JP3539749B2 - Rolling element - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a means for ensuring corrosion resistance in rolling elements in general such as bearing components.
[0002]
[Prior art]
For example, in a semiconductor etching process or a CVD (chemical vapor deposition) process, corrosion of components or the like incorporated in an apparatus becomes a problem because a reactive gas such as a silane-based, fluorine-based, or chlorine-based gas is used. In particular, in the case of rolling elements such as bearing component parts, if corrosion occurs on the surface where rolling friction occurs (track surface, rolling surface of rolling elements, etc.), it leads to deterioration in function and durability, so that measures to prevent corrosion are extremely important. Becomes important. The level of the corrosive atmosphere is different even within the same device, and if it is placed in a place with a high level of corrosive atmosphere, it can be dealt with by using a high nickel alloy or the like. In this case, it is possible to use a martensitic stainless steel or the like.
[0003]
By the way, even in the same part, there is naturally a difference in the manner of corrosion between the part exposed in the atmosphere and the part not exposed to the atmosphere. Corrosion easily progresses in the exposed part. For example, in a case where a bearing is used as a wheel of a carriage (such as a cam follower), the outer surface of the outer ring runs while rolling on guide rails or the like, and thus comes into direct contact with corrosive substances in the atmosphere. It is possible and most likely to cause corrosion.
[0004]
For the reasons described above, conventionally, when a rolling element is used in a place having a relatively low level of corrosive atmosphere, it is formed of martensitic stainless steel, and among the surfaces that cause rolling friction, corrosion is most likely to occur. The exposed surface, that is, the outer diameter surface of the outer ring in the above example, is plated with chromium to improve the corrosion resistance.
[0005]
[Problems to be solved by the invention]
The chromium coating layer is excellent in corrosion resistance and abrasion resistance. In addition, in order to ensure sufficient corrosion resistance, even when forming a relatively thick coating layer of about 5 to 10 μm, it should be performed in a short time by plating. There is an advantage that can be. However, as shown in FIG. 4 in an enlarged manner, the chromium plating layer 12b has a problem of generation of pinholes P, which is a factor that causes rust generation A on the surface of the base material 12 at an early stage. This is because the base material 12 is not covered by the pinhole P, so that the base material 12 is directly attacked by the corrosive substance invading from the pinhole P, and the base metal ( Galvanic corrosion (a phenomenon in which a local battery is formed due to the adhesion of moisture and current flows to cause corrosion) occurs between the iron-based material and the plating layer 12b (chromium), and the corrosion of the base material 12 is accelerated. Because. Such a pinhole P in the chromium plating layer 12b is unavoidable even when the film thickness is relatively large, and as a result, the formation of the plating layer 12b alone is not sufficient as a means for ensuring corrosion resistance. I have to say that it is enough.
[0006]
On the other hand, as a chromium coating method, in addition to a plating method as a wet method, an ion plating method as a dry method is considered, and according to this, a coating layer having excellent denseness and adhesion can be formed. Therefore, the problem caused by the generation of the pinhole is avoided. However, in order to ensure sufficient corrosion resistance, it is necessary to make the film thickness relatively large, and to achieve this by ion plating alone, it takes a great deal of time, the workability is poor, and the cost is high. .
[0007]
Therefore, an object of the present invention is to solve the problem caused by the occurrence of pinholes in the chromium plating layer and to provide a rolling element having good corrosion resistance and durability in a corrosive atmosphere.
[0008]
[Means for Solving the Problems]
Rolling element of the present invention, the surface of the rolling element rolling friction , among the surfaces exposed to the atmosphere , chromium , chromium alloy, chromium and carbon compound or eutectoid, chromium and nitrogen compound or eutectoid Metals, compounds or eutectoids of chromium and phosphorus, compounds or eutectoids of chromium and sulfur, compounds or eutectoids of chromium and oxygen, and compounds selected from compounds or eutectoids of chromium and fluorine A corrosion-resistant coating made of a material is formed, and a lubricating coating made of PTFE is formed on a surface that is not exposed to the atmosphere . The corrosion-resistant coating has a plating layer with a thickness of 5 to 10 μm covering the base material surface. , those which are constituted by the ion plating layer formed on the upper layer of the plating layer.
[0009]
Further, a lubricating coating made of PTFE is formed on the corrosion-resistant coating.
[0010]
[Action]
The ion plating layer is excellent in denseness and adhesion, and covers the surface of the plating layer without unevenness. The chromium plating layer has pinholes, which cause premature corrosion of the base material.In this corrosion-resistant coating, the ion plating layer penetrates deep into the plating layer pinholes. Since the surface of the base material is covered and protected, the problem of base material corrosion in the pinhole is eliminated. Except for the pinholes, the plating layer covers the surface of the base material and effectively protects the surface of the base material from corrosive atmosphere. At the same time, since the ion plating layer covers the surface of the plating layer and functions as a kind of barrier layer for the plating layer, a good corrosion resistance effect of the plating layer is maintained for a long time.
[0011]
By using the corrosion-resistant coating on the surface exposed to the atmosphere among the surfaces of the rolling element that cause rolling friction, and forming the lubricating coating made of PTFE on the surface not exposed to the atmosphere, the use in vacuum is possible. Becomes possible. Generally, a solid lubricant such as a layered material such as molybdenum disulfide, a soft metal such as gold, silver, or lead, or a polymer material such as PTFE or polyimide is often used for lubricating rolling elements in a vacuum. However, among these, the layered material and the soft metal are easily attacked by the reactive gas, and thus are not suitable for use in a corrosive atmosphere. PTFE, on the other hand, is a chemically stable substance that is relatively resistant to reactive gases. Therefore, the lubricating coating made of PTFE has a good lubricating effect on the surface where rolling friction occurs, and also has a function of protecting the base material surface from reactive gases and the like. Corrosion is relatively unlikely to occur in portions that are not exposed to the atmosphere, and therefore, a sufficient corrosion resistance effect can be expected by a lubricating film of PTFE.
[0012]
If wear deterioration due to rolling friction of the corrosion-resistant coating is expected, this can be prevented by forming a PTFE lubricating coating on the corrosion-resistant coating.
[0013]
【Example】
Hereinafter, an embodiment in which the present invention is applied to a cam follower will be described.
[0014]
The cam follower shown in FIG. 1 is suitable for use in vacuum equipment such as an etching apparatus and a CVD apparatus in a semiconductor manufacturing facility. The cam follower includes a stud 1 having a raceway surface formed on the outer periphery of the head, an outer ring 2 having a raceway surface formed on the inner periphery, and a plurality of rollers 3 interposed between the raceways of the stud 1 and the outer rings 1, 2. A cage 4 for holding the rollers 3 at equal circumferential intervals is a main component. A threaded portion 1a is formed at an end of the stud 1 so that the stud 1 can be attached by fastening to a threaded hole of a mating member. The retainer 4 is prevented from being removed from both sides in the axial direction by a flange portion 1 b formed at an end of the stud 1 and a ring-shaped side plate 5 press-fitted into the stud 1.
[0015]
In this embodiment, in the cam follower described above, the outer diameter surface of the outer ring 2 exposed to the atmosphere (the mating surface such as a guide rail) A corrosion-resistant coating 2b made of chromium is formed on the raceway surface of the stud 1, the raceway surface of the outer ring 2, and the rolling surface of the rollers 3 which are not exposed to the atmosphere. In which the lubricating coatings 1a, 2a and 3a are formed. Further, in this embodiment, at least the outer ring of the rolling elements is formed of martensitic stainless steel represented by SUS440C.
[0016]
As shown in an enlarged manner in FIG. 3, the corrosion-resistant coating 2b includes a chromium plating layer 2b1 covering the outer diameter surface of the outer ring 2, and an ion plating layer 2b2 covering the surface of the plating layer 2b1. The plating layer 2b1 is formed by coating the outer diameter surface of the outer ring 2 with chromium by about 5 to 10 μm by electrolytic plating or the like. According to the plating method, a coating process can be performed in a short time even with a coating layer having such a relatively large thickness. The ion plating layer 2b2 is obtained by coating the surface of the plating layer 2b1 with chromium by about 0.2 μm by ion plating. Such an ion plating layer 2b2 has excellent denseness and adhesion, and covers the surface of the plating layer 2b1 without unevenness. Since the ion plating layer 2b2 is as thin as about 0.2 μm, it can be processed in a relatively short time. Further, since the underlying plating layer 2b1 is made of the same kind of metal, the affinity at the layer boundary is high, and the adhesion is high. Is particularly good.
[0017]
As described above, pinholes P are generated in the chromium plating layer 2b1, which causes premature corrosion of the base material. In the corrosion-resistant coating 2b, the ion plating layer 2b2 is formed by the plating layer 2b1. In this case, the metal material penetrates deep into the pinhole P to cover and protect the surface of the base material, so that the problem of base material corrosion in the pinhole P is eliminated. Except for the pinholes P, the plating layer 2b1 covers the base material surface thickly and effectively protects the base material surface from corrosive atmosphere. At the same time, the ion plating layer 2b2 covers the surface of the plating layer 2b1 and functions as a kind of barrier layer for the plating layer 2b1, so that the good corrosion resistance of the plating layer 2b1 is maintained for a long time.
[0018]
In the above description, “a lubricating coating made of crystalline PTFE” refers to a coating in which the crystal structure (molecular structure) of PTFE is not subdivided, such as a so-called sputtering coating. Or by immersing the object in a processing solution. Such lubricating coatings 1a, 2a, and 3a exhibit excellent lubrication performance inherent in PTFE, and enhance the durability of the rolling elements. At the same time, PTFE itself is also a material with excellent corrosion resistance, so that the surface of the rolling element is protected from corrosive substances. As described above, in a semiconductor etching process or the like, a reactive gas such as a chlorine-based gas is used, but the reactive gas itself does not attack the base material by itself, and binds to the moisture in the atmosphere to form an acid. The formation causes the base material surface to corrode for the first time. Therefore, in a portion having a relatively low level of the corrosive atmosphere, the portion not exposed to the atmosphere is relatively unlikely to corrode. Therefore, a sufficient corrosion resistance effect can be expected by the lubricating films 1a, 2a, and 3a of PTFE. it can. In this embodiment, as shown in FIG. 6, the lubricating coatings 1a, 2a, 3a have a continuous island distribution. The continuous island-shaped lubricating film is, for example, a PTFE treatment liquid sprayed onto the object to be treated and attached in the form of an island, and then eluted with an organic solvent to connect the islands. There is an advantage that the amount of dust generation can be reduced (for details, refer to Japanese Patent Application No. 4-203567 filed by the present applicant). In the case where the wear resistance due to the rolling friction of the corrosion resistant coating 2b is expected, a lubricating coating made of crystalline PTFE may be further formed on the corrosion resistant coating 2b.
[0019]
FIG. 2 shows the results of a comparative test of the corrosion resistance of the rolling element having the corrosion-resistant coating 2b having the above structure formed on the surface. The comparative test was performed by a salt spray test (sodium chloride concentration 5%, spray amount 1-2 ml / h, test temperature 35 ° C). The upper column of FIG. 4 shows the case where the corrosion resistant coating 2b (Cr plating + Cr ion plating) as shown in FIG. 3 is formed, the middle column shows the case where only the Cr plating layer 12b is formed as shown in FIG. 5 shows the results obtained by forming a Cr plating layer 12b1 on the Cr ion plating layer 12b2 as shown in FIG. Rust was observed after 290 hours in the case where only the Cr plating layer was formed (FIG. 4), whereas rust was observed after 900 hours in the case where the corrosion-resistant coating 2b was formed (FIG. 3). Did not. In the case where the Cr plating layer was formed on the Cr ion plating layer (FIG. 5), rust was observed in 170 hours, and the corrosion resistance was inferior to the case where only the Cr plating layer was formed (FIG. 4). . This is considered to be due to the fact that the Cr ion plating layer 12b2 is easily damaged during the processing of the Cr plating layer 12b1.
[0020]
The material for forming the corrosion-resistant layer 2b can be selected from not only chromium but also a chromium alloy, a compound of chromium with carbon, nitrogen, phosphorus, sulfur, oxygen, fluorine, or the like, or a folded material.
[0021]
The present invention is not limited to the cam follower described above, but can be applied to, for example, a rolling element in a jig for chucking a wafer in a semiconductor manufacturing facility, a component for ejecting a corrosive gas, a gate valve, and the like.
[0022]
【The invention's effect】
The present invention has the following effects.
[0023]
(1) Since the ion plating layer of the corrosion-resistant coating penetrates deep into the pinhole of the plating layer to cover and protect the base material surface, the problem of base material corrosion in the pinhole is eliminated. In addition to the pinholes , a plating layer having a thickness of 5 to 10 μm covers the base material surface and effectively protects the base material surface from a corrosive atmosphere. At the same time, since the ion plating layer covers the surface of the plating layer and functions as a kind of barrier layer for the plating layer, a good corrosion resistance effect of the plating layer is maintained for a long time.
[0024]
(2) Since a sufficient corrosion resistance can be obtained even when the ion plating layer is relatively thin, the processing time is extremely short as compared with the case where a thick coating layer is formed only by ion plating.
[0025]
(3) Among the rolling frictional surfaces of the rolling elements, the above-mentioned corrosion-resistant coating is formed on the surface exposed to the atmosphere, and the lubricating coating made of PTFE is formed on the surface not exposed to the atmosphere. It can be used in
[0026]
(4) The lubricating coating made of PTFE has a good lubricating action on the surface where rolling friction occurs, and also has an action of protecting the base material surface from reactive gases and the like. Corrosion is relatively unlikely to occur in portions that are not exposed to the atmosphere, and therefore, a sufficient corrosion resistance effect can be expected by a lubricating film of PTFE.
[0027]
(5) When wear deterioration due to rolling friction of the corrosion-resistant coating is expected, this can be prevented by forming a PTFE lubricating coating on the upper layer of the corrosion-resistant coating.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an embodiment of the present invention.
FIG. 2 is a diagram showing the results of a corrosion resistance comparison test.
FIG. 3 is an enlarged sectional view schematically showing a corrosion-resistant coating.
FIG. 4 is an enlarged sectional view schematically showing a chromium plating layer.
FIG. 5 is an enlarged sectional view schematically showing a case where a chromium plating layer is formed on an upper layer of a chromium ion plating layer.
FIG. 6 is an enlarged sectional view schematically showing a lubricating film of PTFE.
[Explanation of symbols]
2b Corrosion-resistant coating 2b1 Plating layer 2b2 Ion plating layer 1a Lubricating coating 2a Lubricating coating 3a Lubricating coating

Claims (2)

Chromium , chromium alloy, chromium-carbon compound or eutectoid, chromium-nitrogen compound or eutectoid, chromium-phosphorus compound on the surfaces exposed to the atmosphere among the surfaces that cause rolling friction of rolling elements Or forming a corrosion-resistant coating composed of a metal material selected from eutectoids, compounds or eutectoids of chromium and sulfur, compounds or eutectoids of chromium and oxygen, and compounds or eutectoids of chromium and fluorine. and, a lubricant film roll was formed element of PTFE on the surface not exposed to the atmosphere, the corrosion resistant coating, a plating layer having a thickness of 5~10μm which covers the base material surface, the upper layer of the plating layer A rolling element , comprising: an ion plating layer formed on the substrate . 2. The rolling element according to claim 1 , wherein a lubricating film made of PTFE is formed on the corrosion-resistant film.

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