Note: Descriptions are shown in the official language in which they were submitted.
12(~889~i
A METHOD OF MANUFACTURING A FRICTION ARTICLE
This invention relates to a method of manufac-
turing a friction article having a pad of friction material
bonded to ferrous backing plate.
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In manufacturing friction articles and in
particular disc brakes for vehicles, it is common practice
for the ferrous based backing plates to be stamped by a
supplier and shipped to a friction material manufacture for
final assembly with a pad of friction material. Due to the
delay in time that often occurs from the time of manufac-
ture of the backing plates to the attachment of the
friction pad, the backing plates may rust or accumulate
grime on the surface thereof. Both rust and grime can
effect a resulting bond between the backing plate and pad
of friction material. Therefore, the backing plates are
uniformly cleaned by being passed through a shot peening or
blast operation. While the shot peening operation
adequately removes rust, grime, oil, grease and any other
surface contaminants, the force associated with the shot
peening operation may distort the ferrous or steel backing
plate which may result in a subsequent rejection of the
friction article. A resin binder is applied to a selected
area of peened-cleaned backing plate and a pad of friction
material is clamped onto the backing plate over the resin
binder. The binder is cured to bond the pad of friction
material to the backing plate. After checking the size of
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the friction article and removing any excess friciton
material, the friction article is painted or resin dipped,
to prevent the formation of ferrous oxides on the surface
of the backing plate when exposed to normal operating
conditions.
If the backing plate has been distorted, the bond
between the pad of friciton material and the backing plate
may not be uniform to withstand the shear forces
experienced during a brake application. If the pad of
friction material is sheared from the backing plate, an
emergency condition exists in the braking system which
could result in the destruction of property.
The completed backing plate could also be
rejected by potential users for lack of dimensional
integrity; such
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as backing plate flatness (T.I.R.). Normally, a grinding
operation would have to be utilized to correct this defect.
According to the present invention there is pro-
vided a method of manufacturing a friction article, the
method including the steps of continually moving a ferrous
based backing plate through a first bath containing first
alkaline solution to clean the backing plate and removinq
the backing plate from the first bath and thereafter con-
tinually moving the backing plate through a first water bath
to rinse the first alkaline solution from the clean backing
plate. The backing plate is then removed from the first
water bath and thereafter continually moved through a second
bath containing a first solution of zinc-phosphate to coat
the entire surface of the clean backing plate. The backing
plate is then removed from the second bath and thereafter
ccntinually moved through a second water bath to neutralize
the reaction between the first 7inc-phosphate solution and
the ferrous based backing plate. The backing plate is then
removed from the second water bath and thereafter continu-
ally moved through a third bath containing a first solution
of chromic acid, the chromic acid having a Ph of about 6.9
in reacting with the zinc-phosphate coating to form a water
insoluble chrome-zinc-phosphate coating on the backing
plate. The backing plate is removed from the third bath and
thereafter continually moved through a dryer to dry the
chrome-zinc-phosphate coating. The backing plate is removed
from the dryer and thereafter being tranported to a first
work station, there is applied a phenolic resin binder to a
selected area of the chrome-zinc-phosphate backing plate. A
pad of metallic based friction material is placed on the
phenolic resin binder, and a compressive force is applied
through a clamp to hold the pad on the selected area. The
backing plate is continually moved through a second oven to
cure the phenolic binder and establish a bond between the
plate and backing plate to produce the friction article.
The friction article is then removed from the oven and a
clamp released from the pad and backing plate. The friction
article is cooled and continually moved through a fourth
bath containing a second alkaline solution to clean any grime,
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oil or grease deposited on the friction article during
curing of the phenolic binder. The cleansed friction
article is removed from the fourth bath and thereafter con-
tinually moved through a third water bath to rinse the
friction article and remove the second alkaline solution
therefrom. The friction article is then removed from the
third water bath and thereafter continually moved through a
fifth bath containing a second solution of zinc-phosphate to
completely coat the entire surface of the friction article.
The friction article is then removed from the fifth bath and
thereafter continually moved through a fourth water bath to
neutralize the reaction between the zinc-phosphate solution
on the backing plate and the metallic elements of the fric-
tion article. The friction article is removed from the
fourth water bath and thereafter continually moved through a
sixth bath containing a solution of chromic acid, the chromic
acid having a Ph of about 6.9 and reacting with the zinc-
phosphate coating to form a water soluable chrome-zinc-
phosphate coated friction article. The friction article is
removed from the sixth bath and thereafter continually moved
through a heater to dry the chrome-zinc-phosphate coated
friction article. After removing the article from the
heater it is continually moved through a first chamber where
a water soluable lacquer is applied to the dried f~-iction
article to seal the surface thereof from the atmosphere and
thereby reduce the formation of oxides with the metallic
elements in the friction article. The friction article is
removed from the first chamber and thereafter continually
moved through a second chamber where the lacquer is dried.
The lacquer coated friction article is removed from the
second chamber and transported to a second work station
where the chrome-zinc-phosphate coating is removed from a
work surface on the friction article as a ~ork surface is
ground to a specific dimension. The friction article is
then packed in a container for distribution to a customer.
According to a specific embodiment of the inven-
tion, the ferrous based backing plate is cleaned through
immersing in the first bath containing an alkaline solution
consisting of phosphates, sodium carbonates and/or sodium
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hydroxide whose temperature is between 65-75c for about 2
minutes wherein grime, oil, grease or any other surface
contaminants are removed without effecting the physical
characteristics of the backing plate. The use of a non-
silicated cleaner is preferred. After removal from this
first bath and neutralization of alkaline solution through a
water bath, the backing plate is inspected for the presence
of ferrous oxide. If ferrous oxide is present, the backing
plate is immersed in a second bath containing approximately
50% by volume of Hydrochloric acid for about 30 seconds.
The Hydrochloric acid reacts with ferrous oxide to produce a
precipatate of ferrous chloride and water to further clean
the ferrous based backing plate. Thereafter the cleaned
backing plate is rinsed in a water bath to neutralize the
Hydrochloric acid and immersed in a third bath containing a
solution of zinc phosphate whose temperature is between 60-
70C for about 10 minutes to produce a zinc-phosphate coat-
ing on the ferrous based backing plate. The zinc-phosphate
coated backing plate is neutralized in a water bath and
thereafter immersed in a fourth bath containing a solution
of chromic acid having a temperature of from 50-60C for
about 30 seconds to creat a chrome-zinc-phosphate coating on
the backing plate. Thereafter the chrome-zinc-phosphate
backing plate is dried and a resin binder applied to a
selected area thereof. A pad of a metallic based friction
material is clamped to the backing plate over the resin
binder. The binder is cured to establish a bond between the
pad and backing plate and produce the friction article.
Depending on the curing process, some grime, oil,
grease, or other surface contaminants may be present on the
backing plate and/or pad of metallic based friction material.
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Therefore, the friction article is returned to a fifth bath
containing a second alkaline solution of phosphates, sodium
carbonates and/or hydroxides, having a temperature of from
65-75 C for a period of 2 minutes to clean the friction
article. After neutralizing the sodium hydroxide in a
water bath, the cleaned friction article is immersed in a
sixth bath containing a-solution of zinc-phosphate having a
temperature of between 60-70C for about 10 minutes to add
an additional zinc-phosphate coating to the backing plate
lo and an initial coating to the pad of metallic based
friction material. The zinc-phosphate coated friction
article is rinsed in a water bath to terminate the
deposition of zinc-phosphate on the friction article before
being immersed in a seventh bath containing a solution of
chromic acid having a temperature of between 50-600 C for
about thirty seconds. The chromic acid reacting with the
zinc-phosphate to create a water insoluble chrome-zinc-
phosphate coating on the friction article. Thereafter, the
friction article is dried and a water soluble lacquer
sprayed thereon to seal the surface and thereby prevent the
formation of oxides on the surface of the friction article.
The friction article is inspected and if needed, ground to
a specific size before proceeding to a shipping container
for distribution to a customer.
An advantage of this invention is that the
chrome-zinc-phosphate coating in addition to enhancing the
bond between the ferrous based backing plate and pad of
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metallic based friction material inhibits corrosion when
the friction article is exposed to the atmosphere.
The invention will now be described with
reference to the accompanying drawings wherein:
Figure l is a schematic illustration of the steps
of chrome-zinc-phosphate coating a backing plate according
to the principles of this invention; and
Figure 2 is a schematic illustration of the steps
of attaching a pad of metallic based friction material to
the chrome-zinc-phosphate coated backing plate to produce a
friction article which in turn is protected with a chromic-
zinc-phosphate coating according to the principles of this
invention.
The backing plate 10 shown in figure 1 is made
from a ferrous based material. Usually backing plates 10
are stamped from a sheet of material having a uniform
thickness. In order to aid in the stamping of the backing
plates, a lubricant is applied to the sheet of material.
The backing plates are directly conveyed from the stamping
machine to a tote box 12 for shipping to a user, normally a
friction material manufacturer. By the time the backing
plate reaches the friction material manufacturer, grime,
oil, grease, rust and other materials may be found on the
surface thereof. Necessitating the first steps of the
invention disclosed herein in figure 1.
A backing plate lO is removed from tote box 12
and placed on a conveyor 15 for delivery to a first bath 14
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containing an alkaline solution of phosphates, sodium
carbonates and/or hydroxides having a Ph of between 11 and
13. To achieve this concentration between 37-53 gm of
sodium hydroxide are added to a liter of solution (water).
The temperature of the solution is maintained between
65-75C. The size of the first bath 14 is selected to
permit continuous movement of the backing plate 10 in the
solution for between 1 and 3 minutes. This alkaline
solution of phosphates, sodium hydroxides and carbonates
(calcium hydroxide is also acceptable) removes grime, oil,
grease, paint, dirt and other surface contaminants, but
does not have an effect on ferrous oxide (rust) that may be
present on the backing plate 10. Therefore, on removal
from the first bath 14, the backing plate 10 is rinsed in a
water bath 16 whose temperature is approximately 5-10C to
neutralize or wash the alkaline solution from the backing
plate 10.
The cleaned backing plate 10 is inspected for the
presence of ferrous oxide. If ferrous oxide is found on
the backing plate 10, the backing plate is immersed in a
second bath 18 containing approximately 50% by volume of
hydrochloric acid whose temperature is about 20C. The
hydrochloric acid reacts with ferrous oxide on the surface
of the backing plate 10 to produce as precipitate of
; ferrous chloride and water and thereby return the surface
of the backing plate to its original ferrous based
condition. The strength of the hydrochloric acid solution
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is such that backing plate 10 need not remain in the second
bath for more than 30 seconds.
If the backing plate 10 does not have any ferrous
oxide on its surface, the immersion in the second bath 18
can be omitted. However, in a continuous flow transmission
line as shown in figure 1, it may be easier to clean all
backing plates with hydrochloric acid rather than devise a
means of selectively diverting backing plates 10 to the
second bath 18 when ferrous oxide is observed on a surface
thereof.
From the second tank 18, the backing plate 10 is
rinsed in a water bath 20 to neutralize and remove any
hydrochloric acid that may be retained on the surfaces
thereof. By maintaining the temperature of the water bath
between 5-10C, the speed of neutralization allows the
backing plate 10 to continuous]y move through the water
bath 20.
On exiting from water bath 20, backing plate 10
is conveyed to a third bath 22 containing a solution of
zinc-phosphate solution which has been heated to a
temperature of between 60-70C.
The concentration o~ zinc-phosphate solution is
obtained by adding from 4-8% by volume of zinc-phosphate
acid ZN H2 P4 to water until a desired Ph of between 2-4
is obtained. The size of this third bath has been selected
such that it takes between 8-12 minutes for a backing plate
10 to pass through the tank. As the backing plate passes
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through tank 22, a coating of zinc-phosphate i9 deposited
on the surface o~ backing plate 10. The thickness of the
zinc-phosphate coating deposited on the surface of backing
plate 10, is dependent on both the concentration of the
zinc-phosphate acid and the time of reaction in this third
bath 22.
Backing plate 10 is conveyed from the third bath
22 to a water bath 24 whose temperature is maintained
between 5-10C. The relatively cold water neutralized the
lQ zinc-phosphate acid and allows the coated backing plate 10
to be directly conveyed to a fourth bath 26.
Fourth bath 26 contains a solution of chromic
acid which has been heated to a temperature of between 50-
60C. The concentration of this solution is obtained by
adding 1 liter of chromic acid to 400 liters of water.
This is a very weak solution and the Ph registers somewhere
between 6.9-7Ø Even though this is a weak solution, when
the zinc-phosphate coated backing plate 10 is immersed
therein, a reaction takes place in a time period of between
20-40 seconds to create a chrome-zinc-phosphate coating on
the backing plate 10. The chrome-zinc-phosphate coated
backing plate 10 is conveyed from the fourth bath 26 into a
dryer 28. The temperature in the dryer is maintained at
approximately 45C. A higher temperature will obviously
decrease drying time.
: The dried backing plate 10 is conveyed to a
station 30 shown in figure 2 where a phenolic resin binder
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is applied to a selected area 32 of the backing plate 10.
Pads 36 of a metallic based friction material
such as disclosed in U. S. Patent 3,835,118 entitled
"Sponge Iron Friction Material", which issued September 10,
1974 are located at a work station 34. A pad 36 is placed
over the selected area 32 on the backing plate 10 and a
clamp 38 attached thereto to provide a compressive force
that holds the pad 36 to the backing plate 10.
The backing plate 10 with pad 36 clamped thereto
is conveyed to an oven 40 whose temperature is about 148C.
The backing plate 10 and pad 36 remain in the oven for
about 12 minutes during which time the resin binder cures
to establish a bond between the backing plate 10 and pad 36
to produce a friction particle 42.
During the curing of the resin binder and the
need to apply a lubricant to the clamp for ease in part
removal, some type of contamination, i.e., oil, grease,
grime, dirt, etc. may be deposited on the friction article
42. Although such contamination would not affect the
operation of the friction article 42 for appearance
purposes it has been decided to further process the
friction article 42 in accordance with the teachings in
this invention. The friction article 42 is conveyed from
the curing oven 40 to a fifth bath 44. The fifth bath 44
contains an alkaline solution of phosphates, sodium
hydroxide and/or carbonates, heated to a temperature of
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between 65-75 C. This alkaline solution is achieved by
adding from 37-53 gm of sodium hydroxide to a liter of
water to produce a Ph of between 11-13. The continuous
moving conveyor moves the friction article 42 through the
fifth bath 44 in a time period of between 1 to 3 minutes.
During this time the alkaline solution removes any
contamination from the surface thereof.
The cleaned friction article 42 is rinsed in a
water bath 46 whose temperature is maintained between 5-
10C. The water bath 46 neutralizes the effect of the
sodium hydroxide.
From water bath 46, the friction article 42 is
conveyed to a sixth bath 48 containing a zinc-phosphate
solution which has been heated to a temperature of between
60-70C. The concentration of zinc-phosphate solution is
obtained by adding from 4-8% by volume of zinc-phosphate
acid (ZN H2 P4) to water until a desired Ph of between 2-4
is obtained. The size of the sixth bath 48 is selected
such that it takes between 8-12 minutes for the friction
article 42 to be conveyed through tank 48. As the friction
article 42 passes through tank 48, an additional coating of
zinc-phosphate is deposited on the backing plate and an
initial coating is deposited on the pad 36.
On removal from the sixth bath 48, friction
article 42 is rinsed in a water bath 50 to neutralize the
reaction coating effect of the zinc-phosphate solution.
The friction article 42 is conveyed from bath 50
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into a seventh bath 52 whîch contains a chromic acid
solution which has been heated to a temperature of between
50-60C. The concentration of this solution is obtained by
adding 1 liter of chromic acid to 400 liters of water.
Since this is a very weak acid solution thePh registers
from 6.9-7Ø Even though this is a weak solution, when
the zinc phosphate coated friction article 42 is immersed
in tank 52, a reaction occurs in a time period of from 20-
seconds to create a water insoluble chrome-zinc-
phosphate coating on the entire friction article 42.
The friction article 42 is conveyed to a dryer 54where the chrome-zinc-phosphate coating is dried before
being transferred to a spray chamber 56.
In the spray chamber 56, a water soluble lacquer
is sprayed on the chrome-zinc-phosphate coating. The
lacquer seals the coating and thus prevents the formation
of oxides that may develop under some atmospheric
conditions. For some application, a dip station may be
utilized instead of a spray chamber 56 to accomplish this
step.
From the spray chamber, the friction article
proceeds to an inspection station 58 where the material is
inspected in accordance to print specifications.
The friction article is then conveyed to a
grinder station 60 where any excess material is removed
from the operational wear surface 43 before being conveyed
to a storage container 62 for shipping to a customer.
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The quality control of the method of manufacture
is checked in the following manner: Friction articles 42
are selectively removed from the production line 15 and
transferred to a test station 64. At test station 64, the
friction article 42 is subjected to a shear test to measure
the strength of the bond between the backing plate lO and
the pad of friction material 36.
In order to evaluate the method of manufacturing
a friction article 42 according to this invention, the
following specific method was performed.
A steel backing plate 10 was placed in the first
bath 14 which contained an alkaline solution of sodium
hydroxide whose temperature is approximately 71C. The
concentration of sodium hydroxide in the solution was
achieved by adding 45 gm of sodium hydroxide to l liter of
water to produce a Ph of about 12. The backing plate 10
was immersed in the first bath 14 for 2 minutes during
which time all grime, grease and oil were removed.
The backing plate after the neutralization of the
sodium hydroxide solution in water bath 16 was conveyed to
the second bath 18 since ferrous oxide was observed on a
surface thereof.
The second bath 18 which contained a 50% by
volume solution of hydrochloric acid at room temperature
(20C), removed the ferrous oxide on the surface of backing
plate 10 in about 30 seconds.
After neutralizing the hydrochloric acid in water
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bath 20, the cleaned backing plate 10 was immersed in the
third bath 22.
The third bath 22 which contained a solution of
zinc-phosphate whose temperature was approximately 65C.
The concentration of zinc-phosphate in the solution was
achieved by adding 6.5% by volume of zinc-phosphate acid to
water until a Ph of 3 was obtained. Since the coating
deposited on the backing plate is dependent on both the
concentrations of the solution and the length of reaction
time, backing plate 10 was retained in the third tank for
10 minutes.
After neutralizing the reaction of the zinc-
phosphate on the ferrous based or steel backing plate 10 in
water bath 24, backing plate 10 was immersed in the fourth
bath 26.
The fourth bath contained a solution of chromic
acid whose temperature was about 55C. The concentration
of the chromic acid was obtained by adding 1 liter of
chromic acid to 400 liters of water. Even with this weak
solution 30 seconds were sufficient for a reaction to occur
which created a chrome-zinc-phosphate coating on the
ferrous or steel backing plate 10.
After drying the chrome-zinc-phosphate coated
backing plate, a phenolic resin binder was applied to a
selected surface and a pad of metallic friction material of
the type disclosed in U. S. Patent 3,835,118 was clamped
onto the backing plate lO over the resin binder.
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The clamped backing plate 10 and pad 36 were
conveyed to oven 40 where the temperature was approximately
148C. The backing plate 10 and pad 36 were retained in
the oven for approximately 12 minutes during which time the
resin cured to create a bond between the backing plate 10
and pad 36 to create a friction article 42.
On removal from oven 40 and al lowed to cool to
room temperature, 20C, friction article 42 was immersed in
fifth bath 44.
The fifth bath 44 which contains an alkaline
solution of sodium hydroxide identical to the first bath
and maintained at a temperature of approximately 71 C. The
friction article 42 was in bath 44 for approximately 2
minutes during which time all visible oil, grease and/or
grime was removed.
After this sodium hydroxide solution was rinsed
off of the friction article 42 in water bath 46, the
friction article was conveyed to the sixth bath 48.
The sixth bath 48 which contained a solution of
zinc-phosphate acid identical to the third bath and
maintained at a temperature of 65C. The zinc-phosphate
reacted with the ferrous based or steel backing plate 10
and the ferrous elements in the pad of friction material to
coat the friction article 42. Since time is an important
element to the thickness of the coating deposited on the
friction article 42, it was determined that 10 minutes were
sufficient for this application.
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After neutralizing the zinc-phosphate acid on the
friction article 42 in water bath 50, the friction article
42 was conveyed to the seventh bath 52.
The seventh bath 52 which contained a chromic
acid solution identical to that in the fourth bath 26 and
maintained at a temperature of 54 C. The chromic acid
reacts with the zinc-phosphate coating on friction article
42 to produce a water insoluble coating of chrome-zinc-
phosphate in about 30 seconds.
The chrome-zinc-phosphate coated friction article
was dried in a hot air oven 54 and conveyed to a spray
chamber 56.
A water soluble lacquer was sprayed on the
friction article 42. The water soluble lacquer dried to
provide a barrier that prevents the formation of oxide on
the coating.
After inspection, the friction article was ground
to the proper size in grinding chamber 60. The normal
procedure would be to thereafter convey this finish product
to container 62 for shipping to a customer.
For evaluation purposes, two sample friction
articles A and B were manufactured in a manner recognized
as prior art. In this method, the backing plate is cleaned
by the shot peening method before a pad of friction
material is attached thereto through the curing of the
phenolic resin binder. The resulting friction articles
were painted with an epoxy paint to provide corrosion
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protection. When samples A and B were tested in shear
machines 64, the friction pad separated from the backing
plate when subjected to 2100 and 1925 Kg of force,
respectively.
Thereafter 7 samples, C-l were manufactured in
accordance with the specific method set forth above. When
samples C-l were tested in shear machines 64, separation
occurred under the following loads: 2800, 2450, 2300, 2460,
2580, 2190 and 2650 Kg.9 respectively. The above test
clearly indicates that the chrome-zinc-phosphate coating
enhances the phenolic resin bond that is produced between
the backing plate and the pad of friction material. In
addition to the chemical attraction between the coated
backing plate, resin binder and pad of friction material,
the relatively low temperatures at which the coating is
applied does not distort the backing plate and which
results in a more uniform surface area for the bond.
Further, it is felt that the chemical reaction between the
chrome-zinc-phosphate coating and the ferrous based backing
plate offers better corrosion protection than that achieved
through conventional painting techniques.
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