| 摘要 |
The parent patent described a pipe extrusion die fitted with an extended mandrel for recirculating cooled air within the profile leaving the die. The downstream end of the mandrel was fitted with spring loaded wheels bearing against the inside of the pipe to keep the mandrel centralised. This addn. describes use of one or more additional internal mandrels linked by cables successively along the inside of the pipe. The additional mandrels have centering rollers at both ends. Used esp. for calibrating pipes made of semicrystalline materials, viz polypropylene or high density polyethylene, to produce pipes with relatively stress free walls by providing similar cooling rates inside and outside the mandrel. Use of multiple mandrels produces sufficient cooling for relatively thick walled pipes without the reduction in extrusion rate which would otherwise by necessary. |
