PROBLEM TO BE SOLVED: To shorten a cooling time while preventing the bump of a cooled object and to reduce the usage of water and steam used in a pressure reducing means in a processing tank, in a vacuum cooling process.SOLUTION: In vacuum cooling the cooled object received in the processing tank, a rapid cooling process for reducing pressure in the processing tank to set pressure P1, and a slow cooling process for further reducing the pressure in the processing tank while lowering a pressure reducing capacity in comparison with that in the rapid cooling process are successively executed. The set pressure P1 is determined to be pressure higher than initial temperature reduced pressure P2 in which a saturated steam temperature in the processing tank becomes equal to a temperature of the cooled object by allowance pressure 3, and the allowance pressure P3 is determined so that the lower the initial temperature reduced pressure P2 is the smaller the allowance pressure is. For example, the set pressure P1 is set to the pressure of a set ratio of the initial temperature reduced pressure P2.COPYRIGHT: (C)2010,JPO&INPIT【課題】真空冷却工程において、被冷却物の突沸を防止しつつ冷却時間の短縮を図り、処理槽内の減圧手段に用いる水や蒸気の使用量の削減を図る。【解決手段】処理槽内に収容された被冷却物を真空冷却する際、処理槽内を設定圧力P1まで減圧する急冷工程と、この急冷工程よりも減圧能力を低くして処理槽内をさらに減圧する徐冷工程とを順に実行する。前記設定圧力P1は、処理槽内の飽和蒸気温度が被冷却物の温度と等しくなる品温換算圧力P2よりも余裕圧力P3だけ高い圧力に設定され、前記余裕圧力P3は、品温換算圧力P2が低くなる程、小さくなるよう設定される。たとえば、前記設定圧力P1は、品温換算圧力P2の設定比率の圧力に設定される。【選択図】図2
