Note: Descriptions are shown in the official language in which they were submitted.
5Zl~
This invention relates to a process for producing
a friction pad.
In the manufacture of organic friction pads it
has been considered essential that all water be removed
from the composition of materials before curing the resin
binder container therein. If the water content is greater
than 2% by weight of the composition of materials, the
heat required to cure the resin in the composition of
materials, in evaporating the water, can cause bubble marks
and/or voids adjacent the surface of the friction pad,
Therefore, all the ingredients in the composition of materials
are dried before being mixed together to form a friction
pad.
However, the density of the dry asbestos as com-
pared to the other ingredients in the composition of
materials requires substantial mixing before a uniform
composition of materials is obtained. Unfortunately, such
mixing causes a portion of the asbestos to become airborne
and polute the surrounding enYironment. Often the amount
of such airborne asbestos exceeds the allowable limits
set in the United States by the Occupation Safety and Health
Act of 1970. In an effort to maintain the quality of air
within the allowable limits, most manufacturers have dis-
covered that extensive air filtration systems are required
in existing structures.
According to the present invention there is
provided a process for producing a friction article,
the process including the steps of mixing a solution of
water and from 4-24% by weight of hexamethylenetetramine
with a composition of materlal which includes a dry phenolic
resin and hexamethylenetetramine powder to form a slurry
and then communicating the slurry to a mold. Process further
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includes a step of compressing the slurry in the mold to
remove up to 95% of the water in the solution to form
a briquette. The briquette is then dried to remove
substantially all of the soluction and thereby reestablish
the dry weight relationship of the phenolic resin and
the hexamethylenetetramine as in the composition of material.
The briquette is then cured to establish a desired shape and
density of the friction pad.
The present invention is a dustless process
for manufacturing organic friction pads without the need
for remodeling existing manufacturing facilities.
In a specific embodiment of the invention, after a uniform
slurry is achieved, it is transported to a storage container.
A fixed volume of slurry is measured into a first mold and a
compressive force is applied to the slurry to remove up to
95% by weight of the water therefrom and create a briquette.
The briquette is removed from the first mold and transported
to a forced air oven or dielectric heater. The internal
resistance of the ingredients in the briquette to an electric
field in the dielectric heater causes the temperature of the
briquette to rise. This temperature rise of the briquette
is from the inside toward the surface. As the temperature
of the briquette increases, water in the briquette is
driven toward the surface and evaporated into the
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5~
surrounding environment. When the water content of the briquette is
about 1% of the total weight of the composition of material, the dry
briquette is removed from the dielectric heater. The dry briquette is
transported to a second mold and a compressive force applied to preform
a friction pad to a desired shape. The preformed friction pad is removed
from the second mold and bent into a desired shape. Thereafter the preformed ;
friction pad is transported to an oven where the temperature is raised
sufficiently to cure the resin contained therein. After curing of the resin,
the friction pad is re~oved from the oven and ground to a final specification.
It is the ob~ect of this invention to provide a process for the manu-
facture of a water slurry briquette from which an organic friction article
can be produced.
It is another object of this invention to provide a process of
manufacturing an organic friction pad in a relatively dust free environment.
It is another object of this invention to provide a slurry process
of manufacturing an organic friction pad.
It is a further object of this invention to provide a method of removing
water from a briquette through a dielectric heater device.
It is a still further object of this invention to provide a method
of water slurry manufacturing an organic friction pad with a means of maintaining
the relationship between the ingredients in the composition of material, even
though some of the ingredients are soluble in water which is ultimately removed
from the organic friction pad.
These and other objects will become apparent from reading this specifica-
tion and viewing the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawing schematically illustrates the steps that make up the
process o manufacturing a brake friction pad according to this invention~
5214
DETAILED DESC~I~TION OF _ HE INVENTION
The drawing illustrates a process for manufacturing an organic
friction pad in accordance to the principles of th~s invention.
Dry ingredients retained in storage containers 10, 12, 14, 16)
x and y are combined into an enclosed batching bin 18 in a desired relation-
ship depending on the specific formula selected for an organic brake friction
pad. These dry ingredients, which for organic brake friction pads always
include as a minimum resin, asbes~os, cashew nut powders, an elastomeric
material, and a friction modifler, are conveyed from the batching bin 78
to the slurry mixer 20. The dry _n~r2dients are tumbled in the slurry mixer
20 for about 10 minutes to disburse the heavier ingredients in the composition
of materials throughout the low density asbestos. Thereafter, wa~er with
hexamethylenetetramine, commonly referred to as hexa, in the solution i3
added ~o the dry ingredients to protuce a slurry 23. When a uniform siurry
23 is achieved, the slurry 23 is dumped from the mixer 20 and transported
on a belt conveyor 22 to a hopper 24 in a briquetting machine 26.
The briquetting machine 26 has a first station where a fixed
volume of slurry is removed from the hopper 24 and poured into a first mold 25.
The first mold 25 is transported to a dewatering chamber 30 at a second
2Q Ytation where a compressive force is applied to the slurry. A pump 32 creates
a force ~hich draws water from the dewatering chamber 30 and com~unicates the
same into a water holding tank 34. The compressive force on the slurry is
such that up to 95~ by weight of the initially added water and hexa are removed
to produce a briquette 36.
The briquette 36 is conveyed into a dielectric dryer 38 and placed
between a first plate 40 and second plate 42. The first plate 40 is connected to
an ad~ustable source of electrical energy 44 and the second plate 42 is connected
to ground 46. The source of electrical energy 44 produces an alternating
electric field between the first and second plates 40 and 42. By adjusting
the output of the source of electrical energy, the frequency of the alternating
elec~rical field is changed. The selected frequency causes the movement of
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the molecules of the material in the briquette 36 to speed up and generate
heat inside the briquette 36. This internal heat drives any water csntainea
in the briquette 36 toward its external surface. A fan 37 passes warm dry
a~r over the external surface of briquette 36 to remove the water as it is
deposited on the surface. The briq~ette 36 is retained in the dielectric
dryer 38 until the water i~ ~he briquette approaches 1~ by weight of the dry
ingredients in the composition of materials and thereater conveyed to a
storage container 43.
The dry briquette 36 is removed from the ~torage container 43 and
placed in a second mold 47. The dry briquetta 36 and second mold 47 are
conveyed to a press station 48. The press station 48 has a cyl~nder 49 which
extends into an oven 51. The temperature of the briquette 36 is raised to
about 350F in the oven 51 and a compressive force of up to 6000 p9i is applied
thereto by cylinder 49 to create a preformed organic friction pad 50 having a
desired density and shape. The preformed organic friction pad 50 is then
conveyed to an oven 54. The temperature in the oven 54 is maintained at about
600F. This 600F temperature cures the resin in the com~osition of material
to form a matrix for holding the other ingredients in a fixed relationship.
The cured organic friction pad 50' is removed from the oven 54 and passed
through a grinder S8 to obtain a brake pad 50" having a final desired
thickness before being packaged in storage container 60.
PREFERRED MODE_OF OPERATIO~ OF THE INVENTION
In order to evaluate the process, a typical organic composition of
material having a large percentage of asbestos was chosen from the following
ingredients in Table 1.
TABLE 1
Material ~ by Weight of Preferred
(Dry Ingredients) Total Mix Limits
Cashew Nut Powders 21 15-25
30*Organic Modifiers 10 6-10
**Inorganic Modifiers 5 4-8
GraRhite or Carbon Particles 1 0-10
Phenolic Resin 17 15-25
Asbestos 46 40-50
. 100~
.,
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* Elastomeric materials, natural and synthetic rubber scrap,
lates, crude molasses, asphalt~c base ~aterials, etc.
** Barytes, whiting, talc, rotten stone, metal powders, etc.
The Pkenolic Re~i~ contains from 7-15% of po~dered
hexa (hexamethylenetetramine) ground together with the
novolak to give an intimate ~ixture.
Since it i8 known that hexa is soluble in water, it ~s necessary
to add hexa to the water in the stoiage container 34 to assure that the
selected mixture of ingredients i~ the batch~ng container 18 are sssentially
lD the same as that in the dry briquette 36. From experiments it has been deter2ined
that from 0-100~ hexa hag a soluble rate of about 46~ by weight. Th~ amou~t of
hexa to be formulated into the water in ~torage chamb~r 34 iR a functloa of the
~oisture content of the briquette 36 after dewateri~g by the press operatioR.
The Phenolic ~esin in the example in Table 1 contains about 10%
poudered hexa. Therefore, the specific compo~ition contains about 1.7% hexa
by weight. In order that the dry briquette 36 has the same hex_ content as
the dry mixture of ingredients in the batching bin 18, it is necessary that
the water in the slurry contain hexa. The following formula can be used to
! calculate the ~olution concentration of hexa required to be added to the
20 water in storage container 34.
Z by weight of hexa in water solution =
1.7 (100-~ ~2 in briquette)
(~ ~2 ln briquette) + 1.7
The percentage of L20 in the briquette 36 czn be obtained by comparing
the weight of the dry ingredients in the composition to the ~eight of the
briquette before drying in the dielectric dryer 38. The following table ~as
prepared to illustrate the various amounts of hexa required in the slurry
water for maintaining the hexa in the composition in a stable condition.
TABLE 2
Moisture Content of Briquette 36 Weight Z hexa in Solution
~?0 by Weight) before drying of Slurry Water
_ _ _ _
24
13
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Prom experimentation it was determined that a dewatering press
pressure of about 6000 psi would remove about 90~ of the water from the slurry
23 and therefore 13% by weight of hexa was added to the slurry water 35 in
container 34.
However, in order to manufacture brake pads, it is necessary
that the water be removed from the slurry rapidly. Therefore, it was
necessary to evaluate the flow of water out of the slurry during the
dewatering process. The flow characteristics can be evaluated through the
following equation:
Q 5 P ~ A
n L
where:
Q = rate of flow
P = pressure across the slurry
L = thickness of filter medium
A - Area of filter
n = viscosity of the fluid
~ = viscous permeability of the slurry
In obtaining operational values for this equation, the
following conclusions were reached:
1. The higher the press pressure in the dewatering
station 26 the better, however, pressure capable of
extruding the slurry 23 into ~he filter (openings 27
in the first mold) are unsatisfactory. Therefore,
a maximum P of 6000 psi was selected.
2. The ratio of A can be optimized by draining wa~er
from all sides of the slurry 23 in the mold 25;
3. Water must pass through 2 permeable layers, the
permeable constant of the dewatering press 30 and the
layers of dewatered slurry. Since the friction
material formula remains constant, the shape of the
first mold 25 must contain as many and as large holes
27 as possible without allowing the slurry 23 to be
extended by the press pressure; and
.
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4. The viscosity, n of the water in the slurry 23
i~ proportional to temperature. The viscosity
of ~ater i8 well known and as illustrated in
the following Table 3 increases with temperature.
IABL~ 3
TemperatUre of ~2 (C) Vlscosity
20.2 1.0
.~1
71 ~40
.35
- In solving this equation for Q it was readily apparent that the
value or ~ controlled the speea at which the water could be removed fro~ the
elurry 23, Therefore, the water in the slurry container 34 was heated to a
temperature of between ~5-85C by emergeut heating coil 64 befare being
communicated by pump 66 to the slurry m~Yer 20.
The composit~on of materials selected from the ingredients in
Table 1 were comblned in a batching bin 18 and placed in the slurry mixer 20.
The heated water wlth 13% hexa in solution 35 were added to the dry ingredients
~n the slurry mixer 20 at a weight ratio of about 2:1. This aggregation of
materials and liquid were mixed for about 10 minutes to produce a smooth and
uniform slurry 23. The temperature of the slurry 23 which was about 75C
at the end of the mlxing sequence wa9 reduced to about 70c after being
conveyed to the hopper 24 in the briquetting machine 26. A volume of slurry
was measured from the hopper 24 a~d poured into a first mold 25. The first
mold 25 was transferred to the dewatering chamber 30 and a force of 6000 psi
spplied to the slurry for 10 seconds by ram 39 to produce a briquette 36.
94% of the initial water and hexa in solution was removed from the slurry 23
in this dewatering procedure. Thereafter, the briquette 36 was removed
from the first mold 35 and placed between the first and second plates 40 and 42
in the dielectric heater 38. The electric field between the first plate 40
and the second plate 42 causes the movement of the molecules of the ingredients
in the briquette 36 to speed up and raise the temperature of the briquette
36. The increase in temperature is greatest at the center of the briquette
ll~S214
,
and proportionally decreas~ng toward the surface of the briquette 36.
This internal heating of the briquette drives the water contained therein
toward the surface of the briquette 36. Fan 37 blows warm dry air over
the surface and removes any water deposited thereon by ~he dielectric
heating process. ~en the water content in the briquette 36 reaches about
1%, the briquette 36 is placed on storage container 43.
The dry briquette 36 upon removal from the storage containèr 43 is
placed in a second mold 47, The second mold 47 and bri~uette 36 were heated -
to a te~pera~re of about 325F. in oven 51. Thereafter, a pressure of about
6000 psi was applied to the briquette 36 by ram 49 for about 8 minutes. The
resulting preformed friction pad 50 has a density of about 1~96gm/cc. The
preformed friction pad 50 is .ransported by conveyor 53 to oven 54. The
preformed friction pad 50 is heated to about 550 E in about 4 hours ~nd
held at this temperature for about 2 hours to cure the resin.to produce a -
cured friction disc 50'. The friction disc 50' ~pon removal from the curing
oven 54 has a density of l.91g~/cc. The cured friction disc 50 is passed
through a grinder 58 and ground to a specific size corresponding to a backing
plate for a disc brake. The ground friction disc 50" was attached to the
backing plate and compared with the test results from a friction pad with the
2a same formula produced through the well ~nown dry mix procedure i~ an Inertial
Dynamo~eter.
The following table is a tabulation of the results of the
comparison test: !
INERTIAL DYNAMO~ETER DOT TEST 101
Dry ~ Slurry Mix
Preburnish
Ef f ectiveness 736 980
Second
Effec~iveness 902 1040
Pinal
Effectiveness 5~6 640
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As evidenced, friction disc 50" produced by the slurry process had a
higher brake effectiveness during each sequence of the braking test.
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