SPRAY PAINTING
extract from Rob Thompson's
book
Spray painting is used to apply color and provide surface
protection. It can be used to coat most rigid materials. A range of finishes
can be achieved from matt to gloss, including soft touch, pearllescent,
iridescent and metallic.
Alternatuve and competing prcesses include:
Dip Molding
Electroplating
Flocking
Metal Patination
Polishing
Vacuum Metalizing
Spray guns are a jet of compressed air to atomize the paint
into a fine mist. The atomized paint is blown out of the nozzle in an
elliptical shape. The coating is applied onto the surface in overlapping
strokes.
Painted surface are nearly always made up of more than one
layer. If necessary, the surface is prepared with filler and primer.
Conventional paints are made up of pigment, binder; thinner
and additives, The role of the binder is to bond the pigment to the surface
being coated. It determines the durability, finish, speed of drying and
resistance to abrasion. These mixtures are dissovled or dispersed in either
water or a solvent.
Two-pack paints are made of resin and the catalyst or
handener.. They bond to the surface in a one-way reaction and are extremely
durable.
Qualit: the level of sheen on the coating is categorized as
matt, semi-gloss, satin and gloss, High gloss, intense and colourful finishes
are produced by the conbination of meticulour surface preparation, basecoat and
top coat.
Typical applications: Spray painting is used in a vast range
of applications including prototyping, low-volume and high-volume production.
COST AND SPEED Jigs may be required, but this depends on the
numbere of the parts and geometry. Cycle time is rapid, but depends on the
size, complexity, number of coats and drying time. Labour costs and typically
high because these tend to be manual processes.
MATERIALS Almost all materials can be spray painted. Some
surfaces have to be coated with an intermediate layer which is compatible with
both the workpiece and the topcoat.
ENVIROMENTAL IMPACTS Water-based paints are less toxic than
solvent borne. Spraying is usually carried out in a booth or cabnet to allow
the paint to be recycled and disosed of safely.