GB843113A - Tubular film manufacture - Google Patents

Abstract

<PICT:0843113/IV(a)/1> <PICT:0843113/IV(a)/2> Apparatus for reducing a continously advancing inflated tubular film to a flattened form and for allowing and regulating the passage of fluid through the flattened section of the film from a portion of the film on one side of the flattened section that is inflated to a certain internal fluid pressure to a portion of the film on the other side of the flattened section that is inflated to a lower internal fluid pressure, comprises a coacting pair of rotatable nip rolls adapted to press against opposite sides of a tubular film passing continuously through the nip, and having either means for radially displacing an annular section of one of the nip rolls relative to an adjoining section thereof or, alternatively, means for controlling the resistance to the displacement by the tubular film of the portion of the resilient surface of such annular section at any moment in contact with the tubular film, relative to the surface of an adjoining section of said nip roll simultaneously in contact with the tubular film, whereby in either case, the effective pressure exerted by the displaceable roll section towards the coacting nip roll may be altered while the apparatus is in operation, without altering the pressure exerted by the other parts of the rolls. As shown in Fig. 1, a roll is constructed from two sections of steel tubing I separated by a space 4 and welded to an inner section of steel tubing 2 provided with two rows of holes equally spaced around its circumference, the holes in the inner tube section providing communication between the interior 3 of this tube section and the space 4 between the outer tube sections. The outer tube sections and space 4 are covered by a continuous rubber sheath 5 which fits closely round the outer tube sections and at 6 crosses the space 4. The roll is provided with closures 7, welded to the ends of the outer tube sections, and with shafts 8, one of which is bored at 9 for connection through a 2-way tap to a vacuum pump and to high pressure air. In operation the roll coacts with a conventional driven nip roll, and the pressure exerted on the central portion of the tubular film passing through the nip of the rolls is adjusted by adjusting the air pressure within the hollow roller. The rubber sheath at 6 tends to bow into the space 4, and a pressure within the roller greater than the air pressure within the tubular film will therefore usually be needed to prevent the flow of air from the interior of the portion of the film on one side of the nip to the interior of the portion of the film on the other side. As shown in Fig. 2, one side of the nip is formed by two idler half rolls 10 rotatably mounted on a shaft 11 and separated from each other by a cylindrical central roll section 12 which revolves in ball bearings round an eccentric mounted upon or forming a part of the shaft 11, which may be rotated by means of a lever 13 to adjust the position of the eccentric with respect to the nip, and hence to control the depth of the aperture in the centre of the flattened film 14 passing through the nip, and therefore the rate of flow of fluid therethrough. Roll 15 is a driven roll of uniform diameter. Instead of a single means for exerting variable pressure at the centre of the film, such means may be provided at both folds of the flattened film. Specification 787,479 is referred to.