How to choose screw structure in injection molding machine?
General - purpose injection molding machine in the screw structure, generally using a strong universal standard diameter screw.When special conditions are required, a conventional lei rod suitable for high or low pressure needs shall be provided.This kind of screw in the general injection molding machine is equipped to meet the injection molding work of common resin.According to the different material properties of injection products, a more reasonable screw structure can be selected.The following are the structural conditions of screw for injection molding products.
(1) screw rod for PVC injection products
Due to the poor thermal stability of rigid polyvinyl chloride resin, high viscosity of the molten material, so the injection pvc-u products with screw should choose small compression ratio (usually take 1.4 ~ 2), and the length to diameter ratio is smaller, the homogenization of the screw (measurement) and loading (transporting) is shorter, and the homogenization of thread groove to the deeper.The head of the screw should be tapered and the injection nozzle should be straight through.
(2) screw rod for ABS and other non-crystalline plastic injection products
The screw structure for injection molding of amorphous plastics such as ABS can be used for screw structure without homogeneous section (metering section) but only feeding section and transition section.This can reduce the material overheating and improve the plasticizing ability and mixing effect of the screw.For injection of amorphous high viscosity frit (such AS PS, PPO, PC, PMMA, AS and POM), a straight through nozzle should be used.
(3) screw rod for injection products of crystalline plastics such as polyethylene and polypropylene
Such as polyethylene, polypropylene crystallization type plastic injection with screw, generally should choose have larger compression ratio (3 ~ 3.5) of the screw, and shall also have the ring of non-return device, this is to ensure that the working efficiency of the injection molding machine, prevent the reverse flow of liquid injection are larger.Because of the low viscosity of the resin, the anti-salivation nozzle should be adopted.