Coating processes – Roller applicator utilized
Patent
1977-09-30
1989-02-21
Beck, Shrive
Coating processes
Roller applicator utilized
4273763, 428937, 428627, B05D 110
Patent
active
048063940
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for producing a wear-resistant layer in accordance with the pre-characterizing clause of claim 1.
The German patent specification No. DE 2208070 describes a method of this kind, according to which a metal base is provided with a thin, wear-resistant layer of a thickness of at most about 0.635 mm, the spraying being effected by plasma flame-spraying and the material used having a grain size in the order of magnitude of -44/+88 .mu.m, for example.
In this known method it is important that the layer is drastically chilled during the spraying-on thanks to the cooling action of the base body, thus creating a micro-structure consisting of titanium-carbide grains which are dispersed in a base matter, the base matter being formed of an austenite conversion product containing martensite. This leads already without further heat treatment to a relatively hard layer in which, due to the plasma spraying process, rounded titanium-carbide grains are present.
However, the layers which can be produced in this way are very limited in their thickness, preferably thicknesses from 0.381 mm to 0.254 mm and of 0.127 mm are stated, since the mentioned structure would otherwise lead to very high internal stress.
The small thickness corresponds to an equally limited life. Besides, the possibilities of mechanical machining are very narrowly limited and the elasticity of the layer is extremely low due to the small grain size of the spraying material and the corresponding structure built up of smallest lamellae.
Wear resistant layers which were produced by flame-spraying without fusing and which have a high hardness thanks to the incorporation of hard materials ("Hartstoffe") such as carbides, silicides, borides, etc. or which consist of hard alloys, appear to be highly sensitive in respect to the formation of cracks due to the occurrence of internal stress in the layer. The thickness of the layer which can be obtained is therefore very limited.
On the other hand, the use of self-fluxing alloys which attain a high hardness after fusing, leads during the fusing process to excessively high temperatures for many applications, which temperatures have very detrimental effects on the base material with respect to distortion, embrittlement and other influences.
The object of the invention is to provrde a method for producing wear resistant layers of great hardness, by which layers of substantially longer life than that of the known layers can be produced and which, furthermore, allows mechanical machining after the spraying operation and is relatively free of problems with respect to internal stress in the layer.
This is attained, according to the invention, by the features of the method as set forth in the appended claims. Claims 2 to 10 describe particular embodiments of the method according to the invention.
It has been found, surprisingly, that when titanium carbide in a metallic matrix is applied by oxy-acetylene flame-spraying without subsequent fusing, a layer is first obtained which has a free-machining property and which is capable of hardening by a subsequent heat treatment at relatively low temperature, thus providing a hardness of 500 to 700 Hv in the final state.
In contrast with the mentioned method which is carried out by plasma flame-spraying, in the present method the material of the layer is molten practically homogenously in the oxy-acetylene flame during the spraying process, with the titanium carbide being dissolved in the matrix alloy. The thus obtained layer of austenitic nature is free-machinable. In the following heat treatment the titanium carbide is then precipitated in very fine grains and uniform distribution.
The layer has a lamellar structure with relatively big lamellae, in accordance with the particle size, so that a greater elasticity of the layer is obtained. Furthermore it is to be noted that the coefficient of expansion of the layer is very near the coefficient of expansion of the matrix alloy.
As a consequence, with the present method there appears practically no
REFERENCES:
patent: 3617358 (1971-11-01), Dittrich
patent: 3779720 (1973-12-01), Ellis et al.
patent: 3896244 (1975-07-01), Ellis et al.
patent: 3941903 (1976-03-01), Tucker
patent: 4395279 (1983-07-01), Houck
Beck Shrive
Castolin S.A.
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