DE1471024C - Process for the production of hard plaster - Google Patents

Description

1 2

It is known to produce plaster by treating in the autoclave according to the invention

powdered raw plaster either heated alone or in process one obtains a loose, proportionate one

Water or steam in an autoclave at temperature - coarse crystalline product which can be poured out

doors between 120 and 17O ⁰ C, whereupon the moist and that with the addition of a small amount of water

Product is dried. Easily stirred up to a pourable consistency for the production of 5

Plaster in this way required amount of water is can. The hard plaster obtained from it is required for

relatively high, so that the mechanical strength of the pourable consistency compared to after ■ known

cured product is not good. Hard plaster of paris produced by the process much less

A method has already been known which products water and has better compressive strength. the

to be produced in an autoclave with less water, to autoclave discharge can be shredded directly while wet,

whose strength should then be better. If necessary, you can add some more water for this.

Gypsum cartilage assumed, however, cartilage material is added.

as a raw product, less easy to process than flour, a so-called α-plaster or hard

and furthermore, this procedure does not result in a plaster of paris. Because of the small amount of water used

Product that has less water for setting 15 also contains lower amounts of organic acids

needed. . or to use their salts as crystallizers,

In order to get a hard plaster of paris, which requires less namely 0.025 to 0.067% calculated on the dry mixing water for the setting and which weight of plaster of paris. The optimal amount of additives leads to higher strength, one has to vary with the type of raw plaster. If one of the autoclaves uses a mixture of gypsum flour and a small amount of water in the gypsum water used with the addition of amber, maleic, mixture, the tendency is also the solid citric, phthalic or malic acid and / or theirs Relatively few substances to separate out, so soluble salts are provided and it is easier to stir during cooking and the mixture vigorously during burning. Because of this need to stir the quiescent state in an essentially mixture, these processes require the 25 homogeneous state to be maintained.
Applying a large amount of water, which eventually It has also been found that avoidance of. completely, e.g. B. by filtration, centrifugation and turbulence drying in the mixture during firing is to be removed. or draining the formation of much larger ones

In the reference "Silikattechnik", 11, 1960, anhydrite crystals favored. This is special

No. 4, pp. 125 to 179, is a report on indicative 30 importance, since larger crystals are more easily fil-

Investigations are given about different possibilities and more easily to a certain grain size

peculiarities of gypsum boiling, however, at the end of this will be crushed, giving maximum compression and

Report pointed out that even larger amounts lead to a firmer, set mass. To

further work is required, due to a preferred embodiment of the invention

of these orientational investigations in the large-scale process, the mixture is essentially

to be able to propose technically applicable procedures. borrowed dormant state heated. The mixture can

Among other things, studies with resting but also very slowly stirred and / or of time

the material in the autoclave and a water content are mixed from time to time in such a way that the formation

about 30 ° / o carried out. It turned out that large crystals are not disturbed

after finishing the boiling treatment of the auto 40. When the burning is finished, it is beneficial to use the

The contents of the clave form a firmly bound, hard mass ₍ mass to move, if necessary with introduction

tiny matted hemihydrate crystals that are made up of additional water in order to discharge from the

only with great difficulty from the autoclave. To facilitate autoclave.

discharged and crushed. The in this way of the above acids or their salts can be one

The plaster produced requires one or more use for pouring consistency. The quantities to be used

high water content. the compressive strength is related to the ratio of water

moderately low. According to this information in the literature - to plaster of paris, and that is obtained with a ratio

The product made by silicate technology is a paste-like mixture at the lower end of the range,

In practice useless, as in the comparison -,.: In the middle of the area a mud-like mi-

attempt is explained. 50 schung and one at the top of the range

The invention now relates to a new method of cooking pourable sludge.

for the gypsum flours using mineral The method according to the invention can be used in isators and allows the production of plaster in an autoclave or other pressure cooker, by high quality. The method according to the invention to lead. The small amounts of water which are necessary for the production of hard plaster of paris by heating a water heat 55 and which must finally be removed from a mixture of gypsum flour and one or more, represent an important economic pre-acids in the form of the amber, lemon, phthalic It is also very useful to use such low levels of men-maleic, itaconic or malic acid and / or their gene of the relatively expensive crystallizers or water-soluble salts or other compounds among mineralizers according to the invention. Pressure is now characterized in that a mass 60. Finally, the process according to the invention can be carried out with 25 to 67% water and 0.025 to 0.067 weight of the same batch size as known processes in percent minerals, based on the dryer - smaller autoclave,
weight of the plaster of paris, in essentially dormant As an additive in the process according to the invention state or under slow and / or intermittent succinic acid and its water-soluble intermittent stirring seem to be heated. To get the best results with the cooking salts. As particularly temperature it is preferable to ^c to 160 C. An expedient citric, maleic, and steam pressure in the autoclave proved from about 2.8 atmospheres to malic acid and soluble salts thereof for the Aufais has proved expedient. After the end of the cooking process, gypsum accumulating as a by-product.

In addition to the organic acids listed above as crystallizers in their free form, one can also use Use derivatives such as methyl succinate and similar esters, as well as itaconic acid.

If the amount of water in the autoclave after boiling is insufficient for discharge and in If a wet mill cannot grind it well, water of the desired temperature can be poured into it Bring in the wet mill to facilitate grinding or the subsequent application of the moist To enable a mixture of piastres.

It is preferred to treat a neutral mixture in the autoclave. Most of the raw plasters contain enough carbonates to neutralize the acidity of the additions.

In general it can be said that the coarser the plaster of paris, the larger the crystals of the half hydrate and the longer the required cooking time at a given pressure and temperature.

The following table shows examples of temperature, time and pressure during dewatering according to the invention summarized.

temperature Vapor pressure time ⁰ C atü Minutes 126 1.4 60 to 200 141.5 2.8 15 to 60 153.0 4.2 10 to 30 160.0 5.25 10 to 20

The invention is illustrated by the following examples.

Example];
A mixture is made from

4000 g plaster of paris (Newark, <1.676 mm).

2666 g water (66.7 percent by weight),

2.6 g succinic acid (0.067 percent by weight), 2.66 g chalk (0.067 percent by weight)

and treated for 30 minutes at a temperature of 141.6 ^C C and a pressure of 2.8 atm without stirring or mixing in an autoclave. The obtained hard plaster crystals had an average width of 45 μm and a length of up to 270 μm.

Example 2
A mixture was made from

4000 g plaster (Mountfiel, 80% <0.152 mm),
1000 g water (25 percent by weight),

1 g succinic acid (0.025 percent by weight),
1 g chalk (0.025 percent by weight)

and 30 minutes at 141.6 ° C and a pressure of 2.8 atm without stirring or mixing in an autoclave treated. The crystals of the plaster obtained had an average width of 45 μm and a length up to 350 μm.

B is ρ ie 1 3
A mixture was made from

101.6 kg plaster, 100% <1 mm, 95% <0.251mm,

67.8 kg of water (66.7 percent by weight),
681.0 g succinic acid (0.067 percent by weight)

and 27 minutes at 141.6 "C and a pressure of 2.8 atmospheres without stirring or mixing in an autoclave treated. The crystal size of the plaster obtained was between 100 and 500 μm.

B e i s ρ i e I 4.

A mixture according to Example 3 was placed in the autoclave for 30 minutes under otherwise identical conditions treated, but stirred every 2 minutes for 5 seconds. Crystals with a Grain size from 100 to 500 am.

Example.

A mixture was made from

127 kg plaster of paris, <1.676mm (Hawton).
j. 84.2 kg of water (66.6 percent by weight).

85Og succinic acid (0.067 weight percentage)

and 30 minutes at 141.6 ⁰ C and a pressure of 2.8 atm in the autoclave heated, while the mixture was stirred every 2 minutes 5 seconds. A plaster with a particle size of 100 to 500 μm was obtained.

B e i s ρ i e 1 6

100 parts plaster of paris, <0.6 mm (Newark).
50 parts by weight of water,
0.05 parts by weight of citric acid.
■ 0.05 parts by weight calcium carbonate

were mixed and treated in the autoclave for 1 hour at 141.6 ° C. and 2.8 atmospheres without stirring. The crystalline hemihydrate consisted of large crystals with a length of up to 500 μm. average 135 μm.

Example7 ■ '

1 s ρ 1 e 1

The recipe corresponds to Example 6, but phthalic acid was used instead of citric acid. Man received roughly the same product.

Example

100 parts of precipitated plaster of paris.
60 parts of water,
0.06 parts maleic acid,
0.06 parts calcium carbonate

were mixed and treated as indicated in Example 6. Hemihydrate crystals were obtained with a Length up to 65 μm, an average of 45 μm.

If malic acid is used instead of maleic acid, the result is a plaster with a grain size of up to 90 μm, an average of 60 μm.

Comparative experiment

In the sense of the instructions from "Silicateehnik". 11, 1960, No. 4, p.! 76. right column, were the following Tests carried out:

A. 300 g finely ground raw chips "1 lawtongypsiim". Purity 99.5%, sieve analysis "100% ^ 0.353 mm. 52% <0.152 mm. 28%, <0.064 mm. Were mixed with 90 cm ^{3 of} water and placed in a tin can on a small surface in the autoclave. For 3 hours When the autoclave was at rest, a steam atmosphere of 2 atmospheres was maintained at 120 ° C. The autoclave and metal container were then opened, and it was found that these contained a hard mass of matted, needle-like hemihydrate crystals that could be extracted from the Container could not be removed. The container with the piaster was broken

now dried in a drying cabinet for 20 hours at 100 ^° C. and then the loss on ignition of 15% is determined.

The dry plaster was now chiseled out of the container and the lumps in a laboratory swing hammer mill ground to 0.15 mm and sieved through an O.178 mm sieve.

The normal pouring consistency of the plaster was determined and it was found that for a pourable mixture 62.5 parts by weight of water per 100 parts by weight of plaster are required.

With normal consistency, the compressive strength of the dry plaster was found to be 23.8 kg / cm ² .

B. The experiment was repeated, but according to the invention 0.18 g of sodium succinate was dissolved in the 90 cm ^{3 of} water used. In this case the cooking time of the plaster in the autoclave would be increased to 8 hours.

After completion of the autoclaving, the container was found to be a soft sludge of contained large, flat hemihydrate crystals over which water stood. The product could be with a Stir spatulas into a slurry that could easily be poured into a porcelain bowl. This was then dried as above.

Loss on ignition after drying 14.8%

The dry product was then ground and sieved as above. A free flowing powder was obtained.

The normal pouring consistency was already achieved with 38.5 parts by weight of water per 100 parts by weight of plaster. The compressive strength of the dry plaster at normal consistency was 46.1 kg / cm ² .

From the above experiments it can be seen that in the case of static autoclaving without the addition of mineralizers you get a hard product that is extremely difficult to work up, but you get through adding a small amount of mineralizers according to the invention to obtain a loose crystalline material, which looks easy to process. With the plaster according to the invention, the pouring consistency is normal much lower, but the compressive strength is almost twice as high as that of the known ones Products for static autoclave treatment without the addition of mineralizers.

Claims (7)

Patent claims: 1. A process for the production of hard gypsum by heating an aqueous mixture of gypsum flour and one or more acids in the form of succinic, citric, phthalic, maleic, itaconic or malic acid and / or their water-soluble salts or other compounds under pressure, characterized in that a mass with 25 to 67 ° / ₀ water and 0.025 to 0.067 percent by weight of the acids and / or their salts, based on the dry weight of the gypsum, in a substantially static state or with slow and / or intermittent stirring is heated. 2. The method according to claim 1, characterized in that up to a temperature of 160 ° C heated. 3. The method according to claim 1 and 2, characterized in that under a pressure of heated to about 2.8 atmospheres. 4. The method according to claim 1 to 3, characterized in that after completion of the Drainage to facilitate discharge the mixture stirs or agitates. 5. The method according to claim 1 to 4, characterized in that after completion of the Introduces water into the autoclave for dewatering. 6. The method according to claim 1 to 5, characterized in that the from the autoclave wet grinds discharged moist product at such a temperature that no setting takes place. 7. The method according to claim 6, characterized in that water is added to the mill.