U.S. patent number RE36,705 [Application Number 09/280,865] was granted by the patent office on 2000-05-23 for pultrusion method of making composite friction units.
This patent grant is currently assigned to Glasline Friction Technologies, Inc.. Invention is credited to Benjamin Booher.
United States Patent |
RE36,705 |
Booher |
May 23, 2000 |
Pultrusion method of making composite friction units
Abstract
A composite friction unit includes a three dimensional composite
body formed of a substantially uniform array of predominately glass
strands of primary reinforcing fibers in matrix of phenolic resin
material, the reinforcing fibers distributed throughout the body in
a predetermined uniform distribution and orientation, and a
substantially uniform array and distribution of secondary fibers
extending transverse to the primary fibers thereby forming a
friction unit having a predetermined size and configuration and
uniform distribution and alignment of fibers throughout.
Inventors: |
Booher; Benjamin (Scottsdale,
AZ) |
Assignee: |
Glasline Friction Technologies,
Inc. (Scottsdale, AZ)
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Family
ID: |
27487980 |
Appl.
No.: |
09/280,865 |
Filed: |
March 29, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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272030 |
Jul 8, 1994 |
5495922 |
|
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032269 |
May 24, 1993 |
|
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647137 |
Jan 29, 1991 |
5156787 |
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Reissue of: |
593184 |
Feb 1, 1996 |
05690770 |
Nov 25, 1997 |
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Current U.S.
Class: |
156/177; 156/179;
156/269; 188/251A |
Current CPC
Class: |
B29B
15/125 (20130101); B29C 70/025 (20130101); B29C
70/521 (20130101); B29C 70/525 (20130101); B29C
70/545 (20130101); D04H 3/08 (20130101); F16D
69/026 (20130101); B29C 70/52 (20130101); B29K
2061/04 (20130101); B29K 2705/10 (20130101); B29K
2707/04 (20130101); B29L 2031/16 (20130101); B29L
2031/7482 (20130101); Y10T 156/1084 (20150115) |
Current International
Class: |
B29B
15/10 (20060101); B29B 11/16 (20060101); B29B
15/12 (20060101); B29C 70/02 (20060101); B29C
70/04 (20060101); B29C 70/00 (20060101); B29C
70/52 (20060101); B29C 70/54 (20060101); D04H
3/08 (20060101); F16D 69/02 (20060101); B29C
070/52 () |
Field of
Search: |
;156/177,178,179,180
;188/251A,251R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Davis; Robert
Attorney, Agent or Firm: Baker & Maxham
Parent Case Text
REFERENCE TO RELATED APPLICATION
This application is a Continuation-in-Part of my application Ser.
No. 08/272,030 filed Jul. 8, 1994, now U.S. Pat. No. 5,495,922,
entitled "UNIFORM COMPOSITE FRICTION UNITS", which is a
Continuation-in-Part of Ser. No. 08/032,269, filed May 24, 1993,
now abandoned, which is a Continuation-in-Part of Ser. No.
07/647,137, filed Jan. 29, 1991, now U.S. Pat. No. 5,156,787,
entitled "PULTRUSION METHOD OF MAKING BRAKE LININGS".
Claims
I claim:
1. A continuous manufacturing process for making composite friction
units comprising the steps of:
selecting a substantially uniform array of predominately glass
strands of primary reinforcing fibers;
wetting said plurality of strands of primary reinforcing fibers
with a phenolic resin material;
pulling said wetted strands of reinforcing fibers in a
predetermined uniform distribution and orientation through a
composite forming die for forming a body having a peripheral
configuration of said friction units;
introducing a continuous array of predominately transverse
secondary fibers between selected pairs of said plurality of
primary fibers prior to entry into said forming die;
solidfying said body by curing said resin; and
selectively cutting said body at least along one path transverse to
said strands into .[.it.]. .Iadd.a .Iaddend.plurality of said
friction units, thereby forming a plurality of friction units
having a predetermined size and configuration and uniform
distribution and alignment of fibers throughout.
2. A process according to claim 1 wherein the step of selecting
said primary reinforcing fibers selecting said fibers to make up
about 50 to about 70% by weight of said body, and said step of
introducing said secondary fibers includes introducing sufficient
secondary fibers to make up from 5% to 20% by weight of said
body.
3. A process according to claim 2 wherein said resin is selected to
contain one to ten percent by weight of powder taken from the group
consisting of rubber, copper, barite, talc, ceramic, and nut shell
flower.
4. A process according to claim 1 wherein said resin is selected to
contain about 2 to 5% by weight of talc powder, about 5 to 10% by
weight of copper powder and 3 to 5% by weight of one of nut shell
flower.
5. A process according to claim 1 wherein said step of cutting said
body is at an angle other than ninety degrees and forms a friction
surface at said angle to the fibers.
6. A process according to claim 1 wherein said step of heating said
resin is carried out by RF prior to entry of the fibers into the
die. .Iadd.
7. A process according to claim 1, wherein in the step of
selectively cutting said body at least along one path transverse to
said strands into a plurality of said friction units, the selective
cutting is performed so that the primary fibers are substantially
parallel to a friction surface on said friction units.
.Iaddend..Iadd.8. A process according to claim 1, wherein in the
step of selectively cutting said body at least along one path
transverse to said strands into a plurality of said friction units,
the selective cutting is performed so that the secondary fibers are
substantially parallel to a friction surface on said friction
units. .Iaddend..Iadd.9. A process according to claim 1, wherein in
the step of selecting the substantially uniform array of primary
reinforcing fibers, the fibers are selected from the group
consisting of individual strands, woven fabrics, matting, stitched
fabrics and combinations thereof. .Iaddend..Iadd.10. A process
according to claim 1, wherein in the step of selecting the
substantially uniform array of primary reinforcing fibers, the
selected fibers are woven fabric. .Iaddend..Iadd.11. A process
according to claim 2, wherein in the step of selectively cutting
said body at least along one path transverse to said strands into a
plurality of said friction units, the selective cutting is
performed so that the primary fibers are substantially parallel to
a friction surface on said friction units. .Iaddend..Iadd.12. A
process according to claim 2, wherein in the step of selectively
cutting said body at least along one path transverse to said
strands into a plurality of said friction units, the selective
cutting is performed so that the secondary fibers are substantially
parallel to a friction surface on said friction units.
.Iaddend..Iadd.13. A process according to claim 4, wherein in the
step of selectively cutting said body at least along one path
transverse to said strands into a plurality of said friction units,
the selective cutting is performed so that the primary fibers are
substantially parallel to a friction surface on said friction
units. .Iaddend..Iadd.14. A process according to claim 4, wherein
in the step of selectively cutting said body at least along one
path transverse to said strands into a plurality of said friction
units, the selective cutting is performed so that the secondary
fibers are substantially parallel to a friction surface on said
friction units. .Iaddend..Iadd.15. A process for making composite
friction units having at least one friction surface, the process
comprising the steps of:
selecting a substantially uniform array of reinforcing fibers, the
fibers impregnated with a resin;
pulling said reinforcing fibers in a predetermined uniform
distribution and orientation through a forming die;
introducing a plurality of secondary fibers to the primary fibers
prior to entry into said forming die, the secondary fibers
transverse to the primary fibers, the primary and secondary fibers
forming a body;
solidifying said body by curing the resin; and
selectively cutting said body into a plurality of said composite
friction units, so that the primary fibers are substantially
parallel to the friction surface. .Iaddend..Iadd.16. A process
according to claim 15, wherein in the step of selectively cutting
said body into a plurality of said composite friction units, the
selective cutting is performed so that the secondary fibers are
substantially parallel to the friction surface. .Iaddend..Iadd.17.
A process according to claim 15, wherein in the step of selecting
the substantially uniform array of reinforcing fibers, the
fibers are impregnated before they are selected. .Iaddend..Iadd.18.
A process according to claim 15, wherein in the step of selecting
the uniform array of fibers, the fibers are selected from the group
consisting of individual strands, woven fabrics, matting, stitched
fabrics and combinations thereof. .Iaddend..Iadd.19. A process
according to claim 15, wherein in the step of selecting the uniform
array of fibers, the selected
fibers are woven fabric. .Iaddend..Iadd.20. A process according to
claim 15, wherein in the step of selecting the uniform array of
fibers, the fibers are selected from the group consisting of glass,
rock, ceramic, carbon, graphite, aramid, wool, cotton, organic
fibers, and inorganic fibers. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to composition friction elements and
pertains particularly to improved friction units and method and
composition for making same.
A friction brake is basically a pair of friction elements, one
rotating and one stationary, brought into engagement to produce a
friction force measured as brake torque for either slowing or
stopping the rotating element. Brakes are designed so that the
brake torque is somewhat proportional to the input force used to
engage the elements. Unfortunately, pressure is not the only factor
that influences the frictional response of the brake elements.
Friction effects between friction elements cause friction force and
brake torque to vary with engaging pressure, speed, and
temperature, and to depend upon deposited interfacial film for
stability.
The rotating element of a brake system is usually a steel disc or
drum, and the stationary element is usually a composition pad or
shoe lining. The materials forming the composition element are the
principle unpredictable variables that have the greatest affect on
the performance characteristics of the brake system. Desirable
materials for the composition element must have good friction, wear
and heat resistant characteristics. This includes good face
resistance, or the ability to maintain good (preferably
substantially uniform) braking with heat buildup.
Until recent years, the predominant material used in the
manufacture of friction pads and discs for brakes, clutches and the
like was asbestos. These were manufactured by a molding process
where each unit was formed in a mold cavity. However, it was
discovered that asbestos is a carcinogenic substance, and that such
use released potentially harmful amounts of it into the
environment. For this reason, some industrialized countries
prohibit the use of asbestos friction materials, and others
including the United States require the use of asbestos to be
phased out over the next few years. Therefore, there exists an
urgent need for safe and effective friction materials and
economical methods of manufacturing the materials into suitable
friction units.
Extensive efforts have been put forth in recent years in an effort
to find suitable environmentally safe materials and compositions
having the desirable wear, heat and other characteristics to serve
as a substitute for asbestos. These efforts have been frustrated by
the many and varied parameters involved, including the range of
needs to be met. For example, different size vehicles require
different size friction pads and often have other variables
including higher operating forces and temperatures.
Attempts to satisfy the need for long life, high friction heat
resistant friction materials have included proposals to utilize
various chopped fibers molded in a bonding matrix, such as a resin.
The friction unit is formed in the traditional fashion by a molding
process, with the fibers randomly oriented and placed in a binder,
such as either a dry powder resin cured under heat and pressure, or
placed in a liquid resin in a mold and cured. Examples of these
compositions and manufacturing methods are disclosed in U.S. Pat.
No. 4,119,591, granted Oct. 10, 1978 to Aldrich, U.S. Pat. No.
4,259,397, granted Mar. 31, 1981 to Saito et al., and U.S. Pat. No.
4,432,922, granted Feb. 21, 1984 to Kaufman et al.
However, friction units made by this method are expensive to
manufacture and have not been satisfactory, because of their lack
of uniformity in performance and durability. For example, units
from the same batch may vary as much as 35% in performance
characteristics. The non-uniformity of results has been found to be
caused largely by a non-uniformity of distribution and orientation
of the fibers in the matrix. This not only creates expensive
inspection and quality control problems, it can also create
maintenance problems, and sometimes even hazardous conditions. For
example, pads that have been matched for performance at initial
installation may vary over their useful life.
In my aforementioned patent applications, I disclosed improved
compositions and methods of manufacture for brake pads and linings.
However, continuous work on perfecting these indicate that further
improvements in both compositions and methods of manufacture are
desirable and have been developed as set forth herein. For example,
insufficient transverse mechanical properties were found to be a
problem among many samples produced by the pultrusion process.
Another problem included excessive voids in some samples.
Accordingly, it is desirable that improved compositions, structures
and methods be available to overcome the above and other problems
of the prior art.
SUMMARY OF THE INVENTION
It is the primary object of the present invention to provide
improved brake friction linings compositions and methods of
manufacturing.
Another object of the present invention is to provide improved
pultrusion process for the manufacture of friction elements.
In accordance with a primary aspect of the present invention,
friction units are manufactured by a pultrusion process and
comprise a composition of a controlled density and orientation of
an array of primary fibers with secondary reinforcing fibers in a
phenolic resin with selected minor quantities of one or more of
various mineral and/or metal powders.
Another aspect of the invention includes friction units made by a
continuous process comprising the steps of selecting and wetting a
uniform array of primary strands of reinforcing fibers with a
liquid phenolic resin material, adding strands of secondary
reinforcing fibers transverse to said primary strands, pulling the
impregnated strands of reinforcing fibers through a composite
forming die for forming a body having at least a portion of the
peripheral configuration of the friction units, and selectively
cutting the body into a plurality of the friction units.
In accordance with another aspect of the invention, a minor
quantity of up to about 5% of milled or chopped fibers are added to
the resin formulation and is picked up with the resin and moves
with the strands of primary reinforcing fibers as they are pulled
through the liquid resin formulation and through a forming die for
forming a body of friction units.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects and advantages of the present invention
will become apparent from the following description when read in
conjunction with the accompanying drawings wherein:
FIG. 1 is a perspective view schematically illustrating an
apparatus and a preferred method of carrying out the invention;
FIG. 2 is a detailed sectional view of a brake pad in accordance
with the invention;
FIG. 3 is a perspective view of a brake shoe lining in a drum type
brake in accordance with the invention;
FIG. 4 is a schematic illustration of an apparatus like that of
FIG. 1 modified for carrying out a preferred method of the
invention; and
FIG. 5 is an enlarged detailed view of elements being assembled in
accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 of the drawing, there is schematically
illustrated the simplest form of an exemplary system for carrying
out a the process of the invention for making brake friction units
in accordance with the invention. The system, designated generally
by the numeral 10, comprises a plurality of creels 12 from which a
plurality of strands 14 of an elongated continuous fiber or arrays
of fiber are drawn and passed through suitable guide means across
suitable guide rollers or bars 16 to and through an impregnating or
wetting bath 18 of a suitable resin such as a phenolic resin. The
fibers may be in the form of individual strands, woven fabrics,
matting, or stitched fabrics of combinations of them.
The fibers or strands 16 are the primary fibers and are coated or
wetted by a resin in any suitable manner. In the illustrated
embodiment they pass into or through a bath of a suitable liquid
resin contained within a reservoir 20 for wetting or impregnating
the fibers or strands. They can also be wetted by resin injection
such as by pumping resin into a ring that surrounds the rovings.
The fibers 14 will in reality number in the hundreds in several
rows which may be parallel and are guided through or beneath
suitable guide roller or other guide means 22 in the resin bath and
over guide rollers or other guide means 24 and into a die 26 for
imparting at least a part of the final shape or configuration of
the friction units.
The strands, particularly if glass fibers, may require a sizing
treatment, i.e. application of a compound or chemical to insure a
good or complete wetting of the fibers and a good bond between the
fibers and matrix. A bulked roving (bunch of strands or fibers) is
preferably used. Bulked roving is produced by a process in which a
standard roving is fractured or splintered by forced cold air. This
provides two useful properties, 1) increased diameter which assists
in providing fill to low glass content pultrusion, and 2) the
"splinters" provide for good mechanical bonding with the resin
matrix.
The resin wetted strands are passed or pulled through the die 26,
where they are shaped into part of the desired configuration and at
least partially cured. The fiber and resin composition is
preferably at least partially cured in the die by any suitable
means such as ultraviolet (UV) radiation, radio frequency (RF),
heating or other means, and the fibers will thereby remain in
tension. The composite unit emerges, or more particularly is pulled
in tension from the die in the form of an elongated continuous bar
or block 28 having at least part of the peripheral configuration of
the brake pad or other article being manufactured. In the case of
brake pads, the bar preferably has the precise peripheral
configuration of the final pad. The bar or block 28 is forced or
pulled from the die 26 by suitable means, such as hydraulic
pullers, tractors (not shown) or the like, and positioned to be cut
into individual friction or brake pad units or pieces in the
illustrated embodiment. The pultrusion process provides a
substantially controlled or predetermined distribution and
orientation of the primary fibers throughout the body of the
friction unit.
In the illustrated embodiment, a suitable cutting apparatus, such
as a band saw 34 supported on its pulleys or rollers 36 and 38, is
movable transverse to the axis or movement of the bar 28 for sawing
the bar into a plurality of brake pads 40. Other suitable cutting
apparatus may be utilized, such as water jets, laser, abrasive or
other means. The cut surface represents the friction surface in
this embodiment, and the fibers are preferably substantially normal
or perpendicular to this surface. It may be desirable in some
instances to provide a different angularity to the fibers in
relation to the friction surface. This can be accomplished by
cutting the friction units from the bar at the desired angle to the
axis thereof.
The brake pads, upon being cut from the bar, fall onto a conveyor
belt 42 and are moved into position held by a jig or fixture 44, 46
for operation of a punch or drill press 48 for forming mounting
holes 50 and 52 in the brake pads for attachment to a backing
plate. The pads or linings may be adhesively bonded to a backing
plate, in which case the holes may be eliminated. The pads are then
accumulated in a suitable storage container or bin 54, where they
are then packaged and shipped. This provides a highly efficient and
economical manufacturing process.
Referring to FIG. 2, a section view through a brake pad 40 is
illustrating glass fibers 14 in a matrix of thermoplastic material
19. The primary fibers 14 are shown substantially perpendicular to
a friction surface 56 of the brake pad 40. Other friction devices,
such as clutch pads, would preferably have similarly oriented
strands or fibers. The density and mixture of primary fibers as
well as secondary fibers may be varied to suit the particular
application. Specifically, in the case of brake shoes, however, the
orientation of the primary fibers may be in a drum transverse to
the drum surface. The fibers are pulled through a die having the
curve or arc of the desired shoe and selectively cut width-wise. In
this application the cut surface does not represent the friction
surface. A secondary preparation step, such as grinding, must be
performed to attain the desired surface.
While brake pads are illustrated in the process, it is apparent
that clutch friction pads and brake shoe type of pads or linings
may also be manufactured by this process. The die is set to shape
one peripheral outline of the emerging articles and can include
annular shapes. In the case of pads for disc rotors, the fibers are
oriented uniformly at an angle preferably normal to the friction
surface for the highest efficiency of manufacture. However, in
certain applications, an orientation parallel to the friction
surface may be satisfactory or even preferred for manufacturing as
well as performance. For example, in a brake shoe and drum
configuration as illustrated in FIG. 3, the fibers may preferably
run parallel to the friction surface for ease of manufacturing.
This orientation is preferred where inner laminate shear strength
is a factor. As illustrated, a typical brake drum 58 is illustrated
having an inner friction surface 60 engaged by a brake shoe lining
62. The lining 62 is formed of fibers, the ends of which are shown
at 64, with the fibers oriented substantially parallel to the
friction surfaces as indicated along arrow 66. This orientation of
the fibers provides for an economical construction of brake
friction units in a pultrusion process. Thin curved pultruded bars
or slabs can be cut as in the FIG. 1 illustration to form the liner
units.
The shoe linings may be formed by the pultrusion process in the
form of a thin arcuate slab, and the linings cut to width as
described above with respect to pads. This provides an economical
technique for producing consistently uniform units. However, where
orientation of the fibers normal to the friction surface is
desired, a rectangular slab may be cut along an arc to form the
curved friction surfaces.
The articles may be cut from the pultruded bar by any suitable
means, such as by laser, water or other means. The present method
and process provides a highly efficient manufacturing process for
the production of high quality friction unit that are asbestos free
and/or a controlled uniform composition and quality. The pultrusion
process enables rapid production and the careful control of fiber
density, mixture, and orientation on a continuous basis.
The primary reinforcing fibers 14 for the brake pads or linings are
preferably glass fiber, but the pad may contain other materials and
fibers or combinations thereof. In addition, other fibers may be
woven or distributed in with the glass fibers in various selected
distributions and proportions to alter and or enhance certain
characteristics. For example, various fibers may be distributed in
various concentrations substantially uniformly throughout the unit
for optimizing various parameters such as inner laminar shear
strength, wear, fade, and cooling. The addition of secondary
reinforcing fibers can be accomplished in several ways. One
preferred way is as illustrated in FIGS. 4 and 5.
Many different fibers or strands and combinations may be utilized,
including but not limited to glass, rock, ceramic, carbon,
graphite, aramid, nomex, wool and cotton fibers of other organic
and inorganic materials. Various metallic fibers such as copper and
aluminum, may also be utilized in various proportions with
non-metallic fibers. In one preferred composition, the fibers are
about 20% by weight of wool or cotton fibers applied in a second
stage wetting process to extend transverse to the remaining
fibers.
The manufacturing system and process, as illustrated, provides for
the controlled predetermined orientation of the primary fibers, as
well as the controlled predetermined uniformity and density of the
primary fibers within the resin matrix. For example, the
composition of the friction device determines many of its
characteristics, such as its durability, heat resistance, and
friction resistance. With this process, the primary fibers may be
controllably distributed and oriented uniformly at any suitable
angle to the friction surface of the brake pad or friction device.
Thus, the process and materials have the capability of providing
superior, predictable and consistent performance.
The process may include the addition of secondary fibers that
extend transverse to the primary fibers in order to add shear
strength to the units. In one form of the process, as illustrated
in FIGS. 4 and 5, dry transverse fibers in the form of stitched
fabric are introduced between selected layers of the primary
fibers. Referring to FIG. 4, a pultrusion system is illustrated and
designated generally by the numeral 72. The system includes a wet
out pan 74 through which a plurality of primary strands 76 or
rovings are passed from a source, such as a plurality of spools or
bobbins (not shown). The primary strands 76 which may number in the
hundreds pass through a first guide 78, of traditional form and a
second guide 80 added in accordance with the present invention. The
guide 80 spreads the primary fibers to accommodate a plurality of
secondary transverse fiber spools 82 which are positioned between
selected pairs of primary fiber strands 76. These spools 82 carry
rolls of short dry transverse fibers 84 which are stitched together
by threads 86, 88 and 90 as shown in FIG. 5. Excess resin stripped
away as the rovings pass through the strippers is returned via
suitable conduit or the like 98 back to the reservoir 74.
The secondary fibers are of a length to extend across the full
width of the array of primary fibers as they pass into and through
a stripper station of one or more strippers designated generally at
92 comprising pairs of stripper bars 94 and 96. The dry transverse
secondary fibers are entrapped between the converging wet rovings
of primary fibers and become woven into a transverse interlock as
illustrated in FIG. 5. For example, it has been found that the
transverse fibers must be about eight inches or more in length in
order to extend fully across a six inch wide production price.
These transverse fibers are carried along with the primary fibers
as they are pulled into and through the preforming and final
forming dies 100 for completion of the friction blanks. The
transverse fibers may be present in the amount of about 1% up to
about 20% of the total fibers.
Milled or chopped fibers such as glass, wool or cotton fibers may
also be added and introduced into the matrix material and are
picked up by the elongated primary strands of fibers as they pass
through the resin. The fibers are in the range of from 1% to about
5% by weight of the matrix material. The short fibers are
preferably in the approximate range of 0.015 inch to about 0.062
inch and dispersed somewhat randomly throughout the matrix. This
dispersement of milled fibers provides multi-axis mechanical
reinforcement, as well as crack and compression resistance in areas
to be machined for mounting purposes. In this process, may be mixed
in the primary resin reservoir, or in the alternative two
reservoirs of resin may be used. In one arrangement a first tank
contains a low viscosity resin to enhance the wetting of the fibers
(preferably predominately glass fibers) as they are passed through.
The fibers then pass through a second tank of higher viscosity
resin containing many of the fillers and chopped wool, cotton or
other fibers. The chopped fibers preferably make up from about 1%
to 5% of the fibers. They will be picked up by the primary strands
of fibers and will generally extend transverse to the primary
fibers with proper modification of the handling equipment. Other
fibers may also be used in this way. These and the transverse
fibers may be used together or in the alternative to achieve the
desired shear strength.
The matrix material may be any suitable resin that is either a
thermoplastic material or non-thermoplastic material, and it may
require various forms of curing. It may be cured, for example, by
cooling, heating, or by the use of UV or other radiation or the
like. However, the materials must be capable of enabling the
forming of the units by the pultrusion process.
One suitable phenolic resin is available from BP Chemicals under
the trademark "CELLOBOND" and product designation J2041L. This
product is described as a high viscosity phenolic for use in heat
cured pultrusion, does not require any catalyst and will provide
reasonably fast line speeds and cure cycles. This provides enhanced
efficiency in production. In some cases, the manufactured unit must
be post cured to assure the best performance. For example, it may
be baked at about 500 degrees Fahrenheit for one or more hours.
Preheating may also be required for larger cross sectional units.
This may be taken care of in any suitable manner, such as by use of
an RF oven and usually requires low temperature from about 80 to
150 degrees Fahrenheit.
Another suitable resin is resorcinol-modified phenolic resin
available under the trademark Rescoriphen from INDSPEC Chemical
Corporation.
The matrix material will be formulated to include heat dissipation
and/or friction modifiers, such as graphite and/or non-ferrous
metallic powders. For example, from about one to ten percent by
weight of one or more fillers and/or modifiers, such as graphite
powder and/or one or more non-ferrous metallic powders, may be
incorporated into the matrix material. Other materials include but
are not limited to mineral fillers, rubber powder, copper powder,
ceramic powder, nut shell flower (such as walnut or cashew). These
may each be in the amount of one percent (1%) to ten percent (10%)
and preferably in the amount of 3% to 5% by weight. Nut flower has
been found to increase the shear strength of the unit and to
enhance the fade characteristics of pads or linings. During
braking, heat breaks down the nut shell flower causing nut shell
oil to combine chemically with the resin polymer molecule in a
process known as chain branching. Thereby, the polymer becomes
stronger and more able to withstand high temperatures that
contribute to brake fade. The ceramic powder is preferably in the
form of hollow spheres of about seven to ten microns. These have
been found to serve as a lubricant in the pultrusion process and to
enhance the hardness and wearability of the friction units.
The resins may be aqueous based and contain compounds or additives
known as molecular sieves to reduce and/or eliminate by product
which may cause voids in the product. Suitable such molecular sieve
materials are available as both sodium activated and hydrated
chabazite in several mesh sizes. These products absorb gases and
water, reduce potential voids or cracks due to gases and vapor. The
typical chemical names are sodium aluminosilicate and calcium
aluminosilicate. These are in powder form and may be added in
amounts of from about 1% to about 5% by weight of resin.
Another additive which has shown to reduce the amount of water
vapor formed during the process is barium sulfate (BaSo.sub.4)
commonly referred to as barite.
The resins may also be non-aqueous based which would eliminate or
reduce the need for molecular sieves. The resin may also be low
condensation resin which produces less water by products.
The fiber to resin matrix may vary from about one part fiber to two
part
resin, up to about three part fiber to one part resin. A preferred
fiber to matrix composition is from about 60% to 75% fiber to 25%
to 40% resin or matrix mix. The matrix preferably has from 5% to
10% by weight of one or more of graphite powder, copper powder,
aluminum powder and the aforementioned powders. In addition, aramid
pulp and other synthetic fiber pulps may be added or distributed
throughout the matrix material.
Certain thermoplastic materials may be desirable for other specific
applications. The thermoplastic material may, for example, be a
suitable polyester and may also have components such as powders of
graphite or other material to aid in friction control and the
dissipation of heat. For example, a one to about ten percent by
weight of graphite powder uniformly distributed throughout the
thermoplastic material aids in the dissipation of heat. Alternate
compositions may include small amounts of other materials, such as
non-ferrous metallic powders, such as copper, aluminum or the like.
For example, a one to ten percent by weight copper powder may also
be utilized to enhance the dissipation of heat. Thus, the
composition must be compatible with the pultrusion process and at
the same time provide satisfactory friction units.
I have discovered that various proportions and compositions of
materials can affect the pultrusion process as well as the
performance characteristics of the brake pad and lining units. For
example, many test samples with many ranges of examples of
compositions have been constructed and tested in order to optimize
friction units. In recent tests the best formulation was found to
be 100 parts resin, 12 parts barite, 12 parts copper powder (SG5),
2 parts nut shell flower, 10 parts butadience-acrylonitrile
elastomer (BAE), 4 parts talc and 113 parts glass fibers. This
formulation produced the best crack free specimens. Die temperature
for a one inch diameter specimen was 300.degree. F.-400.degree. F.
at pull speeds of about 2-3 inches per minute. Core temperature was
in the range of about 120.degree. F.-140.degree. F. Talc was
substituted for graphite and provided lubrication without
decreasing shear strength.
While I have illustrated and described my invention by means of
specific embodiments, it is to be understood that numerous changes
and modifications may be made therein without departing from the
spirit and the scope of the invention as shown in the appended
claims.
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