GB760145A - Improvements in or relating to methods of and means for obtaining a precision fit between members - Google Patents

Abstract

760,145. Making bearings. L'ALUMINIUM FRANCAIS. March 12, 1954 [March 13, 1953; Feb. 9, 1954], No. 7216/54. Classes 83 (2) and 83 (4). [Also in Group XXXIV] A method of obtaining a precision fit which is but little affected by variations in temperature, between two members which are made of materials having different coefficients of thermal expansion, e.g. one member of steel and the other of aluminium or magnesium alloys, and which are fitted one within the other, comprises interposing between the members a liner, e.g. of ebonite, hard rubber or synthetic plastics which has a coefficient of thermal expansion higher than the coefficients of expansion of the materials out of which the said members are made. In an embodiment a ball-bearing assembly 1 is provided with a plastic lining 2 in a recess formed in the outer race and when the bearing is inserted in a housing 4 the precision fit is maintained over wide variations in temperature. Alternatively, the plastic lining may be attached, e.g. by casting, cementing in place or force-fitting to the internal bore of the housing 4. In another embodiment a steel shaft 6 may be fitted within a bore in a light alloy housing 4 with the interposition of a plastic ring 2. When using liners of polyamide base plastics, which lose their elastic resistance properties proportionally with rise in temperature, the lining is cast or injected into a recess 12 (Fig. 5) the bottom of which is joined with circumferential grooves 14 arranged with opposed abutment surfaces 15 and 16. At working temperatures the lining material expands circumferentially and axially, the latter being limited by reason of its attachment to the supporting surfaces 15 and 16 of the inner member. This double expansion produces a proportional deformation in a radial direction, which is added to the linear expansion of the material in this direction, and due to the high coefficient of expansion of the lining the increased clearance between the members, which would otherwise occur due to the coefficient of expansion of the outer member being higher than that of the inner member, is taken up and the precision fit is maintained within allowable tolerances within a temperature range of - 20‹ to 80‹ C.