METHOD OF MANUFACTURE OF ANNULAR FRICTION FACINGS

Abstract: Method of manufacture of planar annular friction facings for friction clutches or brakes. An annular preform of uncured friction material (13) is made by extruding a dough of uncured friction material (13) through a die (12) to form a flat ribbon whose width is substantially equal to the radial width of the facing to be formed, and the ribbon of friction material is caused on emergence from the die (12) to assume a helical form of fine pitch. The diameter of each convolution of the helix is substantially equal to the diameter of the required facing and the convolutions can be parted from the helix and flattened to produce the annular preforms.

Description: "Manufacture of Annular Friction Facings This invention relates to a method of manufacture of annular friction facirJs, particularly but not exclusively, for use in automobile friction clutches or brakes. It is known to manufactlire friction facings by passing the friction material through an extruder so that a dough of 'green' friction material (by 'green1 is meant uncured) emerges out of the extruder die as a flat ribbon whose width is substantially equal to the radial width of the friction facing and t:ht winding the ribbon into a rough preformed annulus of green material, which is then moulded and cured. Such a process is shown in U.S. Patent Specification No. 2,599,826 (Halstead et al). A major disadvantage of winding a broad flat ribbon into an annulus in which the width of the ribbon forms the radial width of the annu us ns tar the radially inner edge ribbon tends @ nr and the outer edge becomes strair@ and may snear in several places. These interruptions ifl the outer periphery of the green friction material annulus cause dislocation and a discontinuity in the reinforcing asbestos fibre array that is distributed through the emergent friction material dough, so t after the preformed annulus has been moulded and cured these dislocations are a potential weakness in the structure of the moulded friction facing. The object of the present invention is to avoid the above problem during the forming of t'ne preformed annulus. Accordingly there is provided a method of manufacture of an annular friction facing for friction clutches or brakes and in 1iding the step or making an annular preform of uncured friction material by extruding a dough of uncured friction material through a die to form a ribbon whose width is substantially eq@ al to the radial width of the facing to be formed wherein the friction material is caused to emerge from the extruder die with a great near velocity on one side of the ribbon that cn the other side, so as to set up a velocity gradient across the ribbon which causes the ribbon to assume a helical form ot form pitch with convolutions ach of a diameter substen- tially equal to the diameter che required facing whereby convolutions can oe Tr,J: Erom the helix and flattened to produce annular preforms. Preferably the friction material is caused to flow through a die which has a continually changing cross-sectional area of flow in the region of the mouth of the die said changing cross-sectional area causing the velocity gradient across the ribbon. The invention will be described by way of example and with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic view of a method according to this invention; Fig. 2 shows a vertical section through the apparatus used in Fig. 1; and Fig. 3 is a horizontal section through the apparatus shown in Fig. 1. Fig. 1 shows a step in a method of manufacture of an annular friction facing for a clutch or brake in which friation material in placed into a hopper 14 of a screw-tyre eztruder il. The friction material can - in any cenvenient .,Y. , eg, po.7eer or granules and it is passed aneng the @@truder in waich it is mixed and plasticised se @@at it is in the form of a plastic dough as it app@@@hes the die 12. The extrudate 13 in the @@@ @@@ lat ribbon of friction material dough emerges from the extruder di± Ath a greater velocity on one side or the ribbon than the other side hence setting up a velchty gradient across the ribbon which causes the ribbon --c assume a helical form of very fine pitch between adjacent convolutfons of the helix. The outer diameter of each of the convolutions of the helix is substantially equal to the outer diameter of the required friction facing. The convolutions of the helical extrudate are then parted from the helix and flattened to produce annular preforms of 'green' friction aterial. Each annular preform can comprise one flattened convo?.1ition or alternatively two convolutions nestled together may be superposed one on the other to form the preform. The width of the ribbon 13 extruded from the die 12 is substantialn equal to the radial width of the annular facing to be formed, and when the ends of a single turn of the coil are abutted together the preform has substantially the same dimensions as the finished facing. Alternatively with two or more coils a "split-ring" type of construction is formed. The preformed annulus of friction material is then mouldcd and cured into the finished facing which is ground down to its final dimensions. Fig. 2 and @@@. 3 sew sections through the apparatus used in Fig. 1, F s the provos own of a sizing die 35 placed onto the mouth of the die 12. The die 12 has a bore 15 shaped so that the flow path there through, has a continuously changing cross-sectional area of flow from when the dough enters the bore 15 until it exits the mouth 16 of the die. The flow path is shaped so that the changing and decreasing cross-sectional area of flow towards the mouth 16 causes a velocity gradient across the extrudate 13 as it emerges trom the mouth 16 of the die. In order to obtain maximum effect for forming a helix on emergence from the die 12 it is necessary to slow down the flow rate of the extrudate prior to it entering the area of changing crosssection. This is achieved by placing barriers 17 in the flow path such that the extrudate material must first pass through the barriers 17 before it enters said area. The degree of obstruction to flow caused by the barriers 17 will depend upon the curvature and radius of the required helical convolution. For each convolution size, an optimum degree of obstruction will have to be derived. When the extr@ia@ 13 exist the mouth 16 of the die it will expand slightly, as is well known during extrusion processes. In order to obtain a uniform extrudate of exceptable tolerances in dimensional size it may be necessary to pass the extrudate 13 through a sizing die 35 which has the required arcuate shape and dimensions as the annular friction facing which is being manufactured.

Claims: Claims 1. A meshod of manufacture ch planar annular friction facings for friction c'iutcks or brakes and including the step of making an annular preform of uncured friction material by extruding a dough of uncured friction material through a die to form a ribbon whose width is substantially equal to the radial width of the facing to be formed, characterised in that the friction material is caused to emerge from the extruder die with a greater linest velocity on one side of the ribbon than on the other side, so as toset up a velocity gradient across the ribbon which - causes the ribbon to assume a helical form of fine pitch with convolutions each of a diameter substantially equal to the dite: : of the required facing whereby convolution can be parted from the helix and flattened to produce annular preforms. 2. A method as claimed in Claim 1, characterised hat convolutions of the extruded helix are superimposed to form a facing A A method as claimed In Claim 2, characterised in that the preform is mede from To convolutions, one superitnposed or, the other, 4. A method @@@ in any preceeding claim, characterised in that the s material is caused to flow through a die of varying cross-sectional arez of flow, said cross-sectional area @@reasing In area so that there is caused the require tt'angt in velocity across the ribbon of extruded material 5. A method as claimed in Claim 4, characterisec in that the friction material immediately after its emergence from the die mouth is caused to pass through an arcuate sizing die of the same cross-sectional dimensions and radius as the require racings. 6. A method as claimed in Cialm 4 and Claim 5, characterised in that aS the friction material enters the die its flow rate is caused to slow by obstructions placed in the flow path, so that its flow rate is reduced prior to the cross-sectional area of flow being varied. 7. An annular friction facing manufactured by a method as claimed in any proceeding claim.

Inventors: MCCOMBIE, ERNEST HUGHES
Applicants: AUTOMOTIVE PRODUCTS PUBLIC LIMITED COMPANY
Application year: 1980
Main classification: B21C23
IPC codes: B29B7, B29C47, F16D69