DE3801130A1 - PROCESS FOR PREPARING A FLUIDIZING STONE AND FLUORING STONES MADE ACCORDING TO THE PROCESS - Google Patents

Abstract

A method of manufacturing refractory insulating bricks includes forming a foaming mixture comprising a slip containing at least in part amorphous silicon dioxide with a grain size less than or equal to 0.3 mu m to which a separately produced foam is added and mixed in or to which a foaming agent is added and which is then beaten into the foamed mixture. An alkaline magnesium or calcium compound is added after the mixing or beating process. The resultant mixture is then moulded to form the bricks which are then dried and optionally fired.

Description

The invention relates to a process for the preparation of Refractory bricks by molding, drying and optionally Burning a mixture of a slip at least partially fine-grained silicon dioxide and optionally other additives and a separately manufactured and added to the slurry and mixed therein or adding a foamer to the slurry and whipping to a foamed mass, wherein an alkaline Mg or Ca compound after mixing or after whipping is added, as well as produced by the method Fire bricks.

From DE-PS 33 26 271 is a process for the preparation of refractory bricks by molding, drying and firing a mixture known, this mixture of a Schlicker, which as a refractory material silica may contain, as well as a separately manufactured and the Slip added and mixed therein foam consists. According to this prior art operation of the Mixture of slurry and mixed foam a small  Amount of magnesium montmorillonite and a small amount of Magnesium oxide malt is added and mixed therein. The Magnesium montmorillonite serves as an adjusting agent and the magnesia icter, which disperses in water is added, serves to rapid solidification to reach. According to this prior art procedure used as silica fused silica or quartz glass, wherein at least 25% by weight thereof in finely divided form below 3 μm should be present.

Object of the present invention is another Process for the production of refractory bricks, in which the addition of the used as an adjusting agent Magnesium montmorillonite is not required and inexpensive starting materials can be used.

To solve this problem, the method which characterized in that as silicon dioxide ultrafine, amorphous silica with a grain size  0.3 μm is used.

The finely divided, amorphous or glassy silica with a particle size of 0.3 μm used according to the invention is an inexpensive starting material, advantageously using the product which is by-produced in the production of ferrosilicon or in the reduction of zirconium silicate to zirconium dioxide Airborne dust accumulates. This means that the finely divided, amorphous or glassy silica, as can be used according to the invention, need not be a product of very high purity, but that so-called technical products, such as are commercially available, can be used. Such SiO ₂ flying dusts, which are also referred to as pyrogenic SiO ₂ , usually have a specific surface area, measured by the BET method, of 10-40 m ² / g and advantageously of 15-30 m ² / g and consist of agglomerates , whose primary particles have a size between 0.1 and 0.3 microns. The grain size, as defined according to the invention, refers to these primary particles.

According to a preferred embodiment of the process according to the invention, up to 75% by weight and preferably up to 50 or 30% by weight, based on the solids constituents of the slip, of fire-resistant or refractory substances having a particle size of more than 1 μm can be added to the slip. These fire-resistant or refractory materials may also be so-called fracture materials, advantageously breakage of silica bricks, ie silicon dioxide materials. Such fracture materials can be used with a grain size of, for example, 1 mm and preferably 0.1 mm. In addition to silicon dioxide materials, however, it is also possible to add Al ₂ O ₃ materials, for example finely divided alumina, calcined alumina, plate clay or molten Al ₂ O ₃ , their maximum grain size also being 1 mm and preferably 0.5 mm, particularly preferably 0, 1 mm should be. By replacing a portion of the finely divided, amorphous silica in the slurry with such refractory or refractory materials with higher grain size is achieved by the fact that refractory bricks can be produced with special desired properties in terms of strength, attack by slag and fire gases, also that the density of the Refractory bricks can be adjusted more easily to desired values.

According to another preferred embodiment is at the production of the refractory bricks the slip or the Mixture of slurry and added foamer before Whipping still up to 5 wt .-% of inorganic and / or added to organic fibers. This makes it possible to mechanical properties of the inventive To improve the process of producing lightweight refractory bricks, this improvement in strength in use of inorganic fibers even after firing while using organic fibers, the burning out when burning the refractory bricks, targeted Cavities or pores formed in the refractory bricks can be.

In the method according to the invention, the mixture of Slip and foam or the foamed slip, i. after the slipping of the slurry, an alkaline magnesium or Ca compound added. The addition of such Connection causes a rapid solidification of the in the Molds poured mixture, as the green moldings after relatively short residence time in the form are fixed and from this can be removed from the mold. These green moldings can after the demolding and then optionally fired become.  

Of course it is possible to use lightweight refractory bricks make larger dimensions and from such stones then by usual cutting the desired formats manufacture.

Compared to the prior art, the inventive Method has the advantage that the silicon dioxide used Starting material not to the required fineness must be ground.

To reduce the water requirement in the implementation of the According to the method of the invention, it may be advantageous to use a add to known condenser. Such liquefiers are commercial products.

The MgO to be added in the process according to the invention or CaO compounds cause the mixture of Slip and foam or the foamed slip one pH between 6 and 10, advantageously from 7 to 9, receives, which leads to the rapid solidification of the mixture. After addition of such Mg or Ca compound must of course, a rapid filling of the mixture in suitable forms take place before the start of solidification.

As suitable Mg or Ca compounds are Magnesiumoxidkauster, ie not deadburned, but still reactive with water under alkaline reaction MgO, Mg (OH) ₂ , lime or calcium called.

For not too large moldings is a Entschalen from the Form in a period of about 20 minutes to 2 hours after the Pouring possible.

After demolding the refractory bricks or the Lightweight preforms at slowly rising temperature up to dried at a maximum of about 150 ° C.

The Feuerleichtsteine or Feuerleichtformteile can then optionally fired, but this is from the desired strength, i. the burning of the Refractory bricks or the Feuerleichtformteile can only after installation at the point of use, i. at the user, done.

If firing is carried out at temperatures of at least 800 ° C., the firing temperature, depending on the starting materials used, can also reach values of up to 1450 ° C., but usually does not exceed a firing temperature of 1100 ° C. If the refractory constituents are only materials based on SiO ₂ .

Compared to the procedure according to DE-PS 33 26 271 the method according to the invention still has the great advantage on that the residence time in the form up to one for the Demoulding sufficient strength is much shorter.

In the method according to the invention, the Mg compound or the Ca compound usually in amounts of 0.1 to  2 parts by weight, calculated as MgO or CaO, per 100 parts by weight the solids contained in the slurry added.

The foam used in the method according to the invention is in a conventional manner with the help of a commercial Foaming agent and water, these usually in one Volume ratio of 1:10 are mixed, by means of a high-speed stirrer produced. At the other Embodiment in which the foaming agent to the added slip is added, the required Foam amount entered into the slurry and also by means of a high-speed stirrer to a stable foam pitched.

By suitable selection of the ratio of slip and foam mass in the first embodiment or by suitable selection of the amount of foaming agent added to the added slip, the density of the finished product can be controlled. If, for example, a density of 0.6 g / cm ^{3 is} desired, at least 16.6 l of foam must be added to 10 kg of solids in the slurry.

The invention will be more apparent from the following examples explains:

example 1

100 kg ultrafine, amorphous SiO ₂ with a maximum grain size of 0.3 microns were added in 45 l of water to a slurry. Separately, a foam mass was prepared from 8 liters of water and 1 liter of a foaming agent. In this case, a foam volume of about 200 l was obtained. The slurry and the foam were stirred together. Subsequently, 0.5 kg of MgO-Kauster dispersed in 5 l of water was added, mixed well, and the resulting mixture was poured into mold. The resulting stones with dimensions of 250 × 500 × 100 mm were then first dried for 24 h in the air, then in a drying oven at a temperature increase of 40 ° C to 100 ° C for a further 24 h, the drying of the light stone was performed.

This lightweight stone had the following properties:

Bulk density (g / cm³) 0.6 Cold pressure strength, KDF (N / mm²) 2.0 Porosity, Pg, (%) 75 Classification temperature, KT, (° C) 900 Thermal conductivity, WLF, (W / m · K) 0.10 at 200 ° C 0.13 at 400 ° C 0.16 at 600 ° C

Another Leichtstein was fired after drying for 4 h at 800 ° C. After firing, the cold crushing strength was 10 N / mm ² .

Example 2

A slurry of 50 kg of the very finely divided SiO ₂ used in Example 1 with a maximum grain size of 0.3 μm, 50 kg of breakage of silica bricks having a maximum grain size of 0.1 mm and 40 l of water was prepared. Separately, a foam mass of 7 liters of water and 0.6 liters of foam with a foam volume of 150 liters was prepared. The foam mass was mixed with the slurry, then 0.55 kg of magnesium carbonate slurried in 5 l of water was added. After thorough mixing, it was quickly poured into a mold. The solidification time was about 40 minutes.

According to the procedure of Example 1, the Drying of the refractory bricks performed, this possessed following properties:

Bulk density, R, (g / cm³) 0.7 Cold pressure strength, KDF (N / mm²) 1.2 Thermal conductivity, WLF, (W / m · K) 0.12 at 400 ° C 0.15 at 600 ° C 0.19 at 800 ° C 0.23 at 1000 ° C Classification temperature, KT, (° C) 1500

Example 3

The procedure of Example 1 was repeated, with 50 kg of finely divided, amorphous SiO ₂ and 50 kg of calcined alumina with a maximum grain size of 0.1 mm and 1 kg of ceramic fibers with an Al ₂ O ₃ content of about 47 wt. % and an application limit temperature of 1260 ° C with 52 l of water were added to a slurry.

Separately, 10 liters of water and 1 liter of foaming agent were added to a foam volume of about 230 liters. Subsequently, 0.4 kg Ca (OH) ₂ , calculated as CaO, was added in the form of a lime milk with a lime milk volume of 4 l.

According to the procedure of Example 1 were Refractory bricks with the following properties after Drying received:

Bulk density (g / cm³) 0.5 Cold pressure strength, KDF (N / mm²) 3.0 Porosity, Pg, (%) 82 Classification temperature, KT, (° C) 1520 Thermal conductivity, WLF, (W / m · K) 0.15-0.25 between 200 and 1000 ° C

Claims (7)

1. A process for the production of refractory bricks by molding, drying and optionally firing a mixture of a slurry of at least partially fine-grained silica and optionally other additives and a separately prepared and added to the slurry and mixed therein foam or adding a foamer to the slurry and whipping to a foamed mass, wherein an alkaline Mg or Ca compound is added after mixing or after impact, characterized in that is used as the silica finely divided, amorphous silica having a grain size of 0.3 microns. 2. The method according to claim 1, characterized, that as ultrafine, amorphous silica the Material used in the manufacture of Ferrosilicon or in the reduction of zirconium silicate to zirconium dioxide as a by-product in the form of Airborne dust accumulates.   3. The method according to claim 1 or 2, characterized, that the slip up to 75 wt .-%, based on the Solid components of the slurry, on fire-resistant or refractory materials with a Grain size can be added above 1 micron. 4. The method according to claim 1 or 2, characterized, that the slip up to 50 wt .-%, based on the Solid components of the slurry, on fire-resistant or refractory materials with a Grain size can be added above 1 micron. 5. The method according to claim 3, characterized, that the slip up to 30 wt .-%, based on the Solid components of the slurry, on fire-resistant or refractory materials with a Grain size can be added above 1 micron. 6. The method according to any one of the preceding claims, characterized, that the slip up to 5 wt .-%, based on the Solid components of the slip, inorganic and / or organic fibers are added. 7. Dried or fired refractory bricks, prepared according to the method of one of the preceding Claims.