WO2011020146A1

WO2011020146A1 - Profiled plasterboard

Info

Publication number: WO2011020146A1
Application number: PCT/AU2010/001055
Authority: WO
Inventors: Dragan Haris; Stipo Kasalo
Original assignee: Dragan Haris; Stipo Kasalo
Priority date: 2009-08-20
Filing date: 2010-08-19
Publication date: 2011-02-24

Abstract

Apparatus for manufacturing plasterboard comprises a forming station in which a slurry of gypsum is spread over a paper layer, a back cover is placed over the slurry, the forming station including means to form the side edges of a continuous length of plasterboard; a conveyor to transfer the continuous length of plasterboard to a cutting station where the plasterboard is cut into elongate sheets; the cut sheets then being transferred to a drying station characterised in that a forming tool is positioned either just before or just after the cutting station to form an indentation across the sheet of plasterboard at predetermined spacing along the length of the plasterboard.

Description

PROFILED PLASTERBOARD Field of the Invention This invention relates to plasterboard and in particular relates to applying a profile to the transverse edges of plasterboard.

Background

The building industry uses both plasterboard, sometimes known as gypsum board, and fibre cement products for internal and external applications. Plasterboard is easier to use and cheaper than fibre cement but is less water resistant in wet areas such as bathrooms, laundries, toilets, kitchens and eaves. Both products are used on a variety of internal and external walls for both domestic and industrial uses . Plasterboard is usually manufactured by spreading a slurry of gypsum, water and other additives over a front paper sheet and then applying a back paper cover to provide a continuous length of a sandwich of slurry and paper.

Suitable formers are typically positioned along the side of this continuous sheet and these formers can be profiled to ensure that the side edges have a desired edge profile, such as a tapered edge.

The slurry is passed over a forming belt and then allowed to set from where it is transferred by rollers to a cutting station in which the continuous board is cut into sheets, these sheets are then sent to a drying zone in which the sheets are usually dried in a stacker. The cutting process cuts a sharp rectangular leading and trailing edge on each sheet.

When two such sheets are hung in a building adjacent to each other it is desirable to place two tapered side edges against one another. A rebate is formed by the two tapered edges on the front side of the sheets. A filler is applied into the rebate to provide a smooth

aesthetically pleasing joint between the sheets prior to painting.

If the trailing and leading edge of two sheets are hung adjacent to each other, then the gap between the two sharp rectangular edges must be filled. This is a difficult process, as the filler has a tendency not to easily adhere to the edges of the sheets. Furthermore, if a tape is applied over the joint it will tend to sit proud of front faces of the sheets and prevent a smooth joint being created.

It is this issue that has brought about the present invention .

Summary of the Invention

According to one aspect of the invention, there is provided a method of manufacturing plasterboard

comprising :

spreading a gypsum slurry over a paper layer, applying a back cover and forming the side edges of a continuous length of plasterboard,

passing the length of plasterboard to a cutting station to cut the plasterboard into sheets, and then transferring the cut sheets to a drier,

wherein the method includes the step of pressing a lateral strip of the plasterboard to form an indentation and cutting the board at the indentation.

The board may be cut before the indentation is made and then pressed along the cut. Alternatively, the cut can be made after the indentation is formed. Preferably, the pressing step is carried out using a tool which has an elongate pressing face with longitudinal tapered edges and a plurality of projections extend from the pressing face for piercing the paper layer. The pressing face may be flat or curved, wherein the curve runs laterally across the face.

In a preferred embodiment the tool is driven by a

hydraulic ram into contact with the plasterboard.

In another embodiment the tool rotates about an axis. The speed of rotation of the tool corresponds with a speed at which the plasterboard is fed past the tool, such that the rotation presses the tool into the board to form the indentation.

In another embodiment, the plurality of projections take the form of an array of V-shaped peaks extending

longitudinally along the tool.

The projections may also take the form of a plurality of teeth in the form of cones, domes or pyramids. The invention also relates to the plasterboard sheets which result from the above method.

According to a further aspect of the invention there is provided Apparatus for manufacturing plasterboard

comprises a forming station in which a slurry of gypsum is spread over a paper layer, a back cover is placed over the slurry, the forming station including means to form the side edges of a continuous length of plasterboard; a conveyor to transfer the continuous length of plasterboard to a cutting station where the plasterboard is cut into elongate sheets; the cut sheets then being transferred to a drying station characterised in that a forming tool is positioned either just before or just after the cutting station to form an indentation across the sheet of plasterboard at predetermined spacing along the length of the plasterboard.

Brief Description of the Drawings

In order that the invention may be more easily understood, embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an overview of part of a process of

manufacturing plasterboard according to a first embodiment of the invention;

Figure 2 is a side view of a first embodiment of a pressing station;

Figure 3a is an isometric view of a pressing tool in the first embodiment of the pressing station; Figure 3b is a side view of the pressing tool of Figure

3 3aa;:

Figure 4 is a side view of a second embodiment of a pressing station;

Figure 5 is an overview of a second embodiment of part of a process of manufacturing plasterboard; Figure 6 is an isometric view of part of a rebate in a plaster sheet made in accordance with the process of the first embodiment or second embodiment; and

Figure 7 is an alternative pressing tool to that

illustrated in Figure 3.

Description of the Preferred Embodiments

A first embodiment of a method for manufacturing

plasterboard is shown in Figure 1, which specifically shows an overview of part of the process.

Not shown in Figure 1 is the part of the process prior to entering the process of Figure 1 where a continuous length of plasterboard is formed by spreading a slurry of gypsum over a front paper layer then applying a back paper layer to the gypsum. Forming tools at the side edges 2 of the plasterboard 1 create a side edge profile along the continuous length of the board.

The continuous length of plasterboard 1 enters the part of the process shown m Figure 1 and is conveyed on conveyor 300 from the left side of the Figure to the right side, in the direction of the arrows .

In the process shown in Figure 1, a strip of the

plasterboard 1 is pressed across its width at a pressing station 100 so as to form a lateral indentation (not shown in Figure 1) in the board 1. The indentation formed along the pressed lateral strip of plasterboard is made in the front face of the board, which faces down onto the rollers of the conveyor 300.

The plasterboard then passes along the conveyor 300 to a cutting station 200 where the board 1 is cut into sheets 3. Each cut is made along the centre of one of the indentations. Each indentation is thus divided down its centre so that one half of the indentation becomes a rebate 70 in the trailing edge 4 of a sheet 3 while the other half of the indentation becomes a rebate 70 in the leading edge 6 of the adjacent sheet.

When two sheets 3 are later hung in a building the rebates at the leading and trailing edges of two sheets can be placed adjacent to one another to form a complete rebate from the front surface 9 of the sheets. A tape can then be applied over the gap between the sheets 3 and a filler added to the rebates 70 to make level the indentation, or depression, with the surface of the sheets and thereby form an aesthetically pleasing and durable joint between the sheets 3.

Once the sheets 3 are cut, they continue to travel on the conveyor 300 to a drier (not shown) where the sheets 3 are dried. In this first embodiment, the pressing station 100 has a reciprocating configuration. This configuration is shown in Figure 2, which shows a side view of the pressing station 100. The plasterboard 1 passes through the station 100 in the direction shown by arrow D. The board 1 is supported on the conveyer 300. The front 9 of the board 1 faces downwards toward the conveyor 300, whereas the back 8 of the board faced upwards . The gypsum slurry 7 at this stage is not yet dry, allowing it to be pressed at pressing station 100.

A pressing tool 22 is located in a gap in the conveyer 300. The tool 22 is a block, which in this embodiment is made of tool steel. It is 1500mm long and extends across the full width of the plasterboard 1. The tool is 90mm wide and each longitudinal edge of the tool has a taper 24. The dimensions of the tool 22 will vary according to the size of the plasterboard and the desired indentation size. On the front face 26 of the tool 22 are rows of conical teeth 28. Figures 3a and 3b show tool 22 in greater detail .

Turning back to Figure 2, on the opposite side of the board 1 to the tool 22 is a skid plate 30 which supports the board 1 while it is being pressed. In the preferred embodiment, the skid plate is also made from steel. The front 32 of the skid plate is smooth and its corners 34 rounded. The skid plate 30 is fixed on a frame (not shown) to the conveyor 300. The skid plate 30 supports the bottom of the board 8, providing a reactive force as pressure is applied by the tool 22. The tool 22 is coupled to a rod 36 which is driven by a hydraulic ram (not shown) . The hydraulic ram drives the tool 22 in the direction indicated by arrow T. The tool is driven upwards into the board 1 by the hydraulic ram. As the gypsum 7 has not yet been dried, the tool leaves an indentation in the front 9 of the board 1. The tool 22 is driven into the board 1 to the depth of the tapers 24 so as to form an indentation.

The teeth 28 on the front face 26 of the tool 22 pierce the front 9 paper sheet and create conical holes m the gypsum 7. When filler is later applied to the finished sheet 3 these holes will allow the filler to "key" into, and bond to, the sheet.

The holes also press the front paper sheet into the gypsum bonding the sheet to the gypsum 7 and reducing the likelihood that the sheet will delaminate from the gypsum layer. Delamination can occur during the drying stage or later on when the sheet is in use. The holes also provide some flexibility to the sheet to stretch in response to the force applied to the tool and present areas of tension developing in the sheet which may also cause delamination.

During the indentation process the plaster board moves in direction D. The tool 22 is free to move in the same direction as the plasterboard. The freedom of the tool 22 to move in direction D allows the board 1 to continue advancing without the need to stop each time an

indentation is to be formed. As the tool 22 engages the board 1, the board pulls the tool 22 in direction D. After the indention has been made the tool 22 is pulled downwards away from the board 1 by the ram. A spring (not shown) biases the tool 22 back into the position shown in Figure 1, ready to make a further indentation in the board 1.

The timing of each indentation depends on the length of final sheet 3 required. For example if a 3 metre sheet is needed, the tool will be driven into the board once every 3 metres of board as it passes the station 100. An optical sensor 3 metres downstream of the pressing station 100 detects the previous indention and activates the hydraulic ram.

Figure 4 shows a second embodiment of a pressing station 400. This station 400 has four tools 50. The tools 50 are fixed at equal spacing around a rotating cylinder 52 that extends across the width of the plasterboard. The tools 50, too, extend the width of the plasterboard and namely extend laterally across the conveyor 300. A skid plate 51 is fixed on the opposite side of the board 1 to the cylinder 52. Unlike the reciprocating configuration discussed above, this station 100 does not require a hydraulic ram but rather operates by driving the cylinder to rotate .

The cylinder 52 may be driven by a servo motor at a specific speed which corresponds to the speed at which the plasterboard 1 is fed through the station 400 on conveyor 300. A sensor may be used to measure the speed at which the board is moving and accurately synchronises the rotation of the cylinder 52. Alternatively, the cylinder 52 may be mechanically coupled to the conveyor 300, for example by a chain drive. This would ensure that the speed of the cylinder 52 and the speed of the board 1 correspond to one another.

The tools 50 in station 400 have a rounded front face 54. Due to the rotating action of the tool on the cylinder 52 the rounded face will impart a flat rebate on the board 1.

Like the earlier embodiment, the tools 50 have tapered edges 56 and conical projections 58. The tapered edges provide the depth for the indentation while the conical teeth 58 bite into the front face 9 and gypsum 7 to allow for better bonding of the filler when joining two adjacent sheets .

Despite the tool 50 being a different shape to the reciprocating tool 22 the rotating motion of the tool applies the same indentation profile. The cylinder 52 drives the tools 50 into the board 1, as it passes, to the depth of the tapers 56.

There are two possible methods for driving the cylinder 52. The first is to us a chair to drive the cylinder 52 continuously at the same speed as the moving conveyor. Using this method, the distance between the indentations (and ultimately the length of the sheets) will be set by the distance between the various tools 50 on the cylinder 52. For example, the cylinder may only have one tool 50. If the circumference of the path on which the tool travels in 3 metres, then the indentations will be 3 metres apart. This method could be used with the chain drive discussed above .

Alternatively, the cylinder 52 may stop rotating after each indentation, allowing the board 1 to continue passing through the station 100. Once an optical sensor, or other detection device, detects that the board has moved a predetermined distance the cylinder 52 would again be driven. This method could be used with the servo motor configuration.

The continuous rotation option requires a less complex control system, but a different cylinder and tool

configuration would be needed for each sheet length. If, on the other hand, the option is used of stopping the cylinder after each indentation then the same cylinder 52 and tool configuration can be used to create several different sheet lengths. As discussed above, the cutting station 200 may be either upstream or downstream of the pressing station 100.

Figure 1 shows a configuration in which the pressing station 100 is upstream. Figure 5 shows the alternative downstream configuration.

In the downstream configuration the board 1 is cut into sheets 3 at the cutting station 100 then flipped at a flipping station 500. The indentation is then made at a pressing station 100. In this embodiment the tool 22, 50 is located above the board 1, while the skid plate 30, 51 is located in a gap in the conveyor 300. Where an existing plasterboard plant is to be modified to introduce the pressing station 100 it may more expedient to use the upstream configuration in some instances, while the downstream configuration may be more expedient in others.

By applying any of the methods described above the trailing 4 and leading edges 6 of each sheet 3 have a complementary rebate 70. The profile of this rebate is shown in Figure 6.

The rebate includes a flat face 72 offset from the front 9 of the sheet 3. The offset face 72 is pierced with a plurality of holes 74. A taper face 76 leads from this offset face 72 to the front face 9 of the sheet 3.

In use, when the trailing or leading edges of two such sheets 3 are hung adjacent to one another, for example on a wall, the two adjacent rebates 70 form a complete rebate with a flat face and two tapered faces on either side of the flat face leading to the front surface of the sheets. The complete rebate can be easily filled to provide a smooth, aesthetically pleasing and durable joint. Filler is applied to the complete rebate using a flat blade or trowel to level the filler with the front face 9. The filler bonds to the taper faces 76, offset faces 72 and holes 74 in the rebates 70.

It is understood that a range of pressing tools could be used with the method of the present invention to form a range of different rebate shapes. Furthermore, the teeth on the tool may also take the form of any suitable piercing protrusion. For example, the teeth 28 could take the form of three or four sided pyramids or rounded domes. Alternatively, the tool may have no teeth at all, leaving the offset face 72 smooth and flat.

The depth of the rebate 70 will depend on the thickness of the sheet 3 and filler which is to be used. For example a 13mm sheet may have a rebate depth of 2.5mm. Thicker sheets may have deeper rebates. The rebate depth could vary from about 2mm to about 6mm. The tool could also have an array of longitudinal V-shaped peaks, rather than teeth, to perforate the offset face 72. Figure 7 shows such a tool 70. The lines of grooves created by this tool has corresponding V-shaped troughs into which the filler can flow and bond to the plaster sheet. Like the toothed tool described above tool 70 has tapers 74 extending along other side to form a

corresponding taper in the rebate in the sheet. Similar V-shaped peaks could be used on a rotating tool.

The sheets 3 that result from the method of manufacturing plasterboard have several advantages over known sheets . Particularly, the gaps between sheets can be filled more guickly and easily, the bond formed between the sheets is robust and the hung sheets provide a superior finish to the final plaster wall. The front sheet is also less likely to delaminate from the gypsum at the trailing and leading edge, as the teeth in the tool assist in fixing the sheet more firmly to the gypsum.

Plasterers who use known sheets typically buy particularly long sheets to reduce the number of joins reguired in a given room. Joins are generally minimised due to the disadvantages experienced when filling between sharp rectangular trailing and lead edges.

However, by using sheets provided by the described method shorter sheets can be used, as the joining process is easier and faster. Short sheets reduce handling and transport costs for the manufacturer, supplier and plaster . It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

Claims

1. Apparatus for manufacturing plasterboard comprises a forming station in which a slurry of gypsum is spread over a paper layer, a back cover is placed over the slurry, the forming station including means to form the side edges of a continuous length of

plasterboard; a conveyor to transfer the continuous length of plasterboard to a cutting station where the plasterboard is cut into elongate sheets; the cut sheets then being transferred to a drying station characterised in that a forming tool is positioned either just before or just after the cutting station to form an indentation across the sheet of

plasterboard at predetermined spacing along the length of the plasterboard.

2. The apparatus according to claim 1 wherein the

forming tool is positioned immediately before the cutting station and at the cutting station the plasterboard is cut into lengths by cutting along the centre line of the formed indentation.

3. The apparatus according to claim 1 wherein the

forming tool is positioned immediately behind the cutting station and the indentation is formed on the cut edge of each sheet.

4. The apparatus according to any one of the preceding claims wherein the following tool is elongate to be longer than the width of the plasterboard and the tool has tapered longitudinal edges .

5. The cutting tool according to any one of the

preceding claims wherein the forming tool has a plurality of projections on one face that in use are forced into the surface of the plasterboard when the indentation is formed.

6. The apparatus according to claim 5 wherein the

projections are in the form of rows of conical, pyramid or rounded dome shaped teeth.

7. The apparatus according to claim 5 wherein the

projections are in the form of lines of V shaped peaks and troughs .

8. The apparatus according to any one of the preceding claims wherein a back plate is positioned behind the plasterboard sheet opposite the forming tool.

9. The apparatus according to any one of the preceding claims wherein a ram drives the forming tool into reciprocal engagement with the plasterboard sheet to form the indentation.

10. The apparatus according to any one of claims 1 to 8 wherein the forming tool is mounted on a cylinder that is axially rotated to bring the tool into engagement with the plasterboard sheet.

11. The apparatus according to claim 10 wherein a

plurality of equally spaced tools are mounted on the periphery of the cylinder.

12. The apparatus according to claim 11 wherein the

cylinder is driven in synchronisation with the speed of the conveyor.

13. A method of manufacturing plasterboard comprising:

spreading a gypsum slurry over a paper layer, applying a back cover and forming the side edges of a continuous length of plasterboard, passing the length of plasterboard to a cutting station to cut the plasterboard into sheets, and then transferring the cut sheets to a drier, wherein the method includes the step of pressing a lateral strip of the plasterboard to form an indentation and cutting the board at the indentation.

14. A method according to claim 13 including cutting the board before the indentation is formed and then pressing the plasterboard along the cut to form the indentation.

15. A method according to claim 13 including cutting the board after the indentation is formed.

16. A method according to claim 13 wherein the pressing step is carried out using a tool wherein the tool has an elongate pressing face with longitudinal tapered edges .

17. A method according to claim 16 wherein the pressing step causes a plurality of projections extending from the pressing face to pierce the paper layer.

18. A method according to either claim 16 or 17 wherein the pressing face of the tool is driven by a cam against the plasterboard.

19. A method according to either claim 16 or 17 wherein the pressing face of the tool is rotated into engagement with the plasterboard.

20. A method according to claim 19 wherein the speed of the rotation of the tool is synchronised with the pressing speed of the plasterboard.

21. A plasterboard sheet manufactured using the method claimed in the any one of claims 13 to 20.