JPH01152008A - Method for gypsum fiberboard production - Google Patents

Abstract

PURPOSE: To produce a fibrous plaster board by a new combination of wet molding and dry recrystallization by preparing a suspension from a beaten fiber material and calcium sulfate dihydrate and dehydrating the same to mold a board and heating the board to recrystallize the same to a hemihydrate which is subsequently converted back into the dihydrate. CONSTITUTION: A suspension consisting of raw material plaster and wet-adjusted fiber is mechanically dehydrated by using an endless filter 13 so that hot distillation moisture becomes about 30-40% to be molded into a board. At this time, a dihydrate is recrystallized into a β-form of a hemihydrate in air and moisture necessary for coagulation is absorbed through the board. The raw material board is dried and calcined in a continuous heating furnace 15 at a board temp. of 100-170 deg.C, pref., 115-140 deg.C. Next, moisture necessary for coagulation is absorbed into a board core part by an absorbing apparatus 17. It is advantageous to set moisture excessiveness to at least 2.5 times a stoichiometric moisture demand. A press 19 is connected after absorption. By this constitution, penetration is equalized and the board is compressed to perform additional dehydration and calibration.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention produces a suspension from crushed fiber material and calcium sulfate dihydrate. t, relates to a method for gypsum fiberboard temperature, which is dehydrated and formed into a board, heated to recrystallize the dihydrate to hemihydrate, and subsequently converted to dihydrate. be.

[Prior art] Gypsum fiber board is a board-like building material made of a mixture of gypsum and fibers, and has a predominant ratio of 1 part gypsum, usually about 80 to 9
0%, and the fibers usually consist of paper fibers.

In known methods for the production of such gypsum fiberboards, the gypsum is first dried and calcined, ie converted from dihydrate to beta hemihydrate. Only the hemihydrate is then mixed dry or wet with the Im-produced fibers and the water necessary for hydration is added.

Gypsum fiberboard made from wet crushed paper fibers in the form of fiber waste is approximately 10-50% lower than dry crushed paper fibers.
It was revealed that it has high bending strength. Not only that, the fibers are more evenly distributed throughout the board, giving the board a better appearance and workability. The shaping of this type of board requires calcined gypsum, a suspension consisting of hemihydrate and pure paper fiber residue with a very high moisture content of 300 to 600%.

Shaping of the board is possible only with large proportion removal. Drum screens and/or filter belts are used for this purpose. However, in this wet method, it has become clear that the screen surface becomes very quickly contaminated by condensed gypsum, which requires a significant amount of cleaning effort and is more likely to cause malfunctions. In order to avoid these drawbacks of the wet method, methods have been proposed for forming building materials made of dihydrates.

In other words, DE-O 82649300 proposes forming a suspension of calcium sulfate dihydrate and fibers by dehydration and drying.

This method does not take advantage of the hydraulic binder properties of gypsum obtained by two recrystallizations to hemihydrate and reversion to dihydrate. For this reason, sufficient board quality cannot be obtained with this method without the addition of a binder. 11 DE-PS 2 818 169 describes a method for producing molded bodies made of gypsum. This method uses natural gypsum without fibers and works with low moisture addition of 5-10% of natural gypsum and high pressing pressure of 6 Mpa during molding, for the production of gypsum products with less pores. It is considered. However, this method is technically not suitable for the production of building materials containing fibers made of gypsum and wet fibers, since the wet-crushed paper fibers can be used to produce 10 to 2
This is because, at an amount of 0%, the moisture content in the molded body is sufficiently low that it cannot be mixed with the raw gypsum at a level between 5 and 10%. Molding by pressing at correspondingly high pressures, especially 6 MPa, is likewise not a problem.

In DE-O82816466, a board is formed from a suspension of dihydrate and fiber waste by dehydration, and this is
It has been proposed to heat to a temperature of 115 to 180° C. under a pressure of 10 bar. Under these conditions, the conversion of dihydrate to alpha hemihydrate takes place.
The shaped body is then cooled, pressed under pressure, stored under greenhouse conditions for about 2 hours to 7 days, and then dried. Since this storage time is too long and therefore uneconomical for industrial manufacturing processes, DE-PS3419558
It is proposed to produce a gypsum/fiber suspension with an H value of 7. According to this, after board treatment for 3 to 50 minutes in saturated air, the conversion of dihydrate to alpha hemihydrate is:
In other words, it is said that the condensation time is significantly shortened by adding (X) in the pressure vessel.

However, in practice it has been found that changes in the pH value also do not significantly shorten the setting time. It is still about 1-3 days. It is easy to speculate that wet processing of the boards at temperatures between 100"C and 160°C liberates substances from the paper fibers that act as condensation retarders. By exchanging water with dewatered boards, ,
The setting time is further reduced to about 9 to 12 hours, but this is still too long for economical production.

[Problem to be Solved by the Invention] The above method resulting from a combination of wet forming of boards consisting of a suspension of dihydrate and wet recrystallization of these boards into wet disintegrated fibers and alpha hemihydrate. Because of the difficulties in this invention, it is an object of the present invention to reach improved results by a new combination of wet forming and dry recrystallization of the board into hemihydrate.

[Means for Solving the Problems] Therefore, according to the idea of the present invention, first, raw gypsum and about 3
A suspension consisting of wet-prepared fibers with a water content of 0.00 to 600% is prepared using suitable equipment, such as a winding cylinder or an endless filter, i.e. about 30% to 600%.
Mechanically dehydrated to 0% thermal moisture, then formed into a board, the dihydrate recrystallized into the hemihydrate β form in air without pressure, and the moisture necessary for condensation was absorbed through the board. It will be done. For the production of gypsum suspensions, it is possible to use both natural gypsum and also chemically generated gypsum, such as, for example, flue gas desulfurized gypsum or phosphogypsum, the latter being particularly suitable due to its good dewatering properties. , is particularly economical since it is obtained with an already high water content.

The board resulting during recrystallization to the beta hemihydrate is virtually completely dry. Particularly advantageous is the circumstance that the recrystallization is carried out at normal pressure and in the atmosphere. The raw material board produced in m water volume already has great stability,
This is obtained by agglomeration of wet fibers and shaping with lots of water. The method according to the invention does not require pressure for forming the board, although if higher board densities are desired, lower pressures of the order of 0.05 to 0.1 MPa can be used, which at the same time smooths the surface. , can be utilized for board calibration and additional dehydration.

Dry calcination of the raw material board is performed at a board temperature of 100°C to 170°C.
C., preferably between 115.degree. C. and 140.degree. The temperature increase during the heating step is then quite small, preferably well above 2° C./min for rapid calcination.

Surprisingly, drying and calcination do not lead to damage to the paper fibers or loss of board strength; on the contrary, the calcined boards have a remarkable inherent stability as well as high elasticity, and therefore their transportation is For example, a roller conveyor can be used without any problems. The combination of wet molding and dry calcination even has the advantage that during type Ii molding, a pure fiber filter layer is created on the board surface, which protects the calcination equipment from contamination by gypsum debris.

Another method obtains the moisture necessary for condensation by absorption into the board parts. Injection, soaking or saturation with water vapor, on the other hand, proved to be of no use, since the dried material initially absorbs moisture well, but then the fibers swell and the moisture is transferred to the board. This is because it does not penetrate deep enough into each part. It therefore lies within the framework of the invention to carry out this method in such a way that the board is flooded with water in stoichiometric excess upon absorption of moisture. Water excess is at least 2.5 times the stoichiometric water demand, better 3-4
It is advantageous to double the amount. Moisture absorbed by the board fills the voids with water.

Due to the absorption action, moisture quickly reaches each part of the board and the underside of the board. Surprisingly, the absorption time was found to be between 30 and 60 seconds, depending on the board thickness and density, and thus much shorter than in the case of the alpha method. This is because dry boards have a higher pore volume and do not require water exchange. Moreover, as a result of excess moisture, the board is completely permeable to water at all points, even though there are differences in permeability. Complete penetration of the board with sufficient water ensures
This is a prerequisite for uniform and complete crystal transformation. The setting time is surprisingly short, from 1.5 to 2 without the addition of accelerators.
．． Until 0 hours. For this reason, the method according to the invention, unlike the known methods, can above all be carried out economically. A press is connected after absorption. This makes penetration more even, further compresses the board, and provides additional dewatering and proofing. A press time of 30 to 60 seconds can increase board density by as much as 10%, for example.

Significant advantages are therefore obtained compared to the current state of the art, which involves calcination under saturated steam and working with the α-form of the hemihydrate. Previous attempts have been made to avoid over-drying the formed board by using saturated steam and to maintain at least the same amount of water in the board as is required for the subsequent rehydration of the hemihydrate to the dihydrate. Therefore, from the point of view of saving energy, the amount of water required for rehydration was only vaporized after the heat of vaporization of the water became significantly high.
However, this expectation remained largely unfulfilled.

During the pressure drop following saturated steam treatment, it became difficult to avoid the moisture remaining in the board escaping by vaporization. This causes the board to dry out excessively, so that ultimately the remaining moisture is completely insufficient for rehydration. The moisture remaining in the board absorbs impurities from the fibers during heat treatment, which retards the setting process of the gypsum and thus makes the process almost economically unfeasible. As well as the discontinuous working mode of this process, the result is that the autoclave is cooled after each heat treatment, so that the heat stored in the autoclave is lost. Finally, there was a desire to improve the strength of the board by using alpha gypsum. α under saturated steam
It was assumed that upon calcination to form a hemihydrate, this would give a higher strength when condensed than the β hemihydrate produced by air calcination. This expectation was also not met.

The strength of the board did not reach the values obtained in the initial tests.

EXAMPLES Further features, details and advantages of the invention will become apparent from the following description, which uses a schematic diagram of the equipment used in the method.

This installation comes from a desulphurization installation from storage 1 (-1, assuming the use of the so-called REA gypsum. The initial material from storage 1 is fed via conveyor 3 and metering device 4 to tank 5. In this, the gypsum becomes a suspension with water from the water tank 2.

The gypsum suspension is wholly or partially ground to the desired particle size in a mill 6, such as a tube mill. This particle size is, for example, Blaine number 1°000 to 3.50.
The finely ground material from the crushing device 6 reaches the silo 7, which can correspond to a fineness between 0 and 0, which corresponds to the conventionally usual fineness.

In parallel with this, waste paper is taken out from storage 8 and supplied to crushing device 10 via conveyor 9, to which water from water tank 2 is simultaneously added. Waste paper is crushed until it becomes fibers. Instead of waste paper, other fibers of vegetable or mineral origin can also be used, and this does not imply a fundamental modification of the method.

The fiber residue consisting of fibers and water produced in the crushing device 10 is
It is sent to a storage tank 11 and from there, the same as the finely ground gypsum coming from the silo 7, is led to a mixer 12. The mixture of fibers and gypsum corresponds to the proportions that suit the respective requirements.

For example, the range is 1:10.

From the mixer 12, the mixture is fed to a device 13 for dewatering at the same time as forming. The device is equipped, for example, as an endless filter machine with rotating dewatering filter belts above and below. The board formed between the filter belts passes through a WI layer distributor 14 into a continuous heating oven 15 in which a drying process takes place as a first processing step. This lasts approximately 15-25 minutes. This is followed by a second processing step in the form of calcination, for which also a time of approximately 15-25 minutes must be allowed. The circulating air under atmospheric pressure then plays the role of the treatment medium; the air temperature is from about 250°C to 300°C in the first half of the continuous heating furnace 15, whereas in the second half it ranges from about 170°C to 190
up to ℃.

The air humidity is therefore clearly below the saturation value, for example 0.1 to 0.5 kg per kg of water.

The formed board enters the continuous heating furnace 15 at ambient temperature (e.g. about 20°C. During the first processing step, the temperature of the board increases to about 100°C due to contact with the hot air. It only dries. Calcination practically does not take place. As long as the board still contains free moisture, its temperature cannot rise above the cooling limit temperature, once the board has passed approximately halfway through the furnace 15. , the free hot air has fallen to almost zero. Now, when the temperature of the board rises again, calcination begins. At this time, in order to avoid too significant a rise in temperature, the temperature of the air circulating in this part of the furnace 15 is kept low.

At the end of the continuous heating furnace 15, the board has a temperature of approximately 130°C.

The dried boards then reach the top of the belt conveyor 16, on which they are irrigated by the absorption device 17. The surface of the board is now completely covered with water as quickly as possible, which can be done by uniformly injecting water through the water inlet line 18. At the same time, the negative pressure chamber 17 on the underside of the board is intended to allow moisture to penetrate and be absorbed into the board as quickly as possible.

At this time, the moisture must be absorbed until the underside of the board is wetted at all locations.

Excess water is pumped back to water tank 2.

The dewatered board then reaches the press 19 where it is pressed to its final density or thickness and its surface is calibrated. For example, bending strength 6 with corresponding equipment
．． 0 to 10. ON/mm2 board densities of 0.9 to 1.20 kp/l are obtained. The press plate is suitably equipped with a filter belt on the underside, which allows additional dewatering and prevents the board from melting and flowing during too rapid pressure build-up. Via a conveyor 20 the boards are then fed to a condensation section 21 . Curing takes place here with the final conversion of hemihydrate to dihydrate. This process takes only 1.5 to 2 hours without adding any set accelerator due to the previous beta calcination process.

Following the drying device 22 there are devices R23 and 24 for crisscrossing the finished boards, which are then placed on top of the stack 24.

[Function] The present invention relates to a method for manufacturing gypsum board, in which a suspension is prepared from fibrous material crushed with calcium sulfate dihydrate, this is dehydrated and transformed into a board, and heated at atmospheric pressure. The dihydrate is recrystallized to the hemihydrate and finally converted back to the dihydrate by addition of water, with a concentration of about 300 to 600
s suspension with a water content of about 30 to 40% by dehydration equipment.
%, the dihydrate is recrystallized to the hemihydrate β form in the atmosphere without pressure, and the moisture required for condensation is absorbed through the board.

[Brief explanation of the drawing]

The drawing is a block diagram for explaining the systematic operation of one embodiment of the present invention. 1 is storage, 2 is water tank, 3 is conveyor, 4 is metering device, 5 is tank, 6 is crushing device, 7 is silo, 8 is storage, 9 is conveyor, 10 is crushing device, 11 is storage tank , 12 is a mixer, 14 is a hierarchical distribution machine, 15 is a continuous heating furnace, 16 is a belt conveyor, 17 is a negative pressure chamber, 18 is a water injection pipe, 19 is a press, 20 is a conveyor, 21 is a condensation section, and 22 is a dryer. Devices 23 and 24 are edging devices. Patent Applicant Pfleider Instori GmbH Land Kompanikage Agent Patent Attorney Ike 1) Determined -1'-.

Claims (1)

[Claims] 1. A suspension is prepared from a fiber material wet-disintegrated with calcium sulfate dihydrate, dehydrated, formed into a board, and heated to reconstitute the dihydrate into a hemihydrate. A method for producing gypsum fiberboard which crystallizes and subsequently converts to dihydrate, the method comprising:
The suspension is dehydrated to a residual moisture content of about 30-40% by a dehydrator, and then formed into a board; the dihydrate is recrystallized into the hemihydrate form in the atmosphere without pressure; A method for producing gypsum fiber board, characterized in that the moisture required for setting is absorbed through the board. 2. Process for the production of gypsum fiber board according to claim 1, characterized in that the drying calcination is carried out at a board temperature between 100°C and 170°C, preferably between 115°C and 140°C. 3. Process for producing gypsum fiber board according to claim 3, characterized in that the board is flooded with a stoichiometric excess of water during imbibition. 4. Process for the production of gypsum fiber board according to claim 3, characterized in that the water excess corresponds to at least 25 times the stoichiometric water demand. 5. For the production of gypsum fiber board according to one of claims 1 to 3, characterized in that, after the absorption of water, the board is calibrated in a press, optionally dewatered and further compacted. the method of.