| 摘要 |
<PICT:0714194/IV (a)/1> To increase the uniformity of wall thickness of extruded thin-walled tubes or sheets the extrusion orifice is provided with a plurality of spaced pockets adjacent thereto, each having means for independently regulating the temperature by heating or cooling the pocket and hence portions of the orifice adjacent thereto. As shown, a heated die 7 has a throughway 17 co-operating with a conical pin 6 to form a circular annular extrusion orifice 16, cooling fluid is circulated in spaced pockets 1, each of 1/8 to 1/2 inch diameter, via pipe 2 and conduit 3 and is controlled by a needle valve 10. The needle valves may be individually adjusted to control locally the temperature round the orifice and hence the thickness of the extruded tube. A hollow mandrel whose temperature is adjusted to be lower than that of the extruded tube and having a diameter between 1.1 and 6 times that of the extrusion orifice may be mounted at such a distance from the orifice that the tube is partly congealed on reaching it. Air may be supplied through conduit 14 to extend the tube. |
