Twin screw extruder is an important equipment in plastic processing machinery. It is not only suitable for extrusion molding and mixing processing of polymer materials, but also has been widely used in food, feed, electrode, gunpowder, building materials, packaging, ceramics and other fields.
High-speed and high-yield extruder can enable investors to obtain large output and high return with low investment All the technical progress of twin-screw extruder is mainly concentrated in the transmission part and the extrusion part. Only by combining the hardware core technology with the software core technology in these two parts can we create the most cost-effective and competitive modern co-rotating twin-screw extruder.
Twin screw extruder is mainly composed of two parts: transmission part and extrusion part.
The transmission part provides torque for the screw, and the strong torque output is the guarantee for the efficient operation of the twin-screw extruder;
The extrusion part is mainly composed of barrels, screw elements and shafts. The materials are plasticized, mixed and extruded in this area. All the technical progress of twin-screw extruder is also concentrated in these two parts, and constitutes the symbol of the renewal of twin-screw extruder.
Compared with other types of twin-screw extruder, a significant feature is the difference of transmission system. Twin screw extruder requires that the power be evenly distributed to two screws in a confined space, which is the torque distribution technology.
Different torque distribution technologies determine the bearing capacity of the gearbox, and even directly affect the life and performance of the whole machine.
Traditional parallel three-axis torque distribution technology (B-type gearbox)
The traditional parallel three-axis torque distribution technology is a mature transmission technology of twin-screw extruder.
The power from the motor is evenly distributed to the two output shafts a and B in parallel, that is, the shafts a and B each bear 50% of the torque. Due to the limitation of the center distance between axes a and B, the gear on axis B is relatively small and the transmitted torque value is limited. Therefore, the b-axis gear is the bottleneck of the bearing capacity of the twin-screw gearbox, which directly determines the power that the gearbox can transmit.
High torque parallel three-axis torque distribution technology (D-type gearbox)
In order to improve the output torque of shaft B, the improved high torque parallel three-axis torque distribution technology has designed two sets of gear transmission on shaft B, so that the output torque of shaft B is theoretically twice that before the improvement, and the high torque output is realized.
The extrusion part is mainly composed of barrels, screw elements and shafts, which is the functional area of twin-screw extruder for plasticizing and mixing. Screw clearance, volume ratio, rotational speed, strength of mandrel and life of screw elements are the key indexes to evaluate the extrusion performance of twin-screw extruder.
The development trend of the international advanced twin-screw extruder is: small screw clearance, large volume ratio, high speed, high strength mandrel, and high abrasion resistant screw elements. With high efficiency and large output, the service life of the whole machine can still be further improved and the product quality is stable.
Small gap technology
Small clearance technology refers to the clearance between the front and rear of the engaged screw edge, the clearance between the thread and the barrel, which is controlled at a very small level (0.15-0.2mm). The stable output of the transmission system and the small and stable runout of the output shaft are the foundation and guarantee of the small clearance technology.
Small gap technology ensures the uniform residence time distribution of materials in the barrel, thus ensuring the stability and consistency of product quality, making precision extrusion and stable extrusion possible.
Screws, barrels and shafts
After the breakthrough of torque distribution technology, the factors restricting the development of twin-screw have undergone fundamental changes. In the past, the restricting factors were the output torque and service life of the gearbox, that is, the strength coefficient of the core shaft was higher than that of the gearbox, but now the strength of the core shaft has become the restricting factor due to the larger strength coefficient of the gearbox.
Therefore, the manufacturers of twin screw extruder now focus their research and development on the mandrel, barrel bushing and screw elements, and develop higher strength shafts, more wear-resistant barrel bushing and screw elements.
Small gap technology, high-efficiency screw elements and reasonable screw combination can further improve the performance of extruder, increase output, reduce energy consumption and improve product quality.