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Car wash aids, detergents, waxes, and
polishes, often advertised by its amazing ability to keep your car
looking showroom new, make up an astounding million-dollar industry.
Our willingness to shell out our hard-earned money speaks volumes
about our collective desire as vehicle owners to maintain the
aesthetics of our cars as well as our realization that paintwork not
only beautifies your vehicle but is also instrumental in protecting
its surface from corrosion.
Car paintwork is affected by the weather, particularly when it's
very hot or very cold. In Malaysia where mid-day bonnet temperature
could rise to a high of 75C and drop to a low of 18C subjects our
paintwork to adverse atmospheric weathering. Aside from that, other
external factors such as ultra-violet exposure, dirt abrasion, acid
rain, surface damage, and even bird droppings can all combine to
damage the car's paintwork.
While a regular maintenance regime is key to giving your car that
like-new look, the first basic ingredient in ensuring your car look
like new year after year is the quality of paint and the
spray-painting process that goes onto the car in the first place.
The most common car paints used today are urethane, acrylic enamel,
and acrylic lacquer. However, the use of acrylic lacquer is rapidly
diminishing. Urethanes and catalysed acrylic enamel are more durable
than acrylic lacquer. During the spray painting process, a thinner
or solvent must be added as the paint passes through the spray gun
so that the paint will properly atomize. Acrylic enamel paints,
especially urethanes, require an additional catalyst which will
chemically harden the paint.
These different types of paint have one thing in common - the toxic
nature of their fumes. That is why it is crucial to use respirators
and other safely gear when working with these products. Paint
finishing and spraying should never be a D-I-Y project and is the
best left to the professionals.
Having said that, however, let's take a quick look at what surface
and paint preparation entails. To start off, the surface must be
dent-free and should not be marred by any weld spots, rust holes or
other similar imperfections.
The smooth surface is then "keyed" by leaving a uniform but sligthly
rough surface to ensure better paint adhension. Next, fine particles
of debris or dust must be removed from the surface and it should be
thoroughly degreased before the painting process can start.
A uniformly fine layer of paint is sprayed onto the surface. The
moment a droplet of paint hits a solid surface, it begins to flow
into a flat thin layer until the surface is thoroughly wetted. Then,
the paint dries when its solvent evaporates. The thickness of the
paint, paint delivery rate, spraying temperature and humidity all
play crucial roles in the uniformity of the paint that has been
deposited on the surface. Too thick (viscous) and the paint will not
flow easily because the solvent depletes as the droplets travel
through the air, solidifying the paint before the droplets even
reach the surface. The result is a rough and unsightly mess.
Spraying temperature that is too high can also cause the same
results as solvent evaporation is accelerated. On the other hand,
paint drips could result if the paint is too thin or the spraying
temperature is too low.
The highly critical viscosity of the paint is measured using a
special viscosity cup. Paint flow through a calibrated hole at the
bottom of the measuring cup. Viscoity is indicated by how long it
takes for the measuring cup to empty. Solvents are also available in
different grades for use in differing spraying temperatures. In
general, there are 3 types of solvents - fast dry for temperatures
19C or below, medium dry for temperatures ranging from 20-23C, or
slow dry for hot conditions above 24C.
Article contributed by AAM
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