FR2775744A1 - Friction part, especially a gearbox synchronizing ring - Google Patents

Abstract

A friction part has a friction layer consisting of hard ceramic particles (1) dispersed in a small quantity of soft nickel or copper based alloy matrix and has an intercommunicating pore network. A friction part comprises a metal substrate coated with a composite friction layer consisting of (by vol.) 20-30% soft nickel or copper based alloy matrix (7) of 250-600 HV hardness, 40-60% dispersed hard ceramic particles (1) of 40-120 mu size and above 2000 HV hardness, and 20-30% intercommunicating pore network. Independent claims are also included for the following: (i) a device comprising two cooperating rotating parts which are immersed in oil and at least one of which comprises a friction part as described above; and (ii) production of the above friction part by a laser spraying process. Preferred Features: The matrix consists of a nickel alloy of composition (by wt.) 15% Cr, 4% Fe, 3% B, 4% Si, <= 1% C, balance Ni and impurities. The substrate consists of a Cu-40Zn-Al brass.

Description

I Friction piece comprising a composite friction surface

  charged with hard particles, its manufacturing process

  and device including such a part.

  The present invention relates generally to a friction part comprising a composite friction surface charged with hard particles, such as ceramic particles, the friction surface of which has both a high coefficient of friction and good resistance to wear. friction. The function of gearbox synchronizers is to bring two rotating parts immersed in oil to the same speed of rotation in the shortest possible time. To do this, one engages to make them rub under high contact pressure, two friction surfaces of opposing parts, namely a female conical ring engaged on a male cone. It is therefore advisable to have rubbing surfaces having both a high coefficient of friction and good resistance to friction wear, and this in the most space

  possible reduction in order to compact the transmission organs.

  A first known solution to this problem is to use threaded brass synchronization rings, this thread ensuring the evacuation of the oil. This solution is limited in engagement effort due to the low wear resistance of the brass beyond

  with a load greater than 1 J / mm2.

  A second solution consists in covering the surface of the ring with a deposit of molybdenum of high hardness, of the order of 850 HV. This solution makes it possible to increase the engagement forces by% while remaining limited in coefficient of friction to a close value

  0.10 and at docking speeds greater than 10 m / second.

  A third solution consists in manufacturing rings from a sintered material, either solid or composite, by co-forming a brass substrate on a sheet of sintered material. This solution which makes it possible to increase the friction forces up to a coefficient of friction

  close to 0.11, has the disadvantage of a higher manufacturing cost.

  A fourth solution, used for more severe synchronization needs, consists in increasing the surface area

  rubbing by making double or even triple cone synchronizers.

  This solution is very expensive due to the increase in the number

of manufactured parts.

  All of the above prior solutions have drawbacks, either that they have limited functional benefits depending on the choice of material, or that they require a larger number of parts, which increases the manufacturing cost. Indeed, the mono-cone solutions are currently reduced in friction capacity due to their limitation for the evacuation of the oil trapped between the floating surfaces. An increase in efforts would speed up the evacuation of the oil, but then at the expense of faster wear of the friction surfaces, not compatible with reliability in service. The multi-cone solution solves this

  problem, but is unfortunately much more expensive.

  The present invention therefore aims to provide a friction piece, in particular a friction piece for synchronizer of

  gearbox, overcoming the above drawbacks.

  The present invention also relates to a device, such

  than a gearbox synchronizer, comprising such a part.

  The present invention also relates to a method of

  manufacture of such a friction piece.

  According to the invention, a friction piece comprising a metallic substrate and a friction surface is produced on this substrate, characterized in that the friction surface consists of a layer of a composite material comprising, by volume, with respect to the total volume of the layer: - 20 to 30% of a soft alloy based on nickel or copper, having an HV hardness of 250 to 600; - 40 to 60% of hard ceramic particles, dispersed within the soft alloy, having an HV hardness greater than 2000 and a particle size of 40 to 120 micrometers; and - a network of communicating pores representing 20 to 30% in

layer volume.

  The friction piece according to the invention, for example a gearbox synchronization ring or cone, comprises a metal substrate made of a suitable metal or alloy, such as a brass, for example a threaded brass. Any type of brass can be used for the substrate

  classic, such as brasses of the Cu-40Zn-Al type.

  The friction surface consists of a layer of a composite material comprising, relative to the total volume of the layer, 30% of a soft alloy based on nickel or copper having an HIV hardness of 250 to 600, of which the function is to form a bonding matrix for bridging the hard ceramic particles in order to avoid their disintegration, but also running in when it rubs with an antagonistic surface. Among the soft alloys based on nickel and copper suitable for the present invention, mention may be made of alloys based on nickel and chromium, such as the Ni-Cr-Si-Fe-B alloys, and in particular the alloy based on nickel containing by weight 15% of chromium, 4% of silicon, 4% of iron, 3% of boron and less than 1% of carbon, the remainder being nickel and possible impurities, as well as alloys based copper such as

  cupro-nickel, cupro-zinc, cupro-tin alloys.

  . We recommend nickel-based alloys such as alloys

  nickel-chromium and in particular the specific alloy above.

  An important characteristic of the soft alloy forming the bonding matrix of the composite friction layer according to the invention, is that this bonding matrix has a network of communicating porosities representing a proportion of 20 to 30% by volume of the layer. This porosity, as will be explained below, is obtained during the deposition by a lack of stacking of the hard ceramic particles and by the use of an amount of soft alloy such that the soft alloy is insufficient to fill the stacking defects of hard ceramic particles, thus leaving a network of pores

communicating.

  Thus, due to the presence of this network of communicating porosities, which represents approximately 20 to 30% by volume of the layer of composite material constituting the friction surface, the evacuation of the oil, when the friction part is used in oil immersion, such as for example when the part is a gearbox synchronizer ring, ensures the evacuation of the oil

  trapped when in contact with an antagonistic rubbing surface.

  This operating mechanism is all the more effective as the oil is first evacuated by the communicating network of pores and then the ceramic particles harder than the soft alloy emerge so as to only rub, so that we establish a diet of

  almost dry friction with respect to the opposing surface.

  The layer of composite material constituting the friction surface also comprises from 40 to 60% by volume of hard ceramic particles dispersed within the soft alloy. As indicated previously, these ceramic particles have a hardness HV (Vickers hardness) greater than 2000 and a particle size ranging from 40 to 120 PLm. Among the hard ceramic particles useful in the present invention, mention may be made of carbides such as tungsten, silicon, tantalum and boron carbides, nitrides such as cubic boron nitride and aluminas. Preferably, carbides are used and

  especially tungsten carbides and silicon.

  b Preferably, the hard ceramic particles are shaped

spheroidal.

  The use of such hard ceramic particles, of hardness HV greater than 2000, makes it possible to obtain a high coefficient of friction greater than 0.15 without friction wear under very heavy loads greater than 2 J / mm2 for speeds of docking of parts of

  friction greater than 10 m / second.

  It follows that a level of synchronization performance is obtained, in the case of friction parts for speed synchronizers, of increased durability in service for a compactness of the

  synchronization function also increased.

  Another advantage of the friction parts according to the invention is that the layer of composite material constituting the friction surface can be produced on a standard product in threaded brass and thus makes it possible to obtain a more efficient final product without modification of

the surrounding architecture.

  In addition, the layer of composite material constituting the friction surface can be produced by a process using a laser deposition technique making it possible to obtain high quality deposits, but with the possibility of formulation evolution and at an operational cost. more

  economical than the methods of the prior art.

  Generally, the layer of hard composite material constituting the friction surface will have a thickness of between 0.1

  and 1 mm, preferably 0.1 to 0.5 mm.

  The rest of the description refers to the indexed figures which

  respectively represent: Figure 1 - a schematic representation of a spraying device for producing a deposit of a friction layer according to the invention; Figure 2 - a schematic view of a composite friction layer according to the invention; and Figure 3 - a schematic view of the friction layer

  composite of Figure 2 after running in on an opposing surface.

  As shown in Figure 1, the starting materials consist of a powder of a hard ceramic material 1, such as tungsten carbide or silicon carbide having a particle size of 40 to 120, tm coated in a metal or alloy of bond 2, for example a layer of nickel 4 to 12 μm thick and, on the other hand, by a powder of a bonding alloy 3 with a particle size of 30 to 70 Bn, for example of a base alloy of nickel or copper, preferably a nickel-based alloy alloyed with chromium, iron, silicon, boron, fluxing elements and

  wetting agents ensuring a good metallurgical bond between the particles.

  These powders are introduced into a spray torch 4,

in the desired proportions.

  These powders in the form of a mixture or separately, are injected under pressure of an inert gas, for example argon, into a nozzle 5 ensuring coaxial flow and focusing of the laser beam 6. By way of example, a beam diameter on piece of 4 mm to thus achieve a homogeneous deposit on a ring 10 mm wide by rotating the latter over three turns with an offset of 3 mm each turn. The laser used in this case has a power of 4 kW, making it possible to deliver 10 g / minute of the powder mixture at a speed of

cm / minute.

  By adjusting the operating conditions of the laser torch 4, it is thus possible to melt during the passage of the powders in the laser beam the only coating of the hard ceramic grains and of the binder powder without affecting the hard ceramic itself, in order to '' get a fault

  stacking hard ceramic grains.

  The substrate is generally deposited on a support and is preheated, the support generally consisting of a good thermal conductor in order to evacuate the heat imparted by the impact of the laser beam. The powders are either mixed beforehand before introduction into the laser beam, or introduced separately, but

  so as to converge in the vortex of the coaxial nozzle 5 of the laser torch.

  When the laser beam 6 passes through, the coating of the hard ceramic powder and the soft alloy powder melt to form a liquid phase while the hard ceramic core remains in the solid state. On impact on the substrate, as the total volume of the liquid phase resulting from the melting of the coating of the hard ceramic powder and of the soft alloy forming a bonding matrix 7 represents a volume less than the interstices of the grains solid ceramic stacked, it creates, as shown in Figure 2, a stacking defect which is not filled by the

  liquid phase and which thus constitutes a communicating network of porosities 8.

  This porosity network representing 20 to 30% by volume relative to the

total volume of deposit obtained.

  The deposit obtained is then rectified to obtain a good matching of the friction surface with an antagonistic friction surface, then is brushed with a flexible but sufficiently hard compliance tool, of the ceramic brush type, to give it a surface texture which is characterized, as shown in FIG. 3, by the emergence of hard ceramic particles 1 with respect to the alloy bonding matrix 7. It follows that during the rubbing contact of an antagonistic surface 9, localized friction is obtained at the level of the hard ceramic particles 1 without wear of the binder matrix 7 in almost dry conditions

  by evacuation of the oil through the through porosities 8.

Claims (14)

  1. Friction piece comprising a metallic substrate and a friction surface on the substrate, characterized in that the friction surface consists of a layer of a composite material comprising, by volume, relative to the total volume of the layer: - 20 to 30% of a bonding matrix (7) made of a soft alloy based on nickel or copper having an HV hardness of 250 to 600; - 40 to 60% of hard ceramic particles (1), dispersed within the soft alloy, having an HV hardness greater than 2000 and a particle size of 40 to 120 gmn; and - a network of communicating pores (8) representing 20 to 30% in layer volume.   2. Friction piece according to claim 1, characterized in   that the hard ceramic particles are spheroidal in shape.   3. friction piece according to claim 1 or 2, characterized in that the soft alloy is a nickel-based alloy Ni-Cr-Fe-B-Si,   possibly containing carbon.   4. A friction piece according to claim 3, characterized in that the nickel-based soft alloy comprises by weight 15% of chromium, 4% of iron, 3% of boron, 4% of silicon, less than 1% of carbon, the   complement being nickel and possible impurities.   5. friction piece according to any one of claims   1 to 4, characterized in that the hard ceramic particles are chosen from particles of tungsten carbide, silicon carbide, carbide   tantalum, boron carbide, cubic boron nitride and aluminas.   6. friction piece according to any one of claims   above, characterized in that the metal substrate is made of brass, of preferably a Cu-40Zn-Al brass.   7. friction piece according to claim 6, characterized in   that the substrate is made of threaded brass.   8. Friction piece according to any one of claims   previous, characterized in that the substrate is a ring of   gearbox synchronization.   9. Device comprising two rotating parts immersed in oil, each of the parts comprising a friction surface complementary to the friction surface of the other part and intended to engage by friction under high pressure with the complementary friction surface of the other part, characterized in that at least one of the friction parts is as defined in any one of the preceding claims.   10. A method of manufacturing a friction part, characterized in that it comprises depositing a composite friction layer on a surface of a substrate by simultaneous laser spraying of a hard ceramic powder (1) having an HV hardness greater than 2000 and a particle size of 40 to 120 gm and of a powder of a soft alloy (3) based on nickel or copper at a temperature such as the soft alloy based on nickel melts to form a liquid phase and the hard ceramic particles remain in the solid state, the total volume of liquid phase being less than the volume of the interstices of the solid grains of stacked ceramic particles. 11. Method according to claim 10, characterized in that the   soft alloy powder has a particle size between 30 and 70 gm.   12. Method according to claim 11, characterized in that   the soft nickel-based alloy comprises by weight, 15% Cr - 4% Fe - 3% B -   4% Si - less than 1% C, the remainder being nickel and possible impurities.   13. Method according to any one of claims 10 to 12,   characterized in that the hard ceramic particles are particles of tungsten carbide, silicon carbide, tantalum carbide, boron carbide, cubic boron nitride, or aluminas, preferably   particles of tungsten carbide or silicon.   14. Method according to any one of claims 10 to 13,   characterized in that the hard ceramic particles (1) are coated in a layer of metal or bonding alloy (2), preferably in a layer of nickel.