Thermoplastic Repairs - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
NOTE
Brush and hands may be cleaned in solvents such as acetone or
methylethylketone.
If solvents are not available, a strong solution
of detergent and water may be used.
4-100. THERMOPLASTIC
REPAIRS. The following procedure will assist in making field repairs to items
made of thermoplastic which are used throughout the airplane. A list of material needed to perform these
repairs is given along with suggested suppliers of the material. Common safety precautions should be
observed when handling some of the materials and tools used while making these repairs.
a.
Surface Preparation:
1. Paint (if applied) and surface dirt must be removed from the item being repaired. Household
cleaners have proven most effective in removing surface dirt.
2. Preliminary cleaning of the damaged area with perchlorethylene or VM&P Naphtha will
generally insure a good bond between epoxy compounds and thermoplastic.
b.
Surface Scratches. Abrasion or Ground-in-Dirt: (Refer to Figure 4-31.)
1.
Shallow scratches and abraded surfaces are usually repaired by following directions on
containers of conventional automotive buffing and rubbing compounds.
2. If large dirt particles are embedded in thermoplastic parts, they can be removed with a hot
air gun capable of supplying heat in the temperature range of 300 °
to 400 F. Use care not to overheat the
material. Hold the nozzle of the gun about 1/4 of an inch away from the surface and apply heat with a
circular motion until the area is sufficiently soft to remove the dirt particles.
3.
The thermoplastic will return to its original shape upon cooling.
c. Deep Scratches, Shallow Nicks and Small Holes: (Less than 1 inch in diameter.) (Refer to Figure
4-33.)
1. Solvent cements will fit virtually any of these applications. If the area to be repaired is very
small, it may be quicker to make a satisfactory cement by disolving thermosplastic material of the same
type being repaired in solvent until the desired paste-like consistency is achieved.
2. This mixture is then applied to the damaged area. Upon solvent evaporation, the hard
durable solids remaining can easily be shaped to the desired contour by filing or sanding.
3. Solvent adhesives are not recommended for highly stressed areas, on thin walled parts or for
patching holes greater than 1/4 inch in diameter.
4. For larger damages an epoxy patching compound is recommended. This type material is a
two part, fast curing, easy sanding commercially available compound.
5. Adhesion can be increased by roughing the bonding surface with sandpaper and by utilizing
as much surface area for the bond as possible.
6. The patching compound is mixed in equal portions on a hard flat surface using a figure eight
motion. The damaged area is cleaned with perchlorethylene or VM&P Naphtha prior to applying the com-
pound. (Refer to Figure 4-33.)
7. A mechanical sander can be used after the compound is cured, providing the sander is kept
in constant motion to prevent heat buildup.
8. For repairs in areas involving little or no shear stress, the hot melt adhesives, polyamids
which are supplied in stick form may be used. This type of repair has a low cohesive strength factor.
9. For repairs in areas involving small holes, indentations or cracks in the material where high
stress is apparent or thin walled sections are used, the welding method is suggested.
Revised: 3/11/81
STRUCTURES
1H5