Bearings – Rotary bearing – Antifriction bearing
Patent
1996-04-09
1998-07-28
Hannon, Thomas R.
Bearings
Rotary bearing
Antifriction bearing
384905, F16C 1722
Patent
active
057854319
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for obtaining temperature-independent mounting of a shaft made of a first material having a first coefficient of thermal expansion in a bearing which interacts with the shaft and which is made of a second material having a second coefficient of thermal expansion. The invention also relates to a bearing arrangement comprising a shaft made of a first material having a first coefficient of thermal expansion and a bearing which interacts with the shaft and which is made of a second material having a second coefficient of thermal expansion. In the present method and the bearing arrangement, the first coefficient of thermal expansion is of a higher value than the second coefficient of thermal expansion.
BACKGROUND OF THE INVENTION
Bearing arrangements exist where, for example, there is a requirement for the construction to have a low weight. Shafts forming part of such a bearing arrangement can in this case be made of light metal, such as aluminium or magnesium, while the bearings are made of steel. As long as these bearing arrangements are used within limited temperature ranges, they can be given the desired properties regarding of freedom from play and low friction.
However, if the bearing arrangements are to be used within very wide temperature ranges, for example between -30.degree. to +60.degree., then problems arise due the considerable differences in the coefficients of thermal expansion of the material of the shafts and bearings. The bearing combination which at room temperature functions entirely in accordance with the requirements set down will, within the upper temperature range, generally be subject to excessively high friction, with the shaft being clamped harder, while the same bearing combination will, within the lower temperature range, have too much play because the shaft has shrunk more than the bearing. In high-precision servo systems, for example, freedom from play and low friction are required in all the bearings occurring therein. Bearing arrangements in accordance with the above which have been exposed to considerable temperature variations do not satisfy the set requirements within the whole temperature range.
SUMMARY OF THE INVENTION
The object of the present invention is to obtain a bearing arrangement of low weight which satisfies the set requirements regarding freedom from play and low friction within a wide temperature range.
The object of the invention is achieved by a method for obtaining temperature-independent mounting in a bearing, which is characterized by arranging, on the shaft made of the first material having the first, higher, coefficient of thermal expansion, an outer shell which surrounds at least the greater part of the circum-ferential surface and is made of a third material having a third coefficient of thermal expansion which is of a lower value than the second coefficient of thermal expansion of the bearing. A bearing arrangement of the present invention characterized in that the shaft made of the first material having the first, higher, coefficient of thermal expansion is provided with an outer shell which surrounds at least the greater part of the circumferential surface and is made of a third material having a third coefficient of thermal expansion which is of a lower value than the second coefficient of thermal expansion of the bearing. By combining two materials, where one material has a higher and the other material a lower coefficient of thermal expansion than the bearing material, lights weight shafts can thus be obtained which have essentially the same thermal expansion as the bearing material. The material which has the greatest material movements is reinforced with an outer layer limiting these to the desired value. The bearing arrangement can therefore be used within a very wide temperature range.
In this connection it is worth noting that it is already known to compensate for different coefficients of thermal expansion in two interacting elements by introducing a third, intermediate
REFERENCES:
patent: 2324676 (1943-07-01), Butterfield
patent: 2590761 (1952-03-01), Edgar
patent: 4218273 (1980-08-01), Feist et al.
patent: 4283096 (1981-08-01), Picard et al.
patent: 5028152 (1991-07-01), Hill et al.
patent: 5073039 (1991-12-01), Shervington
patent: 5249869 (1993-10-01), Mabe
Nilsson Anders
Olsson Stefan
Bofors AB
Hannon Thomas R.
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