Production method for sintered valve guide

Abstract

A production method for a sintered valve guide includes preparing a raw powder which is primarily made of an iron powder and which includes at least a copper alloy powder and a graphite powder. The production method further includes compacting the raw powder into a green compact having an approximately cylindrical shape and sintering the green compact at 950 to 1050° C. The iron powder includes particles, which do not pass through a sieve of 240 mesh, at not less than 40 mass %, and not less than 70 mass % of the powder particles have not more than 0.5 of degree of circularity.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]The present invention relates to a valve guide that may be used for an intake valve or an exhaust valve in an internal combustion engine. Specifically, the present invention relates to a production method for a sintered valve guide that is produced by a powder metallurgical method and has high strength.[0003]2. Background Art[0004]A valve guide may be press fitted in a cylinder head of an engine and has an inner circumferential surface for slidably maintaining a valve that may be driven so as to take fuel gas into a combustion chamber of an internal combustion engine and to exhaust combustion gas. Therefore, the valve guide is required to have high wear resistance so as to not be greatly worn in sliding on the valve and is also required to have good sliding characteristics so as to not wear the valve of the corresponding sliding member.[0005]Valve guides made of a cast iron are generally used, but valve guides have been produc...

AI Technical Summary

Benefits of technology

[0012]Accordingly, an object of the present invention is to provide a production method for improving mechanical strength of a sintered valve guide including a copper alloy phase and a free graphite phase by sintering at 950 to 1050° C.

Problems solved by technology

The machinability of this material is improved but is still inferior to the machinability of a member made of a cast iron, and therefore, further improvement of the machinability of this material is required.

Moreover, in accordance with a trend toward increasing the output from internal combustion engines in recent years, conditions in an internal combustion engine has been severe, whereby a bending load applied to a valve guide is increased.

Therefore, mutual diffusion between iron powder particles is not sufficiently performed and mechanical strength is low in these materials compared with ordinary sintered materials for structural members, which are sintered at 1080 to 1200° C. Consequently, improvement of the mechanical strength is required for coping with the above-described increase in the bending load applied to a sintered valve guide.

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