The machine tube is the same as in the extruder system, it is an important part of extruder. The cylinder and the screw work together, the barrel contain the screw, and the screw turns inside the cylinder. When screw rotation driven plastic moves forward within the barrel, the barrel external heat conduction heat to the plastic tube, combined with the screw thread on the volume shrinking, make the thread groove plastic squeeze, flip and shear action of the various forces are evenly mixed plasticate, along with the move to the front of the barrel at the same time, gradually melting is sticky flow, complete the plasticizing of plastic. The normal operation of the barrel and screw ensures the continuous extrusion molding production of extruder.

The structure of the cylinder is relatively simple. In the large extruder, the structure of the cylinder can be composed of several paragraphs. Because the cylinder is divided into several parts, the length of each segment is reduced, which brings convenience to the mechanical processing cylinder. However, the inner diameter of the machine and the inner hole of a few sections of the machine can be more difficult to achieve the same degree of accuracy. In addition, the sectional cylinder is connected with flanges, and the heating and cooling equipment arrangement of the cylinder can also be difficult, and the temperature control will not be very uniform. In order to save more valuable alloy steel, some large extruders use inner hole and bushing or casting wear resistant alloy layer. Such a cylinder jacket can be cast by ordinary steel to reduce the manufacturing cost of the cylinder.