| 摘要 |
The invention provides a new air ring for use with a die in a blown film process line to apply cooling air to the exterior surface of an extruded tube of film-forming material passing through the air ring. Air is discharged from a first downstream gap in the air ring radially outward from the path of movement of a tube in unexpanded state so as to create a vacuum force that urges the tube outward and causes the cooling air to flow along the surface, permitting the use of much higher velocities than hitherto, the increased cooling permitting increased output for a given size of die. A second upstream gap delivers a tubular stream that precools the tube and prevents it from sticking to the structure between the upstream and downstream gaps. A presently preferred structure consists of a deflector ring spaced from the remainder of the air ring body to form the second upstream gap and having the air from the upstream gap flowing over its inner surface, and an axially movable control ring surrounding the deflector ring, the downstream gap being formed between the deflector and control rings and adjustable in size by axial movement of the control ring. |
