Film blowing die for the extrusion of a tube of thermoplastic melt

摘要

A film blowing die for the extrusion of a tube of thermoplastic melt comprises at least one inner cooling ring and a tube which passes through the blowing die and in which a central tube is arranged, forming an annular space. The annular space is in air-conducting connection with the inner cooling ring. In the annular space, the cooling and supporting air is fed in via lines and this air is drawn off again through the central tube. To permit cooling with air of very low temperatures, the tube feeding in the cooling air is enclosed in the region of the blowing die by two concentric tubes, forming two annular spaces. The two annular spaces are connected to each other in the region of the plane of the outlet die gap of the blowing die by an overflow space closed off from the outside. Warm air is fed into one of the annular spaces and this air is drawn off again through the other annular space.