RU2485426C1 - Manufacturing method of ceramic plate blocks for creep annealing furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: manufacturing method of ceramic plate blocks for a creep annealing furnace involves preparation of ramming mixture, ramming and annealing of the plate. Ramming mixture is prepared from 30 wt % of bauxite with particle size of 3-1 mm, 30 wt % of bauxite with particle size of 1-0 mm and 40 wt % of mixture of joint grinding of dust from electrostatic precipitators of calcination furnaces of alumina production and clay in the ratio of 80: 20, water solution of orthophosphoric acid with density of 1.35 g/cm³, based on 0.05-0.06 l per 1 kg of the weight - more than 100 wt %. After ramming is completed, the block is baked by increasing the temperature of up to 120°C at the speed of 20°C per hour, exposed at 120°C during 24 hours; after exposure ends, temperature is increased at the speed of 50°C per hour to 400°C, exposed at 400°C during 12 hours; then, temperature is increased at the speed of 100°C per hour to 1200°C, exposed during 12 hours and cooled down together with the furnace.

EFFECT: invention allows increasing the strength of ceramic plate blocks of a creep annealing furnace.

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Description

The invention relates to the processing of metals by pressure and can be used in furnaces for dressing large sheets and plates of titanium alloys.

The ceramic plate used in creep-annealing furnaces is designed to accommodate heaters, while the quality of the editing of sheets and plates in the creep-annealing furnace substantially depends on the level of non-flatness of the ceramic plate. In the known method of creep annealing of titanium sheet metal and a furnace for its implementation on a ceramic plate of chamotte concrete blocks with grooves for heaters made along the entire length of the ceramic plate, a steel flat heated plate is installed on which a cage of one or more sheet products is installed ( RU 2357827, publ. 06/10/2009). When implementing creep annealing, the strength of chamotte concrete does not exceed 40 MPa. Moreover, in the temperature range from 600 ° C to 1000 ° C (the operating temperature of the creep annealing furnace is 800 ° C), concrete loses at least 30% of its strength. This is due to the fact that the cement in this temperature range is destroyed, and the sintering of the components of the mixture begins at a temperature of more than 1000 ° C. Since during operation separate sections evenly distributed over the stove surface experience loads of up to 35 MPa, they are destroyed after the furnace is heated to operating temperature, which leads to an increase in the level of non-flatness of the stove, disruption of the operation of some heaters, an increase in the unevenness of the thermal field and the need for frequent repairs.

The objective of the present invention is to increase the strength and increase the service life of the ceramic plate.

To solve this problem, a method of manufacturing blocks of a ceramic plate for a creep-annealing furnace involves preparing the packed mass, stuffing and burning the plate, the packed mass is prepared from 30 wt.% Bauxite fraction 3-1 mm, 30 wt.% Bauxite fraction 1-0 mm and 40 wt.% A mixture of co-grinding dust from electrostatic precipitation kilns of alumina production and clay in a ratio of 80:20, an aqueous solution of phosphoric acid with a density of 1.35 g / cm ³ , at the rate of 0.05-0.06 l per 1 kg of mass - more than 100 wt.%, while first bauxite fractions 3-1 and 1-0 mm are moistened with 2/3 parts of solution phosphoric acid, mix for 1 minute, then add a mixture of co-grinding from electrostatic precipitators of alumina production calcination furnaces and clay, mix for 1 minute, moisten the resulting mixture with the remainder of the phosphoric acid solution and mix for 2 minutes, after filling the block is fired, raising the temperature to 120 ° C at a speed of 20 ° C per hour, incubated at 120 ° C for 24 hours, after exposure, the temperature was raised at a speed of 50 ° C per hour to 400 ° C, kept at 400 ° C for 12 hours, Yes its temperature was raised at a rate of 100 ° C per hour to 1200 ° C, held for 12 hours and cooled together with the furnace.

Large grains of bauxite fractions of 3-1 mm and (to a lesser extent) fractions of 1-0 mm prevent the development of cracks, which increases the heat resistance and strength of high-alumina blocks. The combination of these two fractions of bauxite and a finely ground dust mixture from electrostatic precipitators of alumina and clay calcination furnaces provides (subject to the order of mixing of the charge components from larger fractions to smaller ones) a dense mass packing, which, in turn, determines the high strength of the blocks after firing. The introduction of dust from electrostatic precipitators of calcining furnaces of alumina production guarantees mullite formation during firing. Mullite has a “needle-like” structure, which helps to increase the strength of products. Mullite formation occurs with an increase in volume, which compensates for the shrinkage of other components of the mass during firing, as well as during the service of the products. This is due to the non-shrinking mass. The lack of shrinkage of the blocks allows to achieve a low level of non-flatness of the slab. During the interaction of phosphoric acid with a finely ground component of the charge, viscous phosphate glass forms, which significantly increases the strength of the blocks.

Mixing coarse-grained components of the charge (fractions 3-1 and 1-0 mm) separately from the finely ground component ensures the best packaging of these components. Wetting this mixture with orthophosphoric acid before introducing a finely ground component provides for enveloping large bauxite grains with acid, which, in turn, guarantees the largest contact surface between the finely ground component and the grains of large fractions, the best mixing of the finely ground component with orthophosphoric acid and uniform distribution of this mixture over the mass volume. Therefore, the formation of phosphate glass during firing and mullite formation also occurs uniformly throughout the volume of products, which ensures their uniformity, the absence of areas of reduced strength.

Raising the temperature to 120 ° C and holding it at this temperature for 24 hours ensures the removal of excess moisture from the products, the presence of which would lead to the destruction of products at higher temperatures. When heated to 250-300 ° C, the masses on phosphoric acid harden, but nevertheless continue to absorb moisture. After heating and aging at 400 ° C, the products become non-hydrostatic, that is, they do not absorb moisture. Subsequent heating to 1200 ° C causes sintering of the charge components, which further increases the strength of the products.

A new technical result is to increase the strength of the blocks of the ceramic plate of the creep-annealing furnace while maintaining a low level of their non-flatness.

Example. For the manufacture of printed high-alumina slabs from bauxite mass, the following starting materials were used:

- Chinese bauxite brand "MIDD" fraction 3-1 mm;

- Chinese bauxite grade "MIDD" fraction 1-0 mm (bauxite properties are shown in table 1);

- Nizhneuvelskaya clay according to TU 14-8-336-80 (properties are shown in table 2);

- dust from electrostatic precipitation kilns of alumina production, (properties are shown in table 3);

- thermal orthophosphoric acid according to GOST 10678-76 (properties are shown in table 4).

The packed mass was prepared as follows. Initially, a binder (phosphoric acid) was prepared at the rate of 5.5 liters per 100 kg of mass. The acid was diluted with water to a density of 1.35 g / cm ³ . Then, in a ball mill, a mixture of co-grinding dust from electrostatic precipitators of alumina production calcination furnaces and clay was prepared in a 80:20 ratio. The grain composition of the finely ground mixture should provide a full passage through a 0.063 mm sieve. The packed mass was prepared in a mixer in batches of 100 kg. A solution of phosphoric acid to moisten the mass should have a temperature of not more than 30 ° C. Initially, bauxite fractions of 3-1 and 1-0 mm were loaded into the mixer, moistened with 2/3 parts of the prepared aqueous solution of phosphoric acid, and stirred for 1 minute. Then, a mixture of co-grinding dust from electrostatic precipitators of alumina production calcination furnaces and clay was loaded into the mixer and mixed for 1 minute. The resulting mixture was moistened with the remainder of the phosphoric acid solution and finally mixed for 2 minutes. The finished mass was wiped through a No. 7 sieve.

The plates were stuffed by pneumatic ramming with a striker with a diameter of not more than 40 mm continuously in layers of 8-10 cm. Before filling the next layer, the upper part of the previously packed layer was well loosened to a depth of 10 mm. The density of the packed mass was checked with a pointed metal rod with a diameter of 3 mm and a pointed part with a length of 10 mm, which should not enter the mass by more than 10 mm when pressed by hand. The surface of the product should not have cracks or other defects, the grains should not crumble. Grain spalling indicates an insufficient amount of fine fractions or drying of the mass, which must be moistened with phosphoric acid with a density of 1.35 g / cm ³ .

The plates were fired in an oven at 1200 ° C in the following mode. The firing temperature was raised to 120 ° C at a speed of 20 ° C per hour, the stove was kept at 120 ° C for 24 hours, after exposure, the temperature was raised at a speed of 50 ° C per hour to 400 ° C, kept at 400 ° C for 12 hours, then the temperature was raised at a speed of 100 ° C per hour to 1200 ° C, the stove was kept for 12 hours and cooled together with the furnace. The plates made by the claimed method met the requirements specified in table 5. From the table it is seen that the plate from high-alumina blocks made by the claimed method has a strength of at least 80 MPa, significantly exceeding the loads experienced by the plate during operation. When heated to the operating temperature of the furnace, a decrease in the strength of the plate does not occur.

A method of manufacturing blocks of a ceramic plate for a creep annealing furnace

Table 1 Indicators Norm Mass fraction,% Al ₂ O ₃ , not less 86.0 SiO ₂ , not less 7.0 Fe ₂ O ₃ , no more 2.0 TiO ₂ , no more 4.0 CaO, no more 0.2 MgO, no more 0.1 R ₂ O, no more 0.3 P.p.p. no more 0.35 The density apparent in the grain g / cm ³ , not less 3.15 Mass fraction of moisture,% no more 1,0 Grain composition: Fr. (1-3) mm Fr.> 4.0 mm Not allowed Fr. (3.2-4.0) mm, within 0-10 Fr. (2.0 -3.2) mm 40-60 Fr. (1.0-2.0) mm 40-60 Fr. (0.5-1.0) mm 0-10 Fr. (0-1) mm FR.> 2.0 mm Not allowed Fr. (1.0-2.0) mm, within 0-15 Fr. (0.5 -1.0) mm 35-50 Fr. (0.3-0.5) mm 20-30 Fr. (0.2-0.3) mm 5-15 Fr. (0.1-0.2) mm 5-15 FR. <0.1 mm 0-15

A method of manufacturing blocks of a ceramic plate for a creep annealing furnace

table 2 Indicators Norm Mass fraction,% Al ₂ O ₃ , not less 28 Fe ₂ O ₃ , no more 4,5 Refractoriness, ° С, not less 1670 Humidity,% no more 12 P.p.p. no more fourteen Grain composition Mass fraction,% - Passage through mesh No. 3.2 one hundred - Passage through the grid number 2 98 - Passage through the grid No. 0.5 40

Table 3 Name of indicator Value Fractional composition,% ≤64 μm one hundred ≤8 μm 68 Chemical composition, %: Al ₂ O ₃ within 97-99.2 SiO ₂ , no more 0.15 Fe ₂ O ₃ , no more 0.1 R ₂ O, no more one α-Al ₂ O ₃ within 30-85

Table 4 The name of indicators Value Mass fraction of phosphoric acid N ₃ PO ₄ ,%, not less 73 Density g / cm ³ , not less 1,54

A method of manufacturing blocks of a ceramic plate for a creep annealing furnace

Table 5 The name of indicators Norm Mass fraction,%: - Al ₂ O ₃ , not less 60 - P ₂ O ₅ 2.5-3 Mechanical compressive strength after heat treatment at 1200 ° C, MPa, not less 80 Reversal of corners and ribs not allowed Size Tolerances 0.5 mm

Claims (1)

A method of manufacturing blocks of a ceramic plate for a creep-annealing furnace, including preparing the packing mass, stuffing and burning the stove, the packing mass being prepared from 30 wt.% Bauxite fraction 3-1 mm, 30 wt.% Bauxite fraction 1-0 mm and 40 wt. .% of a mixture of co-grinding dust from electrostatic precipitation kilns of alumina production and clay in a ratio of 80:20, an aqueous solution of phosphoric acid with a density of 1.35 g / cm ³ , from the calculation of 0.05-0.06 l per 1 kg of weight - over 100 wt.%, while first bauxite fractions 3-1 and 1-0 mm are moistened with 2/3 parts of an orthophosphoric acid solution you, mix for 1 min, then add a mixture of co-grinding dust from electrostatic precipitators of alumina-production calcination furnaces and clay, mix for 1 min, moisten the resulting mixture with the remainder of the phosphoric acid solution and mix for 2 min, after stuffing the block is fired, raising temperature up to 120 ° C at a speed of 20 ° C per hour, maintained at 120 ° C for 24 hours, after exposure, the temperature was raised at a speed of 50 ° C per hour to 400 ° C, kept at 400 ° C for 12 h, then raise the temperature at a temperature of 100 ° C per hour to 1200 ° C, incubated for 12 hours and cooled together with the furnace.