Mold-clamping device, injection-molding device, and method for opening and closing mold

A mold-clamping device comprising:

• a fixed mold plate including a fixed mold;
• a movable mold plate including a movable mold;
• a hydraulic cylinder allowing the movable mold plate to approach or be separated from the fixed mold plate;
• a hydraulic pressure supply source supplying a hydraulic fluid to the hydraulic cylinder;
• a control unit performing driving control on the hydraulic pressure supply source;
• and
• a hydraulic pressure sensor that is configured to detect a hydraulic pressure of the hydraulic fluid supplied to the hydraulic cylinder and is configured to output a detection result of the hydraulic pressure of the hydraulic fluid to the control unit,
• wherein the control unit is configured to decrease a flow rate of the hydraulic fluid according to a deceleration gradient set in advance when a movement of the movable mold plate is decelerated according to the deceleration gradient set in advance,
• the control unit is configured to control the flow rate of the hydraulic fluid to increase when the flow rate of the hydraulic fluid is decreased according to the deceleration gradient set in advance by the control unit,
• the control unit is configured to determine whether or not a pressure in the hydraulic cylinder is lower than a predetermined positive pressure set in advance, and
• the control unit is configured to increase the flow rate of the hydraulic fluid when the flow rate of the hydraulic fluid is decreased in a case where the pressure in the hydraulic cylinder is determined to be lower than the predetermined pressure by the control unit.