CS207063B1 - Fire-proof fibrous isolation element - Google Patents

Description

The invention relates to a refractory fibrous heat insulating element based on heat-resistant inorganic fibers, in particular refractory fibers and binders.

It is known to use refractory fibers in the form of loose wool, felt, mats or rigid boards for a variety of purposes where high thermal insulation is required at temperatures up to 1260 ° C and above. These include especially the lining of thermal aggregates, for example the interior of various types of furnaces, combustion chambers, reactors, casting molds, troughs for transporting melt, etc. The low bulk density together with high thermal, insulating ability and sufficient heat resistance enables an approach to furnace design with a significant reduction in lining weight.

The refractory fibers are mainly prepared by pulping aluminum silicate melts and contain - apart from the presence of a small amount of impurities - about 40 to 60% Al2O3 and 60 to 40% S1O2. The heat resistance of these fibers is up to approximately 1250 ° C. By increasing the Al ₂ O ₃ content, or by using additives of certain other oxides, the heat resistance of the fibers can be further increased up to 1600 ° C. Depending on the technological process used in the production of fibers, in particular the fiberizing method, fibers of different length, micronage, granule content, etc. are obtained, which is of particular importance in further processing into products.

Additives of binders are required to achieve higher strengths than can provide a simple felting of the fibers themselves. In view of the preparation of homogeneous, uniformly interconnected elements, in particular plates of uniform thickness and physico-mechanical properties, it is expedient to use wet forming of dilute aqueous suspensions of refractory fibers and binders which are drained in sieve forms, on a sieve drum or on an endless sieve The strip and the resulting wet element are dried after previous pre-pressing. Depending on the type and content of the binder retained in the carpet, elements of different stiffness or even solid plates are thus obtained which retain their strength even at high operating temperatures.

Various inorganic or organic binders or combinations thereof are used as binders in the formation of the refractory fiber elements. The type and amount of binders are mainly determined by the nature of the application of the resulting refractory fiber elements and the requirements that these elements must meet in a given application, particularly in terms of physico-mechanical properties. For example, only organic binders can be used for imparting handling or assembly strengths to products without the need to preserve them in the heat, which, upon installation of the elements, burns out at operating temperatures.

Where the refractory fiber elements are to exhibit sufficient heat resistance, binders which retain their bonding properties even at high temperatures, namely suitable inorganic binders, should be used. Colloidal silicon dioxide, colloidal alumina and the like have proven particularly suitable for this purpose. Typically applied silicon dioxide is used, in particular in the form of aqueous stabilized colloidal sols having a particle size in the range of about 10 to 100 millimicrons.

The disadvantage of the colloidal silica solution is that it is relatively costly and that it is difficult to avoid certain losses in the waste water, so that for some applications where high strengths are not required under the maximum working temperatures, i.e. about 1200-1250 ° C, its use is uneconomical.

It has therefore been proposed to use as a inorganic component of the binder system a high percentage, very fine silica of primary particle size below 1 micrometer, found in non-crystalline form, which is produced in the production of crystalline silicon due to re-oxidation in the gas phase. This fumed silica exhibits certain binding effects in the dewatered and dried carpet of refractory fibers already at normal temperature and in particular in the heat gives the elements the necessary cohesion and strength. To increase the cold handling strength, starch wax was used as the second component of the binder system, which in addition improves the retention of finely dispersed components when dewatering the fiber suspension.

The disadvantage of starch sebum is that it can only be used in limited quantities as it slows down the drainage of the component suspension on the sieve machine and prolongs the drying of the wet carpet, which reduces the performance of the machine. Thus, starch wax is not suitable for higher handling strengths of products which require increased amounts of starch binder.

The aforementioned drawbacks are overcome by the refractory fibrous insulating element prepared from the aqueous suspension of the refractory aluminosilicate fibers and binders of the present invention, which consists of 9.75 to

97.5 wt. 0.2 to 100 parts of refractory fibers

29.5 wt. 0.2 to 9.75 wt. % of starch and 0.001 to 0.02 wt. parts of the flocculating agent preferably polyacrylamide, optionally up to 1 wt. % of the fungicidal composition, preferably bistributyltin oxide, optionally up to 29.25 wt.

parts by weight of clay, preferably kaolin, up to 9.75 wt. parts of cellulose.

The use of starch in an indelible form does not give rise to the aforementioned difficulties in draining and drying the carpet of fibers and reducing line performance; in this form it also retains well in the dewatered carpet of fibers, which improves the use of the binder and increases the purity of the underwater waters. Potato or cereal starch with good binding properties may be used. The binding capacity of the starch in the dewatered carpet is activated by steaming.

It is also possible to use a non-lubricated so-called native starch, in combination with a small amount of starch sebum, so as not to slow down the dewatering and drying of the wet fiber carpet and only to improve the retention of the dispersion components in the dewatering.

For some purposes, it is possible to use clay components as fillers also exhibiting certain binding properties, in particular kaolin, which does not affect the temperature limit of use of the resulting elements. Optionally, a small amount of pulped cellulosic material (cellulose, paper sediment) can also be used, which also improves the retention of the finely dispersed components in the carpet and the handling strength of the article.

The addition of a flocculant improves the drainage of the suspension and the clarity of the underwater water.

Suitable antifungal agents, for example based on bis-tributyltin oxide, chlorinated phenol derivatives and the like, may be added to provide resistance to microbiological infiltration.

Examples

1. In 25 l of water 400 g of aluminosilicate fibers, 20 g of crystalline silk and 20 g of potato starch were mixed. The suspension was drained on a laboratory suction apparatus, and the wet carpet was stored for 1 hour in saturated steam and then dried at 105 ° C. The dewatering of the suspension proceeded rapidly, the resulting element exhibiting a bending strength of 0.64 MPa at a bulk density of 240 kg, m ³ , a bending tensile strength of 0.41 MPa after firing at 1150 ° C.

2. 400 g of aluminosilicate fibers, 80 g of fumed silicon production, 20 g of potato starch and 50 ml of a 0.1% polyacrylamide solution were mixed in 25 l of water. The suspension was dewatered and the wet carpet was steamed and dried as in the previous example. The resulting element exhibited a flexural tensile strength of 0.71 MPa at a density of 262 kg / m ³ , and had a flexural tensile strength of 0.69 MPa after firing at 1150 ° C.

Claims (3)

SUBJECT OF THE INVENTION CLAIMS 1. A refractory fibrous insulating element prepared from an aqueous suspension of refractory aluminosilicate fibers and binders, characterized in that it comprises from 9.75 to 97.5 wt. 0.2 to 29.25 parts by weight of refractory fibers; 0.2 to 9.75 wt. % of starch and 0.001 to 0.02 wt. parts of the flocculating agent, preferably polyacrylamide, optionally up to 1 wt. % of a fungicidal composition, preferably bistributyltin oxide. 2. A refractory element according to claim 1, comprising an additive of up to 29.25 wt. parts of clay, preferably kaolin. 3. A refractory element as claimed in claim 1, comprising an additive of up to 9.75 parts by weight of cellulose.