CS221876B1 - Inorganic fiber elements with increased temperature resistance - Google Patents

Abstract

The invention relates to thermal insulation elements made of mineral fibers, containing uniformly distributed high-temperature aluminosilicate fibers in the structure and prepared wet from diluted aqueous suspensions with the addition of binders and possibly other auxiliary agents. The elements according to the invention show lower shrinkage values and improved thermal resistance compared to insulations based on mineral wool alone and are suitable, for example, in combination with refractory materials as back insulation in industrial furnaces and thermal aggregates.

Description

The invention relates to thermal insulation elements made of inorganic fibers, exhibiting increased temperature resistance.

As is known, inorganic fiber-based materials are particularly good thermal insulators due to the large number of cavities and chambers existing in the fibrous structures filled with air. The relatively small dimensions of these chambers prevent the flow of enclosed air and thus allow the use of its high insulating capacity. With suitably selected bulk densities in order to also limit the amount of heat spreading by conduction, fibrous insulation materials represent a highly effective material, in the applications of which other favorable properties are advantageously used; these include non-flammability, good resistance to a number of external influences, etc. Particularly favorable is the high thermal resistance given by the inorganic nature of the fibers. However, in the temperature range approaching the limit of thermal resistance of a given type of inorganic fibers, a number of changes occur in the fiber itself and on its surface, which have an impact on the properties of the fibers, in particular strength, volume changes, elasticity, etc. In natural fibers (aspen), the expulsion of bound water occurs even at relatively low temperatures; In fibers prepared from the melt, the beginning of crystallization and its consequences on the internal stress of the fibers, etc., are again evident.

For use as high-temperature insulation, volume changes - shrinkage of fibrous insulations - are of decisive practical importance, as they cause operational difficulties and can significantly affect the effectiveness and even usability of the insulation for given temperatures. Therefore, the permissible shrinkage value is usually limited; the amount of shrinkage of individual types of fibrous insulations at different temperatures compared to this limit value, which is usually 3%, then determines their practical temperature resistance. As for the fibers themselves, then ordinary glass fibers can be used for example up to temperatures of 350 to 400 °C, slag fibers up to about 600 °C, basalt fibers up to about 700 °C; for even higher temperatures, refractory aluminosilicate fibers with temperature resistance up to 1,260 °C to 1,450 °C are used, depending on the ratio of basic components used, and more recently, fibers based on pure oxides (AlgO^, ZrOg)> resistant up to 1,600 °C. These last types of fibers successfully replace the classic refractory linings made of heavy materials in modern furnace constructions. The fibers are processed by various technologies, especially using the wet process, into various products, enabling or facilitating the assembly of fibrous insulations. A binder additive is used for the necessary cohesion and handling strength.

The disadvantage of refractory fiber products is generally a relatively high price, which significantly exceeds the price of products made of conventional mineral slag or basalt fibers. This high price adversely affects the installation costs of fibrous refractory linings and reduces the achievable economic effect. It is therefore expedient to combine fibrous refractory linings with cheaper insulation placed on the back of the refractory fiber layer. The higher the temperature resistance of this back insulation, the smaller the thickness of the refractory fiber layer can be used and the greater the achieved economic effect.

As a back insulation, it is possible to apply, for example, calcium hydrosilicate-based boards with fiber reinforcement, reaching a temperature resistance of approximately 1,000 °C. These boards are self-supporting and are suitable for lightweight furnace constructions. It is also possible to use insulating elements made of mineral wool, which is very cheap compared to refractory fibers. The disadvantage in this case is the relatively low temperature resistance of mineral wool, around 700 °C, compared to the resistance of refractory aluminum-silicate fibers (over 1,200 °C) and therefore the need to use considerably large thicknesses of refractory fiber layers on the front side of the fiber lining.

The above-mentioned deficiency is eliminated by elements made of inorganic fibers with increased temperature resistance according to the invention, prepared by wet dewatering and drying an aqueous suspension of components, characterized in that they consist of 99 to 70 wt. % of a fibrous component, containing 95 to 40 wt. % of mineral wool and 5 to 60 wt. % of aluminosilicate fibers and 1 to 30 wt. % of binders. In addition to the above-mentioned components, the elements according to the invention may contain up to 5 wt. % of coagulants, up to 0.005 wt. % of flocculants and up to 5 wt. % of antimigration agents,

22!876 based on the total solids content. It was found that the addition of aluminosilicate fibers to mineral wool, when evenly distributed in the structure of the resulting element, even in relatively small amounts, increases the temperature resistance and decreases the shrinkage values of the elements compared to products made from mineral wool alone. With an increasing content of aluminosilicate fibers in the fiber mixture, the shrinkage values decrease further. For example, an addition of 10% aluminosilicate fibers to mineral wool shifts the temperature resistance limit, given by the shrinkage values of the element below 3%, to approximately 800 °C, an addition of 20% aluminosilicate fibers to approximately 900 degrees Celsius (with 24-hour heating).

As a binder, it is possible to use organic binders, such as latexes, meeting the requirements in terms of stiffness, or flexibility and formability of the resulting insulation, providing harmless and non-corrosive decomposition products and suitable for wet molding technology. Suitable examples are anionic dispersions of terpolymers of vinyl acetate, acrylic acid ester and maleic acid derivative, anionic dispersions of vinyl acetate acrylate copolymers, styrene-butadiene dispersions, or plasticized types of these ter- and copolymers, as well as polyvinyl acetate dispersions, etc., which are precipitated, for example, with aluminum sulfate as an aluminum coagulant and provide a film of satisfactory stiffness, or flexibility. It is also possible to use starch as a binder, preferably potato starch, or starch grease, or a combination of starch and starch grease. It is also possible to use inorganic binders based on colloidal or finely dispersed substances, oxides, hydroxides or hydrolyzing salts, for example colloidal silicon dioxide, aluminum or zirconium compounds, bentonite, etc. It is also possible to use a combination of organic and inorganic binders. To improve the retention and purity of the under-screen water, it is possible to use a small amount of hydrated cellulose; it is also possible to use a flocculant based on polyacrylamide, introduced into the suspension just before the inflow of the molding machine. It is expedient to use an anti-migration agent together with binders that tend to migrate during drying of the elements.

The advantage of the insulating elements made of inorganic fibers with increased temperature resistance according to the invention lies primarily in the fact that they enable the reduction of the cost of fibrous insulating linings of furnace spaces without significantly affecting the properties and quality of the insulation. The advantage of the wet method of preparing the elements according to the invention is the simplicity of homogenization of mineral and aluminosilicate fibers due to their similar behavior in a neutral aqueous environment and ease of dispersion. The procedure is, for example, as follows: in a mixing device, e.g. of the hydropulper type, the fibrous component used in a smaller proportion is first mixed, the second fibrous component, the binders used and possibly other additives are added. The latexes are introduced in the form of a diluted dispersion, starch can be added in powder form or as a starch grease. After mixing, precipitation is optionally carried out with an aluminum sulfate solution, the suspension with a concentration of 0.2 to 5.0 wt. percent is subjected to granule separation and pumped into the storage tank of the screening machine.

A flocculant solution can be added before the inflow. The wet mat, formed in the dewatering section of the screen machine, is subjected to drying, formatting and possibly further processing after thickness adjustment. The suspension of fibers and binders can also be processed by vacuum forming using screen molds into shaped elements.

Example

A series of boards was prepared by mixing the fibrous component and binders in water to form a suspension, which was drained after homogenization and the wet carpet was dried. 400 g of fibrous component was used, containing in a graduated ratio mineral wool, prepared from a batch of 50% basalt and 50% blast furnace slag, and aluminosilicate fibers; a latex based on acrylate copolymers, precipitated with an aluminum sulfate solution, was used as a binder. Furthermore, 10 ml of colloidal silica solution was added per 1 liter of suspension. The size of the prepared boards was 34 x 34 cm; a board made of mineral fibers alone was also prepared as a control sample. The boards were cut into smaller samples, which were heated for 24 hours in a ceramic housing at different temperatures and additional linear changes were measured. The results are shown in Table 1.

Table 1

Additional linear changes in %

plate number % in the mixture of alumina- silicate fibers mineral 600 700 Temperature °C 800 900 1,000 1,100 1 0 100 -0.42 -1 .29 -2.9 >3 2 10 90 -0.35 -0.85 -1.7 >3 3 20 80 -0.29 -0.50 -0.95 -1.75 >3 4 30 70 -0.24 -0.24 -0.48 -1.14 -’,8 >3 5 40 60 -0.21 -0.22 -0.47 -0.94 -1.4 -3.2 6 50 50 -0.20 -0.39 -0.83 -1.4 -3.0 7 60 40 -0.38 -0.73 -1 .3 -2.66 >3

Example 2

Boards were prepared from a mixture of fibers by mixing the fiber component and binders in water to a suspension, which was drained after homogenization as in example 1, the wet carpet was subjected to steaming and drying. Again, 400 g of the fiber component was used, containing in a graded ratio aluminosilicate fibers and mineral wool, which was mixed in 15 l of water; a combination of starch and colloidal silica was used as a binder for each board. Furthermore, an additive of 0.0005 wt. % polyacrylamide was used. As a control sample, a board was again prepared from the mineral fibers alone and the indicated binders. Smaller samples were prepared from the resulting boards measuring 34 x 34 cm, which were heated for 2 hours without a protective sleeve in an electric furnace at various temperatures and additional linear changes were measured. The results are shown in Table 2.

Table 2

Additional linear changes in %

plate number % in fiber blend Temperature °C alumino- silicate mineral 650 750 850 950 1,050 1,150 8 0 100 1.3 2.4 4.4 9 30 70 1.2 1.6 2.4 3.6 10 40 60 1.0 1.3 1.9 2.2 2.6 >3 1 1 50 50 0.88 ’ ,4 1.6 2.3 3.4 12 60 40 0.6 2.1 2.4

Boards were prepared from a mixture of fibers in a similar manner to examples 1 and 2. A 10% colloidal solution of silica was used as a binder, in which the fibers were mixed into a suspension and formed into boards by dewatering. A control sample was again prepared from pure mineral wool and the aforementioned binder. Additional linear changes in the samples of dried boards after 2-hour annealing at a temperature of 800 °C are given in Table 3.

Table 3

Additional linear changes in %

Number of the board % in fiber blend 800 °G/2 hours alumino- silicate mineral 13 - 100 3.2 14 10 90 1.2 15 20 80 0.9 16 30 70 0.65

SUBJECT OF THE INVENTION

Claims (7)

CLAIMS 1. Inorganic fiber elements of increased temperature resistance, prepared by wet dewatering and drying of an aqueous suspension of components, characterized in that they consist of 99 to 70 wt. % fibrous component containing 95 to 40 wt. % mineral wool and 5 to 60 wt. % aluminosilicate fibers, and from 1 to 30 wt. % binder. 2. Inorganic fiber elements of increased thermal resistance, prepared by wet dewatering and drying of the aqueous suspension of the ingredients according to claim 1, characterized in that organic binders, preferably aqueous dispersions of synthetic resins or starch are used as binders. 3. Inorganic fiber elements with increased temperature resistance, prepared by wet dewatering and drying of the aqueous suspension of the components according to claim 1, characterized in that inorganic binders, preferably colloidal silicon dioxide, are used as binder. 4. Inorganic fiber elements of increased thermal resistance, prepared by wet dewatering and drying of the aqueous suspension of the ingredients of item 1, characterized in that a combination of organic and inorganic binders is used as the binder. 5. Inorganic fiber elements with increased temperature resistance, prepared by wet dewatering and drying of the aqueous suspension of the components according to items 1 to 4, characterized in that they contain an additive of up to 5% by weight. % coagulants, preferably aluminum sulphate. 6. Inorganic fiber elements of increased thermal resistance, prepared by wet dewatering and drying of the aqueous suspension of the components according to items 1 to 5, characterized in that they contain up to 0.005 wt. % flocculants, preferably polyacrylamide. 7. Inorganic fiber elements of increased thermal resistance, prepared by wet dewatering and drying of an aqueous suspension of the components according to items 1 to 6, characterized in that they contain up to 5 wt. % antimicrobial agents, preferably cellulose derivatives.