Process plant basics

Plating, anodising, phosphating and electropolishing represent one of the largest surface finishing sectors in the UK manufacturing industry. It plays a vital role in the aerospace, defence and electronics related industries. The automotive industry also has significant applications for the various aqueous surface finishing technologies. In all these uses, corrosion protection, abrasion resistance, hardness, electrical conductivity and lubricity are valuable surface properties.

High quality surface finishing demands thorough cleaning and activation before the finishing 

process can take place. Degreasing with aqueous based alkaline cleaning liquids is usual, although hi-tech components for the aerospace related industries may require organic solvent cleaning under carefully controlled conditions. Surface scale from previous heat treatment processes and any rust on steel components, which might have occurred during intermediate storage, is generally removed by mineral acids. Surface activation with pre-dips may then be necessary before the key finishing stages.

Plating may require two or more deposited surfaces. Whilst zinc or zinc alloy plating on steel is a single deposit, decorative chrome plating on steel

components requires a substrate deposit of nickel before the relatively thin layer of chromium is laid down. Chrome plating plating for arduous external application e.g. for motor vehicles will certainly require two or even three different nickel deposits before the chromium is deposited.

Further treatments are often necessary after the plating stage. These can include the so called "passivate" coatings for plated zinc deposits, designed to enhance corrosion protection and also to provide a range of decorative colours e.g. black, olive drab, yellow or chrome-like blue. Other post treatments may be seals, lacquers, waxes or light oils.