WO1996031314A1

WO1996031314A1 - Building panel machine

Info

Publication number: WO1996031314A1
Application number: PCT/GB1996/000864
Authority: WO
Inventors: Charles David Sinclair Gaskill
Original assignee: Fastrac Building Systems Limited
Priority date: 1995-04-05
Filing date: 1996-04-04
Publication date: 1996-10-10
Also published as: AU5283496A

Abstract

A self-contained factory unit for manufacturing load bearing building panels is provided. The factory unit includes an apparatus comprising means for forming structural foam blocks, means for cutting the foam blocks into strips, means for forming lengths of truss, means for assembling lengths of truss and foam strips together and means for attaching transverse members to the trusses in order to form the load bearing panels. The factory unit also has a source of electrical energy, a source of compressed air, and a prime mover such as an internal combustion engine. The apparatus for forming the truss comprises a plurality of interacting arms which move into and out of engagement with a wire, bending it into a zig-zag shape, and means for attaching a straight wire to each side of the zig-zag shaped wire. The zig-zag wire is then cut to an appropriate length. The lengths of zig-zag wire are then assembled with strips of foam so that the lengths of foam and truss alternate with one another. The trusses and foam strips are then positioned relative to one another so that the trusses project substantially the same amount from the foam strips and trusses. Transverse wires are then attached to the sides of the assembly of foam strips and trusses to form the load bearing panel. The apparatus for attaching strapping wires comprises means for gripping, tensioning and positioning each wire to be welded, and means for welding the wire to the trusses.

Description

BUILDING PANEL MACHINE

The present invention relates to the manufacture of building panels. Building panels manufactured using various aspects of the present invention can be readily assembled to provide the walls and roofs of dwellings. Openings can be easily cut in these panels to provide the openings for doors and windows.

There is a current need to provide housing at a rapid rate and at a low cost in many areas of the world. However those areas of population requiring such forms of housing usually have limited resources of capital and materials. The need to supply the demand indicates the mass production of suitable building components so that the economies of scale can be practised. However it has been the experience of the building industry that producing building components in the factory and then transporting the components for erection on site is not economic. This is particularly the case where the sites for the dwellings may be hundreds if not thousands of miles from any likely factory location.

The present invention therefore seeks to provide in one of its aspects a self-contained factory unit which can be easily transported to a building site so that building components and particular building panels can be manufactured on the site using materials which have a relatively low volume.

The present invention seeks to provide economic methods and apparatus so that building panels can be produced using appropriate chemicals to manufacture phenolic foam blocks and using the foam blocks thus made to construct load bearing building panels.

Polystyrene foam is often used in building panels of this type, however polystyrene is not easily produced in remote areas, or with limited power and resources, and ready-made polystyrene is bulky and thus is inconvenient and expensive to transport.

In another of its aspects the present invention seeks to provide a means of manufacturing trusses which can be combined with lengths of foam block so as to form building panels.

The present invention is defined in the independent claims below, to which reference should now be made. Preferred features of the invention are defined in the dependent claims.

A preferred embodiment of the invention provides a self-contained factory unit comprising a power source in order to drive a generator, a compressor for providing compressed air, means of forming phenolic foam blocks, means for cutting the blocks into strips, means for forming lengths of girder or truss, means for assembling lengths of truss and foam strips and means for attaching transverse members to the trusses in order to form load bearing building panels. The means for forming the phenolic block may comprise an insulated reaction vessel in which the heat to initiate reaction is provided by cooling water from for example the generator of the factory unit .

The thus formed block of phenolic resin foam can be cut into strips by any appropriate means or according to the disclosure in our co-pending GB patent application number 9415657.7.

In particular the present invention seeks to provide an apparatus for manufacturing trusses using wire in which a length of wire is formed into a zig-zag shape and the thus formed wire is welded to two lengths of parallel wire to form lengths of truss equivalent in design to a Warren girder.

The lengths of truss can then be assembled with lengths of foam block and the trusses secured together by transverse lengths of wire so as to provide load bearing building panels.

The lengths of Warren girder can be formed by initially bending a length of wire into a zig-zag shape by means of a plurality of interacting arms which are moved into and out of engagement with the length of wire in a continuous process.

The arms can be mounted on a pair of drive means arranged so that the wire passes between the pair of drive means and the arms are driven continuously and are in contact with a cam surface enabling the arms to move into and out of engagement with the wire.

For example the arms can be mounted in a pivotal fashion between two chains which are driven around a shaped surface.

The thus formed zig-zag wire is passed to a conveyor and thence to a welding head which also receives two substantially straight wires and the straight wires are welded to the zig-zag wire by the welding to form a Warren truss . The welding head can be arranged to reciprocate relative to the direction of travel of the conveyor and can operate so that each substantially straight wire is welded simultaneously at least one location to the zig- zag wire whilst the welding head is travelling.

Alternatively a rotary welding head may be provided at a fixed location to weld the straight wires to the zig-zag wire.

After this welding step has been completed the direction of motion of the welding head is reversed, and the welding head locates adjacent the next position where the two substantially straight lengths of wire are next to be welded to the zig-zag length of wire.

The thus formed length of Warren truss can then be cut to any appropriate length.

The formed strips of phenolic foam are then assembled with lengths of Warren truss so that the lengths of truss and foam alternate with one another. The assembly stage is such that the phenolic foam strips and the Warren truss are positioned so that the peaks of the trusses project the same amount from the phenolic foam resin strips on each side of the assembly.

The lengths of truss can then be secured together by transverse lengths of wire which are welded to the Warren girders on each side of the assembly, and thus a load bearing building panel is formed.

The invention in its various aspects is defined in the independent claims below, to which reference should now be made. Advantageous features of the invention are set forth in the dependent claims . The present invention will now be more particularly described with reference to the accompanying drawings in which:

Figure 1 shows a flow diagram of the manufacturing processes which form part of the present invention;

Figure 2 shows a diagrammatic plan view of the wire bending apparatus;

Figure 3 is a section on line 3/3 in Figure 2,-

Figure 4 is a plan view of a conveyor carrying the zig-zag wire formed in the wire bending machine;

Figure 5 is a diagrammatic plan view of the apparatus for the welding stage of the apparatus;

Figure 6 shows the Warren truss manufactured by the apparatus; Figure 7 shows an initial assembly stage of the apparatus;

Figure 7A shows a part view on arrow A in Figure 7,-

Figure 8 shows a cross-section of a centred stack of phenolic foam strips and Warren trusses; Figure 9 shows a partial front elevation of a completed building panel;

Figure 10 shows a side elevation of the building panel shown in Figure 9; and

Figure 11 is a plan view of the building panel shown in Figures 9 and 10,-

Figure 12 shows a side view of the truss making machine;

Figure 13 shows the truss positioning rack;

Figure 14 shows a perspective view of the knockers assembly; Figure 15 shows a front view of the strap wire shuttle module which pulls, tensions and cuts the transverse wires;

Figure 16 shows a diagrammatic view of the welding array in the strap and weld machine in an embodiment similar to that shown in Figures 12 to 13 except that the strap wire shuttle module is modified; and

Figure 17 shows a plan view of the wire gripper and cutting assembly at the top of a strap and weld machine having two strap and weld modules of the kind shown in Figure 16 showing the rotatable grippers in two different possible positions.

Referring to Figure 1 there is shown a flow diagram of the manufacturing process and apparatus of the present invention. Initially a mild steel wire for example 14 gauge wire is bent 10 in a wire bending apparatus in order to create a zig-zag wire 45. The zig-zag wire 45 together with two substantially straight wires 48, 50 pass to a truss welding apparatus 12 where the straight wires 58, 50 are attached to the zig-zag wire 45 to form a Warren truss 56 which is then cut to length at the cutting stage 14.

The cut lengths of Warren truss 56 are then passed to a first assembly stage 16 where they are assembled with strips of phenolic foam. The foams strips are cut from a block of phenolic foam which is created in a reaction vessel 18. The raw materials for the manufacture of phenolic foam are well known these being phenolic resin, sulphonic acid and a foaming agent. The reaction vessel can be insulated and the reaction can be initiated using heat provided from the generator of the factory unit . The thus formed foam block can be cut into strips by any appropriate means at stage 20.

The foam strips and Warren trusses are initially assembled together at the first assembly stage 16 where they are arranged in alternate layers one on top of the other. It is important that the assembly of the foam strips and trusses is such that the trusses extend from each side of the foam strips by an equal amount. Assembly stage 16 is an approximation of this requirement.

The next stage of the assembly 22 involves the use of the knocker assembly described below in order to ensure that the trusses extend by the same amount on each side of the foam strips. At assembly stage 24 transverse lengths of wire are laid across the Warren trusses on each side of the assembly and the Warren trusses are secured to the transverse wires on each side of the assembly. After the transverse wires have been attached to the assembly the panels are completed apart from any openings required and the building panels can then be passed to a store or used for the immediate erection of dwellings . The third assembly stage may be effected after the second assembly stage or substantially simultaneously with the second stage of assembly.

Referring to Figures 2, 3 and 12, the apparatus for forming a truss comprises two pairs of chains 26, 28 which are driven around preformed tracks 30 and 32 by a chain drive 34. Each pair of chains 26, 28 supports pivotally mounted arms 36 between each chain in the oair. The arms at one end have a roller 38 which engages with the cam surface of the drive track. The cam surface is preferably made of nylon so that no lubrication is needed and thus the maintenance of the machine is -easier. The other end of the arm has an extending tooth 43 for engaging the wire 40 to be shaped.

To form a truss, a wire 40 is first passed through double wire straightening rollers 41. The pairs of chains 26, 28 are driven in the direction of the arrows shown in Figure 2 so that the arms 36 interact and move into and out of engagement with the wire 40. The cam surface of the drive track is shaped so that for most of one revolution of each pair of chains 26, 28 the arms 36 stick radially outwards, but as the chain turns the corner near the infeed section 39 of the wire 40 the arms 36 fold in towards the cam surface and are then pushed out .again after turning the corner to engage with the wire 40. As the wire 40 comes into contact with the arms 36 and as the arms 36 swing out in contact with the wire it is bent into a zig-zag shape as shown in Figure 2. The thus formed wire 45 passes to a conveyor 37 which is driven by a chain 46 and on which the zig-zag wire 45 is located between flights 42.

The conveyor 37 carries the zig-zag wire form 45 towards a shuttling carriage 44 which is driven in a reciprocating fashion by means of pneumatic cylinders. Two substantially straight wires 48, 50 are fed from sets of straightening rollers 52, 54 through tubes 51 towards the shuttling carriage 44 so that the lengths of wire 48, 50 come into contact with the peaks of the zig¬ zag wire form. The shuttling carriage includes a welding head which has at least two electrodes (not shown) enabling the electrodes to secure each length of straight wire 48, 50 to at least one point on the zig-zag wire form 45.

The electrodes locate with the respective peaks of the zig-zag wire form 45 and the welding head travels with the zig-zag wire form 45 whilst welding takes place. When the welding step has ceased the welding head reverses direction to locate with the next peaks of the zig-zag wire form 45 in order to ensure that the straight lengths of wire 48, 50 are connected to the zig-zag wire form 45 at each peak of the zig-zag.

It will be appreciated that the shuttling carriage 44 is repeatedly travelling with the moving wires to weld them together and then reversing its direction of travel to return to its starting location to perform a further welding operation. In this manner a continuous length of Warren truss or girder 56 is manufactured. Figure 6 shows diagrammatically a Warren girder 56 formed by the apparatus described with reference to figures 2 to 5.

In an alternative embodiment a different method and apparatus for welding the two straight wires 48, 50 to the zig-zag wire 45 comprises using a plurality of roller welding heads instead of the shuttling carriage as described above. In this embodiment four sets of roller welding heads, such as copper wheels, are provided, one set on top of the zig-zag wire 45 at each edge of the zig-zag wire with the other sets directly below them beneath the zig-zag wire 45. The sets of rollers are pressed against the straight wires 48, 50 which are in contact with the peaks of the zig-zag wire form 45. A current is passed through the particular roller welding heads located above and below each peak of the zig-zag wire form 45 to effect spot welds. This welding system is easier to run and requires less maintenance than the reciprocating welding system, especially at high speeds.

Phenolic foam blocks are produced by reacting phenolic resin with sulphonic acid in the presence of a volatile blowing agent such as pentane in the insulated reaction vessel 18.

In order to initiate the reaction of the chemicals heat can be supplied to the reaction vessel in the form of the cooling water from the generator of the factory unit.

It will be appreciated as mentioned above that the factory unit includes a prime mover, a generator and a compressor. Electrical power is required to drive the chains and the conveyors and for the electrodes, and compressed air is required to operate the electrodes and other components of the manufacturing plant to be described below.

The phenolic foam block formed in the reaction vessel is cut into strips, step 20, by any appropriate means and the strips of foam 62 together with lengths of Warren girder 56 are assembled in the first assembly stage 16 using the apparatus shown in Figure 7. The apparatus shown in Figure 7 comprises an inclined board 58 on which are provided wooden blocks 60. Foam strips 62 and Warren trusses 56 are alternately stacked on the board 58 and the blocks 60 position the foam strips 62 in relation to the Warren trusses 56 so that the trusses 56 extend by approximately equal amounts on each side of the foam strips. The assembly panel 64 of foam strips 62 and Warren trusses 56 is then clamped together in a frame 66 and the frame and the assembly 64 of foam blocks and Warren trusses 56 is passed to the second-stage of assembly illustrated in Figure 8. Each side of the frame perpendicular to the lengths of phenolic foam 62 and trusses 56 has a knife edge extending along its length which protrudes into the ends of the foam strips, thereby holding them in place. This helps to prevent the foam strips 62 from moving sideways. Referring to Figures 13, 14, 15 and 16 the apparatus for the second and third stages of the assembly comprises two knocker racks 69, a truss positioning frame 80, two sets 47 of welding heads 84, a strap wire shuttle module 89, and a panel supporting structure 78.

The panel supporting structure 78 comprises an indexing conveyor for feeding the panel though the strap and weld machine, and two support frames for supporting the panel frame 66 in an upright position. The assembly panel 64 is then placed on a conveyor with the lengths of foam and trusses substantially horizontal . The conveyor feeds the panel through the apparatus for the second and third assembly stages. Each knocker rack 69 has a number of regularly spaced bumpers or knockers 68 with flat faces to contact the strips -of phenolic foam, which are mounted on a bar 70. The racks are mounted on either side of the path taken by a panel passing through the strap and weld machine. The bumpers 68 extend beyond the bar 70 by an amount greater or equal to the amount by which the trusses have to extend from each side of the foam blocks .

The knockers 68 are moved in unison by moving the bars 70 on each side of the panel assembly 64 towards each other. This action brings the knockers into contact with the foam and centres the foam strips 62 with respect to the trusses 56 so that the trusses extend by substantially the same amount on each side of the foam strips .

When stronger foam materials, such as polystyrene, are used rollers may be provided either side of the assembly panel to position the foam relative to the trusses. However, phenolic foam is fairly soft and rollers would dig into the foam. The knocker assembly of the present invention thus provides an apparatus and method for positioning phenolic foam blocks relative to trusses without damaging the phenolic foam.

Figures 8 shows a side elevation of the assembly 64 at the second stage of assembly of the panel with aligned foam strips. Referring to Figure 13 the truss positioning frame

80 comprises two racks 81, one mounted either side of the indexing conveyor. Each rack 81 has a plurality of regularly spaced fingers 83 which extend towards the panel . Next to each of the truss positioning racks 81 is a welding array 47 for welding the strap wires to the trusses . The welding arrays 47 are shown in Figure 16. Each welding array 47 comprises a plurality of regularly spaced welding heads 84 which comprise a pneumatic piston 88 and two electrodes, a front electrode 86 and a separately moveable backing electrode 85. The backing electrode 85 has a flange portion 87 at its distal end.

Referring to Figure 15, the strap wire shuttle module 89 comprises two rodless cylinders 90, on each of which a shuttle 92 is movably mounted. Each shuttle comprises a wire cutter 93 and wire gripper 95 and two pneumatic cylinders 94, 96 for moving the wire cutters 93 and grippers 95 respectively. At the base of each rodless cylinder 90 there is a set of fixed grippers 98 and a pneumatic piston 97 for moving the rodless cylinder 90. At the top of each rodless cylinder 90 is a wire delivery system 100. The wire is preferably 14g strap wire .

The third stage of the assembly 24 comprises extending a number of equally spaced tensioned wires 72 across each side of the assembly panel 64 and attaching them by welding to each of the trusses 56 in the assembly panel 64. The strapping wires 72 are delivered to the shuttle modules 92 via the wire delivery system 100. To extend each transverse wire 72 the wire grippers

95 on a shuttle 92 at the top of the rodless cylinder 90 first grips the end of the wire 72. The shuttle 92 then moves down to the base of the rodless cylinder 90 drawing out a length of the strap wire 72. The fixed grippers 98 at the base of the rodless cylinder 90 then grip the wire. The grippers 95 on the shuttle 92 release the wire 72 and the shuttle moves back to the top of the system. At the top the grippers 95 on the shuttle then grip the drawn wire 72 near to the wire delivery system 100. The piston 97 at the base of the system 90 then moves the base of the rodless cylinder and, consequently, the grippers 98 holding the wire to the base of the panel so that the drawn wire is held substantially vertically against the assembly panel and is tensioned. To weld the strap wire to the side wires of the trusses in the assembly panel 64 the backing electrode 85 of the welding head is then moved towards the panel assembly so that the flange 87 lies against a foam strip. The welding head 84 is then moved vertically upwards relative to the panel assembly by moving the welding array 47 upwards, so that the flange of the backing electrode is located behind the truss wire at the point where the vertical wire is in contact with the truss wire. Alternatively, the panel could be moved downwards, but it is likely that this would be more difficult.

The truss positioning racks 80 are then moved downwards so that the fingers 83 apply a vertical pressure to the side wires of each truss in the assembly panel. The fingers 83 vertically align the trusses by holding them at the correct position for welding while the welding heads weld each horizontal truss 56 to a vertical strap wire 72.

The piston 88 of the welding head 84 then brings the outer welding electrode into contact with the transverse wire. The transverse wire and truss chord wire are then compressed together and a current is then applied to effect a spot weld, at that point.

The welding heads 84 in the array 47 may weld at the same time as each other or cascade welding may be performed in which case different groups of welding heads will weld at different times. Cascade welding is particularly advantageous where there is a limited power supply, as the maximum power needed is substantially reduced compared to the power needed if all the welding heads weld at the same time.

Next the piston rod 88 is retracted to release the completed wire joint. The welding arrays 47 are then moved downwards so that the flange of the backing electrode 85 is no longer behind a wire. The piston 88 is then fully retracted to avoid fouling the forward movement of the panel as it is moved to the next position.

After welding the wire cutter 93 on the shuttle 90 cuts the wire at the top of the panel and the grippers 98 at the base of the panel release the wire. The cylinder 97 at the base of the rodless cylinder then allows the rodless cylinder to move back to its initial position.

The assembly panel 64 is then moved along by the conveyor into position for the next strap wire to be attached. The strap wire welding cycle is then repeated. The welding and shuttle apparatus on both sides of the assembly panel work simultaneously.

Figures 9 and 10 show respectively side and end views of the completed building panel. Referring to Figures 16 and 17 in another embodiment, the strap and weld machine 67 is identical to that described above except that the strap wire shuttle module is modified. In the embodiment of Figures 16 and 17 the strap wire shuttle module comprises two substantially vertical rodless cylinders 101, on each of which a shuttle is movably mounted. Grippers 102, 106 are provided near the top and bottom respectively of each rodless cylinder 101 and are rotatable around respective vertical axes spaced from the rodless cylinders. A wire cutter 104 is fixed at the top of each rodless cylinders 101. Each shuttle comprises a wire gripper 108. The rodless cylinders 101 are fixed, spaced away from the assembly panel 64 and the rotatable grippers 106, 102 are positioned so that they may rotate between a first position next to the top or bottom respectively of a rodless cylinder 101 and a second position at the top or bottom of the panel assembly. To extend a transverse wire 72 across a side of the assembly panel 64 the wire from the wire delivery system (not shown) at the top of the machine is gripped by the wire grippers 108 on the shuttle. The shuttle then moves down to the base of the rodless cylinder 101 drawing out a length of strap wire 72. The rotatable grippers at the top 106 and bottom 102 of the rodless cylinder then grip the strap wire at the top and bottom respectively. When the wire is gripped between the two rotatable grippers 102, 106, the pneumatic wire cutter 104 at the top of the rodless cylinder 101 cuts the strap wire 72. The rotatable grippers holding the tensioned strap wire 72 then rotate in unison until the strap wire 72 extends substantially vertically across the side of the assembly panel 64. The strap wire is then welded to the truss chord wires according to the method described earlier.

As the shuttle is not involved in gripping the wire during the welding stage, the shuttle can return to the top of the rodless cylinder 101 while the welding is taking place. This increases the speed at which the strap and weld process can be carried out.

Another way in which the speed of the strap and weld process may be increased is by providing two welding stations rather than one as shown in Figure 17. However, this system has the disadvantage that the machine would need a larger power input.

It will be appreciated that the method and apparatus as described above provides an economic and rapid method of forming load bearing building panels from relatively low volume materials in relation to the finished product. The building panels thus formed can be readily erected into walls and roofs of dwellings.

Openings can be easily made in the building panels by cutting the wires and sawing through the foam in order to provide door and window openings. Once erected the panels can be sprayed with concrete or coated with any appropriate local material to make them weatherproof .

Claims

1. Apparatus for manufacturing load bearing building panels comprising means for forming structural foam blocks, means for cutting the foam blocks into strips, means for forming lengths of truss, means for assembling lengths of truss and foam strips together and means for attaching transverse members to the trusses in order to form the loading bearing panels.

2. Apparatus as claimed in claim 1 in which the means of forming the structural foam block comprises an insulated reaction vessel in which the heat to initiate chemical reaction is provided by cooling water from a power source.

3. Apparatus as claimed in claim 2 in which the foam block is cut into strips by any appropriate means.

4. Apparatus as claimed in claim 1 in which the truss is formed by initially bending a wire into a zig-zag shape by means of a plurality of interacting arms which are moved into and out of engagement with a wire.

5. Apparatus for forming a truss by bending a wire into a regular zig-zag shape, the apparatus comprising a plurality of interacting arms which are moved into and out of engagement with the wire, and means for attaching a straight wire to each side of the zig-zag shaped wire at or near to at least some of the peaks of the zig-zag wires.

6. Apparatus as claimed in claims 4 or 5 in which the zig-zag wire is passed to a conveyor and thence to a welding means which also receives two substantially straight wires and the straight wires are welded to the zig-zag wire by the welding means to form a truss.

7. Apparatus as claimed in claim 4, 5, or 6 in which the arms are arranged on two drive means, the wire passes between the two drive means wherein the arms contact a cam surface as they are driven and this forces the arms to move into and out of engagement with the wire.

8. Apparatus as claimed in any of claims 4 to 7 in which the arms are mounted in a pivotal fashion on two chains which are driven around a shaped surface.

9. Apparatus as claimed in any of claims 6 to 8 in which the welding means is a welding head which is driven reciprocally relative to the direction of travel of the conveyor and can operate so that both substantially straight wires are welded simultaneously to at least one respective location on the zig-zag wire whilst the welding head is travelling in the direction of travel of the wire.

10. Apparatus as claimed in claim 9 in which after the welding step has been completed the direction of motion of the welding head is reversed and the welding head locates adjacent the position where the two substantially straight wires are next to be welded to the zig-zag wire.

11. Apparatus as claimed in any of claims 6 to 8 in which the welding means comprises a plurality of roller welding heads .

12. Apparatus as claimed in any of claims 5 to 11 in which the continuous length of truss is cut to any appropriate length.

13. Apparatus as claimed in claim 12 in which lengths of truss are assembled with scrips of foam so that the lengths of truss and foam alternate with one another.

14. Apparatus as claimed in claim 13 in which the trusses and foam strips are positioned relative to one another so that the peaks of the trusses project substantially the same amount from the foam strips on each side of the assembly of strips and girders.

15. Apparatus as claimed in claim 14 in which the lengths of truss are secured together by transverse lengths of wire welded to the truss on each side of the assembly.

16. An apparatus for attaching strapping wires to a panel of alternate layers of foam blocks and wire truss comprising means for gripping, tensioning and positioning each wire to be welded and means for welding the wire to the trusses.

17. An apparatus according to claim 16 in which the means for gripping, tensioning and positioning the wire to be welded comprises a shuttle carrying a wire gripper, the shuttle being moveable up and down to draw the wire through the full^' height of the panel, and at least one set of wire grippers provided at either the top or the bottom of the assembly.

18. An apparatus according to claim 17 in which two sets of wire grippers are provided one at the tope of the panel and one at the bottom of the panel.

19. An apparatus according to any of claims 16 or 18 further comprising means for vertically aligning the trusses for welding.

20. An apparatus according to any of claims 16 to 19 in which the layers of foam and truss are positioned relative to one another so that the peaks of the trusses project substantially the same amount from the foam strips on each side of the assembly of strips and trusses.

21. An apparatus according to claim 13 or 20 in which the trusses and foam scrips are positioned relative to one another by a knocker assembly comprising two sets of equally spaced knockers, positioned on either side of the panel assembly.

22. A method of forming a truss comprising the steps of bending a wire into a zig-zag shape and then attaching a substantially straight wire to each side of the zig-zag shaped wire at or near to at least some of the peaks of the zig-zags.

23. A method according to claim 22 in which the bending step comprises driving a plurality of interacting arms into and out of engagement with the wire.

24. A method according to claims 22 or 23 further comprising the step of passing the zig-zag shaped wire to a conveyor and then attaching the substantially straight wire to the zig-zag wire using a welding head.

25. A method according to claim 24 comprising the steps of driving the welding head reciprocally relative to the direction of travel of the conveyor and welding both substantially straight wires simultaneously to at least one respective location on the zig-zag wire whilst the welding head is travelling.

26. A method according to claim 25 comprising the step, after the welding step, of reversing the direction of motion of the welding head and locating the welding head adjacent the position where the two substantially straight wires are next to be welded to the zig-zag wire.

27. Apparatus as claimed in any of claims 1 to 26 in which the apparatus comprises a self-contained manufacturing unit including a source of electrical energy and a source of compressed air together with a prime mover such as an internal combustion engine.

28. Apparatus for manufacturing load bearing building panels constructed and arranged substantially as herein described and with reference to the accompanying drawings.

29. A method of manufacturing a load bearing building panel substantially as herein described.