Patent GB-474243-A (GB)
Title: Improved apparatus for the production of a plastic material in sheet form
IPC: B29C48/08
Filed: 1936-04-27
Abstract: <PICT:0474243/IV/1> <PICT:0474243/IV/2> Apparatus for extruding plastic material such as cellulose derivative compositions to form sheets comprises a slit-like orifice through which the plastic is extruded, a plurality of means for controlling the thickness of the sheet at spaced intervals across its width as it is extruded, and a plurality of means for measuring the thickness of the extruded sheet at spaced intervals across its width.  Preferably, <PICT:0474243/IV/3> <PICT:0474243/IV/4> the controlling means and measuring means correspond in number and relative position across the width of the sheet.  The extrusion orifice may comprise a fixed lower jaw and an adjustable upper jaw both substantially straight and parallel, and the controlling means may comprise a plurality of adjusting bolts connected to the upper jaw at spaced intervals throughout its length and adapted to control the distance between the upper and lower jaws at spaced intervals.  If desired the lower jaw or both jaws may be adjustable, or the jaws may be fixed and the controlling device may consist of a number of adjustable restricting blocks, or plungers disposed in the extrusion device adjacent to the orifice. The controlling device may consist of means for regulating the pressure or temperature of the plastic at a number of points across the width of the orifice.  As shown in Fig. 1, a sheet 4 of plastic material is extruded into a bath 3 of brine or other liquid which removes solvent from the sheet, and passes through the measuring devices 30, 39.  The extrusion orifice comprises a straight rigid lower jaw 5 and an upper jaw 9 held to the container 8 by bolts 10 passing through slots 11.  As shown in Fig. 2, the jaw 9 is vertically adjusted by bolts 12 and nuts 17, 18, at a plurality of spaced points along its length.  As shown in Figs. 1, 3 and 5, the measuring devices are mounted on a frame 21--23.  A rigid cross-member 27, positioned across the path of the extruded sheet, carries a rigid straight edge 30 adjusted by differential screws 28, 29.  The member 27 also carries a number of brackets 35 which receive the pins 38 of rockers 39.  These rockers bear lightly on the sheet 4 as it passes over the straight edge 30 and are given small angular movements by irregularities in thickness of the sheet.  The rockers carry reflecting mirrors 40. By means of the mirrors 40, 45, 46, and spot lights, the movements of the rockers may be observed on a screen 47.  The screen may be of board, metal, or ground or frosted glass. By adjusting the jaw 9 of the extrusion device by bolts 12, the thickness of the sheet may be made uniform across its width, this condition being indicated when the spots of light from all the rockers 39, lie in a horizontal line on the screen.  The measuring device is preferably placed as near to the extrusion device as can be safely done without danger of marring the extruded sheet.  A modified construction of measuring device is described in which the movement of the rockers is transmitted through lever mechanism and gearing to the needles of a series of dial gauges, one for each rocker.  The jaws of the extrusion device, the rockers, and other parts of the apparatus which come in contact with the brine or other hardening liquid may be made of nickel.  Specification 393,957 is referred to.