CA1105214A

CA1105214A - Phenolic resin bonded friction materials

Info

Publication number: CA1105214A
Application number: CA291,415A
Authority: CA
Inventors: Robert S. Kiwak; Tung Liu
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1976-12-27
Filing date: 1977-11-22
Publication date: 1981-07-21
Also published as: MX150444A; AU515035B2; FR2375495A1; GB1580497A; JPS5382947A; FR2375495B1; AU3160177A; DE2757833A1

Abstract

WATER SLURRY PROCESS FOR MANUFACTURING PHENOLIC
RESIN BONDED FRICTION MATERIALS

ABSTRACT OF THE DISCLOSURE

A process for producing an organic friction article from a composition of materials in a dust free environment. Water is mixed with the composition of organic materials to produce a slurry. A fixed volume of the slurry is communicated into a first mold. The slurry in the first mold is compressed to remove up to 95% by weight of the water to form a briquette. The briquette is conveyed to a force air oven or dielectric heater where the water is further reduced to about 1% of the weight of the briquette. This dry briquette is then placed in a second mold and pressed into the shape of a friction pad. The pressed friction pad is placed in an oven and heated to cure the resin in the composition of materials to complete the manufacture of the organic friction pad.

Description

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 ;~1 ws/ .l~C

11~521~1 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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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~

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 13.~52~4 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.

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~
., 111'f'521~
* 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.

Moisture Content of Briquette 36 Weight Z hexa in Solution ~?0 by Weight) before drying of Slurry Water _ _ _ _ i2~.4 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 .

1~52~4

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 As evidenced, friction disc 50" produced by the slurry process had a higher brake effectiveness during each sequence of the braking test.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a friction article, comprising the steps of:
mixing a solution of water and from 4-24% by weight of hexamethylenetetramine with a composition of material which includes a dry phenolic resin and hexamethylenetetramine powder to form a slurry;
communicating said slurry to a mold;
compressing said slurry in the mold to remove up to 95% of the water in said solution to form a briquette;
drying said briquette to remove substantially all of said solution and thereby reestablish to dry weight relationship of said phenolic resin and hexamethylenetetramine as in the composition of material; and curing the briquette to establish a desired shape and density for the friction article.

2. The process as defined in claim 1. wherein the briquette is cured at a temperature of up to 600°F.

3. The process, as recited in claim 1 or 2 wherein the step of drying includes;
heating the briquette in an oven having a uniform temperature of between 120°-140°F. for a predetermined period of time to evaporate said solution from the briquette;
and circulating air through said oven to remove said evaporated solution from the oven to maintain the relative humidity in the oven below a predetermined range.

4. A process for producing a friction pad, comprising the steps of:
mixing a solution of water and from 13-24% by weight of hexamethylenetetramine with a composition of material which includes a dry phenolic resin and hexamethylenetetramine powder to form a slurry;
transferring said slurry to a mold;
compressing said slurry in the mold to remove the solution and form a briquette having from 5-10% by weight of water therein;
drying said briquette to move additional water and reestablish the dry weight relationship of said phenolic resin and hexamethylenetetramine as in said original composition of material; and compression molding the briquette at a temperature of up to 600°F. to establish a desired shape and density for the friction pad.

5. A dustless process for producing organic friction articles comprising the steps of:
mixing together dry ingredients including a thermo-setting phenolic resin containing from 7-15% by weight of hexamethylenetetramine, asbestos and friction modifiers to form a composition of material;
adding a solution of water and from 4-24% by weight of hexamethylenetetramine to said composition of material to form a slurry;
communicating a fixed volume of said slurry into a first mold;
compressing said slurry in said first mold to remove up to 95% by weight of said solution to form a briquette;
drying said briquette through dielectric heating to heat the briquette from the inside to the outside and remove up to 99% by weight of the water in said solution from the briquette to reestablish substantially the same weight relationship of ingredients therein as in said composition of material; and curing the dried briquette in a second mold to a desired shape and density.

6. The process as recited in claim 5 wherein the step of compressing said slurry includes:
removing up to 95% by weight of said water.

7. The process, as recited in claim 6 wherein said step of compressing said slurry includes:
retaining said solution removed from said slurry in a storage container for reuse in another mixture.

8. The process, as recited in claim 5 further including the step of:
weighing said dry ingredients in order to determine the amount of solution to be added to produce a ratio of water to dry ingredients of 2 :1.

9. The process, as recited in claim 5 further including the step of:
heating said water to a temperature up to 90 C.
before adding to said dry ingredients.

10. A dustless process for producing organic friction articles comprising the steps of:
mixing together dry ingredients including a thermo-setting phenolic resin containing from 7-15% by weight of hexamethylenetetramine, asbestos and friction modifiers to form a composition of material;
adding a solution of water and from 13-24%
by weight of hexamethylenetetramine to said composition of material to form a slurry;
communicating a fixed volume of said slurry into a first mold;
compressing said slurry in said first mold to remove said solution to form a briquette having from 5-10% by weight of water therein;

drying said briquette through dielectric heating to heat the briquette from the inside to the outside and remove water from the briquette and reestablish substantially the same weight relationship of ingredients therein as in said composition of material; and compression molding the dried briquette in a second mold to a desired shape and density.