EP0047284B1

EP0047284B1 - A method of manufacturing a veneer article by hot pressing

Info

Publication number: EP0047284B1
Application number: EP81900660A
Authority: EP
Inventors: Tommy Lykke Christensen Smedegard
Original assignee: Fowo I Nybro AB
Current assignee: Fowo I Nybro AB
Priority date: 1980-03-04
Filing date: 1981-03-02
Publication date: 1984-12-05
Also published as: EP0047284A1; NO151692B; NO151692C; IE810382L; DK147173B; ES500067A0; DK147173C; WO1981002541A1; BE887769A; IT8120118A0; ES8207016A1; IT1169231B; NO813675L; DK92780A

Abstract

When an article having a strongly profiled transition zone (17) between a substantially flat edge zone (16) and a flat or less strongly profiled central panel (9') is hot-pressed from a single veneer ply or a plurality of adhesively bonded veneer plies (6, 7, 8) cracks may occur in the transition zone of the finished article when the prior art is employed. This undesirable formation of cracks is prevented by effecting, at each corner of at least an outer veneer ply (6), an incision in the form of a gap (18, 19) which extends from the periphery of the veneer ply inwardly through the edge zone with by and large parallel edges and which continues in wedge form through the transition zone with the apex of the wedge located at the corner of the central panel where that panel joins the transition zone. The gap width is chosen such that the gap just closes as a result of the inward displacement of veneer material from the edge zone which accompanies the reshaping of the transition zone. The press tool is provided with stops (22) which abut the edges of the flat veneer ply and, thus, locate the ply exactly relative to the profiled portion of the tool. That portion (20) of the upper tool part (13), which moulds the transition zone, may be displaceable relative to the remainder of the tool and spring loaded towards the lower tool part (12).

Description

The present invention relates to a method of manufacturing, by hot-pressing, a polygonal article comprising a single veneer ply or a plurality of adhesively bonded veneer plies, said article having a flat or substantially flat, circumferential edge zone, a polygonal central panel and a strongly profiled transition zone connecting the edge zone and the central panel.
In US-A-1,876,330 is described a method of manufacturing table tops and the like articles, in which a flat central panel is placed in the bottom of a mould cavity and a plurality of edge panels or strips are placed around the periphery of the central panel, where they are supported by bars forming the periphery of the mould cavity. A prefabricated core is then placed on top of the central panel with an interposed adhesive material which is activated by the application of heat and pressure, thereby bonding the central panel and the edge panels to the core.
It is an object of the present invention to provide a method of the kind referred to in the initial paragraph which is simpler, can be carried out more cheaply, and which furthermore can be employed for manufacturing articles consisting solely of one of more veneer plies without any supporting core forming an integral part of the article.
In order to attain that object the method of the invention is characterized in that the outermost veneer ply of the finished article comprises, along each side of the central panel, an edge panel forming at least the edge zone along that side, and in which the grain extends in the direction of the adjoining side of the central panel, and in that prior to the hot-pressing operation said outermost veneer ply is produced by joining flat edge panels edgewise to a flat central panel in the plane of the central panel, and in that said flat edge panels are manufactured with such a shape that at each corner of the central panel there is formed a gap consisting of a wedge-shaped portion which extends through the regions of the edge panels which form the transition zone of the finished article, with its apex located at the corner of the finished central panel, and an adjoining portion having opposed parallel edges extending through the regions of the edge panels which form the edge zone of the finished article to the outer periphery thereof.
It is preferred that both the edge zones and the transition zones are formed by the edge panels and the said gaps lie between adjoining edge panels.
It will be seen that by initially joining the central and edge panels to form a unitary, flat workpiece the manipulation of the component parts, including placing and correctly locating them relative to a press tool, is considerably simplified. The prescribed grain orientation (known per se) in the individual edge panels ensures that even articles in which the transition zone includes sharp angles and/or regions having a very small radius of curvature, can be manufactured without the risk of cracks occurring in response to the pressing operation. It will also be seen that because the article is pressed from a single, continuous workpiece there is no need for incorporating a core in the article and, consequently, it is possible to produce several types of articles which could not be made by the method disclosed in US-A-1,876,330.
From GB-A-485,071 there is known a method of manufacturing trays and similar articles of veneer from a single sheet of veneer, in which several wedge-shaped portions are cut away at each corner of the sheet prior to the press-moulding of the sheet. This known method is applicable only for producing articles with a rather smoothly rounded transition from the central panel to the edge thereof, and even then it is hardly possible to entirely avoid the formation of cracks at places where the veneer is bent transversely to the grain direction.
FR-A-1,358,646 discloses a similar method of forming a tray from a flat workpiece consisting of a plurality of superposed veneer plies in which non-overlapping angular cut-outs are formed at each corner of each ply prior to the lamination and pressing of the plies. This known method suffers from the same disadvantage as the method disclosed in GB-A-485,071.

Brief Description of the Drawings

The invention will be described in more detail below with reference to the schematical drawings in which

Fig. 1 is a plan view of a cabinet door made as a sandwich element with a facing sheet manufactured by a method according to the invention,
Fig. 2 is a section on a larger scale along line II-II of Fig. 1,
Fig. 3 is a plan view approximately on the same scale as Fig. 2, showing the outermost veneer ply of the facing sheet of the sandwich element prior to the pressing of the facing sheet, and
Fig. 4 is a section on a still larger scale through that portion of a press tool which serves for moulding the transition zone of the facing sheet.

Detailed Description

In Figs. 1 and 2 there has been illustrated a sandwich element 1 consisting of a core 2, edge strips 3 along the sides of the core, and two veneer facing sheets 4 and 5 in engagement with and bonded to the opposed surfaces of core 2 and to the edge strips 3 such that they extend to the edges of the element. Core 2 can consist of a foamed plastic material with or without a filler or it can be made as a slab of chipboard. In the drawing element 1 has been shown with a profiled facing sheet 4 and a planar facing sheet 5 but if desired both facing sheets could be profiled with the same or with different cross-section profile.
As shown in Fig. 4 facing sheet 4 is composed of three adhesively bonded veneer plies, viz. a ply 6 of noble veneer which in the finished sandwich element is outwardly oriented, and two so-called backing plies 7 and 8 which can be made of cheaper veneer. As shown in Figs. 1 and 3 outer veneer ply 6 is composed of a central panel 9 and separate edge panels 10 and 11 extending along the longer and shorter sides, respectively, of the central panel and adhesively bonded thereto. The edge panels are cut from the veneer in such a way that within each panel the grain extends by and large in the direction of the edges of the finished facing sheet 4 whereby the corresponding edge panels of the facing sheet of the finished sandwich element, which in Fig. 1 have been designated by 10' and 11', respectively, give the appearance of solid edge strips surrounding a central panel.
The press tool for compression-moulding facing sheet 4, as shown schematically in Fig. 4, comprises a lower tool 12 and an upper tool 13 which both include means (not shown) for heating the tool. Each of the two tool parts is mounted on an associated platen 14 and 15, respectively. The pressing surfaces of toos 12 and 13, which are oriented towards one another, have been profiled corresponding to the desired shape of the finished facing sheet 4 with a flat circumferential edge zone 16 comprising panels 10' and 11', the weakly profiled central panel 9' and a strongly profiled transition zone 17 (see in particular Fig. 2) intermediate the edge zone and the central panel. It will be understood from Figs. 2 and 4 that during the pressing operation the veneer material within the transition zone 17 is subjected to some elongation and this elongation is accompanied by a displacement of the veneer within edge panels 10 and 11 inwardly towards central panel 9. In order to permit this inward displacement without the detrimental effects mentioned above the edge panels 10 and 11 of the initial flat veneer ply 6 are shaped as shown in Fig. 3. This implies that at each corner of the flat veneer ply there is a gap which from the periphery of the veneer ply extends inwardly with parallel edges in a rectilinear portion 18 by and large to that point which in the finished article constitutes the exterior corner of transition zone 17. From there the gap continues as a wedge-shaped portion 19 terminating in an apex at the interior corner of transition zone 17, i.e. at the corner of central panel 9.
As shown in Fig. 4 that part of upper tool 13, which moulds the strongly profiled transition zone 17 and the adjoining, less strongly profiled area of the central panel 9' of the facing sheet, has been made as a separate, frame-like member composed of bars 20 extending parallel to the edges of the workpiece and guided relative to the remainder of the upper tool in such a way that the frame is separately movable towards and away from the lower tool.
The frame is spring loaded towards the lower tool by means of schematically shown compression springs 21 operative between the frame and platen 15.
For manufacturing the profiled facing sheet 4 the three veneer plies 6, 7, and 8 are inserted in flat state into the open press tool together with intermediate adhesive films (not shown) which become activated at the pressing force and temperature so that the bonding and the compression moulding take place in one operation. The intermediate adhesive films could be replaced by an application of adhesive onto the veneer surfaces. In both cases it is advisable to apply to the outwardly oriented surface of the external ply 6 a thin film of a material, which by the application of heat and pressure becomes hard and tough, in order to ensure a smooth surface of the finished facing sheet.
In order to ensure that the incisions or gaps 18, 19 at the edges of veneer ply 6 are exactly located relative to the profiled parts of tools 12 and 13, upwardly projecting stops 22 have been secured to platen 14 of the lower tool for abutment against the precision-cut edges of the veneer ply. For obtaining a good result it is, furthermore, important that the tool parts 12 and 13 are moved towards one another at a relatively low speed so that the necessary time is obtained for the previously mentioned inward displacement of veneer material from edge zone 16 and for the moulding of the material within the strongly profiled transition zone 17.
When manufacturing sandwich elements as those shown in Figs. 1 and 2 with a core of e.g. chipboard, the lower tool shown can be replaced by the prefabricated core with edge strips and one of the facing sheets glued thereto whereby the opposed facing sheet is pressed and bonded to the core in one operation. Especially in this variant the compression moulded facing sheet may often consist of one veneer ply only.
As examples of other veneer articles, which can be manufactured by the technique described above, there may be mentioned waiter's trays, side and gable members for bed frames, front members for drawers, ceiling and wall panels, side panels for loudspeaker cabinets and various decorative elements. For manufacturing finished articles with two visible surfaces, as opposed to the described facing sheets for sandwich elements, it may be advisable, with regard to the appearance of the finished article, to effect the described incisions at least in both outer plies. The polygonal articles in question may also be made with rounded corners.

Claims

A method of manufacturing, by hot-pressing, a polygonal article (4) comprising a single veneer ply or a plurality of adhesively bonded veneer plies (6, 7, 8), said article having a flat or substantially flat circumferential edge zone (16), a polygonal central panel (9') and a strongly profiled transition zone (17) connecting the edge zone and the central panel, characterised in that the outermost veneer ply of the finished article (4) comprises, along each side of the central panel, an edge panel (10,11) forming the edge and transition zones along that side, and in which the grain extends in the direction of the adjoining side of the central panel,
and in that prior to the hot-pressing operation said outermost veneer ply (6) is produced by joining flat edge panels (10, 11) edgewise to a flat central panel (9) in the plane of the central panel,

and in that said flat edge panels (10, 11) are manufactured with such a shape that at each corner of the central panel there is formed a gap consisting of a wedge-shaped portion (19) which extends through the regions of the edge panels which form the transition zone (17) of the finished article, with its apex located at the corner of the finished central panel (9'), and an adjoining portion (18) having opposed parallel edges extending through the regions of the edge panels (10, 11) which form the edge zone (16) of the finished article (4) to the outer periphery thereof.