| 摘要 |
The polyethylene, which has a molecular weight of above 500,000, is extruded from an extruder barrel (1) by a ram (3), the temperature along two thirds to four fifths of the length of the barrel measured from the inlet (6) being within the range of 180 to 230 DEG C, and along one fifth to one third of the length of the barrel measured from the outlet thereof being within the range of 140 to 160 DEG C, the residence time T in minutes of the polyethylene in the barrel (1) and being related to an "equivalent" (defined) barrel diameter D in millimetres, for a barrel length of 1 metre, by the equation:- @@ T = Const. .D<n> where: Const.= 5 . 10<-3> to 5. 10<-2> and n = 1.5 to 3. The ram (3) should be capable of exerting a pressure P in bars, on the polyethylene being extruded, which is related to D and the length L in metres of the extrusion barrel in accordance with the equation:- <IMAGE> where: M1 = 5 . 10<3> to 15. 10<3> M2 = 1 . 10<3> to 2.5 . 10<3> n1 = 0.4 to 2 n2 = 0.1 to 1.5 <IMAGE> |
