Plastic extruder screw type

The screw is one of the key components of the extrusion system of the plastic extruder. It not only plays the role of conveying plastics, but also plays an extremely important role in plastic extrusion, plasticization and molding. Therefore, the screw is reasonably selected. Structure and parameters are an important part of obtaining ideal product quality and output.

In order to meet the needs of different plastic processing, there are many types of screw, the following are common: gradual (equidistance unequal depth), gradient (equal depth is not equal distance), mutant, torpedo head type.

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

(1) The softening of non-crystalline polymers is accomplished within a relatively wide temperature range. Generally, equidistant gradient screws are used. The crystalline polymer melts at a relatively narrow temperature range, and generally isometric screws are used.

(2) On small plastic extruders, such as the φ45 extruder screw, a full thread type with unequal equidistant depths is used. The length and diameter of the screw are relatively small, and it is mainly used for extruding small-section insulating layers and jacket layers. Extrusion speed is faster.

(3) The medium-sized screw adopts the full-thread type with equal distance and thread depth gradient. Its length-to-diameter ratio is larger than that of the small-sized screw, and the pitch of the thread is equal, from shallow to deep from the root. The thread at the end of the thread is deeper, the thread at the root is shallower, so that the plastic has more extrusion volume without affecting the screw strength, the extrusion speed is fast, the plastic is plasticized well, and the insulating layer and the protection are generally produced for the middle and small-sized extruders. The ideal screw for the jacket.

(4) Large screw diameter is generally more than 150mm, such as φ150, φ200, φ250 extruder. There are two types of large screws: one is equidistantly unequal depths, such as φ150 and φ200 extruders; the other is that the screw is divided into three sections, ie equal depth, equal depth, and unequal depth. Φ250 extruder, compression ratio between 2 and 3, length to diameter ratio of about 15:1, mainly used to produce large-section wire and cable insulation and jacket layer.