In order to be able to join two workpieces such as: shaft, gear wheel, unbalanced mass, etc., the process of shrinking is used. The principle of thermal expansion of metals is fundamental.
If, for example, an attempt is made to push a gear onto a shaft at room temperature, an enormous amount of force is required and the joint length of the component would be damaged. However, if the gear is heated to a certain temperature, the inner bore is large enough to be able to slide it onto the shaft without any problems. The gear is then cooled down and the diameter of the inner bore is reduced, so that a force-fit connection with the shaft is created.