US 5,310,329 AGranted

Air shroud device for a blown film extrusion line

OwnerRobert E. Creeinventor

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Abstract

An air shroud device for use in a blown film extrusion line. The blown film extrusion line is of the type which includes a heated extruder for melting and pressurizing a flow of molten plastic resin, an annular die through which the molten resin extrudes and from which it is pulled away along an axis in the form of an expanding bubble, and at least one air cooling ring mechanism defining a plenum surrounding the base of the bubble and having an annular outlet constructed to direct at least one stream of primary cooling air into cooling contact with the base region of the bubble, to flow along the bubble in the direction of film travel, causing the resin to cool as the film expands until a substantially fixed maximum bubble diameter is achieved at a frost line spaced from the annular die. The air shroud device includes an annular air shroud plenum having an annular air outlet, the air shroud device is constructed and arranged to be disposed at a level below the frost line and adjacent to the level of the air cooling ring. The shroud device is coaxial with the film line axis and of relatively large size so that its outlet mechanism is spaced substantially radially outward from the bubble and from the air cooling ring outlet.

Claims19

Dependent claims

In combination an air shroud device and an air cooling means comprising at least one air cooling ring, said air shroud device and air cooling means constructed for use in a blown film extrusion line comprising a heated extruder for melting and pressurizing a flow of molten plastic resin and an annular die through which the molten resin extrudes and from which it is pulled away along an axis in the form of an expanding bubble, said air cooling means having annular cooling ring air outlet lips of predetermined given diameter for disposition closely adjacent to the path of the film, said annular cooling ring air outlet lips being constructed to direct at least one relatively high velocity stream of cooling air into cooling contact with the film in the base region of the bubble, to flow along the bubble in the direction of film travel, to cause the resin to cool as the film expands until a substantially fixed maximum bubble diameter is achieved at a frost line spaced from the annular die,

said air shroud device being constructed for use in cooperation with said annular cooling ring air outlet lips of predetermined diameter and comprising an annular air shroud outlet means in combination with a source of circumferentially uniform air,
said air shroud outlet means constructed and arranged to be disposed at a level below said frost line and coaxial with said film line axis, said annular air shroud outlet means being of substantially larger diameter than the diameter of said cooling ring air outlet lips so that said air shroud outlet means, when positioned in operative position, is spaced substantially radially outward from said annular cooling ring air outlet lips and the path of the film passing thereby,
and said annular air shroud outlet means being so related to its said air source that, in operation, it provides a diffused, relatively low velocity mass of air surrounding the relatively high velocity flow of cooling air from said annular cooling ring outlet lips,
whereby said movement induced from surrounding air by the directed flow of relatively high velocity cooling air from said cooling ring air outlet lips comprises uniform pseudo-ambient air drawn from the outlet region of said outwardly spaced annular air shroud outlet means.

1 more element

A blown film extrusion line, comprising in combination:

a heated extruder for melting and pressurizing a flow of molten plastic resin,
an annular die through which the molten resin extrudes and from which it is pulled away along an axis in the form of an expanding bubble,
air cooling means comprising at least one air cooling ring, said air cooling means having annular cooling ring air outlet lips of predetermined given diameter disposed closely adjacent to the path of the film, said annular cooling ring air outlet lips being constructed to direct at least one relatively high velocity stream of cooling air into cooling contact with the film in the base region of the bubble, to flow along the bubble in the direction of film travel, to cause the resin to cool as the film expands until a substantially fixed maximum bubble diameter is achieved at a frost line spaced from the annular die, and
an air shroud device constructed for use in cooperation with said annular cooling ring air outlet lips of predetermined diameter and comprising an annular air shroud outlet means in combination with a source of circumferentially uniform air,
said air shroud outlet means constructed and arranged to be disposed at a level below said frost line and coaxial with said film line axis, said annular air shroud outlet means being substantially larger than the diameter of said cooling ring air outlet lips so that said air shroud outlet means, in operative position, is spaced substantially radially outwardly from said annular cooling ring air outlet lips and the path of the film passing thereby,
and said annular air shroud outlet means being so related to its said air source that, in operation, it provides a diffused, relatively low velocity mass of air surrounding the relatively high velocity flow of cooling air from said annular cooling ring outlet lips,
whereby air movement induced from surrounding air by the directed flow of relatively high velocity cooling air from said cooling ring air outlet lips comprises uniform pseudo-ambient air drawn from the outlet region of said outwardly spaced annular air shroud outlet means.

4 more elements

Dependencies are inferred from the claim text.