1. Surface quality and dimensional tolerance
After cleaning, grinding and sandblasting, the impeller investment casting is free of micro-cracks, cold shuts, flow marks and other defects through visual inspection and dye penetrant inspection, and the surface quality meets the requirements. The surface of the impeller investment casting is smooth. Through the comparison of roughness standards, it is found that its surface roughness can reach 3.2 μ m. Meet technical requirements. First measure the main dimensions, and then compare the impeller investment casting drawing. Drawing size (290 ± 3.2) φ （116±2.5）、 φ （186±2.8）、 φ (490 ± 3.6) mm, corresponding measured dimensions are 292.8 φ 117.9、 φ 188.6、 φ 493.3 mm, confirm that the dimensional tolerance meets the requirements.
2. Internal quality
The process of hot isostatic pressure treatment for impeller investment casting is as follows: the heating temperature is controlled at (920 ± 10) ℃, the pressure is maintained at 100~140MPa, the holding time is 2~2.5h, and the furnace is cooled to below 300 ℃. The impeller investment casting shall be subject to X-ray flaw detection after hot isostatic pressure treatment. The test results (Table 1) show that there are no casting defects such as porosity, shrinkage cavity, spongy porosity, dendritic porosity, low density inclusion in the impeller investment casting, and the internal metallurgical quality meets the requirements.
|Quality level||Casting wall thickness/mm||Stomata||Shrinkage cavity||Shrinkage cavity||Dendritic porosity||Low density inclusion|
3. Chemical composition
The outer surface of the impeller investment casting is peeled by mechanical processing, and the chemical composition is tested from three areas: the far end of the impeller, the near end of the impeller and the center hub. The test results (Table 2) show that the chemical composition of the impeller investment casting meets the standard requirements.
|Sampling location||Value class||Al||V||Fe||Si||C||N||H||O||Ti|
|Far end of impeller||Measured value||5.98||4.08||0.17||0.08||0.069||0.022||0.0078||0.11||Allowance|
|Near end of impeller||Measured value||6.01||4.10||0.19||0.09||0.070||0.020||0.0080||0.12||Allowance|
|Center hub||Measured value||5.99||4.09||0.18||0.08||0.071||0.021||0.0079||0.13||Allowance|
|All positions||Standard value||5.5-6.8||3.5-4.5||≤0.30||≤0.15||≤0.10||≤0.05||≤0.015||≤0.20||Allowance|