FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 3. Fiberglass and Plastics | 3. Transparent Plastics | 3-22. Forms
AC 43.13-1B
will impose so much stress on the surface of
the plastic that tiny fissures or cracks, called
crazing, will form.
9/8/98
3-21. HEATING. Before heating any trans
parent plastic material, remove all of the
masking paper and adhesive from the sheet. If
the sheet is dusty or dirty, wash it with clean
water and rinse it well. Dry the sheet thor
oughly by blotting it with soft absorbent paper
towels.
NOTE: Wear cotton gloves when
handling the plastic to eliminate finger
marks on the soft surface.
a. For the best results when
hot-forming acrylics, use the temperatures
recommended by the manufacturer. A
forced-air oven should be used−one that is ca
pable of operating over a temperature range of
120 to 374 °F (49 to 190 °C). If the part gets
too hot during the forming process, bubbles
may form on the surface and impair the optical
qualities of the sheet.
b. For uniform heating, it is best to hang
the sheets vertically by grasping them by their
edges with spring clips and suspending the
clips in a rack. (See figure 3-17.) If the piece
is too small to hold with clips, or if there is not
enough trim area, lay the sheets on shelves or
racks covered with soft felt or flannel. Be sure
there is enough open space to allow the air to
circulate around the sheet and heat it evenly.
c. Small forming jobs, such as landing
light covers, may be heated in a kitchen baking
oven. Infrared heat lamps may be used if they
are arranged on 7-or 8-inch centers and enough
of them are used in a bank to heat the sheet
evenly. Place the lamps about 18 inches from
the material.
FIGURE 3-17. Hanging of acrylic sheets.
d. Never use hot water or steam directly
on the plastic to heat it, because this will likely
cause the acrylic to become milky or cloudy.
3-22. FORMS. Heated acrylic plastic will
mold with almost no pressure, so the forms
used can be of very simple construction.
Forms made of pressed wood, plywood, or
plaster are adequate to form simple curves, but
reinforced plastic or plaster may be needed to
shape complex or compound curves.
a. Since hot plastic conforms to any
waviness or unevenness, the form used must
be completely smooth. To ensure this, sand
the form and cover it with soft cloth such as
outing flannel or billiard felt.
b. The mold should be large enough to
extend beyond the trim line of the part, and
provisions should be made for holding the hot
plastic snug against the mold as it cools.
c. A mold can be made for a complex
part by using the damaged part itself. If the
part is broken, tape the pieces together, wax or
grease the inside so the plaster will not stick to
it, and support the entire part in sand. Fill the
part with plaster and allow it to harden, and
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