Page 257 - Mechanical Engineer's Data Handbook

ENGINEERING MATERIALS 245

open-weave fabric are used for building panels. Uses Polyimides
include domestic electrical appliances and electric light
fittings; the melamine type is used for tableware. The These are noted for their high resistance to oxidation
strength is high enough for use in stressed components, and service temperatures of up to 250 "C (400 "C for
but the material is brittle. Electrical, thermal and intermittent use). The low coefficient of friction and
self-extinguishing properties are good. high resistance to abrasion makes them ideal for
non-lubricated bearings. Graphite or molybdenum
Epoxies disulphide filling improves these properties. They are
used for high density insulating tape. Polyimides have
These resins are used extensively. They can be cold high strength, low moisture absorption, and resist
cured without pressure using a 'hardener', or be heat most chemicals, except strong alkalis and ammonia
cured. Inert fillers, plasticizers, flexibilizers, etc., give a solutions.
wide range of properties from soft flexible to rigid solid
materials. Bonding to wood, metal, glass, etc., is good Silicones
and the mechanical, electrical and chemical properties
are excellent. Epoxies are used in all branches of These may be cold or heat cured and are used for
engineering, including large castings, electrical parts, high-temperature laminates and electrical parts resis-
circuit boards, potting, glass and carbon fibre struc- tant to heat (heat distortion temperature 450 "C).
tures, flooring, protective coatings and adhesives. Unfilled and filled types are used for special-duty
mouldings. Organosilicones are used for surface coat-
Epon resins ings and as an adhesive between organic and non-
organic materials.
These can be formulated for surface coatings and have
excellent adhesion, chemical resistance and flexibility. 6.13.3 Laminated plastics
They are used for casting and potting materials,
adhesives, structural laminates and foams. These consist of layers of fibrous material impregnated
with and bonded together by a thermosetting resin to
Phenolics (phenol formaldehyde, PF) produce sheet, bars, rods, tubes, etc. The laminate may
be 'decorative' or 'industrial', the latter being of
PF is the original Bakelite and is usually filled with mechanical or electrical grade.
50-70% wood flour for moulded non-stressed or
lightly stressed parts. Other fillers are: mica for Phenolics
electrical parts; asbestos for heat resistance; glass fibre
for strength and electrical properties; nylon; and Phenolic plastics can be reinforced with paper, cotton
graphite. Phenolics represent one of the best ther- fabric, asbestos paper fabric or felt, synthetic fabric, or
mosets for low creep. Mouldings have good strength, wood flour. They are used for general-purpose mech-
good gloss and good temperature range (150 "C wood anical and electrical parts. They have good mechanical
filled; intermittent use 220 "C), but are rather brittle. and electrical properties.
Applications include electrical circuit boards, gears,
cams, and car brake linings (when filled with asbestos, Epoxies
glass, metal powder, etc.). The cost is low and the
compressive strength very high. These are used for high-performance mechanical and
electrical duties. Fillers used are paper, cotton fabric
Polyester and glass fibre.

This can be cured at room temperature with a Tufnol
hardener or alone at 70-1 50 "C. It is used unfilled as a
coating, for potting, encapsulation, linings, thread 'Tufnol' is the trade name for a large range of sheet, rod
locking, castings, and industrial mouldings. It is used and tube materials using phenolic resin with paper and
mostly for glass-reinforced-plastic (GRP) mouldings. asbestos fabric, and epoxy resin with glass or fabric.