| Large scale compressor is one of the key national infrastructure industry equipment, which is widely used in petrochemistry, metallurgy, air separation, pharmacy and national defense scientific research etc, however, the compressor main shaft may bend in the process of hot assembly. The bending main shaft can easily lead to large vibration in the running of the compressor, which will affect the stable operation of the compressor and its service life, nd even result in the breakdown of the compressor. The residual stress in the main shaft and the friction coefficient between shaft and impeller have an important effect on the bending deformation of the main shaft, but the relevant research is relatively scarce. In this paper, we have carried out numerical simulation and experiment on those two problems.In the measurement of residual stress, the existing residual stress measurement methods or standards is mainly applicable to the specimen with flat surfaces. Considering the compressor shaft is cylindrical body, we combine the experiment with finite element simulation to study validity of the blind hole method to the cylindrical objectives and strain release coefficients A, B in this paper. Firstly, we calibrated the values of A、B, which is presented in the 40NiCrMo7(commonly used in the compressor) plate that had been subjected to stress relief annealing. Then, we got the values of A、B, being-0.28222με/MPa and-0.61412με/MPa respectively. Finally, these two coefficients were obtained by simulation using finite element software ABAQUS. It was found without considering strain hardening of the material,, the predicted values deviate considerably from the experimental results whereas considering the strain hardening phenomenon in simulating, the results obtained are in good agreement with the experimental values. The relative error compared with the experimental results is within 3%. Those simulation results proved that finite element simulation is feasible. Based on the above results, the A,B values of cylindrical specimens were calculated by ABAQUS. It was found in contrast to plate specimen, the relative error of A, B values of cylindrical specimens decrease as the radius of the cylinder increases. The residual stress of cylinder with its radius being larger than 15.00mm can be measured by blind hole method using the calibration strain release coefficients obtained by plate specimen, because the relative error compared to plate coefficients is only about 3.9%. Finally, we used the blind hole method to measure the strain release coefficients A, B of the main shaft of an actual compressor and the residual stress, the A is-0.2858με/MPa, the B is-0.60588με/MPa,and the residual stress value is about 74-118MPa.A high temperature friction coefficient test device was designed and manufactured to examine the friction properties of the main shaft material 40NiCrMo7 and the impeller common materials FV520B. Utilising the device, we can investigate the influence of temperatures and surface roughness on the coefficients of friction. The experimental results show that the coefficient of friction increases nonlinearly, as the temperature increases, when the temperature reaches the initial temperature of the heat assembly(about 300℃), the friction coefficient increases with the increasing of the roughness of FV520B, if the roughness of 40NiCrMo7 is small; the friction coefficient decreases with the increasing roughness of FV520B if the roughness of 40NiCrMo7 is large. The measured friction coefficient is large, which is between 0.5-0.7 at 300℃.The above research results not only offer important parameters for enterprises to solve the main shaft bending problem during heat assembly, but also provide the basis for interference design and alleviation vibration of the compressor when running. |
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