Mixed metal coatings can be supplied with specific advantages such as ductility or high corrosion resistance, especially under certain environments or in contact with other metals. These include Zinc, Tin, Almac and Inverplex.
Almac® coatings are combinations of aluminium and zinc which give substantially increased corrosion resistance compared with zinc. They are more ductile than zinc and are very advantageous when used in contact with aluminium.
Inverplex® is a mixed coating of zinc and tin that has better conductivity(and corrosion resistance) than zinc. It may be supplied passivated and is used for earthing screws.
The components to be coated are placed into a tumbling barrel containing glass beads, reagents and catalysts, which activate and prepare the surface. The coating to be applied is added, in metallic powder form and glass beads of varying sizes ‘cold weld’ the coating on to the activated surface of the component. Similar passivates to electroplating are then applied, prior to drying the parts, lubricants may also be added as part of this process. Mechanical zinc can be used as an undercoat to enhance the performance of organic paint systems.
The barrel plating process involves placing the items to be coated in a perforated barrel-shaped cage that is manufactured from nonconductive material. The barrel is then submerged into a series of tanks containing the appropriate chemical solutions, while a slow tumbling action is used to commence the plating action. This is a very cost effective method of coating parts but may not be suitable for large or complex parts.