| 摘要 |
<PICT:0805858/IV (a)/1> <PICT:0805858/IV (a)/2> Apparatus for the extrusion of thermoplastic material in seamless tubular form comprises, as shown, a die having an annular orifice 12, means for extruding molten thermoplastic material through the orifice to form a seamless tube 11, means for withdrawing the tube continuously from the orifice and for maintaining a substantially constant bubble of a gaseous medium in the section of the tube adjacent to the orifice, and means for blowing a cooling gaseous medium in the form of a continuous annular converging stream completely encircling and simultaneously impinging on to the exterior surface of the tube, said means comprising an annular wind-box arranged symmetrically about the axis of the tube and having an upper and a lower diaphragm 21 and 22, the edges of which are in close proximity to the tube, and an intermediate diaphragm 23, the edge of which is spaced from the tube to form an annular aperture, for separating the wind-box into two sections 19, 20 and having a series of ports 26 in section 19 through which ports a cooling medium, e.g. air, supplied through pipe 24, is directed against the tube, the arrangement being such that the cooling medium is constrained to flow in a direction substantially parallel to the outer surface of the tube on its way to the outlet pipe 29. The cooling means is preferably mounted at least 4 inches from the extrusion die. The diaphragms are preferably adjustable, e.g. iris diaphragms. A number of suitable thermoplastic materials are specified. Specifications 654,550, 664,412 and 716,160 are referred to. |
