The processing section of the twin-screw extruder is mainly composed of the extruder barrel, screw elements and mandrel. It is the functional area of the twin-screw extruder to complete plasticization and mixing. Screw gap, volume ratio, rotation speed, mandrel strength and screw element life are the key indicators for evaluating the performance of twin screw extruders. The development trend of international advanced twin-screw extruders is: small extruder screw gap, large volume rate, high speed, high strength mandrel, high wear-resistant threaded elements. At the same time of high efficiency and large output, the service life of the whole machine can be further improved, and the product quality is stable.
1. Small gap technology of extruder components
The small gap technology refers to the gap between the front and back of the meshing screw, the gap between screw and barrel, and it is controlled at a very small level (0.15-0.2mm). The stable output of the transmission system, small and stable output shaft runout are the foundation and guarantee of the small gap technology. The small gap technology ensures the uniform residence time distribution of the material in the extruder barrel, thereby ensuring the stability and consistency of the product quality, and making precise and stable extrusion possible. Small gap technology is also the basis of the high screw speed. High speed and small gap can ensure that the processed materials are cleaned up in time and quickly sent out of the extruder barrel; and if the screw is running at high speed at the regular clearance level, the materials cannot be cleaned in time with long residence time and unevenness can easily cause material degradation.
2. Extruder screw, extruder barrel and mandrel
After the breakthrough of torque distribution technology, the factors restricting the development of twin-screws have undergone fundamental changes: the previous restrictive factors were the output torque and service life of the gearbox, that is, the strength coefficient of the mandrel was higher than that of the gearbox, but now the stronger is the gearbox. The strength of the mandrel has become a limiting factor, so now the manufacturers of twin-screws have focused their research and development on the mandrel, barrel bushing and screw elements, and developed higher-strength mandrels and more wear-resistant barrels bushings and extruder screw elements. One of the solutions is the use of high abrasion resistant materials manufactured by hot isostatic pressing powder metallurgy molding process (PM-HIP).
Small gap technology, efficient twin screw extruder parts, and reasonable screw combination can further improve the performance of the twin-screw extruder, increase output, reduce energy consumption, and improve product quality. This is the software core technology of the twin-screw extruder. Only by combining these hardware core technologies with software core technologies can we create the most cost-effective and competitive modern co-rotating twin-screw extrusion equipment.