Plasma treatment of metal surface

By production process (manufacturing, processing, storing), contamination of metal parts surface takes place, which is undesirable and harmful.

Metal surface treatment is decontamination of metal surface to the definite purity level. Surface treatment can be carried out by mechanical, physical, chemical, physicochemical and chemicothermal methods.

During mechanical treatment, contamination removal is achieved by mechanical wiping, scraping, milling, exposure to air or water jet, to solid particles (iron shot, glass beads and etc.). Mechanical treatment efficiency can be improved by application of electrically or pneumatically operated tools (wire brushes) and by increase of air and water jets' pressure to 5-63 MPa. Among the advantages of mechanical treatment process are low energy intensity, versatility, ability to remove various contaminations and simpleness of materials recycling, manual labour usage serves as a disadvantage.

Physical treatment mechanism consists in dissolution of contaminants with the help of various solvents and in their subsequent removal from the workpiece surface. Intensification of the treatment process is achieved by placing of ultrasonic vibration into the treatment area, as well as by jet machining and vapor cleaning. As advantages of physical treatment method, high speed of treatment and its quality, waste-free production, ability to make treatment automated and mechanized should be noted. At the same time this method is characterized by occupational hazard, waste disposal complexity, limitation on contamination types.

Physicochemical treatment consist in dissolution, emulsification and chemichal destruction of contaminations (application of solvent and emulsifying agents along with rinsing in synthetic detergent solutions). The ability to increase treatment speed and quality lies in moving (oscillating, rotation) of workpiece during treatment. Among the advantages of physicochemical method are high treatment speed and quality, low energy intensity, moderate-temperature processing (20-500C), ability to make treatment automated and mechanized, among the disadvantages are limitation on contamination types, occupational hazard and existence of waste products.

Chemicothermal method consists in chemichal destruction of contaminations in flame or in alkaline melt at high temperatures (400-4500C), as well as in changing of contamination stractural and volume parameters. Mechanical treatment efficiency can be improved by optimization of alkaline melt composition and process automation. The pluses of this method are high treatment speed and quality, ability to make treatment automated, among the minuses are limitation on contamination types, high energy intensity, parts' deformation and destruction are also possible.

In the treatment mode, electrolyte-plasma technology provides productive surface cleaning of high quality and can remove almost any type of contamination: mineral and organic rust-preventing greases, rust, scale, residual galvanic and lacquer coatings, enamel insulation from electrical wires. Cleaning time is 0,1-0,5 minutes. Along with contamination removal a corrosion-proof coating is generated. Anodic electrolyte-plasma treatment process differs from anodic electrolysis one. Liquid electrolyte does not have contact with a workpiece surface because of steam-gas cover formation, which isoltates the surface from electrolyte and leads to intensive chemical and electrochemical reactions between the workpiece material, anode and electrolyte vapor. This results in anodic oxidation of the metal surface along with a uniform chemical oxide etching. Etching has an effect first and foremost on microroughnesses, where an oxide film is thinner. Furthermore, due to the increased electric intensity in the gap between a part,steam-gas cover and electrolyte, it is the microrelief protuberances that have exposure to rounding, which leads to a decrease of workpiece surface roughness value.

The method is based on the conditions occurring at the surface of electrolytic cell electrodes by using high-voltage direct current. The process provides a complex physical and chemical effect on the material and surface of a workpiece.

The proposed method can be illustrated by defenite examples.

Copper moisture-resistant and heat-resistant enameled wires (series 0.4 and 1.0 micrometers), insulated with lacquer composed of polyesters and polyvinyl enamels, were processed. The processing was carried out in order to make wires ready for soldering and consisted in the removal of insulating enamel and wire surface cleaning.

While using the proposed method, electro-hydrodynamical mode of electrolytic processing is applied. During this mode, the stable steam-gas cover prevents heating of a workpiece (heating reduces solderability of a copper wire and requires additional operations for oxide removal). Firstly, some not a great wire area must be cleaned. After a workpiece being immersed in the electrolyte, a steam-gas cover is generated on the area, where insulation is absent. Because of high temperature in electrical discharge channels, running through the cover, insulation burning takes place. As the surface part, having carbonized insulation, becomes conductive, a steam-gas cover is also generated on it. In the process removal of the residual insulation from the wire and wire surface cleaning take place.

Fats and oils emerging on the electrolyte surface must be periodically removed (pouring, circulation and etc.). For solid waste precipitation (abrasives, rust, dross and etc.) special pan is set.

When galvanic coating is applied with failure or appeared to be defective by production, it must be taken off before recurring galvanic treatment. Electrolyte-plasma technology allows to take such coating off less than for 1 minute. Processing time depends mainly on the thickness and type of a galvanic coating. However, the total time usually does not exceed 1 minute. Because of galvanic coating process being specific, mode of coating removal must be selected peculiarly for each instance.