Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1994-05-19
1996-07-30
Mai, Ngoclan
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75239, 75240, 75244, 75246, 75247, C22C 2912
Patent
active
055407501
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns friction materials for lubricated tribological systems and particularly but not exclusively, for the manufacturing of synchro rings used in manual gear boxes.
The materials for gear boxes are subjected to several requirements, some of them contradictory. On the one hand, it is required to have an efficient lubrication at the gears, that is, a friction coefficient as low as possible between contact surfaces. On the other hand, at the synchros a friction coefficient as high as possible is required as well as a friction coefficient which is constant, independant particularly from temperature, sliding speed and contact pressure.
In synchros it is preferable to avoid oil films or to break them by creating geometrical irregularities by machined grooves, or fine irregularities by using a non-homogeneous material. However, these friction materials have produced variable results according to the functional conditions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a friction material of the above-described type, particularly for synchros, which overcomes the disadvantages of the prior art friction material described above and which can be used to obtain parts of comparatively complex geometry at comparatively low cost.
It is also an object of the present invention to provide a friction material for synchro rings used in manual gear boxes having a high friction coefficient which is constant independent of variations in temperature, sliding speed and contact pressure.
To achieve these purposes, the invention supplies a friction material for lubricated tribological systems consisting of metal matrix with embedded particles of high hardness. The hard particles are of size between 50 and 300 micrometers.
Preferably, the material of the hard particles is chosen between those having a hardness higher than 600 HV 0.1 (Vickers Hardness).
Another difficulty arises from the fact that in modern gearboxes, high pressure lubricants contain certain additives of the type of borates or sulphates, which are intended to reduce the friction between the gears, and to react on the material of the synchro. Preferably, the material of the particles is chosen among those that keep their hardness and have a "passive" surface by reaction in the lubricated tribological system.
As "passive" surface, a surface is understood that originates, when immersed in the environment considered, a continuous reaction layer which constitutes a barrier between the material and the environment.
When the described material is intended to be used in presence of a lubricant with an extreme pressure additive containing boron or sulphur, it is advantageous to choose the material of the particles among the carbides of Cr, Mo, W or V, the nitrides of AI or Mo, and the oxides of Cr, Ni, Zr or Ti, as well as the alloys rich in these elements.
According to a simple version, the matrix is of bronze.
According to another version, it is of steel.
To obtain the material according to the invention, it is advantageous that it is obtained by a mixture of powders having the composition of the matrix and the particles.
Preferably the hard particles constitute 5 to 40% in weight of the total material. For a lower percentage, the desired effect is obtained in an insufficient degree. For a higher percentage than that already stated, the manufacturing of material by sintering or other means, becomes difficult.
Tables I and II show the results of 23 assays and allow a comparision of the performance of examples according to the invention with different reference examples. These assays consisted in testing cylindrical examples of 3 mm diameter on a tribometer. The tribometer is of the pin and disc type and it is equipped in order to ensure the lubrication of the contact, allowing at the same time adjustment of temperature, contact pressure and rotational speed.
Friction coefficients shown in Table II are obtained from the friction forces measured in the tribometer. Sliding speeds have been varied fr
REFERENCES:
patent: 3941903 (1976-03-01), Tucker, Jr.
patent: 4618049 (1986-10-01), Pjlaima et al.
patent: 5114468 (1992-05-01), Akutsu et al.
patent: 5326384 (1994-07-01), Asada et al.
Belair Pascal
Fernandez Antonio R.
Ghaem Magham Farahni Seyed H. R.
Mai Ngoclan
Sintermetal S.A.
Striker Michael J.
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