To make the quality of a finished product constant by lessening variation of the grain size as much as possible.
A load current to be supplied to a main motor 36 during crushing is detected by a load current detection means 37 and the detection value is inputted to a controller 38. The input value of the load current and a set current value are calculated through comparison and when the input value of the load current reaches the upper limits of the set current value, a solenoid valve is activated to be set into the open position from the closed position. An oil in a hydraulic cylinder 6 is drained to lower the hydraulic cylinder 6 and in turn, a crushing head 10 descends. The descent level of the hydraulic cylinder 6 is detected by an ascent/descent level detection means 28 and is entered to the controller 38. The detection input vale and a set ascent/descent value are calculated through comparison, and when the detection input value reaches the set ascent/descent value, the solenoid valve 19 is activated to be set into the closed position from the open position. Consequently, the descent of the hydraulic cylinder 6 is stopped under the closed position and simultaneously the lowering of the crushing head 10 is also stopped.
AKAGAWA HIROMI
NAKAJIMA NORIYUKI
