Electropolishing is an electrochemical process similar to, but the reverse of, electroplating. The electropolishing process smooths and streamlines the microscopic surface of a metal object such as 304, 316, and the 400 series stainless steel. As a result, the surface of the metal is microscopically featureless, with not even the smallest speck of a torn surface remaining.
In electropolishing, the metal is removed ion by ion from the surface of the metal object being polished. Electrochemistry and the fundamental principles of electrolysis (Faraday's Law) replace traditional mechanical finishing techniques, including grinding, milling, blasting and buffing as the final finish. In basic terms, the metal object to be electropolished is immersed in an electrolyte and subjected to a direct electrical current. The object is maintained anodic, with the cathodic connection being made to a nearby metal conductor. During electropolishing, the polarized surface film is subjected to the combined effects of gassing (oxygen), which occurs with electrochemical metal removal, saturation of the surface with dissolved metal and the agitation and temperature of the electrolyte.
Zinc plating is identical to electro-galvanizing in principle because both are electro-deposition processes. However, zinc plating is used on small parts such as fasteners, crank handles, springs and other hardware items ratherthan sheet metal. The zinc is applied as an expendable electrode in a cyanide, alkaline non-cyanide, or acid chloride salt solution. Cyanide baths are the most operationally efficient but can potentially create pollutionand are hazardous.
After alkaline or electrolytic cleaning, pickling to remove surface oxides, and rinsing, the parts are loaded into a barrel, rack, or drum and immersed in the plating solution. Various brightening agents may be added to the solution to add luster, but careful control is needed to ensure a quality product. Post-plating treatments may be used to passivate the zinc surface as well as impart various translucent colors or to extend the life of the coating.
Zinc plating is typically used for screws and other small fasteners, light switch plates, and various small parts that will be exposed in interior or mildly corrosive conditions. For use in moderate or severe environments,the materials must be chromate-conversion coated for additional corrosion protection.
Today zinc/nickel is applied in many fields - but especially in the automotive industry. The corrosion protection in this field has essentially been improved compared with ordinary zinc deposits. The corrosion protection of passivated parts offers also after heat treatment significant advantages compared with classic zinc-plating. The coating excels in a high temperature resistance (e.g. near the engine block), and there is no galvanic corrosion in connection with aluminium.
Zinc/nickel is widely specified by the biggest automotive companies and their suppliers. It is very often applied as a transparent passivated surface. Zinc/nickel is also suitable for black passivation surfaces as well as for organic topcoats.
We offers an alkaline electrolyte for the deposition of ZnNi coatings with a nickel content of 10 - 15%.
The process excels in