Injection molding machine screw type general introduction

1. Conventional injection screw: The general injection molding machine uses a standard medium diameter screw and two conventional screws with high and low pressure, which can be applied to the processing of a wide range of general-purpose plastics and engineering plastics. This screw is also a three-stage type: feeding section, compression section, and homogenization section. It is determined by considering the working characteristics of the pre-molded and injection-molded materials of the injection molding machine.

2. Lengthened injection screw: It is a general-purpose injection screw with higher plasticizing ability and better mixing effect. Compared with conventional screws, its characteristics are: large aspect ratio (20-25), long metering section (30%), The groove in the metering section is shallow (0.04~0.05D), and the compression ratio is large (0.11~012D), so it is beneficial to plasticizing and mixing.

3. Type of rigid PVC injection screw: The characteristics of this screw are: small aspect ratio, short metering section and conveying section, and long compression section; Injection molding of plastics with poor thermal stability such as rigid PVC. In order to reduce the strong shearing effect and material storage and prevent thermal decomposition, this screw is suitable for a "Z" type screw head with a melt flow cavity.

4. Injection screw without metering section: Injection screw without metering section is also called "ZM" screw, which is characterized by no metering section, only feeding section and transition section, so this is a two-stage screw. Because no metering section can reduce melt overheating, increase plasticizing capacity and mixing effect, it is suitable for injection molding ABS and other amorphous materials that prevent shear overheating, such as flame-retardant impact-resistant polystyrene, Polycarbonate, filled polystyrene, polyvinyl chloride, and filled nylon, etc. The length-diameter ratio of the screw without metering section is generally 20, the length of the feeding section and the transition section each account for 50%, and the recommended groove depth for each section

5. Separate injection molding screw: (BM screw) The separate injection molding screw is called "BM" screw, which has been widely used in injection molding. The main screw is characterized by adding a secondary thread in the melting section (transition section, compression section). , Divide the main thread groove into two parts. When the screw rotates, the molten film scraped by the main thread flows into the groove of the auxiliary thread from the gap between the screw rib and the barrel wall, so that the solid bed is separated from the molten pool, so as to keep the solid The good contact between the bed and the inner wall of the barrel is convenient for conveying and heat transfer.

6. Corrugated screw (HPM screw): The corrugated screw is divided into "single wave" and "double wave". The characteristic of the single wave screw is that the bottom diameters of the two adjacent screw grooves are equal, but they are eccentric, and the eccentric distance is equal, and the screw axis is symmetrical. Since the depth of the screw groove changes periodically in a wave shape along the axial direction, the material is subjected to strong extrusion and shearing action during pre-molding, which absorbs a large amount of mechanical energy and converts energy; and when it reaches the trough, the material relaxes and balances energy. Homogenization at each temperature. The polymer that has been melted will quickly pass through the strong shear zone, while the remaining solid material will be forced to undergo periodic changes by strong shear, thereby accelerating the disintegration and melting of the solid bed. The double wave screw can not only improve the plasticizing ability, but also increase the mixing effect. It is suitable for injection molding of materials with fillers, pigments and foaming agents, and can obtain uniform components; it is also suitable for injection molding of heat-sensitive materials such as rigid PVC, which can reduce degradation.

7. Mixing type injection screw: The characteristic of mixing type injection screw is to set mixing elements at the position of the metering section. Based on the analysis of ordinary screw, it is shown that in the transition section, the polymer is initially melted, and a molten film is also formed on the trailing edge of the thread. So the entire solid bed is actually surrounded by a molten film, reducing the melting efficiency. Therefore, in the transition zone, it is still advisable to emphasize stable melting and conveying. After the material is completely melted through the transition section, a mixing zone is added, and a mixing element is set on the mixing zone, so that the material can be further mixed and homogenized. There are three types of mixing elements. Pin type mixing element (IKV mixing element); barrier type mixing element (straight groove mixing element is also called Maddook element); other barrier type mixing element, (split type mixing element is also called DIS type mixing element )