The extruder, barrel and screw rods are made of high quality 38 CRMOALA alloy steel thathave been nitrized and processed in a precision way. It is good in hardness, durable incorrosion resistance. The special designed screw is of high quality, which helps increasethe production capacity. It is applied to blowing the plastic films like low density polytene(LDPE), high density polytene (HDPE) and linear low density polytene (LLDPE). It is widelyapplied to producing the packing bags for foodstuff, clothing, rubbish bag and vest ones.