ELEMENT COMPOSITE DE FRICTION

COMPOSITE FRICTION ELEMENT

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A composite friction element suitable for the manu-
facture of railroad brake shoes of the composition type is
prepared from a mixture of a curable rubber binder having
distributed therethrough a plurality of fillers and a rein-
forcing fiber, at least one of the fillers having an oil ab-
sorption value of at least 30 and the fiber being formed from
an aramid polymer.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A brake shoe characterized by a body of a composite
friction material having a matrix comprised of a vulcanized
rubber binder material having distributed therethrough a
plurality of filler particles including hard mineral fillers,
friction modifiers and a reinforcing fiber, at least one of
the filler particles having an absorptive capacity sufficient
to absorb any binder decomposed during braking, the absorp-
tive filler having an oil absorption value of at least 30 and
being present in the body at a concentration of about 30 to
about 50 percent by weight and the reinforcing fiber being
a polymer characterized by recurring units of the formula
<IMG>
wherein Ar1 is selected from the group consisting of p-
phenylene, a chloro-substituted p-phenylene, and 4,4'-
substituted diphenyl methane and Ar2 is p-phenylene and
the fiber being present is said body at a concentration of
about 0.5 to about 10.0 percent by weight.
2. The brake shoe of Claim 1 wherein the hard mineral
fillers are selected from the group consisting of iron ore,
iron grit, sand, fused silica and aluminum silicate.
3. The brake shoe of Claim 1 wherein the friction
modifiers are selected from the group consisting of graphite,
partially cured cashew resin solids, lead and lead sulfide.
17

4. The brake shoe of Claim 1 wherein the absorptive
filler is selected from the group consisting of alumina
trihydrate, BaSO4, ground shale, anthracite coal, magnesium
oxide and clay.
5. The brake shoe of Claim 1 wherein the polymer fiber
is poly(p-phenylene diamine terephthalamide) -co-poly (4,4'-
diamino diphenyl methane terephthalamide).
6. The brake shoe of Claim 1 wherein the rubber binder
is present in the composite friction body at a concentration
of about 15 to about 30 percent by weight; the hard mineral
fillers are present in the composite friction body at a con-
centration of about 25 to about 50 percent by weight; and the
friction modifiers are present in the composite friction body
at a concentration of about 15 to about 30 percent by weight.
7. A brake shoe characterized by a body of a composite
friction material having a matrix comprised of a vulcanizable
rubber binder material being present in the body at a concen-
tration of about 15 to about 30 percent by weight, the rubber
binder material having distributed therethrough a plurality
of filler particles including hard mineral fillers, the
hard mineral fillers being present in the body at a concentra-
tion of about 25 to about 50 percent by weight, and further
friction modifiers, the friction being present in the body
at a concentration of about 15 to about 30 percent by weight,
at least one of the filler particles having an absorptive
capacity sufficient to absorb any binder decomposed during
18

braking, the absorptive filler having an oil absorptive value
of at least 30 and being present in the body at a concentra-
tion of about 30 to about 50 percent by weight, and a rein-
forcing fiber formed from a polymer characterized by recurr-
ing units of the formula
<IMG>
where Ar1 is selected from the group consisting of p-pheny-
lene, a chloro-substituted p-phenylene, and a 4,4' -substitut-
ed diphenyl methane and Ar2 is p-phenylene and the fiber be-
ing present in the body at a concentration of about 0.5 to
about 10.0 percent by weight.
8. In a brake shoe composition including a quantity
of friction media, quantity of a vulcanizable rubber bond
material, a quantity of synthetic reinforcing fiber being
formed from a polymer characterized by recurring units of
the formula
<IMG>
where Ar1 is selected from the group consisting of p-pheny-
lene, a chloro-substituted p-phenylene, and a 4,4' -substi-
tuted diphenyl methane and Ar2 is p-phenylene, a quantity
of absorptive media, and a quantity of friction modifiers,
the improvement therein comprising,
said friction media comprising hard mineral fillers,
19

said bond material comprising a vulcanizable rubber,
synthetic resin and curing agents to react therewith,
said synthetic reinforcing fiber being of a high strength
chemically inert, and high temperature-resistant and having
physical characteristics of a tensile strength proximating
400,000 psi (28.12 x 106g/cm2), elongation to break proximat-
ing 3 to 4 percent, tensile modulus proximating $.5 x 106 psi
(5.97 x 108 g/cm2) and density proximating 0.052 lb/in3
(1.44 g/cc), and thermal characteristics of decomposition at
a temperature proximating 930°F (500°C) and a 40 percent de-
crease in tensile strength at 500°F (260°C), said fiber being
present in a range by weight of 0.5 to 10.0 percent of the
composition, and
said absorptive media comprising at least one filler
having an oil absorption value of at least 30 to absorb any
of said bond decomposed during braking, said absorptive media
being present in a range by weight of 25 to 50 percent of
the composition.
9. A brake shoe composition as defined by Claim 8 and
further characterized by,
said quantity of said synthetic reinforcing fiber being
further limited to a percentage range by weight of 1.8 to
4.88 percent.
10. A brake shoe composition as defined by Claim 8
and further characterized by,
said hard mineral fillers selected from a group con-
sisting of iron grit and calcined kyanite,

said bond material rubber being a styrene- butadiene
emulsion polymer and said bond material synthetic resin being
cashew polymer, and
said absorptive filler selected from the group consist-
ing of barium sulfate, ground shale rock, alumina trihydrate
and magnesium oxide.
11. A brake shoe composition as defined by Claim 10
and further characterized by,
said hard mineral fillers being in an amount by weight
proximating 37 percent,
said absorptive filler being in an amount by weight
proximating 25 percent.
12. A brake shoe composition as defined by Claim 8 and
further characterized by,
said hard mineral fillers selected from the group con-
sisting of iron grit, iron ore, sand, fused silica and cal-
cined kyanite,
said bond material rubber being a styrene-butadiene
emulsion polymer and said bond material synthetic resin be-
ing cashew polymer, and
said absorptive fillers selected from the group consist-
ing of barium sulfate, alumina trihydrate, magnesium oxide,
rottenstone, anthracite coal and clay.
13. A brake shoe composition as defined by Claim 8
and further characterized by,
said hard mineral fillers being in a range by weight
of 25 to 50 percent,
21

said bond being in a range by weight of 15 to 30 percent,
and said friction modifiers being in a range by weight
of 15 to 30 percent.
14. A brake shoe composition including a quantity of
friction media, a quantity of a vulcanizable rubber bond
material, a quantity of synthetic reinforcing fiber being
formed from an aramid polymer,
said friction media comprising hard mineral fillers,
said bond material comprising a vulcanizable rubber,
synthetic resin and curing agents to react therewith,
said synthetic reinforcing fiber being of a high strength
chemically inert, and high temperature-resistant and having
physical characteristics of a tensile strength proximating
400,000 psi (28.12 x 106g/cm2), elongation to break proximat-
ing 3 to 4 percent, tensile modulus proximating 8.5 x 106psi
(5.97 x 108 g/cm2), and density proximating 0.052 lb/in3,
(1.44 g/cc), and thermal characteristics of decomposition at
a temperature proximating 930°F (500°C) and a 40 percent
decrease in tensile strength at 500°F (260°C), said fiber
being present in a range by weight of 0.5 to 10.0 percent of
the composition, and
said absorptive media comprising at least one filler
having an oil absorption value of at least 30 to absorb any
of said bond decomposed during braking, said absorptive media
being present in a range by weight of 25 to 50 percent of
the composition.
22

Description

r~o~ r
1. Field of the Invention
The present invenkion relates to friction elements
and more particularly, to composite friction element useful as
brake shoes for railroad brakes which element is devoid of
asbestos.
2 The Prior ~rt
Brake shoes for railroad ~rakes of the composition
type are formed of a composite friction material composed of
a rubber binder resin, having distributed therethrough a variety
of fillers and a reinforcing fiber such as asbestos. Examples
oE composite friction elements used in the manufacture of the
brake shoes are disclosed in U.S. Patents 3,835,006 and
U.S. 3,9S9,194.
U.S. 3,885,006 teaches composite friction elements
formed of 15-35~ by weight of a resin binder, 45-65~ by weight
asbestos and 3-10~ by weight of one or more fillers which
function to impart increased hardness and wear resistance to
the brake shoe or function as friction modifiers. Fillers
which are disclosed as imparting increased haxdness to the brake
shoe include barytes such as ~aS04, alumina (A12O3), zinc and
limestone (CaCO3)~ Fillers which function as friction modifiers
include brass powder, iron powder, carbon black, ground cork
and aldehyde condensation products of cashew nut liquid.
U.S. 3,359,194 teaches composite friction elements
which are useful as brake shoes for railroad rolling stock with
relatively soft steel wheels. The friction element is composed :
of 3~25% by weight of a rubber binder, 20-70~ by weight of an
inorganic filler and 2-12~ by weight of a fiber. The fiber
component disclosed in the patent is composed of asbestos
fibers or a cellulosic fiber such as wood, sisal, jute and rayon
-- 1 ~
1~ ~
~7

fibers. The rubber binder is a natural or synthetic rubber or
an elastomeric material which i5 vulcanized or otherwise cured
to form a hard matrix in which the remaining components are
distributed. A phenolic resln at a concentration of 1-30~ is
incorporated in -the composition oE the friction element as a
strengtllening or stiffening agent for the rubber matrix.
Phenolic resins disclosed in the patent include oil modified
two-stage powdered phenol formaldehyde resins and a liquid
resin prepared from natural sources of phenol derivatives
derived from aldehyde reacted cashew nut shell oil and contain-
ing a curing agent such as hexamethylene tetramine. ~mong the
inorganic fillers disclosed in U.S. 3,959,19~ include graphite,
cast iron, iron oxide, calcium carbon~te, b~rytes and carbon
hlack.
~ n forming composite friction elements, the inorganic
fillers are added for various purposes. For example, the hard
mineral fillers such as iron grlt are added for their friction-
al properties, fillers such as lead o~ide are included to
modify the frictional effect of the hard mineral fillers; lead
powder acts as a lubricant and friction modifier; asbestos
fibers as a friction rein~orcing agent contributing high physi-
cal strength to produce uniformly high friction against ferrous
mating surfaces such as railroad car wheels, and withstand high
braking temperatures. The rubber resin binds and holds to-
gether the mixture of materials.
Asbestos has been generally satisfactory as a rein~
forcing fiber for use in friction elements, but recent environ-
mental studies have revealed that asbestos may have a detrimen-
tal effect on the health of those who are exposed to its pre-
sence and, therefore, it is currently desirable to seekalternative compositions in which the asbestos content of brake
shoes is reduced or eliminated

C118~
Heretofore, attempts to substitute other fibers for
asbestos generally have failed to produce satisfactory friction
elements. For example, glass and ceramic fibers fracture in
the mixing procedures used to prepare -the brake shoe composi-
tions with the result that they contribute poor reinforcement.
Furthermore, glass fibers are brittle and tend to break down
at the braking interface during service of the brake shoe and
high wear rates are thereby encountered. Moreover, the non-
porous glass surfaces have a low surface area as compared with
asbestos, and the glass fibers do not absorb products of
decomposition of the organic components caused by heat which
occurs during braking. As a result, when glass fibers are used
as the reinforcing material, Eriction drops preclpitously at
the temperatures generated during braking. This friction drop
due to poor absorption by the reinforcing fibers is known in
the brake shoes industry as "fade".
Organic fibers such as cotton, wood pulp and rayon,
synthetic fibers composed of such organic polymers as poly-
acrylonitrile, polyamide, polyester and the like have low sur-
face area and exhibit poor heat resistance. These latter fibermaterials lose strength at temperatures in the range of 200 -
300F (~3-1~9C) and break down in the same manner as the
rubber binder. In fact~ a small amount of organic fiber is
often added to an asbestos reinforced composite friction
element to introduce a slight controlled "fade" to save the
brake from destruction when the brake is used beyond its rated
capacity.
It is the primary object of the present invention to
provide an asbestos-free composite friction element suitable
for brake shoe application and which is capable of withstanding
high temperatures, has high physical strength~ provides good
braking characteristics particularly applicable to railroad
-- 3 --

braking, and meets the test standards of the AAR ~American
Association of RaiLroads) for brake shoes made with a blend of
organic and/or inorganic materials.
SUMMARY OF THE INVENTION
In accordance with the present invention there is
provided a composite friction element suitable for the manu-
facture of high friction composition type railroad brake shoes
which are devoid of asbestos and will wi-thstand the braking
parameters associated with thedeceleration of railroad loco-
motives, the composite element being comprised of a rubberbinder having distributed therethrough a plurality of fillers
at least one of which has an oil absorption value of at least
30 and a fiber formed from an aramid polymer
Thus, the present invention provides a brake shoe
characterized by a body of a composite friction material having
a matri.~ comprised of a vulcanized rubber binder material having
distributed therethrough a plurality of filler particles includ-
ing hard mineral fillers, friction modifiers and a reinforcing
fiber, at least one of the filler particles having an absorptive
capacity sufficient to absorb any binder decomposed during
braking, the absorptive filler having an oil absorption value
of at least 30 and being present in the body at a concentration
of about 30 to about 50 percent by weight and the reinforcing
fiber being a polymer characterized by recurring units of the
formula
_ _
H H O o
I I 11 11
N - Arl - N - C - Ar2 _
wherein Ar1 is selected from the group consisting of p-pheny-
lene, a chloro-substituted p-phenylene, and 4,4'-substituted
diphenyl methane and Ar is p-phenylene and the fiber being
present in said body at a concentration of about 0.5 to about
-- 4 --

1~L39~7
10.0 percent by weight.
Brake shoes made from the asbestos-free composite
frictionma-terials of the present invention meet the ~AR
standards for hi~h fric-tion composition type brake shoes.
DESCRIPT ON OF THE PRE~ERRED EMBQDIMENTS
The precise composition of the composite-friction
element of the present invention may be widely varied, but in
all instances the element contains a rubber binder represented
at least in part by a vulcanizable rubber or a mixture thereof
containing dispersed filler particles having high oil absorp-
tion values and aramid polymer fibers which impart wear
resistance, afford the desired level of friction coefficient
and which .reinforce or strengthen the composite element as a
whole.
The asbestos-free composite friction element of the
present invention has the following representative compositional
range in approximate percent by weight:
~ 4a -

~;3'~
Component Appro~lmate Percentage
Range by Weight
1. Curable rubber binder 15-30%
2. Hard Mineral Flllers 25~50%
3. Friction ~odifiers 15-30%
4. Reinforcing aramid fiber 0.5-10.0%
5. Absorptive Fillers having an
Oil Absorption Value in
excess of 30 20-50%
If the above-noted components were measured as a
percentage range by volume, the range for each would be much
narrower. Because the density of the above components vary so
significan~ly, the percentage range by weight varies according-
ly. For example, the percentage range by volume of a filler
material such as sand or iron grit would be narrow, but because
of the difference in density of these two materials, the iron
grit becomes a dominant material when viewed in percentage by
weight. The percentage range by weiyht of the other components
are affected accordingly.
The rubber binder used in the practice of the present
invention can be any of the rubber binder materials convention-
ally used by the railroad brake art for the manufacture of
brake shoes. Such rubber materials include unvulcanized
natural and synthetic rubber or elastomeric materials that can
be vulcanized or otherwise cured in situ to form a hard matrix
for the remaining components of the composite friction mater~
ials of the present invention~ Examples of such rubbers are
the butyl rubbers, styrene-butadiene copolymer rubbers,
acrylonitrile rubbers and chlorinated butyl rubber. These
rubbers are vulcani2ed with the aid of vulcanizing catalysts
such as sulfur, 2-mercaptobenzothiazole, tetramethylthiuram
disulfide and mixtures thereof which accelerate the rate of
cure of the rubber~ The vulcanizing catalysts are included
in the rubber binder composition in minor amounts, e.g., at
concentrations in the range of about 1 to about 3 percent by
weight based on the weight of the composite friction element.
- 5 -

37
Also included in the rubber binder composition are
conventlonal rubber fillers such as carbon black, zinc oxide,
lead oxide, lead powder, M~O and ZnO. These fillers are
incorporated in the rubber binder at concentrations ranging
from about 5 to about lS percent by wei~ht based on the weight
of the composite friction element.
Thermosetting resins such as phenol-aldehyde resins
may also be lncorporated in the rubber binder composition as
a strengthening or stiffening agent for the rubber matrix.
The phenolic resin may be a synthetic resin prepared from
conventional organic compounds such as phenol and formaldehyde.
Alternatively, the phenolic resin may be a resin prepared
from natural sources of phenol derivatives such as cashew nut
shell oil, which oils are reacted with aldehydes to impart
thermosetting properties thereto. Typically, the phenolic
resins are incorporated in the rubber binder composition at
concentrations in the range of about ] to about 10 percent by
weight based on the weight of the composite friction element~
Curin~ agents such as hexamethylenetet:ramine are included in
the phenolic resin, in relatively small amounts, e.~., about
0.2 to about 1.0 percent by welght based on the weight o~ the
composite friction element to accelerate the cure of the
phenolic resin.
Hard mineral fillers incorporated in the brake shoe
composition to promote friction in the brake shoes prepared
from the composite friction materials of the present invention
include iron which may be in the form of iron ore or iron grit,
as well as sand, fused silica, and calcined kyanite, i.e.
aluminum silicate.
Friction modifiers incorporated into the composite
friction material to stab:ilize the coefficient of friction of
the brake shoe under a variety of operatin~ and climatic

~3~37
conditions to which the brake shoe will be exposed so as to
provide wear resistance to the shoe may be either organic or
inorganic materials such as graphite, and partially cured
cashew-resin solids, calcined kyanlte (A12SiO5), as well as
lead and lead compounds such as lead sulfide.
Reinforcing aramid polymer fibers suitable for use
in the practice of the present invention as a substitute for
asbestos are commercially available from E.I. Du Pont de Nemours
under the trade mark "KEVL~R". Exemplary of KEVLAR fiber
materials suitable for use in the practice of the present
invention is KEVLAR 29, a continuous filament yarn having the
following physical properties:
TABLE I
KEVLAR 29 Physlcal Properties
Density 0.52 lb~in
Filament Diameter 0~00047 in
Denier per Filament 1.5
**Break Elonyation 1% - 4%
*Tensile Strength 400,000 psi
Tenacity 22 gpd6
**Specific Tensile Stren~th 8 x 10 in
*Modulus 9 x 106 in 480 gpd
**Specific Modulus 2.3 x 108 in
Temperature Resistance Useful properties from
420~ to 500F ~40%
decrease in tensile
strength at 500F).
*Dry yarn test
**Yarn property divided by density
The term "aramid polymer" as used in the present
specification means a synthetic polymeric resin generally
designated in the art as an aromatic polycarbonamide. "Aramid
polymer" is a polymer described in U.S. Patents 3,652,510,
U.S. 3,699,085 and U~S. 3,673,143 and is believed to be of a
composition hereinafter described. ~n these patents, the
polymers disclosed therein include fiber forming polymers of
high molecular weight, e.g. having an inherent viscosity of at
least about 0.7, characterized by recuring units of the formula
- 7 -
'

EI H O O
l l 11 11
N - Ar - N - C - Ar - C- _
wherein Arl is p phenylene and/or chloro-substituted p-phenyl-
ene, and/or 4,4'-substituted diphenyl methane, l.e.,
and/or ~/ ~ and/or ~ ~ C~2
and Ar2 is p-phenylene, i.e.,
~r ~
Illustrative examples of polycarbonamides coming
within the definition of the above formula are poly (p-phenyl-
ene terephthalamide~, chloro-substituted poly (p-phenylene
terephthalamide), and copolymers thereof.
The designatlon of the position of location of the
substituent groups on the aromatic nuclei of the aramid polymer
refers to the location of the substituents on the aromatic
diamine, diacid or other coreactants from which the aramid
polymer is prepared.
Although the aramid polymer or aromatic polycarbon-
amide may consist primarlly of carbonamide links ~-CONH-) and
aromatic ring nuclei~ conforming to the formula above, the
polymer may contain up to 20 mole percent and preferably
0 to 5 mole percent of non-conforming comonomer units which
provide units in the polycarbonamide chain different from
E E O
11 11
- N - Arl - N - and ~C - Ar2 ~ C - ,
such as aromatic carbonamide units whose chain extending ~onds
are coaxial or parallel and oppositely directed, e.g.
-- 8 --
1~

~3'~37
O H H / H
C - ~ ~ N or - N ~ N -
CL
meta-phenylene units, non-aromatic and non-amide groups.
A more comprehensive disclosure of the composition
of aramid polymers is found in U.S. 3,673,143 as well as the
divisional patent thereof, U.S. 3,817,941, the teachings of
which are herein incorporat~d by reference~
Independent analytical tests and infra-red analysis
have indicated that KEVLAR 29 could be predominately (95%
weight) pvly (p-phenylene diamine terephthalamide and could be
chemically described as poly (p-phenylene diamine terepht~al-
amide)-co-poly (4,4'-diamino diphenyl methane texephthalamide).
It is critical to the practice of the present inven-
tion tha~ the reinforciny fibers used in the composite fric-
tion element of the present invention be formed from aramid
polymers. Thus during braking, railroad brake shoes encounter
high quantities of energy in the form of heat generated by
the frictional engayement of the brake shoe with the steel
wheel oE the railroad locomotive so as to raise the interface
temperature of the shoe to temperatures in the order of 2000 F
(1093C). It is believed that due to the relatively high
tensile strength and temperature resistance of aramid fibers, '~
e.g. 400,000 psi (28.12 x 10 g~cm-) and 420 - 500 F (215-260 C) .t
respectively, the aramid fibers when incorporated in the fric-
tion element of the present invention retain their functional
propert~es as reinforcing materials when exposed to the high
temperatures encountered in braking.
It is also critical to the practice oE the present
invention that high absorptive filler materials be used in
combination with the reinforcing aramid polymer fiber. Filler
_ g _
i ,~

~:~L3g~ 37
materials suitable for this function are organic or inorganic
fillers having a high surface area whereby the loss of absorp-
tive capacity resulting from the absence of asbestos is re-
placed by the hi~h absorptlve filler. The term "high absorp-
tive filler" as used in the present specification means a
filler material determined to have an Oil Absorption Value of
at least 30.
The term "Oil Absorptive Value" as used in the
present specification rneans the milliliters of linseed oil
re~uired to wet a predetermined volume of the filler, i.e. 100
cubic centimeters (cc~ of the filler.
In determining the Oil Absorption Value, a 20 grams
por-tion of the filler powder is placed in shallow ceramic
dish and raw linseed oil is metered into the dish from a
burette. The llnseed oil delivered by the burette is stirred
and worked into the powder. The addition of the oil to the
powder causes the powder to agglomerate into small balls which
increase in size and decrease in number as more oil is metered
from the burette into the dish. The addition of the oil is
continued until the oil wetted powder coalesces into a single
mass or ball of powder. The number of milliliters of oil which
cause the coalescence of the powder into an integral, single
balled mass is multiplied by 5 to obtain the oil absorption
number. The oil absorption number is then multiplied by the
specific gravity of the filler, and this latter product is
termed the oil absorption value. Listed below in Table II
are the oil absorption values of a variety of filler materials
useful in the practice of the present invention.
-- 10 --
~.~

TABI.E II
OIL ABSORPTION VALUE OF FILLERS
Filler Oll Absorptlon Value
Alumina Trihydrate, type A 92
Alumina Trihydrate, type B 102
Alumina Trihydrate, type C 78
Barite (Barytes, BaSO4) type A 49
Barite (Barytes, BaSO4) type B 63
Barite (Glassmakers coarse)40
Barite (Glassmakers fine) 72
Rottenstone (Ground Shale, Penna,~ 86
Anthracite Coal (99.9%~325 mesh) 72
~lagnesium Oxide 83
Clay, Georgia ruhber Grade A 138
Clay, Georgla rubber Grade B 140
The examples which follow illustrate the practice of
the present invention.
Examples I - V
A series of composite friction elements were prepared
in which the amounts of the binder components, filler materials
and aramid polymer fiber was varled. The various compositions
of the composite friction materials are summarized in Table III
below.
TABLE III ;1
Binder Components Examples
Percent by Wei~ht
I II III IV V
GRS Syntheti~ Rubber 6.48 6.00 6.00 6.48 6~57
Sulphur 1.76 1.60 1.60 1.76 1.72
Litharge ~PbO) 4.40 4.00 4.00 4.40 --
Cashew Polymer 2.96 2.72 2.72 2.96 2O99
Lead Powder 1.48 1.40 1.40 1.48 --
Carbon Black 0O80 0.72 0.72 0.80 --
Hexamethylene Tetranine 0.40 0.36 0.36 0.40 0.37
MgO 1.96 1.80 1.80 1.96 --
ZnO ~ 5.86
TO~AL BOND20.2418.60 18.60 20.24 17.51
-- 11 --
. r~
~:

Filler ~aterials Examples
Percent by Weight
I II III IV V
Graphite-fine syntheti.c 6.80 7O00 7.00 6.80 --
Galena (PbS) lOo 8411~ 0011~ 00 10 ~ 84 ~~
Cashew Resi.n-Solids10.9210.00 10.00 10. 80 10~ 26
Calcined Kyanite
( 2 3 1 2) 13~ 64 14.00 14.00 13.64 13.70
Calcined Petroleum Coke 6. 04 6O40 6.40 6.04 6.18
White Iron Grit 22~ 8823~ 0023~ 00 22 ~ 8823~ 07
Barytes (BaSO~) 3~ 76 8.20 6.40 3~ 76 7.47
Fused Aluminum Oxide ~- -- Q.40 -- --
Ferrocene ~~ ~ 0~12
Alumina Trihydrate -- -- -- -- 11.72
Shale-~inely ground -- -- -- -- 8.30
Fiber
Aramid Polymer 4~ 881~ 80 _ 3 ~ 20_ 4~ 88 1.79
(REVLAR 29)
100.00100~00 100,00 100.00 100.00
The GRS rubber used in the examples was A 23~ sytrene-
butadiene emulsion polymer. The "cashew polymer" used was a
millable cashew nut shell oil liquid partially polym~rized
which was cross-linked with hexamethy:lene tetramine at control-
led temperatures. The "cashew resin" was one sold as NC-300 by
the Minnesota Mining and Manufacturing Co., this cashew resin
is an ~0% solution in toluene of a polymerized resin derived
from cashew nut shell liquid having a viscosity at 25C, of
10,000 to 18,000 cps and a gel time in minutes of from 20 to 55
at 83C. The calcined petroleum coke was National Carbon~s
W-8300 and the iron grit was Cleveland Metal Abrasive's G-120.
The ingredients of Examples I-V were compounded as
follows:
The rubber component, which was in crumb form and the
iron grit were soaked wlth toluene in a sealed container for
24 hours at about 150 F and thereafter milled in a dispersion
blade mixer. All of the remainlng components except the aramid
polymer fiber were added to the mixture in the container and
the batch was mixed in a dispersion blade mixer and worked to a
12 -

~L3L3~D8~
paste. The aramid polymer fiber was then added and the result-
ing product mixed thoroughly untll uniform. This resulting
mix was then passed through a hammer mill after which it was
dried in an oven maintained at 150F (65C) so as to effect
the complete removal of the toluene contained in the mixture
but not to advance the binder materials beyond the flow point.
The resulting mlxtures of Examples I-V were cold
press formed into a performed briquette. The briquette was
then molded into the shape of a brake shoe in a suitable mold
for a period of one hour at 350F ~177C) and a pressure of
2500 pounds per square inch (1.76 x 105g/cm ) to cure and
harden the mixture.
Brake shoes molded from the composite friction
materials of Examples I-V were subjected to dynamometer and
grade service (drag) tests in accordance with AAR (Association $
of American Railroads) Test Speciication M-926-72.
The dynamometer test subjects 3 randomly selected
brake shoes to a sequence of light braking and heavy braking
stops from speeds of 10-90 mph (16-145 kmh) in a prescribed
sequence. The material lost during the stop tosts is determin-
ed by weighing the shoes be~ore and after the shoe undergoes
the braking sequence. In order for the shoe to be acceptablé,
the average of the accumulated loss in volume of the 3 shoes
must not exceed 1.2 cu. in. tl9.66 cc) per shoe.
Drag tests measure the retarding forces produced
by the test shoe which must exceed prescribed minimum require-
ments, e.g. in the light brake test, the requirement is that
with a brake shoe load of 925 lbs. ~ 25 lbs., ~419 kg + 11 Kg)
the minlmum retarding force produced by the shoes must not be
less than 300 lbs., (136Kg) and in the heavy brake test
(1425 lbs. ~ 25 lbs (646 Kg ~ 11 Kg) load), the retarding
force must not be less than 400 lbs~ (181Kg)
13 -
"
,...

The results of these tests are summarixed in Table IV
below.
TABLE IV
Composite Fric- AAR Dynamometer Test AAR Drag Test
tion Material Materlal lost after Retarding Force
of Example prescribed braking l,ight Heavy
sequence completed Braking Braking
cu. in./shoe (cc~shoe) lbs (Kq)
0~-15A I 0.63 (10.32) 310 (141) 370 (168)
05-22A II 0.46 ( 7.54) 300 (136) 390 ~177)
05-25A III 0.33 ( 5.41) 300-~(136+) 400+(181~)
-24A IV 0.31 ( 5.08) 300~tl36+) 400+(181+)
~25A V 1.24 (20.32) 300~(136~) 400~(181+)
It is seen from the foregolng examples that brake
shoes made from an asbestos-free composition, but with the
inclusion of an aramid polymer fiber and a high absorptive
filler have brake test results acceptable for rai]road braking
service.
For purposes o~ comparison~ the procedure of
Examples I - V were repeated with the exception that a fiber
product other than an aramid polymer fiber was used in the
preparation of the composite friction material, The composi~
tions of the comparative composit~ materials designated by
the symbol "C" are summarized in Table V below.

~3~ 7
TABLE V
COMPARATIVE FRICTION ~TERIALS
Cl C2 C3 C4
3~ O~ D~L~ PERCENT BY WEIGHT
GRS Synthetic Rubber5~58 6O12 6.08 5~62
Sulphur 1. 67 1.84 1.65 1.53
Litharge (PbO) 4.19 4.59 4.13 3. 81
Cashew Polymer 2.79 3. 06 2~78 2~ 57
Lead Powder 1. 40 1~ 53 1.39 1.28
Carbon black 0.74 0.82 0,75 0. 69
Hexam~thylene tetramine 0.37 0.4~ 0. 38 0~ 35
MgO 1~86 2.04 1. 84 1~ 70
Filler Materials
-- -- ~t
Graphite 6.4 -- 6.38 5.89
Galena (PbS) 10.1 11.23 10.17 9.40
Cashew Resin Solids10.3 7.84 10.24 9.47
Iron Grit 21.5 23. 69 ~~ 19~ 83
Barytes (BaSO4) -- -- 14.30 -~
Mullite (Alumlnum Silicate)12.8 14.67 12~79 11~ 82
Petroleum Coke 5.6 6.15 5.67 5~24
Full Cured Cashew Nut
Shell I,iquid ~- 6. 57 ~~ ~~
Fiber
Wollastonite F-l 14.7
Mica ~- 10.06
Cast Iron Fibers
(~'t x 0~0005~) ~~ ~~ 21~46 ~~
Fiberfrax (Aluminum
Silicate) short staple
fiber ~ 20.80
srake shoes molded from the composite friction
materials of comparati~e compositions Cl - C4 were subjected to
the AAR dynamometer and grade service tests in accordance with
the same procedures used to evaluate the brake shoes molded
rom the composite friction materials of Examples I - V. Brake
shoes molded from the composite friction material Cl failed the
AAR dynamometer test by not passing the 70 mph, 6000 lb.
(113 kmh, 2722 Kg~ B~SoL~ stops.
Brake shoes molded from the C2 composite friction
material passed the AAR dynamometer tests but wide fluctuations
were encountered .tn the drag retardation tests and the friction
material was of questlonable physical strength based on the
- 15 -

poor appearance of the shoe af-ter the completlon of the tests.
Brake shoes molded from the C3 composite friction
material when tested by the AAR dynamometer test failed the
drag test and were long on stops.
Brake shoes molded from the C4 composite friction
material failed the AAR dynamometer test and had problems of
blistering and spalling.
l~