The air compressor is an important mechanical equipment for the national pillar industries such as energy and chemical industry. The impeller is the core component of the energy conversion of the air compressor. The strength and performance of the air compressor is directly related to the safety and reliability of the air compressor operation. Gao Song, et al: Strength analysis and structural optimization of the first stage impeller of an air compressor based on Patran and MSCNastran 313 Large air compressor impellers usually adopt welded structure. When the welding process is not tightly controlled, it is easy to form welding defects, reduce bearing capacity, generate stress concentration, and reduce fatigue strength. In addition, the working environment is bad, and it is easy to cause cracks or even breakage of the impeller weldment. Based on Patran and MSCNastran, the strength calculation and structural optimization of the first stage impeller of a certain air compressor are carried out. 1 Impeller Profile 1.1 Impeller Design Parameters The first stage impeller of the air compressor consists of three impeller manufacturing models such as blades, cover discs and shaft plates. The impeller adopts a welded structure, and the welding sequence is to first weld the blade to the cover plate and then weld it to the shaft plate. The blade of the impeller, the material of the cover disc and the shaft plate are all FV502B; the mechanical model of the density of 7 850 2 impeller is kg/m3, the Poisson's ratio is 0. 27, the elastic modulus is 2. The test yield strength is 919~1068MPa. The tensile strength 1.2 impeller design model is based on the design dimensions and welding technical requirements of the impeller shaft, cover disc and blade of the first stage, and the three-dimensional solid model of the impeller under the design conditions is established. The blade is well welded to the shaft plate and the cover plate, and the weld bead is rounded to take the design value. A three-dimensional finite element model of the first-stage impeller design model and the manufacturing model was established using Patran. Because of the incompletely welded area of ​​the manufacturing model and the complicated impeller structure, a three-dimensional finite element mechanical model of the impeller is established by using a tetrahedral ten-node unit (TET 10). The impeller model has a total of about 800,000 units and 1.2 million nodes. 1.3 Impeller manufacturing model After the impeller is manufactured, the weld area is inspected. Most of the weld area of ​​the blade and the shaft disc, the blade and the cover disc are not welded, and the minimum value of the weld rounding is reduced by about 5 mm from the design value, and the maximum value is increased by about 2 mm from the design value. Considering the actual The shape of the incomplete penetration area is complicated, and the unwelded area is simplified. A rectangular area of ​​1 mm x 6 mm is built in the weld to simulate the impeller incomplete penetration state. The elastoplastic finite element method M is used to calculate and analyze the centrifugal stress of the different models of the first stage impeller at the working speed. The material properties are set to rational elastoplastic materials. The solution type is solved with high precision and fast calculation speed. It is suitable for material elastoplasticity. The implicit nonlinearity (SOL 400), the generated bdf file is submitted to MSCNastran for calculation, and the calculation result is transferred to Patran to read the calculation result, and the calculated stress values ​​are all equivalent stresses. For plastic metal materials with complex stress state, the elastoplastic method for stress analysis is scientific and reasonable. 13. The strength conditions and yield criteria are based on the fourth strength theory widely recognized and adopted by the mechanical engineering community. 0. Computer Aided Engineering 3 Calculation results and analysis 3.1 Impeller design model calculation results The centrifugal stress calculation results of the impeller design model at the working speed are shown. It can be seen that the maximum centrifugal stress of the impeller is located at the edge of the long blade inlet and the round of the shaft weld, which is about 15 mm from the inner surface of the shaft, and the maximum centrifugal stress is 970 MPa. The material of this part and the surrounding area yields; The maximum centrifugal stress in the weld zone of the long blade and the cover plate is located at the edge of the inlet edge of the blade and the rounding of the weld of the cover disk, which is about 15 mm from the inner surface of the cover plate, and the centrifugal stress is about 916 MPa; short blade and shaft welding The maximum centrifugal stress in the seam area is located at the edge of the inlet of the blade and the rounding of the weld of the shaft disc, which is about 14 mm from the inner surface of the shaft, and the centrifugal stress is about 883 MPa; the inlet end of the short blade and the weld of the cover disc The centrifugal stress at the rounding is small, about 438 MPa. (a) Centrifugal stress on the intake side (b) Maximum centrifugal stress region Impeller design model Centrifugal stress 3.2 Impeller manufacturing model Calculation result Manufacturing model Centrifugal stress calculation result at working speed see. It can be seen that the maximum centrifugal stress of the impeller is located at the edge of the short blade inlet and the round of the shaft weld, and the maximum centrifugal stress is 1020 MPa; the maximum centrifugal stress of the long blade and the shaft weld is located at the edge of the inlet of the blade. The centrifugal stress is about 998 MPa at the rounding of the weld of the shaft disc; the maximum centrifugal stress in the weld area of ​​the long blade and the cover disc is located at the rounded end of the blade and the rounded weld of the cover disc, which is about the inner surface of the cover disc. 8mm, the centrifugal stress is about 982MPa; the material in the two parts and the surrounding area has yielded; the centrifugal stress at the rounded edge of the short blade inlet and the round of the cover is small, about 432MPa. The maximum centrifugal stress of the manufacturing model Analysis of the calculation results of the area 3.3 impeller (1) The design model and the manufacturing model of the first stage impeller have high stress areas on the inlet side of the blade and the rounding of the weld of the shaft disc and the cover disc. (2) The maximum centrifugal stress of the impeller design model during operation occurs at the edge of the long blade inlet and the area of ​​the shaft weld. The material enters the yield state in this area. The maximum stress in this zone is 970 MPa, which is related to the tensile strength of the material. The test average value of 1066 MPa differs only by 9%, and the safety design margin of the first stage impeller is insufficient. (3) The maximum centrifugal stress during the manufacture of the impeller occurs at the end of the short blade inlet and the weld zone of the shaft disc. The material at this and the surrounding area has yielded. The maximum stress in this area is 1 near the blade material. The average test value of strength is 1066 MPa. The results show that the existence of welding defects increases the centrifugal stress in the high stress zone and the yield zone, which is easy to cause the blade to crack at the inlet side and the weld of the shaft plate and the cover plate. 4 Impeller structure optimization To improve the strength safety margin of the impeller design model, increase the weld rounding in the high centrifugal stress region, and optimize its structural strength. See the optimized centrifugal stress distribution at the operating speed of the impeller. It can be seen that the maximum centrifugal stress is located at the edge of the long blade inlet and the rounding of the shaft weld, and the centrifugal stress is 864 MPa. At this time, the impeller has no part to yield, and the stress level is within the elastic range of the material; the short blade and The maximum centrifugal stress in the weld zone of the shaft is located at the edge of the inlet of the blade and the round of the shaft weld. The centrifugal stress is 804 MPa. The maximum centrifugal stress of the weld zone of the long blade and the cover is located at the edge of the inlet of the blade. The rounded weld is rounded, the centrifugal stress is high, and so on. The strength analysis and structural optimization of the first stage impeller of an air compressor based on Patran and MSCNastran is 722 MPa; the short blade inlet end and the cover are welded. The centrifugal stress level is low, and the maximum centrifugal stress is 450 MPa. (a) Centrifugal stress on the intake side (b) Centrifugal stress of the impeller optimization model in the maximum centrifugal stress region. 5 Conclusion Through the design model of the first stage impeller of a certain type of air compressor, The structural strength analysis of the manufacturing model and the optimization model can be concluded as follows: (1) Both the original design model and the manufacturing model have high stress regions at the edge of the long blade inlet and the round of the shaft weld. (2) There is no plastic deformation in the high centrifugal stress region of the optimized impeller model; the maximum stress of the optimized model is 864 MPa, which is 19% different from the tensile strength of the material, and the safety margin is doubled. (3) The welding quality of the blade and the shaft plate and the cover plate should be improved, and the welding of the blade and the shaft plate and the cover plate should be strengthened. It is found that the welding defect should be eliminated in time to avoid stress concentration and reduce the safety margin of the impeller. Tube&plate Laser Cutting Machine
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