Plastic extruder screw standards and selection techniques

Screw is one of the main key parts of extruder, and plays an extremely important role in plasticizing, extrusion and molding of plastics. Therefore, reasonable selection of screw structure and parameters of plastic extruder is an important link to obtain the quality and output of ideal products.

In order to meet the needs of different plastic processing, there are many kinds of screw structure, there are 4 kinds commonly: gradient type (equal depth and unequal distance), gradient type (equal distance and unequal depth), mutation type, torpedo head type and so on.

The selection of screw structure is mainly based on the physical properties of plastic and extruder production technical specifications to determine.

(1) the softening of amorphous polymer is completed in a relatively wide temperature, generally choose isometric gradual screw. Crystalline polymer melting temperature range is relatively narrow, isometric mutation screw is generally used.

(2) in small plastic extruder, such as φ45 extruder screw is used isometric and not deep full thread type, screw diameter is small, mainly used for extruding small section insulation layer and sheath layer, extrusion speed is faster.

(3) medium-sized screw using isometric and gradual change of the depth of the full thread type, its length diameter ratio is larger than small screw, the pitch of the thread is equal, from the root from shallow to deep. The thread at the end of the thread is deep, the root thread is shallow, so that the amount of plastic extrusion is more, and does not affect the screw strength, extrusion speed, plastic plasticization is good, is the general medium and small extruder insulation layer and sheath layer of the ideal screw.

(4) large screw diameter is generally above 150mm, such as φ150, φ200, φ250 extruder. Large screw adopts two types, one is isometric and unequal depth, such as φ150, φ200 extruder; Two is the screw is divided into three sections, namely isometric depth, isometric depth, isometric depth, isometric depth, such as φ250 extruder, compression ratio between 2 ~ 3, length-diameter ratio in about 15:1, mainly used for the production of large section of wire and cable insulation layer and sheath layer.