Thermal growth
Thermal expansion leads to misalignment
An alignment is always performed on a stopped machine, usually after the performed maintenance or on new placed machinery. An alignment is therefore usually performed in cold condition. In most situations, this is not a problem because the temperature differences during production are marginal. However some machines or production processes have such large temperature differences that the thermal expansion exceeds the alignment tolerances.
Pre-setting
In order to prevent that temperature changes and thermal expansion lead to misalignment, a so called thermal growth measurement can be preformed. During this measurement the thermal and dynamic changes between the offline and running situation are measured. The resulting data can then be used to calculate a pre-setting for the alignment in cold condition. This pre-setting then leads to an optimal alignment in hot running condition.
For larger machines and installations like turbines, generators and compressors there are often theoretically calculated pre-settings available. Experience learns that these pre-settings do not always reflect the actual values. For these machines a thermal grow measurement is highly recommended.
Dynamic setting
Powerful machines with high torques have the characteristic to deform during start-up and load ramping. The setting of these machines, relative to each other or to the foundation, can in some cases exceed the alignment tolerances. The same applies for these cases as for the thermal expansion. By measuring the deformations between the offline and running situation, accurate pre-settings can be calculated guaranteeing an optimized alignment.