EP0153588B2 - Method for the continuous production of shaped articles, in particular slabs, from a mix of plaster of Paris, and fibre materials as well as a device for carrying out the method - Google Patents

Description

The invention relates to a process for the continuous production of moldings, such as boards made of gypsum and fibrous material, in accordance with the features of the preamble of claim 1, and to an apparatus for carrying out the process according to the features of the preamble of claim 10.

With a known method (cf. DE-OS 32 16 886), gypsum fibreboards of satisfactory quality can be produced. However, there is the disadvantage that the statistical scatter for transverse tension and bending strength is relatively large when such gypsum fibreboards are produced in series. It has also been shown that smaller, mostly punctiform resets of fiber nests on the outside of the board lead to small pox-like elevations which, for many uses, impair the quality of such gypsum fiber boards and may therefore require grinding.

The invention has for its object to provide a process for the continuous production of moldings, in particular plates, from gypsum and fibrous material, in which the surfaces of the plates are essentially free of smallpox and in which furthermore optimal strength values of little statistical variation Series production can be achieved. Furthermore, an apparatus for performing the method according to the invention is to be specified.

According to the invention the object is achieved in a method with the features of the preamble of claim 1 by the characterizing features of this claim. With the method according to the invention it is possible to produce very good strength values with less scatter in the continuous manufacturing process. In addition, the plates produced by the method according to the invention have surfaces of high quality which are free from smallpox and therefore do not have to be ground.

The method according to the invention also makes it possible to regulate and measure the addition of water to the metered gypsum-fiber mixture in such a way that the moistened gypsum-fiber mass does not granulate or clump. The limit value depends on the pre-selected mixing ratio and the type of raw materials. The division of the gypsum pulp mass into separate partial streams also has the advantage that the water added is distributed evenly and finely throughout the mass.

Accordingly, with the method according to the invention, sheets with good constant flexural and transverse tensile strengths can be mass-produced, which have a high-quality surface that is free of small pox. The exact dosage of the constituents of the gypsum fibreboard, including the precisely metered addition of as little moisture as possible, also ensures that the time for the drying of the finished pressed panels can be kept optimally short, which also reduces the energy expenditure required.

In practice, it has been shown that an exactly stoichiometric addition of water is relatively difficult since there are always smaller fluctuations in the mixing ratio and in the quality of the raw materials. It can therefore happen that if the water is added excessively, the plates need to be dried later, or if there is too little water added, there is not enough water for the setting reaction of the plaster, which can lead to a weakening of the plates. It can also be disadvantageous that with the stoichiometric addition of water, a residual moisture between 1% and 3% remains, which corresponds to an amount of 5% to 15% of non-set gypsum, which can likewise lead to a weakening of the plate structure. In the range of 0% to 3% residual moisture, the gypsum fiber material undergoes relatively large volume changes, which can have an effect of up to 0.3% linear change in length (3 mm / m). This is particularly disadvantageous when using gypsum fibreboards, where precise dimensioning or tolerances when laying or installing such panels is important. If seamlessly laid panels with a residual moisture of up to 3% are then laid and then dry up to 0% residual moisture, these can tear open when subsequently compensated for the ambient moisture.

Finally, it was found that the setting process takes place disadvantageously with the stoichiometric addition of water. The gypsum crystallizes on the spot because water is not available to transport the calcium sulfate ions. There is therefore a risk that the plate will become a slightly caked aggregate of grains that have retained the original shape of the gypsum grains.

If the surfaces of the molded body are subsequently sprayed with water, the surface is given a firm, uniform structure. However, it has been shown that this advantageous consolidation of the surface does not yet ensure an optimal, good plate quality. It can happen that larger pieces break out of the solidified surface when nailing or screwing the plate.

Overall, the invention thus creates a process in which molded articles, in particular sheets, made from a mixture of gypsum and fibrous material with an optimally short setting and drying time receive a consistently high strength with little scatter.

In order to add the amount of water required for setting to the shaped body, the mass flow is divided into several, separate partial mass flows, each partial mass flow is sprinkled into a layer of the shaped body on the base or the previous layer. Each layer - regardless of the other layers - is moistened with a given amount of water. The supply of total water (including the amount of water for moistening the dry gypsum-fiber mixture) is controlled in such a way that a quantity of water is added to the shaped body that is up to 25% greater than the stoichiometric amount of water that is calculated to set the gypsum-fiber mixture is required. The superstoichiometric addition of water is preferably in the order of magnitude between 15% and 20% (cf. FIG. 4). Since the additional amount of water is distributed in layers, there is no need for remixing and the associated disadvantageous lumping or granulation of the gypsum.

Due to the over-stoichiometric addition of water, sufficient water is available during a setting process to ensure that the calcium sulfate ions are transported in all directions. This ensures that the shaped body crystallizes into well-formed, idiomorphic, needle-shaped crystals that are strongly grown and matted together. As a result, high mechanical strengths of the plate are achieved.

In addition, the over-stoichiometric addition of water increases the plasticity of the plaster when pressed. This means that gypsum material can be pressed into all cavities, which in turn leads to better fiber integration. The plasticity also allows the use of a somewhat coarser grinding plaster, which results in economic advantages. The adhesive force of the wet gypsum also compensates for the restoring forces of the cellulose fibers deformed during pressing. As a result, the press can be opened immediately after briefly pressing, without it being necessary to adapt the pressing time to the setting process. Due to the higher plasticity, the surface of the molded body adapts exactly to the press base, whereby a smooth press base is formed as a smooth surface. On the other hand, if the water is added exactly stoichiometrically, dusty surfaces may occur, or the surfaces of the plates may become pockish if the water is only added slightly above stoichiometric. In the case of a wet process with a large excess of water, on the other hand, structured rollers or screens have to be used, which necessitates regrinding. Grinding losses of the plate in the order of magnitude of at least 3%, but usually 10% must be expected.

With an over-stoichiometric addition of water in the order of up to 25%, preferably about 15% to 20%, the setting process of the gypsum is also considerably accelerated, as a result of which the costs for the setting line in a continuously operating system are considerably lower than in comparable systems.

If, according to a further feature of the invention, the partial mass flows have different mass volumes, layers of different thicknesses can be formed. In order to achieve a central core layer and a large number of scattered layers, the number of partial mass flows is odd. Additives can be added to each partial mass flow; In particular, additives are added to the partial mass flow of the core layer, which is preferably larger in volume.

Similarly, the supply of the individual amounts of water is controlled, which is preferably 15% to 20% above the stoichiometric amount of water in the total amount. The amount of water added to the individual layers after spreading can vary; in particular, a larger amount of water is added to the outer layers of the shaped body than to the inner layers. The amounts of water sprayed on the individual layers can also contain additives; it is expedient to add suspensions or emulsions of pigments and / or synthetic resins to the amount of water in the outer layer of the molding. This can, for. B. a surface decoration, a water-repellent impregnation or a fire retardant can be used directly in the production without a second process step being necessary. The method according to the invention has an advantageous effect here, since it can be used to produce plates with finished surfaces that do not have to be reground. An originally unaccelerated or slightly decelerated basic mixture can also be accelerated shortly before the press by adding accelerator solution (e.g. potassium sulfate).

An advantageous device for performing the method is specified in separate patent claims.

• Fig. 1 eine Vorrichtung zur Durchführung des Verfahrens mit Aufteilung des Massestroms nach dem Feucht-Mischvorgang,
• Fig. 2 eine Vorrichtung gemäß Fig. 1 mit Aufteilung des Massestroms nach dem Trocken-Mischvorgang,
• Fig. 3a bis 3e Schnitte durch Platten verschiedenen Aufbaus,
• Fig. 4 ein Diagramm der Abhängigkeit der Biegezugfestigkeit von der Dichte bei Gipsfaserplatten,
• Fig. 5 ein Diagramm des Abbindeverlaufs von Gipsfaserplatten mit verschiedenen Anteilen überstöchiometrischen Wassers.

Further features of the invention result from the further claims, the description and the drawing, on the basis of which advantageous embodiments of the method according to the invention are explained in more detail. Show it:

• 1 shows an apparatus for carrying out the method with division of the mass flow after the wet mixing process,
• 2 shows a device according to FIG. 1 with distribution of the mass flow after the dry mixing process,
• 3a to 3e sections through plates of different construction,
• 4 shows a diagram of the dependence of the bending tensile strength on the density in the case of gypsum fiber boards,
• Fig. 5 is a diagram of the setting course of gypsum fiber boards with different proportions of superstoichiometric water.

A quantity of fibers is drawn from a fiber bunker 1 by means of motor-driven conveyor belts 20a, 20b and 20c. The conveyor belt 20c is preferably driven by a motor 34. The amount of fiber discharged is pre-metered volumetrically by means of leveling rollers 21 or the like. The leveling rollers 21 are arranged at the end of the last conveyor belt 20c near the exit 22 of the fiber bunker 1.

A continuously operating weighing device 2, for example a belt weigher, is arranged below the outlet 22, for example it weighs the amount of fiber emerging from the fiber bunker 1 and conveys it to a dry mixer 4 via a chute or the like. The output signal of the preferably electronic weighing device 2, which corresponds to the detected weight of the fiber quantity, is fed to an electronic control device 23 which, depending on this output signal, regulates the speed of the drive motor 13a of a screw conveyor 13 of a metering scale 14 assigned to the gypsum metering device 3 via a control line 31.

The control device 23 further regulates at least the conveying speed of the last conveyor belt 20c of the fiber bunker 1 in accordance with a difference value which is formed from the output signal of the belt scale 2 and a setpoint value predetermined by the control device 23. Furthermore, the control device 23 also monitors the predetermined quantity ratio of gypsum / fiber and acts via the control lines 30 and 31 accordingly on the conveying speed of the conveyor belt 20c and the screw conveyor 13 of the metering device 3.

The measured quantity of the continuous weighing of the gypsum fiber mass controls the preselected target size of the fiber mass (F) and the target size of the gypsum quantity (G) in such a way that F / G = constant and G + F = constant.

The dry mixer 4 is preferably a horizontal continuous mixer with a rotating mixer shaft and mixing tools arranged radially thereon, in which the material to be mixed passes through the mixer largely without backflow. This mixer 4 is continuously added at one end with the weight-metered starting quantities of gypsum and fibrous material. At the other end of the continuous mixer 4, the dry mixture of gypsum and fibers emerging from its outlet 4a is conveyed preferably via a conveyor belt 5 with variable speed drive into an intermediate bunker 45 of the gypsum fiber metering device 6. The mixture is drawn off from this intermediate bunker 6a as required via conveyor belts 16a, 16b arranged in the intermediate bunker.

At the end of the last conveyor belt 16b driven by a motor 29, leveling rollers 15 are arranged in the vicinity of the bunker outlet 17, by means of which the amount of the dry mixture consisting of gypsum and fibers to be discharged is volumetrically pre-metered. The dry mixture falls directly on a weighing device arranged under the outlet 17, which preferably consists of a belt scale 7.

The output signal of the belt scale 7 is fed to an electronic control device 18 which controls the conveying speed of the last conveyor belt 16b on the one hand via the control line 32 and a water metering device 8 on the other hand via the control line 33. This is controlled in such a way that such an amount of water is always supplied which is below a limit value above which the moistened gypsum-fiber mixture tends to form granules or lumps. Even with fluctuations in the amount of dry gypsum-fiber mixture in the continuous process, the amount of water added to the dry mixture is always precisely matched to the actual amount in the mixing process, so that there is almost a stoichiometric addition of water during the mixing process.

The controlled metering of the water in a wet mixer 9 can be carried out according to the invention in such a way that the control signal is effective with a delay of the amount of time that the detected mass of gypsum-fiber mixture needs to reach the point (nozzle 8 ') of the water addition.

The dry gypsum-fiber mixture determined by the weight of the belt weigher 7 is fed directly to the moist mixer 9, which is preferably also designed as a continuous mixer with a rotating mixer shaft and mixing tools arranged thereon. Via the water metering device 8 controlled by the control device 18, the precisely metered amount of water is fed to the mixed flow of the wet mixer 9 via nozzles 8 ′ (not shown in more detail). The nozzles 8 'spray the water preferably transversely to the longitudinal axis of the mixed stream passing through the mixer into the cylindrical interior of the mixer 9.

At the outlet 9a of the continuous mixer 9, the gypsum-fiber mixture moistened with water falls into an apportioning device 37 which divides the mass flow into three mass flows, preferably by rhythmic deflection (clocked deflection), on conveyor belts 10a, 10b and 10c which can be driven at variable speed. Each conveyor belt 10a to 10c feeds an intermediate bunker of a spreading machine 11a to 11c known per se. The spreading machines 11a to 11c are constructed identically and have a conveyor belt 36, at least one leveling roller 27 and a discharge roller 28.

A molding line 12 runs under the spreading head 26a to 26c of each spreading machine 11a to 11c, the spreading heads 26a to 26c being arranged one behind the other in the conveying direction 19 of the molding line 12. In the conveying direction 19 of the molding line, a spray nozzle 40 for adding water is provided in front of the first spreading head 26a. Furthermore, a spray nozzle 41 and 42 is arranged between the spreading heads 26a and 26b and 26b and 26c; behind the last spreading head 26c, water is also supplied via a spray nozzle 43. This arrangement ensures that the spray nozzles 40 to 43 do not become dirty and cannot become clogged, since these nozzles lie outside the dust swirling zone between adjacent spreading heads.

Due to the variable drives for the conveyor belts, a speed adjustment of these belts is possible, so that a continuous run is possible taking into account the overall time sequence, that is, the Total residence time between wet mixing and pressing is the same in each shift. The continuous weight-metered addition of the dry mixture to the mixer 9 and the moistening by means of a controllable amount of water as a function of the electrical output signal of the weighing device 7 have made it possible to continuously produce gypsum fiberboard without a large scatter in the strength values. In the exemplary embodiment shown in FIG. 1, the top of the molding line is wetted with water before the application of a first layer 35a of the molded body to be produced on the molding line 12 by means of the nozzle 40. The first partial mass flow of the gypsum-fiber mixture moistened in the manner described above is sprinkled onto the thus moistened molding line 12. The first layer 35a is moved past in the direction of the arrow 19 under the nozzle 41, the outer surface of the layer 35a being re-moistened by spraying with water or a water mist. The second layer 35b is sprinkled on this re-moistened surface of the layer 35a as it passes the scattering head 26b, the outer surface of which is now moistened with water by means of the nozzle 42. The third layer 35c is then sprinkled onto this layer, the outer surface of which is subsequently moistened with water via the nozzle 43. The mat-like shaped body thus formed is compacted in a press arranged downstream of the molding line 12, then cut to length and then deposited for setting and drying. The individual devices of the system according to the invention, such as the weighing devices 2 and 7, the mixers 4 and 9, the metering devices 3, 6 and 8 and the spreading machines 11a to 11c operate continuously, so that plates can be produced continuously without interruption.

It has been shown that by dividing the mass flow into several, preferably three, separate partial mass flows and rewetting, a plate of high strength can be produced. A total of up to 25%, preferably 15% to 20%, water is added above the stoichiometric amount of water, which enables mass transport of calcium sulfate ions in all directions and the gypsum body to crystallize in well-formed, idiomorphic, needle-shaped crystals which interact with one another are grown together and matted. Such a plate has excellent structural properties and shows a significantly higher transverse tensile and bending strength than conventional plates. In particular, an excellent plate surface is achieved, which is free of pox-like elevations and therefore does not have to be reworked.

The effect of the superstoichiometric addition of water on the order of 15% to 20% can be seen from FIG. 4. It shows the bending tensile strength versus density with different water additions. You can see the typical parabolic course. With a higher proportion of superstoichiometric water, higher strengths are obtained. In the range of densities between 1.15 and 1.2 realized in practice, the strength is doubled compared to the stoichiometric addition of water. This diagram clearly shows the positive effect with regard to the higher strength of gypsum fibreboards when water is added in excess of stoichiometry.

Due to the over-stoichiometric addition of water, setting is also considerably faster. This faster setting is shown in FIG. 5 on the basis of the temperature increase that occurs. With the stoichiometric addition of water, setting times of the order of 30 minutes are achieved. The very slow runout of the curve is important here, which indicates an incomplete reaction. In the case of over-stoichiometric addition of water in the order of magnitude of 18% water, setting times of about 10 minutes are achieved, with the temperature increase coming to a standstill very quickly at a higher level. This is an indication of complete setting of the gypsum and graphically illustrates the better structural properties of the boards produced by the method according to the invention.

The plates that can be produced using the method according to the invention are shown in FIGS. 3c to 3e. In Fig. 3a, a plate 35 is shown in section, which was produced by previously known methods. In Fig. 3b, a plate is drawn in section, which is produced by the method according to the invention and in which the transverse tensile and bending strengths are considerably improved and in which the surfaces 38 are also formed much stronger, which can be achieved by spraying the plates with water on both sides is.

The plate produced according to the method further developed according to the invention, in which the mass flow of the gypsum-fiber mixture is divided into separate partial mass flows and each scattered layer is re-moistened with water, the total amount of water supplied to the plate being up to 25% above the stoichiometric amount of water for setting gypsum-fiber mixture scattered to form the molded body, consist of three layers 35a to 35c and are based on a division of the mass flow into an odd number of partial mass flows, namely into three partial mass flows. Three partial mass flows are sufficient to produce a 10 mm thick gypsum fibreboard with high strength and a middle core layer. However, it may be advantageous to choose a higher layer division. The plate shown in section in FIG. 3c was composed of three partial mass flows of the same volume. In the area of the layer boundaries, a higher solidification of the gypsum is achieved. The volumes of the partial flows are selected such that a layer thickness of 1 to 7 mm results after the compression molding. However, the volumes of the partial flows are preferably dimensioned such that that after the compression molding there is a layer thickness of 2 to 3 mm.

The plate shown in section in FIG. 3d was also composed of three partial mass flows. The partial mass flow forming the core layer 35b was provided with a larger mass volume than the remaining partial mass flows of the outer layers 35a and 35c. Additives 44 were added to the partial mass flow forming the core layer.

A light aggregate such as vermiculite or kenospheres can be useful for the core layer. The addition of mica to the core layer and / or the outer layers can significantly improve the fire protection properties of the board. Gypsum can also be mixed into the outer or inner layer as an additive. Also aggregates in the form of other reinforcing fibers such. B. glass rovings useful for the outer layer. Paraffin granules added to the outer layers can also be melted during drying, which results in a deep waterproofing impregnation.

The plate shown in section in FIG. 3e corresponds in structure to the plate from FIG. 3c. However, a pigment additive was added to the amount of water supplied via the last spray nozzle 43, so that a surface 39 of bonded pigment is formed.

To achieve certain shape structures and strengths, it can be advantageous to provide the amount of water supplied to the individual layers for rewetting in different ways. Thus, it may be advantageous to provide the amount of water added to the outer surfaces of the shaped body larger than the amount of water added to the inner layers, as a result of which a smooth, post-processing-free surface can be achieved. In particular, any additives, such as. B. a setting accelerator can be added. These additives are preferably water soluble. It may be expedient to add other additives to the amount of water supplied to the outer layers than to the amounts of water supplied to the inner layers. The additives for the amounts of water in the outer layers are preferably in the form of suspensions or dispersions.

FIG. 2 shows a device for carrying out the method according to the invention, which largely corresponds to the basic structure of the device according to FIG. 1. The same parts are provided with the same reference numbers.

In contrast to FIG. 1, the division of the mass flow into several partial mass flows is already provided at the outlet of the dry mixer 4. The dry premixed amount of gypsum fiber arrives via the outlet 4a of the dry mixer directly into an allocation device 37a which divides the mass flow into individual mass flows of the same or different volume. This division preferably takes place by clocked deflection of the main mass flow onto conveyor belts of the partial mass flows. These conveyor belts open into intermediate bunkers 6a to 6c. In the illustrated embodiment, a division into three partial mass flows is provided; three gypsum fiber metering devices 6a to 6c are arranged accordingly. The structure of the gypsum-fiber metering devices 6a to 6c corresponds to the gypsum-fiber metering device 6 from FIG. 1. The gypsum-fiber metering device opens into a damp mixer 9, which corresponds to the amount of gypsum / fiber mixture drawn off Control device 18 controlled - water is added. Furthermore, the desired amount of additive is supplied to each partial mass flow via an additive metering device 50, the amount being determined by weight from a metering scale 50a and reported to the control device 18. The outlet 9a of the wet mixer 9 opens directly onto one of the conveyor belts 10a to 10c, which feeds the mixture moistened in the partial mass flow directly to an assigned spreading machine 11a to 11c. The division of the mass flow into partial mass flows already after the dry mixer requires a higher system outlay, but the residence time of the moistened mixture up to the press is kept very short, since the moist gypsum-fiber mixture is fed directly to the spreader after leaving the wet mixer 9 Partial mass flow scatters on Formstrasse 12. The device according to FIG. 2 also has the advantage that the additives to be mixed into a partial mass flow can be mixed in dry.

Claims (12)

1. Method for the continuous production of shaped articles, in particular sheets, from a mixture of plaster and fibrous material, in a first continuous mixing process respectively metered quantities of plaster and fibrous material being mixed thoroughly, the dry plaster and fibrous material mixture then being moistened in a second continuous mixing process with the metered addition of a quantity of water, in that before the second mixing process the mass of the dry plaster and fibrous material mixture is continuously measured and the addition of water is adapted to correspond to the measured mass, the moistened mixture being spread on a support to form shaped articles and being subsequently pressed and the total quantity of water supplied lying significantly above the stoichiometric quantity of water required for binding the mixture of plaster and fibrous material, characterised in that the addition of water in the second mixing process is adapted so that the quantity of water added is kept below a limit value, at which the moistened mixture of plaster and fibrous material tends towards granulation or the formation of lumps, the mass flow of the mixture of plaster and fibrous material being divided into mass flows separated from each other, each partial mass flow being spread to form a layer of the shaped article on the support or a preceding layer and an additional quantity of water being added, in that each spread-out layer of the moistened mixture of plaster and fibrous material is subsequently moistened separately with water.
2. Method according to Claim 1, characterised in that the total quantity of water supplied is up to 25%, preferably approximately 15% to 20% greater than the stoichiometric quantity of water.
3. Method according to Claim 1 or 2, characterised in that the separation of the plaster and fibrous material mixture with the metered addition of water takes place after the second mixing process (Figure 1).
4. Method according to Claim 1 or 2, characterised in that the separation of the plaster and fibrous material mixture takes place after the first mixing process and the metered quantity of water is added to the separate partial flows.
5. Method according to one of Claims 1 to 4, characterised in that the partial mass flows are volumetrically different and that additives are added to the individual partial mass flows with subsequent mixing.
6. Method according to one of Claims 1 to 5, characterised in that each partial mass flow is stored temporarily before it enters an associated spreading machine (11a to 11c).
7. Method according to one of Claims 1 to 6, characterised in that the volumes of the partial flows are selected so that after moulding, a layer thickness of respectively 1 mm to 7 mm, preferably of 2 mm to 4.5 mm results.
8. Method according to one of Claims 1 to 7, characterised in that the quantity of water sprayed onto the individual layers (35a to 35c) differs, preferably so that the quantity of water sprayed onto the external layers of the shaped article (35) is greater than that supplied to the internal layer or layers.
9. Method according to Claim 8, characterised in that the quantity of water supplied to the individual layers may include additives, such as suspensions or dispersions, the quantities of water supplied to the external layers being able to contain additives different to those in the water quantities for the internal layer(s).
10. Apparatus for carrying out the method according to Claims 1 to 9, with a first metering device (2, 3) for the metered addition of plaster and fibres into a subsequent first mixer (4), with a second mixer (9) receiving the plaster and fibre mixture, with which a metering device for liquid (8) is associated, and a subsequent spreader device for spreading the moist plaster and fibre mixture onto a moulding line (12) with a subsequent pressing device, characterised in that located between the dry mixer (4) and the second mixer (9) is a metering device (7) which continuously measures the weight and/or volume of the dry mixture of plaster and fibre, and that a water metering system (8) whose outlet (8') opens into the subsequent second mixer (9), is associated with this plaster and fibre metering device (7) and that the spreading device (11) consists of several spreading machines, that in the direction of travel (19) of the moulding line (12), spray nozzles (40; 43) for moistening the surfaces of the spread shaped article are located before and after the external spreader heads (26a, 26c), and that between the spray nozzles (40; 43) in the direction of travel (19) of the moulding line (12) there are several independent spreader heads (26a, 26b, 26c) located behind each other and fed by partial mass flows, for the separate spreading of individual layers (35a, 35b, 35c) of the shaped articles (35), and that in the direction of travel (19) at least one further spray nozzle (41, 42) is provided between the spreading heads.
11. Apparatus according to Claim 10, characterised in that after the moist mixer (9), a feed device (37) is provided, which is followed by several separate spreader machines (11a, 11b, 11c) with spreader heads (26a, 26b, 26c) (Figure 1).
12. Apparatus according to Claim 11, characterised in that after the dry mixer a feed device (37a) is provided for the mass flow of the dry mixture of plaster and fibre, followed by separate metering devices (6a, 6b, 6c) and moist mixers (9) according to the number of partial mass flows, each moist mixer (9) being followed by a spreader machine (11a, 11b, 11c) (Figure 2).

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