Effect of external load on rotor vibration

Rotor dynamic has a major impact to the end product in paper production and thus it is widely been researched for decades. In general, the behavior of rotors is studied only without an external load and research with the load is scarce. However, an unloaded arrangement does not correspond to a real situation. The aim in this study is to develop an external loading device for a rotor and investigate the effects of the external load on a rotor. It is supported by Academy of Finland (TwinRotor, grant number 313675).Since the point of our interest are the loading conditions in a paper machine and the test rotor is paper machine roll, the amount of the load are taken from real paper production conditions as well. There paper machine rolls are under 10 kN/m distributed force exerted from a paper web. In this study, the load is conducted with a relatively narrow belt to the rotor. Thus, developed force can be concerned to be a point load. To achieve similar forces as in the real situations the loading force should be 40 kN, since the test rotor body is 4.0 m long. However, the used force is lower, because a same deflection is achieved with lower force using the point load comparing to a distributed load. The effect of the load on the rotor vibrations is investigated with laser run-out measurements. Measurements are taken with two different loads, in which rotational frequencies from 4 Hz to 18 Hz are used with an increment of 2 Hz. After a signal analysis the frequency response of the rotor with these two loads can be examined; some force amplitudes increased considerably at a specific frequency under the larger load. The observations are presumably results of the bending stiffness variation of the rotor. The study proves the developed system functioning and suitable for simulating external loads of a rotor.