Effect Of Centrifugal Compressor Blade’s Denatured Layer On Remanufacturing And Its Removing

In natural gas project, the state of centrifugal compressor impeller’s surface layer is changed in service for some time, to be completely different from the original state by forming denatured layer, which affects the performance of the compressor. Replace the impeller is difficult because of its larger size, and scrapped directly will cause great waste of resource, therefore it usually is remanufactured. However the presence of denatured layer will have some impact on the remanufacturing process, therefore it is very necessary to reveal the impact and laws on the remanufacturing of denatured layer and its removal method.In this dissertation, high temperature and high pressure reactors were used to simulate the environment of blade and prepare denatured layers with different thicknesses. The influence of denatured layers with different thickness on the subsequent manufacture and mechanism and technology to remove of plasma arc spot were investigated. The changes of the structure of coating were analyzed by means of optical microscope, SEM, EDS and others. Using of micro-hardness, Ansys analysis to analyze the mechanical properties of the coating. Finally, improving and cleaning up the degeneration layer surface by the equipment of plasma arc spot. Deriving and analysis the voltage and current signals by oscilloscope. Using SEM,3D morphology to analyze the treated the surface, morphology of samples. Exploring the mechanisms of removing the plaque layer by arc plasma technology and some causing of phenomena during experiment.The experimental results show that:With the reaction time increases, denatured layer gradually thickens and eventually divides into two layers, and its impact on remanufacturing has become increasingly evident. After plasma spray welding on the surface of the sample obtained by heat preservation after 120 h, there are a lot of sulfide inclusions and pores size 0.5-1.5mm in the interface, and the weld bead is narrow and dark. After using Ansys software to simulate the stress loaded on blade we can found that these sites will have a great stress concentration. Under high cyclic stress as blades, it is very likely cause fatigue crack in these sites.After processing by arc spot, the sample surface exposes metallic luster, and the results of EDS point scan shows that the sulfide has been substantially removed, so the desired goal is achieved. Using the Born-Haber cycle we calculate the energy of sulfide evaporate. It is much smaller than the energy of the arc spot, so the energy of the arc spot is enough to evaporate the sulfide in the range of the arc spot. When handling the surface of sample which has been kept warm for 120 h, there is a small increase in the voltage in the final stage of the process. This corresponds to the delamination of sulfide film:the Cr sulfide of the inner layer has a larger electron work function than Fe sulfide of the surface area. Comparing this voltage signal with the voltage signal of processing oxide, it is found that when processing sulfide the voltage is higher than the oxide about 2V. This is because the oxide is part of the n-type semiconductor and it has a lower electron work function. The increase in circuit current will cause an increase in the number of the arc spot, so the processing rate of speed increases. However, the current’s increase does not cause the arc spot current density’s increase, so it will not have a significant impact on the surface morphology of the treated samples. The difference of the denatured layer’s thickness has a significant impact on the surface morphology after processing:the greater the thickness, the greater the roughness of the surface after treatment.