Coating processes – With post-treatment of coating or coating material – Cooling
Patent
1983-11-16
1985-07-16
Beck, Shrive P.
Coating processes
With post-treatment of coating or coating material
Cooling
4273981, 4273984, 4273985, 427422, 427423, B05D 108
Patent
active
045296316
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to a method of depositing metallic and/or ceramic protective layer on a substrate by thermal projection of powdery materials.
In order to form hard protective layers of a relatively great thickness of metallic or ceramic materials, in general one deposits by thermal projection a number of superimposed elemental layers. The maximum thickness that can be achieved by such a method of a number of layers is however severely restricted and lies in practice between 0.3 and 0.5 mm. This is due in particular to the severe internal stresses which appear in such a protective layer and which can be reduced only partially by a suitable choice of the parameters of projection and whilst accepting an increased porosity of the layer. Furthermore, in particular when it is a question of ceramic materials deposited in a number of superimposed layers, an accumulation of heat occurs at the level of each elemental layer deposited, which leads to a high temperature difference between the substrate and the layer, this temperature difference increasing with each elemental layer and possibly reaching 150.degree. C. This is manifested in general by the formation of cracks and breakdown of the adhesion between the various elemental layers.
The invention proposes to provide a method which enables the application of layers of relatively great thickness, that is to say, in practice up to 3 mm, from materials having a high melting point or ceramic materials, whilst enabling layers of high density to be achieved, that is to say, of very low porosity.
For this purpose the method in accordance with the invention is characterized in that portions of a layer are deposited in succession in the form of adjacent juxtaposed strips, each having a height which corresponds substantially with the thickness of the layer which is to be formed, the substrate being kept during the process of deposition at a temperature less than 300.degree. C. and the difference in temperature between the substrate and a point on a portion of deposited layer, measured at the latest before the depositing of an adjacent portion of layer in the vicinity of the said point, being kept below 100.degree. C. Preferably local cooling is carried out at the level of each portion of layer deposited so that the temperature of the substrate does not exceed 200.degree. C. or even 100.degree. C. and that the said difference in temperature between the substrate and a point on a portion of deposited layer does not exceed 50.degree. or 60.degree. C. The cooling is preferably carried out by means of a device which includes outlet nozzles for cooling fluid, which are pin-point, annular, linear or fan-shaped, or else distributed over an area, the cooling fluids being preferably chosen from water, liquid carbon dioxide, nitrogen, and compressed air, and they may be applied in a combined manner.
The invention will be better understood in the light of the examples given below and of the description illustrated by the attached drawing in which:
FIG. 1 and 2 represent diagrammatically the structure of a protective layer achieved by the method in accordance with the invention.
The portions of layer in the form of strips 1, 2, 3, 4, etc. represented in FIG. 1 are deposited adjacently, side by side upon a substrate 5. Each portion of layer so deposited exhibits substantially the total height H of the layer which is to be formed. This is obtained by a suitable choice of the parameters of projection and of the relative motion between the projection apparatus and the substrate. For the formation of a layer 0.1 to 3 mm thick upon a cylindrical piece one chooses, for example, a constant circumferential velocity of the piece of the order of 5 to 60 m/min and a velocity of translation in the axial direction between 10.sup.-4 and 1 m/min. In the case of the depositing of such a layer upon a plane surface a relative motion between the piece and the projection apparatus is chosen which is effected discontinuously in steps the length of which lies between 0.1 and 20 mm, and a relativ
REFERENCES:
patent: 4191791 (1980-03-01), Lyons
patent: 4279709 (1981-07-01), McIntyre
patent: 4302482 (1981-11-01), Heck
patent: 4457948 (1984-07-01), Ruckle et al.
"Fachbeitrage", Steffens et al, Dusseldorf, BRD, Schweissen und Schneiden, 33(1981), Heft4; pp. 159-164.
Beck Shrive P.
Castolin S.A.
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