Assembly of interference fit parts

The interference fit assembly of mechanical parts is widely used in practice. Reasonable preparation of interference is an important condition to ensure the normal and reliable operation of mechanical parts and to extend the service life of parts.

1 precautions in design of interference fit parts
a. The minimum actual interference after assembly can ensure the correct position between the two parts. For example, when assembling the locating pin, it is not necessary to have too much tightness, only the correct positions of each part are required.

b. The maximum actual interference after assembly can ensure that the two parts will not be deformed or damaged. For example, the assembly of reducer gear shaft and bearing requires a large amount of interference due to its large transmission torque. When the press is used to press in, once the fit is unreasonable, the bearing inner ring may be deformed or crushed.

c. The surface finish of interference fit parts is required to be high. Because the surface of the part is in the form of uneven teeth on the micro level, when measuring the size of the part, the protruding tip on the surface shall prevail. Once assembled, the protruding tip will be squeezed and shrunk, so the unit pressure of the mating surface will drop. The smaller the fitting diameter is, the rougher the machining is, and the worse the tightness of the interference fit is. Therefore, for the parts with important interference fit, the surface should be polished.

d. For parts subject to large axial force or torque, it is better to use additional fastening devices, such as brake screws, flat keys, etc., while selecting suitable interference.

2.assembly method of interference fit
Variable temperature assembly
The variable temperature assembly method is to cool the shaft with an industrial refrigerator. When the diameter is large or the interference is greater than 0.1mm, if the assembly will cause damage to the parts under normal temperature, in this case, the method of cooling the contained parts shall be used for assembly, so that the interference can be reduced or the gap can be formed in a short time, so as to facilitate the assembly of parts. When the parts return to normal temperature, the designed interference will be generated, and the tightening degree is higher than that of pressing at normal temperature. Industrial refrigerators are often used in practice.

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