Installation Guide

Plexiglas
®
acrylic sheet should be handled carefully to avoid
scratching its surface. It is easier to avoid scratches than to remove
them. Scratched surfaces can be restored to a good finish by a
process of polishing and/or sanding. Sawed edges and machined
surfaces can also be polished to a high gloss. Where power-operated
polishing equipment is not available, it is possible to hand-polish
minor scratches from the surface of the sheet. Minor scratches
can be polished by rubbing with soft flannel and a good grade of
automotive paste wax.
Before sanding, buffing, or polishing, clean the Plexiglas
®
acrylic sheet carefully. The buffing wheels and compounds should
also be free from dirt and grit. Separate buffs should be reserved
for Plexiglas
®
acrylic sheet. They should be cleaned by running
the buffing wheel against a hard metal edge to remove hardened
tallow, grease or other binders.
The friction of buffing, sanding, or polishing too long or too
vigorously in any one spot can generate enough heat to soften
or “burn” the acrylic surface, resulting in visual distortion and
possibly discoloration. To avoid this, keep the Plexiglas
®
acrylic
sheet constantly in motion relative to the wheel. Use light
pressure, and change the direction of buffing often. Air-cooled
buffing wheels are often used to help reduce heat of friction.
Polishing techniques vary with the equipment available and the
size or shape of the acrylic parts being polished.
Sanding and buffing cause thickness variations in the scratched
area of the Plexiglas
®
acrylic sheet. If skillfully done, these operations
cause only minor optical distortions that should not be objectionable
for most applications. In critical sections, even minor distortions
may not be acceptable. Such sections, even though scratched,
should not be sanded or buffed. They should be simply washed
and waxed. However, applications that must be sanded should
be sanded by hand, using progressively finer grit paper up to grits
of 12,000. These grits are available as cushioned abrasive cloth.
Sanding
If there is a scratch in the Plexiglas
®
acrylic sheet, it should not
be sanded unless the surface imperfections are too deep to be
removed by light buffing and the resultant optical distortion can
be tolerated. The way to tell if sanding is necessary is to rub your
fingernail over the scratch. If it can be felt, then sanding is
required. Use the finest sandpaper that will remove the
imperfections. Coarse paper can cause scratches deeper than the
original imperfection, and additional finishing operations will be
needed.
First try using 600 grit sandpaper wrapped around a rubber-padded
sanding block. Sand over the scratch using increasingly larger
areas of sanding. If this does not readily remove the scratch,
step down to 400 grit. The sanding should be done in directions
mutually 30° apart to produce a diamond pattern. After sanding
and stepping up to 600 grit, polish the sheet as described below.
Do not use disc or belt sanders dry. The greater danger of heat
generation with mechanical sanders makes the use of water or
oil coolants doubly desirable. Wet sanders are preferred, but dry
orbital sanders can be used with care. Open coat sandpaper
should be used, since it does not become clogged as fast as
closed coat sandpaper.
Machine Buffing
The Plexiglas
®
acrylic sheet should be clean and dry at the start
of each buffing operation. Some polishing compounds leave the
surface clean after buffing. If these materials are not used, washing
should follow the last step in polishing.
If the part has previously been sanded or is deeply scratched,
an abrasive-coated wheel is used first. The abrasive is a standard
polishing compound composed of very fine alumina or similar
abrasive and tallow.
When most of the scratches have been reduced on the first
wheel, the Plexiglas
®
acrylic sheet is buffed on the second wheel
charged only with tallow. These first two wheels should be
air-ventilated cotton muslin rag wheels and should operate at
3,000 to 4,500 surface feet per minute (SFPM). To calculate:
SFPM equals
1
⁄
4 the diameter of buffing wheel in inches multiplied
by the spindle speed in rpm.
The Plexiglas
®
acrylic sheet is next brought to a high polish by
a soft, loose buff in which no abrasive or tallow is used. These
cleaning buffs should be very loose and should be made of
imitation chamois or cotton flannel. The wheels should be 10 to
12 inches in diameter and should run at 3,000 to 4,500 SFPM. A
hand-applied coat of wax may be used in place of buffing on the
finish wheel, if desired.
FINISHING PLEXIGLAS
®
17
ACRYLIC SHEET