In view of the characteristics of large-caliber thick wall pipe which is difficult to overcome the melting sag, Oriplas company adopts the technology of internal and external wall cooling at the same time, which maximizes the uniformity of pipe wall thickness. The technology uses a special structure so that the inner surface of the pipe can be well cooled. The quality of pipe is improved while the energy consumption is reduced, and the molten drop is greatly reduced. Taking sZY90/40 single screw extruder of Oriplas as an example, it is improved on the basis of common barrier-type screw to ensure excellent plasticizing effect at high speed. The shear action is strictly controlled to keep the melt temperature at a low level. The problem of uneven melt heat can be effectively eliminated to obtain the ideal material temperature and prevent the change of material properties due to degradation. Compared with ordinary extruder, the production capacity is about 30%.