Reinforced PTFE
Brochure
Fillers PTFE functions (56kB)
Datasheet
Filled PTFE (82kB)
PTFE is often used with different fillers (like glass fiber, carbon, bronze, graphite) in order to reinforce his mechanical properties.
Glass fiber
PTFE is reinforced with glass fibers, the percentage varying between 5 and 40%. The added glass fiber improves the wear
properties and, to a minor degree, also the deformation strength under load while leaving substantially unchanged the electrical
and chemical characteristics. Glass itself, has a rather poor resistance against alkalis and is easily attacked by hydrofluoric acid. The
coefficient of friction is slightly increased and for this reason, graphite is sometimes added to compensate this side effect.
Carbon
Carbon is added to the PTFE in a percentage by weight between 10 and 35%, along with small percentage of graphite. Also, the
carbon tends to improve to a considerable degree, wear and deformation strength, while leaving practically unchanged the chemical
resistance, but substantially modifying the electrical properties.
Bronze
Bronze, when used as filler, is added in percentages of weight between 40 and 60%. Bronze filled PTFE has the best wear
properties, remarkable deformation strengths and good thermal conductivity, but poor electrical characteristics and chemical
resistance.
Graphite
The percentages used vary between 5 and 15%. Graphite lowers the coefficient of friction and is, therefore, often added to other
types of filled PTFE for improving this property. It improves the deformation under load, strength and, to a minor degree, the wear
properties.
Other fillers
Molybdenum sulfide, though decreasing the coefficient of friction, is sometimes preferred to graphite. Some metal powders
(stainless steel, nickel, titanium), in consideration of their particular resistance to chemical agents, are sometimes used as fillers for
PTFE, even though their wear resistance, with respect to bronze, are inferior. The metal oxides, added to other fillers, give better
wear properties.
Wear
The contact between two sliding surfaces, because of the inevitable friction generated in the contact zone, results in a certain wear
whose magnitude depends on load, speed and time of sliding contact. Theoretically, between these parameters and the resulting
wear exists a relation proportional to:
R=KPVT
where, expressed in the measuring units of table:
R = wear in mm
P = specific load in N/mm2 (referring to the surface - Ø x l - in case of bushes, nipples, etc.)
V = sliding speed in m/sec
T = time in hrs
K = wear factor in mm3 sec/Nmh.
The value of the factor PV after which the coefficient of wear loses its linear behavior, assuming remarkable values with the system
passing from weak to strong wear condition, is known as “PV limit”. This PV limit and the wear factor are, therefore, characteristic
parameters of each material. In practice, however, it can be easily perceived, the wear factor and the PV limit of the same filled
material can vary also with the nature, the hardness and the surface finish of the other contact “partner” with the presence, or not,
of cooling and/or lubricating fluids.
Deformation under load and compressive strength
ties.
rical
cid. The
the
hemical
l
other
e wear
llers for
etter
in wear
lting
system
eristic
lled
or not,
PTFE, like most other plastic materials, has no “elastic zone” where the ratio load/deformation (Young modulus) has a constant
value. This ratio load/deformation depends upon the time of application of the load and the ensuing deformations; this phenomenon
is known as “creep”, and at the removal of the load, there is only a partial return of the deformation to the original state (“elastic
recovery”), so that we are always in the presence of a “permanent deformation”.
Creep, obviously not being a linear function of time, results after just over 24 hrs in deformations which in most cases are not taken
into consideration. With increasing temperature, there is a falling off of the deformation under load properties and consequently of
the compressive strength which is already at 100°C equal to 1/2 of that at 23°C and at 200°C about 1/10th. In any case, PTFE and
in particular filled PTFE, is one of the plastic materials retaining, at high temperatures, optimum deformation properties under load.
To conclude, the elastic recovery in about 50% of the deformations under load, and the permanent deformations are equal to about
50% of the deformations under load. This applies both to filled and unfilled PTFE. The properties of the first are however decidedly
superior. In fact, the deformation under load of the more common types of filled PTFE are about 1/4 of that of the unfilled ones,
while the compressive strength is about the double.
The thermal expansion of filled PTFE is in general inferior to that of unfilled PTFE and always greater in the direction of the moulding
than crosswise. The thermal conductivity is superior to that of unfilled PTFE, particularly when using fillers having a high thermal
conductivity of their own. Filled PTFE therefore have better thermal properties than the unfilled ones.
These properties depend to a large degree upon the nature of the filler. Only PTFE filled with glass fiber possess good dielectric
properties, even though different from those of unfilled PTFE. For example, the volume and surface resistivity, the dielectric
constant and the dissipation factor vary largely with the variation of the humidity and frequency.
Properties Method
Type of
filler %
approx.
Specific
gravity
Tensile
strength
Elongation
at break
Compressive
strength 1%
deformation
Deformation
under load
14N/mm2
for 24h Total P (II)
Deformation
under load
14N/mm2
for 24h Total T ( )
Deformation
under load
14N/mm2
for 24h Permanent
P (II)
Deformation
under load
14N/mm2
for 24h Permanent
T()
Hardness
(shore D 15 sec)
Friction
coefficient
dynamic
ASTM
D792
ASTM
D1457
ASTM
D1457
ASTM
D695
Unit
Unfilled
25%
glass
typical values – FILLED (values at 23 °C)
25%
25%
35%
60%
40%
30%
glass
carbon
carbon bronze
bronze + glass
+ 5%
3%
spec.
graph
MoS2
50%
s.steel
2,17
2,23
2.18
2,10
2,10
3,88
3,15
2,25
3,30
MPa
30
16
15
15
15
14
17
17
18
%
300
260
200
180
80
100
100
300
280
MPa
4,5
7,0
7,0
10,0
11,0
10,5
10,0
7,0
-
ASTM
D621
%
14,5
9,5
6,8
6,5
3,7
6,0
8,0
9,0
4,9
ASTM
D621
%
16,5
13,5
7,0
5,5
3,4
5,6
7,0
12,0
6,0
ASTM
D621
%
8,0
5,0
5,0
3,0
1,0
2,5
4,0
4,5
2,4
ASTM
D621
%
8,5
7,8
4,0
2,8
1,1
3,0
7,0
2,0
ASTM
D2240
-
55
63
60
63
65
65
66
65
64-72
0,05
0,07
0,06
0,06
0,06
0,06
0,13
0,07
-
ASTM
D3028
(0,8m/s,
1Mpa, s.
steel Ra
0.5 ì)
Wear factor (K)
PV limit at
-
2,3
mm 3 sec/Nmh 1
0,00071 0,00106 0,00082 0,00070 0,00041 -
0,0007 -
Nm/mm2 sec
0,365
0,360
0,040
0,400
0,365
0,330
0,545
0,350
-
ant
omenon
lastic
ot taken
ntly of
FE and
er load.
o about
idedly
nes,
moulding
rmal
ric
50%
s.steel
3,30
18
280
-
4,9
6,0
2,4
2,0
64-72
-
-
PV limit at
0,05 m/sec
PV limit at
0,50 m/sec
PV limit at
5,00 m/sec
Coefficient
of
linear
thermal
expansion
from 25 to
100°C
Thermal
conductivity
Dielectric
strength
(short-time
air thickness
0,5 mm)
Dielectric
constant
(50-109 Hz)
Dissipation
factor
Volume
resistivity
Surface
resistivity
(100%
humid.)
-
Nm/mm2 sec
0,040
0,365
0,400
0,365
0,330
0,545
0,350
0,360
-
-
Nm/mm2 sec
0,070
0,475
0,545
0,460
0,400
0,680
-
0,450
0,250
-
Nm/mm2 sec
0,095
0,590
0,800
0,545
0,500
1,020
-
0,540
-
ASTM
E831
°C-1
16x10-5 10x10-5 11x10-5 9,5x10- 5 9x10- 5 9,5x10- 5 9,8x10- 5 8x10- 5 9x10- 5
ASTM
D2214
W/mK
0,23
0,43
0,62
0,64
0,68
0,74
0,68
0,34
0,65
ASTM
D149
kV/mm
55
13
2,5
-
-
-
-
12
-
ASTM
D150
-
2,1
2,5
3,3
-
-
-
-
2,5
-
ASTM
D150
ASTM
D257
ASTM
D257
-
<0,0002 0,003
0,0025
-
-
-
-
0,0012 -
Ohm/cm
1017
1016
1015
103
103
-
-
1016
-
Ohm
1017
1016
1014
103
103
-
-
1015
-
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This is a printed version of Solutions-In-Plastics.info of ERIKS nv.
© ERIKS nv, 2016.