PURPOSE: To enable prevention of spouting of resin through a hopper or an injection nozzle, by a method wherein cubical expansion of molten resin closed up tightly within a heating cylinder is detected through an amount of backward movement of a screw.
CONSTITUTION: At a point of time when a command of a forward or backward movement of a screw 7 or turning of the screw through a controller 4 is completed and the screw 7 becomes a neutral state, a signal of a screw position is applied to the controller 4 through a screw position detector 7d and a register 4a stores a screw position x1. Then an allowable amount Δx of a backward movement of the screw 7 established beforehand is added to the screw position x1 with an adder 4b, the screw 7 is moved backward by being pressed with expansion pressure of molten resin due to pyrolysis of the resin while the neutral state of the screw 7 is being continued. When a screw position comes to an x2, a comparator 4c makes a pylorysis detected signal by deciding that the resin on the inside of a heating cylinder 2d begins the pylorysis when (x2>x1+Δx) is given by comparing the x2 and (x1+Δx) with each other.
GOTO HIDEAKI
NAKAMURA KAZUMITSU
