Types of new screws for screw extruders

Problems with conventional full-helical three-section screws:
① In the melting section, both the solid bed and the molten pool cohabitate in the same screw channel. The molten pool continues to widen and the solid bed gradually narrows, thereby reducing the contact area between the solid bed and the barrel wall and reducing the direct transmission of solids from the barrel wall. The heat of the bed reduces the melting efficiency, resulting in low extrusion volume;
② Large pressure fluctuations, temperature fluctuations and output fluctuations;
③It is not well adapted to the processing of some special plastics for mixing, coloring and other processes.
Commonly used methods to deal with such problems:
Increase the aspect ratio; increase the screw speed; increase the groove depth of the homogenizing section;
In order to overcome the shortcomings of conventional screws, some new screws have been created, mainly including:
①Separate screw
Adding a secondary thread in the compression section overcomes the shortcomings caused by the coexistence of the solid bed and the melt in the same screw groove in conventional screws, and separates the molten material and unmelted material as early as possible, thereby promoting the melting of the unmelted material.
This screw has high plasticizing efficiency and good plasticizing quality. Since there is no solid bed disintegration, output fluctuations, pressure fluctuations and temperature fluctuations are relatively small, and it has the advantages of good exhaust performance and low energy consumption, and is widely used.
②Barrier type screw
A screw in which a barrier section is set up in a certain part of the ordinary screw to prevent unmelted solids from passing through and promote the melting of the solids.
This kind of screw converts mechanical energy into thermal energy through the mixing effect of shearing and eddy currents and performs heat exchange to melt and homogenize the material. The radial temperature difference is small, and the output and quality are better than conventional screws.
③Pin screw
When the material flow passes through the pins, the pins divide the solid material or incompletely melted material into many small material flows. These material flows merge again at a wider position between the two rows of pins. After multiple merges and separations, the plasticizing quality of the material is improved.
The pins are arranged in the melting zone and arranged in the shape of herringbone, ring, etc. The pin shapes include cylindrical, rhombus, square, etc.
Because the pin divides and shunts the molten material multiple times, the mixing, homogenization of the material and the dispersion of the additives are increased. In addition, since the solid fragments continuously absorb heat from the melt during the melting process, it is possible to reduce the melt temperature, so low-temperature extrusion can be achieved.
④Combined screw
It consists of a screw body with a feeding section and various screw elements with different functions, such as conveying elements, mixing elements and shearing elements. By changing the type, quantity, and combination order of these components, screws with various characteristics can be obtained to adapt to the processing requirements of different materials and different parts, and to find the best working conditions.
This kind of screw has strong adaptability and is easy to obtain the best working conditions. It solves the contradiction between universal and special purpose to a certain extent, so it is used more and more widely. However, the design is complicated, the assembly and disassembly of the combined components is troublesome, and it is difficult to implement on a screw with a smaller diameter.