GB815441A - Improvements in or relating to continuous hot press - Google Patents

Abstract

815,441. Pressing fibrous material into boards. HERCULOK CORPORATION. Sept. 11, 1956 [Sept. 16, 1955], No. 27802/56. Class 87(2). [Also in Group XXX) A continuous pressing machine comprises a pair of opposed endless movable belts which are backed on their non-adjacent sides by platens to form an elongated pressing chamber and means for introducing compressed gas through a plurality of openings in the surfaces of the platens adjacent the belts to maintain the platens separated from the belts by a lubricating gaseous layre. Raw matreial, e.g. wood waste, straw &c., is fed from hoppers 10 to pulpers 12, the resulting fibrous material is injected into a rotary drier 16, where the moisture content is lowered to e.g. 10-12 per cent, the dried material passes through a mixer 24 and is sprayed with a resin binder in a chamber 26, thence the material is carried by a gaseous stream to a cyclone separator 28 and falls into a felting chamber 30. Liquid urea or phenol-formaldehyde resins are suitable. The lower belt 34 of two opposed moving steel belts 34, 40 extends below the felting chamber and the fibrous material is deposited on it as a loose mat. At the entrance to the gap between the belts 34, 40 the material is compacted by the passage of the belts between rollers 42, adjusted in their spacing to exert an increasing, relatively high pressure (e.g. 700 lb. per sq. in.). The steel belts are drawn between adjustably mounted platens 52 by rollers 44, which are adjustable. The platens are hollow, their chambers 60 being filled with steam supplied through manifolds 54. Across each platen, dividing the chamber 60, is another chamber 58 and these chambers are supplied with compressed air through manifolds 56 which are coaxially mounted in the steam manifolds 54. The compressed air, thus preheated, emerges through small holes into the spaces between the belts and the platens and forms gaseous layers which reduce friction. To reduce chilling by sudden expansion of the emerging air the holes are counterbored at their exits, thus also distributing the air pressure. The space 68 between each platen and belt is narrow (about 0-001 inch) to minimise drop of pressure at the edges. In view of this narrowness it is preferable to lubricate the belts with e.g. a metal stearate powder. Towards the exit of the press cooling water is substituted for steam in the manifolds 54, similar to but separated from the steam manifolds, to cool the pressed fibres and prevent contained steam pressure from destroying the product. Brushes 48 clean the belts. The pressure between the belts is about 75 lb. per sq. inch, at a temperature of about 345‹F. For pressing plies of wood veneer 122, 124, 126, Fig. 8, a modified arrangement is used in which the upper platen comprises upper and lower sections 88, 90 one slidable in the other. A chamber 100 is formed between the two sections to which heated compressed air is supplied, emerging through counterbored openings 96 to form the gaseous layer. The lower platen has similar openings 96. The joints between the relatively movable platen sections are sealed by gaskets 98 and 116.