Cementitious composite friction compositions

Friction materials intended to be used as brake shoes, brake pads, and other brake components, comprising a composite in which one or more friction modifiers is embedded in a high strength cement matrix. The matrix material exhibits a flexural strength of at least 1,500 psi, a compressive strength of at least about 15,000 psi and a flexural modulus of about 1.times.10.sup.6 psi.

This invention relates to friction compositions which are generally 
comprised of friction modifiers such as particles and fillers embedded in 
a friction binder or matrix. 
More particularly, the invention relates to cementitious composite friction 
materials which provide high performance, asbestos-free, relatively 
inexpensive compositions suitable for use as friction elements in such 
applications as brake shoes and disc brake pads and clutch plate faces for 
cars and light trucks, shoes and discs for railway use, and blocks, shoes 
or discs for heavy duty use and for aviation use. 
Still more particularly, the invention relates to compositions comprising 
high strength inorganic cement binder materials and friction modifying 
filler materials or particles and to the manner in which such compositions 
are prepared. 
Brake shoes composed of various fillers bonded by low strength inorganic 
cement binders have been described in the following United States Patents: 
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Buell 484,404 issued October 18, 1892 
Laeufer et al 
818,833 issued April 24, 1906 
Laeufer et al 
909,617 issued January 12, 1909 
Norman 943,157 issued December 14, 1909 
Newman 1,019,989 issued March 12, 1912 
Steinbaugh 1,076,325 issued October 12, 1913 
Reid 1,205,482 issued November 21, 1916 
Laeufer 1,724,718 issued August 13, 1929 
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and others of a similar nature. 
With the adoption of synthetic resin binders and asbestos fillers, further 
development of such cement bonded friction materials appears to have been 
discontinued. 
The art is in need of improved friction materials having performance and 
cost characteristics that exceed the properties and performance of 
existing friction materials. Desired improvements include higher heat 
stability, improved processability, machining and handling and lower cost. 
An object of the invention is to provide a composition that satisfies the 
foregoing needs. 
Another object of this invention is to provide a friction material which 
retains its effectiveness at the elevated temperatures encountered in 
normal service and which permits more extended service use as compared 
with friction materials in which the principal binder is a phenolic resin, 
such as those described in the prior art, for example in U.S. Pat. No. 
3,879,338. 
A further object of this invention is to provide a friction material having 
a matrix with a flexural strength in excess of 1,500 psi, a compressive 
strength in excess of 15,000 psi and a flexural modulus of about 1.0 
million psi which when modified with suitable friction modifiers produces 
an acceptable braking effect with acceptable wear of the braking surfaces.

SUMMARY OF THE INVENTION 
These and other objects of the invention are accomplished by the 
compositions of the invention which comprise: 
(1) a high strength cement matrix material, and 
(2) one or more tribological additives which control the friction, wear, 
lubrication, and noise characteristics of the resulting composition. 
DESCRIPTION OF EMBODIMENTS 
Each of the constituents of the compositions of the invention and their 
preparation will now be described. 
(1) Cement Matrix Materials 
The friction binder useful in the present invention is a high strength 
cement, that is a cement which in the final composite exhibits a flexural 
strength of at least 1,500 psi, a compressive strength of about 15,000 psi 
or more and a flexural modulus of about 1.0 million psi. 
A wide variety of inorganic cements may be used to develop the high 
strength matrix material in the composites of the present invention. Brake 
linings have been produced in which the tribological additives were 
embedded in matrix materials based on one or more of the following 
cements: 
1. Silica Based Cements, e.g. Portland Cements 
2. High Alumina Cements 
3. Polymer Treated Cements (polymer modified cements, polymer impregnated 
cements) 
4. Other mixtures of Cement forming Ceramic Oxides e.g. Lime, Silica, 
Alumina, Magnesia, Phosphate 
5. Phosphate Based Cements 
Preferred high strength cements suitable for the present invention and 
their preparation are described in the following U.S. Pat. Nos. 4,353,748, 
4,410,366, 4,482,385, 4,501,830, 4,505,753, the disclosures of which are 
incorporated herein by reference and in numerous other patents and 
publications. 
The matrix materials useful in this invention also include the phosphate 
bonded matrix which may comprises the following: 
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Weight % 
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Alumina Cement 25- 75 
Calcined Alumina 8- 35 
Sodium Hexametaphosphate 
8- 25 
Magnesium Oxide 0- 66 
Water 8- 25 
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In addition to cement such as Portland Cement or High Alumina cement, the 
matrix material may include the additives disclosed in the five above 
noted U.S. Patents. For example, as described in Scheetz, U.S. Pat. No. 
4,505,753 the cement is preferably Class H Portland Cement, mixed with 
Min-U-Sil.sup.R, silica fume and a superplasticizer. As described in U.S. 
Pat. No. 4,410,366, the cement is a high alumina cement and a water 
dispersable or water soluble polymer or copolymer. 
More specifically, useful matrix components include the following in the 
indicated proportions, it being understood that the total comprises about 
60% of the composite: 
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Broad Narrow 
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Class H Portland Cement 
0- 40 15- 35 
Min-U-Sil .RTM. Silica 
0- 20 13- 17 
Silica Fume 0- 10 3- 7 
Mighty 150 (Superplasticizer) 
0- 3 2- 2 
Water 2- 20 5- 15 
Alumina Cement 0- 50 20- 45 
Polyvinyl Alcohol/Acetate 
0- 25 4- 17 
Calcined Alumina 0- 30 4- 20 
Sodium Hexametaphosphate 
0- 25 10- 20 
Magnesium Oxide 0- 50 10- 50 
Polyethyleneimine 0- 5 0.5- 2.0 
Wollastonite 0- 50 20- 30 
Polyvinylpyrrolidone 
0- 10 2- 7 
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Tribological Additives 
Virtually every manufacturer of brake linings has its own recipe or 
formulation for the composition it manufactures but in general these are 
comprised of the following principal classes of ingredients: 
(1) Fibers for reinforcement, for wear and heat resistance and for control 
of friction performance; 
(2) Dry lubricants to control friction coefficient, lower the wear and 
provide lubricity to the composition; 
(3) Inorganic fillers such as inorganic powders and/or metal particles to 
improve wear resistance and thermal properties and to control frictional 
characteristics; and 
(4) Various organic fillers: e.g. rubber to control squeal and noise, and 
cashew nut shell resin for processing and desired friction qualities. 
(1) Fibers 
Fibers are a principal constituent in the friction modifying portion of the 
composition of this invention. A preferred material for the fibers is 
chopped steel wool, commercially available in short lengths (0.050"-0.5"). 
Various steels can be used but for reasons of availability and economy, 
wires or ribbons of plain carbon steels like SAE 1020 are suitable. Other 
metal fibers, such as copper or brass, mineral fibers such as glass, or 
synthetic resin fibers such as aramid fibers may be used in place of some 
or all of the steel fiber component. When steel fibers are used, the steel 
fibers usually comprise between 20% and 60% by weight of the friction 
composition. 
(2) Dry lubricants 
One or more of a variety of finely divided dry lubricants may be present in 
the composition including: graphite, petroleum coke, carbon black, 
molybdenum disulfide or sulfur. Suitable graphites are commercially 
available as synthetic graphite in powder form (-20 mesh). Suitable 
petroleum coke, carbon black and other dry lubricants are also 
commercially available. When used, the foregoing materials are usually 
present in amounts between 2.5 and 15% by weight of the friction 
composition. 
(3) Inorganic Fillers 
Other materials which may be included in the compositions of the present 
invention include both soft and hard inorganic filler materials and 
include relatively hard materials such as Al.sub.2 O.sub.3, feldspar, MgO, 
SiO.sub.2, SiC, and softer fillers such as barytes (BaSO.sub.4), kaolin, 
talc, mica, iron oxide and litharge to provide better thermal conductivity 
and enchanced wear resistance, the composition may also include finely 
divided metallic materials such as iron, steel, copper, brass, zinc and 
the like e.g. as described in Rhee et al (BENDIX) U.S. Pat. No. 3,835,118, 
issued Sept. 10, 1974. Amounts of such materials up to about 25% by weight 
of the friction composition have been found beneficial in the friction 
materials of the present invention. 
(4) Organic Fillers 
A small amount of powdered nitrile rubber may be included to reduce squeal 
and other undesired noise in service. Powders of other rubbers such as SBR 
or butadiene rubbers can be substituted for the nitrile rubber. Another 
organic filler which may be present in the compositions of this invention 
intended for service as brake linings is cashew nut shell resin, described 
in U.S. Pat. No. 4,178,278. Other organic fillers known in the art may be 
provided for specific benefits. Up to about 5 weight percent of organic 
filler is generally employed based on the weight of friction composition. 
The friction materials of this invention may be cast from the above 
components or may be formulated as described in the following description 
which is intended to illustrate one mode of practicing the present 
invention and is not intended to limit the same. It will be understood 
that depending on the specific formulation, minor variations may be made 
in the procedure followed in preparing specimens for testing. 
All of the dry ingredients except for the fibers are dry blended. The 
fibers are added slowly while the mixture is being blended. After a 
suitable interval of mixing the material has been dry blended. Blending 
may be performed under vacuum, if desired. The liquids are then added and 
thoroughly mixed with the blended solids, again under vacuum if desired, 
until the material has become homogenous, and the desired consistency has 
been obtained. After extrusion, the material is cut, pressed or rolled 
into the desired shapes and thicknesses. 
The extruded object is wrapped to prevent moisture loss, and placed between 
two platens to retain its shape while it is being cured. 
After these procedures the material is tested for its flexural strength, 
modulus, and frictional properties. 
EXAMPLES 
The compositions of the following examples were prepared according to the 
above described procedure and cured as noted and then tested. The examples 
illustrate the invention but are not intended to limit it. In this 
specification and claims, unless specified otherwise, all parts and 
percentages are by weight and temperatures are in degrees celsius. 
EXAMPLE 1 
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Weight Volume 
Percent Percent 
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Matrix Material 
Class H Portland Cement 
29.1 24.7 
Min-U-Sil .RTM. Silica 
14.2 14.5 
Silica Fume 4.0 4.8 
Mighty 150 (Superplasticizer) 
0.7 1.6 
Water 9.1 24.2 
Friction Modifiers 
Steel Fiber 29.4 10.1 
Graphite 9.1 11.1 
Petroleum Coke 1.1 1.5 
Nitrile Rubber 1.1 2.5 
Cashew Nut Shell Resin 
2.3 5.0 
Weight Ratio, Modifier 
43:57 
to Matrix 
Curing 24 hours at 100% humidity, 20.degree. C. 
24 hours at 100% humidity, 60.degree. C. 
48 hours at ambient conditions 
17 hours at 200.degree. C. 
Flexural Strength 
3250 psi 
After cure 
Modulus after cure 
1.5 .times. 10.sup.6 psi 
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When tested in a "F.A.S.T" tester, the cured composition exhibited braking 
properties which were adequate for many applications. 
EXAMPLE 2 
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Weight Volume 
Percent 
Percent 
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Matrix Material 
Alumina Cement 30.5 9.5 
Polyvinyl Alcohol/Acetate 
6.0 13.2 
Calcined Alumina 10.3 6.8 
Water 11.9 31.4 
Friction Modifiers 
Steel Fiber 28.1 9.5 
Molybdenum Disulfide 
5.8 3.2 
Fused Magnesium Oxide 
2.2 1.6 
Barytes 2.2 1.3 
Nitrile Rubber 1.1 2.4 
Cashew Nut Shell Resin 
2.2 4.7 
Weight Ratio, Modifier 
41:59 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 125.degree. C. 
3 hours oven drying at 175.degree. C. 
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When tested in a "F.A.S.T" tester, the cured composition exhibited braking 
properties which were adequate for many applications. 
EXAMPLE 3 
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Weight Volume 
Percent Percent 
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Matrix Material 
Alumina Cement 28.2 21.6 
Polyvinyl Alcohol/Acetate 
11.1 22.0 
Calcined Alumina 
9.5 5.6 
Water 11.0 26.1 
Friction Modifiers 
Steel Fiber 26.0 7.9 
Graphite 8.4 9.0 
Petroleum Coke 1.0 1.2 
Nitrile Rubber 1.0 2.1 
Carbon Black 3.8 4.6 
Weight Ratio, Modifier 
40:60 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 125.degree. C. 
3 hours oven drying at 175.degree. C. 
Flexural Strength 
2680 psi 
After cure 
Modulus after cure 
1.0 .times. 10.sup.6 psi 
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FIG. 2 is a graph showing the braking properties of this composition when 
tested in a "F.A.S.T" tester. 
When tested on a 1985 automobile, the cured composition exhibited braking 
properties adequate for the car. 
EXAMPLE 4 
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Weight Volume 
Percent Percent 
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Matrix Material 
Sodium Hexametaphosphate 
14.6 16.0 
Alumina Cement (Secar 71) 
28.3 25.0 
Magnesium Oxide 14.1 10.7 
Water 8.8 24.0 
Friction Modifiers 
Steel Fiber 22.2 7.8 
Graphite 7.2 8.9 
Petroleum Coke 0.9 1.2 
Nitrile Rubber 0.9 1.9 
Carbon Black 3.3 4.5 
Weight Ratio, Modifier 
34:66 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 80.degree. C. 
15 hours oven drying at 125.degree. C. 
15 hours oven drying at 200.degree. C. 
15 hours oven drying at 400.degree. C. 
Flexural Strength 3270 psi 
After cure 
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EXAMPLE 5 
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Weight Volume 
Percent Percent 
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Matrix Material 
Sodium Hexametaphosphate 
15.3 16.1 
Alumina Cement 27.5 23.3 
Calcined Alumina 9.2 6.1 
Water 11.5 30.3 
Friction Modifiers 
Steel Fiber 23.5 7.9 
Graphite 7.6 9.1 
Petroleum Coke 0.9 1.2 
Nitrile Rubber 0.9 2.0 
Carbon Black 3.5 4.2 
Weight Ratio, Modifier 
36:64 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 80.degree. C. 
15 hours oven drying at 125.degree. C. 
15 hours oven drying at 400.degree. C. 
Flexural Strength 2700 psi 
After cure 
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FIG. 3 shows the results of a test of this composition as a brake pad in a 
"F.A.S.T" tester. 
EXAMPLE 6 
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Weight Volume 
Percent Percent 
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Matrix Material 
Sodium Hexametaphosphate 
15.1 16.1 
Alumina Cement 27.1 23.9 
Calcined Alumina 9.1 6.1 
Water 11.4 30.3 
Friction Modifiers 
Steel Fiber 23.1 7.9 
Graphite 7.5 9.1 
Petroleum Coke 0.9 1.2 
Silicon Carbide 2.4 2.0 
Carbon Black 3.5 4.2 
Weight Ratio, Modifier 
37:63 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 80.degree. C. 
15 hours oven drying at 125.degree. C. 
4 hours oven drying at 400.degree.C. 
Flexural Strength 2170 psi 
After cure 
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FIG. 4 shows the results of a test of this composition as a brake pad in a 
"F.A.S.T" tester. 
EXAMPLE 7 
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Weight Volume 
Percent Percent 
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Matrix Material 
Sodium Hexametaphosphate 
15.3 16.1 
Alumina Cement (Secar 71) 
27.5 23.3 
Calcined Alumina 9.2 6.1 
Water 11.5 30.3 
Friction Modifiers 
Steel Fiber 23.5 7.9 
Graphite 7.6 9.1 
Petroleum Coke 0.9 1.2 
Nitrile Rubber 0.9 2.0 
Carbon Black 3.5 4.2 
Weight Ratio, Modifier 
36:64 
to Matrix 
Impregnation 
Impregnation with high temperature NOVALAC EPOXY 
Curing 24 hours at ambient conditions 
15 hours oven drying at 80.degree. C. 
15 hours oven drying at 125.degree. C. 
15 hours oven drying at 400.degree. C. 
Impregnation at 200.degree. C. 
Flexural Strength 8530 psi 
After cure 
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EXAMPLE 8 
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Weight Volume 
Percent Percent 
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Matrix Material 
Sodium Hexametaphosphate 
12.5 14.0 
Polyethyleneimine 1.1 2.6 
Magnesium Oxide (Coarse) 
38.3 29.8 
Magnesium Oxide (Fine) 
5.0 3.9 
Water 8.9 24.9 
Friction Modifiers 
Steel Fiber 22.1 7.9 
Graphite 7.1 9.1 
Petroleum Coke 0.8 1.2 
Nitrile Rubber 0.8 2.0 
Carbon Black 3.3 4.6 
Weight Ratio, Modifier 
34:66 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 80.degree. C. 
15 hours oven drying at 125.degree. C. 
Flexural Strength 4030 psi 
After cure 
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EXAMPLE 9 
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Weight Volume 
Percent Percent 
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Matrix Material 
Alumina Cement 27.2 21.0 
Wollastonite 26.1 21.1 
Polyvinylpyrrolidone 
5.4 10.6 
Water 10.8 25.3 
Friction Modifiers 
Mullite 30.0 22.0 
Weight Ratio, Modifier 
30:60 
to Matrix 
Curing 24 hours at ambient conditions 
15 hours oven drying at 80.degree. C. 
15 hours oven drying at 200.degree. C. 
Fired to 1450.degree. C. 
Flexural Strength 
12150 psi 
After cure 
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In the compositions of the invention, the friction modifier and matrix can 
be used in the following weight proportions: 
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Weight % 
Broad Preferred Volume % 
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Matrix 40- 80 55- 70 70- 78 
Friction Modifiers 
60- 20 45- 30 30- 22 
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More specifically the proportions of the various friction modifiers when 
present are as follows, it being understood that the total comprises about 
40% of the composite: 
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Broad Narrow 
(Weight %) 
(Weight %) 
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Steel Fiber 0- 35 20- 30 
Graphite 0- 15 5- 10 
Petroleum Coke 0- 5 0.5- 2 
Cashew Nut Shell Resin 
0- 5 2- 3 
Molybdenum Disulphide 
0- 15 5- 8 
Magnesium Oxide 0- 5 2- 3 
Barytes 0- 5 2- 3 
Nitrile Rubber 0- 5 0.5- 15 
Carbon Black 0- 10 2- 5 
Silicon Carbide 0- 5 2- 3 
Mullite 0- 40 25- 35 
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