Substrate pre-treatment prior to coatings

The main aims in the preparation of a metal surface prior to powder coating may be defined as follows:

  1. The complete removal of all foreign matter, eg. scale, grease, cutting oil, soil, welding splatter, etc.
  2. The conditioning of the surface so as to render it suitable for the coating that is to be applied.
  3. The pretreatment should impart uniformity throughout all treated workpiece surfaces, irrespective of the source of the metal or of the contaminants that might adhere.

As with other methods of organic finishing attention to the pretreatment stage is essential in order to achieve the full potential of the powder coating.

Surface pretreatment may vary depending upon the specific end-use requirements of the finished products – from a single-step cleansing operation to a multi-stage sophisticated pretreatment which deposits a conversion coating on the surface of the metal.

Application of a coating of electrostatically charged particles to an earthed metal surface can only be achieved if the surface is free of any composition which has a high electrical resistance.  The presence of any insulating film on the surface of the workpiece to be coated will limit or in some cases prevent powder being deposited.

Substrates

Steel, aluminium, copper, zinc alloys and galvanised steel are common metals on which powder is used.  In a number of cases where normal service conditions apply, satisfactory properties can be obtained on thoroughly cleaned metal.