JP2001323932A - Rolling support device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling support device that excels in durability against vibration and an impact load or against a high-speed continuous operation and high-temperature standing. SOLUTION: A rolling bearing comprises an outer ring 2, an inner ring 1 and a plurality of rolling elements 3 disposed for rolling motion between the outer ring 2 and the inner ring 1. The rolling elements 3 consist of steel of a Cr content of 3% or more by weight, and have a nitrided layer of a hardness of Hv 900 or more over the surface. The thickness of the nitrided layer is set at 1.5% to 6% of a rolling element diameter Da.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling support device such as a rolling bearing, a linear guide, and a ball screw, and more particularly to a hard disk drive (hereinafter referred to as HDD) and a video tape recorder (hereinafter referred to as VTR). ,
It is incorporated in information equipment such as a digital audio tape recorder (DAT) or in equipment requiring quietness such as a fan motor, a cleaner motor, and a turbocharger of a vehicle.
The present invention relates to a rolling support device suitable for supporting a swinging motion part such as a swing arm which is a part of components such as the above.

[0002]

2. Description of the Related Art Generally, in a rolling support device such as a rolling bearing, a linear guide, and a ball screw, a rolling motion is performed between an outer member, an inner member, and a rolling element constituting the rolling support device. The outer member, the inner member, and the rolling element are repeatedly subjected to contact stress. Therefore, the materials that make up these members are hard,
Properties such as a long rolling fatigue life and good abrasion resistance to sliding are required.

[0003] Therefore, in general, the materials constituting these members include SUJ of Japanese Industrial Standard as bearing steel.
2. Stainless steel, SUS440 of Japanese Industrial Standard
As C or 13Cr martensitic stainless steels and case hardening steels, those obtained by quenching, carburizing or carbonitriding a steel equivalent to SCR420 of Japanese Industrial Standard are often used. These materials are hardened and hardened in order to obtain required physical properties such as rolling fatigue life.
Tempered steel having a hardness of HRC 58 to 64 is used.

[0004] Of the above-mentioned rolling support devices, particularly with respect to ball bearings used for information equipment such as HDDs and VTRs or fan motors, etc., the demands for reduction of torque, sound and noise are very severe. , Finished with extremely high precision. For example, SUJ2, a high carbon chromium bearing steel, is used for a rolling bearing (hereinafter, referred to as a spindle bearing) that supports a rotating part such as a spindle used in an HDD and requires extremely high quietness. Often.

Further, rolling bearings (hereinafter, referred to as swing arm bearings) that support a swinging motion portion such as a swing arm are often required to have a completely dry specification. Stainless steel, SUS
440C or 0.7C-13Cr stainless steel or a similar stainless steel is often used.

[0006] These materials are subjected to quenching and tempering in order to obtain required physical properties such as hardness and abrasion resistance, and the hardness of the bearing ring is HRC 58 to 64. . 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.

[0007]

However, in recent years,
Various problems have been highlighted in the above-described rolling support device due to the increase in portability due to miniaturization of the device. In other words, with the miniaturization of equipment, the chances of falling during transportation and vibration during transportation have increased, and the rolling support devices incorporated in the equipment have been slightly damaged, and the performance of the equipment has been reduced. Recent research has revealed that it can be a cause of degradation.

That is, when an impact load is applied to a device, especially in a small ball bearing or the like, the contact ellipse is small, and the track surface is permanently deformed even with a relatively small impact load, so that the sound deterioration and the rotational torque are reduced. Unevenness and the like occur, and the performance of equipment incorporating a ball bearing or the like deteriorates. This problem is considered to occur due to low yield stress of a soft phase such as retained austenite existing in steel, as described in JP-A-7-103241.
In the case of SUJ2, in order to maintain the hardness required for the ball bearing and reduce the retained austenite, if it is SUJ2, after quenching, it is subjected to sub-zero treatment or tempered at a relatively high temperature of about 220 to 240 ° C. For example, measures are taken to reduce or completely eliminate retained austenite as much as possible to prevent acoustic degradation or the like due to an impact load.

However, in recent years, the possibility of exposure to vibration has increased due to the increase in the portability of the device, and as a result, a minute contact surface between the rolling element of the rolling support device and the inner member or the outer member has been generated. The problem of fretting caused by vibrations and oscillations and the deterioration of sound has become apparent. The invention described in the above publication focuses on acoustic degradation due to an impact load, and does not consider fretting generated by vibration or operation of equipment at all. Also, as a practical matter, relatively small rolling support devices used for information devices such as HDDs and VTRs and other devices requiring quietness are only provided with measures for lubrication, but in terms of materials. No such measures were taken.

With respect to the problem of fretting, the possibility of using ceramic balls such as silicon nitride has recently been studied. Ceramic balls are very hard to be damaged because they have very high hardness in addition to good slidability. Therefore, by using the rolling elements as ceramic balls, adhesive wear is suppressed, and the fretting durability is significantly improved as compared with steel balls. Further, when ceramic balls are used for the rolling elements, the acoustic durability after high-speed continuous operation is very excellent.

[0011] However, the cost of ceramic balls is very high compared to steel balls. In addition, since the elastic modulus is generally significantly higher than that of steel, a large contact surface pressure is applied as compared with that of steel balls. Therefore, there is a problem that sound deterioration is more likely to occur as compared with steel balls.

In addition, since the coefficient of linear expansion is significantly smaller than that of steel balls, there is also a problem that the prestress is released due to a rise in temperature when the device is operated, and the rigidity is reduced.
Furthermore, since ceramics are generally insulators, foreign matter is attracted by the action of static electricity and the defect rate due to dust noise increases, and the specific gravity is extremely small. However, it is not always possible to satisfy the performance of these information devices and other devices that require quietness.

[0013] Further, in the rolling support device, a problem associated with the recent increase in performance (for example, in the case of a spindle bearing, an increase in rotational speed) has newly emerged. Hereinafter, this problem will be described by taking a case where the rolling support device is a rolling bearing as an example. For example, H
In the case of DD, in addition to the downsizing of the device, the rotation speed of the spindle has been further increased in recent years, and higher impact resistance and higher-speed durability are required for the rolling bearings used for this. It is becoming.

Further, in a swing arm equipped with a magnetic head, a voice coil motor having higher power has been used in order to secure high-speed seek characteristics. Therefore, the ambient temperature of a rolling bearing has been increasing. It tends to be higher. As a result, when the rolling bearing is kept at a high temperature for a long time in a stopped state (hereinafter referred to as a high-temperature stationary state), a Brinell mark is formed on the contact surface between the rolling element and the bearing ring, and acoustic deterioration occurs. This problem has become evident, and furthermore, durability against high-temperature standing has been required.

The formation of the Brinell mark by this high-temperature standing is as follows:
It is considered that residual austenite is generated due to accelerated decomposition at the contact site. Therefore, as in the case of preventing the deterioration of the impact load, SUJ2
Then, sub-zero treatment after quenching, or 2
Measures have been taken to reduce or completely eliminate retained austenite as much as possible, such as by tempering at a relatively high temperature of about 20 to 240 ° C., and to prevent acoustic degradation due to standing at higher temperatures than before. I have.

However, the effect of such measures is a level that can prevent acoustic deterioration when the bearing is held at a temperature of about 70 to 80 ° C. for a long time, and is higher than that of the current rolling bearing. High temperature standing at a temperature may not always be sufficiently effective. As HDDs become more sophisticated in the future, it is thought that rolling bearings that are durable even at high temperatures of over 100 ° C. will be required, and further measures will be required. ing.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional rolling support device. The object of the present invention is, firstly, to provide an apparatus incorporating the rolling support device. The purpose is to effectively prevent performance deterioration of the rolling support device due to vibration and impact load accompanying increased portability, and secondly, the rolling support that decreases with higher performance of the device. An object of the present invention is to improve various durability (impact resistance, high-speed durability, durability against high-temperature standing) of the device.

[0018]

Means for Solving the Problems The present inventors first investigated in detail the factors of acoustic degradation due to minute vibrations and swings of equipment, and found that the main cause was damage to rolling elements. Was. That is, in the conventional rolling element made of a general bearing steel such as SUJ2, as shown in FIG. 1, remarkable fretting wear marks (similar to horizontal stripes in FIG. 1) due to vibration and swing occur at a contact portion with the inner ring and the outer ring. In addition, the deterioration of the accuracy of the rolling elements causes acoustic deterioration.

Therefore, a rolling support device such as a ball bearing used for HDDs and VTRs, etc., which is required to be extremely quiet, basically utilizes the characteristics of steel as it is and appropriately modifies the surface of the rolling support device. The study was repeated to see if the performance of the rolling support device could be dramatically improved by forming the porous layer. The surface modification method includes vapor deposition and plating, and the modified coating obtained by these methods has excellent slidability, but it is very difficult to form a uniform modified layer on the surface of a complex-shaped part. Have difficulty. Further, as a rolling member subjected to high shear stress, there is a problem that the interface strength between the base material and the coating film is insufficient, and the coating film may easily peel off or fall off, and thus lack reliability. Is not preferred.

Therefore, the present inventors examined the applicability of nitriding, which is one of the surface modification methods for steel parts. The nitriding treatment includes salt bath nitriding, gas nitriding, ion nitriding, and the like, and has long been used as a surface treatment method for mechanical parts requiring slidability. In general, a product processed into a desired shape is maintained at a temperature of about 500 to 600 ° C., and nitrogen is diffused and penetrated from the surface to cure the product.

The nitrided layer formed on the surface in this way is different from the modified layer deposited and is diffused and infiltrated, and is considered to have higher interface strength. However, in the case of rolling parts that are subject to high shear stress, they receive a large shear stress deeper than the nitrided layer,
Its application is not easy. For these reasons, hitherto, basically, it has only been implemented for the purpose of imparting slidability of various mechanical parts.

Specific examples of the application of nitriding to rolling bearings and other rolling parts are disclosed in JP-A-6-341442 and JP-A-10-131970. In JP-A-6-341442, at least one of the mechanical parts is subjected to salt bath nitriding, and the surface thereof has a hardness of Hv 654 or more.
By forming a compound layer having a thickness of 5 to 20 μm at Hv 830, a rolling bearing excellent in corrosion resistance and suitable for use in a roller clutch for a washing machine has been proposed.

In Japanese Patent Application Laid-Open No. Hei 10-131970, as in Japanese Patent Application Laid-Open No. Hei 6-341442, at least one of the components made of general bearing steel is subjected to a nitriding treatment to improve the corrosion resistance and further improve the corrosion resistance. A rolling bearing which improves seizure resistance by limiting the average particle diameter of nitride in the surface layer to 1 μm or less and which can be suitably used as an auxiliary device such as a water pump of an automobile engine has been proposed.

However, these are focused on corrosion resistance and seizure resistance, and little consideration is given to the core hardness against shear stress, which is indispensable for rolling bearings. Neither does it mention the problems inherent in ball bearings and their solutions. Therefore, the content is extremely insufficient to be applied as a ball bearing for information equipment.

In particular, in Japanese Patent Application Laid-Open No. 10-131970, there is no mention of the depth of the nitrided layer, and it is presumed that the so-called grinding finish is not performed on the surface while the nitriding treatment is performed. Therefore, it cannot be used as a ball bearing for information equipment requiring quietness. Further, Japanese Patent Application Laid-Open No. 5-179401 discloses that a hardened nitride layer of about Hv1000 is formed by performing a nitriding treatment on a predetermined steel containing 3% by weight or more of Cr, thereby making it hard to be damaged by foreign matter. There have been proposals to improve the rolling fatigue life when foreign matter is mixed. However, this invention, like the above-mentioned invention, has no problems specific to ball bearings for information equipment, namely, problems such as quietness, fretting, acoustic deterioration due to impact load, and loss of preload, and methods for solving the problems. Not touched.

Therefore, the present inventors applied the nitriding treatment technology to the rolling element of a rolling support device such as a rolling bearing, and applied the same acoustic processing as a rolling bearing using ceramic balls (hereinafter referred to as a hybrid bearing). Durability and fretting resistance have been improved, and further studies have been made to determine if the problems of hybrid bearings such as impact resistance, preload loss, and problems due to electrostatic action can be solved.

As a result, a predetermined bearing steel is used as the base material of the rolling element, a nitride layer having a hardness of preferably Hv110 or more is provided on the surface layer, and the hardness of the nitride base layer and the thickness of the nitride layer are optimized. It has been found that by adopting such a structure, it is possible to provide a rolling support device such as a ball bearing for information equipment, which is extremely excellent in quietness, fretting resistance, impact resistance and the like. further,
The present inventors have not only the rolling element, but also the outer member and the inner member which are the rolling members constituting the rolling support device,
It has been found that by adopting a configuration similar to that of the above-mentioned rolling element, the durability (high-speed durability, durability against high-temperature standing, and the like) of the rolling support device can be dramatically increased. As a result, it is possible to solve the problems associated with improving the performance of the device in which the rolling support device is incorporated.

Thus, the rolling support device according to the present invention includes an outer member, an inner member, and a plurality of rolling elements rotatably disposed between the outer member and the inner member. , At least the rolling element of the outer member, the inner member, and the rolling element is made of steel having a Cr content of 3% by weight or more, and the surface thereof is A nitride layer having a hardness of at least Hv900 is provided on the layer, and the thickness of the nitride layer is set to 1.5% of the rolling element diameter Da.
Not less than 6% and not less than 1.5% of the rolling element diameter Da and not more than 100
μm or less.

The rolling support device in the present invention includes, for example, a rolling bearing, a ball screw, a linear guide (linear guide bearing), and the like. The outer member and the inner member in the present invention mean an outer ring and an inner ring when the rolling support device is a rolling bearing. Similarly, a ball screw means a nut having a female screw and a screw shaft having a male screw. In the case of a linear guide (linear guide bearing),
Means slider and guide rail.

Hereinafter, the critical significance of the present invention will be described. (Steel as a constituent material of outer member, inner member, and rolling element) Outer member, inner member, which is a rolling member constituting a rolling support device, and bearing steel serving as a base material of the rolling element Is C from the viewpoint of surface properties, especially fretting durability.
High Cr steel containing at least 3% by weight, preferably at least 5% by weight, more preferably at least 8% by weight.

Further, from the viewpoint of quietness, the relationship between the carbon (C) content and the Cr content of the steel is expressed as C% ≦ −0.0
It is preferable to satisfy 5Cr% + 1.41. As a result, the nitride layer formed on the surface
Extremely high hardness is obtained due to precipitation of nitrides and the like, and slidability, fretting resistance, high-speed durability and the like are greatly improved. In addition, the nitride layer is excellent in heat resistance and the like, and when it has certain requirements regarding its thickness, it has the effect of dramatically improving durability against high-temperature standing, impact resistance, and the like. This will be described later.

If the above relational expression is not satisfied,
During the solidification process, coarse eutectic carbides with a major axis exceeding 10 μm are generated. In the case of rolling elements, the problem of disconnection occurs when drawing the material, or in the case of rolling elements, outer members, and inner members, At the time of finishing, there may be a problem that these eutectic carbides hinder the finishing accuracy and the target accuracy cannot be obtained. In order to make the above-mentioned problems less likely to occur, the size of the eutectic carbide contained is
It is preferable that the major axis is 5 μm or less.

Further, the core is subjected to tempering at a very high temperature by the nitriding treatment, and is somewhat softened. In order to suppress the softening of the core, the total content of carbon and nitrogen is preferably set to 0.45% by weight or more. 0.05
It is more preferable to use an alloy containing nitrogen in an amount of not less than% by weight, because the softening can be further suppressed and the carbide can be further refined. Further, in addition to the above components, M
When nitride-forming elements such as o, V, W, Nb, Al, and Si are added in a complex manner, these fine nitrides are precipitated and the durability is further improved. You may.

(Production method of rolling element and quality of finished product) In the production of rolling element, first, a raw ball is manufactured by cold working or cutting work by a header and flashing using a wire rod which has been cold drawn. Then, after quenching, sub-zero treatment and tempering are performed, and rough grinding is performed. afterwards,
A semi-processed sphere described below is produced. At this time, as a measure for preventing surface scratches during handling, it is preferable to increase the surface hardness in advance by mechanical hardening such as barrel or ball peening. These mechanical hardening methods also contribute to inducing the transformation of retained austenite in steel to martensite, and also have an effect of suppressing a reduction in the impact resistance of the rolling support device caused by the rolling elements.

Thereafter, grinding is performed to a target size, that is, a size obtained by adding a set margin to the finished product size (hereinafter, the obtained product is referred to as a semi-processed ball). The set allowance specifically refers to a necessary allowance for performing finishing processing to a target accuracy, but of course includes an amount of expansion and contraction due to nitriding. The accuracy of the semi-finished sphere is preferably not more than 3.0 μm, more preferably not more than 1.0 μm. The reason is as follows.

In general, the nitride layer is formed in a shape following the shape of the processed object. Therefore, when a nitrided layer is provided on a rolling element having poor sphericity and finish processing is performed, the non-uniform grinding is performed, and the thickness of the nitrided layer is not uniform. Because the balance is lost,
Grinding takes a long time to achieve accuracy, and in some cases, the target accuracy cannot be achieved.

The nitriding treatment generally includes gas nitriding, salt bath nitriding, ion nitriding, etc., but ion nitriding lacks mass productivity, is strongly affected by the shape of the processed material, and is uniformly formed on the spherical surface. It is not possible to form a suitable nitrided layer. In addition, the processing temperature of general gas nitriding and salt bath nitriding is 480 to 600 ° C.
The core is softened by tempering.

However, when a load is applied to the rolling support device, a large shear stress is applied in the depth direction, so that the hardness of the base of the nitride layer is also very important. That is, in the case of the above-mentioned general nitriding method, when the nitriding temperature is high, the base material does not have sufficient heat resistance and the core is significantly softened, the strength of the base supporting the nitride layer on the surface becomes insufficient, and the rolling occurs. When the supporting device receives high contact stress, the surface nitrided layer may be damaged. Therefore, it is preferable to secure the core hardness of HRC 57 or more.

If the nitriding temperature is high, the sphericity, the difference between diameters and the like are greatly reduced after the nitriding treatment, which also causes problems in the accuracy and functions of the steel ball. Therefore, the nitriding temperature is preferably set to 450 ° C. or lower, more preferably 420 ° C. or lower. In addition, the lower the processing temperature, the denser the nitride layer, and a poor porous layer is not generated. Therefore, the surface roughness and the waviness after lapping tend to be improved. Specifically, the nitriding method described below can be suitably used.

In the case of general gas nitriding, if the processing temperature is lowered, the reactivity of the ammonia gas decreases. In addition, C
In the case of steel containing a large amount of r, since a dense Cr oxide layer is formed on the surface layer, this may hinder nitridation, making it impossible to form a uniform nitrided layer. Further, in the case of salt bath nitriding, since the melting point of the salt bath is basically high, there is a limit to lowering the treatment temperature.

Therefore, the nitriding process of the present invention includes:
For example, an Nv nitriding process (trade name of Daido Hokusan Co., Ltd.) can be suitably used. In this treatment, as a pretreatment of the nitriding treatment, for example, a process of performing a fluoridation treatment at about 250 to 400 ° C. using a fluorine-based gas such as NF ₃ (nitrogen trifluoride) and a nitriding treatment with an NH ₃ gas are performed. Process.

C that inhibits the nitridation reaction by fluorination
The r-oxidized layer is removed to form a very thin fluoride layer on the surface layer, and the surface is extremely activated. Therefore, even if the subsequent nitriding treatment is performed at a low temperature of about 400 ° C., a very uniform nitrided layer can be formed. As a result, the nitrided layer formed on the surface is very dense, and the accuracy of the rolling elements after nitriding is prevented from deteriorating, and the subsequent finishing can be performed relatively easily.

However, the above process is merely an example, and even in the case of salt bath nitriding, it is possible to set the melting point to 420 to 430 ° C. depending on the composition of the salt bath. Low-temperature salt bath nitriding at about 480 ° C. may be used. As a result, the hardness of the surface layer is Hv90.
Since zero or more nitrided layers are formed, quietness, impact resistance and the like are improved. Further, (Fe, Cr) _2-4 N, C
Since a large amount of fine nitrides such as rN and Cr ₂ N precipitate, various durability as described above is dramatically improved. In order to make the above properties more preferable,
The hardness of the nitrided layer is preferably Hv110 or more,
About 00 to 1400 is particularly preferable.

In addition, when the rolling support device receives an impact load, indentations may be formed on the outer member and the inner member to cause acoustic deterioration. As a countermeasure, it is necessary to reduce residual austenite as much as possible. Is effective as described above. However, in general, the groove curvature of the outer member or the inner member (the outer ring or the inner ring in the case of a rolling bearing) of the rolling support device is designed to be slightly larger than the curvature of the rolling element. In the case of a rolling element which is apt to receive a higher contact stress and has a very hard nitride layer on the surface, the thickness of the nitride layer is an important factor.

The present inventors have studied in detail the thickness of the nitride layer. In order to form a uniform and stable nitride layer, a certain nitriding time is required, and a larger thickness may be preferable in some cases. Furthermore, when the strain rate is relatively high, that is, when receiving an impact load,
As the ratio of the nitrided layer to the stress volume increases, the rigidity of the rolling element surface increases, and as a result, the impact resistance improves. Therefore, the thickness of the nitrided layer needs to be 1.5% or more of the rolling element diameter Da, and more preferably 2.0% or more of the rolling element diameter Da.

However, when the thickness of the nitride layer becomes larger,
Instead of increasing the rigidity of the rolling element surface, outer members such as race rings,
Because indentation may easily occur on the inner member,
The outer member and the inner member are preferably made of bearing steel having a retained austenite of 1% or less. Outer member,
A more preferable embodiment of the inner member will be described later in detail.

Providing a nitride layer that is thicker than necessary leads to an increase in the nitriding time, which leads to an increase in processing costs and processing costs due to a reduction in sphericity after nitriding, and furthermore, the surface texture becomes coarse. This is not preferable because the required accuracy may not be satisfied or various characteristics may be reduced. Therefore, the thickness of the nitrided layer is determined by the rolling element diameter Da.
6% or less or 100 μm or less. When the rolling element diameter Da is 1.667 mm or less, the thickness of the nitrided layer is preferably 100 μm or less.

The rolling elements are subjected to a finishing process after being subjected to a nitriding treatment, so that the target accuracy, specifically, JIS B 1
It is finished to a high-precision sphere of grade 10 or higher described in 501 (including a steel ball grade of a swing arm bearing). In recent years, in ball bearings used for information devices such as HDDs, particularly in bearings for spindles, higher precision balls have been demanded. In this case, it is preferable that the ball be grade 3 or higher, more preferably. Has a sphericity and a diameter difference of 0.05 μm or less, and a surface roughness of 0.003 μR.
a.

The thickness of the nitrided layer on the surface of the finished rolling element manufactured by the above method is very uniform, and it is not only quiet, fretting and impact resistant, but also acoustic durability at high speed rotation. In addition, the burn-in characteristics (acoustic deterioration due to the time-dependent change in the waviness of the rolling element surface) are also improved. (About the manufacturing method of the outer member and the inner member and the quality of the finished product) The steel which is a constituent material of the outer member and the inner member is as described above, and SUJ2 described in JISG 4805.
Needless to say, SUJ3 and similar high carbon bearing steels, and case hardening steels such as SCR and SCM can be used.

However, in order to prevent acoustic deterioration due to an impact load, after hardening and hardening, the residual austenite on the raceway surface is limited by a mechanical hardening method such as sub-zero treatment or shot peening, and further by a method such as tempering. It is preferable to reduce it. The amount of retained austenite is preferably 1% or less, and the hardness is HRC58 in order to withstand abrasion and shear stress.
It is preferable to make the above.

Further, when a carbonitrided layer is formed on the raceway surface, the formation of indentations on the raceway hardly occurs, and the impact resistance is dramatically improved. Therefore, it is preferable to define the quality of the finished raceway ring as follows. The critical significance of the reason and form will be described below. Normally, when carbonitriding is performed on the outer and inner members, the main focus is on ensuring the rolling life under contaminated lubrication by including a large amount of retained austenite on the surface. It is a target. However, as described above, retained austenite is harmful in small rolling bearings and the like that require quietness, and it is not preferable to retain the retained austenite. Therefore, in the present invention, after carbonitriding and quenching, 250 to 32
By performing tempering at a temperature of about 0 ° C., the retained austenite is reduced to 1% or less.

However, in order to obtain a sufficient effect of the nitrided layer, it is preferable that the nitrogen concentration at a depth of 2% of the rolling element diameter Da of the nitrided layer is 0.1% by weight or more. More preferably, it is at least 0.3% by weight. Also,
Rather than directly decomposing the residual austenite after quenching, the quenching is transformed into martensite after quenching by sub-zero treatment or mechanical hardening methods such as shot peening and ball peening. It is more preferable to reduce the value, because higher impact resistance can be obtained. Further, the hardness of the raceway surface of the outer member and the inner member is determined by HRC.
It is preferred to be 62 or more.

The method of manufacturing the outer member and the inner member and the quality of the finished product are the same as those of the above-mentioned rolling element. That is, while being composed of steel having a Cr content of 3% by weight or more, a nitrided layer having a hardness of Hv900 or more is provided on the surface layer, and the thickness of the nitrided layer is set to 1.
5% or more and 6% or less and 1.5% or more of rolling element diameter Da 1
Either one of 00 μm or less. When a nitride layer is provided on the raceway surfaces of the outer member and the inner member, indentations are less likely to occur on the outer member and the inner member, and the impact resistance is dramatically improved.

Hereinafter, a specific manufacturing method will be described using a rolling bearing as an example. First, the bearing ring processed into a desired shape by turning is hardened by quenching and tempering. In some cases, sub-zero processing is performed before tempering. Generally, the accuracy of the race at this point is
For example, the roundness is several tens to 100 μm or more, and when the above-described nitriding treatment is performed, the formed nitride layer is processed unevenly during grinding. In this case, not only the desired nitrided layer cannot be left, but also the stress balance is lost, and the target accuracy cannot be achieved, and the grinding margin increases to take a long time for grinding. For this reason, it is preferable to perform grinding after quenching and hardening, and to finish grinding to at least a circularity of 1 μm or less.

The dimensions of the bearing at this time must be adjusted in consideration of the amount of expansion, since the nitriding treatment causes expansion corresponding to the thickness of the nitride layer. Then, it is subjected to the same nitriding treatment as in the case of the above-mentioned rolling element.
After the nitriding treatment, since coarse particles or foreign substances such as oxides and nitrides adhere to the surface, it is preferable to remove these by a barrel or other mechanical methods.

According to the nitriding method of the present invention, the accuracy does not significantly decrease after the nitriding treatment. However, considering the variation in the amount of expansion and the accuracy thereof, especially in a rolling bearing for information equipment. It is preferable that re-grinding (including lapping) is performed after nitriding. In that case, the roughness of the rolling surface is preferably 0.1 μm or less, more preferably 0.05 μm or less. The other qualities of the nitrided layer are the same as those of the rolling element described above.

[0057]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rolling support device according to the present invention will be described in detail with reference to the drawings. FIG.
1 is a cross-sectional view of a rolling bearing which is an embodiment of a rolling support device according to the present invention. This rolling bearing includes a plurality of rolling elements (balls) 3 and an inner ring 1 located inward thereof.
And the outer ring 2 located further outward than that, and the rolling element 3 is rollingly guided while being held between the inner ring 1 and the outer ring 2. At this time, the inner ring 1 and the outer ring 2 are provided with rolling grooves for guiding the rolling elements 3, and the rolling elements 3
Are equally held by the cage 4 in the rolling grooves. Further, a nitride layer N is provided on the surface of the rolling element 3 by a method described later.

In such a rolling bearing, the quietness and various durability evaluations of the bearings of the embodiment and the comparative example were all performed by using a ball bearing 695 (JIS number). The rolling elements incorporated into the bearings were all wrapped to grade 3 or higher, plastic cages were used for the retainers, and internal rust preventive oil and mineral oil-based grease were used for lubrication.

The rolling element in the present embodiment was manufactured by the following method. In addition, the steel of symbol A-1 which has a component composition of Table 1-A-4 was used for the rolling element material.

[0060]

[Table 1]

First, elementary balls were prepared by using a wire rod having a diameter of 1.5 mm by header processing and flashing, and quenched, sub-zero treated and tempered. Next, after performing rough grinding, ball peening was performed, followed by finishing to a sphericity of 1.0 μm, and nitriding and finishing (lap finishing). The nitriding was performed by a Nv nitriding process at 410 to 440 ° C. for 24 to 48 hours. FIG. 3 shows a schematic view of the rolling element manufacturing process. Through the above steps, a rolling element having a JIS rating of G3 or more, a sphericity and a diameter difference of 0.05 μm or less, and a surface roughness of 0.003 μm Ra or less was obtained.

Table 2 shows the quality of the finished product of this rolling element.
The material symbols are shown in Table 1.

[0063]

[Table 2]

The surface hardness shown in the table is a result of directly measuring the surface of the rolling element with a load of 100 g using a Vickers hardness tester. Core hardness, after embedding the ball in thermoplastic resin,
The Vickers hardness of a core of a cross section obtained by polishing is measured with a load of 100 g and converted to Rockwell C hardness. In addition, the thickness of the nitrided layer is clear after the rolling element embedded in the thermoplastic resin is polished to an appropriate cross-sectional diameter and etched with a marble reagent, and after etching at the cross-sectional diameter of the rolling element on the observation surface and the cross-sectional diameter. Was measured by a microscope, and the true nitride layer thickness was geometrically calculated based on the measured diameter and nitride layer thickness. In the sectional view of the rolling element of FIG.
The white layer shown on the surface of the rolling element is a nitrided layer.

The accuracy of the rolling element according to the present invention is such that the sphericity is 0.05 μm or less and the ball waviness is M.P.
B. (5 to 30 peaks per circumference) 40 npc or less,
H. B. 83 np for (30 to 160 peaks per circumference)
c or less. Although FIG. 4 shows an example of a cross-sectional view of the rolling element of the present invention, it can be confirmed that a very uniform and dense nitride layer is formed.

On the other hand, SUJ2 was used for the bearing ring, and one of the following two heat treatments was performed. The retained austenite in the steel is almost completely decomposed and disappears. (1) After quenching at 820 to 850 ° C., a sub-zero treatment was performed, followed by tempering at 220 to 240 ° C. (described in the column of raceway in Table 3 as “SUJ2”). (2) After carbonitriding and quenching at 820 to 850 ° C, a sub-zero treatment was performed, followed by tempering at 260 to 280 ° C (Table 3).
In the middle raceway column, "SUJ2 + carbonitriding" is described.)

The surface hardness of the raceway surface of the bearing ring was 59.5 in the case of (1) and 62.5 in the case of (2). As a result of measuring the cross-sectional nitrogen concentration distribution by EPMA in (2), the nitrogen concentration at a depth of 2% Da was 0.34% by weight. The sound durability, fretting durability, impact resistance, etc. of the sample ball bearings obtained by combining these rolling elements and races were evaluated.

First, the initial sound was evaluated by measuring the axial vibration acceleration (G value) when the sample ball bearing was operated at a preload of 11.8 N and a rotation speed of 1800 rpm, and then subjected to various evaluation tests. Table 3 shows the evaluation results.

[0069]

[Table 3]

The evaluation of acoustic durability was performed by rotating the shaft at a preload of 11.8 N, a rotational speed of 7200 rpm, a temperature of 70 ° C. for 1000 hours, and then measuring the axial vibration acceleration (G value) again. Was calculated, and the ratio was shown assuming that the case of Comparative Example E-5 made of all SUJ2 was set to 1. Therefore, the smaller the numerical value in Table 3, the better the acoustic durability.

For the evaluation of the fretting durability, a rocking test was performed under the following conditions to determine the amount of sound deterioration from the initial value.
The ratio is shown when the case of Comparative Example E-5 made by UJ2 is set to 1. Therefore, like the evaluation results of the acoustic durability, Table 3
The smaller the numerical value, the better the acoustic durability. The impact resistance was evaluated with various heights (30 cm to 1 cm) in the axial direction with a preload of 11.8 N applied to the ball bearing.
m), and measured by measuring the amount of increase in the G value from before the test. The bearing was rotated at the outer ring, the total weight including the hub was 35 g, and the acceleration when dropped was measured by an acceleration pickup attached to the hub. The acceleration at which the G value increased by 5 mG compared to before the test was determined, and the total SU
The ratio is shown by taking the case of Comparative Example E-5 made of J2 as 1. Therefore, the larger the numerical value in Table 3, the better the impact resistance.

Table 3 shows that the present invention is superior to the comparative example in all of acoustic durability, fretting resistance and impact resistance. Its fretting resistance and acoustic durability are almost equal to or higher than those of Comparative Example E-6 using ceramic balls, and the impact resistance is remarkably improved. It is equal to or more than that of Comparative Example E-5 used.
In particular, those obtained by carbonitriding the bearing rings (Examples D-5 to D-
The effect is remarkable in 10).

On the other hand, the comparative example E-1 is SU
This is an example in which the rolling element surface made of J2 is subjected to nitriding treatment. However, since the Cr content is small, sufficient surface hardness cannot be obtained, and the fretting durability and acoustic durability are inferior. Comparative Example E-2 is an example in which the surface of the rolling element made of SUS440C was subjected to nitriding treatment. However, since coarse eutectic carbides were present, it was difficult to obtain surface accuracy, and the comparative example E-2 was slightly compared with the examples of the present invention. Poor durability.

Comparative Examples E-3 and E-4 are examples in which the thickness of the nitrided layer is less than 1.5% of the diameter Da of the rolling element. Sound deterioration was observed. As described above, the rolling bearing of the present embodiment can prevent acoustic degradation at the time of impact drop, which is a problem specific to the hybrid bearing using the ceramic ball, and can be equal to or more than the hybrid bearing. Although it has improved fretting durability and acoustic durability, it also has the following advantages.

Comparative Example E Using Ceramic Balls
In the case of 6, the silicon nitride (Si ₃ N ₄ ) ceramic has a very large specific resistance of 10 ¹³ Ω · cm to ¹⁴ Ω · cm, so that it is easy to attract foreign substances by the action of static electricity. Trouble is easy to occur. Furthermore, since silicon nitride ceramics have a very small coefficient of linear expansion (2.8 × 10 ⁻⁶ / ° C.), the preload changes due to a temperature change, and torque fluctuations occur. In extreme cases, the preload completely escapes. There is also a phenomenon that it will.

In this embodiment, since steel is basically used, the specific resistance is also 10 ^-5 Ω · cm.
Therefore, it is not so different from SUJ2 in order.
Further, the linear expansion coefficient is also SUJ2 (12.5 × 10 ⁻⁶ /
° C.) and slightly reduced compared (for Table 1 A-4, only 10.8 × 10 ^-6 / ℃), the material of the housing of the bearing ferritic stainless steel (10.4 × 10 ^{- 6}
/ ° C) is often used, and in this case, 0
The preload change at ~ 70 ° C is 0.98N,
This is also advantageous compared to the total SUJ2 of 2.94N. In the case of silicon nitride ceramics, this is a value of 11.8N, so that if the initial preload is about 7.84N at 20 ° C, the preload will be completely removed at 70 ° C.

FIG. 5 shows the relationship between the ratio of the diameter Da of the rolling element to the thickness of the nitride layer formed on the surface of the rolling element and the impact resistance in the drop impact test. As can be seen from FIG. 5, when the ratio is 1.5% or less, there is no difference between the raceway of SUJ2 and the raceway carbonitrided in SUJ2. That is, when the ratio of the thickness of the nitride layer to the diameter Da of the rolling element is 1.5%, it is considered that the acoustic deterioration due to the rolling element has occurred at the time of a drop impact.

When the content is 1.5% or more, the rigidity of the rolling elements increases, the impact resistance is improved, and the race is made of SUJ2.
Is different from that obtained by carbonitriding SUJ2 in orbital theory. That is, unless the ratio of the thickness of the nitride layer on the rolling element surface to the rolling element diameter Da is not more than 1.5%,
It cannot truly prevent sound degradation at the time of a drop impact. In particular, when the ratio of the nitride layer thickness to the rolling element diameter Da exceeds 2%, the effect is large. Further, when the raceway is carbonitrided, the effect of the improvement is further enhanced. This forms an atmosphere in which interstitial elements such as carbon and nitrogen dissolved in martensite fix the dislocations, and furthermore, carbides or carbonitrides precipitated during tempering have an effect of suppressing interlocking of the dislocations. It is thought to be.

However, if the tempering temperature is too high, the solid solution of carbon and nitrogen is further converted into carbides or carbonitrides by the tempering action, and these are gradually aggregated. The effect of fixing is reduced, and the carbides and carbonitrides precipitated during the tempering process agglomerate with each other, so that the dislocation pinning effect is also reduced. That is, since the dislocation strengthening mechanism is relaxed, impact resistance is reduced. Therefore, the tempering temperature is most preferably the temperature at which the retained austenite is almost completely decomposed, and it is not preferable to increase the temper more than necessary. The preferred tempering temperature is 250-320 ° C.

It is considered that the reason why preferable results are obtained by the carbonitriding is that, in addition to the solid solution nitrogen fixing the dislocation, the carbonitride more effectively acts to pin the dislocation. However, as a result of a detailed study by the present inventors, the rolling element diameter D
Unless the nitrogen concentration at a depth of 2% of a was at least 0.1% by weight or more (slightly larger at the outermost surface), the effect was very small. More preferably, the nitrogen concentration at a depth of 2% of the rolling element diameter Da is at least 0.3% by weight or more.

Next, the results of various durability evaluations of a rolling bearing which is another embodiment of the rolling support device according to the present invention will be described. All rolling bearings used
Inner diameter 6.350mm, outer diameter 9.525mm, width 3.17
This is a ball bearing manufactured by Nippon Seiko Co., Ltd. having a dimension and shape of 5 mm. The rolling elements incorporated in the rolling bearings are all those having a diameter Da of 1.0 mm and a grade of 5 or equivalent, a plastic retainer is used as a retainer, and an internal rust-preventive oil and a mineral oil-based grease are used for lubrication. did.

The steels used were the following (steel A, B, C) and high carbon chromium bearing steel SUJ2. The amount of retained austenite in these steels was reduced to 4% or less, and a desired nitrided layer was formed on the surface layers of the rolling elements and races. Further, as a comparative example, evaluation was also made on a case where the thickness of the nitrided layer did not satisfy the requirements of the present invention.

Steel A: C content 0.60% by weight, Cr content 13% by weight, N content 0.15% by weight Steel B: C content 0.80% by weight, Cr content 8.0% by weight Steel C: C content 0.80% by weight, Cr content 4.0% by weight

[0084]

[Table 4]

Table 4 shows the quality of finished products of rolling elements and races and the results of evaluating the durability of rolling bearings using them. The surface hardness in the table is the result of directly measuring the surface of the rolling element and the surface of the end face of the bearing ring with a load of 100 g using a Vickers hardness tester. In addition, for the rolling element, the rolling element embedded in thermoplastic resin is polished to an appropriate cross-sectional diameter and etched with a marble reagent, and the cross-sectional diameter of the rolling element on the observation surface and the cross-sectional diameter of the rolling element are determined. The thickness of the nitrided layer, which is clearly observed after etching, was measured with a microscope, and the thickness was determined geometrically based on the measured diameter and the thickness of the nitrided layer.

In the race, the cut surface of the race embedded in the thermoplastic resin was etched with a marble reagent, and the thickness of the nitrided layer was measured directly. Here, all layers affected by nitridation observed after etching were regarded as nitrided layers. In the case of a rolling element, the thickness of the nitride layer at the cross-section passing through the center (the cross-section that maximizes the cross-sectional area) and the thickness of the bearing ring are set so that the measured thickness of the nitride layer becomes a true value. In the case of the above, the measured value was corrected to the nitride layer thickness in the cross section including the axis.

The durability of the rolling bearing was evaluated in terms of acoustic durability, fretting durability, impact resistance, high-temperature storage durability, corrosion resistance, and the like. First, the initial sound was evaluated by measuring the axial vibration acceleration (G value) when the ball bearing was operated at a preload of 4.9 N and a rotation speed of 1800 rpm, and was subjected to various evaluation tests.

The evaluation of the acoustic durability was performed by pre-loading at 4.9 N, rotating at 15,000 rpm, rotating at a temperature of 70 ° C. for 1000 hours, and then measuring the axial vibration acceleration (G value) again. I went by asking. And all (rolling element and raceway) were shown by the ratio when the value of the comparative example G-1 which is a ball bearing made of SUJ2 was set to 1. Therefore, the smaller the numerical value in the table, the better the acoustic durability.

For the evaluation of fretting durability, a test was performed at room temperature under a preload of 4.9 N, a rocking angle of 8 deg, a rocking frequency of 30 Hz, and a rocking frequency of 10 million times, and then the axial vibration acceleration (G value) was measured again. This was performed by determining the amount of increase in the G value before the test. Then, the ratio is shown when the value of Comparative Example G-1 made of all SUJ2 is set to 1. Therefore, similarly to the acoustic durability evaluation, the smaller the numerical value in the table, the better the fretting durability.

The impact resistance was evaluated by setting the axial load to 9.8.
The load was increased to 294N while increasing by N, and after unloading, the axial vibration acceleration (G value) was measured again, and the increase in the G value before the test was determined. The axial load increased by 5 mG was defined as an impact load. In the table, the ratio when the impact resistance load of Comparative Example G-1 made of all SUJ2 is 1 is shown. Therefore, the larger the numerical value in the table, the better the impact resistance.

The high-temperature standing durability is obtained by applying a preload of 4.9 N, maintaining the temperature at 110 ° C. for 155 hours, measuring the axial vibration acceleration (G value) again, and calculating the amount of increase in the G value before the test. Was performed. Then, those which increased by 5 mG or more were evaluated as defective, and indicated by a cross in the table, and 5 mG
The following items were evaluated as good and represented by a mark. The corrosion resistance was evaluated by performing a wet test under the conditions of 70 ° C. and 95% RH for 2 weeks and determining whether or not rust was generated. In the table, ○ indicates that no rust was observed, X indicates that significant rust was observed, and Δ indicates that rust was observed but was clearly better than Comparative Example G-1. Indicated by

From Table 4, it can be seen that the rolling bearings of the examples (F-1 to F-6) surpass the comparative examples in all the evaluation tests. The thickness of the nitrided layer of these rolling bearings is 10% of the rolling element diameter Da (1.0 mm).
Or less, that is, 100 μm or less. On the other hand, Comparative Example G-1 is an example in which all of the inner ring, the outer ring, and the rolling elements are SUJ2, but is inferior to the above-described example in all items. Further, Comparative Example G-2 is an example in which the inner ring, the outer ring, and the rolling elements were all used without nitriding steel A, which is a martensitic stainless steel, but in all other items except corrosion resistance. Inferior to the previous embodiment.

Further, Comparative Example G-3 and Comparative Example G-4
This is an example in which nitriding steel A is used for either one of the bearing rings (inner and outer rings) and the rolling elements. However, all of the components (the bearing rings and the rolling elements) are the constituent elements of the present invention (steel rings and rolling elements). , The presence / absence of a nitride layer and the thickness), and thus the high-temperature standing durability is not improved. FIG.
An example of a chart in which the rolling bearing of Comparative Example G-1 was subjected to acoustic measurement after being subjected to a high-temperature standing durability test, and the result was subjected to frequency analysis (envelope analysis) is shown. As is clear from FIG. 6, when the temperature is kept at 110 ° C. for a long time, the cause of acoustic deterioration (the presence of Brinell marks) can be confirmed in all the rolling elements, the outer ring and the inner ring. Therefore, this means that unless all the components of the rolling bearing satisfy the constituent requirements of the present invention, the acoustic durability cannot be improved, and in a device in which a rolling support device such as a rolling bearing is incorporated, a rolling bearing or the like is required. It is necessary to take measures against the ambient temperature of the rolling support device.

Comparative Example G-5 is an example in which the inner ring, the outer ring, and the rolling elements all satisfy the requirements of the present invention except for the thickness of the nitrided layer. Therefore, the impact resistance has not been improved. Furthermore, as is clear from Table 4, the rolling bearing of the above-described embodiment is 15000.
It also has acoustic durability against high-speed rotation at rpm,
It is considered that the apparatus can sufficiently cope with high performance.

Further, the rolling bearing of the above embodiment is
Since it is more excellent in corrosion resistance than a conventional SUJ2 rolling bearing, it can be applied to a swing arm bearing or the like when absolutely dry specifications are required. Note that the present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, in the present embodiment, a rolling bearing has been described as an example of the rolling support device. However, the rolling support device of the present invention can be applied to various other types of rolling support devices. For example, a ball screw or a linear guide is used.

[0096]

As described above, in the rolling support device according to the present invention, a very hard and dense nitride layer is provided at least on the surface layer of the rolling element so as to have the most suitable thickness. Therefore, as compared with a general rolling support device, not only quietness but also fretting durability, acoustic durability and impact resistance are excellent.

Further, it is very excellent in high-speed durability and durability against high-temperature standing, which are reduced as the performance of the device in which the rolling support device is incorporated is improved. Further, according to the rolling support device of the present invention, it is possible to solve problems such as impact resistance, preload loss, and acoustic defects due to dust suction due to electrostatic action, which are regarded as problems in hybrid bearings using ceramic balls. This provides a great effect that it can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of fretting wear marks on the rolling element surface.

FIG. 2 is a longitudinal sectional view of a rolling bearing which is an embodiment of the rolling support device of the present invention.

FIG. 3 is a schematic explanatory view of a manufacturing process of a rolling element of the present invention.

FIG. 4 is a sectional view of a rolling element according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between a thickness of a nitride layer of a rolling element and impact resistance.

FIG. 6 is a chart showing acoustic measurement results of a rolling bearing.

[Explanation of symbols]

 Reference Signs List 1 inner ring 2 outer ring 3 rolling element N nitride layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22C 38/18 C22C 38/18 F16C 33/34 F16C 33/34 33/62 33/62 F16H 25/22 F16H 25/22 L 25/24 25/24 AE (72) Inventor Kenji Yamamura 1-50 50 Kugenuma Jinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 AA32 AA42 AA54 AA62 BA70 DA02 EA02 FA31 FA35 GA24 GA53 4K042 AA14 AA22 BA03 CA06 CA07 DA06

Claims (1)

[Claims] 1. A rolling support device comprising: an outer member; an inner member; and a plurality of rolling elements rotatably disposed between the outer member and the inner member. At least the rolling element of the outer member, the inner member, and the rolling element is made of steel having a Cr content of 3% by weight or more, and the surface layer has a hardness of at least Hv900. Rolling, wherein the thickness of the nitrided layer is any one of 1.5% or more and 6% or less of the rolling element diameter Da and 1.5% or more and 100 μm or less of the rolling element diameter Da. Support device.