CS200971B1 - Method of production of magnesium chromium-plated building materials resistant to changes in temples - Google Patents

Abstract

The process is characterized by the fact that spinelitic magnesia is prepared by sintering a mixture of magnesia with chrome ore. From this basic material, a forming mixture is prepared by the usual method, which is heterogenized by the addition of 3-15% chrome ore. From the mixture, compacts are prepared, which are cast into building blocks by the usual method.

Description

The invention relates to a method of producing magnesia-chromium shaped refractory building materials from spinelitic magnesia, prepared by sintering a mixture of magnesia with chromium ore, resistant to sudden temperature changes, intended for lining metallurgical furnaces and vessels, cement and other furnaces.

The resistance of refractory building materials to sudden changes in temperature is characterized by the well-known simplified relationship K = , where O is the strength at high temperatures at which

E is the modulus of elasticity. The higher the value of the K criterion, the higher the relative resistance of the refractory building material to sudden temperature changes.

Magnesiochromite shaped building materials currently prepared from forming mixtures composed exclusively of spinelitic magnesia with a content of from 3 to 15 wt. % chromium oxide /Cr ₂ O^/ or from a mixture of such spinelitic magnesia with sintered magnesia, exhibit very high values of elastic modulus after firing at a temperature of 1600 to 1820 °C, even at the level of the values of elastic modulus of magnesium building materials. The resistance of such magnesiochromite building materials to temperature changes is low. The consequence is that magnesiochromite building materials from spinelitic magnesia with a chromium oxide content /CrgO^/ from 5 to 15 wt. % are not suitable for those places of metallurgical furnaces and vessels in which there is a change in temperature, or to one-sided thermal stress, however, with regard to the very good resistance to the effect of slag, the use of magnesia-chromium building materials made of spinelitic magnesia would be appropriate.

The above-mentioned shortcomings are eliminated by a method for producing magnesia-chromium shaped building materials resistant to temperature changes from spinelitic magnesia, the essence of which is the sintering of a mixture of magnesia with chromium ore according to the present invention, characterized in that the building material shard is heterogefied by introducing chromium ore into the forming mixture, which consists of 85 to 97 wt. % spinelitic magnesia with a silicon dioxide (SiO2) content of 1 to 3.5 wt. %, chromium oxide ( _Cr2O3 ) of 3 to 15 wt. %, 3 to 15 wt. % chromium ore with a content of not more than 4 wt. %, silicon dioxide (SiO2), that the forming mixture contains 20 to 40 wt. % of the fraction below 0.2 mm and 20 to 65% of the fraction from 1 to 6 mm, that the forming mixture is moistened and provided with binders, shaped under a pressure of 70 to 200 MPa into moldings, which after drying are fired at a temperature of 1600 to 1820 °C or the moldings are covered with sheet metal and hardened at a temperature of 50 to 200 °C.

By introducing chromium ore into the forming mixture, when firing shaped building materials at temperatures of 1600 to 1820 °C, their shard is heterogeneous, which significantly reduces the value of the modulus of elasticity E without reducing the strength O. This significantly increases the value of the criterion K. The possibilities of influencing the strength at high temperatures are very limited and therefore, even with their possible slight increase, such significant increases in the value of the criterion K cannot be achieved as are achieved by significantly reducing the modulus of elasticity E by heterogenizing the shard with the addition of chromium ore. This is clearly demonstrated by Example 1.

Heterogenization of magnesia-chromium basic building materials from spinelitic magnesia

200 971, according to the invention, it is possible to use the form and amount of the introduced chromium ore in the forming mixture, from which shaped building blocks are prepared by pressing, in a wide range of applications. The introduced chromium ore can be used in a finely dispersed form in a grain size below 0.2 mm in an amount of 3 to 15% by weight, preferably 7 to 12% by weight, based on the weight of the dry components of spinelitic magnesia and the introduced chromium ore without moisture and binders. It is also advantageous to use the chromium ore in a granular form in the forming mixture with a maximum grain size x _Q = 3 mm, preferably in a grain size below 2 mm and with a proportion of particles smaller than 0.2 mm of up to 40% by weight, based on the weight of the introduced granular chromium ore. Granular chromium ore is introduced into the forming mixture in an amount of 3 to 15% by weight, preferably 5 to 10% by weight, also based on the weight of the dry components of the forming mixture.

Chromium ore, used for the heterogenization of the shards of shaped building materials, introduced into the forming mixture as its component, contains no more than 4% by weight of silicon dioxide /SiO ₂ / and more than 35% by weight of chromium oxide /Ογ,,Ο^/.

The forming mixture from which shaped, magnesia-chromium refractory building materials resistant to temperature changes are made is composed in such a way that it contains a highly dispersed matrix fraction with a grain size below 0.2 mm from 20 to 40% by weight and a granular fraction in which the content of fracking with a grain size from 1 to 6 mm is from 20 to 65% by weight, while in all cases the weight percentages refer to the weight of the dry components of spinelitic magnesia and chrome ore forming part of the forming mixture.

The forming mixture moistened and provided with known binders is, after mixing in the usual manner, pressed under a pressure of 70 to 200 MPa into moldings, which after drying are fired at a temperature of 1600 to 1820 °C. In the case of unfired chemically bound shaped magnesia-chromium building materials, these are fired directly in service after drying after their incorporation into metallurgical furnaces and vessels, cement and other furnaces.

Example 1

The forming mixtures for the preparation of magnesia-chromium refractory building materials were prepared from spinelitic magnesia-chromium clinkers and chrome ore with the properties given in Tables 1 and 2.

Content of main components /%/ Table 1

Main components Spinelitic magnesia Chromium ore I. II. Si0 ₂ 3.05 2.80 2.66 Cr _o 0^ 9.15 14.00 53.80 CaO 1.35 1.10 0.40 MgO 76.70 70.00 20.08

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Granularity of granular fractions Table 2

Graininess Spinelitic magnesia /%/ Chromium ore /%/ I. II. + 3 6.3 10.1 - 2 - 3 25.1 28.4 - 1-2 34.5 36.4 30.5 0.5 - 1 28.6 20.0 35.8 - 0.5 5.5 5.1 33.7

The highly dispersed matrix fractions of spinelitic magnesia and chrome ore had a grain size characterized by a residue on a sieve with openings of 0.09 mm in the range of 8 to 9 wt.%.

The forming mixtures consisted of individual components with properties according to Tables 1 and 2 in the proportions given in Table 3 in weight percentages.

Composition of the forming mixtures /%· wt./ Table 3

Type Spinelitic magnesia Chromium ore I. II. grainy matrix grainy , matrix grainy matrix 1 o c. 70 30 7C 30 3 4 65 30 65 30 5 years 5 6 60 30 60 30 10 10 7 8 70 20 70 • 20 10

The forming mixtures composed according to tab. 3 after moistening with 1% by weight of water and after adding the binders 1% by weight of saturated magnesium sulfate solution /f.IgSO, / and 1% by weight of sulfite leachate solution with a density of 24 °Bé, these weight percentages being based on the weight of the dry components of the forming mixture, were mixed in a known manner, pressed into moldings at a pressure of 100 MPa. The moldings were dried at a temperature of 120 °G for 24 h and fired at a temperature of 1700 °C with a holding time of 5 h at this temperature. The properties of the magnesia-chromite building blocks after firing are given in tab. 4.

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Properties of building blocks after firing Table 4

Type Share _of imported chrome ore True porosity Flexural strength at ₀ 1500 °C OPo Modulus of elasticity E K=^ . E . 10~ ² /% wt./ /% vol./ /MPa/ /GPa/ 1 0 16.3 2.5 125.9 2.0 2 0 15.6 3.9 54.7 7.1 3 ^5X 17.6 2.8 30.5 9.2 4 5 ^times 15.2 3.3 33.7 9.8 5 10 ^times 17.7 2.9 21.5 13.5 6 10 ^times 15.9 3.3 20.5 16.1 7 10 ^xx 17.7 4.3 32.4 13.3 8 10 ^xx 16.7 3.5 29.5 11.9

x chrome ore in granular form xx chrome ore in matrix form

The advantage of the method of producing magnesia-chromium building materials from spinelitic magnesia resistant to temperature changes according to the present invention is evident from the properties listed in Table 4. Building materials of types 1 and 2 have high values of the modulus of elasticity E and low values of the criterion K. In contrast, building materials of types 3 to 8, into the forming mixtures of which chromium ore heterogenizing the slag after sintering was introduced by the method according to the invention, exhibit low values of the modulus of elasticity E and high values of the criterion K, which characterizes their resistance to temperature changes and the effects of one-sided thermal stress.

Claims (3)

200 971 Characteristics of fires after firing Table 4 Species Shares of chromium species Actual porosity Bending strength 01500 ° C OPo Elasticity modulus E K = ^. E. 10 ~ 2 /% w / w /% w / w / GPa / 1 0 16.3 2.5 125.9 2.0 2 0 15.6 3.9 54.7 7.1 3 5 X 17.6 2.8 30.5 9.2 4 5 x 15.2 3.3 33.7 9.8 5 10 x 17.7 2.9 21.5 13.5 6 10 x 15.9 3 3 20.5 16.1 7 10 xx 17.7 4.3 32.4 13.3 8 10 xx 16.7 3.5 29.5 11.9 x chrome ore in granular form x chrome ore in matrix Advantage The method of producing magnesium-rich chromosomes from spinelitic magnesia resistant to changes according to the present invention is evident from the properties given in Table 4. Buildings of types 1 and 2 have high values of elastic modulus E and low value criterion K. In the compositions of the invention, chromium ore heterogeneous after caking was introduced, the low elastic modulus values E and the high K criterion values, which characterize their resistance to heat changes and the effects of one-sided thermal stress. BEFORE THE INVENTION, CLAIMS 1. A method for producing heat-resistant, magnesium-resistant, heat-resistant refractory formulations of spinelitic magnesia prepared by firing mixtures of magnesium with chromium ore, characterized in that a blend of 85 to 97% by weight of spinelite magnesia containing silicon dioxide / SiOg (up to 3.5% by weight and chromium oxide / Cr2O4) from 3 to 15% by weight; % and from 3 to 15 wt. % of silicon dioxide with a SiO2 content of up to 4% by weight. and at least 35% by weight of chromium oxide (Cr2O3) such that a fraction of fraction below 0.2 mm is in the form of 20 to 40% by weight in the blend. and a fraction fraction of from 1 to 6 mm is from 20 to 65% by weight, that the molding composition is wetted and provided with binders, compressed by a pressure of from 70 to 200 MPa for moldings which are fired at 1600 to 1820 ° C after drying or the moldings are coated with a powder and cured at 50 to 200 ° C. 5 2. The method of manufacture according to item 1, the mixture being used with a preferential advantage of more than 2 mm s 3. A process for the preparation of the mixture according to claim 1, wherein the mixture is used in an amount of 200 971, characterized in that the chromium ore as a component forms an amount of 5 to 10% by weight. and in a particle size of less than 3 mm, with a particle size of less than 0.2 mm of not more than 40% by weight. characterized in that the chromium ore, as a component, preferably constitutes 7 to 12 wt. in grain sizes below 0.2 mm.