DESCRIPTION

The invention relates to a method and an apparatus for producing a gypsum plasterboard.

EP 0 759 840 Bl describes an apparatus and a method for producing a gypsum plasterboard including a gypsum core. In the method of EP 0 759 840 Bl, a gypsum slurry flows and spreads out across a first sheet, forming a gypsum core. A second cover sheet is then laid over the core. The second cover sheet is unreeled from a supply roll and passed under an idler roll which guides the cover sheet, smoothes the upper surface of the slurry, and reduces the slurry thickness to a desired value. A coating apparatus is mounted in an area between two decks and comprises a coating roll and a pressure roll adjacent to each other.

In principle, methods, for example, as in EP 0 759 840 Bl, are suitable and useful for preparing a gypsum plasterboard. However, if the production of plasterboards comprises particles of solid gypsum, the particles can break the cover sheets (in particular paper sheets) and stop the gypsum plasterboard production. In particular, solid particles of gypsum (lumps) can proceed in a forming equipment and break the cover sheet (paper). As a consequence, the production must be stopped in order to clean the equipment. Therefore, the known solutions for producing gypsum plasterboards are expensive and inefficient, in particular if solid particles of gypsum are involved in the process.

It is an object of the present invention to propose a method and an apparatus for manufacturing a gypsum plasterboard with solid particles involved in the manufacturing process, which are efficient and, in particular which allow to avoid production stops.

According to the invention, a method for producing a gypsum plasterboard comprises the steps of: a) providing a gypsum slurry containing solid particles, b) depositing the gypsum slurry on at least a first sheet, in particular paper sheet,

c) moving, after step b), the first sheet with the gypsum slurry between two (a first and a second) opposing rolls breaking at least a proportion of the solid particles.

A core idea of the present invention lies in the two opposing rolls that crush at least the largest particles. Thereby, it can be avoided that a cover sheet (paper) breaks and the production process must be stopped. This leads to a more efficient and less expensive production of gypsum plasterboards. Preferably, the first (cover) sheet is a paper sheet. However, other embodiments (e.g. fleece sheets or the like) are possible.

In a preferred embodiment, the gypsum slurry is arranged between the first sheet and a second sheet (preferably before step b)). In general, the gypsum slurry may form (one) core layer. However, it is possible that several gypsum slurries are prepared, forming several core layers. In any case, the first and second sheet should define outer layers with one or more core layers of gypsum in between. The second sheet is preferably a paper sheet (or alternatively, a fleece sheet or the like). In particular, the solid particles are crushed after the combination of first sheet, one or more core layer and the second sheet. All in all, an efficient production and in particular crushing of solid particles is achieved.

Preferably, at least one of the first and second roll is moveable or moved towards or away from the (corresponding) opposing roll. Further, preferably, a lower roll is fixed. Alternatively or in addition, an upper roll may be moveable or moved towards or away from the lower roll. Thereby, a distance between the two rolls can be adjusted so that plasterboards with varying thickness and/or varying (initial) size of solid particles can be produced. This means, the same equipment may be used for different requirements which enhances the overall efficiency of the process.

In a preferred embodiment, the two rolls are placed in a lamination zone

(immediately) before a stabilization zone. The term "lamination zone" preferably means an area of the production zone in which the first (and optionally the second sheet) are combined with the gypsum slurry. The term "stabilization zone" preferably means an area of the production zone in which the combined layers (first sheet, at least one gypsum slurry and optionally second sheet) stabilize (in particular harden) without a (substantial) change of the form (in particular thickness). Preferably, the two rolls are placed so that the breaking of solid particles happens before the stabilization zone is entered, i.e. before the

(substantially) final thickness is achieved. Hence, it can be efficiently avoided that too large solid particles result in damaged (cover) sheets.

At least one of the two rolls may be driven by a traction of the first and/or second sheet. For example, the first roll may essentially be driven by the first (cover) sheet. The second roll may be (essentially) driven by the second (cover) sheet. This means, it is not necessarily the purpose of the two opposing rolls to transport the sheets. On the contrary, in a preferred embodiment, the two rolls are passive elements (with respect to the actuation of their rotation) and are (only) provided in order to break the particles (and optionally in order to guide the cover sheets in a certain direction). Thereby, the structure of the rolls may be very simple which enhances the efficiency of the method.

The first and/or second roll may have a diameter of at least 100 mm, preferably at least 150 mm, further preferably at least 170 mm. With such a diameter, the breaking (crushing) of solid particles is very efficient and reliable.

Preferably, rotational axes of the two rolls are arranged in the same (vertical) plane. Thereby, the breaking of particles is very reliable and efficient.

The first roll may be integrated in a first (lower) forming table. The term "forming table" means preferably an element which defines the (final) thickness (in general : shape) of the gypsum plasterboards. Alternatively or in addition, the second roll may be integrated in a second (upper) forming table. Portions of the first and/or second table on an entry side of the two opposing rolls are preferably angled in relation to each other. Portions of the first and/or second table on an exit side of the rolls may be parallel to each other. In particular, the entry side of the two opposing rolls may form a funnel. Such funnel structure brings the one or two sheets together with the slurry so that after the combined layers have passed the two opposing rolls, a predefined thickness of the plasterboards is achieved. In particular, a portion of the first and/or second table on an entry side of the rolls may have an angle of at least 5%, further preferably at least 10% and/or less than 30%, further preferably less than 25% (with respect to a horizontal plane). In an embodiment, the last portion of a funnel defined by portions of the first and second table on an entry side of the two opposing rolls is formed by the two opposing rolls. For example, at least the last 6 mm of the lamination is done by the two opposing rolls.

A plate thickness of the final plasterboards may be less than 1.0 times, preferably less than 0.8 times, further preferably less than 0.7 times the diameter of the (largest) particles within the slurry. In general, the "diameter" of particles should preferably be understood as "sieve diameter". The "sieve diameter" should preferably be defined by a minimum distance between two parallel borders of a virtual sieve through which the corresponding particle may just pass (wherein the corresponding particle would not pass a sieve with two parallel borders having a smaller distance). In the case of spheric particles, the diameter is for example the diameter of the spheres. In the case of cubic particles, the diameter is the length of an edge of the cube.

Alternatively, the particle diameter may be calculated by the maximum diameter of the corresponding particle (being defined by the two points on the surface of the particle having the maximum distance from each other).

A minimum distance between the two rolls may be less than 1.0 times, preferably less than 0.8 times, further preferably less than 0.7 times the diameter of the largest particles within the slurry.

A plate thickness of the final plasterboard may be less than 18 mm, preferably less than 12 mm, further preferably less than 10 mm. In general, the present invention allows to produce comparatively thin plasterboards even under the use of a gypsum slurry containing comparatively large particles.

A minimum distance between the two rolls may be less than 20 mm, preferably less than 14 mm, further preferably less than 12 mm. Thereby, it is efficiently possible to break large particles.

At least one of the sheets, preferably the second (upper) sheet, is guided by at least one idler roll provided in addition to the two opposing rolls. Further preferably, the idler roll is arranged at an entry end of the second (upper) table. Idler rolls, in order to guide a sheet within a gypsum plasterboard production are (as such) known. However, the combination of an idler roll with one of the two opposing rolls on the same side of the gypsum layer allows an efficient guidance and breaking of larger particles. Moreover, if the idler roll is arranged at an entry end of the second (upper) table, the overall disturbance of the corresponding sheet (paper sheet) is minimised.

As an independent aspect of the present invention, an apparatus for producing a gypsum plasterboard in particular according to the above described method, comprises a forming table and two (a first and a second) opposing rolls for breaking at least a proportion of solid particles within a gypsum slurry being deposited on a sheet, in particular paper sheet, wherein at least the first roll is integrated in the forming table. A (minimum) distance between the first and second roll is preferably less than 20 mm, further preferably less than 15 mm. Both opposing rolls may be integrated in a corresponding forming table. For example, the first roll may be integrated in a first (lower) forming table. The second (upper) roll may be provided in a second (upper) forming table. In essence, it is possible to efficiently and reliably produce even thin plasterboards with a gypsum slurry containing larger particles (in their initial state). The term "minimum distance" preferably means the minimum of the distance if the distance as such is variable. In any case, the (minimum) distance between the two opposing rolls may be more than 5 mm, preferably more than 8 mm.

At least one of the first and second roll may be moveable towards or away from the (corresponding) opposing roll. A maximum distance may be 0.5, preferably 2 times the minimum distance. For example, the distance may vary between 5 mm and 30 mm, preferably 10 mm and 20 mm. The lower roll may be fixed.

Alternatively or in addition an upper roll may be moveable towards or away from the other roll.

At least one of the two opposing rolls is freely rotatable so that it can be driven by a traction of the first and/or second sheet.

The first and/or second roll has a diameter of at least 100 mm, preferably at least 150 mm, further preferably at least 170 mm. Rotational axes of the two rolls are preferably arranged in the same (vertical) plane. The first roll may be integrated in a first (lower) forming table. The second roll may be integrated in a second (upper) forming table. At least one idler roll may be provided in addition to the two opposing rolls for guiding at least the first and/or second sheet, preferably wherein the idler roll is arranged at an entry end of the second (upper) table.

As an independent aspect of the invention, a system is proposed, comprising an apparatus of the pre-described kind and a gypsum slurry with solid particles. Preferably a minimum distance between the two opposing rolls is less than a diameter of the largest solid particles.

As an independent aspect of the present invention, a use of two opposing rolls and/or a use of the apparatus of the pre-described kind and/or a use of the system of the pre-described kind is proposed, for breaking particles in a gypsum slurry within a process for producing gypsum plasterboards, in particular according to the pre-described kind.

The enclosed figures show an embodiment and (further) aspects of the invention.

Fig. 1 : A schematic illustration of an upper and lower forming table of an apparatus for manufacturing plasterboards;

Fig. 2: a side view (as partial cross-section) of Fig. 1;

Fig. 3: a schematic illustration of a lower and upper forming table with two paper sheets and a gypsum slurry;

Fig. 4: the arrangement of Fig. 3 after a forward movement of the gypsum slurry; and

Fig. 5: the arrangement of Fig. 4 after a further forward movement of the gypsum slurry.

Figs. 1 and 2 show an embodiment of a first (lower) forming table 10 and a second (upper) forming table 11 of an apparatus for producing a gypsum plasterboard. The apparatus may comprise further components (e.g. mixers for the gypsum slurry or transport means or cutting means etc., not being shown in the figures). Two (a first 12 and a second 13) opposing rolls are provided. The first roll 12 is integrated in the first table 10. The second roll 13 is integrated in the second table 11. At an entry end 14 of the second table 11, an idler roll 15 is provided. The idler roll 15 (compare Fig. 3) guides a second (cover) sheet 16 of paper so that the second sheet 16 is guided between the forming tables 10 and 11. A first sheet (of paper) 17 moves along the first table 10 (compare Fig. 3). By the movement of the sheets 16, 17, the rolls 12, 13 rotate as shown by arrows 18. The arrangement of Fig. 3 may be divided in a lamination zone 19 and a stabilization zone 20. Within the lamination zone 19, a gypsum slurry 21 is arranged between and bonded with the (cover) sheets 16, 17. The lower table 10 comprises an angled portion 22. Correspondingly, the upper table 11 comprises an angled portion 23. The angled portions 22 and 23 define together with the rolls 12, 13 a funnel 24 so that the progressing sheets 16, 17 approach each other in order to form a gypsum plasterboard . At an exit side 25 of the two opposing rolls 12, 13, the opposing surfaces of the forming tables 10 and 11 are parallel to each other so that the thickness of the gypsum layer between the sheets is constant and may define a gypsum plasterboard with its final thickness.

The gypsum slurry 21 comprises solid particles, wherein (exemplarily) one solid particle 26 is shown.

As can be seen in Fig. 3, the solid particle 26 is still far away from the two opposing rolls 12, 13. However, together with the movement of the gypsum slurry 21 in the direction of the two opposing rolls (in Fig. 3 to the left), the particle 26 approaches a space 27 between the two opposing rolls. Because the diameter of the particle 26 is larger than a distance between the two opposing rolls, the particle is compressed by the two opposing rolls 12, 13 and finally breaks (as shown in Fig. 5). Therefore, the broken particle 26 does not disturb the further process, e.g. break the sheets 16, 17.

Both rolls 12, 13 may be fixed to the corresponding forming table 10, 11. The upper table 11 may be moveable in a vertical direction (together with roll 13). The two rolls, 12, 13 are placed (just) before the stabilization zone 20 within the lamination zone 19. The diameter of the rolls may be (approximately) 150 mm (or could be larger). The rolls must have a sufficient resistance in order to be able crush (break) the particles. The crushing strength is therefore dependent on the resistance of the rolls 12, 13 and their geometry (in particular diameter). As can be seen, both rotation axes of the rollers are (precisely) in the same vertical plane and parallel. In general, the method and apparatus of the present invention is exceptionally advantageous if comparatively thin plasterboards should be produced. The thinner the plasterboards, the more likely a production stop occurs because any lumps (solid particles) do not pass the forming table. The inventive solution is, in this regard, simpler and more efficient than known solutions (e.g. optimisation of the mixer, a production stop and raising the forming table when a paper break is detected with a sensor, chemistry in the mixer or the use of a grid after the outlet pipes are connected to the mixer). The present method and apparatus permits the reduction in size of any solid particles (lumps) so that lumps which are initially larger than a distance between the two (cover) sheets 16, 17 become smaller. By the rolls, a very high crushing strength may be achieved.

Reference numerals

10 first (lower) forming table

11 second (upper) forming table

12 first (lower) roll

13 second (upper) roll

14 entry end

15 idler roll

16 second sheet

17 first sheet

18 arrow

19 lamination zone

20 stabilization zone

21 gypsum slurry

22 angled portion

23 angled portion

24 funnel

25 exit side

26 solid particle

27 space