Abstract: In a gear pump assisted thermoplastic extrusion system, the speed of operation of the gear pump is adjusted in relation to fluctuations in both the rate of product output from the system and the rate of material input to the system to precisely maintain a desired weight per unit length of the extruded product within close tolerances.

Abstract: A gear pump assisted screw conveyor extrusion system utilizing a cartridge heating device disposed axially within the screw and having the drives for the gear pump and the screw correlated in speed to create relatively little pressure in the thermoplastic material being extruded such that relatively little mechanical working thereof occurs. The thermoplastic material is melted in the screw conveyor primarily by heat transfer from the cartridge heater and the gear pump is utilized for conveying the melted material under pressure to a subsequent work station. A relatively deep material-conveying spiral channel is provided in the screw for maximized extrusion output per revolution of the screw and minimized mechanical energy generation by the screw. A motionless mixer may be employed intermediate the screw and the work station to homogenize the melted material for reducing temperature gradients therein.

Abstract: An improved sealing sleeve for the rotating drive shaft of a gear pump or other fluid conveying system has an internal axial bore for receiving the shaft, an intermediate cavity formed in the bore and oppositely-handed helical channels extending in the bore on opposite sides of the cavity. The inward helical channels are of a hand relative to the shaft rotation for effectively pumping viscous fluid entering the annular spacing between the shaft and sleeve toward the cavity while the oppositely-handed outward helical channels effectively resist and overcome such pumped fluid flow, creating a static containment of the viscous fluid to produce a viscous seal about the shaft. Cooling fluid is conveyed through an annular passageway about the outward helical channels to solidify any viscous fluid entering the adjacent region of the outward channels to produce an outward essentially mechanical seal about the shaft.