JP2008025728A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing usable in coolant without lubrication by lubricating oil. <P>SOLUTION: An inner ring 1, an outer ring 2, and balls 3 of a deep groove ball bearing are composed of steel of SUJ2 or the like. At least one of a whole of an outer circumference face of the inner ring 1 including a raceway surface 1a, a whole of an inner circumference face of the outer ring 2 including a raceway surface 2a, or a whole of a surface of the ball 3 is coated with a lubricating coating L. The lubricating coating L is composed of: a substrate layer M comprised of at least one type of metal from Cr, W, Ti, or Si; a middle layer F comprised of the metal or carbon; and a surface layer C comprised of diamond-like carbon containing carbon and hydrogen, and the three layers are formed in an order of the surface layer C, the middle layer F, and the substrate layer M from the surface side. A ratio of the carbon in the middle layer F is increased from a substrate layer M side toward a surface layer C side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rolling bearing used in carbon dioxide as a refrigerant.

In conventional air conditioners, chlorofluorocarbons (CFCs) have been used as refrigerants. In the air conditioner, chlorofluorocarbon and a mineral oil-based lubricating oil soluble therein are mixed, and this mixture is used as a lubricant for a bearing incorporated in the air conditioner.
However, the refrigerant is changed from CFCs to hydrofluorocarbons (HFC) and carbon dioxide because certain types of chlorofluorocarbons cause damage to the earth's ozone layer. Alkylene glycol (PAG) and polyol esters have been used.

For example, Patent Document 1 discloses a compressor in which a rolling bearing is lubricated with a mixture of HFC as a refrigerant and HFC and a lubricating oil soluble in the refrigerant. Patent Document 2 discloses a sliding member in which a binder composed of a polyamideimide resin, a polyimide resin, and an epoxy resin and a solid lubricant are combined and applied to a compressor.
JP-A-8-177864 JP 2005-89514 A

However, since the ozone depletion coefficient of HFC is not zero, the problem of adversely affecting the global environment still remains. Further, the PAG and polyol ester soluble in the refrigerant have not been sufficiently lubricated. When the mixing ratio with respect to the refrigerant is increased in order to compensate for insufficient lubricity, there is a problem that the refrigerant capacity is lowered.
Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a rolling bearing that can be used in a refrigerant without being lubricated with lubricating oil.

  In order to solve the above problems, the present invention has the following configuration. That is, the rolling bearing according to claim 1 of the present invention includes an inner ring, an outer ring, and a plurality of rolling elements that are freely rollable between the inner ring and the outer ring. The following five conditions are satisfied in the rolling bearing used in the above.

Condition A: The inner ring, the outer ring, and the rolling element are made of steel.
Condition B: A lubricant film is coated on at least one of the raceway surface of the inner ring, the raceway surface of the outer ring, and the rolling surface of the rolling element.
Condition C: The lubricating coating is composed of an underlayer made of at least one metal of chromium, tungsten, titanium, and silicon, an intermediate layer made of the metal and carbon, and diamond-like carbon containing carbon and hydrogen. And a surface layer.
Condition D: The three layers are arranged in the order of the surface layer, the intermediate layer, and the base layer from the surface side of the lubricating coating.
Condition E: The proportion of carbon in the intermediate layer increases from the base layer side toward the surface layer side.

  Since such a rolling bearing is provided with a lubricating coating having excellent lubricity, it can be used in a refrigerant such as carbon dioxide without being lubricated with lubricating oil. In addition, since an intermediate layer and an underlayer are interposed between the inner ring, the outer ring, and the steel, which is the base material of the rolling element, and the surface layer, diamond-like carbon having excellent lubricity (hereinafter referred to as DLC). There is also excellent adhesion between the surface layer made of steel and the base steel. Particularly, since the proportion of carbon in the intermediate layer increases from the base layer side to the surface layer side, the adhesion between the surface layer and the base material steel is further improved.

The rolling bearing according to claim 2 according to the present invention is the rolling bearing according to claim 1, wherein a hydrogen content in the diamond-like carbon is 20 atomic% or more and 30 atomic% or less. To do.
When the hydrogen content is less than 20 atomic%, the friction coefficient of the lubricating coating in the refrigerant increases. On the other hand, if it exceeds 30 atomic%, the hardness of the DLC becomes insufficient, and the lubricating coating may be easily worn.

Furthermore, the rolling bearing according to claim 3 according to the present invention is the rolling bearing according to claim 1 or 2, wherein the surface layer has a surface hardness of 30 GPa or more and 45 GPa or less.
The surface hardness of the surface layer can be controlled by conditions at the time of forming DLC (for example, the type and amount of hydrocarbon gas used as a raw material for DLC). If it is less than 30 GPa, the surface layer is likely to be destroyed by abrasion powder or the like, and if it exceeds 45 GPa, the elastic modulus increases, so that cracking is likely to occur due to stress.

  The rolling bearing of the present invention can be used in a refrigerant without being lubricated with lubricating oil.

Embodiments of a rolling bearing according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial longitudinal sectional view showing a configuration of a deep groove ball bearing which is an embodiment of a rolling bearing according to the present invention, and FIG. 2 is an enlarged sectional view showing an A portion of FIG. .
The deep groove ball bearing of FIG. 1 includes an inner ring 1 having a raceway surface 1a on an outer peripheral surface, an outer ring 2 having a raceway surface 2a facing the raceway surface 1a of the inner ring 1 on an inner peripheral surface, and both raceway surfaces 1a and 2a. There are provided a plurality of balls 3 arranged so as to be freely rollable, and a cage 4 for holding the plurality of balls 3 between the raceway surfaces 1a, 2a at equal intervals over the circumferential direction of the bearing. In addition, although the corrugated cage etc. which consist of low carbon steel can be used as the retainer 4, the retainer 4 does not need to be provided.

  The inner ring 1, the outer ring 2, and the ball 3 are made of steel such as SUJ2 (high carbon chromium bearing steel type 2). At least one of the entire outer peripheral surface of the inner ring 1 including the raceway surface 1 a, the entire inner peripheral surface of the outer ring 2 including the raceway surface 2 a, and the entire surface of the ball 3 is covered with a lubricating coating L. In FIG. 2, the lubricating film L formed on the raceway surface 1a of the inner ring 1 is illustrated, but the illustration of the lubricating film L formed on the outer peripheral surface of the portion other than the raceway surface 1a is omitted. It is.

  As shown in FIG. 2, the lubricating coating L includes an underlayer M made of at least one metal selected from chromium (Cr), tungsten (W), titanium (Ti), and silicon (Si), and the metal And an intermediate layer F made of carbon and a surface layer C made of diamond-like carbon containing carbon and hydrogen. The three layers are formed from the surface side by the surface layer C, the intermediate layer F, and the lower layer. It is formed in the order of the formation M.

The proportion of carbon in the intermediate layer F increases from the base layer M side toward the surface layer C side. The DLC constituting the surface layer C is mainly composed of carbon and hydrogen, but the proportion of hydrogen among the atoms constituting the DLC is preferably 20 atomic percent or more and 30 atomic percent or less. Furthermore, the surface hardness of the surface layer C is preferably 30 GPa or more and 45 GPa or less.
Since such a rolling bearing is provided with the lubricating coating L, it can be used in a refrigerant such as carbon dioxide without being lubricated with lubricating oil. And it can be used conveniently as a bearing which supports rotating parts, such as a scroll, a screw, and a rotary compressor.

Next, a method for forming the lubricating film L on the inner ring 1, the outer ring 2, and the balls 3 will be described. An object to be treated (inner ring, outer ring, or ball) degreased with oil is placed in an unbalanced magnetron sputtering apparatus 504 (hereinafter referred to as UBMS apparatus) manufactured by Kobe Steel, Ltd., and sputtering using argon plasma is used. The surface of the workpiece was bombarded for 15 minutes. This bombardment process was performed by applying a negative power to the workpiece by introducing argon gas into the chamber with the target power set to zero and the pressure in the chamber set to about 1 × 10 ⁻² Pa. .

  Next, chromium was sputtered on the object to be processed in an argon gas atmosphere using chromium as a target (bias voltage was −50 to −100 V), and a base layer M having a thickness of 0.2 μm was formed. Then, while continuing the chromium sputtering, carbon sputtering with carbon as a target was started. An intermediate layer F made of chromium and carbon and having a thickness of 0.3 μm was formed on the base layer M by such sputtering. At this time, since the sputtering efficiency of carbon was gradually increased while the sputtering efficiency of chromium was gradually decreased, the proportion of carbon in the intermediate layer F gradually increased from the base layer M side toward the surface side. It was. Further, the sputtering of chromium was terminated, and a surface layer C having a thickness of 2 μm was formed on the intermediate layer F while introducing methane gas into the chamber only for sputtering of carbon.

  If film formation is performed by such sputtering, the adhesion between the layers of the lubricating coating L (the base layer M, the intermediate layer F, and the surface layer C) is extremely excellent and the surface layer has excellent lubricity. The adhesion between C and the base steel is very good. Further, the lubricating film L in which the composition of the layer is continuously and gradually changed from the base layer M made of chromium to the surface layer C made of DLC can be formed.

  The UBMS apparatus can be equipped with a plurality of targets used for sputtering, and can control the sputtering efficiency of each component arbitrarily by independently controlling the sputtering power source of each target. is there. For example, in the process of forming the intermediate layer F and the surface layer C in the above case, the power of the sputtering power source (DC power source) of the carbon target is simultaneously reduced while the power of the sputtering power source (DC power source) of the metal target is reduced. (At this time, a negative bias voltage is applied to the object to be processed).

In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in this embodiment, the lubricating film L is formed by sputtering using a non-equilibrium magnetron, but a pulsed laser arc vapor deposition method, a plasma CVD method, or the like can also be used.
In the present embodiment, the deep groove ball bearing has been described as an example, but the rolling bearing of the present invention can be applied to various types of rolling bearings. For example, radial ball bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, self-aligning roller bearings and other radial type rolling bearings, and thrust type ball bearings and thrust roller bearings such as thrust roller bearings.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. A bearing having the same structure as the deep groove ball bearing shown in FIG. 1 is prepared with various changes in the hydrogen content in the DLC constituting the surface layer by changing the amount of methane gas supplied when the surface layer is formed. Then, a rotation test was performed. In addition, the measurement of the content rate of hydrogen in DLC was performed by Elastic Recoil Detection Analysis.

This rotation test was conducted in carbon dioxide of 1.05 × 10 ⁵ Pa at room temperature without lubrication with a lubricating oil. The conditions for the rotation test are an axial load of 20 N and a rotation speed of 2000 min ⁻¹ . And the outer ring | wheel temperature at the time of rotation was measured, and the lubricity of the surface layer was evaluated. The results are shown in the graph of FIG. From this graph, it can be seen that when the hydrogen content in the DLC is 20 atomic% or more and 30 atomic% or less, the surface layer is excellent in lubricity, and the calorific value is low.

Next, in order to investigate the relationship between the surface hardness of the lubricating coating (surface layer) and the wear resistance, a ball-on-disk friction and wear test was conducted. The test method will be described below with reference to FIG.
A test ball 12 made of SUJ2 is placed on a horizontal test plate 11 made of SUJ2, and carbon dioxide is loaded while applying a pressure (surface pressure 0.7 GPa) in the direction of pressing the test plate 11 to the test ball 12. Under the atmosphere, the test ball 12 was rotated in the horizontal direction at a sliding speed of 0.5 m / s (rotational movement time was 2 hours). And the amount of wear was evaluated by the depth (wear depth) of the run trace which arose on the surface of test flat plate 11.

  The test flat plate 11 has a disk shape with a diameter of 62 mm and a thickness of 7 mm. The surface of the test flat plate 11 is covered with a lubricating coating 13 having the same configuration as the lubricating coating L described above, and the surface roughness is 0.004 μmRa. The test ball 12 is a ball having a diameter of 8 mm. Further, in the ball-on-disk friction and wear test, a lubricant such as grease or lubricating oil was not used. Furthermore, the surface hardness of the lubricating coating 13 (surface layer) was measured with a microhardness meter.

The results are shown in the graph of FIG. From this graph, it can be seen that when the surface hardness is 30 GPa or more, the wear amount is small and the wear resistance is excellent.
Note that the hydrogen content in the DLC can be changed by adjusting the methane gas introduced into the chamber. Further, the surface hardness of the surface layer can be changed by a bias voltage at the time of film formation. Therefore, as shown in the graph of FIG. 6, it is possible to form surface layers having different surface hardness even when the hydrogen content is the same.

It is a fragmentary longitudinal cross-section which shows the structure of the deep groove ball bearing which is one Embodiment of the rolling bearing which concerns on this invention. It is the expanded sectional view which expanded and showed the A section of FIG. It is a graph which shows the result of the rotation test of a bearing. It is a figure explaining the test method of a ball on disk friction abrasion test. It is a graph which shows the relationship between the surface hardness of a lubricating film (surface layer), and abrasion resistance. It is a graph which shows the relationship between the hydrogen content of DLC, and surface hardness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring 1a Raceway surface 2 Outer ring 2a Raceway surface 3 Ball L Lubricant coating M Underlayer F F Intermediate layer C Surface layer

Claims (3)

In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to roll between the inner ring and the outer ring, and used in carbon dioxide as a refrigerant, the following five conditions are satisfied: Rolling bearing characterized by satisfaction.
Condition A: The inner ring, the outer ring, and the rolling element are made of steel.
Condition B: A lubricant film is coated on at least one of the raceway surface of the inner ring, the raceway surface of the outer ring, and the rolling surface of the rolling element.
Condition C: The lubricating coating is composed of an underlayer made of at least one metal of chromium, tungsten, titanium, and silicon, an intermediate layer made of the metal and carbon, and diamond-like carbon containing carbon and hydrogen. And a surface layer.
Condition D: The three layers are arranged in the order of the surface layer, the intermediate layer, and the base layer from the surface side of the lubricating coating.
Condition E: The proportion of carbon in the intermediate layer increases from the base layer side toward the surface layer side.   2. The rolling bearing according to claim 1, wherein the hydrogen content in the diamond-like carbon is 20 atomic% or more and 30 atomic% or less.   The rolling bearing according to claim 1 or 2, wherein the surface layer has a surface hardness of 30 GPa or more and 45 GPa or less.

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