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The technical requirements of different kinds screw

Standard injection screw: General injection molding machine should use standard pitch diameter screw, matched with two high and low pressure conventional screws, widely applicable to the manufacturing of general-purpose plastics and engineering plastics. The screw is three-stage, including feeding section, compression section, and homogenization section. The design of the screw is determined by the working features of the injection molding machine.

Extended injection screw: It is a universal type injection screw, which has good plasticizing capacity and compounding performance. The features: high draw ratio (20 - 25), long metering section (30%), light groove in metering section (0.04 - 0.05D), high compression ratio (0.11 - 012D). It is suitable for plasticizing and compounding.

Rigid PVC injection screw: the features: low draw ratio, short metering section and transmission section, long compression section, deep groove in metering section, low compression ratio. It is suitable for injection moulding of rigid PVC and other plastics with poor thermal stability. In order to reduce the strong shearing action, and to prevent overheating decomposition, it is advisable to match this screw with “Z” screw head with melt flow.

Injection screw without metering section: this screw is also called ZM screw. It has no metering section, but only feeding section and transition section, so it is a two-stage screw. Because no metering section can reduce the overheating of the melt, and improve plasticizing and mixing performance, this screw is suitable for ABS injection and other amorphism materials. For example, it can be used to manufacture flame retardant anti-shock polystyrene, polycarbonate, filled polystyrene, polyvinyl chloride, filled nylon, etc. The draw ratio of this screw is generally 20, with the feeding section and transition section occupy 50% respectively. The grooves in the sections are deep.

Separated injection screw: this screw is also called "BM" screw, and has been widely used in injection molding. The feature of this screw is that there is a vice-screw added to the melting section(transition section or compression section), dividing the main screw into tow parts. When the screw rotates, the melt film scraped by the main screw will flow into the vice-screw’s groove through the gap between the screw flight and feeding barrel, separating the solid bed from the molten bath, so as to keep good contact between the solid bed and the inner wall of the feeding barrel, convenient for transportation and heat transfer.

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