Shrink fitting is a method used in making mechanical joints when axles, bushings and similar are to be fitted inside a part with a hole. The hole is made slightly too small for fitting at even temperature, which means that the outer part needs to be heated or the inner part needs to be cooled.
Heating the outer part may take a long time, and in some cases metallurgical reasons may prevent heating altogether. However, cooling the inner part will not affect the property of the metal, and can be achieved much faster.
When using liquid nitrogen as a coolant, a temperature difference of up to 200 oC can be achieved. In order to cool the inner part it should be kept in liquid nitrogen (temp. -196 oC), which will make it shrink enough to fit in. The joint becomes durable when the temperatures of the parts are even.
Shrink fitting with liquid nitrogen is an ideal solution for these types of joints.