GB754935A - Improvements in or relating to continuous presses - Google Patents

Abstract

754,935. Double-belt moulding machines. VOELSKOW, P. Jan. 15, 1954, No. 1326/54. Class 87(2) An arrangement for continuously pressing wood chips, synthetic resin copolymers as plywood and plastic material into sheets or for squeezing liquid out'of moist material between endless conveyer bands has, on that side of each endless band which is remote from the material, one or more fixed pressure members, and, between the bands and the pressure members, closely juxtaposed rolling elements which transmit pressure to the bands, at least one of the two endless bands being so arranged that it can be connected to a source of high frequency electric energy so that it can act as an electrode for the dielectric heating of the material, the band being arranged in an electrically insulated manner for the purpose. The material of the endless bands which are rigid enough not to bend between the rolling elements, is suitable for the purpose and material for which the press is to be used, e.g. for rolling plastic strips the bands may be of strip steel or of steel wire fabric with a rubber or plastic covering, or for squeezing water out of moist material the bands may be of steel wire fabric with a covering of filter material. The rollers 5, Fig. 1 are of high-grade steel of small diameter and close together and may revolve freely in the space between the bands 2 and the pressure members 4. It is preferably to guide the rollers to prevent canting or side movement, one way being to shroud their ends in cup-shaped members which are linked together to form chains. Another way is to mount the rollers 9 on rods 10, Fig. 4, which are connected by links 11, 11<1>, the rollers in this case being short and staggered to give uniform pressure distribution. Ribs may project from the surfaces of the pressure members to guide the rollers 9. A flexible sheet metal cage may be provided for guiding the rollers. Again, the rollers 28, Fig. 6, may be grooved for spring wire stirrups 30 which also fit into grooves in sliding shoes 31, of bronze or aluminium alloy for good heat transfer, to which the stirrups are secured by hooked ends. The chains of rollers may run in an oil bath. As shown in Fig. 1 the ends of the pressure members 4 are curved so that the material is gradually compressed as it enters, and the space between them is adjustable. A pressure member may be arranged to tilt in either direction as in Fig. 8, by forming it of two parts 16, 18, with a pad 17 between consisting of a sheath containing liquid supplied through a bore connected to a pressure gauge whereby the pressure on the material may be controlled, the spacing between the pressure members also being controllable by screws or cams. The moulding or pressing temperature may be controlled by heating or cooling the bands 2, by gases which may be circulated by pressure and suction, or electrically. Or the pressure members may have holes or slots to allow gas to flow into the space between the bands. Heating may also be dielectric, one or both of the moving bands being an electrode or electrodic for a high frequency alterating voltage; alternatively, separate platelike electrodes, connected together. may be placed above and below the material before it enters the machine, and a highfrequency field set up between them and the moving bands so that the material is pre-heated dielectrically. If the material is in more layers than one a band-like auxiliary electrode may be used, placed between the layers, preferably composed of separate plates insulated from one another and impressed with voltage through sliding contacts so that the alternating field is confined to a definite part of the pressing space. Fig. 10 shows a modification in which end rollers 21 are used at one end only, those at the inlet end being replaced by appropriately shaped pressure members 24 with the small rollers 25 between them and the bands 22. Fig. 10 also shows a second stage in which the material 23, sufficiently consolidated is subjected to the direct rolling action of a chain of rollers 26.