Injection molding machine and method of adjusting control condition for reverse rotation of screw in injection molding machine

An injection molding machine having a screw provided with a check valve, rotational drive means for driving the screw to rotate, axial drive means for driving the screw to move axially and rotational force detection means for detecting a rotational force exerted on the screw, and that performs a reverse rotation process of rotating the screw in a direction opposite to a direction of rotation of the screw in a metering process, on a control condition, after completion of the metering process and before start of an injection process, said injection molding machine comprising:

• back-flow amount index detection means for detecting one or more physical amounts indicative of state of a molding operation and serving as indices of a back-flow amount of resin flowing backward through the check valve during a forward motion of the screw,
• evaluation value calculation means for obtaining an evaluation value by inputting the detected physical amounts as the indices of the back-flow amount to an evaluation function for evaluating the control condition of the reverse rotation process, and
• control condition selection means for repeating molding operations with a set value of the control condition of the reverse rotation process varied within a predetermined range, and selects a value of the control condition with which the highest evaluation value is obtained by said evaluation value calculation means, to be set for the reverse rotation processes in continuous molding operations.