DE3140419C2 - Ready-to-use binder preparation for the production of ready-to-use, storage-stable, thixotropic, refractory, carbon-containing casting compounds - Google Patents

Abstract

The invention relates to a binder preparation for the production of carbonaceous, refractory casting compounds of high thixotropy. It contains carboxylic acids, especially polymeric and oxycarboxylic acids, as well as reactive aluminum compounds and amorphous silica. The highly thixotropic casting compounds, which can be mixed with little water, can be compressed to low porosity using strong vibration.

Description

The invention relates to a ready-to-use binder preparation for the production of ready-to-use and storage-stable, thixotropic, refractory casting compounds, in particular carbon-containing compounds based on silicon dioxide, Aluminum silicate, aluminum oxide, zirconium silicate and silicon carbide.

Monolithic refractory masses are currently deformed by ramming, singing, spraying and pouring. Each of these processing methods has certain disadvantages which are known to the person skilled in the art. As a binder for masses that are deformed by the casting process, cements, water glasses and phosphates have so far been used proven. Vibration technology is predominantly used today for compressing hydraulically setting casting compounds used. It enables a texture-free and thus tension-free production of complicated, large-format components. The simple and quick processing of catfish predestines this method for production of mass products. Masses that are to be compacted by means of Vlbration should, if possible, be have high thixotropy, so that the stencils are removed as quickly as possible after compaction is complete the masses can be heated. The lifespan of such masses is far longer than that of ramming masses. High demands are made on the binders for the production of thixotropic channel masses. the Theological properties of the masses must be influenced in such a way that a bronze casting is possible. Another requirement is that the strength of the final product be at least that of must correspond to tamped masses.

A disadvantage compared to tamped fittings, however, is the lower compression and thus In the greater porosity of vibrated components. In particular, carbonaceous masses are only allowed to stand under produce great difficulties as casting compounds. For this reason, carbonaceous masses In the Usually compacted by pounding. When delivering blast furnace channels z. B. However, this is an expensive one Work life that requires a certain routine and care on the part of the staff. Still arise Layers during tamping, which in turn can lead to flaking and underflow, whereby the durability is significantly reduced.

DEOS 28 15 094 already describes a process for the production of refractory masses and furnace channel masses described by means of continuous casting, in which small amounts of mixing water are used to compact under Vlbration will. The refractory mixture made up of alkali silicate and phosphate with a binder is through Precautions to slow down and delay premature setting as much as possible, flowable for a long time held. This is done by using a sparingly soluble, only gradually in solution and setting reaction entering phosphate and by kneading with an agent which makes the grain surface hydrophobic such as Fat, oil or paraffin; In addition, water or liquid alkali metal may only be used immediately before use be admitted. As a result of these complex measures with delayed solubility, hydrophobizing Kneading and then adding alkali metal catalyst can only be removed after it has set, which takes a long time.

In DE-OS 29 24 356 a binder for refractory glazing materials is described which, in addition to reactive Contains clay and silica sol cement as an essential ingredient.

The latter, however, has the disadvantage that it makes the casting compound difficult to process due to premature setting, does not keep and does not make it storable. The binder therefore consists of two delivery components, namely a dry one made from reactive clay and cement and a liquid made from silica sol, which are only supplied separately can be stored and, because of the cement content, are only combined to form casting compounds immediately before use may be. Because of its lack of thixotropy, this casting compound is difficult to process and develop only after 1 or 2 hours is it sufficiently green that the stencil can be removed.

The GB-PS 13 60 183 describes the production of refractory Gle.ßmassen, in which the resistance of the End product against thermal changes and alternating stresses due to additional salt components Casting compound is to be improved. The components with such an effect represent a very heterogeneous group of substances dar; there are phosphates, pyrophosphates, polyphosphates and phosphoric acid, various silicates, borates and Slllclumborld, sodium aluminate, sodium tungstate, Lithlumfluorld, magnesium and also allphatic Hydroxy acids and citric acid including their esters and ammonium citrate are called. A reference to thlxotropes Behavior during vibration casting and a prevention of premature setting of the casting compound can cannot be taken from this group of substances.

A major disadvantage of the known binder combinations must be seen in the fact that they cannot be delivered ready for use and the compositions produced with them are not storage-stable. It is Therefore, the aim of the invention is to develop a binder mixture that is both ready-to-use itself and has a long shelf life available lsi, as well as the production of storage-stable, ready-to-use carbon-based refractories Allowed for flow casting with vibratory compaction. The composition of this binder must be Disadvantages of the known binders - premature setting or measures to prevent this should - report and after flushing and vibrating without loss of time, further processing immediately enable. As high a thixotropy as possible is required, so immediately after completion of the compaction the stencils can be removed and the masses can be heated up by vibration.

A ready-to-use binder preparation for the production of ready-to-use, storage-stable, thixotropic, carbonaceous, refractory casting compounds based on reactive aluminum compounds and amorphous Found silica, which is characterized in that it also contains polymeric carboxylic acids and / or Oxycarboxylic acids, but does not contain phosphate, cement, alkali silicate or clay.

The content of polymer carboxylic acid and / or oxycarboxylic acid is essential for the properties of thixotropy and the temporary bond, by means of which the water-free cast compounds can be cast by vibration, compressible and immediately demoldable are essential. As polymer carboxylic acids, for. B. polyacrylic acid, Polymethacrylates, polymalelic acid and similar polymeric carboxylic acids are used; preferably polyacrylic acid and poly methacrylic acid are suitable. Citric acid, tartaric acid, Malic acid, lactic acid and similar oxycarboxylic acids into consideration. Also low molecular weight carboxylic acids like z. B. Formic acid can be used. The acids mentioned are preferably found in the form of their neutral ones or acid salts use, in particular the salts of sodium, aluminum and ammonium and organic ammonium compounds come into consideration. Your share in the binder preparation is 1 to 50% by weight, preferably 10 to 30% by weight. As reactive aluminum compounds, for. B. reactive alumina, aluminum hydroxide, aluminum hydroxychloride, aluminum sulfate and aluminum formate be used. Their content in the binder preparation can be between 1 and 80 percent by weight, preferably between 5 and 50%.

The amorphous silica can be in liquid form as a silica sol or in solid form as an amorphous powder finely distributed, which can react with the carboxylic acids. The amount of salt is in the range from 1 to 70%, preferably 5-40% of the binder preparation.

The binder preparation is also characterized in that it is free from phosphate, cement, alkali silicate and sound is. The absence of these groups of components will cause premature setting and Solidification avoided and ready for use and storage stability achieved. This applies to both the binder preparation as a completely assembled prefabricated binder, as well as for those with this binder and with refractory material prepared, thixotropic pourable and vibratable casting compounds. It can also be one that has already been turned on Casting compound can be stored in immediately pourable form without setting prematurely and their Losing usability. A content of phosphates, cement and alkali silicate would lead to premature aging Setting and solidifying lead and thus the desired task of obtaining a storable casting compound, thwart. The addition of clay as a plasticizing and binding agent is also not included in the binding agent preparation necessary; it is thereby achieved that the mass has a lower shrinkage during firing, which is a represents another advantage. Due to the absence of phosphates, cements, alkali silicate and clay, the difficulties associated with premature setting of compositions containing such components avoided, which otherwise by various complex or annoying measures such. B. as late as possible Combination of the reactive mixture components, reduction in solubility, etc. must be countered.

This binder preparation makes it possible, together with carbon-containing backfill masses, on the base of silicon dioxide, aluminum oxide, aluminum silicate, zirconium silicate and silicon carbide ready-to-cast masses to manufacture. The carbon is generally present in these masses in the form of graphite or pitch. the The binder preparation is mixed with the respective filler compound without any further additives. These. Mixtures are characterized by the fact that they contain very small amounts of mixing water, depending on the porosity the raw materials are sometimes even lower than in the case of ramming masses, can be made to flow. You own an extraordinarily high thixotropy and can only be compacted by very strong vibration. Here porosities of 16% and less can be achieved.

Immediately after compaction by vibration, the casing must be removed and the mass heated up will. During the drying process, the mass hardens. First of all, there is a temporary one Setting through further polymerization of the carboxylic acid compounds. The further setting takes place through Reaction of the colloidal silica with the reactive aluminum compounds. In a reducing atmosphere, As is the case with the use of carbon-containing furnace channel masses, there is then an additional solidification through the carbon lattice, which arises as a result of carbonization of the organic components.

Example I.
Composition of the binder according to the invention:

a) polymethacrylic acid 20% (wt.)

Citric acid 5% (wt.)

Ammonia 25% 8% (wt.)

Aluminum hydroxychloride 30% (wt.)

Amorphous silica 20% (wt.)

Water 17 * (wt.)

b) polyacrylic acid 15% (wt.)

Aluminum hydroxide 20% (wt.) Alumlniumformlat 5% (Gev.) Amorphous silica 40% (wt.)

Water 20% (wt.)

Example II Application of the binder according to the invention:

From 60% (weight) bauxite coarse fraction

20% (wt.) Bauxlt-Felnmeh! ; ^; 20% (wt.) Silicon carbide and carbon

was together with

4% (wt.) Binder according to example I a) and 2 " 5.5% (wt.) Mixing water

a casting compound (A) mixed and compacted by Vlbration.

As comparison mass (B) was -'i 60% (wt.) Bauxlt coarse fractlon

15% (by weight) bauxite felling flour 5% (by weight) binding clay 20% (wt.) Silicon carbide and carbon

. <"and - instead of the binder according to the invention - with

4% (wt.) Aluminum phosphate and 5% (wt.) Mixing water

·> * Mixed. By stamping on the fishing ram, 25 strokes per side were compacted.

Both masses had after drying at 110 ⁰ C, a density of 2.55 g / ml, ie Gesamiporosität of about 25% was the same for both. Subsequently, test specimens were fired in a step firing at 500, 750, 1000, 1250 and 1500 ° C for 5 hours reducing weight and then examined for density and flexural strength. * · 'The following values resulted:

Flexural strength N / mm ²

Temperature "C / 5h 110 500 750 1000 1250 1500 ^{4 <} ground A 2.5 3.7 3.4 2.8 2.8 3.4 Comparative mass B 2.1 2.8 2.5 1.6 1.6 0

The volume weights, which were between 2.41 and 2.48, were practically identical. When it comes to flexural strength there was a clear increase at all temperatures when the binder according to the invention was used in the casting compound, compared with the use of aluminum phosphate in the tamped compound. This improvement is also based on a better sintering of the mass, because of the Vlbratfons method less texture formation and greater matting is achieved.

The addition of the binder makes it possible to compress carbonaceous masses by means of Vlbration so that the degree of compaction corresponds to that of tamped masses. The flexural strength, which is particularly important for the use of these masses, is equal to that of ramming masses.

The binder thus not only meets the strength requirements to be placed on a refractory casting compound, but also allows production due to its alkali-free and phosphate-free composition Ready-to-use and storage-stable, carbonaceous casting compounds that can be processed by vapor-casting. This now makes it possible to manufacture complex, large-format components in a very short space of time without texture, which generally increases the durability. By Use of the binder can also include the use of clay as a plasticizing and binding agent can be dispensed with, whereby a lower shrinkage of the mass is achieved as a further advantage.

Claims (6)

Patent claims: 1. Ready-to-use binder preparation for the production of ready-to-use, storage-stable, thixotropic, carbon-containing and refractory casting compounds, based on reactive aluminum compounds and amorphous Silicic acid, characterized in that it additionally contains polymeric carboxylic acids and / or oxycarboxylic acids, but does not contain phosphate, cement, alkali silicate or clay. 2. Binder preparation according to claim 1, characterized in that it is used as a polymeric carboxylic acid Contains polyacrylic acid and / or polymethacrylic acid. 3. Binder preparation according to Claims 1 and 2, characterized in that it contains the carboxylic acids as sodium, aluminum or ammonium salts and / or in the form of organic ammonium compounds contains. 4. Binder preparation close to claims 1 to 3, characterized in that its content of Carboxylic acid and carboxylic acid salts is 1-50%, preferably 10-30%. 5. Binder preparation according to Claims 1 to 4, characterized in that it is 1-80%, preferably Contains 5-50% of a reactive aluminum compound. 6. Binder preparation according to Claims 1 to 5, characterized in that it is 1-70%, preferably Contains 5-40% amorphous silica.