The shrink fitting of two workpieces (e.g. gearwheel, unbalanced mass, shaft, etc.) leads to a friction-locked connection. This is a method based on the principle of the thermal expansion of metals.
If for example a gearwheel is heated to a temperature at which the internal bore is so big that it can be pushed easily to a shaft and said gearwheel is then cooled, the diameter of the inner bore is reduced to such an extent that a friction-locked connection to the shaft is guaranteed.
At room temperature, these components could only be connected with enormous effort. Moreover, the connection at room temperature can lead to possible damage at the fitting length (scoring).