In European Patent Application published under No. 482810 is disclosed a method of producing end tapers in a gypsum board. In an embodiment (see column 10, lines 26-46), a gypsum board stops for a few seconds before entering the dryer. Its cut end is positioned against a stop plate and then pressed.

The major disadvantage of such a process is that it can only press one gypsum board at a time. This results in a lost of time which reduces the working rate of the gypsum board production line.

It is an object of this invention to provide technical solutions which, in particular, avoid the above-mentioned disadvantage.

According to one aspect, the invention relates to a process for the production of a hydraulic binder board having at least one tapered cut end, comprising the steps of: i) spraying a softening liquid on at least one cut end of the board ; ii) waiting for the softening liquid to penetrate the board; and iii) applying pressure on said at least one cut end of said hydraulic binder board.

According to a further aspect, the invention relates to a process for the production of hydraulic binder boards having tapered cut ends, comprising the steps of : a) moving at least one first hydraulic binder board having first and second cut ends on a conveyor until it reaches a pressing area ; b) moving at least one second hydraulic binder board having first and second cut ends on the conveyor until it reaches said pressing area and its first cut end contacts the second cut end of said at least one first hydraulic binder board ; c) applying pressure on first cut end of said at least one first hydraulic binder board ; d) applying pressure on both second cut end of said at least one first hydraulic binder board and first cut end of said at least one second hydraulic binder board ; and e) applying pressure on second cut end of said at least one second hydraulic binder board.

A further object of the invention is a production line for hydraulic binder boards having at least one tapered cut end, comprising : - means for spraying a softening liquid on at least one cut end of the board ; and means for applying pressure on sait at least one cut end of said board.

Yet a further objet of the invention is a production line for hydraulic binder boards, comprising : 1) means for moving at least one first hydraulic binder board having first and second cut ends on a conveyor until it reaches a pressing area ; 2) means for moving at least one second hydraulic binder board having first and second cut ends on the conveyor until it reaches said pressing area and its first cut end contacts second cut end of said at least one first hydraulic binder board ; 3) means for applying pressure on first cut end of said at least one first hydraulic binder board; 4) means for applying pressure on both second cut end of said at least one first hydraulic binder board and first cut end of said at least one second hydraulic binder board ; and 5) means for applying pressure on second cut end of said at least one second hydraulic binder board.

The processes and the production lines of the invention are particularly suitable for the manufacture of gypsum boards, and in particular four-tapered edges gypsum boards.

Other objects, features and advantages will become more apparent after referring to the following specification and accompanying drawings in which : Figure 1 is a view in perspective elevation of a gypsum board production line according to this invention ; Figure 2 is a schematic view of the pressing area before the application of the compressive loads ; Figure 3 is a schematic view of the pressing area during the application of the compressive loads ; Figure 4 is a schematic view of the pressing area after the application of the compressive loads ; Figure 5 is a schematic perspective view of the pressing area showing the presses.

DETAILED DESCRIPTION OF THE INVENTION Without wishing to be limited to any hydraulic binder, the following specification will be directed to the production of gypsum boards.

Referring to Figure 1, it can be seen a general process flow diagram comprising the well known units, that is, a calcination unit 1, a pumping unit 2, a stucco dosing unit 3, a dry additiving unit 4, a wet additiving unit 5, a water adding unit 6, a foam adding unit 7, a face paper feeding unit 8, a mixer unit 9, a back gray paper feeding unit 10, a cutting unit 11, a wet discharge 12, a wet transfer unit 13, a waiting area 14, a dryer unit 15, a dry discharge 16, a dry transfer unit 17, a trimming unit 18, a packaging unit 19 and a storage unit 20.

Such a gypsum manufacture line is described for example in European Patent Application published under No. 482 810.

According to the invention, the process for the production of gypsum boards further comprises steps to impart a taper to the cut end of a board.

As used herein, the term"edge"refers to the finished edge of the board extending parallel to the direction of board travel, whereas"end"refers to the cut end of the board extending transverse to the edges.

According to the invention and as visible in Figure 2, in order to produce a taper on the cut ends of boards, a first board 24 is moved to a pressing area. A further movement of the board may be stopped by a gate 32.

Then a second board 25 is also moved to the pressing area until its cut end 25a comes into contact with cut end 24b for the first board 24. As can be seen in Figures 2-4, each of boards 24,25 has a cut end (24b or 25a respectively), in an abutting position with a cut end of the other board (see the centre of the figure).

Next, compressive loads are applied on all cut ends 24a, 24b, 25a, 25b. The loads are generally applied downwards, preferably against the face paper of the board.

The first compressive load applied by press 21 and the third compressive load applied by the press 23 are generally substantially equal. The second compressive load applied by press 22 is generally about twice the amount of the first compressive load.

The compressive loads are preferably applied simultaneously.

Figure 3 represents the situation while the presses are applying the compressive loads on the boards.

Figure 4 represents the situation after the presses have applied the compressive loads on the boards.

The presses 21-23 may be heated presses.

The forms of the pressing plates of presses 21,22 and 23 are more visible in Figure 5.

Plate 26 of press 21 has the form of a prism the section of which is a right triangle with truncated angles.

Plate 28 of press 23 has a form similar to that of plate 26.

Plates 26 and 28 are mounted on presses 21 and 23, symmetrically with respect to plate 29, in a way that they taper in thickness toward the center of the gypsum boards.

Plate 29 of press 22 has the form of a prism the section of which is an isoceles triangle with truncated angles, the top of the isoceles triangle being turned to the board plate to be pressed.

The abutting position of the boards brings the advantage that the application by press 22 of a single compressive load can create two tapers at the time on the cut ends of plates 24 and 25 which are in contact.

Preferably, the boards to be pressed according to the invention have a low density, i. e. less than 9 kg/m2.

In a preferred embodiment visible in Figure 1, steps a) to e) are applied similarly to third and fourth boards.

In other words, a third board is moved preferably simultaneously with first board 24, in a parallel manner, so that its longitudinal edges are parallel to the longitudinal edges of first board 24 and its cut ends are aligned with cut ends 24a, 24b of first board 24. A fourth board is also is moved preferably simultaneously with second board 25, in a parallel manner, so that its longitudinal edges are parallel to the longitudinal edges of second board 25 and its cut ends are aligned with cut ends 25a, 25b of second board 25.

The size of the presses 21-23 is obviously adapted accordingly. Consequently, when press 21 presses first cut end 24a of first board 24 it then simultaneously presses the first cut end of the third board, when press 22 presses second cut end 24b of first board 24 and first cut end 25a of second board 25, it simultaneously presses the second cut end of the third board and the first cut end of said fourth board and when press 23 presses second cut end 25b of second board 25, it simultaneously presses the second cut end of the fourth board.

In a further embodiment, a fifth board is aligned with the first and third boards and a sixth board is aligned with the second and fourth boards. Press 21 then presses the first row of boards (lut, 3rd and 5th), press 23 presses the second row of boards (2nd, 4th and 6th) and press 22 presses one cut end of the boards of both the first and second rows. Optionally, additional boards can be added to the first and second rows.

In yet a further embodiment, a third row of board is also pressed. Pressing plate. 28 of press 23 is then replaced by a pressing plate similar to pressing plate 29 of press 22. A new press is then provided and has pressing plate 28 installed on it and aligned with the pressing plates of presses 21-23. The boards of the third row are arranged so that their (first) cut ends contact the (second) cut ends of the second row.

Optionally, additional row of boards can be added to the first, second and third rows. The cut ends of all rows may then be pressed simultaneously.

As to the speed of load application and applied pressure applied on the boards, they essentially depend on the core of the board and the elected embodiment, i. e. on the process carried out, which can be a wet process or a dry process.

Wet process According to this embodiment, the steps a) to e) of the process are carried out before the boards are dried.

The pressing is then located upstream from the dryer 15 with reference to the board travel (see Figure 1).

The pressing area may be located just before it, i. e. in the waiting area 14, where the boards are conventionally brought by the conveyor means of the production line.

Alternately, the pressing area may be an adjoining area 30 of the production line, where the boards may be moved from the waiting area 14 by conventional moving means (not shown) such as a conveyor comprising an endless belt revolving about end rollers.

An interesting feature of this embodiment is that the pressing steps take place while the boards are waiting before entering the dryer. As a result, the waiting time is used to press the boards, that is, no additional time is needed to press the boards and the rate of the production line is not decreased by the pressing steps.

Further, the compressive loads are applied while the boards are still wet.

The pressure may for example be from 3 to 8Q kg/cm2, preferably from 5 to 30 kg/cm2, for a board having a density of 8.8 kg/m.

After the pressing step, the boards can enter the dryer 15 as in a conventional process.

Dry process In this embodiment, the steps a) to e) are carried out after the boards are dried.

The pressing area 31 is therefore located downstream from the dryer 15.

The boards may then be taken at the end of the production line, from the stacker of the storage.

In order to avoid a breakage of the boards, the pressing steps c) to e) are preceded by the steps of : i) spraying a softening liquid on at least the cut ends of the boards; and ii) waiting for the softening liquid to penetrate the boards i. e. the paper and the core of the boards.

The production line therefore comprises means for spraying a softening liquid on at least the cut ends of the boards.

These spraying means are located between the dryer 15 and the pressing area 31 or they may located in the pressing area 31.

They may be conventional spraying means well known by those skilled in the art.

The softening liquid may be water, alcohol, spirits, propylen glycol or any agent having a high vaporization speed.

The waiting time is generally from 2 to 20 seconds, preferably about 10 seconds.

The pressure applied by the presses in this embodiment is usually higher than in the wet process for the same type of board.

The pressure may then be for example from 5 to 100 kg/cm2, preferably from 25 to 60 kg/cm2, for a board having a density of 8.8 kg/m2.

After the pressing steps, the boards may be moved from beneath the presses and transferred to the storage unit 20 or to a special storage area, where they become dry before being used or sent to the customer.

The boards may also be transferred to a booker and booked face to face or they can be directly skipped in a stacking operation by a suitable stacker well known in the industry.

Alternately, in order to allow a direct dispatch, the process comprises a subsequent step in which the pressed boards are dried in an additional dryer (not shown) which may be a heated blower dryer or an infrared dryer.

Since the pressing area 31 is located after the dryer 15, the production rate of the line is not impaired either in this embodiment.

Preferably, the production line comprises means for the obtention of tapered edges, for example a tapered edge belt which is placed along the edge of the continuous belt and extends beneath the setting gypsum board, tapering in thickness toward the center of the gypsum board (see for example Figure 5 of EP-A-482 810).

Thus, boards having a taper on each of their four sides can be obtained as visible from Figure 5.