Page 307 - Engineering Plastics Handbook

Polyamide-imide (PAI) 267

compounds. Seal rings are placed on the transmission to prevent trans-
mission oil from leaking out the shaft. The excellent friction and wear
properties of polyamide-imides permit their use where rotational speeds
averaging 3000 rpm are standard. They also must handle the resistance
to many different automotive fluids at temperatures that reach 150°C.
Polyamide-imide thrust washers can handle the cyclic compression and
abrasive wear when placed against metal for the entire life of the vehi-
cle. Valve body check balls must endure millions of cycles without fatigue
or rupture, again at elevated temperatures and in harsh chemical envi-
ronments. They must have the ability to seat against the orifice and
provide a leakproof seal and then open without delay. Polyamide-imide
compounds are one of the few materials that can handle these tough
application requirements and still be a cost-effective part to manufacture
due to injection-molding capability.

Race car suspension bushings. Due to their superior friction and wear
properties, polyamide-imides are being incorporated in the suspensions
of endurance race cars. Recently a race team upgraded its Ferrari to sus-
pension bushings machined from extruded polyamide-imide tube. The
switch was made because the factory bushing material wears out
and has to be changed between every race. Worn bushings, which
make car handling sloppy, are not an issue even in 24-h endurance
races (Fig. 12.12).

Aerospace
The endurance benefits and performance characteristics of polyamide-
imides qualify them to be an excellent replacement for metal in aerospace
components. Inherent nonflammability, chemical resistance, and superb
strength at elevated temperatures allow polyamide-imide compounds to
be used in metal applications once unheard of for plastic materials. Neat
resin, friction and wear, along with glass- and carbon-reinforced polyamide-
imide compounds are incorporated in a variety of parts and locations in
aerospace vehicles.

Aerospace composite adhesives. In addition to molded parts, polyamide-
imides are used as the high-strength adhesives and polymer matrix in
aerospace composites. One particular area is honeycomb composites
[19]. The adhesives and polymer matrix are critical because the ulti-
mate strength of the honeycomb is often directly dependent on the
strength of the bond between the honeycomb layers. The polyamide-
imide resin is dissolved in an appropriate solvent and applied to the
honeycomb fabric, using a bonding technique to achieve the desired