Bearings – Bearing-surface treatment
Reexamination Certificate
1999-09-17
2001-09-18
Hannon, Thomas R. (Department: 3682)
Bearings
Bearing-surface treatment
C384S492000
Reexamination Certificate
active
06290398
ABSTRACT:
This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP98/01563 which has an International filing date of Apr. 2, 1998, which designated the United States of America.
1. Technical Field of the Invention
This invention relates to a ball-and-roller bearing. More particularly, it is a bearing which is suitable for use with those parts of which a high level of lubrication is required, including the crank journal of a two-cycle, or kerosene engine, a ship, the cylinder head of a four-cycle engine, a supercharger such as a turbocharger, and the actuator for the hydraulic control of a hydraulic suspension. It can, of course, be used for supporting various other rotating parts, too.
2. Background of the Related Art
A common ball-and-roller bearing has surfaces hardened by heat treatment on e.g. the tracks of its inner and outer races and its balls. The inner and outer races and balls are usually made of a bearing steel designated as SUJ by JIS, hardened by lowering their temperature from the range of 900-930° C. to an appropriate level, and tempered at a temperature of 160-180° C. depending on the temperature prevailing in the environment in which the bearing will be used.
The hardening treatment for a ball-and-roller bearing as stated above is, however, likely to bring about a large amount of strain and thereby a large dimensional variation due to the transformation of its structure from martensite to austenite and a large temperature variation. The dimensional variation calls for the grinding and ultrafinish treatment of the parts as heat treated, and these additional steps add to the cost of bearing manufacture. It is impossible to employ a very high tempering temperature, since it is necessary to keep the amount of residual austenite at an appropriate level to prevent any dimensional change, or hardness reduction at the temperature prevailing in the environment in which the bearing is used, and it is, therefore, conventions usual to use a ball-and-roller bearing only at a temperature up to about 170° C.
A high temperature bearing steel, such as M50 according to AISI or SKH4 according to JIS, gives a ball-and-roller bearing of higher grade which can withstand use at a temperature up to about 400° C., but as it is considerably more expensive than SUJ according to JIS, the bearing is so expensive that its use is limited to a special case.
There is also known a bearing having surfaces covered with hard chromium coating, but their coating is likely to peel easily off the track surfaces of the races.
It is, therefore, an object of this invention to provide a ball-and-roller bearing which is less expensive than any known product and yet can withstand use at a temperature at which it has hitherto been possible to use only a product made of a material of higher grade.
DISCLOSURE OF THE INVENTION
[Structural Features]
(1) A ball-and-roller bearing according to a first aspect of this invention has at least one of its members made of a metallic material containing an alloying element having a high affinity for nitrogen, and having a nitrided layer on its surface free from any oxide.
(2) According to a second aspect of this invention, the metallic material as stated at (1) above is a carburizing or nitriding steel.
(3) According to a third aspect of this invention, the metallic material as stated at (1) above is a stainless steel.
(4) According to a fourth aspect of this invention, the nitrided layer as stated at (1) above includes a compound layer formed as a film on the surface and a diffusion layer formed from nitrogen diffused under the compound layer.
(5) According to a fifth aspect of this invention, an oxide film is formed on the nitrided layer.
[Functions]
According to an essential feature of this invention, a nitrided layer is formed on the surface of a metallic material which is generally considered as being of low grade, after oxide has been removed from its surface, so that even such a material may have a hardened surface and be useful as a substitute for a common material for the known ball-and-roller bearing (hardened bearing steel of the SUJ series according to JIS), or a material of higher grade (high-temperature bearing steel, such as M50 according to AISI or SKH4 according to JIS). Examples of the metallic material on which the nitrided layer is formed, or the metallic material containing an alloying element having a high affinity for nitrogen are carburizing steel (e.g. of the SCM series according to JIS), nitriding steel (e.g. of the SACM series according to JIS) and stainless steel (e.g. of the SUS series according to JIS).
The nitrided layer formed on the surface of carburizing or nitriding steel after the removal of oxide therefrom gives it a surface hardness which is comparable to that of a common material (bearing steel of the SUJ series according to JIS as hardened by heat treatment), and the nitrided layer formed on the surface of stainless steel after the removal of oxide therefrom gives it a surface hardness which is comparable to that of a material of ultrahigh grade (e.g. a sintered ceramic material consisting mainly of silicon nitride).
Moreover, as the nitrided layer is formed on the surface of the metallic material not directly, but after oxide has been removed therefrom, nitrogen undergoes a higher rate of diffusion, and the nitrided layer is formed at a lower temperature in a shorter time, so that the thermal straining of the material is less likely to occur. As a result, it is possible to omit any after-treatment, such as grinding, that has been required of the known product of a common material, and it is, therefore, possible to achieve a reduction of manufacturing cost. The nitrided layer can be formed at a still lower temperature in a still shorter time on the metallic material containing an alloying element having a high affinity for nitrogen.
Thus, this invention makes it possible to give an inexpensive metallic material of low grade the hardness which is comparable to that of any known material of common or high grade, and accomplish its hardening treatment by a simpler process, and thereby at a lower cost.
The oxide formed on the nitrided layer on a bearing according to the fifth aspect of this invention gives its surface a still higher level of corrosion resistance. [Advantages]
According to this invention, any of the members of a ball-and-roller bearing is made of a metallic material of low cost and grade instead of any known material of common or high grade, and a nitrided layer is formed on its surface after the removal of oxide therefrom, and gives it a higher level of properties which is comparable to that of any known material of common or high grade. As a result, the bearing is inexpensive, and yet has excellent properties, including wear, heat and corrosion resistances, which make it suitable for use under harsh conditions.
The removal of oxide from the surface of the metallic material enables nitrogen to undergo a high rate of diffusion to form the nitrided layer. Therefore, the nitrided layer can be formed at a low temperature in a short time to a relatively large depth as compared with what can be formed on any known material of common grade, and while the thermal straining of the material is less likely to occur, the nitrided layer is of high density and smoothness, and does not require any grinding, or other after-treatment that has hitherto been necessary, but enables the bearing to be manufactured at a lower cost.
The oxide formed on the nitrided layer on a bearing according to the fifth aspect of this invention gives it a still higher degree of corrosion resistance and makes it suitable for use in a corrosive environment.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modif
Fujiwara Hideki
Kimura Haruo
Birch & Stewart Kolasch & Birch, LLP
Hannon Thomas R.
Koyo Seiko Co. Ltd.
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