Internal mixer

An internal mixer of the type including a mixing chamber rotatably accommodating mixing rotors therein, a hopper frame erected on said mixing chamber, a charge hopper provided on one lateral side of said hopper frame for charging a mixing material therethrough, and a floating weight provided in said hopper frame for upward and downward movements therein, said floating weight being held in an upper lifted position when charging a mixing material into said mixing chamber and then lifted down into a lower pressing position in a mixing stage to apply pressure on the charged material in said mixing chamber, characterized in that:

• said floating weight is dimesioned to have an axial length sufficient for closing an inlet opening formed in the side wall of said hopper frame in communication with said charge hopper, when in said lower pressing position;
• a pressing means for pressing said floating weight resiliently against said mixing material;
• a lift means for lifting said floating weight up and down in said hopper frame, said lift means being provided separately from said pressing means and having a hydraulic cylinder mechanism including a hydraulic lift cylinder formed internally of said floating weight, a piston slidably received in said lift cylinder, a piston rod extended upward from said piston into said hopper frame, and a liquid tight seal through which said piston rod extends.