A METHOD OF MANUFACTURE OF A FRICTION FACING AND CARRIER ASSEMBLY AND APPARATUS THEREFOR

Abstract: A method and apparatus for the manufacture of a friction facing and carrier assembly (2) in which the friction facings (20, 22) are bonded on opposite sides of a carrier plate (14). The first facing (20) is first bonded to the carrier plate (14) and the second facing (22) is then bonded to the subassembly by means of bonding apparatus (58). The second facing (22) is placed in an annular cavity (83), and resilient elastomeric adhesive (24) is laid in bead form on the exposed surface of the facing. The first facing and carrier plate assembly (12) is placed onto a support surface (84) adjacent the cavity and flattened into contact with the adhesive (24). Hot air is passed through the apparatus to initiate cure of adhesive (24).

Description: A METHOD OF MANUFACTURE OF A FRICTION FACING AND CARRIER ASSEMBLY AND APPARATUS THEREFOR This invention relates to a method and apparatus for the manufacture of a friction facing material and carrier assembly for a clutch driven plate. In particular the invention relates to a method of manufacture of a facing and carrier assembly of the type disclosed in the applicants patent application WO-A-90/08908 which describes a carrier assembly having a first array of friction material bonded to one side of a carrier plate by a relatively rigid adhesive and a second array of friction material bonded to the other side of the carrier plate by a relatively resilient adhesive. The carrier plate ' is formed from spring steel and has an array of circumferentially spaced outwardly projecting paddles at its outer periphery to which the friction facings are attached. The structure allows the facings and carrier to flex circumferentially. The flexibility of the carrier plate and the different nature of the two bonds formed between two facings and the carrier plate gives rise to problems during manufacture. According to the present invention there is provided a method of manufacture of a friction clutch and carrier assembly in which a first annular friction facing is bonded to one side of a relatively flexible carrier plate by a first heat cured adhesive, and a second friction facing is bonded to the other side of the carrier plate by a second resilient elastomeric adhesive, said method comprising bonding the first friction facing to the carrier plate by means of a first heat cured adhesive, placing the second friction facing in an annular cavity, flattening the second facing in the cavity, placing adhesive on the exposed face of the facing so that the adhesive protrudes above the mould, placing the carrier and first bonded facing over the cavity with the carrier plate adjacent the adhesive and spanning the cavity, causing the first facing and carrier plate to be flattened and thereby cause the carrier plate to be pressed into contact with the adhesive, and inducing an initial cure in the second adhesive. Conveniently the first facing is bonded to said one side of the carrier plate at an elevated temperature for a required time period and the first facing and carrier plate are held in a fixture under load in a frusto conical configuration during the curing process to form a carrier plate and bonded facing assembly. Also according to the present invention there is further provided apparatus for manufacture of a friction facing and carrier assembly comprising a carrier plate and a first friction facing bonded to the side of the carrier plate by a first relatively rigid . adhesive and a second friction facing bonded to the other side of the carrier plate by a second elastomeric adhesive, the apparatus including a bonding apparatus comprising two parts, a first part having an annular cavity with a flat base therein to receive a second friction facing, a flat support surface to support a carrier plate coaxially over the cavity, the depth of the cavity being such that elastomeric adhesive applied in bead form to the facing projects above the support surface: and a second part having a clamping means for clamping a portion of the carrier plate to said support surface and a pressure plate having a flat surface for pressing against the exposed face of a first facing to flatten the first facing and carrier plate and cause the carrier plate to contact with the elastomeric adhesive. Conveniently the apparatus further includes a bonding jig for assembly of the first friction facing to the' carrier plate to form a first friction facing and carrier assembly said bonding jig comprising a fixture having a lower frusto conical former on a base on which at least one first facing and carrier assembly is placed, and an upper matching frusto conical former which clamps the assembly to the lower former under a predetermined load. The invention will be- described by way of example and with reference to the accompanying drawings in which Fig 1 is a plan view of a friction facing and material carrier assembly of the type to be manufactured. Fig 2 is an enlarged radial section on the line II-II of Fig 1. Fig 3 is a schematic flow chart showing the method of manufacture of the facing and material carrier of Pig 1. Fig 4 a bonding jig of the type used to cone the carrier plate and first friction facing bonded thereto during a first stage of the manufacturing process. Fig 5 is a bonding apparatus for bonding a second friction facing to the carrier plate by means of a resilient elastomeric adhesive. and Fig 6 and 7 show a rigid bond and carrier plate sub-assembly. With reference to Figs 1 and 2 a friction material and carrier assembly is shown at 2 and forms part of a friction clutch driven plate which is used in a clutch, for example, a diaphragm spring clutch of a motor vehicle. The carrier assembly 2 comprises a flat steel carrier plate 4 of disc form centrally apertured at 6 to accommodate an internally splined hub (not shown) when the assembly is incorporated in the driven plate. Also the carrier plate is formed with windows 10 for torsional vibration damping springs and holes 12 for stop rivets as is known in the trade. At its periphery the carrier plate 4 has a plurality of outwardly projecting paddles or spokes 14 integral with the main body of the carrier plate. The spokes are flat being substantially equi-angularly spaced by slots 16 about a central axis X about which the assembly 2 is intended to rotate in use. In the example shown there are thirty spokes 14 and thirty slots 16. Circumferentially each spoke extends over about 7 degrees of arc and each slot over about 5 degrees. If desired the number, size, shape and spacing of the spokes can be varied. The spokes 14 are axially pliable in the sense of being leaf springs capable of flexing resiliently along directions substantially parallel to the axis X. This enables the carrier plate 4 at the spokes 14 to be sinuously flexible circumferentially. First and second co-axial annular friction facings 20 and 22 are respectively bonded to opposite faces of each spoke 14. The first friction facing 20 is bonded to the spokes by an adhesive 23. The adhesive 23 is REDUX 8£, (trade mark) which is heat setting nitrile phenolic resin adhesive. Various heat setting phenolic resins may be used as the adhesive, as well as other sythetic resin adhesives. The second friction facing 22 is bonded to the spokes 14 by an elastomeric material 24 which.- is adhered directly to the friction facing 22 and to the spokes 14. The elastomeric material 24 in this embodiment is a silicone rubber which is disposed as beads 24a - 24c between the facing 22 and the spokes 14. The silicone is a room temperature vulcanising (RTV) material which is subjected to heat and a moist atmosphere to promote curing to create the adhesive bond between the facing 22 and the spokes. The application of that heat also has the effect of curing the heat setting phenolic resin layer 23. The rubber is disposed on the facing in paste form. The elastomeric layer 24 is of an appreciable thickness so that it can act as resilient cushioning permitting movement of friction facing 22 in the axial direction relative to the paddles 14. On the other hand the adhesive layer 23 is by comparison non - or substantially non-resilient so that it provides no or substantially no cushioning for the friction facing 20 relative to the paddles 14. Each friction facing 20,22 can be formed of any suitable friction material and may be of a non-asbestos type. The method of manufacture of the facing and carrier assembly 2 is shown in Fig 3. The facings 20,22 are passed into a cleaning unit 50 for washing and removal of any contamination. The first facing 20 then passes into an adhesive applicator 51 where the Redux adhesive is applied to one side of the facing 20. Simultaneously the carrier plate 4 passes through a degreaser 52 and then to the adhesive applicator 51. The facings 23 and the carrier plates 4 with the adhesive thereon then pass into a drying area 53 to remove the adhesive solvent. The solvent can be removed at an elevated temperature or can be removed over 24 hrs. at room temperature. The facings 20 may be recirculated back through the adhesive applicator 51 for receiving a second layer of adhesive. The facings 20 and carrier plates 4 are passed to an assembly fixture 54 where the facings 20 are bonded to the carrier plate 4. Details of the fixture are shown in Fig 4, and will be described in detail, but basically the facing 20 and carrier plate 40 are assembled coaxially on the fixture 54 and the formed sub assemblies 12 (see Fig 6) are held under a load on a frusto conical former. A plurality of sub assemblies 12 may be arranged one on top of the other in the fixture 54. A load of about 190 psi (about 13.5 bar)- is exerted on the facing and carrier assemblies 2. The fixture 54 holding the sub assemblies 12 is then put into a curing oven 55 and held at 180 - 190 C for 5 hours or 230, 240 degrees centigrade for two and half hours to cure the Redux adhesive and bond the respective facings 20 to their respective carriers 4. The fixture 54 with sub-assemblies 12 held in-situ is then removed from the oven 55 and allowed to cool at a location 56 for up to 24 hours. The sub-assemblies 12 of facing 20 bonded to the carrier 4 will hereinafter be referred to as rigid bond sub assemblies. The rigid bond sub assemblies 12 can be fed back into the cleaning unit 50 or can go directly to a loading fixture 57 for temporary storage. The second facings 22 having passed through the clearing unit 50 are also held in the locating fixture 57 for temporary storage. The second facings 22 and rigid bond sub assemblies 12 may then be transferred by robot 59 from the locating - fixture 57 to the bonding apparatus 58 shown in an open condition 58A and a closed condition 58B. The details of the bonding apparatus 58 are shown in Fig 5. Basically the second facing 22 is placed in a lower part of the apparatus, a layer of elastomeric adhesive 24 is applied by the robot 59 in a continuous bead form 24A as disclosed in our patent application WO-A-91/10842, and the rigid bond sub assembly 12 is placed on the lower part of the apparatus coaxially of the facing 22 with the carrier plate 4 in contact with the adhesive. The bonding apparatus is then closed with the upper part exerting a clamping load on the facings and carrier assembly 2. The assembly 2 is held under a load of about 6-7 kgs for 5-10 minutes whilst hot air at a temperature of upto 60 C is blown through the assembly to initiate the curing processes. The assembled facings and carrier plate 2 are removed from the bonding apparatus 58 and are then passed into a curing oven 61 and are held in conditions of 30 C and 40% humidity for about 50 minutes. This accelerates the initial curing process. The assemblies 2 may then be loaded on a storage fixture 62 and pass into a curing area 63 where they are held for 24 hours in a water laden atmosphere at a temperature of 40 C, and then pass on to oven 55 for postcuring. Alternatively the assemblies 2 could be held at 48 hours at ambient temperature. The conditions of post cure are a temperature of 180 C for about 5 hours. The finished assemblies 2 are now ready for testing. Because of the curing at 180 C for 5 hours during the two bonding processes water is removed from the friction facings 20/22. When the rigid bond sub assembly 12 and the finished assembly 2 subsequently return to normal equilibrium conditions the fingers 20,22 re absorb water and the assembly 2 tends to distort because of the resilient nature of the carrier plate 4. This problem can be amelionated by forming the rigid bond sub assembly 12 in a frusto conical form with the facing 20 held in a concave configuration with the inner surface formed by facing 20 and the outer surface formed by the carrier plate 4. An angle of conicity of has been found to prevent distortion for a 267mm diameter facing. For other diameter facings different angles of conicity may be necessary. The rigid bond sub-assemblies 12 are held in a frusto conical configuration by use of the assembly fixture 54 shown in FLg 4. The assembly fixture 54 comprises a lower plate 61 having an upper surface 62 with a concave frusto conical surface having a conicity thereon. The lower plate 61 is mounted on springs 63 which act between a base plate 64 and the lower plate to bias the lower plate 61 upwards. The lower plate 61 is guided on a coaxial boss 71 fixed to the base plate 64. The base plate 64 rests against a housing 66 includes a annular retaining ring 65 which limits the upward movement of the lower plate 61. A hydraulic actuator 67 is located in a coaxial cylindrical cavity 68 in the housing 66 and has a reciprocating piston 69. The piston 69 can act against a coaxial central strut 72 having a head 73 which can abut the base plate 64 to move the base plate 64 upwards against the bias of the springs 63 (as shown in the right hand side of Fig 4) . The upper end portion 7^ of the strut 72 is intended to accommodate a cooperating screw threaded nut 75. The nut 75 bears against an upper plate 76 having a lower convex frusto conical surface 82 with degree conicity to match the concave surface 62 on the lower plate. The rigid bond sub assemblies 12 are placed with a first carrier plate 4 against the lower plate 61 and the facing 20 placed coaxially on top of the carrier plate 4. The carrier plate 4 centres on the boss 71 and the facing 20 centres on pins 77 located in the lower plate 61 and which extend through the radially inner ends of the slots 16 in the carrier plate. A stack of alternate carrier plates 4 and facings 20 is built up and the piston 69 is then retracted and the spring 63 apply a clamping load to the stack of sub-assemblies 12, causing them to dish. The springs 63 exert a load of 190 psi (13.5 bar) and by screwing the nut 75 into contact with the upper plate 76 whilst the spring load is relieved, any pressure differences due to tolerances in the thickness of facings can be removed. The bonding apparatus 58 is shown in detail in Fig 5 and comprises two parts, an upper part 81 and a lower part 82. The lower part 82 has an annular cavity 83 having a flat base to receive the friction facing 22, and a flat support surface 84 to support a carrier plate 4 so that in use the inner margin of the carrier rests on a radially inner portion of the support surface 84 and the outer ends of the paddles 14 rest on radially outer portion of the support surface 84 so that the carrier plate 4 spans the cavity 83. The depth D of the cavity 83 is such that the adhesive bead 24 when laid onto the facing 22 will protrude above the cavity. In this case we have a bead of about 2.8mm diameter and a height of 2.5mm between the facing and the support surface. Circumferentially spaced pins 85 arranged around the inner periphery of the support surface 84 serve to coaxially locate carrier plates 4 with respect to the axis of the rotation. Pins 86 arranged around the outer periphery of the support surface 84 also help —locate the carrier plates. The lower part 82 houses a friction facing centring means comprising a central coaxial cam 87 pivotally connected to three circumferentially spaced radial arms 88 having upright pins 89 located on the radially outer ends thereof. Backward and forward rotation about the axis of the cam 87 causes the arms to move radially in and out and the pins 89 act on the outer periphery of the facing 22 to centre the facing with respect to the annular cavity 83. The base of the cavity 83 is connected by apertures 91 and passageway 92 to an annular chamber 93 which in turn is connected to an outlet passage 94 which is connectable to a vacuum source. A second passageway 95 leads through the lower part 82 and opens onto the upper surface thereof. The passageway 95 is connectable to a source of hot air. The upper part 81 comprises a clamping ring 96 formed of spaced arcuate pads 106 which in use clamps a radially inner portion of the carrier plate 4 to the support surface 84. The clamping pads 1-6 are attached to a housing 97 which is in turn connected to a piston 98 of a hydraulic or pneumatic actuator. The housing 97 has a coaxial cavity 99 facing the lower part 81 which houses another actuator 101, which is fixed to the housing and has a reciprocable piston 102 to which a pressure plate 103 is attached. The pressure plate is axially movable relative to the housing 97 and the clamping ring 96 by the actuator 101 and is guided for the movement by circumferentially spaced pins 104 fixed to the pressure plate and guided by bushes 105 in the housing 97. In use a facing 22 is placed in the cavity 83 and centered thereon by the centring mechanism 87,88,89. Vacuum is applied to the apertures 91 through the passageway 94 to hold the facing in its centered position. The elastomeric adhesive 24 is applied in beads in a desired bead pattern for example a continuous spiral, or concentric circles having link portions between adjacent circles, to the exposed surface of the facing 20 and the rigid bond sub assembly 12 placed over the cavity 83 and centred by the pins 84. The upper part 81 is then moved by the actuator 98 so that the clamping ring 96 (shown in dotted lines) hold the inner portion of the carrier plate 4 flat on the support surface 84. The pressure plate 103 is then moved by the actuator 101 to press against the facing 20 and cause it to flatten, and press the carrier plate 4 into contact with the beads of adhesive. The actuator 101 applies a load of about 7 kgs. Hot air at 60 C is then passed through the passageway 95 and then through the cavity 83 so that it circulates through the assembly 2 and around the adhesive 24 to initiate cure.

Claims: CLAIMS 1. A method of manufacture of a friction facing and carrier assembly in which a annular friction facing is bonded to one side of a resiliently flexible carrier plate by a first heat cured adhesive, and a second friction facing is bonded to the other side of the carrier plate by a second resilent elastomeric adhesive, said method comprising bonding the first friction facing to the carrier plate by means of a first heat cured adhesive, placing the second friction facing in an annular cavity, flattening the second facing in the cavity, placing adhesive on the exposed face of the facing so that the adhesive protrudes above the mould, placing the carrier and first bonded facing over the cavity with the carrier plate adjacent the adhesive and spanning the cavity, causing the first facing and carrier plate to be flattened and thereby cause the carrier plate to be pressed into contact with the adhesive, and inducing an initial cure in the second adhesive. 2. A method as claimed in Claim 1 wherein the inner periphery of the carrier plate is clamped against a bottom mould surface before said load is applied to the facing. 3. A method as claimed in Claims 1 or Claim 2 wherein the adhesive is applied to the friction facing in the form of concentric beads or stripes, and hot air is blown through the mould cavity whilst the resilient elastomeric adhesive undergoes a initial cure, and said load is being applied. 4. A method as claimed in any one of claims 1 to 3 wherein the assembled facings and carrier plate, are then post cured in three stages, first at a o temperature of 30 C for 40 - 60 mms in a humidity of about 40%, secondly left to stand for 24 to 48 hours at up to 40 degrees Centigrade in a moisture laden atmosphere, and thirdly heated to 180 C for 5 hours. 5. A method as claimed in any one of claims 1 to 4 wherein the first facing is bonded to said one side of the carrier plate at an elevated temperature for a required time period, and the first facing and carrier plate are held in a fixture under load in a frusto conical configuration during the curing process to form a _ carrier plate and bonded facing assembly. 6. A method as claimed in Claim 5 wherein the conical configuration is a concave configuration with the outer surface of the cone being formed by the carrier plate and the inner surface formed by the first facing. 7. Apparatus for the manufacture of a friction facing and carrier assembly comprising a carrier plate and a first friction facing bonded to the side of the carrier plate by a first relatively rigid adhesive and a second friction facing bonded to the other side of the carrier plate by a second _ elastomeric adhesive, the apparatus including a bonding apparatus comprising two parts, a first part having an annular cavity with a flat base therein to receive a second friction facing, a flat support surface to support a carrier plate coaxially over the cavity, the depth of the cavity being such that elastomeric adhesive applied in bead form to the facing projects above the support surface: and a second part having a clamping means for clamping a portion of the carrier plate to said support surface and a pressure plate having a flat surface for pressing against the exposed face of a first facing to flatten the first facing and carrier and cause the carrier to contact with the elastomeric adhesive. 8. Apparatus as claimed in Claim 7 wherein the flat base of the annular cavity in the bonding apparatus has apertures therein which open into the cavity and which are connectable to a source of vacuum to apply vacuum to the cavity. 9. Apparatus as claimed in any one of Claims 12 to 14 wherein the cavity is connectable to a source of gaseous atmosphere. 10. Apparatus as claimed in any one of Claims 7 to 9 wherein the first part of the apparatus includes a cam operated device which acts on the outer periphery of the " second friction facing to centre said facing with respect to the cavity. 11. Apparatus as claimed in any one of Claims 7 to 10 wherein said clamping means comprises clamping pads connected to a first actuator, and the pressure plate for flattening the first facing is connected to a second actuator for axial movement independently of the clamping pads. 12. Apparatus as claimed in any one of Claims 7 - 11 wherein, the pressure plate is a flat plate which cooperates with the first part of the bonding apparatus to form a passageway for the delivery of fluid into the mould cavity for curing the elastomeric adhesive. 13. Apparatus as claimed in any one of claims 7 - 12 and further including a bonding jig for assembly of the first friction facing to the carrier plate to form a first friction facing and carrier assembly said bonding jig comprising a fixture having a lower frusto conical former on a base on which at least one first facing and carrier assembly is placed, and an upper matching frusto conical former which clamps the assembly to the lower former under a predetermined load. 14. Apparatus as claimed in Claim 13 wherein the fixture can hold a stack comprising a plurality of said facing and carrier assemblies. 15. Apparatus as claimed in Claim 13 or 14 wherein the clamp load is applied by springs.

Inventors: CUTHBERTSON ALEC TREVOR, GRIFFIN MALCOLM, HAILSTONE GRAHAM THOMAS, MILLING JOHN LESLIE, WARD ROBERT JAMES, CUTHBERTSON, ALEC, TREVOR, GRIFFIN, MALCOLM, HAILSTONE, GRAHAM, THOMAS, MILLING, JOHN, LESLIE, WARD, ROBERT, JAMES
Applicants: AUTOMOTIVE PRODUCTS PLC, CUTHBERTSON ALEC TREVOR, GRIFFIN MALCOLM, HAILSTONE GRAHAM THOMAS, MILLING JOHN LESLIE, WARD ROBERT JAMES
Application year: 1993
Main classification: F16D69
IPC codes: F16D13, F16D69