MIL-HDBK-1110
a) Metallic. Steel shot and grit are the most
commonly used metallic abrasives. Metallic abrasives are used to
remove mill scale, rust, and old paint and provide a suitable
anchor pattern. The advantages of metallic abrasives include
longer useful life (can be recycled many times), greater impact
energy for given particle size, reduced dust formation during
blasting, and minimal embedment of abrasive particles. The
disadvantages include blast cleaning equipment must be capable of
recycling, abrasives must be kept dry to prevent corrosion, and
the impact of steel shot on metal surfaces may cause formation of
hackles on the surface. These hackles are relatively long
slivers of metal and must be removed mechanically by sanding or
grinding before coating to prevent pinpoint corrosion through the
paint film.
b) Natural Oxides. Silica is the most widely used
natural oxide because it is readily available, low in cost, and
effective. Sand particles range from sharply angular to almost
spherical, depending on the source. OSHA and EPA regulations
have restricted the use of sand in many areas. Nonsilica sands
(generally termed "heavy mineral" sands) are also being used for
blast cleaning. However, they are generally of finer particle
size than silica sand and are usually more effectively used for
cleaning new steel than for maintenance applications.
c) Synthetics. Aluminum oxide and silicon carbide are
nonmetallic abrasives with cleaning properties similar to the
metallics and without the problem of rusting. They are very
hard, fast-cutting and low-dusting, but they are costly and must
be recycled for economical use. They are often used to clean
hard, high tensile strength metals.
d) Slags. The most commonly used slags for abrasives
are by-products from metal smelting (metal slags) and electric
power generation (boiler slags). Slags are generally hard,
glassy, homogeneous mixtures of various oxides. They usually
have an angular shape, a high breakdown rate, and are not
suitable for recycling.
e) Cellulose Type. Cellulose type abrasives, such as
walnut shells and corncobs, are soft, low density materials used
for cleaning of complex shaped parts and removing dirt, loose
paint, or other deposits on paint films. Cellulose type
abrasives will not produce a profile on a metal surface.
f) Dry Ice. Special equipment is used to convert
liquid carbon dioxide into small pellets which are propelled
against the surface. Since the dry ice sublimes, the abrasive
leaves no residue. The method can be used to remove paint from
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