Title of Invention

"METHOD AND MOULD OF MANUFACTURING A RING-SHAPED FRICTION LINING"

Abstract

Method of manufacturing a ring-shaped friction lining, in particular for a clutch, consisting of a friction material comprising fibres, the said method consisting of injecting a material (M) into a mould having two parts (11, 21, 31, 41, 51-12, 42, 52) able to move axially with respect to each other and defining, when they are pressed against each other, a cavity (13) corresponding to the required ring shape, characterized by the fact that the supply of material (M) to the cavity is effected by a channel extending as far as the cavity from an injection point (17) situated on or very close to the axis (A) of the cavity (13), the said channel being defined between the two parts of the mould and having a shape of revolution.

Full Text

The present invention concerns friction linings, more particularly friction linings in the form of a ring, such as for example friction linings for motor vehicle clutch discs. Since friction linings are subjected to severe mechanical and thermal stresses, they must have high tensile strength, a low bending modulus, a high damping coefficient and high thermal stability at high temperature. These characteristics are obtained with composite materials reinforced with fairly long fibres. Used at a high speed of rotation, such linings must moreover have very good resistance to centrifugal force; this requires a preferentially circumferential arrangement of the fibres. The aim of the present invention is to propose a method of manufacturing such a friction lining which makes it possible to easily obtain such an orientation in symmetry of revolution at every point on the lining. According to the invention, one method of manufacturing a friction lining in the form of a ring, in particular for a clutch, consisting of a friction material comprising fibres, the said method consisting of injecting a material into a mould having two parts able to move axially with respect to each other and defining, when they are pressed against each other, a mould cavity corresponding to the required ring shape, is characterised by the fact that the supply of material to the cavity is produced by a channel extending as far as the cavity from an injection point situated on or very close to the axis of the cavity, the said channel being defined between the two parts of the mould and having a shape of revolution. Advantageously, the friction material comprising fibres is obtained from a thermosetting polyester resin coating the fibres. Advantageously, the friction material comprising fibres is obtained by impregnating the fibres by means of a thermosetting polymer with a very low viscosity in the molten phase and then introducing the impregnated fibres into a mixture based on filled vulcanisable elastomer with a high viscosity in the molten phase. The material thus obtained is preferably introduced directly into the mould. The polymer is advantageously a phenolic resin. The mixture is preferably a terpolymer of ethylene, propylene and a dihedron or EPDM; in a variant, the mixture is a copolymer of styrene and butadiene or SBR, or a copolymer of butadiene and acrylonitrile or NBR. The mixture advantageously also contains a polymer with a very low viscosity in the molten phase; this polymer is the same as that used for the impregnation of the fibres. The impregnation of the fibres is preferably carried out in an injection screw, the fibres being introduced continuously into the said screw, which cuts them to length. Advantageously, the mixture based on elastomer is produced directly in a so-called secondary injection screw. The mixture based on elastomer is preferably introduced into the secondary injection screw in the form of powder, pellets or strips. Another object of the invention is a mould for implementing the above method which comprises two parts able to move axially with respect to each other and defining, when they are pressed against each other, a cavity in the form of a ring intended to be supplied with material, the injection point being situated on or very close to the axis of the cavity along which the two parts of the mould are mounted so as to be able to move with respect to each other. Advantageously, the two parts of the mould have opposite faces which are complementary and able to be moved with respect to each other between at least two positions, a so-called supply position in which they are at a distance from each other and a so-called closure position in which they are in contact with each other. The opposite faces are preferably parallel. Advantageously, the opposite faces are perpendicular to the axis of the cavity. One of the opposite faces is preferably carried by a deformable element, the two opposite faces being, in their supplied position, axially at a distance from each other which increases from their opposite faces close to the axis as far as their opposite parts close to the cavity in the form of a ring, whilst in their closure position they are in contact with each other. The face carried by the deformable element is advantageously, in the supplying position, conical in shape, the other face being perpendicular to the axis. One of the parts of the mould preferably carries a piston adapted to reduce the volume defined by the opposite faces. Advantageously, one of the two mould parts is in two pieces, roughly annular, a so-called external piece and a so-called internal piece connected peripherally by a thermally insulating material. The external piece is preferably associated with heating means. Advantageously, the internal piece is associated with cooling means. The two parts are preferably in two roughly annular parts mounted so as to slide axially with respect to each other, the parts disposed furthest towards the outside being adapted to define the ring-shaped cavity and carried by a carousel. The injection point is advantageously connected to the discharge from two independent injection screws. The two injection screws preferably extend parallel to each other. Another object of the present invention is a friction lining moulded in the form of a ring whose friction material comprises fibres obtained by the above method. Another object is a friction lining moulded in the form of a ring whose friction material comprises fibres, having the characteristics of the above mould. In the lining, the inclination of the fibres with respect to the tangents to the overall circular shape of the lining is on average greater close to the inside diameter than close to the outside diameter of the ring-shaped lining. In order to give a better understanding of the object of the invention, a description will now be given, by way of purely illustrative and non-limiting example, of the embodiments depicted in the accompanying drawings. In these drawings: - Figure 1 is a schematic view in partial section of a mould according to the invention; - Figure 2 is a partial view of Figure 1 and shows the two parts of the mould defining the cavity in their supply position; - Figure 3 is similar to Figure 2, the two parts of the mould being in the closed position; - Figures 4 and 5 are similar to Figures 2 and 3, respectively, and show a variant ,- - Figures 6 and 7 are similar to Figures 2 and 3, respectively, and show another variant; - Figures 8 and 9 are similar to Figures 2 and 3, respectively, and show another variant; - Figures 10 and 11 are similar to Figures 2 and 3, respectively, and show yet another variant. Referring to Figures 1 to 3, a mould can be seen which comprises two mould parts 11, 12 roughly of revolution about an axis A and able to move axially with respect to each other; here the mould part 12 is fixed and the mould part 11 can be moved with respect to the mould part 12. The two mould parts 11, 12 have a cavity 13 which, when they are pressed against each other, Figure 3, has the shape of a ring intended to be supplied with material M. The two mould parts 11, 12 have complementary opposite faces 15, 16 able to be moved with respect to each other between two positions, a so-called supply position, Figures 1 and 2, in which they are at a distance from each other, and a so-called closed position, Figure 3, in which they are in contact with each other. In the form depicted in these figures, the opposite faces 15, 16 are parallel and perpendicular to the axis A, which is the axis of the ring-shaped cavity 13. The fixed mould part 12 has a splayed channel 14 passing through it centrally, the cross-section of which increases as the movable mould part 11 is approached and whose entry 17 constitutes the injection point situated here on the axis A. The injection point 17 is connected to the discharge from an injection pot 100 which conventionally comprises a closure plug 101, a supply chamber 102, an injection piston 103 and a valve 104. The material M contains fibres, such as glass fibres for example, fairly long; this may be a thermosetting polyester resin coating the fibres. Here the material M comprises fibres introduced into a vulcanisable elastomer mixture with a high viscosity in the molten phase; this mixture is for example a terpolymer of ethylene, propylene and a diene, or EPDM; this may also be a copolymer of styrene and butadiene, or SBR, or a copolymer of butadiene and acrylonitrile, or NBR. Advantageously, with a view to their introduction into the molten elastomer mixture, the fibres are impregnated in advance with a thermosetting polymer with a very low viscosity in the molten phase; such a polymer is for example a phenolic resin; this thermosetting polymer contributes to the mechanical strength of the friction material. Here high viscosity means a viscosity greater than 40 Mooney ML(l+4), and very low viscosity, a viscosity below 10 Mooney ML(1+4); these values are obtained by consistometric measurements carried out at 100 degrees on a Mooney-type rheometer whose spindle is rotating continuously at a speed of 2 revolutions per minute. An injection screw 105, Figure 1, impregnates the fibres; a hopper 107 receives the impregnation material, such as a phenolic resin; the fibres 108 are introduced continuously and it is the screw 105 itself which cuts them to length, which is on average at least 5 millimetres; thus this screw 105 provides the plasticisation of the impregnation polymer and the impregnation of the fibres; this screw 105 also receives the elastomer from a secondary screw 106 which extends parallel to the screw 105; thus the secondary screw 106 directly supplies the screw 105, which carries out the mixing proper; the elastomer, or more precisely the elastomer-based mixture, is introduced in the form of powder, pellets or strips; in the example depicted in Figure 1, it is a strip 109. The elastomer-based mixture conventionally contains filler, catalysts, accelerators and inhibitors; it could also contain polymer impregnating the fibres, in a quantity- which might range up to 50 per cent by weight of the polymer contained in this material. By virtue of this provision, the elastomer-based mixture has a lower viscosity once it is plasticised and the final mixture is more homogeneous. As can be seen, the plasticised mixture is produced and introduced directly at the injection point. A mixture which has given satisfaction has the following composition by weight: 10 to 15% polymer 20 to 30% EPDM elastomer 15 to 20% filler (carbon black and mineral filler) 30 to 50% glass fibres. Naturally, arrangements are made to limit the deterioration of the fibres: channels with a large cross-section, limited curvature, screw profiles, lengths of screws; in addition, the operating parameters are chosen so the final mixture is homogeneous and even with regard to its rheological and rheometric behaviour; absence of segregation or separation of phases. The parameters for monitoring the functioning of the two screws 105 and 106, for example speed and temperature, are adjusted independently from one screw to another in order better to control the degrees of progress with the plasticisation and polymerisation. Naturally heating means, not shown, are associated with the screws 105 and 106. The mixture thus produced is injected centrally at 17; the supply to the cavity is effected through a channel, defined between the two mould parts 11, 12, having a shape of revolution. Consequently the material injected propagates between the fixed mould part 12 and its moving part 11, from the injection point 17 towards the cavity 13, forming a circular layer of material whose diameter increases during injection; the material undergoes deformations during the increase in diameter of the layer, these deformations extending circumferentially, that is to say tangentially to the circular envelope of the layer; thus, at the time of injection, the fibres, entrained by the moving material, are oriented tangentially to the overall circular shape of the ring-shaped lining, which is favourable to its strength under centrifugation. It is found that the inclination of the fibres with respect to the tangents to the overall circular shape of the lining is on average less great close to the inside diameter than close to the outside diameter of the ring-shaped lining; the strength under centrifugation is of course not affected thereby. In their supply position, the two mould parts 11 and 12 are at a short distance from each other, for example at no more than 5 millimetres from each other; the quantity of material injected is such that, whilst the injection begins when the mould is open, it ends before the mould is closed; by way of example, during the injection for at least half of the material necessary for filling the cavity, the two mould parts 11, 12 are spaced apart by approximately one millimetre, or even less. Figures 4 and 5 show a mould variant in which the moving mould part 21 comprises a piston 27 whose diameter is such that, when the mould is closed, it constitutes the internal cylindrical wall of the cavity 13, in line of course with the inside diameter of the ring. Thus the face of the moving part 21 of the mould which is opposite the face 16 of the fixed part 12 of the mould comprises in particular the bottom 23 of the cavity and the front face 25 of the piston 27. According to the variant in Figures 6 and 7, in the supply position of the mould parts 31 and 12, the passage for the supply of friction material of the cavity 13 from the injection point 17 has a thickness, measured parallel to the axis A, which increases from the axis A towards the cavity 13: the two opposite faces of the two mould parts 31 and 12 are, in their supply position, axially at a distance from each other which increases from their parts close to the axis A as far as their opposite parts close to the ring-shaped cavity 13; this arrangement facilitates, when the mould closes, the transfer of material to the cavity 13. It is preferred, apart from the cavity 13, for the opposite faces of the two mould parts 31 and 12 to be in contact when the mould closes; to do this, the face of the moving part 31 is at least partly formed by the external face of an elastic element 32 with a roughly conical shape held, in this prestressed position, by a strut 33; by virtue of this arrangement, by contact with the face 16 of the mould part 12, the elastic element 32 finds on closure of the mould a flat configuration, Figure 7, whilst being in abutment on a central stud 35. Behind the elastic element 32 there is defined a cavity 34 allowing its deformation; this cavity 34 can be taken advantage of in order to make a pressurised fluid circulate therein and control the deformation of the element 32. In the example shown, the opposite face 16 of the fixed mould part 12 is planar and perpendicular to the axis; in a variant, it is also conical. As can be remarked, the opposite faces of the two mould parts are in contact when the mould is closed; thus, in line with these, there is no loss of material between successive injections. When the mould is closed, the external area where the ring- shaped depression is heated for a certain length of time with a view to polymerising the lining; however, it is desirable for the material remaining in line with the injection point 17 not to polymerise and to remain fluid for the following injection. According to the variant in Figures 8 and 9, the two mould parts 41 and 42 are in two roughly annular pieces, a so-called external piece, respectively 43 and 44, and a so-called internal piece, respectively 47 and 48, connected peripherally by a thermally insulating material, annular in shape, respectively 61 and 62; these insulating materials prevent the heat contributed to the external pieces 43 and 44 being conducted to the internal pieces 47 and 48. It is also possible to provide, as depicted in the figures, channels 45 and 46, in the internal pieces 47 and 48, respectively, through which a cooling fluid passes. In Figures 10 and 11, the two external pieces are in two roughly annular parts mounted so as to slide axially with respect to each other; it is the parts disposed radially furthest towards the outside, 53 and 54, which are adapted to define the ring-shaped cavity; able to be moved axially with respect to the parts 55 and 56 closest to the axis, the latter can be spaced apart by sufficiently great distance, Figure 11, so that the parts 53 and 54 furthest towards the outside can be carried by a carousel equipped with several similar pieces: consequently the cycle time is very short and the central sprue does not have time to polymerise. In these figures, it can also be noted that the external part 53 of the moving part 51 of the mould carries an annular recess 53 which slightly radially extends a part of the ring-shaped cavity, a recess which receives the external part 54, of the other part 52 of the mould, like a piston; consequently a high pressure can be applied to the material present in the cavity without this pressure being applied to the entire internal diameter of the ring-shaped cavity. WE CLAIM: 1. Method of manufacturing a ring-shaped friction lining, in particular for a clutch, consisting of a friction material comprising fibres on average at least 5 millimetres, the said method consisting of injecting a material (M) into a mould having two parts (11, 21, 31, 41, 51-12, 42, 52) able to move axially with respect to each other and defining, when they are pressed against each other, a cavity (13) corresponding to the required ring shape, characterised by the fact that the supply of material (M) to the cavity is effected by a channel extending as far as the cavity from an injection point (17) situated on or very close to the axis (A) of the cavity (13), the said channel being defined between the two parts of the mould and having a shape of revolution and wherein the friction material comprising fibres is obtained by impregnating the fibres (108) by means of a thermosetting polymer (107) with a very low viscosity in the molten phase, inferior of 10 Mooney ML (1+4), and then introducing the impregnated fibres into a mixture based on a filled vulcanisable elastomer (109) with a high viscosity in the molten phase, superior to 40 Mooney ML (1+4). 2. Method as claimed in claim 1, wherein the friction material comprising fibres is obtained from a thermosetting polyester resin coating the fibres. 3. Method as claimed in claim 1, wherein the material thus obtained is introduced directly into the mould. 4. Method as claimed in one of the preceding claims, wherein the polymer (107) is a phenolic resin. 5. Method as claimed in one of the preceding claims, wherein the mixture (109) is a terpolymer of ethylene, propylene or a dihedron or EPDM. 6. Method as claimed in claims 1 to 4, wherein the mixture (109) is a copolymer of styrene and butadiene or SBR. 7. Method as claimed in claims 1 to 4, wherein the mixture (109) is a copolymer of butadiene or acrylonitrile or NBR. 8. Method as claimed in one of the preceding claims, wherein the mixture (109) also contains a polymer with a very low viscosity in the molten phase. 9. Method as claimed in claim 8, wherein the polymer is the same (107) as that used for the impregnation of the fibres. 10. Method as claimed in one of the preceding claims, wherein the impregnation of the fibres is carried out in an injection screw (105), the fibres (108) being introduced continuously into the said screw (105), which cuts them to length. 11. Method as claimed in one of the preceding claims, wherein the mixture based on elastomer (109) is produced directly in a so-called secondary injection screw (106). 12. Method as claimed in claim 11, wherein the mixture based on elastomer (109) is introduced into the secondary injection screw (106) in the form of powder, pellets or strips. 13. Mould for implementing the method as claimed in one of claims 1 to 12, comprising two parts (11, 21, 31, 41, 51-12, 42, 52) able to move axially with respect to each other and defining, when they are pressed against each other, a ring-shaped cavity (13) intended to be supplied with material (M), the injection point (17) being situated on or very close to the axis (A) of the cavity (13) along which the two parts of the mould (11, 21, 31, 41, 51-12, 42, 52) are mounted so as to be able to move with respect to each other, the two parts of the mould (11, 12, 31, 41, 51-12, 42, 52) having opposite faces (15, 16) which are complementary and able to be moved with respect to each other between at least two positions, a so-called supply position in which they are at a distance from each other and a so-called closed position in which they are in contact with each other, the opposite faces (15, 16) being parallel and perpendicular to the axis (A) of the cavity, characterized by the fact that one of the opposite faces is carried by a deformable element (32), the two opposite faces being, in their supply position, axially at a distance from each other which increases from their opposite parts close to the axis (A) as far as their opposite parts close to the ring-shaped cavity (13), whilst in their closed position they are in contact with each other. 14. Mould as claimed in claim 13, wherein the face carried by the deformable element (32) is, in the supply position, conical in shape, the other face being perpendicular to the axis (A). 15. Mould as claimed in one of claims 13 to 14, wherein one of the parts of the mould (21) carries a piston (27) adapted to reduce the volume defined by the opposite faces. 16. Mould as claimed in one of claims 13 to 15, wherein one of the two parts of the mould (41, 51-42, 52) is in two roughly annular pieces, a so-called external piece (43, 44) and a so-called internal piece (47, 48) connected peripherally by a thermally insulating material (61,62). 17. Mould as claimed in claim 16, wherein the external piece (43, 44) is associated with heating means. 18. Mould as claimed in one of claims 16 or 17, wherein the internal piece (47, 48) is associated with cooling means. 19. Mould as claimed in one of claims 16 to 18, wherein the two parts are in two roughly annular parts (53, 55-54, 56) mounted so as to slide axially with respect to each other, the parts (53, 54) disposed radially furthest to the outside being adapted to define the ring-shaped cavity and carried by a carousel. 20. Mould as claimed in one of claims 16 to 19, wherein the injection point (17) is connected to the output of two independent injection screws (105,106). 21. Mould as claimed in claim 20, wherein the two injection screws (105, 106) extend parallel to each other. 22. Friction lining moulded in the shape of a ring, whose friction material comprises fibres, obtained by the method according to one of Claims 1 to 12. 23. Friction lining moulded in the shape of a ring whose friction material comprises fibres, wherein the mould is according to one of claims 13 to 21.

Documents:

2356-DELNP-2004-Abstract-(21-02-2012).pdf

2356-DELNP-2004-Abstract-(26-08-2011).pdf

2356-delnp-2004-abstract.pdf

2356-DELNP-2004-Claims-(21-02-2012).pdf

2356-DELNP-2004-Claims-(26-08-2011).pdf

2356-delnp-2004-claims.pdf

2356-DELNP-2004-Correspondence Others-(21-02-2012).pdf

2356-DELNP-2004-Correspondence Others-(26-08-2011).pdf

2356-delnp-2004-correspondence-others.pdf

2356-DELNP-2004-Description (Complete)-(26-08-2011).pdf

2356-delnp-2004-description (complete).pdf

2356-DELNP-2004-Drawings-(26-08-2011).pdf

2356-DELNP-2004-Form-1-(26-08-2011).pdf

2356-delnp-2004-form-1.pdf

2356-delnp-2004-form-18.pdf

2356-DELNP-2004-Form-2-(26-08-2011).pdf

2356-delnp-2004-form-2.pdf

2356-DELNP-2004-Form-3-(26-08-2011).pdf

2356-delnp-2004-form-3.pdf

2356-delnp-2004-form-5.pdf

2356-DELNP-2004-GPA-(26-08-2011).pdf

2356-delnp-2004-gpa.pdf

2356-delnp-2004-pct-210.pdf

2356-DELNP-2004-Petition-137-(26-08-2011).pdf

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