Dispersion coatings

General

Dispersion coating is a wet process in which the coating material is finely distributed in a solvent as a dispersion (solid in fluid). This mixture is atomised by pressure air to a mist and sprayed on the workpiece.

Procedure

The procedure of applying the coating is divided into the steps:

• preparation of the work piece
• (wet) application of the coating
• drying
• sintering

Preparation of the work piece

In order to achieve sufficient adhesion to the substrate, the surface areas to be coated must be prepared by first removing any grease. This is done by organic solvents of by burning out at temperatures of approx. 400°C. In the following step, the work pieces are cleaned and roughened mechanically by sand blasting. The crimping effect of the coating to the work piece substrate can be enhanced by applying an adherence agent (primer).

(Wet) Application of the coating

The coating material is applied uniformly. The coating thickness depends on the system used; it may vary in thickness from a few micro-metres right up to 200 µm (0.2 mm).

Drying

The so-called wet layer is heated up in a furnace at temperatures less than 100°C until the major part of solvent has been evaporated.

Sintering

This is followed by heating to a higher temperature until an irreversible reaction takes place: fusion of the materials, netting of bonding agents.