Fatih GÜNDÜZ 030060144 (9th week)

Chromate Coating:

Chromate Coating is formed on base metals such as zinc, cadmium,magnesium, or aluminium by the combined action of sodium chromate and dilute sulphuric acid. The dissolution of the base metal in the dilute acid increases the pH of the solution adjacent to the metal surface facilating the reduction of chromium to chromium ions. At some critical pH basic chromium chromate is precipated on the base metal surface forming the chromate coating. The Chromate Coating is relativelly more corrosion resistant compared to phosphate coating and is amenable for painting but has low abrasion resistance.

(Engineering Chemistry, Sivasankar, p.486)

Rack Plating:

Rack Plating is used for parts where the apperance of surfaces is critical e.g. decorative strips,faucets, or slower heads. Here, workpieces are mounted on racks or jigs and dipped into the processing solutions. Electrical current is fed through the complete racks when they are immersed in the processing bath. In order to guarantee that only the workpieces and not the rack itself is coated, racks are resistant to chemicals and coated with non-conductive coatings. The only uncoated parts of racks are constants where the workpieces are mounted, in order to ensure proper flow of electrical power to the substrate workpieces.

(Modern Surface Technology, F.-W. Bach,A. Laarmann,T. Wenz, p.111)

Electroless Plating:

In electroless plating, metal ions in solution are reduced to metal atoms and are deposited on the substrate surface without using electrical energy. [It is a tchnique of depositing a noble metal from its salt solution on a catalytically active surface of a less nobel metal by employing a suitable reducing agent without using electrical energy.] The reduction is accomplished by the presence of a reducing agent. The reducing agent supplies the electrons for the reduction of metallic ions to metal which gets deposites over the substrate surface giving a uniform thin coating.

(Engineering Chemistry, Krishnamurthy Et Al., p.123)

Stud Welding:

Stud Welding is a semiautomatic or automatic arc welding process. An arc is drawn between a metal stud and the surface to which it is to be joined. When the end of the stud and the underlying spot on the surface of the work hace been properly heated, they are brough togetter under pressure.

(Welding: principles and applications, L. F. Jeffus, p.708)