Method for providing a dried cementitious material in a production of a building panel and press unit

Abstract

The present invention is related to a method for providing a dried cementitious material (3) comprising: providing a cementitious material (1) with a first water content in a predetermined form and thereafter drying the cementitious material (1) by arranging the cementitious material (1) in a press unit (10) in between a first contact element (11) and a second contact element (12), wherein the cementitious material is subjected to defined pressure conditions and defined thermal conditions for a predetermined time to expel water in liquid form from the cementitious material (1) to provide the dried cementitious material (3) with a second water content. A press unit is also claimed, comprising a first contact element (11) and a second contact element (12) at an adjustable distance and which can be heated, for providing a dried cementitious material (3), especially in the production of a building panel.

Description

[0001] Method for providing a dried cementitious material in a production of a building panel and press unit

[0002] The invention relates to a method for providing a dried cementitious material, especially in a production of a building panel, and a press unit according to the respective independent claim.

[0003] The technical field relates to the production of building panels, especially cementitious building panels, e.g. the continuous or sequential production of gypsum building panels.

[0004] Cementitious materials are materials based on at least a binder and at least a liquid, generally water. A cementitious material can be present in different states, comprising a chemically hardenable state, a hardened state, and intermediate states. For cementitious materials, the hardening process is a chemical reaction, i.e. a setting or curing process. Especially it is a chemical reaction involving water. Such reaction may, for example, comprise an incorporation of water into the crystalline structure of the product (e.g. a hydration).

[0005] In the process of producing products of cementitious materials, the starting materials are typically provided in form of slurries of a mineral binder material - generally in presence of further co-components - in water. This water is mainly free - i.e. unbound (liquid) - water like solvent water, water acting as suspension agent, or the like.

[0006] The binder of cementitious materials typically is mineral-based. Herein, the term ‘mineral’ also comprises such chemical compounds that are artificially made but essentially identical to naturally occurring mineral compounds, for example FGD gypsum.

[0007] For gypsum-based materials, the hardening is a setting process, for cement-based materials it is a hydraulic setting process. During the hardening process, some free water (unbound water, “liquid water”) is incorporated into the crystalline structure of the hardened product (hereinafter referred to as “bound water”). Accordingly, in the hardened state of the cementitious material, an amount of water is chemically or physically tightly bound into the crystalline structure (e.g. water of crystallization for gypsum-based materials, water of crystallization and pore water, also called capillary water, for cement-based materials) and therefore no more available as liquid (free) water. Depending on the amount of free water before hardening and possible drying processes, there still can be free water in the hardened cementitious material. Water that didn’t react during the hardening reaction is referred to as excess water.

[0008] Herein, the term “cementitious material” is equally used for the hardenable composition, for the already hardened product as well as for the intermediate states during hardening. Especially, cementitious materials comprise compositions wherein the binder is cement and / or a cement modification and / or gypsum (calcium sulfate dihydrate) and / or a calcium-sulfate modification (further hydration levels of calcium sulfate like anhydrite, a-hemihydrate, p- hemihydrate, bassanite, selenite).

[0009] Hereinafter, building panels shaped from a cementitious material are referred to as “cementitious building panels”. The production of a cementitious building panel comprises several working steps. First, a slurry is mixed by the cementitious binder, water and additives that is then formed into a desired mold or shape, for example a panel shape. The panels of wet cementitious material then will be cut and dried.

[0010] As cementitious building panels are formed from the initial slurry, they have a high water content that makes the step of drying crucial for the quality of the resulting building panel. In a conventional method, the wet cementitious material, e.g. a wet gypsum panel, is dried only in a heating furnace. Due to the increase in heat, the liquid water (i.e. free water) within the cementitious material evaporates, and the water vapor ascends from the material. For example, 3 kg of water evaporates from a wet standard cementitious (gypsum) wallboard (thickness 12,5 mm) with a basis weight of 1 1 ,5 kg / m2, so that the wallboard with a weight of 8,5 kg / m2is considered dry in typical cases.

[0011] The energy demand of this method is based on the enthalpy of vaporization which amounts to 2088 kJ / kg for water at 100 °C and 1013 mbar. As the lower limit of the required energy is given by the enthalpy of vaporization, the state of the art method of providing a dried cementitious material accounts for a huge part of the energy consumption of the overall production of building panels. To overcome the problem of high energy consumption known in the prior art, the invention provides a method for providing a dried cementitious material, especially in a production of a building components, preferably of building panels, and a press unit according to the respective independent claim. Advantageous aspects are the subject matter of the dependent claims.

[0012] The invention comprises a method for providing a dried cementitious material, especially in a production of a building component, comprising:

[0013] - (a) providing a cementitious material having a first water content, hereinafter referred to as “wet cementitious material”, in a predetermined form; and thereafter

[0014] - (b) reducing the water content of the wet cementitious material by arranging the wet cementitious material in a press unit in between of a first contact element and a second contact element, wherein the wet cementitious material is subjected to defined pressure conditions and defined thermal conditions for a predetermined time, to expel water in liquid form from the wet cementitious material to provide a cementitious material having a second water content, hereinafter referred to as “dried cementitious material”.

[0015] The dried cementitious material can be the final product or an intermediate in the production of a building component. In particular, the building component is a building panel. Examples for such building panels are gypsum boards, gypsum fiberboards, cement boards, concrete boards etc. However, other molds than panels can be dried by the method according to the invention, too.

[0016] According to the invention, the second water content of the cementitious material is lower than the first water content, i.e. the dried cementitious material has a lower water content that the wet cementitious material. The means that herein, the terms “wet” and “dried” represent two different states of water content, but do not give any information about the absolute values without further specifications. Especially, the terms “dried does not mean the absolute absence of water.

[0017] Hereinafter, the process of reducing the water content is shortly referred to as “drying” and can only be realized by step b above or a combination of step b above and further drying steps. The water to be removed during the drying process is mainly free water. Accordingly, the [free water] / binder ratio is suitable to characterize the drying process. Hereinafter, the [free water] / binder ratio is given as parts by weight of free water to one part of binder, for example a [free water] / binder ratio of 0.5 means 0.5 parts by weight of free water to 1 part by weight of binder, which is 1.5 parts of weight binder + free water. In this concern, binder refers to the binder in the respective state, i.e. including water of crystallization and pore water, where applicable.

[0018] Depending on the cementitious material - like type of binder, additives, type and amount of aggregates etc. -, the [free water] / binder ratio of the wet cementitious material can have different values. For example, the [free water] / binder ratio of the wet cementitious material may range from 0.1 to 5, or even more. For gypsum-based binders, [free water] / binder ratios of the wet cementitious material typically and preferably are in the range of 0.15 to 1 , more preferably in the range of 0.55 to 0.75, and most preferred in the range of 0.6 to 0.7. For cement-based binders, the [free water] / binder ratio can be in the same range as defined for gypsum, however, depending on the type of cement and the type and amount of aggregates, the [free water] / binder ratios may differ from these values. Especially for the wet cementitious material - the slurry -, the water content, i.e. the [free water] / binder ratio, can have higher values.

[0019] The intended [free water] / binder ratio of the dried cementitious material also varies, depending on the circumstances. In many cases, the drying according to step b above leads to [free water] / binder ratio of about 0.05 to 0.2, for example. It can be advantageous to not fully dry the material before the chemical reaction of the hardening process has fully finished, especially if the presence of specific amounts of residue water is crucial to guarantee for required product performance. In other cases, when step b does not lead to the finally [free water] / binder ratio, a further drying step may follow (as mentioned above). In preferred embodiments, the final [free water] / binder ratio - achieved by the drying process of step b above or in combination of the drying process of step b above with other drying steps, as defined below - is in the range between 0.0 and 1 .5, preferably less than 1 , very preferred less than 0.8 and most preferred less than 0.4.

[0020] Generally, as already mentioned, the step of drying the wet cementitious material by arranging it at a press unit according to step b above may be supplemented by further drying steps, for example conventional drying steps. For example, a step of vacuuming an amount of excess water may be inserted upstream step b, i.e. between the step of providing the wet cementitious material in a predetermined form (step a above) and the step of reducing the water content of the wet cementitious material according to step b above. Additionally or alternatively, a common heating furnace can be installed downstream the drying process of step b above, to further reduce the contend of free water of the final product.

[0021] In one preferred embodiment of the invention, the step of drying the wet cementitious material by arranging it at a press unit according to step b above is the only drying step of the method according to the invention, sufficiently expelling the water up to a intended quantity of water that remains in the final product.

[0022] Expelling the water in liquid form allows drying the wet cementitious material without the need to add the enthalpy of vaporization to the water within the cementitious material. Only a fraction of the water evaporates in this method. This way, the potential energy savings are estimated typically up to 20 to 25 %, even up to 50% in special cases, per building panel.

[0023] According to a preferred aspect the step of providing a wet cementitious material comprises to provide a wet gypsum-based material (gypsum or gypsum fibre material) in a planar form or as a slurry. Thus, the method can be introduced at various steps of the production process. Furthermore, the step of providing a wet cementitious material is carried out in separate steps (sequentially) or continuously. Drying wet gypsum-based material as slurry in seperate steps allows to press the slurry into a predetermined form such as a panel while simultaneously drying the slurry. Drying the material continuously allows the drying of long cementitious boards that can be cut after the drying process.

[0024] Defined pressure conditions can mean a constant pressure or a time-dependent pressure profile during the drying according to step b. According to an advantageous aspect the step of drying - step b above - the wet cementitious material comprises pushing the first contact element against the wet cementitious material at the pressure of 0.5 t / m2to 9 t / m2, especially a constant pressure within this range or a time-dependent pressure profile within this range or with a final pressure within this range. Varying the pressure while keeping the other parameters fixed will lead to a different amount of expelled water.

[0025] Defined pressure conditions can mean a constant temperature or a time-dependent temperature profile during the drying according to step b. According to a further advantageous aspect the step of drying - step b above - the wet cementitious material comprises applying thermal energy (heat) to increase the temperature of at least parts of the wet cementitious material to 100 °C to 220 °C, especially a heat leading to a constant temperature within this range or a time-dependent temperature profile within this range or with a final temperature within this range. The temperature is chosen in this range as it lays above the boiling point of water at standard pressure.

[0026] Furthermore, the combination of the applied pressure and temperature is chosen to generate a vapor pressure within one side of the wet cementitious material, to cause a pressure gradient throughout the wet cementitious material which expels the water in liquid form. Thus, only a small fraction of the water within the wet cementitious material evaporates close to the surface touching the first contact element. The evaporated water, meaning steam, is larger in volume than liquid water. As the first contact element is pressed against the material, the steam cannot leak directly through the surface. Instead the vapor pressure on this side of the cementitious material increases. The resulting pressure gradient drives the steam through the material which then pushes the water to the opposing side towards the second contact element and expels it. Accordingly, it is advantageous to only heat the first contact element, especially to the above mentioned temperature conditions, and to let the second contact element at ambient temperature or even cool it down. Alternatively, it can also be advantageous to heat both elements, but the first contact element significantly more than the second contact element.

[0027] Pressure and / or temperature profiles can be adapted to cause mild drying effects at the beginning of step b - where the amount of free water is still quite high - and to effect somewhat more drastical conditions only for a short time at the end of step b, to still expel water when the amount of water in the cementitious material already is at a lower level. This can be achieved by continuously or stepwise enhancing the pressure and / or continuously or stepwise enhancing the temperature during the drying time.

[0028] Advantageously, the second contact element drains the expelled water via appropriate means. The water is separated from the cementitious material and can no longer retract after the applied pressure is reduced.

[0029] Preferably, the drainage or discharge of water at the contact area between the cementitious material and the second contact element may be realized via a structured surface of the second contact element. Especially, the second contact may comprise drainage channels - e.g. grooves, notches or the like - in its surface at the contact area to the cementitious material, wherein such drainage channels advantageously are extending essentially parallel to the contact area. Such drainage channels may extend isolated (without crossing each other) or may build a channel network (with a number of branches). Each channel should have an outlet for the water at an edge of the contact area (generally at an edge of the second contact element).

[0030] Alternative to a structured surface or in addition to it, the second contact element may drain the expelled water by penetration holes through the second contact element (i.e. extending from one surface of the contact element to its other surface), e.g. by using a perforated second contact element. Penetration holes may be arranged essentially vertical to said contact area, and / or they may be arranged oblique to it. Penetration holes may extend essentially linear through the contact element, or they may be curved, bent or the like.

[0031] In an advantageous modification of the method according to the invention, the sides and / or outer parts of the mold, especially the panel, are not covered by pressure sustaining elements. Then the cementitious material itself can act as a pressure barrier. This modification offers the option to press out wet water over the open sides and / or outer areas of the molded cementitious material, especially the panel.

[0032] According to a further development of the invention, reduced ambient pressure (e.g. vacuum) at the end of the means to expel the water and / or the sides and / or outer parts of the mold supports to extract the liquid water.

[0033] Preferably, the step of drying the wet cementitious material comprises applying the predetermined pressure and the predetermined heat for the predetermined time in the range of 2 min to 30 min. In interaction with the other parameters - such as thickness of the board, density of the board, granulation of cementitious material and other parameters leading to a variation of vapour permeability resistance of the board and drying product -, the time can thus be adapted to the entire production process.

[0034] It is preferred that the step of drying the wet cementitious material comprises collecting the expelled water, i.e. in a extractable drawer below the press unit. First, the collection of water serves to verify the drying process as the amount of the expelled water can be estimated. Additionally, the expelled water can be treated which can enhance the sustainability of the products, like building panels.

[0035] In case of conventional drying methods, typically the hardening process has already progressed to a certain extent when drying starts. The method according to the invention can start to a much earlier state of the hardening, it is even possible that hardening has barely started when drying is started. This means that there is a certain competition between the initially free water necessary for incorporation into the crystalline structure of the product (bound water) and the free water expelled by drying. Further, if drying measures are too drastic, at least parts of the bound water can be removed from the crystalline structure again (called calcination), which reduces the quality of the product. Therefore, the person skilled in the art did not expect that the method according to the invention would run satisfactorily and successfully, and also would result in products of good quality, suitable for the intended applications. However, the assumed disadvantages did not occur, or where they did, to a far lesser extent than feared.

[0036] For some types of cementitious materials, the speed of this hardening reaction determines the applied processing - faster is mostly better. In those cases, the heating process of the method according to the invention is likely to speed up the hardening reaction, in addition to the drying effect. This is an advantage regarding the overall time of the production process of the intended product.

[0037] Another aspect of the invention relates to a press unit comprising a first contact element and a second contact element in an adjustable distance and which can be heated for providing a dried cementitious material, especially in a production of a building component, by subjecting a cementitious material with a first water content to defined pressure conditions and to defined thermal conditions for a predetermined time to expel water in liquid form from the cementitious material to provide a dried cementitious material with a second water content. The press unit is designed in such a way to enable providing a dried cementitious material in a production of a building panel expelling the water in liquid form. Since the water must not be evaporate, the enthalpy of vaporization can be saved in the drying process.

[0038] Such a press unit can be used and adapted for the method of the invention in any of the embodiments as described herein.

[0039] Preferably, at least the first contact element can be heated. Optionally, the second contact element can also be heated, or cooled. Very preferred, the process temperature of the first contact element can be controlled independently from the process temperature of the second contact element.

[0040] According to a particularly advantageous aspects the press unit comprises first and the second contact elements in the form of rollers or plates. Rollers enable the continuous drying process of long boards. The press unit comprising plates as contact elements can be used to press the cementitious material into plates upon drying.

[0041] According to another preferred aspect the second contact element is water-permeable, grooved, perforated or a grid as to drain the expelled water. This way the water cannot gather at the second contact element and retract into the cementitious material.

[0042] In the following drawings, the invention is illustrated in context of exemplary embodiments, in which

[0043] Fig. 1a shows a schematic illustration of an exemplary of the press unit with plates as first and second contact elements;

[0044] Fig. 1 b shows a schematic illustration of an exemplary of the press unit with rollers as first and second contact elements; and

[0045] Fig. 2 shows the method of drying the wet cementitious material to a dried cementitious material

[0046] Fig. 1a and Fig. 1 b show a schematic illustration of an exemplary embodiment of the press unit 10 with first and second contact elements 11 , 12 in the form of plates and rollers, respectively.

[0047] Regardless of which mentioned embodiment is considered, a wet cementitious material 1 in a predetermined form is arranged in between the first contact element 11 and the second contact element 12. Thereby, wet cementitious material 1 can be a wet gypsum based material in a planar form or a slurry. The first contact element 11 is then pressed against the wet cementitious material 1 by a pneumatic arm 4 at defined pressure conditions in range of 0.5 t / m2to 9 t / m2. Additionally, the first contact element 11 is heated to defined temperature conditions in range of 100 °C to 220 °C for a predetermined amount of time from 2 min to 30 min. The water that is expelled by this process accumulates at the second contact element 12 which exhibits a structured surface being water-permeable, grooved, perforated or a grid that the water can be drained.

[0048] In the shown embodiment of the press unit an extractable drawer 5 is positioned beneath the second contact element 12. It collects the expelled water after it is drained by the second contact element 12. In Fig. 1a, the wet cementitious material 1 is statically hold between the first and second contact elements 1 1 , 12. In Fig. 1 b, the wet cementitious material 1 is continuously moved between the first and second contact elements 1 1 , 12 into direction a. Fig. 2 shows the cementitious material throughout a process of the invention in steps. In the first step, there is the wet cementitious material 1 hold at the location 20. It is then arranged in the press unit 10. After the afore described method is applied, the now dried cementitious material 3 is removed from the press unit 10 and can be processed further at location 30, e.g. a cutter.

Claims

Claims1 . Method for providing a dried cementitious material (3) comprising: providing a cementitious material (1 ) with a first water content in a predetermined form; drying the cementitious material (1 ) by arranging the cementitious material (1 ) in a press unit (10) in between of a first contact element (1 1 ) and a second contact element (12) , wherein the cementitious material is subjected to defined pressure conditions and defined thermal conditions for a predetermined time to expel water in liquid form from the cementitious material (1 ) to provide the dried cementitious material (3) with a second water content.

2. Method according to claim 1 , wherein the step of providing a cementitious material (1) with the first water content comprises to provide a wet gypsum based material in a planar form or as a slurry.

3. Method according to claim 1 or 2, wherein the step of providing a cementitious material (1 ) with the first water content is carried out in separate steps or continuously.

4. Method according to any one of the proceeding claims, wherein the step of drying the cementitious material (1 ) with the first water content comprises pushing the first contact element (2) against the cementitious material (1 ) with the first water content at a constant pressure or a time-dependent pressure profile in the range between 0.5 t / m2to 9 t / m2.

5. Method according to any one of the proceeding claims, wherein the step of drying the cementitious material (1 ) with the first water content comprises applying a constant heat or a time-dependent heat profile to increase the temperature of the wet cementitious material (1 ) to 100 °C to 220 °C.

6. Method according to any one of the proceeding claims, wherein the combination of the applied pressure and temperature conditions are chosen to generate a vapor pressure within one side the wet cementitious material (1 ) to cause a pressure gradient throughout the wet cementitious material (1 ) which expels the water in liquid form.

7. Method according to any one of the proceeding claims, wherein the second contact element (2) drains the expelled water via a structured surface.

8. Method according to any one of the proceeding claims, wherein the predetermined time is in the range of 2 min to 30 min.

9. Method according to any one of the proceeding claims, wherein the step of drying the wet cementitious material (1 ) comprises collecting the expelled water, i.e. in a extractable drawer (5) below the press unit (10).

10. Press unit (10) comprising a first contact element (1 1 ) and a second contact element (12) in an adjustable distance and which can be heated for providing a dried cementitious material (3), especially in a production of a building component, by subjecting a cementitious material (1 ) with a first water content to defined pressure conditions and to defined thermal conditions for a predetermined time to expel water in liquid form from the cementitious material (1 ) to provide a dried cementitious material (3) with a second water content.1 1 . Press unit (10) according to claim 10, wherein the first contact element can be heated.

12. Press unit (10) according to any one of claims 10 or 1 1 , wherein the second contact element can be heated or cooled independently of the first contact element.

13. Press unit (10) according to any one of claims 10 to 12, wherein the first and the second contact elements (1 1 , 12) are rollers or plates.

14. Press unit (10) according to any one of claims 10 to 13, wherein the second contact element (12) is water-permeable, grooved, perforated or a grid as to drain the expelled water.

15. Method according to any one of claims 1 to 9 using a press unit according to any one of claims 10 to 14.

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