PROCEDURE AND APPARATUS FOR IMPROVING A PLASMA ACCELERATOR PLATING APPARATUS USED FOR DIAMOND PLATING

Abstract: A procedure and an apparatus for improving a plating apparatus used for diamond plating, in which plating process a first arc is started between a first electrode (1') and a firing element (5') placed in connection with it, another arc is started by means of the first one between the first electrode (1') and a second electrode (3) and a plasma spray formed from material released from the first electrode (1') is directed towards the material to be plated. That surface (10') of the first electrode from which material is released is abraded continuously during the plating process by an arrangement whereby the emitting surface and at least one grinding element (11', 5') placed in contact with it are brought into motion relative to each other.

Description: Procedure and apparatus for improving a plasma accelerator plating apparatus used for diamond plating. The present invention relates to a procedure and an apparat for improving a plating apparatus used for diamond plating, defined in the introductory part of claim 1. Diamond and diamondlike films have properties resembling tho of corresponding traditional diamonds. The first property hardness. Another significant mechanical property is-a l friction coefficient. The resistance to wear is also exce lent. Moreover, such a plating remains unchanged in all kno bases and acids. Thus, diamondlike platings and films are specially applicable for the coating of bodies subject to we and corrosion, such as non-lubricated bearings. Another n table feature is the high refraction coefficient of diamonds. WO publication 89/06708 presents an apparatus for diamo plating. The apparatus described in said publication works forming from carbon by means of a plasma accelerator a plas spray which is accelerated and deflected towards the bo under plating. The plasma accelerator has a cylindrica graphite cathode. The conducting rod serving as a firin device is placed inside the cathode. During plating, carbon in the form of charged ions and un charged atoms is released from the cathode. That surface o the cathode which releases carbon is subject to wear, whic may manifest itself e.g. in the form of microscopic hole appearing in the cathode surface, producing spongy structures At first, the arc is normally started from the cathode sur face, but with the progress of wear the starting of the ar occurs more and more frequently at the bottom of the holes Gradually the holes are covered up and the cathode become incapable of emitting a plasma pulse. For this reason, the cathode surface has to be smoothed out This is generally effected by removing the cathode an refacing it e.g. by turning. This is a complicated procedure SUBSTITUTESHEET Moreover, it is impossible to keep the plating apparatus running continuously for a long time. Typically, the cathode has to be refaced at a few hours' intervals. The object of the present invention is to achieve an improve¬ ment to 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 equivalent according to what is presented in the claims. 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 con- tinuous use of the plating apparatus as it does not require removal of the cathode for grinding or turning. In the following, the invention is described in detail by the aid of an example by referring to the attached drawing, in which fig. 1 presents a diamond plating apparatus as described in WO publication 89/060708 and fig. 2 an improvement accord¬ ing to the present invention. Using a plasma accelerator, a plasma spray is produced from carbon and accelerated towards the body to be plated. The plasma spray is deflected by means of a magnetic field, where¬ upon it hits the surface of the body under treatment. Both the plasma accelerator and the body under plating are placed in a vacuum. The plasma accelerator has a cylindrical cathode 1 consisting of solid carbon. The cathode is connected to the negative ter¬ minal 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 its one end is connected to the positive terminal of the first voltage source and to the other terminal of the first capacitor Cl . Connected to the terminals of capacitor C1 are also a diode D and an adjustable resistor R. The cathode 1 is partly and the anode 3 completely sur¬ rounded by the coil 4. Inside the cathode 1 is a conducting metal rod 5. Together with a second voltage source 6 and a second capacitor C2, the cathode 1 and the metal rod 5 form a firing circuit. The sec¬ ond voltage source 6 is adjustable. The cathode 1 is connected to the positive terminal of the second voltage source 6 and to one terminal of the second capacitor C2. The metal rod 5 is connected to the negative terminal of the second voltage source 6 and to the other terminal of the second capacitor C2. A sheet 7 is plated by means of the plasma accelerator as follows. From the first voltage source 2, the first capacitor C1 , connected in parallel with it, is charged. From the second voltage source 6, the second capacitor C2, which is connected in parallel with this voltage source, is charged until a spark-over occurs in the air gap between the cathode 1 and the metal rod 5, producing an arc in this air gap. This arc dis¬ charges the second capacitor C2 and strikes another arc be¬ tween the cathode 1 and the anode 3. In this situation, the cathode 1 begins to release carbon in the form of charged ions and uncharged atoms. The arc between cathode 1 and anode 3 causes the first capacitor C1 to be discharged. The arc is extinguished when the capacitor voltage falls below the level required for sustaining an arc. In this way, the carbon ions and atoms form a pulse-shaped plasma spray. The pulse duration is determined by the capacitance of capacitor Cl . Connected in parallel with the first capacitor C1 are a diode D, whose function is to eliminate the opposing voltage pro¬ duced at the terminals of the first capacitor Cl by the oscil¬ lating circuit formed by the first capacitor Cl and the wind- ing 4, and an adjustable resistor R protecting the diode D. The plasma spray is accelerated by the magnetic field gener¬ ated by the winding 4. Since the winding has a bent shape, the charged ions passing through the hole 8 in the anode 3 are de¬ flected by the magnetic field, whereas the uncharged particles advance straight ahead without encountering the sheet 7 and are thus separated from the charged ions. The sheet 7 to be plated is placed near that end of the winding 4 which is con¬ nected to the first voltage source 2 and first capacitor C1. Since the magnetic field generated by the winding deflects the charged ions but not the uncharged particles, the sheet to be plated is only bombarded by ions accelerated by the magnetic field. Fig. 2 presents an improvement to a diamond plating apparatus as provided by the invention. It has a solid barlike graphite cathode 1 ' . The firing electrode 5' is placed near the end face {emitting surface) 10' of the cathode, from which the carbon used for the plating is released. The firing electrode, whose lower surface is in contact with the cathode, is a rectangular body of a width nearly equal to the radius of the cathode. Placed on the plasma surface is also an abrading tool 11' provided with a sharp abrading surface which has a width slightly exceeding the radius of the cathode and is placed in contact with the end face (emitting surface) of the cathode. During plating, the cathode 1 ' is rotated about its longitudi- nal axis 12' by means of a rotating mechanism (not shown). Thus, the end face (emitting surface) 10' of the cathode is continuously ground by the abrading tool and therefore remains smooth all the time. The cathode surface is also abraded by the firing electrode. The rotating mechanism can also be pro- vided e.g. with hydraulic equipment designed to push the cathode forwards according to the wear of the plasma surface e.g. up to the abrading tool 11', which in this case also serves as a motion limiter. It is obvious to a person skilled in the art that different embodiments of the invention are not restricted to the ex¬ amples described above, but that they may instead be varied within the scope of the following claims.

Claims: CLAIMS 1. Procedure for improving a plating apparatus used for dia- mond plating, in which plating process a first arc is started between a first electrode (1 ' ) and a firing element (5' ) placed in connection with it, another arc is started by means of the first one between the first electrode (1 ' ) and a second electrode (3) and a plasma spray formed from material released from the first electrode (1 ' ) is directed towards the material (7) to be plated, characterized in that that surface (10') of the first electrode from which material is released is abraded during the plating process by using an arrangement whereby the emitting surface and at least one grinding element (11', 5' ) placed in contact with it are brought into motion relative to each other. 2. Procedure according to claim 1 , characterized in that the motion is a rotary motion. 3. Apparatus for improving a plating apparatus used for dia¬ mond plating, designed for implementing the procedure of claim 1 , said plating apparatus being provided with electrodes (1 ' ,3) and a firing element (5' ), a first arc being started between said first electrode ( '1 ) and the firing element (5' ) placed in connection with it, said first arc being used to start a second arc between the first electrode (1 ' ) and the second electrode (3), in which apparatus a plasma spray formed from material released from the first electrode (1 ' ) is directed towards the material (7) to be plated, characterized in that the apparatus is provided with at least one abrading element (11 ' ,5' ) by means of which that surface (10') of the first electrode from which material is released is abraded during the plating process by an arrangement whereby the emitting surface and at least one grinding element (11', 5' ) placed in contact with it are brought into motion relative to each other. 4. Apparatus according to claim 3, characterized in that it has a rotating mechanism connected to the first electrode (1 ' ) and used to rotate said electrode, and that the grinding ele¬ ment is fixedly mounted. 5. Apparatus according to claim 3, characterized in that the grinding element is an abrading tool (11 ') or equivalent. 6. Apparatus according to claim 3, characterized in that the grinding element is the firing element (5'). 7. Apparatus according to claim 3, characterized in that it is provided with means for compensating the wear of the first electrode, said compensating means moving the first electrode according to the degree of wear so that the emitting surface remains essentially at the same location.

Inventors: ANTTILA ASKO, KOSKINEN JARI, ANTTILA, ASKO, KOSKINEN, JARI
Applicants: ANTTILA ASKO, KOSKINEN JARI, ANTTILA, ASKO, KOSKINEN, JARI
Application year: 1992
Main classification: H05H1
IPC codes: C23C14, H01J37, H05H1