CA1059736A - Method of producing fibre-containing building members - Google Patents
Method of producing fibre-containing building membersInfo
- Publication number
- CA1059736A CA1059736A CA199,358A CA199358A CA1059736A CA 1059736 A CA1059736 A CA 1059736A CA 199358 A CA199358 A CA 199358A CA 1059736 A CA1059736 A CA 1059736A
- Authority
- CA
- Canada
- Prior art keywords
- calcium sulfate
- hemihydrate
- gypsum
- water
- sulfate hemihydrate
- 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.)
- Expired
Links
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/26—Drying gases or vapours
- B01D53/265—Drying gases or vapours by refrigeration (condensation)
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- 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
- C04B11/00—Calcium sulfate cements
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- 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
- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
- C04B11/024—Ingredients added before, or during, the calcining process, e.g. calcination modifiers
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- 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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F11/00—Control or safety arrangements
- F24F11/89—Arrangement or mounting of control or safety devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
- F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
- F24F3/14—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification
- F24F3/153—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification with subsequent heating, i.e. with the air, given the required humidity in the central station, passing a heating element to achieve the required temperature
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
- F25D21/002—Defroster control
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
- F25D21/02—Detecting the presence of frost or condensate
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Thermal Sciences (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Analytical Chemistry (AREA)
- Inorganic Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Producing Shaped Articles From Materials (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
- Paper (AREA)
- Nonwoven Fabrics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
This invention relates to the production of building members and, in particular to the production of plates. The member is produced by forming a mixture of a fibrous substance with a sulfatic binding agent and an amount of water which is a multiple of the amount of water necessary to set the binding agent. The main amount of excess water is removed from the fleece mechanically before the setting process begins, the mould is shaped and subsequently dried. The process is characterized in that the sulfatic binding agent is a calcium sulfate hemihydrate in which the specific surface area of the particles, in the aqueous suspension, does not alter or alters only to an unsubstantial amount until the main amount of excess water is removed mechanically from the fleece.
This invention relates to the production of building members and, in particular to the production of plates. The member is produced by forming a mixture of a fibrous substance with a sulfatic binding agent and an amount of water which is a multiple of the amount of water necessary to set the binding agent. The main amount of excess water is removed from the fleece mechanically before the setting process begins, the mould is shaped and subsequently dried. The process is characterized in that the sulfatic binding agent is a calcium sulfate hemihydrate in which the specific surface area of the particles, in the aqueous suspension, does not alter or alters only to an unsubstantial amount until the main amount of excess water is removed mechanically from the fleece.
Description
~q3 5~73~
Fibre-bearing building members can be produced by mixing fibrous substances such as for example cellulose fibres, glass wool, rock or mineral wool, fibre asbestos and the like, with hydraulic or non-hydraulic binding agents and water, with shaping of the mixtures.
When hydraulic binding agents are used, an aqueous suspen-sion can be made continuously from the binding agents and the fibre substances. The excess water is removed by a suction action from the aqueous solution, after it has been produced and shaped. The remaining moulding material is dried after the pressing operation. The removal by suction is effected on a con-tinuously moving endless suction support which can be in the form of a water-pervious belt such as a cotton belt or a metal sieve belt. The water is,sucked from the shaped suspension through the water-pervious belt, by vacuum suction heads which are arrang-ed below the belt. After removal of the moulding, the remains of the moulding material are removed from the water-pervious belt with knocking means and by sponging off with water. The water which is removed by the suction action, and the cleaning water, are used to make the supsension which is used as the starting material.
If fibre-bearing building members are to be produced using non-hydraulic binding agents, the starting materials can be produced in the presence of an amount of water which is suffi-cient for, or which is in excess of the amount required for, setting the non-hydraulic binding agent, and the starting mater-ials may possibly be pressed, and then dried.
28 An example of producing plates from fibres and gypsum as the ~ - 2 - i~
~ .
105973~
non-hydraulic binding agent is found in German patent specifica-tion No 647465,- published June 17, 1~37. In accordance with this specification, gypsum, asbestos fibres and water are formed into a mixture which is dry to the touch and which is subsequently pressed into mouldings~ After the pressing operation these mouldings are moistened with size water, and dried.
.
- 2a -1~159~736 In accordance with German patent specification No. 934395, published September 22, 1951 spinable glass fibres can also be dry mixed with gypsum, and then water added. It is however also possible for the spinable fibres to be mixed simultaneously with gypsum and water. These mixtures which should contain approxlmately the amount of water necessary for setting of the gypsum, are then caused to set, while being shaped.
German patent specification No. 1123244, published August 16, 1962 discloses another possible way of producing plat~s. In ac-cordance with this specification, in a dry condition or with the ad-dition of an extremely small amount of water, the starting materials such as fibres, hydraulic or non-hydraulic binding agents, are shaped in the form of plates which are provided wi~h coverings such as wet fine muslin cloths, from which water can be evaporated into the plate blank moulding while this is being pressed.
In accordance with French patent specification No. 1461690, published December 9, 1966 it is said to be of advantage to intro-duce into a mould gypsum or other sulfate-bearing binding agents in the form of dry dust or grains, and subsequently or simultaneously to moisten them with water. The water required for this purpose can be introduced in the form of steam or water bound on other substancesO
German Offenlegungsschrift No. 1571466, published December 17, 1970 also discloses a method of producing plates and shaped members from gypsum, wherein the gypsum which is mixed with the fibr~ component is introduced in a dry condition into a mould, and, during or after this step, moistened with an amount of water which is just sufficient for setting of the gypsum. It can also be of advantage for the moulding to be compacted by the action of a i(~3~ pressure.
~- - 3 -~S9736 German Offenlegungsschrift No. 2103931, published August 31, 1972, discloses a method wherein fibres and gypsum are mixed on a conveyor belt, a so-called pre-shaping belt. This mixture is then transferred on to a second conveyor belt r a ~o-called pressing belt, and at the same time moistened with an amount of water which is approximately sufficient to cause the gypsum to set. The plate in web form which is produced in this manner is pressed and cut into plates from which a residual moisture content of from 10 to 15% by weight must then be removed by drying.
When using a gypsum-water mixture of pourable consistency, which may possibly contain fibre substances, in which the amount of water is from 3 to 6 times the amount required for setting of the gypsum, the excess water must be removed by drying in a method step following the shaping step. The best known example of such an operation is the production of gypsum pasteboard plates.
In this case thepourable gypsum-water mixture is placed on a pasteboard web whose longitudinal eclges are folded upwardly.
The pasteboard web which is filled wi-th the gypsum-water mixture is subsequently covered with an addi~ional pasteboard web.
After the gypsum has set, the excess water is removed by drying from the plate web, which is cut into plates. In this method the relationship by weight of water to gypsum is from approximately 0.6 to 1Ø
As disclosed in German patent specification No. 928219, published April 28, 1955, however it is also possible to put into a mould glass fibre fleeces whose fibre thicknesses are more than 0.025 mm, together with a gypsum-water mixture, and to allow this to set. In German patent specification No. 825377, published 3~ November 15, 1951, it is recommended that a fibre belt should be ~ - 4 -~L059736 drawn through a gypsum-water mixture of suitable consistency, and introduced into moulds, the excess water being pressed out.
: In accordance with German patent specification No. 1092361, published August 27/ 1964, textile fibre substances, asbestos or cellulose can also be used for the production of gypsum plates/ if they are firstly suspended in ample water and a mixture of glass fibre bunches which are fixedly connected, with gypsum and water, is introduced into the resulting suspension. The excess water in the resulting mixture is removed by suction after the shaping operation, and the remaining .
- 4a -residue is pressed into the form of plates which are then dried.
It has also already been proposed, in German patent specifi-cation No 1104419, published May 5, 1966, to produce an aqueous suspension from fibres and sulfatic binding agents such as gypsum. The aqueous suspension includes a large excèss of water over and above the amount necessary for setting of the sulfatic binding agent, and also retarding agents. This suspension is continuousl~ formed into a fleece configuration from which the water is removed before the sulfatic binding agents begin to set.
Several layers of this fleece are wound on to a roller and, being firmly pressed one upon the other, removed therefrom. The plate blank is dried after setting of the binding agent.
` Accordingly, the technical development in the production of fibrebearing gypsum plates led to three main possible methods.
In accordance with one of these methods; attempts were made to keep the amount of water to be added to the starting materials, as low as possible. In this case use was made of the observa-tions that, in the presence of an amount of water which is approximately sufficient to cause the gypsum present to set, the gypsum which sets to calcium sulfate dihydrate forms a solid body of low pore volume. In this way it shoul~ be possible to produce building members of suEficient strength.
The second possible method is producing a pourable mixture, from gypsum, fibres and a limited excess of water, and performing a casting process with the mixture to produce building members with the strength values which satisfy the requirements set in connection with the particular intended use. In this method the 28 excess water is removed only by drying.
~L~59736 The third possibility for producing fibre-bearing gypsum plates is substantially characterised in that the moulding materials contain substantially larger amounts of water than are required for making the mixture pourable and for setting of the amounts of gypsum which are contained in such materialsO In order to produce a building member of sufficient strength, it is necessary for the moulding materials to be compacted by the main amount of excess water being removed mechanically therefrom, before the gypsum sets. These last methods suffer from techni-cal disadvantages particularly when the hemihydrate gypsum ismade into a suspension by using the water which was removed as excess water from a-previous such suspension. This excess water contains dihydrate crystals which, upon being mixed with calcium sulfate hemihydrate, act as crystallisation seeds, to promote the precipitation of small calcium sulfate dihydrate crystals out of the fluid component of the gypsum-bearing suspension, and thus act as setting accelerators. It is known that the conversion, which is referred to as setting, of calcium sulfate hemihydrate into calcium sulfate dihydrate in the presence of water is based on the fact that the hemihydrate is more highly soluble in water than the dihydrate. Accordingly, the formation of dihydrate crystals can be retarded by reducing the solubility or the speed of dissolution of the hemihydrate crystals. The retarding agents which are required for the purpose however also cause a reduction of the dihydrate crystals in the excess water which is produced when making the plates and which can be used again as the mixing water. With manipulation it is possible to find an equilibrium 28 between the accelerating act~on ofthe crystallization seeds ~ S973~ i and the effects of the retarding agent, such as to ensure a stiffening time which is suitable for continuous production of plates. For these previously known methods, use is made of a mixture comprising fibre substances and plaster of Paris in a ratio by weight of 0.1 to 0.4, which mixture is made into a suspension with an amount of water which is ten times the weight of gypsum, and then formed into a fleece from which the major part of the excess water is removed again by suction. In this the fibre component acts as a filter accessory in the excess 1~ water suction removal operation. ~s however, as is known,plaster 7 of Paris disperses very finely in water, an over-increased amount of fibres had to be added to the fibre-gypsum-water mixture ln 7 order for the suction removal operation to be carried out in a technically acceptable time; without causing excessive finely divided gypsum to be removed from the fleece due to an excessive suction action. Obviously these necessary conditions frequently cause the strength, and the degree of dewatering, of the end products to be reduced. In addition there is the danger that an excessive amount of calcium sulfate dihydrate is contained in crystalline form in the excess water. As in many cases the excess water cannot be used again for forming the suspension, and can only be discarded, disproportionately high losses of water and binding agent must be accepted.
The attempt was therefore made to find ways of reducing such losses of water and binding agent, and nonetheless avoiding an unnecessarily high proportion of fibres, when producing puilding members which are produced from a mixture of fibres, sulfatic binding agents and water, wherein the water content of such mix-29 tures should be a multiple of the amount of water necessary for ~059736 setting of the sulfatic binding agent. However, the reduction in the proportion of fibres should not be accompanied by a reduc-tion in the strength of the building member.
There was found a method of producing fibre-bearing build-ing members, in particular plates, by forming a fleece from mixtures of fibrous substances with sulfatic binding agents and an amount of water which is a multiple greater than the amount of water necessary for setting of the sulfatic binding agents, wherein the main amount of excess water is removed mechanically from the fleece before the setting process begins, and the fleece is shaped into a moulding, possibly with a pressing treatment, the moulding being dried after the setting process. In accord-ance with this method the sulfatic binding agent used is a calcium sulfate hemihydrate in which the particle specific surface area does not alter or alters only to an unsubstantial extent, in the aqueous suspension, until the main amount of excess water is removed mechanically from the fleece.
The method of the invention is based on the observation that, ~ in the case of all hemihydrate gypsums which are produced in dry ; 20 methods, the individual gypsum particles decompose immediately after they are moistened with water. The gypsum particles seem to swell from the inside outwardly, and break up. The rapidity and the extent of decomposition depends on the degree of purity of the raw gypsum, and on the nature of the calcining method.
The rapidity and extent of decomposition is particularly high when using a very pure raw gypsum which is dewatered under a very low steam partial pressure, in accordance with the technical conven-tional modes of operation.
29 Due to the decomposition of the individual particles of the ~0~;9736 calcium sulfate hemihydrate upon contact with water, the number of very fine gypsum particles and thus the specific surface area of the gypsum is quite considerably increased. This increase in the number of very fine gypsum particles, and the corresponding increase in the specific surface area of the gypsum, results however in a considerable extension in the time required for removal of the excess water by a suction action. In spite of this increase in the suction removal time, the degree of dewatering of the fleece is poorer, so that the fleece retains a high water content which must be removed by drying in the final stage of the method, which requires the application of a considerable amount of energy. The very fine gypsum particles, which are produced by the calcium sulfate hemihydrate particles decomposing in an apparently explosion-like manner, when in the presence of water, rèmain suspended as solid matter in the excess water, and are removed by suction with the excess water, due to the extremely fine nature of such particles. Th:is disadvantage can be overcome to a limited extent by an over-increased proportion of fibres so that they can perform to the desired extent their function as a filter when the water is removed by suction. It was however also noted in this connection that the strength of the fibre~bearing building members is reduced again when using higher proportions of fibre than those which are the optimum for the respective fibre-bearing building member in question.
It was found that these disadvantages can be overcome if the sulfatic binding agent used is a calcium sulfate hemihydrate in which the specific surface area of the particles does not alter, or alters to an only inconsiderable extent, in aqueous suspension, 29 until the main amount of the excess water has been removed from g _ ~159736 the fleece. This delay in decomposition of the particles is not iaentical to the known action of retarding the setting time, which is caused by adding so-called retarding agents. It may even be desirable to add to the gypsum-fibre suspension so-called accelerating agents, such as potassium, iron or zinc sulfate, ; which take effect after the main amount of excess water has been removed and which shorten the time for stacking of the fibre-bearing building member, to that of setting. It was further recognised that it is particularly advantageoùs to use a calcium sulfate hemihydrate whose specific surface area, measured in accordance with the slaine method, in aqueous suspension, is from 500 to 6000, preferably from 1500 to 4000 sq.cm/g. Calcium sulfate hemihydrates of thiskind can be producedby means of any raw materials which are conventionally used in the gypsum industry and which preferably contain less than 3% by weight of clay, these being referred to hereinafter as 'raw gypsum'.
The raw gypsum used can be for example natural or synthetic calcium sulfate dihydrates which are converted in per se known ; manner into a hemihydrate with the above specified specific surface area. In addition, the ca~cium sulfate hemihydrates to be used in accordance with the invention can also be produced by crystalline transformation of calcium sulfate hemihydrate having a different specific surface area; the addition of additives which influence the crystallisation tendency can be of advantage. Also, 25 - calcium sulfate hemihydrates which can be used in accordance with the invention can equally be produced by dehydrating set calcium sulfate hemihydrate, in which case small amounts of additives such as chlorides of magnesium, calcium, cobalt or tin, or 29 potassium or magnesium perchlorate can possibly be added to a raw ~L~S9736 gypsum of this kind.
With the above ~pecified specific surface area of the hemihydrate used, in aqueous suspension, the calcium sulfate hemihydrate enjoys optimum suitability for the method according to th~e inven-tionl whose aim is to maintain this optimum suitability during the processing time until the main amount of excess water has been mechanically removed from the fleece.
The above-mentioned optimum specific surface area of the hemihydrate can be achieved by the particular particle size of -the dry calcium sulfate hemihydratel being at least substantially unaltered due to the action of the watex over the period in question. Thus, the mechanical decomposition of the individual particles of the calcium sulfate hemihydrate in the presence of water can be controlled for example by the calcium sulfate hemi-; 15 hydrate to be used, being produced from a raw gypsum which is previously ground to the necessary degree of fineness, by heat-ing in aqueous suspension or by dry cooking in the presence of chlorides of magnesium, calcium, cobalt or tin, or in the pre-; sence of calcium or magnesium perchlorate, in the amounts of from 0.05 to 0.8 and preferably from 0.1 to 0.4% by weight. The above-mentioned additives prolong the decomposition time of the gypsum particle. The suitable amount of such additive substances can be easily determined in each case by simple preliminary tests.
It is also possible however for decomposition of the calcium sulfate hemihydrate particles to be prevented by protective coatings. The method according to the invention can therefore be advantageously carried out by using a calcium sulfate hemihydrate which was produced from a raw gypsum which was previously ground 29 to the necessary degree of fineness, by cooking in the presence ~6~S973i6 of substances which form around the gypsum particles a coating layer which retards decomposition of the gypsum particles in an aqueous medium. Such layer-forming substances are for example polyvinyl acetate or silicone. The method of the invention can be carried out in a particularly advantageous manner: by using a calcium sulfate hemihydrate which was produced by cooking from a raw gypsum which was previously ground to the necessary degree of fineness, in the presence of from 0.05 to 1.0 and preferably ; from 0.1 to 0.5% by weight of silicone emulsion.
The essential action of this alternative operation lies in retarding decomposition of the calcium sulfate hemihydrate parti-cles, calculated from the moment of admixing the water, at least until the end of the operation of removing by suction the excess water contained in the fleece.
Maintaining the protective layer substantially beyond this moment would result in retardation of the setting process which in many cases is not desired. The life of the protective coating which is required in each specific case can be easily determined by means of simple preliminary tests, with reference to the description given herein.
Instead of using calcium sulfate hemihydrate as the sulfatic binding agent, it is also possible to use a mixture of calcium sulfate hemihydrate with less than 10% by weight and preferably from 3 to 6~ by weight of cement. -It has also been found advantageous for from 0.001 to 0.2%
by weight of a flocculating agent, preferably polyacrylamide, to be added to the suspension con-taining the calcium sulfate hemihy-drate.
29 In accordance with a variant of the invention, the calcium sulfate hemihydrate used is a calcium sulfate hemihydrate in the a-form, which is produced by dehydration from raw gypsum or from hemihydrate by crystalline transformation, and in which the mean ration between the largest and the smallest diameters of a particle lies between 1.0 and 4.0 and preferably 1.5 and 3Ø
Calcium sulfate hemihydrate in its a-form frequently occurs in needle or plate-shaped crystals or bunch-like crystal com-plexes. A calcium sulfate hemihydrate in its a-form which is present in approximately mono-crystal form, is particularly suit-able for carrying out the method of the invention. This calcium sulfate hemihydrate does not decompose in aqueous suspension, but changes its particle size only by virtue of the dissolution of its particles, which is necessary for the setting process.
The specific surface area of the particles of the calcium sulfate hemihydrate in its a-form, as measured in accordance with the Blaine method, in aqueous suspension, should advanta-geously be from 500 to 6000 and preferably from 1000 to 4000 ~ s~. cm/g.
1/ It is unimportant, for carrying out this method according to the invention, whether the a-form calcium sulfate hemihydrate is produced directly with the necessary level of grain fineness, or whether it is ground down to the necessary level of fineness, from a coarser grain range, in a dry or a wet process.
The method according to the invention can also be carried out by using a calcium sulfate hemihydrate in the form of an a-hemihydrate which was produced from gypsum which occurs in the production of phosphoric acid, by cooking in the presence of additives which influence the crystallisation tendency. A by 29 product which occurs when producing phosphoric acid from raw ~)5973~ii -- phosphate and sulfuric acid is a gypsum which comprises for example approximately 90% o calcium sulfate dihydrate, and which includes only small amounts of acid. This gypsum can be convert-ed into the a-hemihydrate, for example by heating in a 35~
calcium chloride solution. However, this firstly results in needle-like crystals with properties which are unfavourable from the point of view of technical application. For this reason substances were added to the~crystallisation pan, which improve the crystallisation tendency of the resulting a-hemihydrate gypsum such that this occurred in the form of short, compact and uniform crystals. Additives which have been found particularly suitable and which are preferabiy used for influencing the crystallisation tendency are cis-ethylene dicarboxylic acids, for example maleic acid or the anhydride thereof, in aadition the alkaline salts of citric acid phthalic acid and the anhydride thereof, and sulfite lyes.
Obviously the method according to the invention can also be carried out by using mixtures of calcium sulfate in the ~-hemihydrate form and the -hemihydrate form, if the ~-hemi-hydrate fulfils the condition that the specific surface area ofits particles in aqueous suspension does not alter or alters only to an unsubstantial extent, until the main amount of excess water has been mechanically removed from the fleece. In this case the sulfatic binding agent used is p~eferably a mixture of ~-hemihy-drate and from 30 to 70% by weight of a-hemihydrate.
Instead of using pure a-calcium sulfate hemihydrate or a mixture of a- and ~-calcium sulfate hemihydrate as the sulfatic binding agent, it is also possible to use a mixtu-e thereof with 29 less than 10% by weight and preferably from 3% to 6% by weight of cement.
~L~59736 Carrying out the variant of the method according to the invention avoids very fine gypsum particles being produced by calcium sulfate hemihydrate particle decomposition, which is thought to occur in the manner of an explosion, in the presence of water. Such very fine gypsum particles firstly remain suspended in the form of solid matter in the excess water, and are sucked away therewith because of their extreme fineness.
Evr~n i~ the last-mentioned disadvantage can to a limited extent be overcome by a super-increased amount~of fibres which act as a filter when the excess water is removed by suction, these higher levels of fibre content frequently result in end products whose strength is not at an optimum.
It is particularly advantageous for this method according to the invention to use a calcium sulfate hemihydrate, in particular in a-form, whose specific surface area, as measured in accordance with the Blaine method, in aqueou~; suspension, is from 500 to 6000 and preferably from 1000 to ~1000 sq. cm/g. As the individ-ual particles of the-~a-calcium sulfate hemihydrate do not decompose in the presence of water, it is possible for this specific surface area of the a-calcium sulfate hemihydrate to be maintained during thè whole processing time of the f~leece which is formed from calcium sulfate, fibres and a large excess of water, in fact until the moulding is produced.
The a-calcium sulfate hemihydrate which is to be used in accordance with the invention has little sensitivity of reaction on dihydrate seeds and therefore makes it unnecessary to add -setting retarding agents to the mixture comprising sulfatic 23 binding agents, fibres and an excess amount of ~ater.
~059736 As already mentioned, the method according to the invention provides that the particles of the calcium sulfate hemihydrate used to not change, or change only to an unsubstantial extent, in respect of their particle size, until the moulding is produced, even though the particles are in aqueous suspension. This pre-vents the occurrence of very fine calcium sulfate particles which require an increase in the amount of fibres in the fleece to be produced. However, the reduction in the amount of very fine calcium sulfate particles also results in a considerable increase in the speed of suction removal, without substantial amounts of calcium sulfate and fibres being entrained wlth the water removed. In this way the starting mixtures`icomprising fibres, sulfatic binding agents and water can also be more rapidly introduced into a mouldO
In accordance with the method of the invention, when produc-ing gypsum plates, the production capacity of the apparatus used, in particular winding roll machines, can be considerably increas-ed in comparison~with the previously known methods. In additio~
when using the method according to the invention it is now possible to carry out the manufacture of flbre-bearing construc-tion material plates, using sulfatic binding agents, on Four-driniers, which can also be provided with metal sieves. It was not possible for these plate producing machines to be used for carrying out the previously known methods, as excessively long suction removal times and unacceptable fouling of the conveyor belts had to be tolerated. These disadvantages are eliminated by means of the method according to the invention.
28 In addition, the method according to the invention provides ,~ .
l~S'~736 fibre-bearing construction members which always remain constant in quality, in particular as regards strength.
The moulded members which remain after the excess water has been removed by the suction action still contain from 5 to 30%
,~
by weight of free water which is removed by drying in per se known manner.
Fibre-bearing building members can be produced by mixing fibrous substances such as for example cellulose fibres, glass wool, rock or mineral wool, fibre asbestos and the like, with hydraulic or non-hydraulic binding agents and water, with shaping of the mixtures.
When hydraulic binding agents are used, an aqueous suspen-sion can be made continuously from the binding agents and the fibre substances. The excess water is removed by a suction action from the aqueous solution, after it has been produced and shaped. The remaining moulding material is dried after the pressing operation. The removal by suction is effected on a con-tinuously moving endless suction support which can be in the form of a water-pervious belt such as a cotton belt or a metal sieve belt. The water is,sucked from the shaped suspension through the water-pervious belt, by vacuum suction heads which are arrang-ed below the belt. After removal of the moulding, the remains of the moulding material are removed from the water-pervious belt with knocking means and by sponging off with water. The water which is removed by the suction action, and the cleaning water, are used to make the supsension which is used as the starting material.
If fibre-bearing building members are to be produced using non-hydraulic binding agents, the starting materials can be produced in the presence of an amount of water which is suffi-cient for, or which is in excess of the amount required for, setting the non-hydraulic binding agent, and the starting mater-ials may possibly be pressed, and then dried.
28 An example of producing plates from fibres and gypsum as the ~ - 2 - i~
~ .
105973~
non-hydraulic binding agent is found in German patent specifica-tion No 647465,- published June 17, 1~37. In accordance with this specification, gypsum, asbestos fibres and water are formed into a mixture which is dry to the touch and which is subsequently pressed into mouldings~ After the pressing operation these mouldings are moistened with size water, and dried.
.
- 2a -1~159~736 In accordance with German patent specification No. 934395, published September 22, 1951 spinable glass fibres can also be dry mixed with gypsum, and then water added. It is however also possible for the spinable fibres to be mixed simultaneously with gypsum and water. These mixtures which should contain approxlmately the amount of water necessary for setting of the gypsum, are then caused to set, while being shaped.
German patent specification No. 1123244, published August 16, 1962 discloses another possible way of producing plat~s. In ac-cordance with this specification, in a dry condition or with the ad-dition of an extremely small amount of water, the starting materials such as fibres, hydraulic or non-hydraulic binding agents, are shaped in the form of plates which are provided wi~h coverings such as wet fine muslin cloths, from which water can be evaporated into the plate blank moulding while this is being pressed.
In accordance with French patent specification No. 1461690, published December 9, 1966 it is said to be of advantage to intro-duce into a mould gypsum or other sulfate-bearing binding agents in the form of dry dust or grains, and subsequently or simultaneously to moisten them with water. The water required for this purpose can be introduced in the form of steam or water bound on other substancesO
German Offenlegungsschrift No. 1571466, published December 17, 1970 also discloses a method of producing plates and shaped members from gypsum, wherein the gypsum which is mixed with the fibr~ component is introduced in a dry condition into a mould, and, during or after this step, moistened with an amount of water which is just sufficient for setting of the gypsum. It can also be of advantage for the moulding to be compacted by the action of a i(~3~ pressure.
~- - 3 -~S9736 German Offenlegungsschrift No. 2103931, published August 31, 1972, discloses a method wherein fibres and gypsum are mixed on a conveyor belt, a so-called pre-shaping belt. This mixture is then transferred on to a second conveyor belt r a ~o-called pressing belt, and at the same time moistened with an amount of water which is approximately sufficient to cause the gypsum to set. The plate in web form which is produced in this manner is pressed and cut into plates from which a residual moisture content of from 10 to 15% by weight must then be removed by drying.
When using a gypsum-water mixture of pourable consistency, which may possibly contain fibre substances, in which the amount of water is from 3 to 6 times the amount required for setting of the gypsum, the excess water must be removed by drying in a method step following the shaping step. The best known example of such an operation is the production of gypsum pasteboard plates.
In this case thepourable gypsum-water mixture is placed on a pasteboard web whose longitudinal eclges are folded upwardly.
The pasteboard web which is filled wi-th the gypsum-water mixture is subsequently covered with an addi~ional pasteboard web.
After the gypsum has set, the excess water is removed by drying from the plate web, which is cut into plates. In this method the relationship by weight of water to gypsum is from approximately 0.6 to 1Ø
As disclosed in German patent specification No. 928219, published April 28, 1955, however it is also possible to put into a mould glass fibre fleeces whose fibre thicknesses are more than 0.025 mm, together with a gypsum-water mixture, and to allow this to set. In German patent specification No. 825377, published 3~ November 15, 1951, it is recommended that a fibre belt should be ~ - 4 -~L059736 drawn through a gypsum-water mixture of suitable consistency, and introduced into moulds, the excess water being pressed out.
: In accordance with German patent specification No. 1092361, published August 27/ 1964, textile fibre substances, asbestos or cellulose can also be used for the production of gypsum plates/ if they are firstly suspended in ample water and a mixture of glass fibre bunches which are fixedly connected, with gypsum and water, is introduced into the resulting suspension. The excess water in the resulting mixture is removed by suction after the shaping operation, and the remaining .
- 4a -residue is pressed into the form of plates which are then dried.
It has also already been proposed, in German patent specifi-cation No 1104419, published May 5, 1966, to produce an aqueous suspension from fibres and sulfatic binding agents such as gypsum. The aqueous suspension includes a large excèss of water over and above the amount necessary for setting of the sulfatic binding agent, and also retarding agents. This suspension is continuousl~ formed into a fleece configuration from which the water is removed before the sulfatic binding agents begin to set.
Several layers of this fleece are wound on to a roller and, being firmly pressed one upon the other, removed therefrom. The plate blank is dried after setting of the binding agent.
` Accordingly, the technical development in the production of fibrebearing gypsum plates led to three main possible methods.
In accordance with one of these methods; attempts were made to keep the amount of water to be added to the starting materials, as low as possible. In this case use was made of the observa-tions that, in the presence of an amount of water which is approximately sufficient to cause the gypsum present to set, the gypsum which sets to calcium sulfate dihydrate forms a solid body of low pore volume. In this way it shoul~ be possible to produce building members of suEficient strength.
The second possible method is producing a pourable mixture, from gypsum, fibres and a limited excess of water, and performing a casting process with the mixture to produce building members with the strength values which satisfy the requirements set in connection with the particular intended use. In this method the 28 excess water is removed only by drying.
~L~59736 The third possibility for producing fibre-bearing gypsum plates is substantially characterised in that the moulding materials contain substantially larger amounts of water than are required for making the mixture pourable and for setting of the amounts of gypsum which are contained in such materialsO In order to produce a building member of sufficient strength, it is necessary for the moulding materials to be compacted by the main amount of excess water being removed mechanically therefrom, before the gypsum sets. These last methods suffer from techni-cal disadvantages particularly when the hemihydrate gypsum ismade into a suspension by using the water which was removed as excess water from a-previous such suspension. This excess water contains dihydrate crystals which, upon being mixed with calcium sulfate hemihydrate, act as crystallisation seeds, to promote the precipitation of small calcium sulfate dihydrate crystals out of the fluid component of the gypsum-bearing suspension, and thus act as setting accelerators. It is known that the conversion, which is referred to as setting, of calcium sulfate hemihydrate into calcium sulfate dihydrate in the presence of water is based on the fact that the hemihydrate is more highly soluble in water than the dihydrate. Accordingly, the formation of dihydrate crystals can be retarded by reducing the solubility or the speed of dissolution of the hemihydrate crystals. The retarding agents which are required for the purpose however also cause a reduction of the dihydrate crystals in the excess water which is produced when making the plates and which can be used again as the mixing water. With manipulation it is possible to find an equilibrium 28 between the accelerating act~on ofthe crystallization seeds ~ S973~ i and the effects of the retarding agent, such as to ensure a stiffening time which is suitable for continuous production of plates. For these previously known methods, use is made of a mixture comprising fibre substances and plaster of Paris in a ratio by weight of 0.1 to 0.4, which mixture is made into a suspension with an amount of water which is ten times the weight of gypsum, and then formed into a fleece from which the major part of the excess water is removed again by suction. In this the fibre component acts as a filter accessory in the excess 1~ water suction removal operation. ~s however, as is known,plaster 7 of Paris disperses very finely in water, an over-increased amount of fibres had to be added to the fibre-gypsum-water mixture ln 7 order for the suction removal operation to be carried out in a technically acceptable time; without causing excessive finely divided gypsum to be removed from the fleece due to an excessive suction action. Obviously these necessary conditions frequently cause the strength, and the degree of dewatering, of the end products to be reduced. In addition there is the danger that an excessive amount of calcium sulfate dihydrate is contained in crystalline form in the excess water. As in many cases the excess water cannot be used again for forming the suspension, and can only be discarded, disproportionately high losses of water and binding agent must be accepted.
The attempt was therefore made to find ways of reducing such losses of water and binding agent, and nonetheless avoiding an unnecessarily high proportion of fibres, when producing puilding members which are produced from a mixture of fibres, sulfatic binding agents and water, wherein the water content of such mix-29 tures should be a multiple of the amount of water necessary for ~059736 setting of the sulfatic binding agent. However, the reduction in the proportion of fibres should not be accompanied by a reduc-tion in the strength of the building member.
There was found a method of producing fibre-bearing build-ing members, in particular plates, by forming a fleece from mixtures of fibrous substances with sulfatic binding agents and an amount of water which is a multiple greater than the amount of water necessary for setting of the sulfatic binding agents, wherein the main amount of excess water is removed mechanically from the fleece before the setting process begins, and the fleece is shaped into a moulding, possibly with a pressing treatment, the moulding being dried after the setting process. In accord-ance with this method the sulfatic binding agent used is a calcium sulfate hemihydrate in which the particle specific surface area does not alter or alters only to an unsubstantial extent, in the aqueous suspension, until the main amount of excess water is removed mechanically from the fleece.
The method of the invention is based on the observation that, ~ in the case of all hemihydrate gypsums which are produced in dry ; 20 methods, the individual gypsum particles decompose immediately after they are moistened with water. The gypsum particles seem to swell from the inside outwardly, and break up. The rapidity and the extent of decomposition depends on the degree of purity of the raw gypsum, and on the nature of the calcining method.
The rapidity and extent of decomposition is particularly high when using a very pure raw gypsum which is dewatered under a very low steam partial pressure, in accordance with the technical conven-tional modes of operation.
29 Due to the decomposition of the individual particles of the ~0~;9736 calcium sulfate hemihydrate upon contact with water, the number of very fine gypsum particles and thus the specific surface area of the gypsum is quite considerably increased. This increase in the number of very fine gypsum particles, and the corresponding increase in the specific surface area of the gypsum, results however in a considerable extension in the time required for removal of the excess water by a suction action. In spite of this increase in the suction removal time, the degree of dewatering of the fleece is poorer, so that the fleece retains a high water content which must be removed by drying in the final stage of the method, which requires the application of a considerable amount of energy. The very fine gypsum particles, which are produced by the calcium sulfate hemihydrate particles decomposing in an apparently explosion-like manner, when in the presence of water, rèmain suspended as solid matter in the excess water, and are removed by suction with the excess water, due to the extremely fine nature of such particles. Th:is disadvantage can be overcome to a limited extent by an over-increased proportion of fibres so that they can perform to the desired extent their function as a filter when the water is removed by suction. It was however also noted in this connection that the strength of the fibre~bearing building members is reduced again when using higher proportions of fibre than those which are the optimum for the respective fibre-bearing building member in question.
It was found that these disadvantages can be overcome if the sulfatic binding agent used is a calcium sulfate hemihydrate in which the specific surface area of the particles does not alter, or alters to an only inconsiderable extent, in aqueous suspension, 29 until the main amount of the excess water has been removed from g _ ~159736 the fleece. This delay in decomposition of the particles is not iaentical to the known action of retarding the setting time, which is caused by adding so-called retarding agents. It may even be desirable to add to the gypsum-fibre suspension so-called accelerating agents, such as potassium, iron or zinc sulfate, ; which take effect after the main amount of excess water has been removed and which shorten the time for stacking of the fibre-bearing building member, to that of setting. It was further recognised that it is particularly advantageoùs to use a calcium sulfate hemihydrate whose specific surface area, measured in accordance with the slaine method, in aqueous suspension, is from 500 to 6000, preferably from 1500 to 4000 sq.cm/g. Calcium sulfate hemihydrates of thiskind can be producedby means of any raw materials which are conventionally used in the gypsum industry and which preferably contain less than 3% by weight of clay, these being referred to hereinafter as 'raw gypsum'.
The raw gypsum used can be for example natural or synthetic calcium sulfate dihydrates which are converted in per se known ; manner into a hemihydrate with the above specified specific surface area. In addition, the ca~cium sulfate hemihydrates to be used in accordance with the invention can also be produced by crystalline transformation of calcium sulfate hemihydrate having a different specific surface area; the addition of additives which influence the crystallisation tendency can be of advantage. Also, 25 - calcium sulfate hemihydrates which can be used in accordance with the invention can equally be produced by dehydrating set calcium sulfate hemihydrate, in which case small amounts of additives such as chlorides of magnesium, calcium, cobalt or tin, or 29 potassium or magnesium perchlorate can possibly be added to a raw ~L~S9736 gypsum of this kind.
With the above ~pecified specific surface area of the hemihydrate used, in aqueous suspension, the calcium sulfate hemihydrate enjoys optimum suitability for the method according to th~e inven-tionl whose aim is to maintain this optimum suitability during the processing time until the main amount of excess water has been mechanically removed from the fleece.
The above-mentioned optimum specific surface area of the hemihydrate can be achieved by the particular particle size of -the dry calcium sulfate hemihydratel being at least substantially unaltered due to the action of the watex over the period in question. Thus, the mechanical decomposition of the individual particles of the calcium sulfate hemihydrate in the presence of water can be controlled for example by the calcium sulfate hemi-; 15 hydrate to be used, being produced from a raw gypsum which is previously ground to the necessary degree of fineness, by heat-ing in aqueous suspension or by dry cooking in the presence of chlorides of magnesium, calcium, cobalt or tin, or in the pre-; sence of calcium or magnesium perchlorate, in the amounts of from 0.05 to 0.8 and preferably from 0.1 to 0.4% by weight. The above-mentioned additives prolong the decomposition time of the gypsum particle. The suitable amount of such additive substances can be easily determined in each case by simple preliminary tests.
It is also possible however for decomposition of the calcium sulfate hemihydrate particles to be prevented by protective coatings. The method according to the invention can therefore be advantageously carried out by using a calcium sulfate hemihydrate which was produced from a raw gypsum which was previously ground 29 to the necessary degree of fineness, by cooking in the presence ~6~S973i6 of substances which form around the gypsum particles a coating layer which retards decomposition of the gypsum particles in an aqueous medium. Such layer-forming substances are for example polyvinyl acetate or silicone. The method of the invention can be carried out in a particularly advantageous manner: by using a calcium sulfate hemihydrate which was produced by cooking from a raw gypsum which was previously ground to the necessary degree of fineness, in the presence of from 0.05 to 1.0 and preferably ; from 0.1 to 0.5% by weight of silicone emulsion.
The essential action of this alternative operation lies in retarding decomposition of the calcium sulfate hemihydrate parti-cles, calculated from the moment of admixing the water, at least until the end of the operation of removing by suction the excess water contained in the fleece.
Maintaining the protective layer substantially beyond this moment would result in retardation of the setting process which in many cases is not desired. The life of the protective coating which is required in each specific case can be easily determined by means of simple preliminary tests, with reference to the description given herein.
Instead of using calcium sulfate hemihydrate as the sulfatic binding agent, it is also possible to use a mixture of calcium sulfate hemihydrate with less than 10% by weight and preferably from 3 to 6~ by weight of cement. -It has also been found advantageous for from 0.001 to 0.2%
by weight of a flocculating agent, preferably polyacrylamide, to be added to the suspension con-taining the calcium sulfate hemihy-drate.
29 In accordance with a variant of the invention, the calcium sulfate hemihydrate used is a calcium sulfate hemihydrate in the a-form, which is produced by dehydration from raw gypsum or from hemihydrate by crystalline transformation, and in which the mean ration between the largest and the smallest diameters of a particle lies between 1.0 and 4.0 and preferably 1.5 and 3Ø
Calcium sulfate hemihydrate in its a-form frequently occurs in needle or plate-shaped crystals or bunch-like crystal com-plexes. A calcium sulfate hemihydrate in its a-form which is present in approximately mono-crystal form, is particularly suit-able for carrying out the method of the invention. This calcium sulfate hemihydrate does not decompose in aqueous suspension, but changes its particle size only by virtue of the dissolution of its particles, which is necessary for the setting process.
The specific surface area of the particles of the calcium sulfate hemihydrate in its a-form, as measured in accordance with the Blaine method, in aqueous suspension, should advanta-geously be from 500 to 6000 and preferably from 1000 to 4000 ~ s~. cm/g.
1/ It is unimportant, for carrying out this method according to the invention, whether the a-form calcium sulfate hemihydrate is produced directly with the necessary level of grain fineness, or whether it is ground down to the necessary level of fineness, from a coarser grain range, in a dry or a wet process.
The method according to the invention can also be carried out by using a calcium sulfate hemihydrate in the form of an a-hemihydrate which was produced from gypsum which occurs in the production of phosphoric acid, by cooking in the presence of additives which influence the crystallisation tendency. A by 29 product which occurs when producing phosphoric acid from raw ~)5973~ii -- phosphate and sulfuric acid is a gypsum which comprises for example approximately 90% o calcium sulfate dihydrate, and which includes only small amounts of acid. This gypsum can be convert-ed into the a-hemihydrate, for example by heating in a 35~
calcium chloride solution. However, this firstly results in needle-like crystals with properties which are unfavourable from the point of view of technical application. For this reason substances were added to the~crystallisation pan, which improve the crystallisation tendency of the resulting a-hemihydrate gypsum such that this occurred in the form of short, compact and uniform crystals. Additives which have been found particularly suitable and which are preferabiy used for influencing the crystallisation tendency are cis-ethylene dicarboxylic acids, for example maleic acid or the anhydride thereof, in aadition the alkaline salts of citric acid phthalic acid and the anhydride thereof, and sulfite lyes.
Obviously the method according to the invention can also be carried out by using mixtures of calcium sulfate in the ~-hemihydrate form and the -hemihydrate form, if the ~-hemi-hydrate fulfils the condition that the specific surface area ofits particles in aqueous suspension does not alter or alters only to an unsubstantial extent, until the main amount of excess water has been mechanically removed from the fleece. In this case the sulfatic binding agent used is p~eferably a mixture of ~-hemihy-drate and from 30 to 70% by weight of a-hemihydrate.
Instead of using pure a-calcium sulfate hemihydrate or a mixture of a- and ~-calcium sulfate hemihydrate as the sulfatic binding agent, it is also possible to use a mixtu-e thereof with 29 less than 10% by weight and preferably from 3% to 6% by weight of cement.
~L~59736 Carrying out the variant of the method according to the invention avoids very fine gypsum particles being produced by calcium sulfate hemihydrate particle decomposition, which is thought to occur in the manner of an explosion, in the presence of water. Such very fine gypsum particles firstly remain suspended in the form of solid matter in the excess water, and are sucked away therewith because of their extreme fineness.
Evr~n i~ the last-mentioned disadvantage can to a limited extent be overcome by a super-increased amount~of fibres which act as a filter when the excess water is removed by suction, these higher levels of fibre content frequently result in end products whose strength is not at an optimum.
It is particularly advantageous for this method according to the invention to use a calcium sulfate hemihydrate, in particular in a-form, whose specific surface area, as measured in accordance with the Blaine method, in aqueou~; suspension, is from 500 to 6000 and preferably from 1000 to ~1000 sq. cm/g. As the individ-ual particles of the-~a-calcium sulfate hemihydrate do not decompose in the presence of water, it is possible for this specific surface area of the a-calcium sulfate hemihydrate to be maintained during thè whole processing time of the f~leece which is formed from calcium sulfate, fibres and a large excess of water, in fact until the moulding is produced.
The a-calcium sulfate hemihydrate which is to be used in accordance with the invention has little sensitivity of reaction on dihydrate seeds and therefore makes it unnecessary to add -setting retarding agents to the mixture comprising sulfatic 23 binding agents, fibres and an excess amount of ~ater.
~059736 As already mentioned, the method according to the invention provides that the particles of the calcium sulfate hemihydrate used to not change, or change only to an unsubstantial extent, in respect of their particle size, until the moulding is produced, even though the particles are in aqueous suspension. This pre-vents the occurrence of very fine calcium sulfate particles which require an increase in the amount of fibres in the fleece to be produced. However, the reduction in the amount of very fine calcium sulfate particles also results in a considerable increase in the speed of suction removal, without substantial amounts of calcium sulfate and fibres being entrained wlth the water removed. In this way the starting mixtures`icomprising fibres, sulfatic binding agents and water can also be more rapidly introduced into a mouldO
In accordance with the method of the invention, when produc-ing gypsum plates, the production capacity of the apparatus used, in particular winding roll machines, can be considerably increas-ed in comparison~with the previously known methods. In additio~
when using the method according to the invention it is now possible to carry out the manufacture of flbre-bearing construc-tion material plates, using sulfatic binding agents, on Four-driniers, which can also be provided with metal sieves. It was not possible for these plate producing machines to be used for carrying out the previously known methods, as excessively long suction removal times and unacceptable fouling of the conveyor belts had to be tolerated. These disadvantages are eliminated by means of the method according to the invention.
28 In addition, the method according to the invention provides ,~ .
l~S'~736 fibre-bearing construction members which always remain constant in quality, in particular as regards strength.
The moulded members which remain after the excess water has been removed by the suction action still contain from 5 to 30%
,~
by weight of free water which is removed by drying in per se known manner.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for producing fibre-bearing building members, in particular plates, by forming a fleece from mixtures of fibrous substances with sulfatic binding agents and an amount of water which is a multiple greater than the amount necessary for setting of the sulfatic binding agents, wherein the main amount of excess water is removed from the fleece mechanically before the setting process begins, and the fleece is shaped into a moulding, the moulding being dried after the setting process, characterised in that the sulfatic binding agent used is a calcium sulfate hemi-hydrate in which the particle specific surface area is not altered to any substantial extent by physical disintegration the aqueous suspension, until the main amount of excess water is removed mechanically from the fleece and in which the calcium sulfate hemihydrate used has a specific surface area, measured in accordance with the Blaine method, in aqueous suspension, of from 500 to 6,000 sq.cm/g.
2. A process as claimed in claim 1 in which the calcium sulfate hemihydrate used is produced from a raw gypsum which is ground to the necessary degree of fineness and by heating an aqueous suspension thereof in the presence of 0.05 to 0.8 % by weight of at least one member of the group of chlorides of magnesium, calcium, cobalt or tin, or calcium or magnesium perchlorate.
3. A process as claimed in claim 1 in which the calcium sulfate hemihydrate used is produced from a raw gypsum which is ground to the necessary degree of fineness and the resultant product is dry cooked in the presence of 0.05 to 0.8 % by weight of at least one member of the group of chlorides of magnesium, calcium, cobalt or tin or calcium or magnesium perchlorate.
4. A method as claimed in claim 1 in which a calcium sulfate hemihydrate is used, which was produced from a raw gypsum which was previously ground to the necessary degree of fineness, by cooking in the presence of substances which form around the gypsum particle a coating layer which retards decomposition of the gypsum particle in the aqueous medium.
5. A method as claimed in claim 4 in which a calcium sulfate hemihydrate is used which was produced by cooking from a raw gypsum which was previously ground to the necessary degree of fineness, in the presence of from 0.05 to 1.0 % by weight of silicone emulsion.
6. A method as claimed in claim 1, claim 2 or claim 3 in which a mixture of calcium sulfate hemihydrate with less than 10% by weight of cement is used as the sulfatic binding agent.
7. A method as claimed in claim 1, in which 0.001 to 0.2 % by weight of a flocculating agent is added to the suspension containing calcium sulfate hemihydrate.
8. A method as claimed in claim 7 in which the flocculating agent is polyacrylamide.
9. A method as claimed in claim 1 in which the calcium sulfate hemihydrate used is an .alpha.-calcium sulfate hemihydrate which is produced from raw gypsum by dehydration or from hemihydrate by crystalline conversion , and in which the mean ratio between the largest and the smallest diameters of a particle is from 1.0 to 4Ø
10. A method as claimed in claim 9 in which the calcium sulfate hemihydrate used is an a-hemihydrate which was obtained from gypsum produced in the production of phosphoric acid, by cooking in the presence of additives which influence the cry-stallisation tendency.
11. A method as claimed in claim 9 in which the sulfatic binding agent used is a mixture of .beta.-hemihydrate and .alpha.-hemihydrate.
12. A method as claimed in claim 11 in which the sulfatic binding agent used is a mixture of .beta.-hemihydrate and from 30 to 70% by weight of .alpha.-hemihydrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2336220A DE2336220C2 (en) | 1973-07-17 | 1973-07-17 | Process for the production of fiber-containing structures |
| DE19732337374 DE2337374A1 (en) | 1973-07-23 | 1973-07-23 | METHOD FOR MANUFACTURING FIBER-CONTAINING BUILDINGS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1059736A true CA1059736A (en) | 1979-08-07 |
Family
ID=25765502
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA199,358A Expired CA1059736A (en) | 1973-07-17 | 1974-05-07 | Method of producing fibre-containing building members |
Country Status (10)
| Country | Link |
|---|---|
| AR (1) | AR215567A1 (en) |
| AT (2) | AT355482B (en) |
| BR (1) | BR7405848D0 (en) |
| CA (1) | CA1059736A (en) |
| CH (1) | CH609658A5 (en) |
| DD (1) | DD111571A5 (en) |
| ES (1) | ES426211A1 (en) |
| IL (1) | IL44747A (en) |
| IT (1) | IT1023832B (en) |
| LU (1) | LU69977A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4485633A (en) * | 1982-10-18 | 1984-12-04 | The Coca-Cola Company | Temperature-based control for energy management system |
-
1974
- 1974-04-29 AT AT351574A patent/AT355482B/en not_active IP Right Cessation
- 1974-05-01 IL IL44747A patent/IL44747A/en unknown
- 1974-05-02 LU LU69977A patent/LU69977A1/xx unknown
- 1974-05-06 DD DD178308A patent/DD111571A5/xx unknown
- 1974-05-07 CA CA199,358A patent/CA1059736A/en not_active Expired
- 1974-05-08 IT IT12777/74A patent/IT1023832B/en active
- 1974-05-10 AR AR253684A patent/AR215567A1/en active
- 1974-05-10 CH CH643374A patent/CH609658A5/en not_active IP Right Cessation
- 1974-05-11 ES ES426211A patent/ES426211A1/en not_active Expired
- 1974-07-16 BR BR5848/74A patent/BR7405848D0/en unknown
-
1978
- 1978-01-18 AT AT36478A patent/AT351574B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| AT355482B (en) | 1980-03-10 |
| CH609658A5 (en) | 1979-03-15 |
| IT1023832B (en) | 1978-05-30 |
| BR7405848D0 (en) | 1975-05-13 |
| AR215567A1 (en) | 1979-10-31 |
| ATA36478A (en) | 1979-01-15 |
| AT351574B (en) | 1979-07-15 |
| DD111571A5 (en) | 1975-02-20 |
| LU69977A1 (en) | 1974-09-25 |
| ATA351574A (en) | 1979-07-15 |
| ES426211A1 (en) | 1976-11-16 |
| IL44747A (en) | 1977-10-31 |
| IL44747A0 (en) | 1974-07-31 |
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