The correct selection method of screw type

As one of the important parts of the extrusion system of the plastic extruder, the screw not only plays the role of conveying plastic that cannot be ignored, but also plays an extremely important role in the difficulty of plastic extrusion, plasticization, and molding. Reasonable selection of screw structure and parameters is an important part of obtaining ideal product quality and output.

In order to meet the needs of different plastics processing, there are many types of screws, the common ones are the following: gradient type (equal depth unequal depth), gradient type (equal depth unequal depth), mutation type, torpedo head Type and so on.

The selection of screw type is mainly determined according to the physical properties of the plastic and the production technical specifications of the extruder.

(1) The softening of non-crystalline polymers is completed in a relatively wide temperature. Generally, equidistant gradual screws are used. The melting temperature range of crystalline polymers is relatively narrow, and isometric abrupt screw is generally used. (Guide: Measures to prevent locking of stainless steel fasteners)

(2) On small plastic extruders, for example, the screw of the φ45 extruder adopts a full-threaded type with equal intervals and unequal depths. The length of the screw is relatively small, and it is mainly used for extruding small cross-section insulation and The sheath layer has a faster extrusion speed.

(3) The medium-sized screw adopts a full-threaded type with equidistant and gradual thread depth. Its length-to-diameter ratio is larger than that of a small screw, and the pitch of the threads is equal, starting from the root from shallow to deep. The thread at the end of the thread is deeper and the thread at the root is shallow, so that the amount of plastic extrusion is more, without affecting the strength of the screw, the extrusion speed is fast, and the plastic is well plasticized. It is a general medium and small extruder for the production of insulation and protection. Ideal screw for jacket.

(4) The diameter of large screw is generally above 150mm, such as φ150, φ200, φ250 extruder. The large screw adopts two types, one is equal distance and unequal depth, such as φ150, φ200 extruder; the other is the screw is divided into three sections, namely equal distance and equal depth, equal distance and unequal depth, unequal distance and unequal depth, such as The φ250 extruder has a compression ratio of 2 to 3 and a length-to-diameter ratio of about 15:1. It is mainly used to produce large cross-section wire and cable insulation and sheath layers.

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