Research On The Main Shaft Bending Mechanics In Shrink-fit Of A Large Scale Centrifugal Compressor

The large scale centrifugal compressor is a kind of energy conversion device. Because The large scale centrifugal compressor has a lot of advantages including of large air displacement, high efficiency, well running stability, and so on, it has been widely applied in the petroleum industry, chemical industry, metallurgical industry, power industry, refrigeration industry, etc. However, during the thermal assembly of the compressor’s main shaft and impellor, the main shaft often bends. Especially, the larger the main shaft is, the bigger the bending deformation. Once the bending happens, the manufacturer must spend time repairing it. Sometimes, the main shaft would be discarded if the bending deformation is too serious. At present, there are a lot of works about the structure strength analysis, impellor blade optimization, flow passage design, surge analysis, reliability design, and so on, but there are only few mechanics analyses of the compressor rotor when it was assembled. Therefore, this thesis studies on the main shaft bending mechanics in shrink-fit of a large scale centrifugal compressor based on finite element analysis, on-site survey and experiment.Firstly, this thesis establishes a finite element model based on the physical model provided by the manufacturer. In order to describe the problem as accurately as possible, the finite element model considers the effect of the deadweight of the assembly entity and the contact between the impellor and the table. Using this model, the thesis analysis the influences of the inhomogeneous temperature field, friction coefficient (FC), magnitude of interference (MI) and contact length on the bending deformation of the main shaft. Besides, the thesis carries out an experiment on effect of surface roughness on the FC. It is founded that the inhomogeneous field temperature field is a main factor that results in the main shaft bending. However, the bending deformation firstly increases with the cooling time, and then decreases with the cooling time. Finally, the bending deformation will reach to a small value when the whole temperature of the assembly entity decreases to room temperature. It should be pointed out that the final value of the bending deformation is associated with the FC and MI. Further study shows that the final bending deformation increases with the FC and MI while the MI is small, and then the final bending deformation begins to decrease with the MI and becomes insensitive to the FC when the MI is bigger than a critical value. As for the effect of the contact length in axial direction, the result shows that final bending deformation decreases with the decreasing in contact length. Finally, the experiment shows that the FC between the impellor material (FV520B) and the shaft material (40NiCrMo7) ranges from0.12to0.26with the surface roughness of the two materials. In general, the FC decreases with surface roughness of FV520B, but increases with the surface roughness of40NiCrMo7. Furthermore, the FC is insensitive with the normal pressure. Based on these results, this thesis provides an improvement measures to decrease the final bending deformation of the main shaft.