IL44747A - Method of producing fibre-containing building members - Google Patents

Description

Method of producing fibre-containing building members Gypsum-Research S.A. containing building members can be produced by mixing brous substances such ns for example ■cellulose fibres , glasswool , rock or minora].— wool, fibre -asbe&tos and the -like, with •hydrau!l ic -or--non-hydraulic · binding ft age s end water, with shaping °f the mixtures.

When hydraulic binding agents are used, on' aqueous suf. erision can be made continuously from the binding agents and the fibre substances. The excess water is removed by a sue ion. action from the aqueous solution, after it has boon produced and shaped. The remaining moulding material is dried after the pressing operation. The removal by suction is effected on a continuously moving endless suction support which can bo in the form of a wator-pcrvious belt such as a cotton bolt or1 a metal clove belt. The water is sucked from the shaped uusponsio through the water-pervious belt, by vacuum suction heads which are arranged below the belt. After re oval^of the moulding, the remains of the' moulding material are removed from the water-p'crvious belt v/ith knocking means and by sponging o f· v/ith v/ater. The water v/hich is removed by the suction action, and the cleaning v/ater, are used to make the suspension v/hich is used as the startin i ' _ . ' i material. . containing · ' If fibre-fcewi-ng building members are to be produced using non-hydraulic binding agents, the starting materials can be produced in the presence of an amount of v/ater v/hich is sufficient for, or v/hich is in excess of the amount required for, c'-tting the non-hydraulic binding agent, and the smarting m teri l may possibly be pressed, and then dried.

An example of producing plates from fibres and gypsum as the non-hydraulic binding agent is found in German patent specification No 6^?; 5· In accordance with this specification, gypsum, asbestos fibres and v/ater are formed into a mixture v/hich is dr v o the touch jand v/hich is subsequently pressed into mouldings. After the pressing operation those mouldings are moistened v/ith siao . ater, and dried..; ,,·,,, .

In accordance with- German patent specification No » spina l¾ class fibres can alco be' dry mixed with gypsum, and then water added. It is however alco possible for the spinablo fibres to be mixed simultaneously v.dth £y»-u and water. These mixtures which should contain approximately the amount of water necessary for setting of the gypsum, ore then caused to set, while being shaped. '. '· . ' " , German patent specif cation No ;11222 f discloses another possible way of' producing plates. In accordance with this specification, in a dry condition or v.dth the addition of an extremely small amount Of water, the starting materia such as fibres, hydraulic or non-hydraulic binding agents, are shaped in the : . form of plates which are provided .with coverings such as wot fine muslin cloths, ϊ ' ί from which water can be evaporated into the plate blank moulding while this is being pressed.

In accordance with French patent specification No 1^61690 , it is said to be of advantage to introduce into a mould gypsum or other sulfate-bcaring binding agents in tho form of dry dust or grains, and subsequently or simultar.eo to moisten them with water. The water required for this purpose' can be introduce in the form of steam or water bound on other substances. · ' German Offenlegungsschrift No 1571^66 also discloses a method of producing plates and shaped members from gypsum, v/horein the gypsum 'which is mixed with I tho fibre component is introduced in a dry condition into a mould, and, during . i 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 bo compacted by the action of a pressure. · German Of enlegungsschrift No 2103931 discloses a method wherein fibres and gypsum are mixed on a conveyor bolt, a so-called pre-shaping belt. This . 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 ••forra · which -io-produccd-in ..-this -manner-..is .prec30.d..and cut .into plates from JB which a residual moisture content of from .10 to 1¾ό weigh must then be removed by drying. ··.: :; j When using a gypsum-water mixture of pourable consistency, v/hich may possibly contain fibre substances , in which, the amount 'of water is from J to 6 times the amount required for setting of the gypsum, the excess water must ;, J bo removed by dryinc in a method step following the shaping step. The best known examplo of such an operation is the production of gypsum pasteboard plates,. j In this case the pourable gypsum-water mixturo is placed on a pasteboard web whose jlongitudinal edges arc folded upwardly. The pasteboard web which is filled with the gypsum-water mixture is su jsequently covered with an additional pasteboard web. After the gypsum bajs'set, the excess water is removed by drying from the plate web, hich is cut into plates. In this method the relationship by weight of water to gypsum is from approximately 0.6 to 1.0. . ' ' As disclosed in 'German patent specification No 2321 however it is also possible to put into a mould glass fibre fleeces whoso fibre thic)uiesse3 j are more than 0.025 mm, together wijth a gypsum-water mixture, and to allow ! I ■ this to set. In German patent specification No 8 ^277 it is recommended that i a fibre bolt should be drawn through a gypsum-water mixture of suitable j consistency, and introduced into moulds, the excess water being pressed out.

In accordance with German patent specification No 1092J61, textile fibre ! substances, asbestos or cellulose can also bo used for the production of gypsum plates, if they are firstly suspended in ample water and a mixture of glass fibre bunches v/hich 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, .end. the remaining ··· - - residue is pressed into the form of plates which are then dried.

It has also already been proposed, in German patent specification No. 1104419, to produce an aqueous suspension . from fibres and sulfatic binding agents such as gypsum. The aqueous suspension includes a large excess of water over and above the amount necessary for setting of the sulfatic binding agent, and also retarding agents. This suspension is continuously 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.

British Patent Specification 1204541, discloses a discontinuous method for the manufacture of reinforced plaster articles which requires the use of moulds. This process cannot be utilised for any continuous process.

Accordingly, the technical development in the production ing of fibre-i0n"j¾i¾ gypsum plates led to three main possible metr hods. 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 observations 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 should be possible to produce building members of sufficient 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 excess water is removed only by drying.

The third possibility for producing fibre-containing , gypsum plates is substantially characterised in that the mould ing 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 materials.

In crier to produce- a building member of sufficient strength, it is ' necessary for the moulding material/3 to be compacted by the ' main amount of (. excess water' eing removed mechanically therefrom, before the · gypsum sets. These laat methods suffer from technical disadvantages particularly when e hem: hydrate gypsum in made into a /suspension by using the water which was removed an excess water from a previous such suspension. 'This excess water contains dihydrate crystals which , upon being mixed with Calcium sulfate ac to hemila dratej .s crystallisation seeds,/promote the' recipitation of small calcium sulfate dihydrate crystals out of the fluid component of the gypsum-bearing; suspension, and thus act as sotting 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 cry.otals can be retarded by reducing ■ the . olubility or the speed of dissolution of the hemihydrate crystals. The retarding agente which are required for this purpose however also cause a · reduction of the dihydrate crystals in the excess water which is produced when :ma.king the plates and which can be used again as tfro mixing water. With manipulation it is possible to find an equilibrium between the accelerating action of the crystallisation seeds and the effects of the retarding agent, i-:uch 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 e.nd plaster of Paris in a ratio by weight of 0,1 . to OJr, which mixturo 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 water suction removal operation. As however » as is known , : laster of Paris disperses very firml in water, an over-increased amount of fibres had to be added to the fibre-eyj/suw-water mixture in .order for the suction -removal Operation to be carriRl out in a technically acceptable time', without causing excessive finely divided c cum to be removed from the fleece due to. an o:c¾acivo auction action.

Cbviouely these necessary conditions frequently cause., the strength, HVA the dec ee of devatcring,of the end products to bo reduced. In addition' here is the danger that an cxcescive amount of calcium sulfate dihydrate is contained f .' . in crystalline form in the excess ater. As in many cases the excess water cannot bejused e.gain for forming the suspension, and can only bo discarded, ί ' 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 unnecessari¾,-h:i.gh proportion of fibres, when producing .building members which are produced from a mixture of fibres, sulfatic binding agents and water, wherein the water content of such mixtures should be u multiple of the amount of water necessary for setting of the sulfutic binding agent. However,' the reduction in the proportion of fibrca should not be accompanied by a reduction i the strength '■ ' ' · ,· i .. , of the building member.

Co n-f^i ni no.

There was found a method of producing ibre-b-uisiag ouilding members, in by the winding roll process particular plates/, by fox'ming 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 v/ater 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, pos.ribly with a pressing treatment, the moulding being dried after the setting process. In accordance with this method the sulfatic binding agent used is a calcium sulfate hemihydrato in which the1 particle specific s rf ce area does not alter or alters only to an unsubstantial extent, in tho aqueous cuspensicn,'jntil the main' mount of excess water' is removed "rwicbariical!l from the fleece. ."'.,·■ ' .

The method of tho invention is based on . the observation that, in the case of all hemihydratc gypsums which are produced in dry methods, the individual gypsum particles decompose immediately after they are moistened with water.

The gypsum particles, eeom to swell 'from tho iniide outwardly, and brc;:k. up.

The vapidity and the extent of decomposition depends o the' degree of purity of the rav) gypsum, on nature of the calcining method. The rapidity and j ; extent of decomposition is particularly high when using a very pure rav.- gypsum which is dewatered under a very low steam partial pressure, in accordance with the technical conventional modes of operation..

Due to the decomposition of tho individual particles of the calcium sulfate hemihydrate upon contact with wuter, 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 tho 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 tho 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 hemihydrato particles decomposing in an apparently explosion-like manner, when. 'in the presence of water, remain, suspended as solid matter in the excess water, and are removed by suction with the excess water, clue to the extremely fine nature of such particles. This disadvantage'' can be overcome to 2 limited fcxtcnt by an over-increased proportion of fibres BO th they can perform to the do.v.ired extent their function as a filter when the water s removed by auction. It was. however also noted in this connection that the s re g h of the fibre-bearing building members iu reduced again when using higher proportions of fibre than tho e which are tho optimum for the respective fibre-bearing building member in question. , ! ' It was found that these disadvantages can bo overcome if the eulf& tic-binding agent used is a -calcium sulfate hemihydrate in- which the epecific surf ce area of , he particles does not altor,.or alters to an only inconsiderable extent, i in aqueous suspension,until the main amount of the excess water has been removed from the fleece. This' delay in decomposition of the particles is not identical to tho known action of retarding the sotting time, which ie caused by adding so-called retarding agents. It may even be desirable to add to the gypsum-fibre suspension so-called accelerating agents, ouch as potassium, iron or zinc sulfate] which take effect after the main amount of excess water has been removed and which shorten tho time for stacking of the fibre-bearing building member , to that of setting. It was further recognised that' it is particularly advantageous . to use a calcium sulfate hemihydrate whose specific surface area, measured in accordance with the Blaine method, in' aqueous suspension, is fromiWto 6000, preferably from 150Ό to ^000 sq.cm/g.jCalcium sulfate hemihydrutes of this . -.1 kind can be produced by means of any raw materials which are conventionally "· used in tho gypsum industry and whichj preferably contain less than y/ by weight of clay, these being referred to hereinafter as 'raw gypsum'.' The raw gypsum used can bo 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 calcium sulfate hemihy rates to be used in accordance, with the invention can also be produced by crystalline transformation of calcium sulfate hemihydrate' having, a dif erent · specific surface area; the addition - fadditives 'which influence -the crystallisation ^te denc can be of advantage . 'Also , calcium sulfate hemihydrate which "can 'bd used in accordance -wi fc the invention can equally. bo .produced by. dehydrating set calcium sulfate hemihydrate, in which case small amo ts of j additives such as chlorides of magn sium, calcium, cobal or tin, or potassium or magnesium perchlorate can possibly be added to a raw gy um of this kind.

With the above specified specific surface area of the hemihydrate used in aqueous suspension, the calcium sulfate hemihydrate enjoys optimum suitability for the method according to the invention, whose aim is to m.vintai 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 particula ' particle s'iz.c of the dry calcium sulfate hemihydrato , being at least substantially unaltered duo to the action of the water 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 hemihydrate to be used, being produced, from a raw gypsum which is previously ground to the necessary degree of fineness, by heating in aqueous suspension or by dry cooking in the presence of chlorides of magnesium, calcium, cobalt or tin, or in the presence of calcium or magnesium perchlorate, in amounts of from 0.05 to 0.8 and preferably from 0.1 to Ο. ο 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 bo prevented,by protective coatings. The method , according to the invention can therefore be advan ageously carried out by . ! ' , ..... 10 using a calcium eulfato hcmihydro.te which wab produced from a raw g yun which was previously ground, to the noceuaary decree of fineness, by c ok^y; in the presence of substances which form around the gypsum particles coating layer v/hich retards decomposition of the gypsum particles in an aqueous medium. Such layer-forming substances are for exam le polyvinyl acetate or silicone'. The method of tho invention can be carried out in a particularly advantageous manner by us ng a calcium sulfate homihydrate whi'.;h was produced by cooking from a raw gypsum which was previously ground to the nocessary degree of fineness, in tho presence of from 0.05 to 1.0 and preferably from 0.1 to O.yo by weight of silicone emulsion.

The essential, action of this alternative operation lies in retarding decomposition of the calcium sulfate .hemihydrate particles, calculated from the moment of admixing the wuter, at least until the end of the operation . of removing by suction tho excess wo.ter.. containod in the fleece.

Maintaining the protective layer substantially beyond this moment would result in retardation of the sett ng process v/hich in many cases is not .

• I · " desired. The life of the- protective coating wh'ich is required in each specific case can be easily determined by means of simple preliminary tests, ■ ' i with reference to the description given herein.

Instead of using calcium sulfite hemihydrate as the suli'atic binding ■ agent, it is also possible to use a mixture of calcium sulfate hemihydr l It has also been found advantageous for, from O.COl to O . Z/o by weight of a flocculating agent, preferably polyacrylemid , to be added to the suspension containing the calcium crul uto hemihydrate.. '· particularly suitable for carrying' out the method of the invention. This calcium sulfate hernihydrate 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. ' . ·' '· z The specific surface area oi'j the particles oi' the calcium xvlxa o hexihydrato in its a- form, a« measured in accordance with the B fc nt; ncthod, in nqueour; suspension, should ndvairtngcously be from 00 to GOOO .md. pre i' rb-i?..γ from 1000 to Ί000 sq. cm/g.

■ If is unimportant, for carrying out t rs method according to the invent:.0:1 whether the a- orm calcium sulfate hemihydratc; i produced, directly with' he necessary level of grain fineness, or whether it ic ground down to the necessary level of- fine-noes, from a coarser grain range, in a dry or a wet process. , .

TheV method according to the invention con also be carried out by lining a calcium sulfate hemihydrate in the form of an a-hentihydrate 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-product which occurs when producing phosphoric acid from raw phosphate ond sulfuric acid is a gypsum which comprises for example approximately $0}ί of calcium sulfate dihydrate, and which includes only email amounts of acid. This gypsum can be converted i'nto the α-hemihydrate, for example by heating in a calcium chloride solution. However, this firstly results in needle-like crystals with properties which are unfavourable from the point of view of technical application. For thj.3 reason substances were added to the cry^tall sat? pan, which improve the cry all ation te denc of the resulting a-h-i-mihydrato gypsum such that this occurred in the form of chert, compact and uniform crystals. Additives which have been found particularly suitable ond which are preferably used for influencing the' crystallisation tendency are cis-ethylcne ■ dicarboxylic ucido, for example muleic acid or the anhydride thereof, in addition the alkaline salts of citric acid, phthalic acid and the anhydride thereof, and sulfite lyes. 44747/2 - 14 Obviously the variant of the method according to the invention can also be carried out by using mixtures of calcium sulfate in the β-hiemihydrate form and the a-hemihydrate form, if the β-hemihydrate fulfils the condition that the specific surface area of its particles in aqueous suspension does not alter or alters only to an unsubstantial extent, until the main amount of excess water has been mechanically removed from the fleece. In this case the sulfatic binding agent used is preferably a mixture of β-hemihydrate with from 30 to 0$ by weight of a-hemihydrate.

Instead of using pure o-calcium sulfate hemihydrate or a mixture of a- and β-calcium sulfate hemihydrate as the sulfatic binding agent,, it is also possible to use a mixture thereof with less than 10 by weight and preferably from 3 to 6 by weight of cement.

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. Even if 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. 44747 2 - 14a - 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 aqueous suspension, is from 500 to 6000 and preferably from 1000 to 4000 sq. cm/g. As the individual 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 the whole processing time of the fleece 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 eulfatic binding agents, fibres and an excess amount of water.

As already mentioned, the method according to the invention p ovides that the particles of the calcium sulfate hemihydrate sed do not ch nge, or 'change only to an unsubsta tial extent, in respect .of their particle size, ^ until the moulding is produced, ' even though the particles are in a ueous suspension. This prevents 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 tho speed of auction removal, without substantial amounts of calcium sulfate and fibres being entrained with the. water removed. In this ■way the starting mixtures comprising fibres, sulfatic binding agents and v/ater .can also be more rapidly introduced into a mould.

In accordance with the method of the invention, v/hen producing gypsum plates, the production capacity of the apparatus used, in particular winding roll machines, can be considerably increased in comparison v/ith the previously known methods. In addition, when using the method , according to the invention it is now possible to carry out the manufacture of fibre-bearing construction material plates, using sulfatic ' binding agents, on Fourdriniers , · which can also be provided v/ith 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 arc eliminated by means of t method according to the invention. ■ · , 'In addition, the method according to the'invention provides 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 3Q¾ by weight of free water which is removed by drying in per cc known manner.

Claims (1)

1. containing A method in particular the winding roll process i by forming a fleece from mixtures of fibrous substances with and an of water which is a multiple greater th the amount necessary for setting of the binding the main amount of excess water is removed from the fleece mechanically before the process and the fleece shaped into a possibly with a pressing the moulding being after the setting characterised in that the ic binding agent used is a calcium sulfate hemihydrate in which tho particle specific surface area docs not alter or most only to on unsubstantial extent in the aqueous until the water is removed mechanically from the j A method according to claim characterised in that the calcium sulfate hemihydrate used has a specific surface measured in accordance with the Blaine in aqueous from 500 to preferably from to OOO method according to characterised in that a calcium sulfate hemihydrate is is produced from a raw gypsum which is previously ground to the n cessar of by heating in aqueous suspension or by dry cooking presence of chlorides of cobalt or or in the presence of calcium or magnesium in of from to and proferably from to by Λ mothod according to claim characterised in that a calcium sulfate hemihydrate is was produced from a raw gypsum which is previously ground to necessary degree of by cooking in the presence of substances which form around the gypsum particles a coating layer which decomposition of the gypsum particles in the aqueous ø AG A method according to characterised in thn a sulfate is used roduced by cooking raw which was previously ground necessary of in the presence from to and preferably to by weight of silicone A iriet od according to claims 1 to characterised in that is made of a mixture of calcium hemihydrate with less than by and preferably from to by weight of as the A according to claims 1 to characterised in that from foe to by weight of a agent is added to the suspension containing calcium sulfate A method according to claim characterised in that the agent added is A method according to claim 1 characterised in that the calcium used is an sulfate drate which is produced from raw gypsum by dehydration or from hemihydrate by crystalline and in which the mean ratio between largest and the smallest diameters of a particle is from to and preferably from to A method according to claim characterised in that the calcium sulfate hemihydrate used is an which was tained from gypsum produced in the production of phosphoric by cooking in the presence of additives which influence the lisation A method according to claims 9 and characterised in that the sulfatic binding agent used is a mixture of and A method according to claim characterised in that the sulfatic binding used is a mixture of with from 30 to weight of A method of producing substantia insufficientOCRQuality