Phosphating Plant

In the past, more often than not, manufactures had been inclined to ignore or underplay the importance of precleaning and pretreating a component/article in a methodical and scientific manner, prior to paint finishing. It was the general belief that all that mattered to the finish of a component was the paint alone, and that the durability of the finish could be improved by merely applying more coats or a thicker one.

Let us examine the results of painting a product which has not been precleaned and pretreated properly.

First of all. it is to be noted that a product, after going through various operations, when brought for painting will have any or more of the following contaminants on its surface: dirt, grease, rust, scale. Direct painting on such components without removing the impurities on their surface results in a sketchy coat or an inferior finish. The coat of paint does not adhere properly to the surface, and there is a tendency for the paint film to fail or peel off. moreover, there is a gradual deterioration’s of the painted surface since there is rust formation underneath the paint coat and this creeps slowly to the adjoining areas without being arrested. One often finds a painted surface thus freckled with rust spots. It is, therefore, obvious that a good appearance or durability cannot be achieved by the application of paint on an uncleaned and untreated metallic surface.

Precleaning of the surface alone does not also ensure a good quality finish. A cleaned surface is a very active one, and when exposed to atmosphere it is again liable to get rusted or oxidized within a very short time. Even if the component is immediately painted, any rust spot trapped underneath the paint film, or any chipping off of the paint from an area at any point of time, will result in rust formation and also rust creep, eventually destroying the paint film.

Therefore, the need to provide surface protection for the component after cleaning will be recognized. This is achieved by treating the cleaned surface in suitable solutions, whereby a certain thickness of a protective coat is formed which prevents rust formation and rust creep. In addition, the pretreated component presents a very good adhesive surface for the application of paint.

The precleaning stage normally consists of a degreasing and a derusting/pickling operation for the removal of all contamination from the surface of the component to be painted. Water rinse operations after each solution operation /treatment are a 'must' in order to prevent carry over of one solution into another.


In the pretreatment or surface protection stage there is a phosphating/ chromatising operation which provides the protective coat and later, after a cold water rinse, a passivating operation, wherein the phosphate coat is made less active, further reducing the chances of rust formation.

In general, there are two alternative pretreatment systems, or phosphating systems as they are called, viz. the dip system ( cold or hot process ) and the spray system. The former is the conventional system and can be used for almost all applications, whereas the latter is specialized, and is normally very effective and economical for articles having even, straight surface, and also a large volume of production.

It has been reassuring to note that in recent times there has been a growing awareness of the prime importance of pretreatment in a painting set- up, and that it is no longer considered as an unwanted or luxury item in a paint shop. Descriptions of pretreatment plants installed and working in various modern establishments will follow shortly.

Meanwhile, ask for details of our complete painting plants consisting of pretreatment and stoving equipment, conveyor, spray booths and spray painting equipment.