Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Patent
1993-05-07
1995-08-08
Bueker, Richard
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
118715, 118725, C23C 1600
Patent
active
054395259
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a device for coating, by means of gas diffusion, hollow workpieces made of heat-resistant alloys, such as Ni, Co or Fe base alloys, whose outer and inner surfaces are connected with one another by bores. The device comprises a container which has at least one gas supply line and one gas removal line. The gas removal line is connected behind the inner surfaces of the workpiece to be coated, and has a donor metal in the form of a donor metal body which completely surrounds the outer and inner surfaces of the workpiece to be coated while maintaining a gap.
From U.S. Pat. No. 2,910,382, a process is known for producing surface alloys on metal components. For this purpose, a donor metal in the form of a sintered body is placed at a distance opposite the component surfaces to be coated and, while the inner surfaces are also coated, the hollow spaces of the component are filled with sintered bodies made of donor metal so that a sintered body is situated also opposite the component surfaces in the hollow spaces.
This known process has the disadvantage that inner surfaces which are inaccessible or have a complex design cannot be coated because it is not possible to introduce a donor metal body into the pertaining hollow spaces of the component.
From the European Patent Document EP 0349420, a device is known for the simultaneous coating by gas diffusion of outer and inner surfaces. In the case of this device, the components to be coated are arranged in the upper area of a box. In the lower area, the box has a carrier gas supply line and a carrier grid for receiving an activator powder and donor metal granulates. This device has the disadvantage that forming heavy donor metal gases must rise from the donor metal granulates to the components to be coated, in which case, corresponding to the barometric height formula, a dilution of the donor metal gases occurs in the vertical direction which disadvantageously results in differences in layer thicknesses on the components as a function of their geodetic height with respect to the donor metal. In addition, the device has the effect that the inner surfaces of the component, with an increasing distance of connecting bores between outer and inner surfaces, have smaller coating thicknesses until the coating in the component interior is completely absent.
It is an object of the present invention to provide a device for coating by gas diffusion by which a uniform coating of a hollow component on the outer and inner surfaces is ensured, particularly in the case of long, narrow and inaccessible hollow spaces.
This object is achieved by a device according to the present invention which has the above-described characteristics and in the case of which workpiece holders are arranged in the container. The container holds the workpieces at a geodetically low height with respect to a donor metal. The hollow spaces are free of donor metal, and the gas removal line is constructed as an overflow device or as a front-connected siphon whose overflow level is positioned at the height of the uppermost surface of the workpiece to be coated.
This device has the advantage that, in the interior of the component as well as on the outside, coating thicknesses are obtained which have low thickness fluctuations. By means of the complete surrounding of the component with donor metal, while a gap to the donor is maintained, the surface of the component is supplied with a constantly high concentration of donor metal gas without any diluting effect of the donor metal gas as a result of its high carrier gas proportion, and without donor metal particles in the interior of the component so that the danger of a clogging of the hollow spaces and of the bores between the outer and inner surfaces is avoided.
Using the workpiece holders, which hold the workpieces at a geodetically low height with respect to the donor metal, the components are advantageously held in an inexhaustible high-concentration donor metal gas source. The gas source forms as
REFERENCES:
patent: 2910382 (1959-10-01), Vulliez
Peichl Lothar
Walter Heinrich
Bueker Richard
MTU Motoren - und Turbinen-Union Muenchen GmbH
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