ENSACO® Conductive Carbon Black for polymer ... - Timcal Graphite

18
Self lubricating
polymers
NThe choice of a polymer-based self lubricating
solid for a particular application depends
mainly upon the operating conditions of:
temperature, chemical environment and the
maximum values of pressure (p) and sliding
speed (v). For each polymer or composite
material, a pv limit is quoted, which corresponds
to the pressure times the sliding speed
at which the material fails, either due to unacceptable
deformation, or to the high frictional
energy dissipated causes surface melting,
softening and excessive wear.
NThe pv limit of a polymeric material may
be increased by increasing its mechanical
strength (resistance to deformation), thermal
conductivity (reduction in surface temperatures)
and by decreasing friction (reduces frictional
heating). In practice, thermoplastics
(with the exception of PTFE) are mainly used
as pure solids, since their wear resistance and
frictional coefficient, are satisfactory for
most applications. Solid lubricant fillers or
fibre reinforcement (glass fibres, carbon
fibres, textiles) are only employed under the
more extreme conditions of load and speed.
NThe major polymers employed as self lubricating
solids/composites, are illustrated
below.
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Typical applications for TIMREX® Graphite and Coke
Thermoplastics Thermosetting polymers
polyamides*
polyester
polyacetal*
polyethylene (HDPE, UHMWPE)
Polycarbonate
poly (ether etherketone)*
polyphenilenesulphide*
polysulphone*
epoxy resins*
phenolic resins*
unsatured polyester*
polyimides*
Major polymers employed as self lubricating solids.
* polymers in which graphite
may be incorporated
N Graphite powder is widely used in polymer
composites, either alone or in combination
with reinforcing fibres, PTFE or various inorganic
fillers, e.g. mica, talc (bottom, right
table). Applications include gears, dry sliding
bearings, seals, automotive and micro-mechanical
parts. The properties of graphite which
favour its use in polymer composites are:
low friction lamellar solid
(reduces friction);
tendency to form a transfer film
on the countersurface
(assists in wear reduction, particularly
when graphite is applied as water based
dispersion i.e. LB 1300);
high thermal conductivity
(decreases temperature rise due to
frictional heating);
electrical conductivity
(prevent build-up of static charge which
may be a problem in some cases);
chemically inert
(used in conjunction with PTFE in
corrosive environments);
high thermal stability
(favours use in high temperature
applications, e.g. polyimide graphite
composites may be used up to 350°C).
Polymer Graphite content Other additives
polyacetal
polyamide 6
polyamide 11
polyamide 12
polyamide 6.6
polysulphone
polyphenilenesulphide
polyphenyleneoxide
PTFE
polymide
polymide
polymide
phenolic / epoxy resin
polyester thermoset
10%
5%
10%
30%
5%
15-30%
10%
10%
15-40%
15-40%
15%
40%
5-20%
5-20%
Examples of the use of graphite in self lubricating polymers.
-
-
glass fibre
PTFE
-
inorganic filler
glass fibre
inorganic filler
glass fibre
-
PTFE
CF
CF/glass fibre
CF/glass fibre
-
-
25%
15%
-
10%
30%
20%
10-20%
-
20%
10%