Center screw distance is relatively small, and the output structure requires a high rotational accuracy, design and processing of the product difficult. Most of the domestic market, parallel twin-screw extruder gearbox is designed in the 1990s to introduce foreign technology, due to differences in materials and production processes, the prevalence of low-power, low bad reliability, noise, sealing performance defect. These pins are provided in the melting zone, the pins can be solid bed broken, destroyed two-phase flow, the solid and liquid mix together, so that the end of the dissolved solid pieces of material with the contact area has increased capacity to promote melting . If the pin is provided in the melt conveying zone, its main role is split stream, increasing the interface, change the direction of the stream, so that the stream rearranged. Multiple shunt, confluence, change the direction of flow, so that the melt composition and temperature homogenization. The mixing section are provided in an ordinary screw homogenizer inwardly grooved structure segment end having an outer diameter equal to the outer diameter of the screw. Trench divided into several groups, the convergence zone between each material. The material is split groove, will sink into the convergence zone, and then split, convergence, the principle is similar to the pin type. Separate screw is characterized by the melting zone in addition to the original one screw pattern (called the primary screw), but also added a thread (called additional thread) having an outer diameter slightly smaller than the outer diameter of the main thread, the main and auxiliary lines lead different secondary thread from the beginning of the end of the feed section (and in this segment associated with the feed), after a few threads are gradually and the main thread of the segments intersect.

　　Wear flat twin screw will screw in the machine barrel rotation, the friction between the two materials and to make screw and barrel work surface gradually wear: Screw diameter gradually reduced, the inner diameter of the cylinder is gradually increased. Thus, the gap with the diameter of the screw and barrel, with the gradual wear and tear and a little bit of both increased. However, due to the resistance in front of the cylinder head and manifold has not changed, which increases the material being extruded when the leakage flow forward, that is, material from the diameter of the gap to the direction of feed flow quantity. Resulting in decreased production of plastic machinery. This phenomenon has also caused material in the machine barrel residence time, resulting in material decomposition. If polyvinyl chloride, hydrogen chloride gas generated by the decomposition strengthened the screw and barrel corrosion.