GB2392930A - Blockwood panel and door blank - Google Patents

Abstract

In the furniture industry, there can be offcut material, such as wood, produced which has varying sheet thickness and short lengths so that this frequently has to be wasted. The invention provides a method of returning the pieces to a block form 1 so that it can be reused. The method comprises cutting the material into sticks 2, preferably with a width of 25 mm, arranging the sticks 2 in a thin block formation with the cut stick edges on the outside of the surface of the block 1, and bonding the sticks together to form a solid block 1 having the thickness of the cut stick width. The block 1 can be provided with skins (4, fig 3) and a frame (6, fig 3) to form a panel or door. The block may have good fire retardance properties incorporated into the construction, it may also have a conduit for electrical wiring and an opening for a window pane.

Description

t -1 This invention relates to a wood panel construction. It relates in

particular to a construction that can form a solid body for the production of a wood core for a panel or door. In the manufacture of wood products such a furniture items, there are offcuts produced which are frequently of a sheet material having thicknesses of, for example, between nine millimetres and twentyfive millimetres. This material is not able to be reused by the furniture industry and consequently it has to be disposed of as economically ! as possible. Because these offcuts are a mixture of sheet thicknesses and of short and long lengths it is difficult for a practical manufacturing use to be found for this material.

I have now discovered a method by which it is possible to return the offcut material to a solid block form so that it can still provide a useful article of manufacture.

According to the invention, there is provided a method of constructing a block from a structural sheet material which is provided in areas which may be of differing thickness, the method comprising the steps of cutting the sheet material areas into sticks of a predetermined width, arranging the cut sticks in a thin block formation with the cut stick edges on the outside surface of the block, and bonding the stick material together to form a solid block having the thickness of the cut stick width. The cut sticks may be arranged side by side in overlapping fashion in the block formation so that a rigid plane body will be formed.

The width of the cut sticks may be in the range of 6 to 60 millimetres. A preferred width is 12 to 25 millimetres.

The structural sheet material may be a solid wood board or a manufactured board

-2 such as a chipboard. The use of a mineral based board or boards with fire retardant properties is also a possibility.

The bonding of the wood sticks may be effected by an adhesive which is applied to at least some of the sticks by a spotting technique or in a continuous application by a roller technique. A surface skin of a suitable material such as a wood chipboard may be attached to the major surfaces of the block formation also by an adhesive action. The attachment of the surface skin may be effected at the same time as the adhesive for the wood sticks is cured, for example, by a radio frequency heating technique.

Some alternative materials for the surface skin layer include veneers, paper, fleece, MDF, plywood, mineral boards or those boards which have fire retardant properties. The invention also relates to a block construction, a fabricated panel or a door construction when made by the aforementioned method. The panel or door construction may be modified as necessary to have optimum properties for acoustic, fire or security protection purposes.

By way of example, some particular embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a front elevation of the initial core block assembled from cut sticks, Figure 2 is a partial end view of the block assembly with surface skin layers, Figure 3 is a partial side view of the assembly with an added hardwood ripping edge, Figure 4 shows the completed door blank, Figure 5 shows a core block for an alternative door model including a window

-3 aperture, Figure 6 shows a detail of a frame for a glass panel, Figure 7 shows front and side views of a door with an internal fitted conduit for electrical wiring, and, Figure 8 depicts an acoustic panel construction.

The construction of the wood stick core of the invention begins with the obtaining of the necessary offcut sheet material and then cutting this into sticks of 25 millimetres in width. The width of the sticks given in this example determines the thickness of the wood block core to be constructed. The sticks are provided with square ends so that each one is able to make a square butt joint with another stick at the end thereof. The provision of the butt joints also helps to ensure that any air pockets in the door construction will be .. mmmsed. The sticks are then provided with a glue layer on their uncut surfaces and assembled on the electrode plate of an electrical radio frequency heating machine. The sticks are located with their cut edges positioned uppermost so that an assembly 25 millimetres in thickness will be formed. Adjacent sticks are located so that a joint between two sticks in one row is supported by having the joints in the adjacent rows spaced away from this first joint. This arrangement is depicted in Figure 1 which shows an assembly I of the sticks 2 arranged in a rectangular pattern. The assembly of sticks is held in position by top and side pressure support bars (not shown) positioned close to the electrode plate.

An electrode plate of the machine is then closed down on the stick assembly and the machine is operated to apply pressure to compress the assembly. The electrical

power is applied, heat is generated between the electrode plates and the glue component becomes cured to a hard resin which secures the sticks together to form a block.

The solid core block may then be removed from the electrode plates and when sanded to form a smooth surface on both faces it then forms a useful structural body for many purposes. The core block can be improved by securing a surface skin of a chipboard material, ten millimetres in thickness, to both major surfaces of the core. The securing of the surface skins may be done by using the same glue compound that was used for the block core and placing the core block with a surface skin on both sides between the electrode plates of the heating machine. Figure 2 is a partial end view of the core block 3 carrying a surface skin layer 4 on both sides.

A further application of the electrical energy then results in the formation of a rigid board material which is fully bonded throughout and which is substantially free of air pockets. As an alternative to a radio frequency heating method, the core can be assembled by using a cramping method and the skins bonded to the core in a cold pressing technique.

A suitable edge ripping strip of hardwood or softwood may be attached round the perimeter or specified edges of the board so that a door construction will be formed.

Figure 3 shows in a partial side view the core block 3 carrying the surface skin layers 4 and with an attached edge ripping strip 6. The edge ripping strip 6 may be arranged to carry an intumescent material insert if this is required to be present in a door intended for fire protection purposes.

Figure 4 shows the completed door blank 7.

Of course, the operation of bonding the surface skins and forming the stick assembly into the core block could be carried out very suitably in a single heating

-5 operation if this was required. Any offcuts of the wood material that might be produced in the construction of the door blank (both core and/or skin material) may be returned again to the beginning of the process so that they are recycled for making further wood sticks for the next door to be made.

The operation of applying the glue layer to each of the wood sticks was done in the present example by passing each stick between double rollers of an electric glueing machine. It is not of course essential that every single stick should receive a glue layer since the adhesively secured surface skins on the door construction will hold any loose sticks in their correct places. The presence of some dry joints in the length or width of the construction may even serve to improve the dimensional stability of the completed door blank. The particular glue used for the door construction was a urea formaldehyde adhesive with a separate application hardener which was designed to be cured under radio frequency heating conditions.

Figure 5 shows an alternative stick assembly 1 for a door which incorporates a window aperture 8. To make this, as shown in Figure 6, the required glass plate for the window is cut to size and mounted in or surrounded by a wood frame 9. The frame 9 is then inserted in the core block structure during the assembly process. The core block structure is then heated to cure the glue layers and the two surface skins are applied in a second heating stage. Each surface skin will be provided with a cutout area which corresponds to the position of the window aperture 8. The cut-out areas are formed by a routing operation and a template is used to align the required cut-outs in the skins with the window aperture. The second heating stage then secures the parts together to form the

-6 required door and window combination.

To make a door with a fitted conduit for electrical wiring as depicted in Figure 7, when making the assembly of sticks for the core block 3, each stick through which the conduit is required to pass will be provided in advance with a premachined through hole.

In the assembly operation, these sticks will be correctly located with respect to one another by passing a lining tube 11 through the aligned holes. Upon curing the block assembly with the surface skin layers, the resulting door may have been provided with the required electrical wiring conduit. The usual ripping strip or an appropriately prepared ripping strip will of course be attached at the door edges to conceal the surface skin joints.

Figure 8 shows an acoustic panel 12 construction. This can be used for example in an open plan office situation and it can have good acoustic damping properties.

The wood panel construction method of the invention has been found to be flexible in its operation since it is applicable for use with materials of different thicknesses and if required it is able to produce doors and panels from comparatively thin sheet starting materials. The method is applicable to doors intended for security and acoustic purposes and additionally for fire protection doors. The thickness of the surface skins can be adapted as necessary to give a predetermined level of fire resistance and intumescent strips could be incorporated if wanted. The avoidance of any air pockets in the door construction can be expected to have a favourable effect on the fire resistance.

The construction method is able to be used with offcut wood products from the furniture industry and this can enable general manufacturing wood wastage to be reduced.

The wood offcuts are comparatively inexpensive to obtain and this can lead to a low

material manufacturing cost for the wood panel construction of the invention.

Additionally, since offcuts from the door construction are able to be recycled it is considered to be an environmentally friendly process. It is not of course essential that only offcut materials should be used for the door construction and, in a suitable situation, wood sticks made from new sheet material could be used. In addition, sheet material offcuts from mill manufacturers or merchants slow moving stocks would be most suitable.

The foregoing description of embodiments of the invention has been given by way

of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, instead of the glue compound being a urea formaldehyde adhesive, this could be a suitable alternative compound such as a PVA or a resorcinol adhesive. The invention can allow doors with a specified level of fire resistance to be manufactured since the thickness of the core block and of the surface skins can be adapted as necessary to meet a particular requirement. For fire resistant doors intended to meet higher specifications, incombustible materials can be

used that are available in twelve or eighteen millimetres or in smaller or greater sheet thicknesses. Additionally, the width of the sticks to be cut does not have to be limited to twentyfive millimetres and this could be some alternative constant width, if this was required. In the case of a door construction, one modification to improve the fire resistance would be to include at the door top a few horizontally directed core sticks cut from a Class '1' or Class 'O' shipboard, MDF or non- combustible sheet material prior to the application of the core skins. The chipboard core stick system could alternatively be used

-8 to construct a skeletal inner core for a door which would include predetermined void areas that were available if required to be filled with expanded foam that was non fire-rated or 2 4 hour fire rated. After application of the core skins, the resulting lightweight door would have a conventional external appearance but an improved fire resistance.

Claims (10)

-9 CLAIMS

1 A method of constructing a block from a structural sheet material which is provided in areas which may be of differing thickness, the method comprising the steps of cutting the sheet material into sticks of a predetermined width, arranging the sticks in a thin block formation with the cut stick edges on the outside surface of the block, and bonding the stick material together to form a solid block having the thickness of the cut stick width.

2 A method as claimed in Claim l, in which the cut sticks are arranged side by side

in overlapping fashion in the block formation so that after bonding a rigid plane body is formed.

3 A method as claimed in Claim 1 or 2, in which the cut sticks have a width in the range of 6 to 60 millimetres.

4 A method as claimed in Claim 3, in which the width is in the range of 12 to 25 millimetres.

5 A method as claimed in any one of Claims 1 to 4, in which the structural material is a natural or manufactured wood or mineral board.

6 A method as claimed in any one of Claims 1 to 5, comprising the further step of applying one of more surface skins to the resulting block by an adhesive bonding process.

7 A method as claimed in any one of Claims 1 to 6, comprising the additional step of applying an edge ripping strip to the bonded block edge.

8 A fabricated block construction when made by a method as claimed in any one of Claims l to 7.

-10

9 A fabricated panel or door construction when made by a method as claimed in any one of Claims 1 to 7.

10 A panel or door substantially as hereinbefore described with reference to any one of the accompanying drawings.