This will normally involve rings designed to achieve the minimum percentage of spring compression at which bearing retention can be guaranteed when at maximum clearance, leaving the remainder of the spring compression range available to handle any external radial loads, machining tolerances or dimensional changes caused by differential thermal expansion of the mating components. Most tolerance rings would be designed such that the elastic zone was maximised. This caters for maximum component tolerances and differential expansion.
In a typical electric motor bearing mount: Alumina housing, 608 bearing, H9 tolerance on the bore and a temperature range of 20°C to 100°C an HVL22x7SS tolerance ring with a 0.33mm wave height would be used giving a radial clearance of 0.297mm to 0.320mm across the machining tolerance range.
‘Light duty’ variants of the standard ring design are available which allow some axial movement of the bearing where, for example, pre-loading is used. The standard ‘heavy duty’ ring design provides axial retention and is used where higher eccentric radial loads are expected.
For a typical bearing fit (OD to housing) Tolerance Rings enable the relaxation of machining tolerances and reduction of press fit forces compared to conventional interference fit into steel housing with various tolerances on the bore.
For a ball bearing in an aluminium housing the differential thermal expansion will quickly reduce the force needed to disassemble and at fairly moderate temperatures for many applications, the bearing will be loose. A correctly designed tolerance ring in a simple fixing application or bearing assembly utilises the elastic range of wave compression to compensate and maintain a positive retention force to much higher temperatures.
The tolerance ring tends to centre a bearing or other parts with each wave pushing towards the centre. With a free mounting arrangement eccentricity will usually be in the region of 2-3% of radial clearance.