Specific and complicated design - It is different from traditional single screw extruders because of its unique working principle. The spiral of the screw is detached three times at the circumference and forms the so-called kneading screw. In those gaps are the stationary kneading pins, which are fixed inside the kneading casing. While the screw is circumrotating once, the axis is also moving reciprocate once. Due to such specific moments, the material is not only sheared between the pins and kneading flights, but also inverted. It improves the effectiveness of kneading by moving transversely and length ways. Hence, it can provide high-quality dispersive and distributive mixing and the efficiency is twice better than twin screw extruders. In addition, the wear parts such as feeding and kneading parts of screw, liner bushes and kneading pins are designed to element-type, and can be replaced individually when one of them is broken. It saves a lot instead of changing the whole screw. While for traditional single screw extruders and some twin screw extruders, that is impossible. Moreover, according to different kinds of polymer materials, the combination of kneading parts and feeding parts of the screw can be changed accordingly so as to make the kneading efficiency best.