US1997308A - Friction element - Google Patents

Description

April 9, 1935. 1. J. NovAK FRICTION ELEMENT Filed Feb. l5, 1932 Patented Apr. 9, 1935 UNlTEo STATES PATENroFFlcE FRICTION ELEMENT Izador J. Novak, Bridgeport, Conn., assgnor to Raybestos-Manhattan, Inc., Bridgeport, Conn., a corporation of New Jersey Application February i5, 1932, serial No. 593,023

s claims. (ci. lss-251) The present improvements relate more partion and upkeep. Rolls 10 to 15 feet long ticularly to the production of brake linings of and 3 to 5 feet in diameter are considered the hard formed segmental type wherein the modern practice in producing sheet packing. binder comprises rubber or other suitable binder Again, in order to make sheets of fair thicknesses 5 in minor proportion to asbestos nbre. 0n a sheet peeking 1`0llY that iS, between 5 It is Well known in the art of making brake ele' and re 0f an inch, e fairly lOng nbre eSheStOS lining of the hard segmental type, wherein rubis essential and such grades run from $150.00 to ber or other suitable binder is used in minor pro- $300.00 Der t0n et the present. time BY the portion relative to the asbestos, to make up a, `method to be hereinafter described, short bres lo mixture of rubber, asbestos and solvent Afor the ranging in cost from approximately $30.00 to rubber, and to dry out the solvent and sheet the $80.00 per ton are advantageously used, and lons asbestos and rubber on a pair of horizontal rolls i'DTeS are entirely U-nneCeSSaly. A150, eXDenSiVe having eyen surface speed, one roll being heated Sheet peeking 1011S are dispensed With entirely, and the other being cooled, whereby a sheet is and comparatively inexpensive equipment Subformed on the heated roll as the solvent dries out Stituted- The development of the present invenl5 of the compound, and pressure is applied through tion contemplates the production of a single ply the oold roll to densify the sheet. After the sheet unitary structure of unwoven asbestos With a is formed to the desired thickness, Which, it may binder Comprising lllbbel 01 Othel` Suitable Inebe added, is rarely above ,a of an inch', the rolls terial whereby any desired thickness may be are stopped, and the sheet is stripped from the produced, and short bre asbestos is used to ad- 20 hot roll. vantage. Tapes made according to the present Because of the fact that it is diineult to build invention are admirably suitable for the producup thicknesses ysubstantially greater than le of tion of hard formed unwoven brake lining Segan inch on rolls of this type, in makinggreater InentS.

thicknesses such as those used in brake lining, Among the advantages therefOel 0f the pres-ent 2 which range commonly between'zand 1/4 0f an invention ascompared with processes now in use inch, it has been necessary in the past to secure OI making this type 0f brake lining, iS that the these thicknesses by laminating 'two or more nal product isa Single ply unitary Structure havsheets from the sheeting machine above deing no lamina-tions or plies, which of course, elimiscribed by means of rubber cement, or other cenates danger of delamination. Another advan- 30 ments. A type of, segmental brake lining now tage is the speed of production due to the speed v on the market comprises laminated -sheet packwith which an extruding machine can be operated ing wherein sufficient sulphur is used With the as compared with present methods of manufacrubbel to produce hard rubber, and Where the ture. This, of course, is of importance from the desired developed length and Width and is cured manufactured, in addition to decreasing all of. hard by heat While held to a curvature. the costs entering into manufacturing. Another Another type comprises sheet packing Wound incidental advantage resides in the use of an exon a mandrel with 'ne brass Wires and cementtruding machine costing comparatively little 40 ing material between the convolutions, the Whole initially and to maintain and operate, as coln- 40 thereafter being cured hard While held under pared with a set of sheeting 101ls Which have a pressure`- After cure, the segments arey cut from high initial cost and expensive maintenance cost the cylinder thus produced. It will be appreciand which require skilled labor for operation. ated by those skilled in the art, that because of 'Ihe use of an extluding machine alSO 'results in the laminated structure necessarily inherent in the advantage of not having an expensive machine brake linings made from these sheets, there is idle when it is necessary to shut down for any always the danger oi delamination under the reason. This will be obvious from the fact that severe abuse encountered in use. Also, the cost a battery of extruding machinescanbe purchased of production necessarily includes the cost of and operated for the relative cost of one set of :il making sheet packing, which latter cost is high sheeting rolls. because of the fact that during one cycle, only a Another advantage is the flexibility of the asbesthin sheet may be produced. Furthermore, such ltos fibre quality, there being a minimum bre rolls for making sheet packings are necessarily length as stated above which can be sheeted on large in size, and must be held to accurate disheet packing rolls, but there being no minimum F5 mensions, which means high cost of installato the nbre length which can be extruded from 55 laminated Sheet packing is cut into strips of the standpoint Aof economy in labor cost per unit 35 an extruding machine. In addition, the use of present process eliminates or substantially decreases the necessity for using rubber cement for plying, which is an expensive item in conventional processes of manufacture. Other objects and advantages will be apparent from the accompanying drawing and following detail description.

In the drawing, Fig. 1 is a top plan view of an extruded tape.

Fig. 2 is a sectional view taken on the line 2-2 of Fig` 1.

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1.

On one mode of carrying out this invention, compound of approximately the following composition is prepared by mixing in a Werner-Pfleiderer dough mixer:

. Parts Smoked sheet 14.0 Litharge 4.5 Sulphur 9.0 Carbon black 3.0 Short asbestos fibre grade XX 60.0

Benzol 126.0

It will be noted that I preferably use a lowrproportion of solvent for a reason which will be explained later. The above mixing necessarily further loosens up the asbestosfibres and distributes the fibres and other ingredients throughout the mass of the compound. The plastic mass resulting from the above mixing is fed into the hopper of a standard extruding or tubing machine such as is used in making rubber tubing, insulated wire, automobile treads, etc., which is provided with an orifice at the head so designed as to give the desired cross-section, preferably a tape l of about the width of the finished brake lining and a thickness of extruded tape which contains the necessary amount of solid material desired for the finished density. As the asbestos fibres obviously run in all directions throughout the mass of the materiaL'when extruded, they run in all directions throughout the mass of the tape as shown best at 2y in Figs. 2 and 3. This is particularly advantageous because it makes a strong product, after the subsequent compression and hardening, i. e., stronger and less likely to separate into laminations .than would be the case if the tape were built up in laminations or all the fibres ran parallel to the length of the tape. Also the sides of the die orifice smooth and surface trowel as' it were, the surface of the tape resulting in aformationras shown best at 3 in Figs. l and 3. It will be seen that I am extruding a composition which contains considerable solvent. On drying out this solvent, the residual solids are left in a porous but uniformly boundrondition without breaks or laminations, and must later be compressed to allow for the pore space occupied by the solvent in designing the orifice of the tubing machine. With the above compound for a finished thickness of approximately .180", it is necessary to make a wet tape of approximately .343.

`On leaving the head of the tubing machine, the extruded tape l may be taken up on a moving belt and carried through a heated drying chamber to remove the solvent, which, of course, may be recovered, if desired. At the end of the drying chamber, the partially or completely dried tape is fed into a takeup device which winds it into rolls of suitable diameter for easy handling. This step of winding the porous ribbon on a reel is of course, for convenience, and is not a necessary or essential step of the process.

If the drying is not complete at this poi it, the rolls should be placed in a drying oven aid the stock dried until the solvent is completely removed. This, when a. volatile solvent is used, is necessary to prevent blistering in later curing operation. f

At this point, the product is a flexible spongy tape with the fibres in the interior running in all directions which must be further compressed to the required density for brake lining. 'I'his is accomplished by passing the tape l through pressure rolls so gauged as to give the'desired cornpression though of course, other means of compressing the tape may be employed. For instance, in the above stated example, it is approximately .343 thick and is compressed in these rolls to approximately .180 the density being approximately one oz. per cubic inch. Because of the nature of this composition, such compression takes place quite easily Without substantial stretching or distortion of the tape. Any such deformation strains in any direction are of course, resisted by the fibres which run in all directions. Y

After the tape I has been compressed to size, which may be as above described, or in a hydraulic press, it is cut into pieces of the desired developed length of the segment to be made. These pieces have now the exact width, length and thickness of the finished segment. They are now placed in curved forms of the desired curvature and while so held, are subjected to heat sufcient to vulcanize the rubber or harden the other binder contained therein, which may be 27E-325 F. more or less, for 1 to 4 hours, more or less, 'depending on the thickness of the finished segment, the temperature and the types of binder and 4accelerator used.

In the above composition, the cure is approximately 3 hours at about 325 F. This may be materially shortened by the use of rapid rubber accelerators. Y 'Ihe curing is accomplished ordina- ,rily by placing the forms in heated ovens but it may also be advisable in some cases to conduct the cure in the ordinary type of heated mold under hydraulic pressure. The finished segment is now ready for application to -brake shoes. It may or may not be machined on the surface, according to the accuracy desired. As a matter of fact, the above described process produces a segment which is smooth and well within the limits necessary for segmental brake vlinings of this type.

Because of the fact that it is a unitary mass of fibres, uniformly distributed throughout the mass and running in all directions therein, densely compacted and having no laminations, it gives very satisfactory results in service and shows no tendency to break down and disintegrate. Its tensile strength is of the order of 5000-6000 pounds per square inch and its hardness 21-25 Brinell, using a 500 kg. load on a 1 mm. ball. If the amount of solvent used is. too great, two things will occur on attempting to extrude the composition: (l) The composition will not feed through the worm because of its slipperiness, and 2) what material passesthrough the worm and through the head will show theeffect of individual lumps of compound and there will be breaks and separated portions of extruded stock from which no satisfactory tape can be made. In order to avoid this, it is necessary, to limit the amount of solvent to such a quantity as will produce a solid extruded tape without breaks. It may also be desirable to introduce certain resinous materials such as oil-soluble phenol resin v Parts Oil soluble phenol resin Rubber 10 Litharge 4.5 Sulphur 9` Carbon black 3 XX asbestos fibre 60 Benzol 126 of this method over the lamination of thin sheets prepared on costly machinery is obvious.

It may be found desirable to omit the last step in this process, that ofA curing in forms, and to substitute a partial cure to produce a flexible un-A woven tape which may be marketed in rolls, as in the present flexible Woven brake lining. This of course, would be included Within the scope `of the present invention.

It may also be advisable to introduce, either in commotion with rubber or as binders in their own right, other materials such as phenol resins, stearin pitch, casein, cellulose-acetate, viscose, drying oils and the like. Any of these changes would of course, modify the handling ofthe extruded tape, but would not affect the intent of this invention, which is to provide an economical method of producing any desired thickness of asbestos, binder and solvent by, extrusion through a predetermined orifice, where the nature 'of the compound is such that such extrusion could not take place except by the use of an extending solvent in considerable proportion. lt is obvious to those skilled in the art that a mixture such as above designated without the "use of a solvent would not be extruded because of the relatively small volume of rubber or other binder and asbestos, and because of the fact that asbestos, because of its brous nature, is very dimcult to extrude without some means of extending it and preventing it from packing in the'head of an extruding machine.

ln the vtvvo illustrations given, l have cited the use of benzol as a solvent. It is to be understood of course, that any other type of solvent suitable for the purpose may be employed. I do not Wish to be limited to benzol. It is also to be understood that the relativeproportions of constitu-v4 ents as well as the cited lengths, widths and thicknesses of the intermediate and final p'roducts set out in the specification are merely illustrative and may be variedwidely within the scope of the invention. The subject matter ofthe present claims is also disclosed in a pending application by Abert andWhitelaw, No. 376,-

639, nled July 8, 1929, whichkhas become Patent No,`\1,932,919, assigned to the assignee of this application, Raybestos-Manhattan,A Inc.

I have described in the above specification, the use of a standard tubing machine in which the force necessary for extrusion is developed by the action of a revolving worm on a plastic composition, but it is obvious thatthis force may also be developed in other mechanical devices, such as for example, a ram and cylinder, and it is to be understood that no limitation-as to the type of extrusion apparatus is intended.

I' claim as my invention: I

l. A friction lining which will not de-laminate in use, which comprises a hard, dense body of fibrous asbestos and a hardened binder in the form of a continuous unlaminated strip of the cross section desired, the 'breson the surface exhibiting the greatest longitudinal positioning gradually becoming less markedffyas the fibres approach the center of the lining .where the number Vof longitudinally vplaced fibres noticeably decreases relative to the surface.

2. A friction lining which will not de-laminate in use, which comprises a'hard, dense `body of brous asbestos 'and a vulcanized rubber inthe form of a continuous unlaminated strip of the cross section desired, the fibres on the surface exhibitmg the greatest longitudinal positioning gradually becoming less marked as the bres approach the center of the lining Where the number of longitudinally placed fibres noticeably dethe fibres approach the centerof the lining Where the number of longitudinally placed fibres noticeably decreases relative to the surface.

IzADoR J. NovAK.

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