The two most important processes of plastic molding are injection molding and extrusion molding. Screw is the key component in the whole molding process, so the importance of screw has been emphasized. We know that there are various kinds of single screw, such as separation, mixing and compression decompression single screw. Among them, the compression and decompression screw is divided into energy transfer (ET) screw and wave shaped screw.
Like ordinary single screw, corrugated screw is still divided into solid conveying section, compression section and metering section, but the difference is that from the compression section, the thread has an eccentric distance, and the screw groove is wavy when it is unfolded. During extrusion and plasticization of unplasticized polyvinyl chloride (UPVC) materials, in addition to spiral conveying and certain thermal process, they also undergo intermittent action of wave peaks and troughs to promote the materials to receive periodic compression - decompression action, during which the molecules produce stress relaxation. In this way, the temperature of the material will not rise continuously due to continuous shearing and non rubbing during the plasticizing process of UPVC, so as to degrade, which greatly improves the quality of UPVC products.
After years of efforts, it has reached the practical stage and should be vigorously promoted and applied. South China University of Technology mainly studies double waveform screw, exhaust or extruder screw, while the background chemical college focuses on the research of corrugated screw for injection molding. This paper focuses on this kind of corrugated injection screw.

In recent years, with the increasing output of extruders and driving power, the screw speed has also increased. In order to effectively improve the ability of bearing one-way torque, it is very important to analyze and study the failure and stress causes of extruder screw mandrel. Why to obtain better plasticizing effect and production capacity? Large diameter screw and ultra deep screw groove are the development trend of extruders in recent years. The greater the torque the shaft bears, the more the mandrel breaks during the operation of the extruder. Therefore, it is of great significance to study the causes of the failure of the extruder screw mandrel for improving the production capacity and product quality of the extruder.

In plastic processing industry, reasonable assembly structure and processing precision of components shall be selected; The correct design of screw structure and shape, the adoption of new materials and the treatment of screw surface are effective measures to reduce screw surface wear and corrosion and improve productivity.

In addition to the extruder screw, the barrel and nozzle are also very important in the processing and production of the extruder plasticizing device. Next, simply accept the structural characteristics of these two parts.
The extruder barrel is a straight barrel, which is closely matched with the screw. The radial clearance between the screw and the barrel is generally 0.2M (0.008in); The clearance of extruder with screw diameter no more than 40mm is about 0.15mm (0.006in). The barrel is usually made of bimetal by center casting. When the plasticizing device requires exhaust, an exhaust port shall be opened on the barrel. Open the feeding port at the feeding end of the barrel. The feeding mouth is connected with the hopper, and the solid plastic particles are added to the extruder through the hopper.
The nozzle of the extruder is pushed onto the main casting sleeve. The tip of the nozzle is usually rounded, and the radius of the arc is slightly smaller than the radius of the matching main casting sleeve to achieve good sealing. The radius should be large enough to avoid excessive wear. In the American standard, the radius of magic spray is. 0.5 in and 0.75 in; In European Union standards, sneezing radii are 10mm, 15mm, 20mm and 30mm. The nozzle can be either a straight through type or a switch device
Set. Straight through nozzles are generally recommended for the processing of heat sensitive integrators and high viscosity polymers, such as hard PVC, thermosetting resins, and elastomers. Figure 1.12 shows the structure of a straight through nozzle.

1. The screw barrel shall be straight.
2. The screw barrel shall be designed to withstand the working pressure of the extruder. These pressures may be as high as 70-140 MPa (10000-20000 psi), even higher in injection molding.
3. The inner wall of the screw barrel should be more wear-resistant than the screw barrel of the extruder, because the screw barrel is easier to replace than the screw barrel, and the reprocessing is cheaper than the screw barrel.
4. The support at the rear end of the screw barrel shall be sliding support, which is allowed to expand when the screw barrel is heated. The rigid support will cause the bending of the screw barrel, which may cause serious damage to the screw and the screw barrel.
5. In order to improve group conveying, the feeding section of the screw can be grooved. The slotting and digestion section shall ensure good cooling capacity to take away the heat generated by high friction and prevent the melting of materials accumulated in the tank. In addition, the trench shall be sloped and the depth gradually becomes shallow to minimize the chance of material hanging in the structure grains.
6. If there is no air outlet, it shall be offset, and the side wall of the opening shall be tangent to the inner wall of the cylinder to reduce the chance of the plastic melt hanging on the front of the air outlet, as shown in Figure 2.20. Compared with the traditional symmetrical exhaust port design, it is easy to block the material at the bottom of the exhaust port. The opening of the exhaust port can be designed to tilt downward to avoid cooling the material flowing into the extruder screw.

1、 The assembly clearance between the extruder screw and its supporting transmission shaft is too large, and the two shaft centerlines are not concentric when rotating, resulting in too large error.
2、 Extruder screw is bent and deformed, and the straightness of the shaft centerline exceeds the tolerance.
3、 The perpendicularity between the end face of the extruder barrel and the end face of the connecting flange of the base and the centerline of the barrel can not be guaranteed, and the error is large.
4、 When the extruder screw is assembled in the extruder barrel, the concentricity error of the two parts is large.