Air ring for cooling blown plastic film

摘要

An air ring (12) for supplying cooling air to a hot extruded plastic film (14) after the film (14) has been extruded from an annular extrusion die (16) at an elevated temperature has an annular body (18,22) which surrounds the tubular film (14) after the film has left the extrusion die (16). The said body (18,22) has a circumferentially extending air passage (25) through which air can be supplied from an external source and which directs cooling air from the passage between the body and the film. A circumferentially extending series of individually operable actuators (40) are each operable to vary the flow of cooling air to cause the film (14) to become nearer to or further from the body (18,22) at its circumferential location to cause the thickness of the film (14) at said location to decrease or increase. <IMAGE>