How to choose the screw structure conditions in the injection molding machine?
The screw structure of the general-purpose injection molding machine generally adopts the standard middle diameter screw with strong versatility. When special conditions require, a conventional rod suitable for high pressure or low pressure needs to be equipped. This kind of screw configuration in general injection molding machine can basically meet the injection molding work of commonly used resins. According to the different properties of injection products, a reasonable screw structure can be selected. The structural conditions of several screws for injection molding products are presented below, and reference selection is made when supplying them. 1. Screws for rigid PVC injection products Due to the poor thermal stability of rigid polyvinyl chloride resin and the high viscosity of the melt, the screw used for injection molding rigid polyvinyl chloride products should be selected with a smaller compression ratio (generally 1.4~2), a smaller length-to-diameter ratio, and a smaller screw. The homogenization section (metering section) and the feeding section (feeding section) are shorter, and the thread groove of the homogenization section is deeper. The head of the screw should be tapered, and the injection nozzle should be a straight-through type. 2. Screws for non-crystalline plastic injection products such as ABS The screw structure for injection molding of amorphous plastics such as ABS can be used without a homogenization section (metering section) but only a feeding section and a transition section. This can reduce the overheating of the melt and improve the plasticizing ability and mixing effect of the screw. For the injection of amorphous high-viscosity melts, straight-through nozzles should be used. 3. Screws for crystalline plastic injection products such as polyethylene and polypropylene The screw for injection molding of crystalline plastics such as polyethylene and polypropylene should generally be selected with a screw with a larger compression ratio and a non-return ring device. This is to ensure the working efficiency of the injection molding machine and prevent the melt during injection. Larger reflux. Due to the low melt viscosity of this resin, a salivation prevention nozzle should be used. hwaqtester.