Barrel screw is an important part of injection molding machine. Its functions are transportation, compaction, melting, stirring and exerting pressure on plastics. All these procedures are completed by rotating the screw in the barrel. When the screw rotates, the plastic will produce friction and mutual movement between the inner wall of the barrel, the bottom surface of the groove, the front surface of the rib and the plastic. The forward pushing of plastic is the result of this combination of motion and produces friction. Heat is also absorbed to increase the plastic temperature to melt the plastic. The structure of the screw will directly affect the degree of these effects. In order to improve the plastic quality, the screw can be designed as a separate screw, barrier screw or open screw.