Air cooling ring for plastic film with independent lubricating air for film guide surface

Claim 1

In an air ring for cooling the exterior of a hot extruding tube of plastic film, including a ring-form plenum supplied with cooling air, means defining a generally inwardly progressing cooling air flow path receiving air from the plenum and leading to an annular cooling orifice that discharges cooling air into contact with the plastic film, means defining a film guide surface upstream along the film path preceding said orifice, and means for supplying air to move with the film between the film and the guide surface, that improvement comprising a circumferentially arranged lubricating air bleed port means communicating with air from said plenum independent of said inwardly progressing cooling air flow path, said bleed port means communicating with a bleeded air passage extending inwardly from said bleed port means to an annular lubricating air outlet positioned in advance of said guide surface, and valving means independent of said cooling air flow path for adjusting the flow of bleeded lubricating air, said bleed port means comprising a set of circumferentially spaced-apart discrete holes, said bleed passage being of sufficient length in the direction of flow to enable the discrete flow from said bleed holes, to produce a merged, substantially uniform lubricating flow at said lubricating outlet, said bleed holes being arranged in an annular wall, said valve means comprising a circular array of bleed port closures connected for movement together to simultaneously, dependently vary the bleeded flow through said set of holes, said bleed port closures being moved together by moving a tension band to which said closures are attached, and said band being wrapped around said annular wall.