Advantages of three-screw extruder

Advantages of three-screw extruder

How to maximize benefits in less time is a topic that today's production enterprises are constantly pursuing. The extruder has developed from the initial plunger type and single screw type to the parallel twin screw type and conical twin screw type, etc. and the development of the polymer processing industry has experienced unprecedented prosperity.

The three-screw extruder has attracted much attention with its flexible geometric arrangement, multiple meshing zones forming multiple changes in the flow direction and flow rate of the material, and the distribution of particles in the spatial position has produced extremely beneficial effects, and has attracted much attention with excellent mixing characteristics, small length-diameter ratio and high production capacity.

Due to the low thermal conductivity of plastics, large diameter extruders (¢130mm or more) may have a large amount of "static" material in each thread groove during processing, resulting in uneven plasticization. This problem cannot be solved by increasing the screw speed, because it will cause fluctuations and cause the flow mark to thicken. Although this can be solved by increasing the screw length-to-diameter ratio, this approach has limitations and increases many of the negative effects caused by the screw cantilever. The use of small diameter, short length diameter ratio of multi-screw combination is one of the effective ways to solve this contradiction.

Single screw has no meshing area, twin screw has a meshing area, three screws arranged in a zigzag have two meshing areas, triangular arrangement of three screws have three kneading areas, three-screw extruder meshing area increases, the rolling area doubles, and the material is efficiently extruded, crushed, kneaded, calendered and stretched during operation. It is this efficient mixing effect that enables the three-screw to obtain the same quality and output production conditions without the large diameter and large length-diameter ratio of single screw or twin screw, fully reflecting the efficient mixing and homogenization characteristics, compactness and economy of the three-screw extruder.

In order to increase production and improve product quality, the screw diameter must be increased for single screws and twin screws, the length-to-diameter ratio must be increased, and the drive power must be doubled. If the screw of the twin screw extruder with a diameter of 45mm is increased to 70mm, although the productivity of the latter is three times that of the former, the driving power also needs to be increased by more than one time per unit area. If a twin screw with a screw diameter of 45 mm is changed to a triple screw with a diameter of 45 mm, the output of the latter will be doubled, twice as much as the former, and the driving force will be less than 1.5 times that of the former.

How are the three screws arranged?

Due to the continuous expansion of the application field of screw extruders, the development and innovation of extruders have been promoted. The three-screw extruder with three screws arranged in "one" and the three-screw extruder arranged in three screws and triangles are new models developed in recent decades.

The three screws of the three-screw extruder arranged in the "one" line are of equal length and diameter, the middle main screw diameter is large, the diameter of the two auxiliary screws is small, and the main and auxiliary screws mesh with each other and rotate in reverse. This design, expand the rolling area, strengthen the kneading effect, has a better plastic effect, not only increases the output, and the energy consumption does not increase much, due to the existence of two meshing areas, the rolling area doubles to shorten the screw length, reduce the negative impact caused by the screw cantilever.

The three-screw extruder with an inverted shape in the center of the screw is an innovation in the field of extrusion. Compared with the aforementioned two "one" three-screw extruders, the three-screw arrangement of the fully meshed three-screw constitutes a unique three-screw presence, which has an extremely complex impact on the flow direction, flow rate and spatial position distribution of materials. It makes it possible to obtain high output and high mixing quality results with multi-screw combinations with small diameter and small length-diameter ratios.

Advantages of three screws:

1. High shear efficiency and good plasticizing effect

A pair of screws has one meshing point, while three screws have three meshing points. That is, it is equivalent to three pairs of twin screws, so the shear efficiency is high and the material is easy to plasticize. When the experimental pigment content is 15% blue masterbatch, the screw is withdrawn for inspection, and it is seen that the material has been plasticized in the middle of the full length of the screw, indicating that its plasticization effect is good.

2. Dense training function & good dispersion effect

The three screws are arranged in a triangle to form a closed space in the central area. Every time the screw rotates, the space passage area of the center area of the same section changes three times, and the strong backlog and kneading of the material in the machine is doubled, so it is uniformly plasticized and dispersed. Therefore, the machine is an extruder with very good dispersion integrating densification and extrusion. Practice has proved that the carbon black content can reach 55% when producing carbon black masterbatch, the magnesium hydroxide content of low-smoke halogen-free flame retardant cable material can reach 90%, and the calcium carbonate content of PP or PE masterbatch can reach more than 85%, and the effect is very good.

3. High yield and low energy consumption

Its output is twice that of the specification and same power twin screw extruder. For the production of the same number of products, the cost of manpower, space, etc. required is multiplied. And because of its short length-to-diameter ratio, the power of the host and heater decreases and saves energy.

4. Good exhaust performance

The exhaust port of the machine does not have any material accumulation, no blockage and other phenomena, the reason is that almost all the materials are sucked into the mixing area in the center of the screw, and the dense training area is equivalent to a melt pump, so there will be no material. Therefore, the machine can achieve a high vacuum degree and improve the quality of the product.

5. Short residence time in the barrel and hard to be degraded

The length-diameter ratio of the three-screw extruder is short, the length to diameter ratio of 22 is equivalent to the 66 length-diameter ratio of the twin screw, and the residence time of the material in the barrel can be shortened by one-third, so the machine is suitable for heat-sensitive and degradable materials.

Three-screw extruder has been well applied in the preparation of functional plastics, the preparation of high-brightness coatings and convenient food processing, and has begun to attract attention with its excellent mixing characteristics, better capacity ratio, and smaller length-diameter ratio.