Note: Descriptions are shown in the official language in which they were submitted.
` This invention relates generally to composition
type railroad friction materials and, more particularly,
to such materials which feature the use of synthetic fibers
and the absence of asbestos and lead.
BACKGROU~D OF THE INVENTION
Most of the composition type railroad friction
materials in use today include asbestos and lead. An ex-
ample of this type of material is shown in U.S. Patent No.
3,168,4~7 - Spokes et al. Some environmentalists have
warned of possible problems caused by the use of lead in
friction materials. As a result, d~mand has developed
for a lead-free friction material. xamples of some com-
position friction materials which exclude lead are U.S,
Patents Nos. 3,492,262 - Griffith and 3,959,1~4 - Adelman.
The former patent discloses a composition which has no
lead and includes up to 16.5~ by weight asbestos fiber,
while the latter patent discloses some compositions which
delete lead and have up to 11.1% by weight asbestos fiber.
2Q More recently, certain environmentalists have
pointed out that possible problems may be cause~ by the
use of asbestos fiber in friction materials. Thus, it
may be desirable to eliminate asbestos as well as lead
from composition fxiction ~terials, U,S. Patent No.
3,g59,194 has scme examples which utilize cellulosic fiber
in a range of 3.5-8.0~ by weight as a substitute for as-
bestos, although the patent is not concerned with elimina-
ting asbestos in friction materials.
As~estos has traditionally been used in frictlon
3Q materials because of its high heat resistance and strength
~nd its low cost. A direct substitution of cther types
_]
11~)3384
of fiber for asbestos is expensive, since other fibers
cost much more than asbestos, and difficuit, since no known
fiber combines all of the desirable qualities of asbestos
noted above. It is known to use high-content carbonized
or graphitized fibers in aircraft friction ma.erials,
as shown in U.S. Patent No. 3,552,533 - Nitz. The use
of glass fiber in friction materials is disclosed in
several patents. U.S. Patent No. 3,743,069 - Barnett
relates a clutch facing consisting almost entirely of
hundles o~ continuous glass fil~ments. U.S. Patent No.
3,627,606 - Bentz teaches a glass-filament- reinforced
fabric clutch facing impregnated with ~ cement containing
lead (litharge), U.S. Patent No. 3,713,934 - Morton dis-
closes a clutch facing composed of glass and asbestos.
None of these friction materials would be suitable for
railroad brake shoe use, since they are either too ex-
pensive and/or conta~n lead or asbestos.
It is, ~herefore, an object of this invention
to provide lead-free, asbestos-free, high coef~icient of
~riction, composition friction materials which feature a
low fiber content including synthetic fiber and low wear
rates.
SU~ARY OF THE INVENTION
. . _ . . _
I have discovered that railro~d brake shoes that
meet A.A.R. ~Association of American Railroads) standards
for ~rake shoes can be made from compositions ha~ing a low,
non-asbestos fiber content which includes synthetic fiber.
The friction materials according to this invention comprise,
by weight, 0.5-11.0% non-asbestos fiber, including at least
0 5% synthetic ~iber, 66-81~ filler and 14-21% org~nic
3384
binder. A preferred embodiment of this composition
friction material for railroad car use contains 2.7-3.5%
synthetic fiber, 74-82% filler and 16-19% organic binder.
DETAILED DESCRIPTION O~ THE INVENTION
The criterion for suitability of a composition
friction material for railroad car brake shoe use is the
ability of the friction material to pass the standards
set forth in the A.A.R. Specification M-926-72, February
13, 1973 Revision. Some of the pertinent dynamometer
performance test criteria called for in this A.A,R. Speci-
fication are as follows:
1. Instantaneous Retardinq Force During 45 Minute
Dynamometer Drag Test:
Drag Retar ~ ~orce
Heavy load 400 lbs. min.
Light load 300 lbs. min.
2~ Static Coefficient of Friction:
9 Test Average - .38 min.
3. Stop Distances From 90, 70, 50, 30, 10 mph Under
Light and Heavy Brake Shoe Loads (all stop dis-
tances must be within varying tolerances).
4. Wear Loss:
Drag Tests (total) - 0.60 in3 max.
Test Stops (total per sequence) - 1.20 in3 max.
As used herei~, the term "synthetic fiberU means
fiber made from a substance which does not naturally occur
in a fibrous state and includes glass, polyester and kao-
wuol. The term "synthetic fiberU ex dudes All forms of
cellulose, which naturally occurs in a fibrous state, but
3384
also
which can~be processed into a different fibrous form
(e.g., rayon). Some example mixes used a single type of
synthetic fiber, while others used several types of syn-
thetic fibers in combination. Other example mixes con-
tained a mixture of synthetic and cellulose fibers. All
mixes were totally free of asbestos and lead.
Organic binders, such as styrene butadiene rubber
(SB~), nitrile butadiene rubber (NBR) and modified phenolic
and cashew resins were used, Curing agents for the
organic binders included sulfur, zinc oxide and hexamethy-
lene tetramine.
A number of filler materials were used in vary-
ing combina~ions to produce the necessary low wear rate,
haxdness and high coefficient of friction. The fillers
used were cast iron grit, kyanite, cashew nut particles,
red iron oxide (hematite), black iron oxide, powdered
alumin~, graphite, barytes, coke, kaolin, cryclite,
carbon black and zinc powder.
Examples of the mixes formulated and tested
are shown below and denoted Mixes A-R. The compositions
of ingredients are expressed in weight percentages:
MIX A
Weight %
Glass Fiber 3.02
Organic Binder 18.63
rubber 15.74
resin 2.89
Curative Agents 1.64
Filler Materials 76.71
iron grit 12.11
kyanite 12.11
powdered alumina 0.27
black iron oxide 8.46
barytes 21.21
coke 22.55
MIX B
Weiqht %
Glass Fiber 2.91
Organic Binder 17.25
rubber 14.47
resin 2.78
Curative Agents 1.62
Filler Materials 78.22
iron grit 23.37
kyanite 11.68
powdered alumina 0.26
graphite 7.90
barytes 20.42
coke 11.68
cryolite 2.91
~33384
MIX C
Weight
Glass Fiber 1.61
Organic Binder 16.98
rubber 12.03
resin 4.95
Curative Agents 1.54
Filler Materials 79.85
iron grit 24.54
kyanite 13.99
powdered alumina 0.48
graphite 3.92
barytes 17.11
coke . 14.99
cryolite 4.82
MIX D
Weight
Glass Fiber 1.62
Or~anic 8inder 17.18
rubber 14.59
resin 2.59
Curative Agents 3.08
Filler Materials 78.13
iron grit 24.75
kyanite 14.11
powdered alu~ina 0,26
graphite 7.65
barytes 16.22
coke 15.12
3B4
MIX E
Weiqht %
Polyester Fiber 0.71
Organic Binder 18.93
rubber 10.98
resin 7.95
Curative Agents 1.24
Filler Materials 79.11
iron grit 13.36
kyanite 20.60
: powdered alumina 0.53
graphite 8.73
barytes 19.10
coke 11.44
cryolite 5.35
MIX F
Weight %
Glass Fiber 3.20
Organic Binder 19.74
rubber 16,68
resin 3.06
Curative Agents 1.74
Filler Materials 75.32
kyanite 12.84
hematite 16.04
cashew particles 1.28
powdered alumina 0.28
graphite 6.40
barytes 22.44
coke 16.04
-- 7 --
i~iL6)3384
MIX G
Weight
Glass Fiber 2,87
Organic Binder 17.69
rubber 14.95
resin 2.74
Curative Agents 1.56
Filler Materials 77.90
iron grit 23.02
kyanite 11.51
powdered alumina 0.26
graphite 5,74
barytes 20.12
coke 14.38
cryolite 2.87
3384
MIX H
Weight %
Fiber 3~59
glass 3.06
cellulose 0.53
Organic Binder 17.81
rubber 6.64
resin 11.17
Curati~e Agents 2.39
Filler Materials 76.22
graphite 6.99
barytes 13.87
coke 7.31
kaolin 3.62
powdered alumina0.53
iron grit 22.37
kyanite 13.17
hematite 8.36
il~)3384
MIX J
Weight
Fi~er 2.16
glass 1.45
cellulose 0.71
Organic Binder 17.82
rubber 15.06
resin 2.76
Curative Agents 1.57
Filler Materials 78.45
kyanite 11.59
powdered alumina0.26
iron grit 23.19
graphite 5~78
barytes 20.26
coke 14.48
cryolite 2.89
-- 10 --
384
MIX L
Weiqht %
Fiber 3.32
cellulose 0.50
polyester 0.33
kaowool 2.49
Organic Binder 19.57
rubber 2.99
resin 16.62
Curative Agents 2.65
Filler Materials 74.48
iron grit 31.08
kyanite 12.44
graphite 6.70
barytes 15.56
coke 4.98
powdered alumina0.50
kaolin 3.22
384
MIX M
Weight %
Glass Fiber 3.24
Organic Binder 16.97
rubber 9.46
resin 7.51
Curative Agents 1.17
Filler Materials 78.64
iron grit 24.71
kyanite 14.09
powdered alumina1.01
graphite 1.98
barytes 16.81
coke 10.26
cryolite 4.86
carbon black 4.92
- 12 -
lg~;~3~4
MIX N
Weiqht %
Glass Fiber 3.19
Organic Binder 16.90
rubber 14.35
resin 2.55
Curative Agents 1.60
Filler Materials 78.31
iron grit 24.34
kyanite 13.88
powdered alumina0.26
graphite 7.78
barytes 17.16
coke 10.11
cryolite 4.78
MIX O
Weight %
Glass Fiber 6.21
Organic Binder 16.99
rubber 4.92
resin 12.07
Curative Agents 3.79
Filler Materials 73.01
iron grit 31.12
kyanite 12.46
graphite 6.63
barytes 12.12
coke 7.62
zinc powder 3.06
-
il~;)33B4
MIX P
Weiqht %
Fiber 6.85
glass 6.34
cellulose 0.51
Organic Binder 17.36
rubber 5.02
resin 12.34
Curative Agents 2,40
Filler Materials 73.40
iron grit 31.75
kyanite 12.71
graphite 6.85
barytes 13.89
coke 5.08
zinc powder 3.12
_ 14 _
~33~34
MIX R
W ignt %
Fiber 9.56
glass 3.18
cellulose 6.38
Organic Binder 18.32
rubber 10.21
resin 8.11
Cura~ive Agents 4.51
Filler Materials 67.61
iron grit 26.67
kyanite 15.21
barytes 6.38
coke 11.17
powdered alumina 1.08
carbon black 7.10
The performance of these composition friction
materials against the A.A.R. standards is shown below,
where P = passed test and F = failed test:
1~33~4
TEST RESULTS - EX~MPLE MIXES
Static Wear Loss (in3) Drag Tests Stop Distances
Coeff. of Light Heavy Light Heavy
Mix Friction Drag/Stops Drag Drag ~SL BSL
A .347 .16/.33 P P P P
B .514 .09/.33 P P P P
C .570 .11/.26 P P P P
D .480 .23/.56 P P P P
E .390 .17/.57 P P P P
~ .563 .33/.18 P P P P
G .515 .11/.33 P P P P
H .397 .23/.56 P P P P
J .597 .10/.32 P P P P
L .494 .17/1.03 P P P P
M .457 .15/.59 P P P P
N .544 .12/.31 P P P P
O
p
20 R
All of the above mixes passed all of the A.A.R.
performance tests, with the exception of Mix A ~
which exhibited slightly low coefficients of friction.
Mix L showed a relatively high weax rate, although within
the A~A.R. standards.
It can be seen from the above test results that
friction materials made from compositions including various
synthetic fibers alone, in combination with other synthetic
fiber, or in combination with cellulose fiber can meet
rigorous A.A.R. standards and exhibit low wear rates.
The best wear rates were ex~ibited by Mixes A, B, C, G
~ ;33~ ~
and N, which contained from 1.61-3.19% of a single syn-
thetic fiber, and by Mix J which contained a low
total content fiber mixture of synthetic and cellulose
fibers.
Overall fiber content ranged from 0.71% poly-
ester (Mix E) to 9.56% glass and cellulose (Mix R),
~inder content ranged from 16~90% (Mix N) to 19~74% (Mix
F), while filler content was from 67.61% (Mix R) to 79.85%
. (Mix C). The amount and type of curative agents is mainly
dependent on the amount and composition of the organic
binder used.
In summation, I have discovered that composition
friction materials suitable for railroad use can be formu-
lated, without the use of lead or asbestos, by using a
relatively low content of various synthetic fibers alone,
in combinations, or in combination with cellulose fiber.
2Q
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