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
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
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.