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Shrink Fits

Shrink fit (transverse press) is the non-forcible inserting of the part after previous hole heating or after shaft cooling. In case of shrink fit, the effective interference also decreases to a certain level due to "subsidence". The decrease, however, is significantly smaller than in the case of force fit. The value of subsidence depends on the roughness of the connected areas. The loading capacity of shrink fit coupling is approximately 1.5 times higher than in the case of force fits. The selection of heating or cooling depends on dimensions of the parts and technical possibilities. During the hole heating, it is necessary to observe that the temperature when structural changes in material occur (in case of steel, it is approximately 200C/395F to 400C/750F) is not exceeded. Heating of outer parts is usually done in a oil bath (up to 150C/300F) or gas or an electric furnace. Parts with small diameters have to be heated to a much higher temperature than ones. Cooling of shafts is usually done rather with smaller couplings, using carbon dioxide (-70C/-95F) or condensed air (-190C/-310F). For couplings with large assembly interferences, a combination of both methods may be used. Shrink fitting is unsuitable for parts made of heat-treated steel and in case of a heated part fitted on a hardened one. In such case, it is necessary to cool the inner part or force fit the coupling.

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