Needle roller bearing

Abstract

The object is to efficiently subject steel retainers of needle roller bearings to heat treatment in a short period of time even in small-lot production using compact treatment facilities, thereby producing retainers having improved resistance to wear and surface damage and high in fatigue strength and fracture strength as a whole. The steel retainer 3, which retains needle rollers 2, is formed from a steel plate containing 0.15 to 1.10% by mass of carbon. After forming, the steel plate is subjected to induction heat treatment comprising induction hardening and induction tempering. Such heat treatment can be carried out efficiently in a short period of time, using compact treatment facilities, even in small-lot production. The retainer 3 thus formed is sufficiently resistant to wear and surface damage, and is high in fatigue strength and fracture strength as a whole.

Description

TECHNICAL FIELD [0001] The present invention relates to a needle roller bearing including needle rollers as rolling elements. BACKGROUND ART [0002] A steel retainer is used to retain needle rollers of many of radial type needle roller bearings, in which the needle rollers are arranged along a cylindrical surface having a central axis, and thrust type needle roller bearings, in which the needle rollers are arranged around a central axis so as to extend in radial directions. Some of such needle roller bearings, of which the needle rollers have a small diameter, include only the retainer besides the rolling elements, and others further include at least one bearing ring selected from inner and outer bearing rings. Because needle roller bearings of either of the above types are thin compared to rolling bearings including other rolling elements, but are still sufficiently large in load capacity, by using such bearings, it is possible to reduce the size of devices and machines such as indu...

AI Technical Summary

Benefits of technology

[0020] By subjecting the steel retainer of the needle roller bearing according to the present invention to induction heat treatment comprising at least induction hardening over the entire area and entire thickness thereof, using induction heat treatment facilities which need no adjustment of atmosphere, are compact in size and can be used for small-lot production, it is possible to efficiently handle such steel retainers of needle roller bearings, which are typically small in size and thickness, during heat treatment thereof. The retainers thus obtained have improved resistance to wear and surface damage and high in fatigue strength and fracture strength as a whole. Because induction heat treatment uses electricity, a clean energy source, the load on the global environment is minimum.

Problems solved by technology

A long time is also necessary to diffuse carbon and nitrogen.

This increases the number of parts in one lot, which in turn increases the number of unfinished parts, thereby increasing the lead time.

Moreover, it is necessary to dispose of waste oil such as hardening oil, which increases the load on the global environment to an unignorable level.

A long time is needed to grow such films to a sufficient thickness.

As with the abovementioned surface heat treatment, the number of parts in one lot increases, so that the number of unfinished parts increases, thus increasing the lead time.

Also, it is necessary to dispose of waste liquid such as plating liquid, which increases the load on the global environment.

If the treatment facilities stop due to blackout or any other trouble during surface heat treatment or surface chemical treatment for surface modification, a large number of retainers being treated will become defective.

A long time and a huge cost are required to recall such defective retainers and restart the facilities.

But if such surface hardening is applied to a retainer of a needle roller bearing as a kind of roller bearing disclosed in Patent document 2, because such a retainer has a large number of pockets, it takes an extremely long time to harden only the surface thereof near the respective pockets.

Further, because the bridges defining the pockets of such a retainer are subjected to compressive stress and tensile stress due to skewing when the needle rollers alternately move forward and backward relative to the retainer, it is difficult to increase the fatigue strength and fracture strength of the entire retainer by surface hardening alone.

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