Patent GB-798194-A (GB)
Title: Method and apparatus for producing films of organic thermoplastic material
IPC: B29C48/03
Filed: 1956-02-08
Abstract: <PICT:0798194/IV (a)/1> <PICT:0798194/IV (a)/2> <PICT:0798194/IV (a)/3> <PICT:0798194/IV (a)/4> <PICT:0798194/IV (a)/5> <PICT:0798194/IV (a)/6> A heat - softened organic thermoplastic material is continuously extruded as a unitary thin, substantially planar sheet radially outward from a central feed point, the sheet is slit radially at fixed points spaced about its circumference, and each of the separated sheets thus formed is grasped individually and conveyed radially away from the central feed point at a linear rate at least as great as the rate of extrusion of the central unitary sheet.  As shown in Figs. 1 and 2 (a simplified plan view of a preferred apparatus for carrying out the process and a vertical cross-section along the line 2-2 of Fig. 1), hot plastic film-forming material is extruded radially as a sheet 59 from the circumferential orifice slit 13 of a vertically disposed head of extruder 12, and portions of the edge of the extruded sheet are grasped and fed to the nips between draw rolls 19, 22 and 21, 23. These are driven at the rate required to effect the desired thickness reduction of the central sheet 59 as it is stretched between the orifice 13 and the relatively cool surface of the draw rolls.  Stretching is effected simultaneously in all directions within the sheet and to a uniform degree over its entire area. The extruder diehead comprises an end plate 10 and dependent core 11 concentrically mounted over the end of a vertically disposed extruder barrel 12, with uniform radial clearance between the core 11 and barrel 12 and between the end of barrel 12 and the lower surface of end plate 10.  The extruder head is centred with respect to the draw rolls, the pairs of which are arranged as the sides of a closed octagon and are preferably mounted alternately above and below the horizontal plane of the sheet.  Rolls 19, 21 are hollow metallic idler rolls internally cooled by circulating cold water through tubes 62 to an axial bore in each end and driven by the rolls 22, 23.  The several rolls 22, 23 are driven simultaneously and at the same peripheral speed by a common drive mechanism, as shown in Figs. 1, and 3-6.  A vertical stub shaft 24 mounted on base-plate 14 at each of the angles of the octagon carries a sprocket 27, and an endless chain 30 engages all of the sprockets. One of the shafts 24 carries another sprocket 26 which engages drive chain 25 (Figs. 1 and 4) driven by a power source (not shown).  Chain 30 also engages sprockets 31 mounted near the base of vertical shafts 32, one of which is positioned beneath and externally of each set of upper driven rolls 23 (Figs. 4 and 5). The shafts 32 carry bevel gears 36 at their upper extremity and each such gear 36 engages a similar gear 37 mounted on a rotatable horizontal shaft 38 which carries a sprocket 40 driving pressure roll 23 through chain 41 and sprocket 42 mounted on axial shaft 43 of roll 23.  In a similar manner, chain 30 engages sprockets 44 mounted near the base of vertical rotatable shafts 45, each of which is positioned beneath and externally of each set of lower driven rolls 22.  Each shaft 45 carries at its upper end a bevel gear 46 (Fig. 4) engaging a bevel gear 47 mounted on a rotatable horizontal shaft 48 which carries a sprocket 49 driving pressure roll 22 through chain 50 and sprocket 51 mounted on axial shaft 52 of roll 22.  Chain 50 also engages sprocket 53 (Figs. 3, 4 and 6) mounted on the end of horizontal shaft 54 secured near each end of which are bevel gears 55, each of which drives a horizontal shaft 56 which, in turn, drives another shaft 57 at right angles thereto and carrying at its outer end a rotary cutter disc 58.  This is positioned to engage the central film 59 just as it reaches the upper surface of rolls 19 and the lower surface of rolls 21, to sever the film into sheets 60 of the width of the rolls 19 and 21. From the draw rolls the finished sheets are taken continously to storage or wind-up rolls 63.