Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2001-08-29
2003-08-05
Schwartz, Christopher P. (Department: 3683)
Bearings
Rotary bearing
Antifriction bearing
C148S318000
Reexamination Certificate
active
06601993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rolling bearing device such as rolling bearing, linear guide and ball thread and particularly to a rolling bearing device having an excellent corrosion resistance and durability which can be used also in usage requiring non-magnetic properties.
2. Description of the Related Art
In general, a rolling bearing device such as rolling bearing, linear guide and ball thread makes a rolling movement by the external member, internal member and rolling elements constituting the rolling bearing device. Thus, the external member, internal member and rolling elements are repeatedly subjected to contact stress. Therefore, the material constituting these members is required to be hard, withstand load and exhibit a prolonged rolling fatigue life and a good abrasion resistance against slippage.
Therefore, as the material constituting these members there is normally often used SUJ2 of JIS as bearing steel, SUS440C of JIS or 13Cr martensite-based stainless steel as stainless steel or steel corresponding to SCR420 or SCM420 of JIS as case-hardened steel.
These materials are repeatedly subject to shearing stress under a high face pressure. In order to obtain required physical properties such as resistance to shearing stress and prolonged rolling fatigue life, bearing steel is subjected to hardening and tempering to have a surface hardness of HRC of from 58 to 64before use. Case-hardened steel is subjected to carburizing or carbonitriding followed by hardening and tempering to have a surface hardness of HRC of from 58 to 64 before use.
On the other hand, an apparatus utilizing magnetic field or apparatus, which shows a drop in measuring accuracy under the influence of magnetic field such as semiconductor producing machine, liquid crystal producing machine, apparatus utilizing electron rays, medical inspection apparatus and linear motor car, is subject to disturbance of ambient magnetic field when driven by rotation or the like or inhibition of smooth driving if the driving portion is formed by a magnetic material. Therefore, a rolling bearing device for use in the foregoing purposes needs to be formed by a non-magnetic material.
A rolling bearing device is used in various atmospheres. For example, the rolling bearing device to be used in a corrosive atmosphere as in facilities for the production of liquid crystal and semiconductor or food machine is required to have an excellent corrosion resistance. However, when the rolling bearing device to be used in such a corrosive atmosphere is formed by the foregoing bearing steel, the resulting rolling bearing device runs short of corrosion resistance and thus early undergoes rusting or elution to end its life. Accordingly, the rolling bearing device to be used in the foregoing corrosive atmosphere is often formed by stainless steel, which is excellent in corrosion resistance.
Stainless steels are roughly divided into five groups, i.e., austenite-based stainless steel, ferrite-based stainless steel, austenite-ferrite binary stainless steel, martensite-based stainless steel, precipitation hardening stainless steel. A rolling bearing device is subject to great shearing stress or abrasion at the contact site of the external member or internal member with the rolling elements. Therefore, the rolling bearing device is mainly made of martensite-based stainless steel, which is hard and excellent in abrasion resistance. SUS440C, which is hardest in these martensite-based stainless steels, is often used. However, martensite-based stainless steel such as SUS440C has a deteriorated corrosion resistance as compared with other stainless steels and thus is not necessarily on a satisfactory level for use in a corrosive atmosphere.
On the other hand, austenite-based stainless steel, ferrite-based stainless steel, etc. are excellent in corrosion resistance but do not have sufficient hardness required for rolling bearing device and thus sometimes leave something to be desired in durability such as abrasion resistance and rolling fatigue life.
Therefore, in the case where sufficient corrosion resistance is required, martensite-based stainless steel or case-hardened steel to be used is subjected to carburizing or carbonitriding, and then plated with hard Cr or coated with raydent fluoride or other various corrosion-resistant films to have an improved corrosion resistance. However, since the coating film which has been deposited discontinuously to the base metal can easily come off, the resulting rolling bearing device can leave something to be desired in corrosion resistance when used in a corrosive atmosphere.
On the other hand, as the non-magnetic material there has heretofore been normally used a beryllium-copper alloy, ceramic or the like. However, the beryllium-copper alloy can be easily oxidized, and its oxidation product is harmful. Thus, the use of the beryllium-copper alloy has become more and more difficult. Further, since the beryllium-copper alloy has a hardness HRC as low as 40, the resulting rolling bearing device leaves something to be desired in durability.
Ceramic is disadvantageous in that it is very expensive and can be very hardly produced in a large-sized or thin form.
Therefore, in recent years, with the yearly growing demand for higher quality and reliability, Mn—Cr—V or Mn—Cr—Ni—V precipitation hardening austenite non-magnetic steel has been used more and more as a non-magnetic material substitute for beryllium-copper alloy or ceramic. However, these materials can be very difficultly worked and thus require a high degree working technique. In addition to these disadvantages, these materials are disadvantageous in that they attain a hardness HRC of about 45 at maximum and leave something to be desired in corrosion resistance.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the foregoing problems with the conventional rolling bearing device and provide a rolling bearing device excellent in both corrosion resistance and durability which can be used also in usage requiring non-magnetic properties.
Paying their attention to austenite-based stainless steel, which is particularly excellent in corrosion resistance and undergoes work hardening when subjected to plastication such as cold working, among the foregoing stainless steels, the inventors made extensive studies to find a rolling bearing device which satisfies requirements for both corrosion resistance and durability and thus can be used in a corrosive atmosphere and also in usage requiring non-magnetic properties.
As a result, it was found that when reduction working (plastication) attaining a percent area reduction of equal or more than 25% is conducted so that the constituent members made of austenite-based stainless steel undergo work hardening to have a surface hardness HRC of equal or more than 35 at an intermediate step during the working of predetermined austenite-based stainless steel into desired shape to prepare constituent members of rolling bearing device such as external member and internal member, the resulting rolling bearing device can be secured with sufficient durability as well as with drastically improved corrosion resistance as compared with those made of the conventional martensite-based stainless steel.
The rolling bearing device according to the invention comprises an external member, an internal member, and a plurality of rolling elements rollably provided interposed between the external member and the internal member, wherein at least one of the external member and the internal member is formed by an austenite-based stainless steel and has a surface having a hardness HRC of equal or more than 35 formed by plastication that attains a percent area reduction of equal or more than 25%.
A rolling bearing device comprising members having the foregoing arrangement exhibits an extremely high surface hardness and hence an excellent durability. Further, since these members are formed by an austenite-based stainless steel, the resulting rolling bearing device exhi
NSK Ltd.
Schwartz Christopher P.
Sughrue & Mion, PLLC
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