GB903499A - Method and apparatus for forming a mat from particulate material - Google Patents

Abstract

A process for forming a mat from particles of material, e.g fibres, to form hardboard, paper &c., comprises discharging a stream of gas containing particles admixed with resin binder into the air above a foraminous member, e.g. a conveyer belt. The stream preferably has a gas-to-particle ratio of 18 to 47 cubic feet per pound and a velocity of 4,000 to 8,000 cubic feet per minute before discharge, reducing to 2,500 above the conveyer belt. In a preferred form of apparatus wood fibres are dried in a cyclone 12 to a moisture content of 8 to 12%, by weight, and mixed with additives, e.g. 8 to 12% of a resin binder and 0,5 to 4% of a water-repellant such as wax, either before or after classification into fine and coarse fractions in a separator 14, the fractions being conveyed in controlled air-to-fibre ratio streams through conduits 15, 16 respectively, to a series of felting heads 26, 28, 29 having laterally elongated and oscillatable nozzles 31, 32, 33 extending into an elongated housing 36 and disposed above a moving conveyer belt 46 over which they discharge a progressively expanding stream of fibres which are deposited on the belt in alternate coarse and fine layers, the latter preferably to the outside surfaces of the mat. The housing 36 is laterally divided into compartments 43, 44, 45 by partitions 41, 49 having adjustable sole plates 42, 50 and these partitions and the end walls 38 may be vibrated to prevent fibres sticking to them. Shave-off rotors 57 level the fibrous mat, excess fibres being returned by suction conduits 59 to a point in advance of the felter. Multiple suction chambers 61, 62, 63 retain the fibres on the belt 46, air and fines drawn through the mat being returned by a fan 65 and conduit 64 either to a point ahead of the felter <PICT:0903499/IV(a)/1> or through conduits 71, 72, 73 to manifolds in fluid communication with the compartments 43, 44, 45. Spaced between the belt 46 and sidewalls of the housing 36 are troughs 51 having upwardly divergent walls the innermost of which is extended and turned over to form a vertical edge member to the belt, the troughs collecting fibres falling clear of the belt for return to the felter by fans 55 and conduits 56. To compact the mat an endless belt 60 is sited between compartments 44 and 45, the final high pressure for board formation, e.g. to a S.G. of from 0,8 to 1,2, being effected in a press (not shown).