FR2787046A1 - Mechanical friction component intended for operation in lubricated medium, e.g. gear box synchronizing ring, comprises matrix prepared from iron-based particles, copper phosphite and graphite, and optionally reinforcing particles - Google Patents

Abstract

Matrix comprises iron-based particles, 2-7, preferably 4-6, weight % copper phosphide (Cu3)P, and, up to 1, preferably 0.5, weight % graphite. Reinforcing particles of Vickers hardness at least 2000 HV, in amount 2-20, preferably 5, volume parts per 100 volume parts matrix particles, are chosen from oxide, nitride and/or carbide type particles. The reinforcing particles are preferably aluminum oxide, niobium carbide and titanium nitride, and they preferably have a coating having a different chemical nature, e.g. alumina coated with titanium nitride (TiN). The iron particles constituting the matrix and the reinforcing particles have average size 20-100 microns , preferably 40-50 microns . Independent claims are given for: (a) utilization of the component as a gear box synchronizer ring; and (b) a process for the production of the mechanical friction component.

Description

Mechanical friction part and its manufacturing process The present

  invention relates to a mechanical friction part, obtained by sintering, intended to operate in a tribological system

  lubricated, a process for preparing such a part as well as its use

  tion in particular as a gearbox synchronizer ring.

  Certain mechanical parts such as the synchronization rings

  niser must work in a lubricated environment in contact with high hardness steel. The function of these parts is to ensure flexible and rapid passage of speeds whatever the conditions of temperature, contact pressure and speed of friction. For this it is necessary

  obtain a relatively high and stable coefficient of friction,

  i.e. independent of temperature, speed and pressure conditions

if we.

  Brass, the most commonly used material for this function

  tion, gives satisfaction for most operating conditions, except at low temperature (shifting at start-up) and under

  high pressures (downshifting).

  The use of sintered steels for the manufacture of synchronizer rings requires - either the deposition of a molybdenum coating on the part of the idler gear in contact with the ring, - or the production, by co-sintering, of a friction layer on the

  active surface of the synchronization ring.

  These methods are expensive, however, and do not lead to

  cement performance superior to that of brass.

  Yet another approach has been to make sintered synchronizer rings made mainly of copper and particles

based on chromium (FR-A-2 698 808).

  The three approaches mentioned, namely the deposition of molyb-

  dene, co-sintering and the use of bronze-based shades imply high manufacturing costs without offering an improved performance of the

  friction behavior for the application which interests us.

  The Applicant has now discovered that it is possible

  significantly improve the friction behavior of mechanical parts

  nics operating in a lubricated medium, and in particular to obtain parts having a relatively high coefficient of friction and independent of operating conditions, by using for the manufacture of such parts a sintered material consisting of a relatively soft matrix based on powders of iron and copper phosphide (Cu3P), which matrix

  may contain particles of higher hardness.

  The present invention therefore relates to a mechanical friction part, produced by sintering, intended to operate in a lubricated medium, which part consists of an iron-based matrix and

  of copper phosphide and possibly contains particles of ren-

high hardness.

  Another object of the invention is the use of the mechanical part.

  as sintered defined above in particular as a synchronizing ring

gearbox sister.

  Yet another object of the present invention is a method

  for manufacturing a mechanical friction part having the characteristics

described above.

  Other objects will appear on reading the description and

examples that follow.

  The material used to make the friction parts of the pre-

  sente invention comprises on the one hand a matrix formed by iron-based particles and particles of copper phosphide (Cu3P) and, on the other

  part, possibly reinforcing particles.

  The powders which can be used to form the matrix are iron-based powders consisting of particles having an average size comprised

  between 20 and 100 gm, preferably between 40 and 50 gm.

  Copper phosphide is added to these iron-based powders

  form of fine particles. The amount of Cu3P recommended is general-

  between 2 and 7% by weight and preferably between 4 and 6% by

  weight relative to the total matrix.

  It is also advisable to add to this mixture of powders

  mant the matrix, a small amount of carbon intended to increase the hardness of the matrix of the finished product. Carbon is usually added in the form of graphite powder in amounts not exceeding 1% by weight, and preferably at most equal to 0.5% by weight relative to the total matrix. To this mixture of powders forming the matrix (powder based on iron associated with a powder of Cu3P and, optionally of graphite), one can add particles having a reinforcing role and which have a hardness much higher than that of the particles forming the matrix. The Vickers hardness of these reinforcing particles is generally at least equal to

2000HV.

  It is important to note that the addition of reinforcing particles

  High hardness is optional. Indeed, the experimental examples

  rates presented below show that a material obtained from a mixture of an iron-based powder and a copper phosphorus powder has excellent friction characteristics and does not require

  necessarily the addition of particles of higher hardness.

  The reinforcing particles are chosen from particles

  oxide type, nitride type or carbide type or a combination

  of these. By way of example, such particles of reinforcement can be indicated

  necessarily alumina (A1203), niobium carbide (NbC) and nitride of

  titanium (TiN), or a combination thereof.

  It is also possible to use composite particles of reinforcement.

  cement, namely particles carrying a coating of a chemical nature

  that different from that of the nucleus. An example of such particles,

  killing a particular embodiment of the present invention, are alumina particles coated with a deposit of titanium nitride which will

  subsequently designated as A1203 (TiN).

  The reinforcing particles have an average size of the same order of magnitude as that of the iron-based particles forming the main fraction of the matrix, namely a size between 20 and 100 im and

preferably between 40 and 50 inm.

  These particles are added in an amount of 2 to 10 parts by volume, and preferably in an amount of 5 parts by volume, per 100 parts by volume.

  of particles constituting the matrix.

  The material forming the mechanical parts of the present invention

  tion, consisting of a matrix based on iron powder, Cu3P particles and, optionally, reinforcement particles of high hardness

  gives the parts an excellent friction behavior in a lubricated environment

  reliable and in particular a relatively high coefficient of friction which varies very little as a function of operating conditions such as temperature, contact pressure and speed of friction. This material therefore has a considerable advantage over brass, commonly used for these applications, and whose coefficient of friction decreases

  strongly and undesirably at low temperatures and for fast

  its and high friction pressures.

  Thanks to their mechanical properties described above, the parts

  these mechanics are particularly suitable for use in

  as gearbox synchronizer rings. The present invention

  tion therefore also relates to the use of mechanical friction parts as synchronizer rings in gearboxes of motor vehicles. In such use in a lubricated environment with very variable operating conditions, they are advantageously distinguished from brass, the material most used in the prior art,

  by a very reliable friction behavior, in particular at low temperatures

high pressure.

  Another advantage of the friction parts of the present invention

  lies in the fact that they can be produced according to a conventional process.

  than cold compaction followed by sintering under a controlled atmosphere,

  commonly used in mass production.

  The present invention therefore also relates to a method of manufacturing mechanical friction parts which can be used in particular as a synchronizer ring. This process consists in dry mixing the different powders forming the matrix and, if necessary, the powder or powders of reinforcing particles, until a homogeneous mixture is obtained, in carrying out a cold compaction of the mixture of powders in a mold

  having an appropriate shape, then sintering the green pieces under an atmosphere

  controlled sphere at a temperature of around 1120 C.

  This simple process results in massive, ready-to-assemble parts that do not require additional processing and which exhibit

  therefore a relatively low manufacturing cost.

  Good control of the cold compaction process allows

  elsewhere to get finished products at odds.

  The following example is intended to illustrate the invention without

  as much present a limiting character.

Example

  Synchronizer rings made of different materials

  rials according to the present invention.

  The table below presents the nature and the quantity of

  reinforcement cules added to a base of iron powder and Cu3P particles. All the materials presented also contain 0.5% by weight of graphite added to the matrix in powder form. The powders were dry mixed, cold compacted in a suitable mold, then

  sintered under a controlled atmosphere at a temperature of around 1120 C.

  Cu3P material reinforcing particles __15 A (% by weight) a) chemical nature quantity (% by volume) a)

A 5 0

B 5 A1203 (TiN) 5

C 5 A1203 5

  D 5 NbC 5 a) expressed relative to the total weight of the matrix (iron powder + Cu3P + graphite) Figures 1 and 2 show examples of microstructures

  obtained by micrography. Figure 1 corresponds to the material A made up of

  killed iron, carbon and copper phosphorus. Its metallographic structure

  phique is composed of ferrite, perlite and cementite. Figure 2

  shows the structure of the same material to which particles have been added

hard alumina (material C).

  These different materials were used for tribolo-

  gics carried out on a disc-disc type tribometer. For different temperatures of oil bath and contact pressure, the friction speed was varied between 0.1 m / second and 2.8 m / second. The materials A to D presented as examples in the table above have a hardness of the order of 150 - 180 HV and are in friction against a workpiece

  antagonist in steel with a hardness greater than 600 HV.

  Figure 3 shows the variation, depending on the sliding speed.

  the coefficient of friction of the different materials A to D and, to

for comparison, brass.

  These results were obtained in a series of tests at low time.

  temperature (20 C) and at a high contact pressure (56 MPa), conditions

  in which the performance of brass is particularly unsatisfactory.

  doing. It can be seen that at this temperature and this pressure, the coefficient of friction of the materials indicated by way of examples of the

  present invention remains essentially stable when the speed of friction

  much increases, while under the same conditions that of brass

decreases dramatically.

Claims (10)

  1. Mechanical friction part, produced by sintering, intended to operate in a lubricated medium, characterized in that it is made of a material consisting (A) of a matrix formed by particles based on iron and particles of phosphide copper (Cu3P) and, optionally, (B) of reinforcing particles.   2. Mechanical part according to claim 1, characterized in that the reinforcing particles have a Vickers hardness at least equal to 2000 HV.   3. Mechanical part according to one of claims 1 and 2, character-   in that the reinforcing particles (B) are chosen from among the   oxide, nitride or carbide particles or a combination thereof this.   4. Mechanical part according to claim 3, characterized in that   that the reinforcing particles are chosen from aluminum oxide   nium, niobium carbide and titanium nitride or a combination of these.   5. Mechanical part according to claim 3, characterized in that   that the reinforcing particles are particles bearing a coating   ment of a different chemical nature such as alumina particles   (A1203) bearing a coating of titanium nitride (TiN).   6. Mechanical part according to any one of claims   above, characterized in that the matrix (A) contains from 2 to 7%,   preferably 4 to 6% by weight of copper phosphide particles.   7. Mechanical part according to any one of claims   above, characterized in that the proportion of reinforcing particles   cement (B) is between 2 and 10 parts by volume, and is preferably   rate equal to 5 parts by volume, per 100 parts by volume of particles constituting the matrix (A).   8. Mechanical part according to any one of claims   above, characterized in that the matrix additionally contains up to 1% by weight, preferably up to 0.5% by weight of carbon added under graphite form.   9. Mechanical part according to any one of claims   above, characterized in that the iron particles constituting the matrix (A) and the reinforcing particles (B) have an average size in the range from 20 to 100 µm, preferably from 40 to µm. 10. Use of a mechanical part according to any one   of the preceding claims as a synchronizer ring for   motor vehicle gearboxes.   1il. Method of manufacturing mechanical friction parts   according to any one of claims 1 to 9, characterized in that one   dry mixing - a powder of iron-based particles, - a powder of Cu3P particles, - optionally, a powder of reinforcing particles, and - optionally, a graphite powder, in the appropriate proportions until obtaining a homogeneous mixture, in that this mixture of powders is subjected to cold compaction in an appropriate mold, and in that the part thus obtained is densified by sintering in a controlled atmosphere at a temperature of the order of 1120 C.