amount of retained austenite, and thus shares good impact resistance and fretting durability.

From the above results, in order to make these various properties compatible, the hardness is high (fretting durability),
It is clear that a smaller amount of retained austenite (impact resistance) is better. Preferably, the hardness is Hv75.
0 or more is ensured, and the amount of retained austenite is 4% or less, preferably completely 0. Note that, here, an example in which Mo is alloyed by 1% is illustrated, but tempering softening resistance may be increased by, for example, Si or Cr.

Next, an embodiment of the ball bearing of the present invention will be described. The evaluation of quietness and durability of the bearings of the example and the comparative example created as the embodiment are all ball bearings 695
(JIS call number).

[0054]

[Table 9]

Table 9 shows the chemical components of the materials used for the bearing rings. In the table, No. No. 1 satisfies all the conditions of the ball bearing. 2-No. 4 is a conventional product. No. No. 2 is a conventional 13Cr martensitic stainless steel. No. 3 is SUS440C; 4 is SUJ2. After turning all the materials, the heat treatment described below was performed, and the finishing was finished by grinding to produce a bearing ring.
No. No. 1 is 980 ° C. to 1020 ° C .; 2 and No. 2 For No. 3, after holding at 1020 ° C. to 1060 ° C. for 30 minutes, quenching, sub-zero treatment at −75 ° C. to −95 ° C. for 1 hour, and then 1.5 ° C. at 150 ° C. to 170 ° C.
Tempering was performed for an hour. In addition, No. 830 for 4
C. to 870 C. for 30 minutes, then quenched,
Sub-zero treatment for 1 hour at
Tempering was performed at 0 ° C. to 240 ° C. for 1 hour.

The rolling elements subjected to the nitriding treatment include No. 1 and No. 1 Using the materials of 4,
After forming the coarse spheres, quenching / tempering and rough grinding were performed. Further, gas nitriding treatment was further performed at 410 ° C. to 530 ° C. for 24 hours to 48 hours, and finally finished to an accuracy of grade 3 or more described in JIS B1501. Next, the bearing ring and the rolling element were assembled and subjected to various evaluations as a bearing. Note that a plastic cage was used for the cage, and a mineral oil-based grease was used for lubrication of the bearing. Table 10 shows the finished product quality of the bearing ring and the rolling elements. For races,
A-1 to A-3 are examples in which retained austenite is 4% or less, preferably 2% or less, and other B-1 to B-6.
Is a comparative example. As for the rolling elements, A-1 to 1-3 are examples having a nitrided layer having a surface hardness of Hv900 or more, and B-1 to B-6 are comparative examples.

[0057]

[Table 10]

Next, Table 11 shows the acoustic defect rate (HB Anderon value of 4.0 or more) due to ball flaws when acoustically inspecting each of the 500 ball bearings of the embodiment and the comparative example. Show. In the ball bearing according to the example of the present invention, it can be confirmed that the defect rate is higher than that of the comparative example.

[0059]

[Table 11]

Next, regarding the function evaluation of the bearing, a quietness evaluation, a fretting durability evaluation, a corrosion resistance evaluation of the outer ring alone, and the like were carried out. Table 12 shows the evaluation results. For the evaluation of quietness, the ball bearings of the above-described embodiment and the comparative example were sampled n times.
= 20 with an Anderon meter. B value, H. B
The values of the materials S shown in Table 9 above were determined.
The ratio of the respective average values when the average value of the UJ2 ball bearing is 1 is shown. In addition, the fretting durability evaluation was performed on the number of samples n = 4 under the conditions described below, and the anderon value after the test was measured to calculate the average value.
J-2 (B-5, B-6) is shown as a ratio when 1 is set.
The corrosion resistance was evaluated at 35 ° C. and 5 ° C. in accordance with JIS Z2371 after completely degreased the outer ring of the bearing with acetone.
% NaCl aqueous solution for 2 hours.
No rusting A, partial rusting B, marked rusting C
It was rated on a scale.

(Fretting test) Pressurization: 1.5 kgf Outer ring swing condition: 8 deg, 30 Hz (inner ring fixed) Number of swings: 100,000 times Mineral oil-based grease enclosed

[0062]

[Table 12]

The inner ring, the outer ring, and the rolling elements in Table 12 are examples in which all the materials satisfying the above-mentioned conditions are used.
Although it has quietness equal to or higher than SUJ2 shown in Fig. 5,
It is inferior in fretting resistance compared to the examples of the present invention shown in A-1 to A-3. B-2 is SUJ
This is an example using a rolling element obtained by nitriding No. 2; however, the hardness after nitriding is lower than that of stainless steel, and the fretting resistance is inferior to the examples of the present invention. Further, B-3 is a conventionally used 13Cr stainless steel. However, since coarse carbide of about 3 to 5 μm exists, the bearing made of SUJ2 shown in B-5 and the embodiment of the present invention are not used. It is inferior in quietness, and sufficient fretting resistance cannot be obtained. B-4 is an example of SUS440C, but has a larger carbide than B-3 and has a maximum of 30 μm.
It also has the lowest degree of quietness because it also contains a certain amount of carbide. In the example of SUJ2 shown in B-5, although quietness is good, sufficient corrosion resistance and fretting resistance cannot be obtained. In the embodiment of the present invention, the quietness is equivalent to B-5 in which the race and the rolling elements are all made of SUJ2, and the fretting resistance is remarkably good. Also, A made of a material satisfying all the above conditions is used.
Comparing A-1 consisting of -1 and SUJ2, corrosion resistance,
The result of A-1 is better in both the fretting resistance and the above-mentioned No. SUJ described in 4
No. 2 rather than No. 2 It is preferable to use those described in 1.

A comparison was made between the case where ceramics were used for the rolling elements and the example of the present invention. Impact resistance is 5kgf from 5kgf to 35kgf on the bearing.
After applying an axial load for each time, the anderon value was measured and evaluated by the ratio when the initial anderon value of B-5 was set to 1. In the comparative example, all the races and rolling elements are S
The B-5 made of UJ2 and the bearing ring were made of SUJ2, and the rolling element used was B-7 using Si3N4. The test results are shown in FIG. In the embodiment of the present invention, B-
It has almost the same impact resistance as that of No. 5, and it is understood that the impact resistance is good. However, in the case of B-7 using ceramic balls for the rolling elements, the impact load was low.

[0065]

As described above, according to the rolling device of the present invention, a high-hardness nitrided layer is provided on the surface and the roughness of the rolling surface is reduced at the same time. The durability of fretting during operation can be improved, and at the same time, the decrease in impact resistance, which is regarded as a problem in hybrid bearings, can be suppressed, and problems such as preload loss can be eliminated. In addition, its use is not limited to information equipment and fan motors, but also has a great effect that it can be suitably used for ball screws, linear guides and other linear motion parts that require wear resistance and seizure resistance, and machine tools. Play. In addition, the ball bearing has a great effect, such as a reduction in the defective rate due to a ball flaw which is a problem in production.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a two-cylinder wear test.

FIG. 2 is an explanatory diagram of a ball rod life test.

FIG. 3 is an explanatory diagram of a 4-ball type baking limit test.

FIG. 4 is an explanatory diagram showing impact resistance of a ball bearing.

[Explanation of symbols]

 10 is a cylindrical test piece

Claims (1)

[Claims] 1. A rolling device in which a rolling element is provided between an outer member and an inner member, and the rolling element rolls while contacting the outer member and the inner member. And at least one of the inner member and the rolling element is made of bearing steel,
And having a nitrided layer of Hv800 or more on the surface of the finished product,
And at least the rolling contact surface has a surface roughness of 0.1 μmR.
(a) A rolling device characterized in that the rolling device is subjected to finish processing below.