Brochure: Carbon Additives for Polymer Compounds - Timcal Graphite

TYpICAL AppLICATIonS FoR TIMREX® GRApHITE And CokE
20
Filled pTFE
Polytetrafluoroethylene (PTFE) exhibits a very
low coefficient of friction and retains useful mechanical
properties at temperatures from -260
to +260 °C for continuous use.
The crystalline melting point is 327 °C, much
higher than that of most other semi-crystalline
polymers. Furthermore, PTFE is nearly inert
chemically and does not adsorb water, leading
to excellent dimensional stability. On the one
hand, these characteristics of PTFE are very
useful in the matrix polymer of polymer-based
composites which are used in sliding applications.
On the other hand, PTFE is subjected to
marked cold flow under stress (deformation
and creep) and reveals the highest wear among
the semicrystalline polymers.
However, these disadvantages are very much
improved by incorporating suitable fillers, allowing
the use of PTFE in fields otherwise precluded
to this polymer.
The treated PTFE is generally known as filled-
PTFE. There are many kinds of filled- PTFE
composite because various fillers are incorporated
into PTFE and one or more materials can
be used simultaneously. Usually, these fillers are
in form of powders or fibers intimately mixed
with the PTFE.
The addition of fillers to the PTFE improves or
modifies its properties depending upon the nature
and quantity of filler:
• remarkable increase in wear resistance;
• decrease of deformation under load and of
creep;
• reduction of thermal expansion;
• some types of filler increase the thermal and
electric conductivity.
Filled PTFE is often not as strong and
resilient as virgin PTFE. Sometimes, the filler
limits the resistance to chemical agents and
modify the electrical properties.
TIMREX® GRApHITE
And CokE FILLERS In FILLEd-pTFE
TIMREX® pC 40-oC Coke
TIMREX PC 40-OC Coke is calcined at high temperatures
offering low sulphur concentration,
low content of oversize particles, high apparent
density and high chemical stability against most
chemical substances. TIMREX® PC 40-OC Coke
is added to the virgin PTFE in a percentage by
weight between 10 and 35% along with small
percentage of graphite.
Compounds made of PTFE and TIMREX® PC
40-OC Coke have excellent wear resistance
and deformation strength and compared to the
virgin PTFE, they have practically unchanged
chemical resistance and friction behaviour.
Typical final materials that can be produced
with coke filled PTFE are:
engineering design components, slide bearings,
valve housing and valve seats for chemical applications,
piston sealing and guiding elements
for dry-running compressors.
TIMREX® kS44 Synthetic Graphite
NTIMREX® KS 44 is a Primary Synthetic Graphite
obtained by the full graphitisation of amorphous
carbon materials through the well known
Acheson process. The process parameters in the
Acheson furnace such as temperatures and residential
times are all optimised in order to achieve
the perfect degree of crystallinity and the lowest
level of impurities whereas others minor adjustments
are made during the material sizing and
conditioning.
The percentage of TIMREX® KS 44 used in the
filled PTFE vary between 5 and 15%.
TIMREX® KS 44 can be used alone or in combination
with glass or coke.
TIMREX® KS 44 lowers the coefficient of friction
and is, therefore, often added to other types of
filled PTFE for improving this property (and also
to improve the lifetime of the cutting tools during
for instance the production of gaskets and
seals). It improves the deformation under load,
strength and, to a minor degree the wear. Like
coke, it serves well in corrosive environments.
PTFE filled with TIMREX® KS 44 are often used in
steering and shock-absorber gasket, bearings as
well as in slide films for anti-static applications.