GB2279293A - Construction boards containing mineral fibre lamellae - Google Patents

Abstract

Mineral fibre lamellae (22) are arranged edge-to-edge in a long series to form a construction board (26a, b, c). The lamellae (22) are angled non-perpendicularly to the longitudinal direction of the series. A construction panel is made by sandwiching a set of such boards (26a, b, c) between stiff outer layers (27), typically of metal. The inclination directions of the lamellae (22) alternate from one board to the next, to reduce lines of potential weakness. The series of angled lamellae may be assembled by conveying a series of mineral fibre lamellae in a conveying direction with the lamellae aligned transversely but non-perpendicularly relative to the conveying direction, compressing the lamellae edge to edge by transition from a faster conveyor to a slower conveyor and applying a retaining layer such as open mesh fabric or net to one or both surfaces of the edge to edge compressed lamellae. <IMAGE>

Description

MINERAL FIBRE BOARDS, COMPOSITE PANELS AND METHODS OF MAKING THEM This specification relates to the manufacture of boards comprising mineral fibre lamellae, and composite panels in which such boards are held between stiff outer layers.

The use of mineral fibre (in particular, rock wool and glass wool) as a basis material in constructional panels is well known. Mineral fibre materials have good thermal and acoustic insulation properties and a long lifetime. There are however difficulties in making panels and boards of high structural integrity, owing to the nature of the basic fibre material. It is made as an elongate slab in which the fibres extend predominantly longitudinally (in the machine direction), fixed to one another by a binder. If the slab is simply laid between outer metal layers, the resulting panel has inadequate integrity out-of-plane because the mineral fibres are easily pulled apart.

It has therefore become common to use "lamellae", elongate strips of mineral fibre material obtained by slicing the basic strip transversely. Lamellae can be laid edge-to-edge in an array with the exposed fibre ends at the face of the array, giving the desired out-of-plane integrity. There are drawbacks. Many lamellae are needed, because the thickness and width of the available basic mineral fibre material are limited. Consequently any panel of substantial size has a large number of lamellae, a large number of boundaries between lamellae and a large number of positions of potential structural weakness. The inter-lamella joins represent regions of potential stress concentration where the panels typically fail by buckling of the stiff outer plates, especially along the minor axis of a rectangular panel.

Furthermore, the fibres of the basic slab material pull apart more easily in the thickness direction than in the width direction of the material. This makes lamellae appreciably more vulnerable to being pulled apart in the minor axis direction of the lamella than in the major axis direction, i.e. they are liable to internal failure along their lengths.

This invention is concerned with novel dispositions of lamellae in a mineral fibre board, typically used between outer layers to make a panel.

In one aspect of our invention, a mineral fibre board has a series of elongate mineral fibre lamellae held together edge-to-edge to form an array which has side edges generally longer than the lamellae, and in which the lamellae extend transversely from one side edge to the other, non-perpendicularly to the side edges.

In this way, the interfaces between adjacent lamellae can be angled to forces arising along the primary directions of the panel in use, and such forces can resolve along the angled interfaces to the perimeter of the construction in a manner less likely to cause buckling.

Furthermore, the "angling" of the lamellae takes the direction of greatest weakness within the lamella material out of coincidence with the primary panel/board directions, which are the directions most likely to be associated with buckling forces.

Normally, the two side edges of the board will be parallel, and in particular the board will usually be rectangular, particularly an elongate rectangle.

The angle made by the lamellae with the side edges is to some extent a matter of choice and may depend on the end use of the product, but typically will be not more than 850, e.g. less than 800. Conversely it will typically be at least 45 , usually at least 55 , e.g. at least 650.

Preferably the lamellae are held together in the array by one or more retaining layers, secured e.g. by adhesion over one or both faces of the array.

It is also particularly preferred that the lamellae be compressed together edge-to-edge in the array.

In a further aspect of the invention we provide a panel which comprises a plurality of mineral fibre boards, as described above, arranged side-by-side between outer layers.

Preferably the panel is rectangular and the boards are elongate rectangles longitudinally aligned with the long dimension of the panel.

The outer layers are usually metal, but any other suitable material may be selected according to the prevailing knowledge of the skilled man.

Since the lamellae are inclined to the sides of the boards, they will be angled in the panel to the joint lines between adjacent boards. It is particularly preferred, and simple to arrange with the present invention, that the lamellae of adjacent boards are not parallel across the join line. In particular, it is preferred that they be inclined in the same direction relative to the join line e.g. so as to form a "herringbone" or chevron" pattern. Such a construction avoids coincidences of the directions of lamella-lamella joint lines, or of directions of relative weakness within lamellae, for adjacent boards across the panel. Such coincidences would potentially create a line of weakness across a larger part of the panel.

A rectangular panel typically buckles along its minor axis. The angled lamellae have their own structural weakness as well as their joint directions moved out of coincidence with this primary buckling direction. Where the boards are elongate rectangles longitudinally aligned with the long dimension of the panel, the presence of the longitudinal inter-board joints is not a problem since the failure does not occur along the major axis of a rectangle.

In a further aspect of the invention, we provide a method of making a mineral fibre board which comprises arranging a plurality of mineral fibre lamellae edge-to edge in a series and fastening them together in an elongate array, in which the lamellae extend from side-toside of the array non-perpendicularly. A corresponding further aspect provides a method of making a panel in which outer layers are fixed to the faces of such a board.

The present construction has significant advantages from the process point of view, in that it is simple to make. Earlier proposals involving the staggering of lamellae have involved complications in positioning the lamellae in the array. In most cases, this has had to be done manually.

While the present construction can be made manually, it is particularly well adapted to a continuous manufacturing method in which the successive lamellae are conveyed sequentially and fixed together into the array on a conveyor line, the lamellae being positioned on the conveyor line non-perpendicularly relative to the conveying direction to create the characteristic feature of our new concept.

The conveyor line is preferably used for compressing the lamellae edge-to-edge, as well as for the fastening together of the lamellae which is preferably by the adhering of one or more facing layers.

Our own EP-A-449414 describes a continuous process of relevant type, and the method disclosed in that document is preferred for the present concept. That is, the lamellae are desirably compressed edge-to-edge on the conveyor line by a transition from a faster conveyor to a slower conveyor. The angling of the lamellae relative to the conveying direction can be achieved by placing each lamella on the conveying line at an appropriate angle, or by aligning them suitably once they are on the conveyor.

Typically this will produce an array with serrated edges formed by the squared ends of successive lamellae.

The method may therefore further comprise straightening the edges by trimming. In some circumstances, particularly if the lamellae are angled at 450, the serrations may be retained for interlock purposes.

By using this continuous process, the array can be made to any desired length. In particular, it can be made to match the length of a desired finished panel. This reduces the number of inter-board joining lines and hence reduces the extent of potential weakness.

Embodiments of the invention are now described by way of example, with reference to the accompanying drawings in which: Figure 1 shows a typical use of lamellae; Figure 2 shows a disposition of lamellae in a known type of panel; Figure 3 shows the disposition of lamellae in a board embodying the invention; Figure 4 shows a board embodying the invention; Figure 5 shows the disposition of lamellae in a panel embodying the invention, and Figure 6 shows a process embodying the invention for making a mineral fibre board.

Firstly, Fig. 1 shows conventional steps for making a panel using lamellae. An elongate slab 1 of binder-fixed mineral fibre, typically rock wool, has fibres running predominantly in its longitudinal direction. An elongate transverse slice or lamella 2 is cut from its end, and turned 90" so that the cut fibre ends face up and down. A number of the lamellae 2 are arranged in series to form an array 3 (Fig. l(b)) in which they are butted together, long edge to long edge, with the prevailing fibre direction pointing out of the major faces of the array 3.

Usually, the array 3 is compressed in the longitudinal direction as indicated by the arrows A.

A retaining sheet 5, typically an open-weave fabric or net, is then adhered or fused to both the major faces of the array 3. The array 3 can then be handled as an integrated product, a mineral fibre board 6.

To make a constructional panel, the mineral fibre board 6 is sandwiched between two outer layers 7, typically metal layers, and the layers are stuck on to form an integrated panel. The number of fibre boards 6 needed to make the panel will depend on the size of the panel. The width of the boards 6 is limited by the available width of mineral fibre material 1. At present, the maximum width available is only about 1200mm, and so most panels need to use more than one board.

Fig. 2 shows a layout of two boards 6a, 6b arranged side by side in a rectangular panel. The primary direction of buckling failure in a rectangular panel is normally across the minor axis of the panel. The joints 17 between adjacent lamellae within a board are relatively weak and stress concentrates at them. Also, the lamellae themselves are most weak in-plane across that same direction. Since the joints 17 and lamellae of the adjacent boards 6a, 6b all run in the same direction, along the minor axis, there is a serious vulnerability to failure of the panel.

Although this problem has been appreciated in the past, the proposed solutions involve staggering of the lamellae e.g. in "brickbond" type patterns, and are very difficult to make.

Figure 3 shows a layout according to our new concept.

A mineral fibre board comprises a plurality of mineral fibre lamellae 22 extending in a straight series which is elongate in the direction indicated by arrow B. The lamellae 22 are positioned with their elongate edges butted together, as previously. The difference is that the longitudinal direction of each lamella 22 is inclined or canted to the principal direction B of the series, and likewise to the direction of its two long sides 23,24, by an angle Ú.

Figure 4 shows a mineral fibre board 26 made by cutting a rectangular section of the construction shown in Fig. 3, and facing it on both its major faces with a retaining layer 25. A suitable retaining layer is an open-mesh fabric or net as has been used conventionally.

However other material may be used if appropriate. The long sides of the board 26 are trimmed, to smooth down the serrations seen in Fig. 3 and which result from the basic rectangular shape of the lamellae 22.

Figure 5 shows how three such boards 26a, 26b, 26c may be arranged in a rectangular panel in which the boards 26 are sandwiched between two outer layers 27 - usually metal sheets e.g. of aluminium - which are stuck to the major surfaces of the boards in a manner known per se.

Fig. 5(a) shows the lamella layout as though one of the outer layers 27 were not present. It will be seen that in each of the boards 26, the lamellae are inclined to the primary axes of the panel itself, as a natural consequence of being inclined to the primary rectangular axes of the boards 26. The inclinations of the boards are alternated, so that two boards 26a, 26c whose lamellae are inclined in the same direction are separated by a board 26b whose lamellae are inclined in the opposite direction. That is, the lamellae of the middle board 26b form a chevron or herringbone pattern with the lamellae of the adjacent board on either side. Alternatively stated, from the point of view of the butt-joint lines 36 between two boards 26, the lamellae of the two boards adjacent a given joint line are inclined in the same direction away from perpendicularity to that joint line 36.

This has an important structural consequence. The most common practical cause of panel failure is the existence of forces tending to bend the panel (e.g.

perpendicular to the plane of Fig. 5), resulting in buckling across the short direction of the rectangle.

Buckling across that short axis is also the typical failure mode when compressive forces are applied in the plane of the panel. In the present panel, all the lamellae 22 and their joint lines are inclined at the angle Ú relative to the primary buckling direction i.e.

the primary weaknesses of the mineral fibre "core" are not aligned with the primary buckling tendency. Rather, loads otherwise tending to cause failure can be resolved along the rather stronger lengthwise direction of the lamellae.

Furthermore, because the lamellae of adjacent boards are inclined in different directions, "alternative" primary failure lines, oblique to the minor axis of the rectangle, are not created.

Figure 6 shows a process by which the mineral fibre boards may advantageously be made. For further background, reference should also be made to our earlier European patent application EP-A-449414.

A production line, shown in plan view in Figs. 6(a) and side view in Fig. 6(b), comprises sequentially an introductory conveyor 30, a first gripping conveyor 40, a second gripping conveyor 50; a retaining layer application station 55, a heating conveyor 60, a cooling conveyor 65 and a trimming station 70.

The production line and its conveyors are linear, in a direction B'.

Mineral fibre lamellae 22 are placed sequentially on the conveyor, loosely adjacent one another and with their fibre direction pointing perpendicularly to the conveyor direction, with their respective axes of elongation forming an angle Ú with the horizontal perpendicular to the conveying direction B'. The first gripping conveyor 40 grips the series of angled lamellae 22 and imposes on them a certain conveying speed. The second gripping conveyor 50 is travelling more slowly than the first one, so that the lamellae 22 are compressed together at the compression transition 45 between them. Retaining plates 46 are provided, to prevent the lamellae buckling out of line as they are compressed longitudinally i.e. in the direction B'. The compression thrust is taken up between the first and second gripping conveyors 40,50.The compressed series of lamellae then passes to the retaining layer application station 55. This has supply rolls of a suitable retaining layer material, typically an open-weave fabric, and means for sticking the open-weave fabric 56 to the surface of the lamella array. A preferred means is a fusible web adhesive 57, also fed from a roll supply between the glass cloth and the lamella array surface. An integral heat fusible net is also suitable. The compressed lamella array, with both its surfaces covered with the retaining layer 56 and the means for adhering it, then passes through a heating conveyor 60 which applied heat from heaters 61 e.g. infrared heaters, and fuses the adhesive 57 so that the retaining layer 56 is stuck to the surface of the lamella array. The array then passes through a cooling conveyor 65 which keeps it in shape and compression while the adhesive sets.

The side edges of the continuously-formed product are serrated. It is therefore passed through a trimming station 70 at which opposed cutters 71 of any suitable type act to trim and straighten the serrated edges.

The resulting continuous product is extremely convenient, since it can be cut to any desired length in the direction B' according to the size and shape of the panel to be made. Furthermore it eliminates the painstaking manual alignment of lamellae which has been previously necessary in staggered lamella lay-ups.

The mineral fibre material, retaining layer material, adhesives, adhesion methods and outer layer materials for the panels may all be of types already known by the skilled person in this field, taking into account our above-mentioned European patent application.

More specifically, the mineral fibre material will usually be a resin-bonded glass or rock fibre material having a typical density range of 30 to 200kg/m3.

The size of the lamellae will typically vary between 400 and 1200mm long, 50 and 200mm wide (across the cut face) and between 10 and 300mm thick (in the fibre direction).

The angle U will usually be between 50 and 450, more usually between 10 and 400. Where the board is produced by the continuous process, the lower angles are preferred because they are more stable under compression on the production line. For example, a range of 50 to 350 might be used. However the choice of angle may also take into account the end use, as mentioned above.

Claims (13)

CLAIMS:

1. A construction board comprising a series of mineral fibre lamellae arranged edge-to-edge, the series having parallel side edges defining a longitudinal direction thereof and the lamellae extending non-perpendicularly across the longitudinal direction.

2. A construction board according to claim 1 in which each lamellae extends from one side edge to the other.

3. A construction board according to claim 1 or claim 2 in which the lamellae are angled at from 450 to 850 to the longitudinal direction.

4. A construction board according to claim 3 in which the lamellae are angled at more than 650 to the longitudinal direction.

5. A construction board according to any one of the preceding claims in which a permeable retaining layer is secured over one or both major facets of the series of lamellae to hold it together.

6. A construction board according to any one of the preceding claims in which the lamellae are compressed together edge-to-edge.

7. A construction panel comprising at least one construction board according to any one of claims 1 to 6 sandwiched between stiff outer layers.

8. A construction panel according to claim 7 in which the outer layers are metal layers.

9. A construction panel according to claim 7 or claim 8 which is rectangular, and the longitudinal direction of the or each construction board is aligned with the long dimension of the rectangle.

10. A construction panel according to any one of claims 7 to 9 in which plural construction boards are arranged side edge to side edge, with the lamellae of adjacent construction boards being aligned in opposite senses relative to their longitudinal direction.

11. A method of making a construction board, comprising conveying a series of mineral fibre lamellae in a conveying direction, with the lamellae aligned transversely but non-perpendicularly relative to the conveying direction; compressing the lamellae edge-to-edge in the conveying direction, by transition from a faster conveyor to a slower conveyor; and applying a retaining layer to one or both surfaces of the edge-to-edge compressed lamellae, to retain them in the compressed state.

12. A method according to claim 11, comprising straightening uneven edges of the resulting compressed series of lamellae by trimming.

13. A construction board, construction panel or method of making either of these, substantially as any described herein with reference to the accompanying drawings.