Patent GB-1055565-A (GB)
Title: The production of wood products having a hardened surface layer
Inventor: HARTESVELDT CARROLL HENRY VAN
IPC: B27M1/02
Filed: 1963-08-22
Abstract: 1,055,565. Woodworking; laminates. HOOVER BALL & BEARING CO. Aug. 22, 1963. No. 33369/63. Headings B5L and B5N. [Also in Division B6] A method of forming a wood product having a hardened compressed layer on the surface comprises preheating a surface layer of a wood workpiece, subjecting the surface layer to a progressively increasing pressure step to compress the layer, and then subjecting the layer to further heat while maintaining the pressure on the layer. In apparatus for carrying out the method and forming a hardened layer on both sides of the workpiece, the pressure is applied to the surfaces of the workpiece 16, Fig. 1, by sloping surfaces 19, 19<SP>1</SP> on mandrels 22, 22<SP>1</SP>. The workpiece is first coated on both its surfaces by shims 20, 20<SP>1</SP> of brass or flexible steel and moved by a bar 18 between a pair of preheating blocks 21, 21<SP>1</SP> having elements 21a, 21a<SP>1</SP> which heat the workpiece to a temperature above 212‹ F. to soften the surface fibres of the workpiece. The surface layers are then compressed by the sloping surfaces 19, 19<SP>1</SP> on the mandrels 22, 22<SP>1</SP> which have elements 22a, 22a<SP>1</SP> to heat the workpiece to a temperature between 300‹ F. and 360‹ F. which stabilizes the compressed layers. The workpiece continues its movement by passing between cooling blocks 23, 23<SP>1</SP> having chambers for a fluid which cools the workpiece to below 210‹ F. to prevent liquid in the workpiece forming into steam. The surfaces of the workpiece may be preheated before they engage the preheating blocks 21, 21<SP>1</SP> by infra-red heaters disposed above and below the path of movement of the workpiece. The shims may be anchored to the leading end of the workpiece and graphite or oil employed between the shims and mandrels. The bar 18 for moving the workpiece between the mandrels is pulled by cables which run along the sides of the workpiece and are drawn by a motor-driven winch. In an alternative arrangement, the pressure is applied to the workpiece by a roller 61, Fig. 7, backed by rollers 62, 63, 64. The Specification includes formulµ for determining the length L, Fig. 6, and height H of the sloping surfaces 19, 19<SP>1</SP>, and the corresponding dimension H, L of the roller shown in Fig. 7 to produce the necessary pressures of the workpiece and form the compressed layers. The surfaces may be impregnated with a sealant, such as a resin, wax or thermosetting resin which is cured during passage through the apparatus. A decorative sheet impregnated with a B-stage resin may be laid on the upper surface of the workpiece from a supply roll and is joined to the resin coated upper surface during passage of the workpiece through the apparatus. The impregnation of the workpiece may be effected by soaking in a water solution of unpolymerized phenolic resin components which becomes cured during processing by the heated mandrels. A phenolic resin layer can be produced by using impregnated alpha-cellulose paper, curing it to the B-stage and placing it on the impregnated board. Other resins of the phenolic, aldehyde condensation or polymerizable unsaturated polyhydric alcohol-polycarboxylic acid polyester type may be used.