PURPOSE: To prevent the rapid deterioration of an auxiliary descaling agent and to reduce the cost of production by applying ultrasonic vibration in one of plural descaling stages.
CONSTITUTION: A material 1 to be treated is sent to a salt bath 3 through a pretreating tank 2 such as a washing tank, and it is sent to a hot water tank 4, where a film of solidified salt formed on the surface of the material 1 is cracked by rapid cooling and stripped together with scale sticking directly to the material 1. The material 1 is successively put in a primary pickling tank 5 and a secondary pickling tank 6 contg. HF/HNO3. The material 1 pulled up from the tank 6 is put in an ultrasonic cleaning tank 7 filled with water and provided internally with an ultrasonic vibrator, and scale remaining on the surface of the material 1 is removed by generating ultrasonic waves. The material 1 may be further sent to a pickling tank 7' or a descaling line 8 to repeat descaling.
HISAMOTO TSUYOSHI
KONDO TSUGIO
UCHIDA TSUMIAKI
