Distortion behavior of hydro turbine blade castings during heat treatment processes under variation of seasonal temperature
Distortion often appears at the corners of heavy turbine blade castings during heat treatment processes, so a great machining allowance is generally set in production which directly results in cost increase. In this paper, a novel real-time measuring technology is developed for non-contact measuring the deformation behavior of heavy steel castings in heat treatment process. It was employed to measure the distortion and the temperature field of a batch of heavy turbine blade castings at cooling stage in normalizing process. Three inflection points appear in the distortion-time curves, and the residual distortion is affected by the regional area of not finished martensite transformation when the second inflection point appears. When the mean air temperature falls into the range of 10°C-20°C, the residual distortion is small; when it is lower than 10°C, positive distortion appears; when it is higher than 20°C, negative distortion appears. The distortion varies with seasonal temperature, which is directly responsible for the great machining allowance given in production
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