| 摘要 |
The method permits selective cooling of tubular plastic material as formed to provide for an exchange of internal cooling air through the central opening of the blow head. Air supply rings having outlet slots facing the tubing, as well as air guide surfaces of small axial length, are provided inside the tubing and spaced from the annular die orifice to serve to support the tubing. The interior cooling air supply rings have axially directed passages for the flow of cooling air while the exterior air supply ring or rings deliver air at higher temperatures to provide a substantial thermal differential between the tube surfaces as formed to provide a flare-top edge upon severance. Also, the method permits forming a foam-film composite of thermoplastic materials by the blown bubble co-extrusion process.
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