Structure of turbine shell is complex,with large difference of wall thickness,and strict dimensional accuracy controlling.The surface defects,shrinkage porosity,cracks and other problems are also easy to come out.Based on the analysis of the structure,quality requirements and service conditions of the turbine shell,corresponding solutions from the aspects of casting process,pouring process,sand molding and heat treatment process were given.The adoption of the cores assembly structure,1.5％-1.9％of shrinkage ratio and anti-deformation tie pieces ensured the dimensional accuracy of the airway.The measures of bottom gating system,reasonable rising speed of liquid steel and so on avoided inclusion or shrinkage porosity defects and ensured the internal quality of the casting.The casting surface quality and the feeding effect of the air-pass wall were assured by using of chromite molding sand.A dedicated plate was used to fix the casting and proper heating and cooling rates were controlled,which prevented the casting from deformation during heat treatment process.
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维普
