FR2836970A1 - PROCESS FOR THE MANUFACTURE OF A CROWN-SHAPED FRICTION TRIM OF WHICH THE FIBER-CONTAINING FRICTION MATERIAL, INJECTION MOLD FOR CARRYING OUT THIS METHOD, AND FRICTION TRIM OBTAINED THEREBY - Google Patents

Abstract

Method of manufacturing a crown-shaped friction lining, in particular for a clutch, made of a friction material comprising fibers, which method consisting in injecting a material (M) into a mold having two parts (11, 21, 31, 41, 51-12, 42, 52) movable axially with respect to each other and defining, when they are joined to one another, an imprint (13) corresponding to the crown shape desired: the material is fed with the impression (M) via a channel extending to the impression from an injection point (17) located on or very close to the axis (A) of the imprint (13), said channel being defined between the two parts of the mold and having a shape of revolution. Injection mold for the implementation of this process and friction lining thus obtained.

Description

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 The present invention relates to friction linings, and more particularly to crown-shaped friction linings, such as for example the friction linings of clutch discs of motor vehicles.

 The friction linings being subjected to severe mechanical and thermal stresses, they must have a high tensile strength, a low flexural modulus, a high damping coefficient, a great thermal stability at high temperature.

 These characteristics are obtained with composite materials reinforced by rather long fibers.

 Used at high rotational speed, such seals must moreover have a very good resistance to centrifugal force; this requires an arrangement of the fibers which is preferably circumferential.

 The object 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 any point of the lining.

 According to the invention, a method of manufacturing a friction lining in the form of a crown, in particular for a clutch, made of a friction material comprising fibers, which method consisting in injecting a material into a mold having two axially movable parts one with respect to the other and defining, when they are joined to one another, an imprint corresponding to the desired crown shape, is characterized in that the supply of the imprint with material is produced by a channel extending to the impression from an injection point located on or very close to the axis of the impression, said channel being defined between the two parts of the mold and having a shape of revolution .

 Advantageously, the friction material comprising fibers is obtained from a thermosetting polyester resin coating fibers.

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 Advantageously, the friction material comprising fibers is obtained by impregnating the fibers using a thermosetting polymer of very low viscosity in the molten phase, then by introducing the impregnated fibers into a mixture based on vulcanizable elastomer loaded with high viscosity. in the molten phase.

 Preferably, the material thus obtained is introduced directly into the mold.

 Advantageously, the polymer is a phenolic resin.

 Preferably, the mixture is a terpolymer of ethylene, propylene and a dihedral or EPDM; alternatively, the mixture is a copolymer of styrene and butadiene or SBR, or a copolymer of butadiene and acrylonitrile or NBR.

 Advantageously, the mixture also contains a polymer of very low viscosity in the molten phase; this polymer is the same as that used for the impregnation of the fibers.

 Preferably, the fibers are impregnated in an injection screw, the fibers being introduced continuously into said screw which cuts them to length.

 Advantageously, the elastomer-based mixture is produced directly in a so-called secondary injection screw.

 Preferably, the elastomer-based mixture is introduced into the secondary injection screw in the form of powder, pellets or strips.

 The subject of the invention is also a mold for implementing the above process which comprises two parts which are movable axially with respect to one another and which define, when they are joined to one another, an imprint in the form of a crown intended to be supplied with material, the injection point being located on or very close to the axis of the imprint along which the two parts of the mold are mounted movable, one with respect to the 'other.

 Advantageously, the two parts of the mold have opposite faces which are complementary and movable relative to each other between at least two positions, a so-called feeding position in which they are at a distance from one another. other, and a so-called closed position in which they are in contact with one another.

 Preferably, the facing faces are parallel.

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 Advantageously, the facing faces are perpendicular to the axis of the imprint.

 Preferably, one of the facing faces is carried by a deformable element, the two facing faces being, in their feeding position, axially at a distance from each other which increases from their close facing parts from the axis to their facing parts close to the imprint in the shape of a crown, while in their closed position they are in contact with one another.

 Advantageously, the face carried by the deformable element is, in the feeding position, of conical shape, the other face being perpendicular to the axis.

 Preferably, one of the parts of the mold carries a piston adapted to reduce the volume defined by the facing faces.

 Advantageously, one of the two mold parts is in two generally annular parts, a so-called external part and a so-called internal part connected peripherally by a thermally insulating material.

 Preferably, the external part is associated with heating means.

 Advantageously, the internal part is associated with cooling means.

 Preferably, the two parts are in two generally annular parts mounted to slide axially with respect to each other, the parts arranged radially outermost being adapted to define the impression in the form of a crown and carried by a carousel.

 Advantageously, the injection point is connected to the outlet of two independent injection screws.

 Preferably, the two injection screws extend parallel to each other.

 The present invention also relates to a friction lining molded in the shape of a crown, the friction material of which comprises fibers obtained by the above process.

 It also relates to a friction lining molded in the shape of a crown, the friction material of which comprises fibers, having the characteristics of the above mold.

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 In the lining, the inclination of the fibers with respect to the tangents to the generally circular shape of the lining is on average greater in the vicinity of the internal diameter than in the vicinity of the external diameter of the crown-shaped lining.

 To better understand the object of the invention, we will now describe, by way of example, purely illustrative and not limiting, embodiments shown in the accompanying drawings.

 In these drawings: - Figure 1 is a schematic view in partial section of a mold according to the invention; - Figure 2 is a partial view of Figure 1 and shows the two parts of the mold defining the imprint in their feeding position; - Figure 3 is similar to Figure 2, the two parts of the mold 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, we see a mold which comprises two mold parts 11,12 generally of revolution about an axis A and axially movable relative to each other; here, the mold part 12 is fixed and the mold part 11 is movable relative to the mold part 12.

 The two mold parts 11, 12 have an imprint 13 which, when joined to one another, FIG. 3, has the shape of a crown intended to be supplied with material M.

 The two mold parts 11, 12 have complementary facing faces 15, 16 movable relative to each other between two positions, a so-called feeding position, FIGS. 1 and 2, in which they are at a distance.

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 from one another, and a so-called closed position, FIG. 3, in which they are in contact with one another.

 In the form shown in these figures, the facing faces 15, 16 are parallel and perpendicular to the axis A, which is the axis of the imprint 13 in the form of a crown.

 The fixed mold part 12 is crossed centrally by a flared channel 14 whose section increases as one approaches the mobile mold part 11 and whose inlet 17 constitutes the injection point located here on axis A.

 The injection point 17 is connected to the outlet of an injection pot 100 which conventionally comprises a plug 101, a supply chamber 102, an injection piston 103, a valve 104.

 The material M comprises fibers, such as glass fibers for example, rather long; it can be a thermosetting polyester resin coating the fibers.

 Here, the material M comprises fibers introduced into a vulcanizable elastomeric mixture of high viscosity in the molten phase; this mixture is for example a terpolymer of ethylene, propylene and a diene, or EPDM; it can 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 elastomeric mixture, the fibers are previously impregnated with a thermosetting polymer of 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, by high viscosity is meant a viscosity greater than 40 Mooney ML (1 + 4), and by very low viscosity, a viscosity less than 10 Mooney ML (1 + 4); these values are obtained by consistometry measurements made at
100 degrees on a Mooney rheometer whose mobile continuously rotates at a speed of 2 revolutions per minute.

 An injection screw 105, FIG. 1, ensures the impregnation of the fibers; a hopper 107 receives the impregnation material, such as a phenolic resin; the fibers 108 are introduced continuously and it is the screw 105 itself which cuts them

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 at length, which is on average at least 5 millimeters; thus, this screw 105 ensures the plasticization of the impregnation polymer and the impregnation of the fibers; 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 feeds the screw 105 which performs the actual mixing; the elastomer, or more precisely the mixture based on elastomer, is introduced in the form of powder, pellets or strips; in the example shown in FIG. 1, it is a strip 109.

 The elastomer-based mixture conventionally contains fillers, catalysts, accelerators, inhibitors; it could also contain polymer impregnating the fibers, in an amount up to 50 percent by weight of the polymer contained in the material.

 Thanks to this arrangement, the elastomer mixture has a lower viscosity once it is plasticized and the final mixture is more homogeneous.

 As can be seen, the plasticized mixture is produced and introduced directly to the injection point.

A mixture having given satisfaction to the following composition, by weight:
10 to 15% polymer
20 to 30% of EPDM elastomer
15 to 20% filler (carbon black and mineral filler)
30 to 50% glass fibers.

 Of course, measures are taken to limit the deterioration of the fibers: channels with a large section, limited curvature, profiles of the screws, lengths of the screws; in addition, the operating parameters are chosen so that the final mixture is homogeneous and regular as regards its rheological and rheometric behavior: absence of demixing or phase separation.

 The parameters for controlling the operation of the two screws 105 and 106, for example speed and temperature, are adjusted independently from one screw to another to better control the degrees of progress of the plasticization and of the polymerization.

 Of course, heating means not shown are associated with the screws 105 and 106.

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 The mixture thus produced is injected centrally at 17; the impression is supplied by a channel, defined between the two mold parts 11, 12, having a shape of revolution.

 Consequently, the injected material propagates between the fixed part of the mold 12 and its movable part 11, from the injection point 17 towards the cavity 13 by forming a circular sheet of material whose diameter increases during the injection; the material undergoes deformations during the growth of the diameter of the ply, these deformations extending circumferentially, that is to say tangentially to the circular envelope of the ply; thus, during injection, the fibers, entrained by the moving material, orient tangentially to the generally circular shape of the crown lining, which is favorable to its resistance to centrifugation.

 It can be seen that the inclination of the fibers with respect to the tangents to the generally circular shape of the lining is on average greater in the vicinity of the internal diameter than in the vicinity of the external diameter of the crown-shaped lining; the centrifugation behavior is of course not affected.

 In their feeding position, the two mold parts 11 and 12 are at a short distance from each other, for example at most 5 millimeters from each other; the quantity of material injected is such that, while the injection begins when the mold is open, it ends before the mold is closed; by way of example, during the injection for at least half of the material necessary for filling the impression, the two mold parts 11, 12 are spaced about a millimeter, see less.

 Figures 4 and 5 show a mold variant in which the movable mold part 21 comprises a piston 27 whose diameter is such that, when the mold is closed, it constitutes the internal cylindrical wall of the cavity 13, at right heard from the inside diameter of the crown.

 Thus, the face of the movable part 21 of the mold which is opposite the face 16 of the fixed part 12 of the mold notably comprises the bottom 23 of the cavity and the front face 25 of the piston 27.

 According to the variant of FIGS. 6 and 7, in the position of supply of the mold parts 31 and 12, the passage for the supply of friction material

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 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 mold parts 31 and 12, are, in their feeding position, axially at a distance from each other which increases from their parts close to the axis A to their opposite parts close to the imprint 13 in the form of a crown ; this arrangement makes it possible to facilitate, when the mold is closed, the transfer of the material to the imprint 13.

 It is preferred that outside the cavity 13 the facing faces of the two mold parts 31 and 12 are in contact when the mold is closed; to do this, the face of the movable part 31 is at least partly constituted by the external face of an elastic element 32 of generally conical shape retained, in this prestressed position, by a spacer 33; by virtue of this arrangement, by contact with the face 16 of the mold part 12, the elastic element 32 finds, when the mold is closed, a flat configuration, FIG. 7, while being supported on a central pin 35.

 Behind the elastic element 32 is defined a cavity 34 allowing its deformation; this cavity 34 can be used to circulate a pressurized fluid therein and control the deformation of the element 32.

 In the example shown, the opposite face 16 of the fixed mold part 12 is planar and perpendicular to the axis; alternatively, it is also conical.

 As can be seen, the facing faces of the two mold parts are in contact when the mold is closed; thus, in line with these, there is no loss of material between successive injections.

 When the mold is closed, the external zone where the crown impression is is heated for a certain time in order to polymerize the filling; however, it is desirable that the material remaining in line with the injection point 17 does not polymerize and remains fluid for the next injection.

 According to the variant of FIGS. 8 and 9, the two mold parts 41 and 42 are in two generally annular parts, a so-called external part, respectively 43 and 44, and a so-called internal part, respectively 47 and 48, connected peripherally by a material. thermally insulating, annular in shape, 61 and 62 respectively; these insulating materials prevent the

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 heat supplied to the external parts 43 and 44 to be conducted to the internal parts 47 and 48.

 It is also possible to provide, as shown in the figures, channels 45 and 46, in the internal parts 47 and 48, respectively, through which a cooling fluid passes.

 In FIGS. 10 and 11, the two external parts are in two generally annular parts slidably mounted axially with respect to each other; these are the parts radially outermost, 53 and 54, which are adapted to define the imprint in the form of a crown; axially movable relative to the parts 55 and 56 closest to the axis, the latter can be spaced apart by a sufficiently large distance, FIG. 11, so that the parts 53 and 54, the outermost, can be carried by a carousel equipped with several similar parts: therefore, the cycle time is very short and the central core does not have time to polymerize.

 In these figures, it is also noted that the external part 53 of the movable part 51 of the mold carries an annular recess 59 which slightly extends radially a part of the impression in the form of a crown, recess which receives the external part 54, of the another part 52 of the mold, in the manner of a piston; therefore, significant pressure can be applied to the material present in the impression without this pressure being applied over the entire internal diameter of the impression in the form of a crown.

Claims (20)

1. A method of manufacturing a friction lining in the form of a crown, in particular for a clutch, made of a friction material comprising fibers, which method consisting in injecting a material (M) into a mold having two parts (11, 21, 31,41, 51-12,42, 52) movable axially with respect to each other and defining, when they are joined to one another, an imprint (13) corresponding to the shape in the desired crown, characterized in that the material is fed to the impression (M) by a channel extending to the impression from an injection point (17) located on or very close to the axis (A) of the imprint (13), said channel being defined between the two parts of the mold and having a shape of revolution.  2. Method according to claim 1, characterized in that the friction material comprising fibers is obtained from a thermosetting polyester resin coating fibers.  3. Method according to claim 1, characterized in that the friction material comprising fibers is obtained by impregnating the fibers (108) using a thermosetting polymer (107) of very low viscosity in the melt phase and then in introducing the impregnated fibers into a mixture based on vulcanizable elastomer (109) loaded with high viscosity in the molten phase.  4. Method according to claim 3, characterized in that the material thus obtained is introduced directly into the mold.  5. Method according to one of claims 3 or 4, characterized in that the polymer (107) is a phenolic resin.  6. Method according to one of claims 3 to 5, characterized in that the mixture (109) is a terpolymer of ethylene, propylene and a dihedral or EPDM.  7. Method according to one of claims 3 to 5, characterized in that the mixture (109) is a copolymer of styrene and butadiene or SBR.  8. Method according to one of claims 3 to 5, characterized in that the mixture (109) is a copolymer of butadiene and acrylonitril or NBR.  9. Method according to one of claims 3 to 8, characterized in that the mixture (109) also contains a polymer of very low viscosity in the molten phase. <Desc / Clms Page number 11> <Desc / Clms Page number 12>  on the other which increases from their opposite parts close to the axis (A) to their opposite parts close to the imprint (13) in the form of a crown, while in their closed position they are in contact one from the other.  19. Mold according to claim 16, characterized in that the face carried by the deformable element (32) is, in the feeding position, of conical shape, the other face being perpendicular to the axis (A) .  20. Mold according to one of claims 15 to 19, characterized in that one of the parts of the mold (21) carries a piston (27) adapted to reduce the volume defined by the facing faces.  21. Mold according to one of claims 14 to 20, characterized in that one of the two mold parts (41,51-42, 52) is in two generally annular parts, a so-called external part (43,44 ) and a so-called internal part (47,48) connected peripherally by a thermally insulating material (61,62).  22. Mold according to claim 21, characterized in that the external part (43,44) is associated with heating means.  23. Mold according to one of claims 21 or 22, characterized in that the internal part (47,48) is associated with cooling means.  24. Mold according to one of claims 21 to 23, characterized in that the two parts are in two parts (53,55-54, 56) generally annular and mounted to slide axially with respect to each other, the parts (53,54) arranged radially outermost being adapted to define the imprint in the shape of a crown and carried by a carousel.  25. Mold according to one of claims 14 to 24, characterized in that the injection point (17) is connected to the outlet of two independent injection screws (105,106).  26. Mold according to claim 25, characterized in that the two injection screws (105,106) extend parallel to one another.  27. Friction lining molded in the shape of a crown, the friction material of which comprises fibers, characterized in that it is obtained by the method according to one of claims 1 to 13. <Desc / Clms Page number 13>  28. A friction lining molded in the shape of a crown, the friction material of which comprises fibers, characterized in that the mold is according to one of claims 14 to 26.  29. Friction lining according to one of claims 27 or 28, characterized in that the inclination of the fibers relative to the tangents to the generally circular shape of the lining is on average greater in the vicinity of the internal diameter than near the outside diameter of the crown-shaped packing.