GB708342A - Improvements in method of and apparatus for the continuous production of flat homogeneous, or stratified materials - Google Patents

Abstract

In a method of continuously treating films, sheets, or strips, containing or consisting of synthetic resin, to smooth the material or to subject it to heat and pressure, the material to be treated, on passing between plates or tools, is subjected thereby to pulsating pressure or thrust impulses of short duration. Sheets or strips may be formed of thermoplastic synthetic resins and cellulose derivatives, with or without fibrous or other filling material. The material may be carried between the pressing members on flexible bands 76, Fig. 7, of metal to provide good heat conduction. To obtain frequent impulses of high pressures, e.g. 60-300 per minute of 50-100 kg. per sq. cm., pulsating hydraulic pressure is used. In Fig. 7 the pressure is applied to both sides of the material 60. An upper stationary part 61 has two chambers 62, 63 with a flexible diaphragm 64, e.g. of steel or bronze, across their openings and a lower part 66 has a chamber 74 cylindrical at its upper part to accommodate a piston 68. Hydraulic fluid fills the spaces in the chambers, and pipes 72, 73 lead to a pump which generates pulsating pressure which is applied to the top of the material through the diaphragm 64 and to the bottom of the material through the piston 68. The material is also heated and cooled from both sides by heating the liquid in the chamber 62 and cooling that in the chamber 63, and placing on the piston heating plates 69 opposite 62 and cooling plates 70 opposite 63. To obviate the need for using power to overcome the inertia of parts such as pistons or movable pressure plates, pulsating pressure may be imposed through diaphragms on both sides of the material, but where high pressures are necessary, diaphragms are not strong enough and an arrangement as shown in Fig. 6 is used, where a piston 53 is caused to oscillate against one side of the material and squeeze it intermittently against a fixed part 49, which has heating and cooling plates 50, 51. There may be oscillating pistons on both sides, acting against one another. When the material is less than about 0.5 mm. thick a diaphragm provides the advantage that it equalizes the distribution of pressure. This feature may be incorporated in an arrangement such as in Fig. 6 by making the head 52 of the piston such that it acts as a diaphragm. Other arrangements may include diaphragms which do not transmit pulsating pressure but act solely as cushions, having a space behind them filled with a substance such as grease. With some materials, e.g. thermoplastic synthetic resins, better results are obtained if the material passes over a roller, which may be heated or cooled. The conveyer band may then be very thin or not used at all, the roller acting as the conveyer, as in Fig. 10. Fig. 10 also shows another means for generating pulsating pressure, i.e. a piston 92 actuated by a crank 93 and transmitting the impulses through liquid filling a chamber 91 to the pressure plate 87, which is concave and may be heated or cooled as at 89. The roller 86 may also be heated or cooled, as at 88. In this construction there are interposed between the liquid and the pressure plate a diaphragm 94 and an intermediate plate 94a with heat insulation between it and the plate 87, In a simpler arrangement the parts 94a and 87 are dispensed with and the chamber 91 closed by a diaphragm, curved to the shape of the roller through which the impulses are transmitted directly to the material, heating or cooling in this case being applied to the liquid. Several pressing devices may be applied to the periphery of one roller, e.g. three spaced at 90 degrees with their operations synchronized <PICT:0708342/IV (a)/1> <PICT:0708342/IV (a)/2> <PICT:0708342/IV (a)/3> <PICT:0708342/IV (a)/4> to give simultaneous impulses, whereby the material may be progressively treated. Another arrangement is shown in Fig. 12 which illustrates means for combining mechanically and hydraulically produced impulses. The mechanical means applied to the lower press plates 106, 107 comprise two rows of oppositely inclined bars 110 with rounded ends which bear in rows of sockets on opposite sides of a plate 108 and similarly in sockets in a base 113 and a cross-piece 112 guided on spacing bolts 111. When horizontal movement of the plate 108 (which is positioned by springs) causes the inclination of the bars to be more towards the vertical, the distance between 112 and 113 is increased and the plates 106, 107 press on the underside of the material; thus horizontal reciprocation of the plate 108 results in vertical reciprocation of the plates 106, 107. A double piston and cylinder arrangement for generating hydraulic impulses has two spaces 121 for the liquid closed by a common diaphragm 120, the liquid being heated in one space and cooled in the other, labyrinth packing being fitted in the division between the spaces. The mechanical and hydraulic combination widens the range of materials that can be treated by one apparatus, deformation being produced by the longer stroke of the mechanical side and higher pressures by the diaphragm, which is relieved of undue deflection; and higher and lower frequency impulses can be applied simultaneously by the hydraulic and mechanical means respectively. The bands or rollers may have surfaces suitable for imparting a polished, matted or other required finish to the material, or a separate band or other tool may be inserted between the conveyer belts and the material for the same purpose; if desired the tools may be passed through without the conveyer belt.