The screw with large aspect ratio can obtain low temperature homogeneous melt, stable extrusion and high plasticizing ability. However, the injection screw is only used for pre molding, and the stability of the discharge has little effect on the quality of the products, and the time and temperature course of plastic plasticization is longer than that of the extrusion screw. Therefore, the ratio of length to diameter of injection screw does not need to be as long as that of extrusion screw. Generally between 18 -, the length is rarely more than 4 (except for special screw such as exhaust), which meets the use requirements. From the point of view of design, manufacture and use, it is also hoped to use screws with similar effect and shorter length. Because of this, it will bring benefits to the manufacturing of screw barrel, shortening the length of the fuselage, reducing the weight of the machine and cleaning the barrel. In order to ensure the required plasticizing capacity and quality, for screws of general structure,