CA1248882A - Composite friction member - Google Patents

Abstract

COMPOSITE FRICTION MEMBER

ABSTRACT

A nonmetallic friction member is constructed of a bulk graphite component bonded to a resin impregnated carbon cloth component. The friction member is particularly useful for brake and clutch devices, especially multiple disc-type brakes for aircraft. The member may be in the form of a rotor or stator. If driving slots are provided, : :
the member may be reinforced with resin impregnated carbon cloth at these slots.

Description

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BACKGROUND OF THE INVENTION
This invention relates to friction members and particularly to nonmetallic, heat resistant~ disc-type friction members ~or brakes or clutches.
Difficulties can often arise with brakes and clutches in high energy situations. For example, problems ~an arise in high energy brakes such as those used in air-craft, where the brake device must absorb great quantities o~ heat and withstand extremely high temperatures durlng the br`aking operation. When the engaging surfaces of the ~~ brake become overheated, decreases in the coefficients of friction can result. Overheating can also cause dis~
tortion o~ the brake which causes rapid wear. One way to alleviate these problems is by the use o~ "heat sink'l materials within the brake which draw heat away from the engaging surfaces and the surrounding structures.
Generally, heat slnk elements are heavy and massive. Often times, as in aircra~t brakes~ when it is desirable to reduce weight and/or mass, brakes are expected to accommodate the heat created during braklng operations, provide an effective and sustained braking action, and be lightweight a:nd compact.
Steel has been used as a heat sink material, but its weight and mass are disadvantages when lightweight and compact brakes are required. Lighter weight metals (such as beryllium) with;heat absorptlon characteristics similar to steel have been used as heat sink ~aterials where weight ls critical,~ but the cost of such metals is a disadvantage.
Nonmetallic brake materials have~been proposed~
to solve heat problems in situations where~weight and mass~

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are critical. Carbon cloth laminate discs of the type disclosed in U.S. Patent 3,730,320, assigned to the present assignee, have been proposed, but these are still considered by many to be expensive from both ma-terial and processing S standpoints. Other carbon cloth laminate discs are disclosed in U.S. Patents 3,552,533 and 3,548,979.
Relatively inexpensive forms of lightweight bulk graphite have been proposed as a brake friction member.
However, problems can arise when bulk graphite is used by itself as a friction member due to its brittleness and impact strength which are insufficient for high energy applications.
Furthermore, bulk graphite does not have sufficient friction characteristics for an adequate friction surface.
Composites of heat sink materials and friction 1~ materials have also been proposed. Some friction materials resist deterioration and wear under the most severe operating temperatures when used in combination with a heat sink element. For example, carbon cloth laminate materials have been used as a friction face by mounting them on some type of ~0 heat sink core material, such as metal in U.S. Patent 3,306,401. A satisfactory bond between two such materlals is difficult due to the different coefflclents of thermal expansion of the materials, which causes separation of the materials upon extreme heating. Fabrication of such compo-sites is thus dificult because the llnlng is typically~ ~mounted in small segments by rivets, clamps, or other mechan-ical means to avoid problems of thermal expansion in the lining and the core.

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SUMMARY OF THE INVENTION
This invention seeks to provide a low weight, compact friction member which ls inexpensive, easily manu-factured, and long wearing.
This invention also seeks to provide a composite friction member with a heat sink core material and a friction ` material which maintains its coefficient of friction at e~treme temperatures.
Still further this invention seeks to provide a composite friction member which is capable of being secured together as a unit without the use of clamps, rivets, etc.
Still further this invention seeks to provide a composite friction member with a friction material and a heat sink material having essentially the same thermal expansion characteristics such that separation and distortion of the materials will not occur under working conditions.
In a particular embodiment the composite friction member of the invention comprises two carbon components, the first being substantially carbon free bulk graphite and the second being carbon cloth impregnated with carbonized resln.
Preferably, the composite friction member is disc-shaped with the components in a sandwich arrangement. The friction component preferably ls constructed of a plurality of cloth plies with each ply being compri~sed of arcuate segments of fabric. If drIve sIots are to be;machlned at -the driving periphery, carbon cloth relnforclng material may be used at `;
the driving periphery to add strength.

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Thus in one aspect of the invention there is provided a friction member for use in a disc brake. The member comprises a first disc-shaped carbon component having two radially extending faces and consisting essentially of S bulk graphite or a pyrolyzed thermosetting resin, and a second carbon component comprising at least one ply of carbon cloth impregnated with a carbonized resin, wherein the second carbon component is bonded to a face of the first carbon component.
In another aspect of the invention there is pro-vided a carbon brake disc comprising a brake disc core plate and at least one carbon/carbon composite wear plate. The core plate is a mixture of a bonding agent and particulate carbon, which mixture has been molded to form a core plate and subsequently pyrolyzed to form a bulk graphite core plate. The carbon/carbon composite wear plate contains a fabric; and means is provided to secure the wear plate to said core plate to form the brake disc.
The invention also provides a disc brake which

2~ includes a rotor and a statorj wherein at least one of the rotor or stator is a friction member of the invention.
In the drawings:
Fig. 1 is an elevation of a unitary disc-like composite friction member according to a preferred embodiment of the present invention;
Fig. 2 is a sectiona1 view of the disc taken along :
line 2-2 of Fig. l;

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Fi~. 3 is a portion o~ the ~rlction member o~
~igs. 1 and 2 showing certain deslgn ~eatures.
DESCRIPTION OF A PRESENTLY PREFERRED EMBODIMENT
_ Referring to Flg. 1, a composite friction member according to the present invention is shown as a disc 10 having an outer periphery 19 and an inner periphery 18. me inner periphery 18 includes circumferentiall~
spaced slots 17 which de~ine teeth 22. The teeth 22 ~re designed to engage with splines 14 o~ a typical torque device 15 which may be part o~ an overall brake structure. The disc 10 is shown and described here as a stator; however, it is understood that a disc such as this may also be used as a rotor wherein slots such as 17 would be at the outer periphery 19 ~or engagement Nith an appropriate torque devicè.
As is more clearly seen in Fig. 2 the disc 10 is shown as a unitary annular body having flat parallel faces 16 for ~rictional engagement with other di~cs or brake parts. The disc 10 comprises a carbon core component 11 bonded to two carbon friction facing components 12. E3ch frictlon facing component 12 is bonded to one side of the core component 11.
The carbon friction facing components 12 are each shown as preferably composed o~ layers or pl~es o~
pyrolized, clo~ely woven carbon cloth, such ~s square woven cloth as seen in Fig~ owever, it 1s understood that the ~acing components 12 can be composed o~a sing1e layer or ply of pyrolized carbon cloth. Carbon cloth can be ~.ade in accordance with processes well known in the art and, therefore, such processes wi11 not be described here.
Carbon cloth coated with a~high temperature thermo~etting resin such as phenolic is readily available commercially.

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These resins are used for their ability to convert into carbon or graphite upon pyrolization~ me cloth is pyrolized for the final properties desired which usually depend on the carbon content o~ the fabric. The term 'carbon" when used herein includes graphite as well as other commonly used forms of carbQn. Thus~ the fabric or cloth used in accordance with this invention may be graphite cloth as well as these other forms of carbon depending upon the degree of pyrolization undergone by the fabricO
Each ply of the carbon friction facing components 12 is preferably composed o~ segments such as 25 in Figs.
1 and 3, of square woven carbon fabric with each segment 25 having curved inner and outer peripheries 26 and 27.
The segments are thus arcuate and generally subtend an angle of pre~erably from 1~5 to 180. As shown in Fig~ 19 the subtended angle "a" of an arcuate segment 25 is 60. It is understood that other arcuate lengths from 0 to 45 and over 180 may also be used if desired.
The segments preferably have cords or threads 32 constituting the warp of the ~abric which extend in a direction tangential to the inner and outer peripheries, 26 and 27, of the strips at the centerline 33. This provides ~or greater strength in the peripheral direction for the disc 10 shown in this embodiment. It is understood that for other strength requirements the cords or threads 32 may be at difPerent angles and the segments 25 may be assembled with~the cords or threads 32 crossing at an angle to provide balanced strength characteristics for particular applications where the stresses on the disc 10 are more severe in other directions.
In the pre~erred embodiment, the arcuate segmented f~bric strips are spliced or ~utted 28 at their ~2~8882 ends 29 to ~orm an annular ply. By building up layers of plies, a friction facing component 12 ls formed.
By staggering or of~setting the splice locations 31 between adjacent plies, maximum strength is obtained in the friction facing component 12.
The carbon core component 11 is composed essentially of a unitary, substantially homogeneous block o~ carbon substantially free of carbon cloth. Presently, the most pre~erred embodiment of the carbon core component 11 is a unitary block of bulk graphite. Bulk graphite is readily available commercially and can easily be machined into a desired size and shape to form a carbon core component such as 11.
The carbon core component 11 can also be a block of pyrolized thermosetting resin such as phenolic. Resins such as these are also readily available commercially. They can easily be molded into a desired size and shape and subsequently pyrolized, resulting in less machining and less waste. These resins can be reinforced with various fillers ~or added strength.
Depending upon use~ the thickness of the ~ composite disc 10 can be varied by varying the thickness o~ the carbon cloth in the ~riction ~acing component 12, the number o~ sheets composing the ~r1ction facing component 12, the thickness o~ the core component 11~ or by any combination thereof.
Because o~ the low~impact strength of the bulk graphite core component 11, the friction facing components 12 must carry much of the impact load applled to the member 10.
Preferably, the friction facing component~s 12 taken together comprise at least 50~ of the total thicknèss oY the member.
Because o~ this at leas~ 50% thlckness, the member will be able to withstand the impact ~orces ~ter the ~rictlon facing components 12 have been worn considerably.

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If the carbon core component 11 is o~ such material that it may not be able to withstand the stresses applied to it at the locations of its drive slots 17~
the disc 10 may be built with added carbon reinforcing components 13 at the drive periphery in which drive slots such i~s 17 are machined. The carbon relnforcing components 13 may be composed o* a ply or layers of plies of pyrolized square woven carbon cloth similar to that used in f~cing components 12. Rein~orcing clips 21 may be placed over the teeth 22 and may be secured by rivits 23 located as close as is practical to the drive edges 24 of the slots 17.
The clips 21 and rivits 23 will give added strength to the teeth 22 a.nd will prevent delamination due to high be~ring loads of the carbon reinforcing component 13.
Although the manufacturing method is not a critical aspect of this invention~ to better understand the construction~
a method of manufacturing the composite disc 10 is set forth.
To form the friction facing components 12, the carbon cloth coated with thermosetting resin is cut up ~0 into arcuate segments 25. The segments are then spliced or butted 28 at their ends 29 to form an annular ply.
Layers of plies are then built up in an assembling fixture.
A~ter one friction facing component 12 h&s been built up in the annular conflguration, the carbon core com-ponent 11 which is in a desired size and ~hape, is pl1ced in the fixture on top of the firBt friction facing component 12. This is followed by a simil~r friction Pacing component 12 built up in a similar manner as the Pirst component 12.
In the situation where a carbon reinforeing component 13 is to be used around one periphery, the ~ame proe~s3 i~
used, except th~t the core component:~Il will have either a smaller outside diameter or a larger inside diamet~r, lZ~

depending upon whether the relnforcing component 13 is necessary for drive slots 17 on the outer periphery 19 or the inner periphery 18, respectively. The carbon reinforcing component 13 may be built up in a similar manner as the friction facing components 12.
For example, in Figo 1~ since the composite disc 10 has slots 17 on its inner periphery 18, the core component 11 has the same outside diameter as the facing units 12, but it has a reduced inside diameter. The reinforcing component 13 will be o~ a similar annular disc-like configuration, but will have an outside diameter equal to the enlarged inside dia~eter of the core component 11 and an inside diameter equal to the friction facing component 12 inside diameter. The ~inish thickness of the reinfor~ing component 13 will be the same as that of the core component 11. mùs, all components can be solidly bonded together with no gaps.
After all components have been arranged in the annular con~iguration in the assembling fixture, they are moved as a unit to a curing press to cure thethermosetting resin and to mold the components into a unitary disc. Several processes known in the art can be adapted to cure the thermosetting resin and to carbonize and graphitize the ~forementioned composite disc 10.
Although a stru~ture o~ the type d1sclosed for the purpose illustrating one embodlment of the invent1on is especially suitable for installatiorl in aircraft disc brakes, it should be understood, o~ course, that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set forth 1n the appended cla1ms.

Claims (14)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a disc brake which includes a rotor and a stator wherein at least one of said rotor or stator is a nonmetallic composite friction member, the improvement wherein said friction member comprises:
a. a first disc-shaped carbon component having two radially extending faces and consisting essentially of bulk graphite; and b. a second carbon component comprising at least one ply of carbon cloth impregnated with a carbonized resin, wherein the second carbon component is bonded to a face of the first carbon component.

2. A disc brake as defined in claim 1, in which the second carbon component comprises not less than about 50% of the thickness of the member.

3. A disc brake as defined in claim 1, in which at least one carbon cloth ply comprises arcuate segments of closely woven carbon fabric.

4. A disc brake as defined in claim 3, wherein the second carbon component comprises a plurality of carbon cloth plies, each ply comprising arcuate segments of closely woven carbon fabric, the fabric segments of each ply being butted together such that the location of the abutment is staggered in relation to the location of abutment in an immediately adjacent ply.

5. A disc brake as defined in claim 1, in which another second carbon component is bonded to the first carbon component such that the first carbon component forms a core between the two second carbon components.

6. A disc brake as defined in claim 5, in which the member is of annular disc-like configuration.

7. A disc brake as defined in claim 6, the disc-like member having an outer periphery and an opening which defines an inner periphery and in which one periphery consists essentially of the second carbon component.

8. A disc brake as defined in claim 7, in which the one periphery has annularly spaced drive slots.

9. A disc brake as defined in claim 1, in which the carbon cloth ply is graphite.

10. In a disc brake which includes a rotor and a stator wherein at least one of said rotor or stator is a nonmetallic composite friction member, the improvement wherein said friction member comprises:
a. a first disc-shaped carbon component having two radially extending faces and consisting essentially of pyrolyzed thermosetting resin;
and b. a second carbon component comprising at least one ply of carbon cloth impregnated with a carbonized resin, wherein the second carbon component is bonded to a face of the first carbon component.

11. A disc brake according to claim 10, wherein said first component consists essentially of a pyrolyzed phenolic resin.

12. In a disc brake which includes a rotor and a stator wherein at least one of said rotor or stator is a nonmetallic composite friction member, the improvement wherein said friction member comprises:
a. a first disc-shaped carbon component having two radially extending faces and consisting essentially of a member selected from the group consisting of bulk graphite and pyrolyzed thermosetting resin; and b. a second carbon component comprising at least one ply of carbon cloth impregnated with a carbonized resin, wherein the second carbon component is bonded to a face of the first carbon component.

13. A carbon brake disc, comprising:
a brake disc core plate and at least one carbon/
carbon composite wear plate, said core plate consisting essentially of a mix-ture of a bonding agent and particulate carbon wherein said mixture has been molded to form a core plate and subsequently pyrolyzed to form a bulk graphite core plate, said carbon/carbon composite wear plate containing a fabric, and means for securing said carbon/carbon composite wear plate to said core plate to form a brake disc.

14. A carbon brake disc according to claim 13, wherein a carbon/carbon wear plate is secured to each side of said core plate.