It is sometimes desired to perforate tiles of cementitious material such as gypsum, particularly for use as ceiling tiles. It is known from GB-A-2 309 985 to perforate gypsum tiles in a press in which an array of punches on a flat punch plate is moved down onto and through the surface of a gypsum tile. If some of the punches are sufficiently long to penetrate through the tile to form through perforations, they co-operate with a perforate die plate below the tile.

The reciprocating vertical movement of the press requires that the tiles are stationary as they are punched; this is inconvenient in a continuous line for the production of perforated tiles. Thus, it has been desired to provide an apparatus for punching tiles such as tiles of a cementitious material such as gypsum which can punch the tiles as they move past the punch apparatus.

According to a first aspect of the invention there is provided a punch roller comprising a rotatable cylindrical roller and a plurality of punch elements removably located on the roller.

Preferably, the roller comprises: a rotatable cylindrical roller core and a cylindrical roller sleeve removably fixed around the roller core, the plurality of punch elements being removably mounted on the roller sleeve.

Preferably, the punch elements screw into holes in the roller sleeve.

Preferably, the cylindrical roller sleeve is bolted to the roller core.

Preferably, the punch elements each comprise a threaded punch sleeve through which extends a punch having a flattened head to prevent it from passing through the punch sleeve in one direction. The punch elements are screwed into the roller sleeve so that the flattened punch heads bear onto the roller core and are in tight engagement therewith; this prevents the punches moving within the punch sleeve The body of the punches is elongate, and preferably has a saw tooth profile on the face which impinges on the tile and longitudinally corrugated sides; the use of such a punch to perforate gypsum tiles is disclosed in United Kingdom patent application no. 98 07775.3.

The invention also provides, in a second aspect, punch elements for the punch rollers of the first aspect.

In a third aspect, the invention provides a roller punch installation comprising a punch roller according to the first aspect of the invention mounted above a continuous belt of articulated rigid plates. Preferably, a flexible belt overlies the plate belt between the plate belt and the roller.

In the fourth aspect, the invention provides a method of providing punched plasterboard tiles comprising: providing a roller punch installation according to the third aspect of the invention ; rotating the punch roller; supporting plasterboard on the continuous belt or belts; and moving the plasterboard on the belt or belts into the nip between the punch roller and the belt or belts, thereby to punch the plasterboard

In this specification, the word inner'when used with reference to the punch roller or a part of the punch means toward the centre line of the punch, except where the context requires otherwise; the word outer'has the corresponding meaning.

The invention will be further described by way of example with reference to the accompanying drawings in which: Figure 1 shows schematically a punch roller according to a preferred embodiment of the first aspect of the invention including a punch element according to an embodiment of the second aspect of the invention; Figure 2 shows a partial cross section through the sleeve of the punch roller of Figure 1; Figure 3 shows in cross section a punch element of the punch roller of Figure 1; Figure 4 shows a punch roller according to a second preferred embodiment of the first aspect of the invention; Figure 5 shows diagrammatically cross-section through the roller punch shown in Figure 4 along the line V-V of Figure 4; and Figure 6 shows diagrammatically an elevation of an installation incorporating a punch roller according to the first aspect of the invention.

The punch roller 10 shown in Figure 1 comprises a steel roller core 12 having axles 14 at each end and two steel roller sleeves 16,16'surrounding the core 12. For ease of mounting on the core 12, the sleeves 16,16'are split along lines 18,18'. The sleeves 16,16'are removably fixed to the core 12 by bolts; exemplary bolts are shown in Figure 1 at 20, but it will be appreciated that more bolts may be employed.

The roller sleeves 16,16'have a plurality of threaded holes 22 (Figure 2) in them. These holes are in a random

array except that a narrow clear strip 24 (delineated by the imaginary dashed lines in Figure 1) each side of the split lines 18,18'of the sleeves 16,16'is free of holes. Into the holes 22 are screwed punch elements 26 (Figures 1 and 3). Each punch element 26 consists of a cylindrical punch sleeve 28 having a threaded outer surface which co-operates with the threaded holes 22 in the roller sleeves 16,16'. The outer end of the punch sleeve 28 terminates in a head 30 having flats for the application of a wrench. Figure 1 shows fewer punch elements 26 on the roller sleeves 16,16'than will normally be present.

An elongate punch 32 extends through the punch sleeve 28.

The punch 32 has a flattened head 34 at its inner end and is flared at its outer end 36. The head 34 and flare 36 hold the punch 32 loosely in the punch sleeve 28 so that it does not fall out when the punch element 26 is removed from a roller sleeve 16,16'. The punch 32 is not, however held tightly in the punch sleeve 28, and can rotate freely within it when the punch element is not on the roller sleeve.

The cross section of the punches 32 at their outer ends will vary from punch to punch. Preferably, the end faces of the punches have a saw tooth profile 38, and the sides of the punches are corrugated. This design of punch has been found to be particularly effective in penetrating gypsum tiles.

A punch element 26 can be made by drilling a central bore through a stainless steel bolt of appropriate size; the head of the bolt provides the head 30 of the punch element. A steel punch 32, without a flattened head 34, is introduced into the bore from the head end, and the inner end-of the punch flattened to make the flattened head 34.

To prepare the punch roller for use, two roller sleeves 16,16'are bolted onto a roller core 12 by means of bolts 20. As many punch elements 26 as are required are screwed into the threaded holes 22 in each roller sleeves 16,16'.

It is not necessary that all the holes 22 in the roller sleeves 16,16'be occupied by punch elements 26; some may be left empty. Preferably a spring washer is interposed between the punch element head 30 and the roller sleeve 16,16'. The punch elements 26 are screwed hard onto the roller core 12 by means of the head 30 of the punch sleeve 28. The flattened heads 34 of the punches 32 bear hard onto the roller core 12 preventing longitudinal or rotational movement of the punches within the punch sleeves 28. The punch roller 10 is mounted, by means not shown, for rotation over a line along which gypsum tiles are moved.

A one piece roller may be used instead of the separate roller core and roller sleeve of the preferred embodiment.

In this case, the holes receiving the punch elements are blind holes in the roller surface. Their depth is such that the flattened heads 34 of the punches 32 bear firmly on the bottom walls of the holes when the punch elements 26 are firmly screwed into the holes.

In another, preferred embodiment of the invention, shown in Figures 4 and 5, the punch roller 40 consists of a fixed one piece roller section 42 from which extends an axial roller core 44 of the same length as the one piece section 42. There is an axle at each end of the punch roller. A removable roller sleeve 46 similar to one of those shown in Figure 1 is mounted on the core 44 in the same manner as that shown in Figure 1. Both the removable sleeve 46 and the fixed roller section 42 carry punch elements. 48, 48'. The punch elements 48 on the sleeve 46 are mounted in the same way as those shown in Figure 1, in

holes through the sleeve 44. The punch elements 48'on the fixed roller section 42 are mounted in blind holes in the in the circumferential surface of the fixed roller section. In Figure 5, neither the holes nor the punch elements are shown.

In use, the punch roller 10 is rotated at a speed and in a direction such that the punches 32 protruding from its surface move with gypsum tiles carried under the punch roller. The gap between the upper surface of the tiles and the punches 32 is set so that the punches penetrate the desired distance into the tile. Punches of different lengths may be employed if desired to provide holes of different depths in the tile. The punch roller of the present invention is suitable for use with all types of gypsum tiles, including gypsum fibreboard tiles.

After punching with the punch roller of the present invention, the tiles can be subjected to further surface treatment. It is particularly preferred that the tiles be passed under a pin roller to supplement the perforations made by the punch roller with pin holes.

It is preferred that sheets of plasterboard of conventional size are punched by the punch roller of the present invention, rather than individual tiles. Each plasterboard provides eight tiles in a 4 by 2 array; the boards pass under the punch roller so that two tiles are punched at a time. The circumference of the roller sleeve 14 corresponds to the length of one tile; unpunched lands between each tile are left by the clear areas 24 of the roller sleeve surface. Lands between the pairs of adjacent tiles on the board are left by the space between the two sleeves 16,16'on the roller core 12. The punched plaster board is passed under a pin roller and cut into eight tiles.

The pattern of holes made in the tiles is determined by the location of the holes 22 in the roller sleeves 16, 16', 42,44 which are occupied by punch elements 26,48, 48'and the orientation of the punches 32 within the punch elements.

The array of holes 22 in the surface of the preferred punch rollers described is random, to facilitate the provision of a random pattern on the tiles. If a regular pattern is required, the holes 22 may be in a regular array.

The punch roller of the present invention allows the continuous punching of gypsum tiles without the need for the tiles to be stationary during the punching process.

It also allows the location and orientation of punches to be varied easily; punches can be removed from and introduced into the roller sleeve readily, and a punch can be rotated in its punch sleeve by loosening the punch sleeve in the roller, rotating the punch and retightening the punch sleeve in the roller. Thus, the pattern given to tiles by the punch rollers of the invention can be readily varied. When one 46 or two 16,16'removable roller sleeves are employed, rather than a single fixed roller, one or both of the sleeves can be removed and replaced by another carrying a different pattern of holes 22. Thus, if the desired pattern cannot be achieved with a particular sleeve, it is a simple matter to replace it with another sleeve having a different disposition of holes in it. The spacing between the two sleeves 16,16' of the roller punch 10 shown in Figure 1 or between the sleeve 46 and fixed roller section 42 of the roller punch 40 shown in Figure 4 can be adjusted to allow the punching of a range of widths of plasterboard. Punched tiles will usually be made by punching plasterboards to form in 2 X 4 array of tiles; the punch roller is long enough to punch two tiles across the width of the board, and the

circumference of the roller punch is the length of a tile.

In the cores of the punch rollers 10,40 shown in figures 1 and 6, the lateral spacing between pairs of tiles can be changed by changing the spacing between the two roller sleeves 16,16'or the sleeve 46 and the fixed roller section 42. The longitudinal spacing between tiles can be varied by accelerating the rotation of the roller punch.

If a one piece roller is used, the roller can be replaced to change the pattern of holes in the roller surface or the length of the roller (and thus the width of the plasterboard on which the punch can be employed), or both.

A further significant advantage of punch rollers of the invention is that a particular pattern of punches can be precisely specified so that identical tiles can be produced on different punch rollers, possibly at different sites. Each punch roller can have an identical roller sleeve, having the same array of holes through it, and the shape, length and orientation within the punch sleeve of the punch used in each hole can be specified.

Figure 6 shows diagrammatically a preferred roller punch installation incorporating a punch roller 50 according to the invention; the punch roller 50 may be as shown in Figures 1 or 4 or it may be a one piece roller punch, and carries punch elements, (not shown).

The punch roller 50 is mounted over a continuous plate belt 52 made up of articulated metal plates 54 (only a part of the upper run of the plate belt 52 is shown). A continuous fabric belt 56 overlies (on the upper run) the plate belt 52 and the punch roller 50 (only a part of the upper run of the fabric belt 56 is shown). The spacing between the punch roller 50 and the fabric belt 56 on the plate belt 52 at the nip therebetween is the thickness of the plasterboard to be punched; this spacing is adjusted

to accommodate a range of thicknesses of plasterboard, conveniently by vertical movement of the roller punch 50.

In use, plasterboard 58 is carried in the direction of the arrow A in Figure 6 by the belts 52,56 into the nip between the punch roller 50 and the belts. The roller punch rotates in the direction shown by the arrow B in Figure 6; the circumferential speed of the roller punch is the same as that of the plasterboard. In the nip, the punches on the punch roller penetrate the plasterboard to punch the desired pattern therein. The metal plates 54 of the plate belt adequately support the plasterboard 58 as it is punched by the punch roller 50. Preferably, the plate belt 52 travels slightly faster, by about 2% than the fabric belt 56 ; this ensures that the plasterboard is drawn through the nip between the punch roller and the belts.

The invention thus provides a method and apparatus for punching plasterboard tiles which allows the pattern of holes in the tile to be replicated readily and to be changed readily.