Surface Coating of Miscellaneous Metal Parts
and Products:
virtual
tour
Surface Coating
Main : 1 : 2 : 3 : 4 : 5
Painting vs. Surface Coating
 Paint
is a generic term typically used to identify a wide range of surface
coating products, including conventional solvent-borne formulations,
varnishes, enamels, lacquers and water-based systems. Normally,
painting is a process where a liquid consisting of several components,
when applied, dries to a thin plastic film. Traditionally, major
constituents of these paints are solvents. However, non-liquid paints
such as powder coatings and high solids paints have also been
developed. These newer materials have led to the use of the term
coating instead of the term paint. In general, the function of
all paints and coatings is to provide an aesthetically pleasing
colored and/or glossy surface, as well as to help metal and other
substrates withstand exposure to both their environment and everyday
wear and tear.
Coating Operations
 The coating operation is a critical step in the metal parts industry.
In many cases, the coatings must provide aesthetic appeal, but
in all cases they must protect the metal from the atmosphere in
which it will be used. Both enamels and lacquers are used, although
enamels are more common. Coatings are often shipped by the manufacturer
as a concentrate but thinned prior to application. Most of the
coatings contain several different solvents including ketones,
esters, alcohols, aliphatics, ethers, aromatics, and terpenes.
 Single or double coatings are applied in conveyor or batch operations.
Spraying is usually employed for single coats. Flow and dip coating
may be used when only one or two colors are applied. For two-coat
operations, primers are usually applied by flow or dip coating,
and topcoats are almost always applied by spraying. Electrostatic
spraying is also common.
Surface coating may be performed in a spray booth or in an open
environment. Some previously open surface coating operations have
been enclosed and the exhaust vented through a stack. Surface coatings
may be applied manually or with automatic devices such as spray
guns.
 There are both job shop and captive surface coating operations.
Job shop operations fill orders to various manufacturer specifications,
and thus change coating and solvent conditions more frequently than
do captive companies. Captive operations fabricate and coat products
within a single facility and may operate continuously with the same
solvents. Job shop and captive operations differ in emission control
systems applicable to coating lines, because not all controls are
technically feasible in toll situations.
A manual two-coat operation may be used for large items like industrial
and farm machinery. The coatings on large products are often air-dried
rather than oven-baked, because the machinery, when completely assembled,
includes heat-sensitive materials and may be too large to be cured
in an oven. Miscellaneous parts and products can be baked in single-
or multipass ovens.
Coating Composition
 The major components of solvent-borne paints and coatings are solvents,
binders, pigments, and additives. In paint, the combination of
the binder and solvent is referred to as the paint "vehicle." Pigment
and additives are dispersed within the vehicle. The amount of
each constituent varies with the particular paint, but solvents
traditionally make up about 60% of the total formulation. Typical
solvents include toluene, xylene, MEK, and MIBK. Binders account
for 30%, pigments for 7 to 8%, and additives for 2 to 3%. Environmental
issues surrounding paints usually center around solvents and heavy
metals used in the pigments. Binders and other additives can also
affect the toxicity of the paint depending on the specific characteristics
of the paint.
Main : 1 : 2 : 3 : 4 : 5
|
