Developments in Metal Pre-Treatment

SYNOPSIS

Advances in the field of metal pre-treatment are described with particular reference to the preparation of metals for painting.

The cost of heating spray plants can now be reduced by the use of cleaners and phosphating solutions which operate at low temperatures. For dip installations a new surface layer technique reduces heating costs by 75% or more.

The special requirements of one-coat finishes and acrylic paints can be met by thin, smooth phosphate coatings. Recent work has shown that phosphate coating refinement can be obtained by modification of the processing solutions with polyphosphates or inhibitors. Details of the peroxide accelerated zinc phosphate process are given with particular reference to the car industry. The use of thin iron phosphate coatings for strip steel and other applications is described. New control methods and improved plant designs prevent rinse water blistering of paint in large installations and a solvent drying process is now available for the immersion treatment of plated or phosphated articles to eliminate water marks and rinse water contamination.

Alkaline derusting processes find particular application for the treatment of high tensile steels to avoid hydrogen embrittlement and for components which must not be subjected to any loss of metal.

Developments in the treatment of aluminium are given with particular reference to the aircraft industry. The expanding uses for Chromate films on zinc and aluminium for corrosion prevention are described.