Chemistry: electrical and wave energy – Processes and products – Vacuum arc discharge coating
Patent
1994-11-09
1996-05-21
Weisstuch, Aaron
Chemistry: electrical and wave energy
Processes and products
Vacuum arc discharge coating
20429841, 427580, C23C 1432
Patent
active
055185967
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a plating apparatus used in a diamond plating process and a method of operating the plating apparatus.
BACKGROUND OF THE INVENTION
Diamond and diamondlike platings and films have a number of properties resembling those of corresponding traditional diamonds. The first property is hardness. Another significant mechanical property is a low friction coefficient. The resistance to wear is also excellent. Moreover, such a plating or film remains unchanged in all known bases and acids. Thus, diamondlike platings and films are especially applicable for the coating of bodies subject to wear and corrosion, such as non-lubricated bearings. Another notable feature is the high refraction coefficient of diamonds.
WO publication 89/06708 presents an apparatus for diamond plating. The apparatus described in this publication works by forming from carbon by means of a plasma accelerator a plasma spray which is accelerated and deflected toward the body to be plated. The plasma accelerator has a cylindrical graphite cathode, A conducting rod serving as a firing device is placed inside the cathode.
During plating, carbon in the form of charged ions and uncharged atoms is released from the cathode. The surface of the cathode which releases carbon is subject to erosion, which may manifest itself, e.g., in the form of microscopic holes appearing in the cathode surface, producing spongy structures. At first, the arc is normally started from the cathode surface, but with the progress of erosion the starting of the arc occurs more and more frequently at the bottom of the holes. Gradually the holes are covered up and the cathode becomes incapable of emitting a plasma pulse.
For this reason, the cathode surface has to be smoothed out. This is generally accomplished by removing the cathode and refacing it, e.g., by turning. This is a complicated procedure, however. Moreover, it is impossible to keep the plating apparatus running continuously for a long time. Typically, the cathode has to be refaced every few hours.
SUMMARY OF THE INVENTION
The object of the present invention is to achieve an improvement in diamond plating equipment using known techniques. The procedure of the invention for improving a plating apparatus is characterized in that the plasma surface of the cathode is continuously ground by means of a grinding blade or other equivalent grinding device.
Using the procedure of the invention, it is possible to achieve a decisive improvement in the usability of a diamond plating apparatus. The procedure of the invention allows continuous use of the plating apparatus as it does not require removal of the cathode for grinding or turning.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention is described in detail by the aid of an example by referring to the attached drawings, in which:
FIG. 1 presents a diamond plating apparatus as described in WO publication 89-06708; and
FIG. 2 presents a diamond plating apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Using a plasma accelerator, a plasma spray is produced from carbon and accelerated toward the body to be plated. The plasma spray is deflected by means of a magnetic field, whereupon it hits the surface of the body under treatment. Both the plasma accelerator and the body being plated are placed in a vacuum.
Referring to FIG. 1, the plasma accelerator has a cylindrical cathode 1 consisting of solid carbon. The cathode is connected to the negative terminal of a first voltage source and to one terminal of a first capacitor C1. A discoidal anode 3 with a hole in the middle is connected to a cylindrical coil 4 made of copper wire. The coil has a bent shape and one end thereof is connected to the positive terminal of the first voltage source and to the other terminal of the first capacitor C1. Also connected to the terminals of capacitor C1 are a diode D and an adjustable resistor R. The cathode 1 is partly surrounded by the coil 4 and the anode 3 is completely surrounde
REFERENCES:
patent: 4849088 (1989-07-01), Veltrop et al.
patent: 5078848 (1992-01-01), Anttila et al.
Gilmour, A. S. et al., "Pulsed Metallic-Plasma Generators", Proceedings of the IEEE, vol. 60, No. 8, Aug. 1972, pp. 977-991.
Anttila Asko
Koskinen Jari
Kubovcik Ronald J.
Suomen Itsenaisyyden Juhlarahasto Sitra
Weisstuch Aaron
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