GB792744A - Improvements relating to film extrusion apparatus - Google Patents

Abstract

A lip member for a film extrusion apparatus comprises an elongated component formed with a longitudinal slot to define a first flange, and a second flange interconnected on one side of the elongated component by a longitudinal web, the said one side being adapted to define an extrusion lip; the first and second flanges and longitudinal web constitute an integral unit, and the first flange is provided with a number of holes for the passage of screws to hold it to the body of the extrusion apparatus, the second flange having lateral slots located adjacent to the holes in the first flange and dividing the second flange into segments; the apparatus also includes a hole in each segment, a screw loosely and slidably mounted in the hole in each segment and threadably engaging the first flange, a spring engaging each slidably mounted screw and serving to urge the respective segment of the second flange towards the first flange, the open side of the longitudinal slot being provided, adjacent the slidably mounted screws, with threaded arc portions in the inner surfaces of the flanges, and a tapered screw threadably engaging with each arc portion. The springs serve to maintain the arc portions in firm engagement with the tapered screws, whereby rotation of a tapered screw in the lip member causes the respective segment of the second flange to move away from <PICT:0792744/IV (a)/1> <PICT:0792744/IV (a)/2> <PICT:0792744/IV (a)/3> or towards the first flange, with consequent flexure of the longitudinal web at the segment. As shown in Figs. 2 and 3, two coacting lip members 21 identical in construction are attached to the flat bottom 2 of a film extrusion head 1 by means of screws 24 extending through holes 23 in the upper flange portion 22 of each lip member 21, the flat upper surface of the flange portion 22 fitting against the flat bottom 2 of the extrusion head 1. The screws 24 are disposed in the longitudinal open-ended slot 25 between the upper flange portion 22 and the lower flange portion 27 of each lip member. In the lower flange portion 27, immediately below the head of each screw 24, is a hole 28 for the insertion of a tool to adjust the screws. A narrow lateral slot 29 (Figs. 1 and 3) extends from each hole 28 to the outer edge of the lower flange 27 of the lip member and divides the flange into a number of segments. The upper and lower flanges 22, 27 are united on one side by longitudinal webs 30 (Fig. 2), which together form a tapered orifice through which liquid film-forming material from the inside of the cylindrical supply chamber 4 may flow to the flat portions 31 of the lip members 21, which flat portions define a narrow longitudinal extrusion orifice or slit. Screws 32, which are threadably engaged in respective holes 33 in the upper flange 22, extend through holes 34 (of larger diameter than the screws) in the lower flange 27. Between the head of each screw 32 and the outer surface of the lower flange 27 is a washer 35 and a coil spring 36. The row of screws 32 is spaced a sufficient distance from the longitudinal web 30 of the lip member 21 to permit of flexing of the web 30 (within the elastic limits of the material) and consequent movement of the flat portion 31 of the lip member towards or away from the corresponding portion 31 of the other lip member, the portions of the extrusion slit corresponding with each segment of the lower flange 27 thus being narrowed or widened. The open side of the longitudinal slot 25 between the upper and lower flanges 22, 27 has threaded arcuate portions 37 in the inner surfaces of the flanges, the bisecting vertical planes of which arcuate portions pass through the centres of the screws 32. Threadably engaged with the arcuate portions are tapered screws 38 having polygonal shaped heads 39 adapted to be rotated by a complementary tool (not shown) for adjusting the screws towards or away from the extrusion orifice. Each spring 36 ensures that in each segment the threaded arcuate portion of the lower flange 27 is always in engagement with its tapered screw. The cylindrical feed chamber 4 (Figs. 1 and 2), is located in a longitudinal channel 3 of the extrusion head 1, the outer wall of the chamber 4 being spaced from the wall of the channel 3 to provide a space for the circulation of a heat-exchange fluid. A number of diagonal passages 6 communicate with this space and with horizontal passages 7 in end-plate 8, to which is attached a bell-shaped hub 10 adapted to receive a metal tube 11, 12 communicating with the feed chamber 4. The smooth cylindrical portion 13 of the hub is journalled in a bearing on a frame (not shown). Heat-exchange fluid is supplied to the extrusion head 1 through a number of openings 19 provided in a cap 14 fixed to the hub 10, which openings communicate with a space between the tube 11 and the inner surface of the hub 10. The cap 14 is provided with a worm-wheel 16 for rotating the extrusion head 1 to the required position. The apparatus permits local adjustments to be made in the width of the extrusion slit to ensure the production of film of uniform thickness across its width.