A few Knowledge of Extruder screw

First, the type of Extruder Screw Barrel

In order to meet the different needs of the plastics processing, screw type are many common are the following: the graded (equidistant ranging deep) gradient type (such as deep equidistant) mutant, torpedo head type.

1, screw

The screw type of selection is determined based primarily on the physical properties of the plastic and the extruder production technical specifications.

(1) The softening of the non-crystalline polymer is in a relatively wide temperature range, generally optional Isometric Gradient screw. Crystalline polymer melting temperature range is relatively narrow, screw generally used isometric mutation.

Equidistant ranging deep thread type (2) in a small extruder, such as φ45 extruder screw is used, the aspect ratio of the screw is small, mainly used for extrusion of the insulating layer and the sheath layer of the small-sectional extrusion speed.

(3) medium screw thread type equidistant thread depth gradient, its aspect ratio is larger than the small screw thread pitch equal, from the roots from shallow to deep. Deep thread of the threaded end, the root of the thread shallow, so the amount of plastic extrusion more without affecting the screw strength, extrusion speed, plasticizer, is generally small and medium-sized extruder production insulating layer and retaining ideal sheath screw.

(4) large screw diameter is generally more than 150mm, φ150, φ200, φ250 extruder. Two types of large screw, First equidistant ranging from deep, such as φ150, φ200 extruder; the screw divided into three, that is equidistant and so deep, equidistant ranging from deep, not equidistant ranging from deep, as φ250 extruder, a compression ratio of between 2 to 3, an aspect ratio of about 15:1, is mainly used for the production of large cross section of the wire and cable insulation and jacketing layer.

Second, the screw of the main parameters

The main parameters of screw diameter, aspect ratio, compression ratio, the pitch, the width of the spiral groove, spiral groove depth, helix angle, the gap between the screw and barrel, these parameters have a great impact on the extrusion process and performance.
screw diameter Ds
Screw diameter, the outer diameter of the thread, the production capacity of the extruder (extrusion amount) approximation, proportional to the square of the screw diameter, the other conditions the same, a screw diameter slightly increases will cause a significant increase of the extrusion amount, and its impact than even the Screw rotation increased extrusion capacity. It is commonly used screw diameter to characterize the technical parameters of the standard size of the extruder.

Screw aspect ratio L / Ds

The working portion of the screw length L and the ratio of the screw diameter Ds known as aspect ratio, and certain other conditions (such as a screw diameter), to increase the aspect ratio means to increase the length of the screw. L / Ds value is large, the temperature distribution reasonably conducive to the mixing and plasticization of the plastic, the plastic is heated in the barrel, time is also longer, the plasticization of the plastic will be fully and more evenly. To improve the quality of machine plastic. If the plasticizing quality requirements remain unchanged under the premise, the aspect ratio increases, the rotational speed of the screw can be increased, thereby increasing the amount of plastic extrusion. However, the selection of a large aspect ratio, the the screw power consumption will increase accordingly, and the increase in machining and assembly of chicken difficulty of screw and barrel; screw bending possibility will increase, will cause the screw and barrel inner wall abrasion, reduce service life. Further, the heat-sensitive plastic, an excessively large aspect ratio due to stay a long time thermal decomposition, impact plastic plasticizing and extrusion quality. Therefore, to take full advantage of the aspect ratio increased advantages when selected according to the physical properties of the processing of plastic extruded product quality requirements.