Patent GB-1020379-A (GB)
Title: Dies for extrusion of plastic film
IPC: B29C48/08
Filed: 1964-12-10
Abstract: 1,020,379. Extrusion die for films. ALLIED CHEMICAL CORPORATION. Dec. 10, 1964 [Dec. 23, 1963], No. 50356/64. Heading B5B. An extrusion die for making films comprises a pair of elongate supporting blocks 11, 12 clamped together in abutting relation (bolts 18) but being gapped along one longitudinal end thereof, a flexible insert 14 in the gap between said blocks and carried by one of the blocks (11), one edge portion of said flexible insert defining one lip of an exit gap 13 for the die, a die cavity insert 15 disposed directly opposite said flexible insert and carried by the other block (12), one edge portion of said die cavity insert being disposed opposite the said one lip and defining the other lip of the exit gap, means at the exit gap end of the die for adjusting the position of the flexible insert (bolts 24) so as to adjust the exit gap and means at the end of the die opposite the exit gap and positioned in the area of abutment between the two supporting blocks (wedge 28), for adjusting the relative position of the two supporting blocks and thus adjusting the exit gap. Inserts 14, 15 are preferably removably mounted in the die so as to facilitate substitution of different inserts with different die cavities, so that the same die can be used to make different web widths. Wedge 28 may extend at least substantially the full longitudinal extent of the extrusion die and is positioned in an opening defined by the longitudinally extended sides 31, 29 in the supporting blocks, at least one of said sides being inclined, and means are provided for adjusting the position of the wedge and securing the wedge in the adjusted position (bolts 34, threaded sockets 35). A shim 45 may be provided which, in the die of Fig. 1 and that of Fig. 3 (not shown), is clamped between the flexible insert 14 and the die cavity insert 15 to control the relative spacing of these two inserts and thus control the width of the exit gap. The die cavity insert 15 is of generally oblong shape, has relatively narrow surfaces 38, 39 defining the margins of the oblong, said surfaces being in substantially the same plane and surrounding the die cavity and the flow path 41 leading therefrom to the land 37 defining one lip of said exit gap, said land being formed by one of said longitudinally extending, relatively narrow surfaces, said die cavity 16 being machined into said insert and being inclined from the median area towards the opposite ends of the die cavity, the inclination being in a downward direction 43, 44, the same as the direction of flow through the flow path in the die and the shim having a longitudinally extending portion 46 adapted to bear against the said longitudinally extending relatively narrow surface opposite said land the shim having depending portions 47, 48 on the opposite ends of said first mentioned portion adapted to bear against the opposite shorter marginal areas of said oblong surface. Adjustment of the position of wedge 28 in its opening 29 can be effected to change the thickness or depth of the flow path from die cavity 16 to exit gap 13 as well as the width of the exit gap to give optimum flow for any given resin. In the construction of Fig. 1 and that of Fig. 5 (not shown), in which the bolts 18 are threaded into openings 20 in block 12 the clearance 23 enables the head portion of the bolt to move within the block 11, so that the position of the die cavity insert 15 may be changed relative to flat insert 14 to effect the desired adjustment. In the apparatus of Fig. 2, the clearance 23 permits the desired adjustment to be effected by the adjustment wedge 28. The die of Figs. 4 and 5 (not shown) differs from that of Figs. 1 and 3 in that no shim is used. As shown, the upper bearing surface of the insert 15 (36, Fig. 3), here shown at 36<SP>1</SP>, is positioned in a plane spaced somewhat from the plane of the land 37. The distance surface 36<SP>1</SP> extends from the plane of the land 37 (i.e., to the left in Fig. 5) is equal to the width of the exit gap, subject to adjustment of this width by positioning the wedge 28 in its opening 29 and the adjustment effected of the contour of the exit gap by the adjusting bolts 24. As shown, 51 is a key positioned in aligned openings in supporting blocks 11 and 12 to facilitate registry of these two blocks. A key 52 is positioned in aligned openings at the upper portion of the flat flexible insert 14 and die cavity insert 15 to facilitate proper alignment of these members 53 is a gasket positioned in an opening running the full length of the die cavity 16, the sides thereof and the flow path 41 to provide a liquid-tight seal for the die cavity, the flow path and the end of the exit gap. A pressure equalizing channel 54 may be provided in the die cavity insert 15, positioned just above the exit gap 13, i.e. just above the upper edge of land 37, and extends the full length of the exit gap. Differential expansion or contraction of the lips of the exit gap is prevented, since the ends of the flexible insert 14 and die cavity insert 15 are free to expand or contract with temperature changes, so that the exit gap once adjusted remains uniform. If the members 14 and 15 are made of the same material any expansion or contraction will be the same for both members. Thus control of film thickness is enhanced. Flow path 41 is readily adjusted by means of the wedge 28. This adjustment also effects adjustment of the width of the exit gap. By means of the screws 34 the wedge can be moved so that one end is positioned in its opening at a different level from the other if required. Thus the flow path may be adjusted to compensate for flow path shape and so assist in obtaining optimum flow. The transverse profile of the outflowing extrudate can be controlled by adjustment of the exit gap at localized points along its length by means of bolts 24. In the apparatus of Figs. 1 and 3, a further adjustment of exit gap width is provided by shim 45 which permits quick adjustment of the width of the exit gap by replacement of one shim with another, the ultimate fine adjustment being made by wedge 28 and bolts 24.