EP4263463A1 - Production of gypsum moulded bodies on a cycle press using grinding dust - Google Patents

Production of gypsum moulded bodies on a cycle press using grinding dust

Info

Publication number
EP4263463A1
EP4263463A1 EP20845773.9A EP20845773A EP4263463A1 EP 4263463 A1 EP4263463 A1 EP 4263463A1 EP 20845773 A EP20845773 A EP 20845773A EP 4263463 A1 EP4263463 A1 EP 4263463A1
Authority
EP
European Patent Office
Prior art keywords
grinding dust
gypsum
mass
mixture
fibres
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20845773.9A
Other languages
German (de)
French (fr)
Inventor
Jürgen BURCZECK
Bernd Pietschmann
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Knauf Gips KG
Original Assignee
Knauf Gips KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Knauf Gips KG filed Critical Knauf Gips KG
Publication of EP4263463A1 publication Critical patent/EP4263463A1/en
Pending legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B18/04—Waste materials; Refuse
    • C04B18/16—Waste materials; Refuse from building or ceramic industry
    • C04B18/167—Recycled materials, i.e. waste materials reused in the production of the same materials
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
    • C04B28/142—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements containing synthetic or waste calcium sulfate cements
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

  • the invention relates to a process for the production of a gypsum moulded body, in particular gypsum fibre boards, wherein grinding dust of gypsum fibre products is used.
  • the invention is further concerned with the mixture used in the process, the gypsum moulded body obtainable by the process, and the use of grinding dust for the production of a gypsum moulded body.
  • the production of gypsum fibre products often causes formation of grinding dust as a waste product.
  • This grinding dust is generated e.g. when the gypsum products are subjected to a finishing including surface grinding and/or sawing.
  • the grinding dust has mostly been disposed of as waste material in the landfill.
  • US 5632848 describes an equipment for the continuous processing of boardlike products containing gypsum such as fibreboards (fibre boards) and wallboards, wherein waste-type materials are considered as a source of calcium sulphate.
  • gypsum such as fibreboards (fibre boards) and wallboards
  • waste-type materials are considered as a source of calcium sulphate.
  • US 5632848 mentions the transformation of scrap gypsum wallboard by grinding and calcining, in order to obtain a suitable starting material.
  • CONFIRMATION COPY EP 0490160 A1 describes a method for the production of plate-like or blockshaped gypsum building materials provided with a pore structure, wherein calcium sulphate alpha hemihydrate, water and optionally additives are mixed to form a pourable slurry, which is subjected to a suitable shaping process. Grinding dust from the production of the gypsum building materials can be recycled for the production of the slurry.
  • DE 4127932 A1 relates to a method and apparatus for making fibre- reinforced gypsum boards in a multi-layer continuous filtration process by adding a suspension of gypsum and wet-processed fibres, preferably from waste paper. Grinding dust obtained in the process can be recycled be feeding it into a calcining plant where it is transformed into a material to be reused.
  • WO 2017/098482 A1 describes the production of a moulding such as plane boards by pressing a non-sticky free-flowing granular cementitious or gypsum-based precursor composition.
  • the gypsum-based precursor composition comprises calcium sulphate hemihydrate; water; guar gum and/or a hydrolysed polyvinyl alcohol; and a gelling agent. Since the binder system is on an organic basis, no separate drying step is required. A hydraulic press is used for pressing.
  • WO 2019/001677 A1 refers to a method of producing a gypsum slurry and a method of manufacturing a gypsum product such as gypsum board with the gypsum slurry.
  • the gypsum slurry may comprise wet ground gypsum paper component and stucco, wherein the solid content of the wet ground gypsum paper component with respect to the stucco may be from 0.5 to 10 wt.%.
  • a disadvantage of conventional processes for preparing gypsum products considering use of waste materials generated during production of gypsum products such as grinding dust is that the grinding dust is subjected to calcination for activation, which is energy consuming.
  • the grinding dust is subjected to calcination for activation, which is energy consuming.
  • only a relatively small proportion of grinding dust is added to fresh raw materials such as stucco, for instance the grinding dust generated in the process as such for re-use.
  • the grinding dust generated has mostly been disposed of as waste material in the landfill up to now.
  • the object of the invention was to provide a method for preparing gypsum products in which grinding dust of gypsum fibre products can be re- used in large proportions without the need of energy-intensive calcination treatment beforehand.
  • the invention therefore relates to a method as defined in claim 1 as well as the mixture used therein, a corresponding gypsum moulded body obtained by the inventive process, and the use according to the further independent claims.
  • Preferred embodiments of the invention are indicated in the dependent claims.
  • the present invention concerns a process for the production of a gypsum moulded body comprising the steps of:
  • step (iii) drying the gypsum moulded body, wherein, in the mixture provided in step (i), the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the fibres (a:b) is in the range of 25:1 to 5:1.
  • the benefit of the invention is that grinding dust of fibre gypsum products can be re-used in large proportions without the need of energy-intensive calcination treatment beforehand. The disposal of waste material can be avoided. This is environmental-friendly and advantageous from an economical point of view, too. In addition, an even improved bending tensile strength could unexpectedly be observed for plates manufactured by the inventive process compared to plates obtained by conventional processes.
  • the inventive process is for the production of a gypsum moulded body.
  • the gypsum moulded body may be any article known by the skilled person.
  • the gypsum moulded body to be produced is preferably a gypsum fibre board, in particular a gypsum fibre board for a raised floor or a raised floor element, respectively.
  • the dimensions of the gypsum moulded body can vary depending on the intended application.
  • standard dimensions for gypsum fibre boards (or gypsum plasterboards) e.g. the following ranges may be given: thickness of 10 - 42 mm, width of 1000 - 1250 mm, length of 1500 - 3000 mm.
  • the width and length for raised floor elements are general smaller, for instance both independently in the range of 300 to 800 mm, preferably 620 mm, more preferably 600 mm, whereas the thickness can be in the range of 28 to 45 mm. If needed, smaller (e.g. 20 mm) or larger dimensions are, of course, also possible.
  • the process of the invention comprises the step of (i) providing a mixture comprising: a) grinding dust obtained from gypsum fibre products; b) fibres; and c) water.
  • the mixture is obtained by mixing the essential components and optionally further components with each other. Any suitable mixing device may be used. It is preferred to use a high-performance mixer, e.g. an Eirich mixer or a compulsory mixer. A compulsory mixer is preferred because a stronger granulation effect can be obtained. Moreover, the mixing time can be reduced and the homogeneity of the mixture is improved.
  • a high-performance mixer e.g. an Eirich mixer or a compulsory mixer.
  • a compulsory mixer is preferred because a stronger granulation effect can be obtained.
  • the mixing time can be reduced and the homogeneity of the mixture is improved.
  • the order of addition of the components is arbitrary. Generally, it is suitable to mix the grinding dust and the fibres in the mixer until a homogeneous premixed dry mixture is obtained (duration e.g. 1 to 3 min) and subsequently adding water and further mixing in order to achieve an appropriate dispersion (duration e.g. about 1 to 5 minutes depending on the mixer used).
  • a homogeneous premixed dry mixture is obtained (duration e.g. 1 to 3 min) and subsequently adding water and further mixing in order to achieve an appropriate dispersion (duration e.g. about 1 to 5 minutes depending on the mixer used).
  • One or more further additives, in particular a retarder can be added to the system in dry or liquid form at any suitable time in the mixing operation.
  • the mixture is mixed until an earth-moist consistency is achieved, that is, the mixture is preferably an earth-moist mixture.
  • earth-moist consistency is not unambiguously defined but known to the person skilled in the art. He knows that the correct addition of water is important for the processing properties and for the obtaining the required properties of the set mixture like bending tensile strength.
  • the earth-moist consistency may therefore be tested in a simple and practicable test, the so- called snowball test. This may be done by forming a snowball-like clod in the hand. If it is not possible to form such a clod, the mixture may be too wet. The snowball should not disintegrate when opening the hand, otherwise the mixture is too dry. A slight adherence of the mixture should remain on the hand. The snowball may show a slight gloss on its surface because of a thin film of liquid.
  • Component a) is grinding dust obtained from gypsum fibre products.
  • the fibres in the gypsum fibre products may be paper fibres, recycled paper fibres, glass fibres, chopped fiberglass, cellulose fibres, wood fibres, mineral fibres, plastic fibres, or combinations thereof, preferably paper fibres, recycled paper fibres or combinations thereof.
  • the grinding dust may be a waste product, which is generated in the production of the gypsum fibre products.
  • the gypsum fibre products from which the grinding dust is derived may be paper fibre-reinforced gypsum products, preferably may be gypsum fibre boards, i.e. the grinding dust is preferably obtained from the production of gypsum fibre boards.
  • Gypsum fibre boards generally may be gypsum boards with fibres.
  • the fibres may be all kinds of fibres, e.g. paper fibres, recycled paper fibres, glass fibres, chopped fiberglass, cellulose fibres, wood fibres, mineral fibres, plastic fibres, or combinations thereof, preferably paper fibres, recycled paper fibres or combinations thereof.
  • the grinding dust is obtained from surface grinding and/or obtained from sawing the gypsum fibre products, in particular gypsum fibre boards.
  • Surface grinding includes grinding of the surface and/or edges of the product. Grinding and/or sawing operations are usually carried out in a finishing step during the production after the gypsum fibre raw product has been formed.
  • Surface grinding may be suitable e.g. to smooth the surfaces and/or remove defects such as burrs.
  • Sawing may be suitable e.g. to cut the products into dimensions and/or forms as desired.
  • the grinding dust used may be (grinding dust) obtained from surface grinding, (grinding dust) obtained from sawing or a mixture thereof. It is preferred that 60 to 100 % by mass, preferably 90 to 100 % by mass, of the grinding dust is (grinding dust) obtained from surface grinding of the gypsum fibre products. It is more preferred that the grinding dust is (grinding dust) obtained from surface grinding.
  • the grinding dust of the gypsum fibre products has the composition of the gypsum fibre products from which it is derived. Since the gypsum fibre products are setting during the production, the specific composition can also depend on the point of time the grinding dust is generated.
  • the grinding dust is added to the mixture, that is, it is added in uncalcined form.
  • calcination is the practice of dehydrating gypsum mainly into calcium sulphate hemihydrate, also called plaster or stucco, which includes heating the gypsum to evaporate most of the crystalline water, usually at a temperature of at least 120°C.
  • calcination of grinding dust is not necessary, because during the drying process (to get rid of the excessive water) of the gypsum fibre products from which the grinding dust is derived calcium sulphate hemihydrate is generated.
  • the content of hemihydrate in grinding dust obtained from surface grinding may be higher than the content of hemihydrate in grinding dust obtained from sawing.
  • the grinding dust comprises 40 to 90 % by mass, preferably 60 to 80 % by mass, of calcium sulphate hemihydrate, based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust.
  • the term "based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust” means that the fibres contained in the grinding dust are not considered for calculation. For instance, for a grinding dust including 10 % by mass fibres, the residual 90 % are the basis (100%) for calculation.
  • the grinding dust contains fibres, preferably paper fibres, in particular recycled paper fibres.
  • the grinding dust comprises 6 to 15 % by mass, preferably 8 to 13 % by mass, of fibres, preferably paper fibres, in particular recycled paper fibres, based on the total weight of the grinding dust.
  • the grinding dust comprises, based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust,
  • the grinding dust may also contain calcite (CaCOs) and/or quartz, usually both in traces.
  • calcite CaCOs
  • quartz usually both in traces.
  • Component b) are fibres.
  • the fibres may be paper fibres, recycled paper fibres, glass fibres, chopped fiberglass, cellulose fibres, wood fibres, mineral fibres, plastic fibres, or combinations thereof, preferably paper fibres, recycled paper fibres or combinations thereof.
  • the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass, preferably 90 to 10 % by mass, of the solids weight of the mixture.
  • the mass ratio of a) the grinding dust to b) the fibres (a:b) in the mixture is in the range of 25:1 to 5:1 , preferably 15:1 to 7:1 . It should be noted that the fibres contained in the grinding dust belong to component a), and are assigned thereto with respect to this ratio.
  • Component c) is water.
  • the mass ratio of the combined mass of a) the grinding dust and b) the fibres to the mass of c) water ((a+b)/c) is in the range of 0.3 to 0.9, preferably 0.4 to 0.8.
  • the mixture may optionally comprise one or more additives, which are known by the skilled person in this technical field.
  • additives are a retarder, a foaming agent, an accelerator and/or further gypsum types such as stucco and/or stemming from different sources.
  • At least one retarder is added to the mixture.
  • suitable retarders are proteinaceous sources, which contain amino acid oligomers or synthetic compounds mimicking the same, chelates, such as DTPA and EDTA, or polyacrylic acid compounds.
  • chelates such as DTPA and EDTA
  • polyacrylic acid compounds An example for a commercial product is Retardan® P from the company Sika, which is a Ca salt of polycondensed amino acids.
  • the total amount of additives is preferably less than 20 % by mass, more preferably less than 10 % by mass, based on the solids weight of the mixture.
  • the process of the invention comprises the step of (ii) placing the mixture provided in step (i) or a part thereof into a mould and pressing the mixture by means of a press to form the gypsum moulded body.
  • the process is a discontinuous process, i.e. each gypsum moulded body is formed in sequence.
  • the mixture may be prepared in amount which is sufficient to prepare one gypsum moulded body or more than one gypsum moulded body. In the latter case, of course only a part of the mixture is used for preparing the moulded body.
  • the mould used obviously depend on the shape and dimension of the moulded body to be produced. Generally, a simple box, e.g. a box of metal, is suitable.
  • the mould will be arranged in cooperation with the press to be used.
  • the mixture or a part thereof is placed in the mould, e.g. by pumping or pouring. It is suitable to homogenously distribute the mixture placed in the mould before pressing. Thereafter the mixture placed in the mould is pressed by means of a press to form the gypsum moulded body.
  • the press may be a hydraulic press.
  • the press is preferably a cycle press, in particular a hydraulic cycle press. Manufacturers of suitable hydraulic cycle presses are for instance the company Bussmann or Siempelkamp.
  • the pressing process with the press is done by pressing a movable ram from above onto an immovable support surface.
  • the mould can be mounted on the support face.
  • suitable discharge means may be mounted.
  • a plastic plate can be mounted on both the underside of the ram and on the top of the support surface, which is provided with rectangular depressions as drainage channels.
  • the water can collect in these depressions, and the water may be actively sucked into them by means of an applied negative pressure and fed into the water circuit of the production line via drainage pipes.
  • the pressing is preferably sufficiently high to achieve a compression or compaction of the gypsum moulded body formed. As a result, increased bulk densities are obtained.
  • the pressure applied by the press to the mixture in the mould may be e.g. in the range of 0.9 kg/mm 2 to 4.0 kg/mm 2 , preferably 1.1 kg/mm 2 to 2.0 kg/mm 2 .
  • the duration of the pressure application may be in the range of 20 s to 240 s. Higher or lower durations are also possible.
  • the bulk density of the gypsum moulded body obtained, in particular gypsum fibre board may be e.g. in the range of 1 100 to 1900 kg/m 3 , preferably 1200 to 1700 kg/m 3 .
  • the gypsum moulded body or gypsum fibre boards, respectively is a raised floor element. Due to the high load during application, compacted gypsum fibre boards having a high bulk density, e.g. in the range of 1400 to 1700 kg/m 3 , preferably 1500 to 1650 kg/m 3 , are suitable as raised floors.
  • the (formed) gypsum moulded body is dried in step (iii). The drying results in setting or hardening of the product.
  • the (formed) gypsum moulded body may be removed from the mould before, during or after the drying step.
  • the drying step can be carried out at ambient conditions, e.g. at a temperature of 15 to 40°C and air atmosphere. Heating is possible, if desired. It may be suitable to dry the moulded gypsum bodies under standardised conditions with respect to temperature, atmosphere and humidity to obtain a uniform quality of the products.
  • the gypsum moulded body is dried to constant weight.
  • a dryer which is adapted or designed for the relatively low residual moisture of the moulded gypsum bodies is preferred.
  • An optional and preferred further step may be the step of (iv) finishing the gypsum moulded body prepared.
  • the finishing suitably includes grinding of the surfaces and edges thereof, i.e. surface grinding and/or sawing.
  • the grinding dust obtained in step (iv) may be reused as grinding dust in step (i).
  • the finishing step is common for these products. Finishing may be carried out after step (iii).
  • the invention also relates to a mixture for the production of a gypsum moulded body, the mixture comprising a) grinding dust gypsum fibre products; b) fibres; and c) water wherein the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the fibres (a:b) is in the range of 25:1 to 5:1.
  • the invention also relates to a gypsum moulded body, obtainable by the inventive process as described above.
  • the invention also relates to a use of grinding dust of fibre gypsum products as a starting material for the production of a gypsum moulded body, wherein the grinding dust is used in uncalcined form.
  • the press used is a hydraulic cycle press of the manufacturer Bussmann.
  • the press ram can apply a maximum pressing pressure of 87 kg/cm 2 .
  • a steel moulding box is mounted on the supporting surface.
  • the internal dimensions of the moulding box are 610 - 610 - 200 mm 3 .
  • a plastic plate is mounted on both the underside of the ram and on the top of the support surface, which contains rectangular depressions as drainage channels. The water collects in these depressions, and the water is actively sucked into them by means of an applied negative pressure and fed into the water circuit of the production line via drainage pipes.
  • a grinding dust produced in the production of gypsum fibre boards during the surface sanding of the board surfaces can be used.
  • the dust may contain e.g. approximately 60 - 80 % by mass of calcium sulphate hemihydrate, 10 - 30 % by mass of calcium sulphate dihydrate, 7 - 12 % by mass of calcium sulphate anhydrite, as well as traces of calcite (CaCOa) and quartz.
  • the given percentages are based on total weight of the grinding dust excluding the mass of the paper fibres contained in the grinding dust. In this regard, grinding dust contains approx. 10 % by mass of recycled paper fibres based on the total weight.
  • the grinding dust (approx. 90 % by mass) and waste paper fibres (approx. 10 % by mass) are premixed dry in a high-performance mixer (e.g. Eirich mixer or compulsory mixer) until a homogeneous mixture is obtained (duration approx. 120 seconds).
  • a retarder can be added to the system in dry or liquid form.
  • water water-solid value approx. 0.6
  • the mixture is mixed (approx. 2 to 3 minutes depending on the mixer used) until an earth-moist consistency is achieved.
  • the mass is pressed into panels on a cycle press.
  • the mass is placed in a moulding box (610 x 610 x 200 mm 3 ), evenly distributed and pressed with a pressure of 0.87 kg/mm 2 (corresponds to the maximum performance of 300 bar for the press used).
  • a pressure of 0.87 kg/mm 2 corresponds to the maximum performance of 300 bar for the press used.
  • the manufacturing process may be modified accordingly, especially with regard to the finishing of the pressed mouldings (e.g. grinding of surfaces and edges).
  • Grinding dust is produced during the production of gypsum fibre boards, wherein surface grinding dust is obtained from surface grinding and sawing dust is obtained from sawing.
  • HH proportion refers to the amount of calcium sulphate hemihydrate in the grinding dust, based on the mass of the grinding dust excluding the mass of the paper fibres contained in the grinding dust. The differences in the amount of hemihydrate in the grinding dust result from different products, from which the grinding dust is derived, different thicknesses of the surface to be grinded on these different products, different drying conditions and the (undetermined) mixing ratio of grinding dust obtained from surface grinding and the grinding dust obtained from sawing.
  • Stucco Stucco from Knauf Gips KG
  • GD 1 mixture of surface grinding dust and sawing dust, HH proportion 44.5 % by mass
  • GD 2 mixture of surface grinding dust and sawing dust, HH proportion 34.6 % by mass
  • GD 3 mixture of surface grinding dust and sawing dust, HH proportion 6.7 % by mass
  • Vinnapas EP 3360 aqueous polymer dispersion made of vinylacetate and ethylene Retardan P Ca salt of polycondensed amino acids, Sika
  • Sample 2 is according to the invention. Samples 1 , 3 and 4 are reference examples. The drying temperature was 40 °C. Sample 1 is a common formulation according to the prior art. Table 1
  • sample 1 exhibits a significant granulating effect.
  • One test plate of sample 1 was broken during removal from the mould.
  • the mixture of samples 2 and 3 exhibits a significant granulating effect, but the granules are homogeneously moisturized.
  • the panels were prepared according to the general procedure described above. Two test plates (600 x 600 x 20 mm 2 ) were prepared for each formulation and two smaller pieces (400 x 300 mm 2 ) were cut out of each of them, which were used as samples (for formulation of Sample 1 : Sample 1_1 , 1 _2 etc.).
  • the parameters given in the following tables 2 and 3 were determined in accordance with EN 15283-2:2009-12. Table 2 includes the values for specimens based on samples 1 and 2 (invention), whereas Table 3 includes the values for specimens based on samples 3 and 4.
  • the hemihydrate content is high and the variations are relatively small (63.7 - 79.3 %), variations with the same product minimal.
  • the previously used material based on a mixture of grinding dust obtained from surface grinding and the grinding dust obtained from sawing having a HH content of 6 - 44.5 %, significantly more HH is contained; variations between different products are significantly lower.

Abstract

The invention relates to a process for the production of a gypsum moulded body comprising the steps of: (i) providing a mixture comprising a) grinding dust obtained from gypsum fibre products; b) fibres; and c) water; (ii) placing the mixture or a part thereof into a mould and pressing the mixture by means of a press to form the gypsum moulded body; and (iii) drying the formed gypsum moulded body, wherein the combined weight of a) the grinding dust and b) the recycled paper fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the recycled paper fibres (a:b) is in the range of 25:1 to 5:1. The invention also relates to the mixture used in the process, the gypsum moulded body, obtainable by the process, and the use of grinding dust for the production of a gypsum moulded body.

Description

Production of gypsum moulded bodies on a cycle press using grinding dust
Description
The invention relates to a process for the production of a gypsum moulded body, in particular gypsum fibre boards, wherein grinding dust of gypsum fibre products is used. The invention is further concerned with the mixture used in the process, the gypsum moulded body obtainable by the process, and the use of grinding dust for the production of a gypsum moulded body.
Prior art
The production of gypsum fibre products often causes formation of grinding dust as a waste product. This grinding dust is generated e.g. when the gypsum products are subjected to a finishing including surface grinding and/or sawing. Up to now, the grinding dust has mostly been disposed of as waste material in the landfill.
Processes for the production of a gypsum moulded body by means of cycle press are state of the art. Generally, hydratable gypsum derived from gypsum raw materials is used in these processes as the binding agent.
US 5632848 describes an equipment for the continuous processing of boardlike products containing gypsum such as fibreboards (fibre boards) and wallboards, wherein waste-type materials are considered as a source of calcium sulphate. As an example, US 5632848 mentions the transformation of scrap gypsum wallboard by grinding and calcining, in order to obtain a suitable starting material.
CONFIRMATION COPY EP 0490160 A1 describes a method for the production of plate-like or blockshaped gypsum building materials provided with a pore structure, wherein calcium sulphate alpha hemihydrate, water and optionally additives are mixed to form a pourable slurry, which is subjected to a suitable shaping process. Grinding dust from the production of the gypsum building materials can be recycled for the production of the slurry.
DE 4127932 A1 relates to a method and apparatus for making fibre- reinforced gypsum boards in a multi-layer continuous filtration process by adding a suspension of gypsum and wet-processed fibres, preferably from waste paper. Grinding dust obtained in the process can be recycled be feeding it into a calcining plant where it is transformed into a material to be reused.
WO 2017/098482 A1 describes the production of a moulding such as plane boards by pressing a non-sticky free-flowing granular cementitious or gypsum-based precursor composition. The gypsum-based precursor composition comprises calcium sulphate hemihydrate; water; guar gum and/or a hydrolysed polyvinyl alcohol; and a gelling agent. Since the binder system is on an organic basis, no separate drying step is required. A hydraulic press is used for pressing.
WO 2019/001677 A1 refers to a method of producing a gypsum slurry and a method of manufacturing a gypsum product such as gypsum board with the gypsum slurry. The gypsum slurry may comprise wet ground gypsum paper component and stucco, wherein the solid content of the wet ground gypsum paper component with respect to the stucco may be from 0.5 to 10 wt.%.
A disadvantage of conventional processes for preparing gypsum products considering use of waste materials generated during production of gypsum products such as grinding dust is that the grinding dust is subjected to calcination for activation, which is energy consuming. In other process, only a relatively small proportion of grinding dust is added to fresh raw materials such as stucco, for instance the grinding dust generated in the process as such for re-use. As a result, the grinding dust generated has mostly been disposed of as waste material in the landfill up to now.
Accordingly, the object of the invention was to provide a method for preparing gypsum products in which grinding dust of gypsum fibre products can be re- used in large proportions without the need of energy-intensive calcination treatment beforehand.
Detailed description of the invention
In the investigations underlying the present invention, it has unexpectedly been found that these objectives can be achieved by the production method for gypsum moulding bodies with mould pressing and using grinding dust in a particular composition.
The invention therefore relates to a method as defined in claim 1 as well as the mixture used therein, a corresponding gypsum moulded body obtained by the inventive process, and the use according to the further independent claims. Preferred embodiments of the invention are indicated in the dependent claims.
Accordingly, the present invention concerns a process for the production of a gypsum moulded body comprising the steps of:
(i) providing a mixture comprising a) grinding dust obtained from gypsum fibre products; b) fibres; and c) water
(ii) placing the mixture or a part thereof into a mould and pressing the mixture by means of a press to form the gypsum moulded body; and
(iii) drying the gypsum moulded body, wherein, in the mixture provided in step (i), the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the fibres (a:b) is in the range of 25:1 to 5:1.
The benefit of the invention is that grinding dust of fibre gypsum products can be re-used in large proportions without the need of energy-intensive calcination treatment beforehand. The disposal of waste material can be avoided. This is environmental-friendly and advantageous from an economical point of view, too. In addition, an even improved bending tensile strength could unexpectedly be observed for plates manufactured by the inventive process compared to plates obtained by conventional processes. The inventive process is for the production of a gypsum moulded body. The gypsum moulded body may be any article known by the skilled person. The gypsum moulded body to be produced is preferably a gypsum fibre board, in particular a gypsum fibre board for a raised floor or a raised floor element, respectively.
The dimensions of the gypsum moulded body can vary depending on the intended application. As standard dimensions for gypsum fibre boards (or gypsum plasterboards) e.g. the following ranges may be given: thickness of 10 - 42 mm, width of 1000 - 1250 mm, length of 1500 - 3000 mm. The width and length for raised floor elements are general smaller, for instance both independently in the range of 300 to 800 mm, preferably 620 mm, more preferably 600 mm, whereas the thickness can be in the range of 28 to 45 mm. If needed, smaller (e.g. 20 mm) or larger dimensions are, of course, also possible.
The process of the invention comprises the step of (i) providing a mixture comprising: a) grinding dust obtained from gypsum fibre products; b) fibres; and c) water.
The mixture is obtained by mixing the essential components and optionally further components with each other. Any suitable mixing device may be used. It is preferred to use a high-performance mixer, e.g. an Eirich mixer or a compulsory mixer. A compulsory mixer is preferred because a stronger granulation effect can be obtained. Moreover, the mixing time can be reduced and the homogeneity of the mixture is improved.
The order of addition of the components is arbitrary. Generally, it is suitable to mix the grinding dust and the fibres in the mixer until a homogeneous premixed dry mixture is obtained (duration e.g. 1 to 3 min) and subsequently adding water and further mixing in order to achieve an appropriate dispersion (duration e.g. about 1 to 5 minutes depending on the mixer used). One or more further additives, in particular a retarder, can be added to the system in dry or liquid form at any suitable time in the mixing operation.
It is preferred that the mixture is mixed until an earth-moist consistency is achieved, that is, the mixture is preferably an earth-moist mixture. The term “earth-moist consistency” is not unambiguously defined but known to the person skilled in the art. He knows that the correct addition of water is important for the processing properties and for the obtaining the required properties of the set mixture like bending tensile strength. The earth-moist consistency may therefore be tested in a simple and practicable test, the so- called snowball test. This may be done by forming a snowball-like clod in the hand. If it is not possible to form such a clod, the mixture may be too wet. The snowball should not disintegrate when opening the hand, otherwise the mixture is too dry. A slight adherence of the mixture should remain on the hand. The snowball may show a slight gloss on its surface because of a thin film of liquid.
Component a) is grinding dust obtained from gypsum fibre products. The fibres in the gypsum fibre products may be paper fibres, recycled paper fibres, glass fibres, chopped fiberglass, cellulose fibres, wood fibres, mineral fibres, plastic fibres, or combinations thereof, preferably paper fibres, recycled paper fibres or combinations thereof. The grinding dust may be a waste product, which is generated in the production of the gypsum fibre products. The gypsum fibre products from which the grinding dust is derived may be paper fibre-reinforced gypsum products, preferably may be gypsum fibre boards, i.e. the grinding dust is preferably obtained from the production of gypsum fibre boards.
Gypsum fibre boards generally may be gypsum boards with fibres. The fibres may be all kinds of fibres, e.g. paper fibres, recycled paper fibres, glass fibres, chopped fiberglass, cellulose fibres, wood fibres, mineral fibres, plastic fibres, or combinations thereof, preferably paper fibres, recycled paper fibres or combinations thereof.
In a preferred embodiment, the grinding dust is obtained from surface grinding and/or obtained from sawing the gypsum fibre products, in particular gypsum fibre boards. Surface grinding includes grinding of the surface and/or edges of the product. Grinding and/or sawing operations are usually carried out in a finishing step during the production after the gypsum fibre raw product has been formed. Surface grinding may be suitable e.g. to smooth the surfaces and/or remove defects such as burrs. Sawing may be suitable e.g. to cut the products into dimensions and/or forms as desired.
The grinding dust used may be (grinding dust) obtained from surface grinding, (grinding dust) obtained from sawing or a mixture thereof. It is preferred that 60 to 100 % by mass, preferably 90 to 100 % by mass, of the grinding dust is (grinding dust) obtained from surface grinding of the gypsum fibre products. It is more preferred that the grinding dust is (grinding dust) obtained from surface grinding.
The grinding dust of the gypsum fibre products has the composition of the gypsum fibre products from which it is derived. Since the gypsum fibre products are setting during the production, the specific composition can also depend on the point of time the grinding dust is generated.
It should be also clear that the grinding dust is added to the mixture, that is, it is added in uncalcined form. As is known by the skilled person, calcination is the practice of dehydrating gypsum mainly into calcium sulphate hemihydrate, also called plaster or stucco, which includes heating the gypsum to evaporate most of the crystalline water, usually at a temperature of at least 120°C. Here, calcination of grinding dust is not necessary, because during the drying process (to get rid of the excessive water) of the gypsum fibre products from which the grinding dust is derived calcium sulphate hemihydrate is generated. Preferably, during the drying process of the gypsum fibre products from which the grinding dust is derived calcium sulphate hemihydrate is produced on the surfaces of the gypsum fibre products. Therefore, the content of hemihydrate in grinding dust obtained from surface grinding may be higher than the content of hemihydrate in grinding dust obtained from sawing.
In a preferred embodiment, the grinding dust comprises 40 to 90 % by mass, preferably 60 to 80 % by mass, of calcium sulphate hemihydrate, based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust.
The term "based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust" means that the fibres contained in the grinding dust are not considered for calculation. For instance, for a grinding dust including 10 % by mass fibres, the residual 90 % are the basis (100%) for calculation.
Due to the above-mentioned high proportion of calcium sulphate hemihydrate, which can set, energy-intensive calcination is no longer necessary in the inventive production process for gypsum moulded bodies such as raised floor elements. The high proportion of the hemihydrate also improves the bending tensile strength of the products. Thus, the production of gypsum moulded bodies according to the invention is not only cheaper than in by conventional processes, but also environmental-friendly due to excluding the energy-intensive step of calcination.
The grinding dust contains fibres, preferably paper fibres, in particular recycled paper fibres. In a preferred embodiment, the grinding dust comprises 6 to 15 % by mass, preferably 8 to 13 % by mass, of fibres, preferably paper fibres, in particular recycled paper fibres, based on the total weight of the grinding dust.
In a preferred embodiment, the grinding dust comprises, based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust,
60 to 80 % by mass of calcium sulphate hemihydrate,
10 to 30 % by mass of calcium sulphate dihydrate,
7 to 12 % by mass of anhydrite.
The grinding dust may also contain calcite (CaCOs) and/or quartz, usually both in traces.
Component b) are fibres.
The fibres may be paper fibres, recycled paper fibres, glass fibres, chopped fiberglass, cellulose fibres, wood fibres, mineral fibres, plastic fibres, or combinations thereof, preferably paper fibres, recycled paper fibres or combinations thereof.
The combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass, preferably 90 to 10 % by mass, of the solids weight of the mixture.
The mass ratio of a) the grinding dust to b) the fibres (a:b) in the mixture is in the range of 25:1 to 5:1 , preferably 15:1 to 7:1 . It should be noted that the fibres contained in the grinding dust belong to component a), and are assigned thereto with respect to this ratio.
Component c) is water.
A rather low amount of water is suitable to obtain an advantageous mixture in step (i) having an earth-moist consistency. In a preferred embodiment, the mass ratio of the combined mass of a) the grinding dust and b) the fibres to the mass of c) water ((a+b)/c) is in the range of 0.3 to 0.9, preferably 0.4 to 0.8.
Due to the low moisture content of the mixture, a correspondingly reduced drying energy is required, which is a further benefit of the invention.
In the process according to the invention, the mixture may optionally comprise one or more additives, which are known by the skilled person in this technical field. Examples for optional additives are a retarder, a foaming agent, an accelerator and/or further gypsum types such as stucco and/or stemming from different sources.
In a preferred embodiment, at least one retarder is added to the mixture. Examples for suitable retarders are proteinaceous sources, which contain amino acid oligomers or synthetic compounds mimicking the same, chelates, such as DTPA and EDTA, or polyacrylic acid compounds. An example for a commercial product is Retardan® P from the company Sika, which is a Ca salt of polycondensed amino acids.
The total amount of additives, preferably at least one retarder, is preferably less than 20 % by mass, more preferably less than 10 % by mass, based on the solids weight of the mixture.
The process of the invention comprises the step of (ii) placing the mixture provided in step (i) or a part thereof into a mould and pressing the mixture by means of a press to form the gypsum moulded body.
In particular, the process is a discontinuous process, i.e. each gypsum moulded body is formed in sequence. The mixture may be prepared in amount which is sufficient to prepare one gypsum moulded body or more than one gypsum moulded body. In the latter case, of course only a part of the mixture is used for preparing the moulded body.
The mould used obviously depend on the shape and dimension of the moulded body to be produced. Generally, a simple box, e.g. a box of metal, is suitable. The mould will be arranged in cooperation with the press to be used. The mixture or a part thereof is placed in the mould, e.g. by pumping or pouring. It is suitable to homogenously distribute the mixture placed in the mould before pressing. Thereafter the mixture placed in the mould is pressed by means of a press to form the gypsum moulded body. The press may be a hydraulic press. The press is preferably a cycle press, in particular a hydraulic cycle press. Manufacturers of suitable hydraulic cycle presses are for instance the company Bussmann or Siempelkamp.
In general, the pressing process with the press, in particular the cycle press, is done by pressing a movable ram from above onto an immovable support surface. The mould can be mounted on the support face. In order to be able to drain off any water that may escape from the press body during the pressing process, suitable discharge means may be mounted.
For instance, a plastic plate can be mounted on both the underside of the ram and on the top of the support surface, which is provided with rectangular depressions as drainage channels. The water can collect in these depressions, and the water may be actively sucked into them by means of an applied negative pressure and fed into the water circuit of the production line via drainage pipes.
The pressing is preferably sufficiently high to achieve a compression or compaction of the gypsum moulded body formed. As a result, increased bulk densities are obtained.
The pressure applied by the press to the mixture in the mould may be e.g. in the range of 0.9 kg/mm2 to 4.0 kg/mm2, preferably 1.1 kg/mm2 to 2.0 kg/mm2.
The duration of the pressure application may be in the range of 20 s to 240 s. Higher or lower durations are also possible.
The bulk density of the gypsum moulded body obtained, in particular gypsum fibre board, may be e.g. in the range of 1 100 to 1900 kg/m3, preferably 1200 to 1700 kg/m3. According to the preferred embodiment, the gypsum moulded body or gypsum fibre boards, respectively, is a raised floor element. Due to the high load during application, compacted gypsum fibre boards having a high bulk density, e.g. in the range of 1400 to 1700 kg/m3, preferably 1500 to 1650 kg/m3, are suitable as raised floors. After completion of the pressing operation, the (formed) gypsum moulded body is dried in step (iii). The drying results in setting or hardening of the product.
The (formed) gypsum moulded body may be removed from the mould before, during or after the drying step. The drying step can be carried out at ambient conditions, e.g. at a temperature of 15 to 40°C and air atmosphere. Heating is possible, if desired. It may be suitable to dry the moulded gypsum bodies under standardised conditions with respect to temperature, atmosphere and humidity to obtain a uniform quality of the products. Preferably, the gypsum moulded body is dried to constant weight. A dryer, which is adapted or designed for the relatively low residual moisture of the moulded gypsum bodies is preferred.
An optional and preferred further step may be the step of (iv) finishing the gypsum moulded body prepared. The finishing suitably includes grinding of the surfaces and edges thereof, i.e. surface grinding and/or sawing. The grinding dust obtained in step (iv) may be reused as grinding dust in step (i). The finishing step is common for these products. Finishing may be carried out after step (iii).
The invention also relates to a mixture for the production of a gypsum moulded body, the mixture comprising a) grinding dust gypsum fibre products; b) fibres; and c) water wherein the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the fibres (a:b) is in the range of 25:1 to 5:1.
The invention also relates to a gypsum moulded body, obtainable by the inventive process as described above.
The invention also relates to a use of grinding dust of fibre gypsum products as a starting material for the production of a gypsum moulded body, wherein the grinding dust is used in uncalcined form.
All process steps, materials, features and statements related to the process described above equally apply to the inventive mixture, the inventive gypsum moulded body and the inventive use, where applicable so that reference is made thereto.
In the following, the present invention will further be illustrated by means of examples, which should however not be construed as limiting in any way to the scope of this application.
Examples
General procedure for production of panels
The press used is a hydraulic cycle press of the manufacturer Bussmann. The press ram can apply a maximum pressing pressure of 87 kg/cm2. To shape the panel, a steel moulding box is mounted on the supporting surface. The internal dimensions of the moulding box are 610 - 610 - 200 mm3. In order to be able to drain off any water that may escape from the press body during the pressing process, a plastic plate is mounted on both the underside of the ram and on the top of the support surface, which contains rectangular depressions as drainage channels. The water collects in these depressions, and the water is actively sucked into them by means of an applied negative pressure and fed into the water circuit of the production line via drainage pipes.
A grinding dust produced in the production of gypsum fibre boards during the surface sanding of the board surfaces can be used. The dust may contain e.g. approximately 60 - 80 % by mass of calcium sulphate hemihydrate, 10 - 30 % by mass of calcium sulphate dihydrate, 7 - 12 % by mass of calcium sulphate anhydrite, as well as traces of calcite (CaCOa) and quartz. The given percentages are based on total weight of the grinding dust excluding the mass of the paper fibres contained in the grinding dust. In this regard, grinding dust contains approx. 10 % by mass of recycled paper fibres based on the total weight.
The grinding dust (approx. 90 % by mass) and waste paper fibres (approx. 10 % by mass) are premixed dry in a high-performance mixer (e.g. Eirich mixer or compulsory mixer) until a homogeneous mixture is obtained (duration approx. 120 seconds). A retarder can be added to the system in dry or liquid form. After subsequent addition of water (water-solid value approx. 0.6), the mixture is mixed (approx. 2 to 3 minutes depending on the mixer used) until an earth-moist consistency is achieved.
The mass is pressed into panels on a cycle press. For this purpose, the mass is placed in a moulding box (610 x 610 x 200 mm3), evenly distributed and pressed with a pressure of 0.87 kg/mm2 (corresponds to the maximum performance of 300 bar for the press used). After the pressing process, the boards were dried under laboratory or pilot plant air.
For production on an industrial scale, the manufacturing process may be modified accordingly, especially with regard to the finishing of the pressed mouldings (e.g. grinding of surfaces and edges).
The following examples are carried out according to this general procedure unless amendments or more precise specifications are indicated below.
Samples
Grinding dust is produced during the production of gypsum fibre boards, wherein surface grinding dust is obtained from surface grinding and sawing dust is obtained from sawing. HH proportion refers to the amount of calcium sulphate hemihydrate in the grinding dust, based on the mass of the grinding dust excluding the mass of the paper fibres contained in the grinding dust. The differences in the amount of hemihydrate in the grinding dust result from different products, from which the grinding dust is derived, different thicknesses of the surface to be grinded on these different products, different drying conditions and the (undetermined) mixing ratio of grinding dust obtained from surface grinding and the grinding dust obtained from sawing.
The following starting materials are used for preparing panels:
Stucco: Stucco from Knauf Gips KG
GD 1 : mixture of surface grinding dust and sawing dust, HH proportion 44.5 % by mass
GD 2: mixture of surface grinding dust and sawing dust, HH proportion 34.6 % by mass GD 3: mixture of surface grinding dust and sawing dust, HH proportion 6.7 % by mass
Vinnapas EP 3360 aqueous polymer dispersion made of vinylacetate and ethylene Retardan P Ca salt of polycondensed amino acids, Sika
The following formulations shown in table 1 are used to prepare panels.
Sample 2 is according to the invention. Samples 1 , 3 and 4 are reference examples. The drying temperature was 40 °C. Sample 1 is a common formulation according to the prior art. Table 1
The mixture of sample 1 exhibits a significant granulating effect. One test plate of sample 1 was broken during removal from the mould.
The mixture of samples 2 and 3 exhibits a significant granulating effect, but the granules are homogeneously moisturized.
The panels were prepared according to the general procedure described above. Two test plates (600 x 600 x 20 mm2) were prepared for each formulation and two smaller pieces (400 x 300 mm2) were cut out of each of them, which were used as samples (for formulation of Sample 1 : Sample 1_1 , 1 _2 etc.). The parameters given in the following tables 2 and 3 were determined in accordance with EN 15283-2:2009-12. Table 2 includes the values for specimens based on samples 1 and 2 (invention), whereas Table 3 includes the values for specimens based on samples 3 and 4.
Table 2
Table 3 The bending tensile strength for both sample 1 and 2 satisfies the requirements of the standard (> 5.5 N/mm2), wherein bending tensile strength of inventive sample 2 is higher than that of reference sample 1. The reason for this unexpected result is unknown. The bending tensile strength for both samples 3 and 4 does not satisfy the requirements of the standard. The bending tensile strength of the plates prepared with grinding dust seems to depend on the HH proportion included in the grinding dust.
Analysis of surface grinding dust
Ten samples of grinding dust obtained from surface grinding were collected in a plant producing gypsum fibre board on different products. The content of hemihydrate of the samples was determined by X-ray diffraction. The paper fibres contained in the samples were not considered with respect to the values given in following table 4.
* The samples were collected at different times.
Table 4
The hemihydrate content is high and the variations are relatively small (63.7 - 79.3 %), variations with the same product minimal. Compared to the previously used material based on a mixture of grinding dust obtained from surface grinding and the grinding dust obtained from sawing having a HH content of 6 - 44.5 %, significantly more HH is contained; variations between different products are significantly lower.
It is expected to have even better results with a proportion of hemihydrate up to 90 %, since the hemihydrate is functioning as binding agent in the system (by reacting with water to calcium sulphate dihydrate), so a higher stability (e.g. bending tensile strength) of the gypsum moulded body is expected.

Claims

Claims A process for the production of a gypsum moulded body comprising the steps of:
(i) providing a mixture comprising a) grinding dust obtained from gypsum fibre products; b) fibres; and c) water
(ii) placing the mixture or a part thereof into a mould and pressing the mixture by means of a press to form the gypsum moulded body; and
(iii) drying the gypsum moulded body, wherein, in the mixture provided in step (i), the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the fibres (a:b) is in the range of 25:1 to 5:1 . The process according to claim 1 , wherein the press is a cycle press. The process according to any one of the preceding claims, wherein the grinding dust is obtained from surface grinding and/or sawing of the gypsum fibre products, wherein it is preferred that 60 to 100 % by mass, preferably 90 to 100 % by mass, of the grinding dust is obtained from surface grinding of the gypsum fibre products, wherein the grinding dust is more preferably obtained from surface grinding. The process according to any one of the preceding claims, wherein the grinding dust comprises 40 to 90 % by mass of calcium sulphate hemihydrate, preferably 60 to 80 % by mass of calcium sulphate hemihydrate, based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust, and/or the grinding dust comprises 6 to 15 % by mass, preferably 8 to 13 % by mass, of fibres, preferably paper fibres, in particular recycled paper fibres, based on the total weight of the grinding dust. The process according to any one of the preceding claims, wherein the grinding dust comprises, based on the mass of the grinding dust excluding the mass of the fibres contained in the grinding dust,
60 to 80 % by mass of calcium sulphate hemihydrate,
10 to 30 % by mass of calcium sulphate dihydrate,
7 to 12 % by mass of anhydrite. The process according to any one of the preceding claims, wherein the gypsum fibre products from which the grinding dust is derived are gypsum fibre boards, and/or wherein the gypsum moulded body to be produced is a gypsum fibre board, in particular a gypsum fibre board for a raised floor. The process according to any one of the preceding claims, wherein in the mixture provided in step (i), the mass ratio of the combined mass of a) the grinding dust and b) the fibres to the mass of c) water ((a+b)/c) is in the range of 0.3 to 0.9, preferably 0.4 to 0.8. The process according to any one of the preceding claims, wherein the mixture further comprises one or more additives, preferably at least one retarder, wherein the total amount of additives is less than 20 % by mass, preferably less than 10 % by mass, based on the solids weight of the mixture. The process according to any one of the preceding claims, wherein the grinding dust is added to the mixture in uncalcined form. The process according to any one of the preceding claims, further comprising a step of (iv) finishing the prepared gypsum moulded body including grinding of the surfaces and edges thereof and/or sawing. - 18 -
1 1. A mixture for the production of a gypsum moulded body, the mixture comprising a) grinding dust of gypsum fibre products; b) fibres; and c) water wherein the combined weight of a) the grinding dust and b) the fibres amounts to 80 to 100 % by mass of the solids weight of the mixture, and the mass ratio of a) the grinding dust to b) the fibres (a:b) is in the range of 25:1 to 5:1 .
12. The mixture according to claim 11 , wherein the mixture is as defined in any of claims 3 to 9.
13. A gypsum moulded body, obtainable by a process according to any one of claims 1 to 10. 14. Use of grinding dust of gypsum fibre products as a starting material for the production of a gypsum moulded body, wherein the grinding dust is used in uncalcined form.
15. Use according to claim 14, wherein the grinding dust is as defined in any of claims 3 to 6.
EP20845773.9A 2020-12-16 2020-12-16 Production of gypsum moulded bodies on a cycle press using grinding dust Pending EP4263463A1 (en)

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DE4039319A1 (en) * 1990-12-10 1992-06-11 Sicowa Verfahrenstech METHOD FOR PRODUCING PLASTER BUILDING MATERIALS
DE4127932A1 (en) 1991-08-23 1993-02-25 Bold Joerg Fibre-reinforced plasterboard mfr. - using by=product gypsum and waste paper
WO1993011085A1 (en) * 1991-11-25 1993-06-10 Carl Schenck Ag Fiber gypsum board and method of manufacturing same
RU2125029C1 (en) * 1997-07-16 1999-01-20 Акционерное общество "Авангард" Composition for fibrous heat- and sound-insulation material and method of manufacturing thereof
DE10336569B4 (en) * 2003-08-08 2005-07-21 Siempelkamp Handling Systeme Gmbh & Co Method for producing fire-resistant gypsum fiberboards and apparatus for carrying out a method for producing fire-resistant gypsum fiberboards
EP2418184B2 (en) * 2010-08-12 2021-02-17 Lindner GFT GmbH Method for manufacturing alpha-calcium sulphate hemi-hydrate
US10570062B2 (en) * 2013-10-07 2020-02-25 Knauf Gips Kg Method for producing a gypsum plasterboard
WO2017098482A1 (en) 2015-12-11 2017-06-15 Zetland Technologies Limited Construction elements
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