RU66994U1 - DEVICE FOR INTERFERENCE OF REFRACTORY BRICKES IN THE COVER OF THE MARTIN FURNACE - Google Patents

Abstract

The invention relates to a refractory lining system for an open-hearth vault of an open-hearth furnace. The purpose of the utility model is to increase the masonry resistance of the main arch of the open-hearth furnace by improving the conjugation of refractory bricks. The problem is solved by replacing metal plates with sealing plates made of plastic refractory material. The claimed device for connecting refractory bricks in a roof of an open-hearth furnace containing sealing plates in rows and between rows of bricks, characterized in that the sealing plates are made of plastic refractory material, the plates for pairing the rows have the form of a trapezoid, repeating the configuration of the arch, overlap and cover each other some bricks. Sealing plates for installation between rows of bricks are made with the upper sides bent by 20-40 mm at right angles. On the upper part of the sealing plate installed between the rows, a layer of non-drying adhesive coated with a protective removable film removed before installation is applied to fix the plate during assembly. The technical result of the claimed utility model is a significant increase in the service life of the expansion and suspension arch of the open-hearth furnace.

Description

The invention relates to a refractory lining system for an open-hearth vault of an open-hearth furnace. Improving the masonry resistance of the main arch is one of the main tasks in the operation of the open-hearth furnace, because the arch works in the most difficult conditions and its durability determines the overhaul duration of the campaign. In the process, the main arch is exposed to high temperature, splash of slag and metal, dust, gas-alternating medium, etc., which led to the use of basic refractories for the open-hearth furnace arch, and the large mass of the arch required the creation of its special design.

A number of stringent requirements are imposed on refractory structural materials for lining the roof of an open-hearth furnace:

- high (≥1800 ° С) fire resistance;

- high strength under load at high temperatures (the temperature of the onset of deformation under a load of 0.2 MPa should be at least 1500 ° C);

- constancy of volume at service temperatures;

- low (not more than 25%) porosity;

- high heat resistance (at least 15 heat shifts during water cooling),

- compressive strength of at least 25 MPa;

- high chemical resistance to gases of a flame space, melting dust and splashes of molten slag and metal;

- resistance to uneven heating along the length and width of the arch (small KLTR);

- resistance to high gas pressure at the roof;

- dimensional accuracy and the correct shape, which allows for masonry with thin seams;

- resistance to mechanical wear.

The resistance of the refractory masonry in an open-hearth furnace is significantly affected by the intensity of purging the bath with oxygen. With the intensification of the process, incomplete combustion of CO released from the bathtub and creating a reducing atmosphere is possible, which naturally destroys the refractory as a result of the reduction of its oxides, while the oxidizing atmosphere increases the resistance of the refractories. In addition, an increase in the oxygen purge intensity leads to an increase in unevenness of the arch wear.

However, at present, there are no refractories that combine equally all the necessary operational properties.

Magnesite-chromite refractories are used for the refractory lining of the expansion-suspension arch of the open-hearth furnace.

Magnesite-chromite refractories have the following operational properties: compressive strength - not less than 85 MPa, porosity - not more than 20%, the temperature of the onset of deformation under load ≥1500 ° С, heat resistance - more than 5 heat exchangers (1300 ° С - water). The temperature coefficient of linear expansion of these refractories is (8.5-10) · 10 ^-6 1 / deg, refractoriness 1900-2340 ° C [1, 2].

In Russia, the expansion and suspension arch of A.S. Frenkel’s design is mainly used. The features of this design is the reinforcement with steel pins of all the bricks of each row of the vault. In the middle of the row, the arch is expanded by driving a castle, which has the shape of a sharp wedge of brick, as a result of which microcracks or chips form on neighboring bricks from a strong shock load. With the help of a extension (steel strip, bar, plate), the arch is attached to the suspension structure [3].

During operation, as a result of heating, it expands. Since the lining is heated unevenly, i.e. there is a high vertical temperature gradient, namely, the lower part of the arch is heated to temperatures of ≥1800 ° С, and the upper - to 300-800 ° С, then the bricks experience high shear deformation, as a result, some joints are wedged, and on the lower part of the arch chips or microcracks are formed. In addition, chipping of pieces of bricks occurs, because as a result of deformation, their friction against each other between the rows begins, which leads to the formation of through cracks in the seams between the rows. These factors contribute to the acceleration of lining wear during operation.

The appearance of through slots causes an increase in heat loss due to the release of hot gases, which entails a decrease in the productivity of furnaces and an increase in the consumption of energy. In addition, this process leads to an increase in harmful emissions into the environment and environmental degradation in the workplace.

Chemically active hot gases and brown smoke (melting dust containing up to 95% Fe ₂ O ₃ ) accumulate in the cavities of non-through cracks, which react with the brick material accelerating its destruction.

In connection with the above, a number of measures are being taken at metallurgical enterprises aimed at increasing the durability of the design of the expansion-suspension arch, namely, various methods of filling the seams are used. The most common way is laying steel plates with a thickness of 0.6-2 mm between the bricks in a row during assembly. Plates are put on during assembly of the arch on connecting rods and adjoin the surfaces of bricks. When laying subsequent rows to reinforce them with each other on the lateral surface of each brick of the previously laid row, lay gaskets with the upper sides bent by 10-15 mm at right angles [4]. At high temperatures, steel plates oxidize and form magnesium ferrite with MgO bricks.

MgFe ₂ O ₄ with a melting point of 1750 ° C and magnesiouustite (Mg, Fe) O (T _pl. ~ 1700 ° C), which firmly weld the bricks together. According to [5], magnesium ferrite is already formed at 500 ° C, the amount of which rapidly grows to 1300 ° C, further heating leads to its rapid dissolution in periclase with the formation of magnesiuustite, which ends only at 1300 ° C. However, upon cooling, a phase transition occurs - the decomposition of a solid solution based on MgO in the MgO-MgFe ₂ O _{4 system} , with magnesium ferrite being released in its free state almost completely. As a result, microcracks occur during cooling, which impairs the thermal stability of the masonry. In addition, a small amount of the solid solution phase can form with the structure of the spinel Mg (Cr _1-x Fe _x ) ₂ O ₄ , which is formed with an increase in volume, which is one of the reasons for the destruction of the refractory. Thus, there is a heterogeneity of the material in volume, due to the disequilibrium of the process, namely, in the reaction products can be: Fe, Fe ₂ O ₃ , MgFe ₂ O ₄ , Mg (Cr _1-x Fe _x ) ₂ O ₄ .

The use of steel plates as spacers between bricks can significantly reduce the formation of cracks between bricks in the rows of the arch and between the rows, which prevents the penetration of aggressive gases into the cracks. However, this method has several disadvantages, which significantly reduce the service life of the arch.

The disadvantages of the method of sealing joints with steel plates are:

1. the destruction and chipping of the plate material as a result of the above reactions at high temperatures, which sharply limits the service life of this design (no more than 400 heats),

2. steel plates do not have sufficient ductility and do not accept the surface relief of the mating brick, which leads to the preservation of residual gaps,

3. as a result of evaporation of Fe, Fe ₂ O ₃ at high temperatures from a metal melt and their penetration into the lining in the material

steel plates becomes porous, brittle, therefore less gas tight,

4. the heterogeneity of the material in the zones leads to a deterioration in heat resistance,

5. significant weighting of the entire structure, which leads to an increase in deformation stresses,

6. increase in thermal conductivity of the entire structure, which leads to additional heat loss,

7. The high cost of metal plates.

Another method used at some metallurgical enterprises is the method of filling the cracks between the bricks after heating and during operation with the powder of Fe ₃ O ₄ scale, which also directly reacts with MgO to form a gas-tight sintered layer [1]. This method is effective to reduce heat loss, increase furnace productivity and reduce environmental pollution. However, it has a number of drawbacks, namely, the cracks are not filled to the full depth, as well as the fact that the backfill process is carried out on a red-hot arch manually, which represents an increased danger to the life of the worker.

The most effective combined method with the simultaneous use of steel plates and iron oxide powder. However, this combined method does not eliminate the above disadvantages.

The aim of the invention is to improve the quality of conjugation of refractory bricks in the arch of the open-hearth furnace by replacing metal plates with sealing plates of plastic refractory material described in the patent [6].

The prototype was taken products, which are steel plates, and the design of the device for pairing the plates in the expansion-suspension arch of the open-hearth furnace, described in [4].

Plastic refractory material includes components in the following ratio, wt.%:

refractory filler with

inorganic binder 50.0-95.0 elastomer 3,5-21,1 carbon material 0.5-15.0 plasticizer 0.5-10.0 release agent 0.5-4.0

Refractory filler is represented by corundum, periclase, silica or mixtures thereof in the following proportions, wt%:

corundum 70.0-75.0 periclase 25.0-30.0 or corundum 70.0-75.0 silica 25.0-30.0

Inorganic binder having a composition, wt%:

Na ₂ O - 1.0-5.0; SiO ₂ - 60.0-80.0; Al ₂ O ₃ - 4.0-18.0; CaO - 0-25.0; TiO ₂ - 0.3-1.6; Fe ₂ O ₃ - 3.0-15.0; MgO - 0-3.0; or Na ₂ O - 26.0-28.0; In ₂ O ₃ - 24.0-26.0; SiO ₂ - 46.0-48.0 is introduced into the refractory filler in the ratio, wt%: refractory filler - 85.0-95.0, inorganic binder - 15.0-5.0.

To solve the task of improving the conjugation of bricks in the open-hearth suspension arch of the open-hearth furnace, periclase, corundum and Al-Mg spinel, which provide the highest refractoriness (≥1800 ° С), were selected as fillers from all those proposed in [6].

The plastic refractory material used for the manufacture of plates, unlike steel plates, has several advantages:

- the material has low thermal conductivity compared with steel, which provides better thermal insulation of the structure;

- technological during installation, as due to plasticity, it has the ability to fully mate with the surface relief of the mating bricks. Thus, plates of this material do not require great accuracy in their manufacture to ensure a tight joint with a brick and fill in all the bumps, chips, gaps;

- when installing a castle brick, due to the plasticity of the plates installed between the bricks, increased loads are not created and chips and microcracks are not formed;

- has increased chemical resistance with respect to molten slag, metal, and gases due to chemically resistant fillers MgO, Al ₂ About ₃ , as well as the formation of Al-Mg spinel during operation;

- retains plasticity due to the elastomer, which is part of the material, in the temperature range from -40 ° C to 300 ° C, compensating for the load from the thermal expansion of the brick, so chips and microcracks are not formed;

- in the temperature range from 300 ° C to 600 ° C, the material retains residual ductility due to the carbon frame remaining after the removal of volatiles from the organic binder, which compensates for the loads from thermal expansion of the lining;

- in the temperature range above 600 ° C, the carbon partially burns out, and the material acquires plasticity due to the fusible inorganic binder;

- in the temperature range above 1000 ° C, the material (due to the inorganic binder) is sintered into a solid monolithic gas-tight mass, which retains residual ductility to working (~ 1650 ° C) temperatures. The resulting dense cake is homogeneous (in phase

the composition is single-phase), has a melting point above 1850 ° C, does not have components (Fe, FeO, Fe ₂ O ₃ ) volatile at high temperatures, the gas density of the arch increases and significant energy savings are ensured;

- upon cooling, the material of the plates does not crumble, but remains in the form of a monolith, which allows the plates to be reused;

- due to the fact that the seams of the lining of the arch are reliably closed during the entire period of operation of the arch, the burning of parts of the device for suspension of the arch is excluded.

Thus, the use of plastic refractory material instead of steel plates will significantly increase the service life of the expansion-suspended arch of the open-hearth furnace.

The dimensions, configuration of the plates, their articulation with bricks in a row corresponds to the prototype [4] - figure 1 The method of joining rows of bricks differs from the prototype (figure 2). According to [4], metal plates with upper sides bent by 20-40 mm at right angles are hung on the side surface of each brick. The use of plates of plastic refractory material for this purpose allows you to install such plates simultaneously on several bricks. Given the technology of manufacturing plates of plastic refractory material, the optimal plates are for overlapping 5-6 bricks (figure 3). The plates are installed in a row with an overlap of 10 mm, which provides the necessary gas tightness and monolithic gaskets. Plates of this size made of metal cannot provide the necessary gas tightness and other operational properties of the gaskets due to the lack of the necessary ductility of the metal.

The described design of the plates can be used for a spacer arch of any configuration, taking into account the specific dimensions of the bricks.

Masonry using plastic refractory material avoids a number of undesirable processes during operation. The amount of Fe ₂ O ₃ participating in the reaction is not large, and is determined only by the capillary suction of Fe ₂ O ₃ from brown gas and metal sprays. Therefore, the amount of the formed MgFe ₂ O ₄ phase is small and the undesirable reactions associated with it described above have little effect. In this case, a small amount of MgFe ₂ O ₄ plays the role of one of the components of the inorganic binder introduced to form a dense monolithic cake with filler MgO, Al ₂ O ₃ or mixtures thereof in the ratio of spinel. If the filler is Al-Mg spinel, then part of MgFe ₂ O ₄ is included in the solid solution Mg (Al _1-x Fe _x ) ₂ O ₄ . The phases formed are chemically stable and do not have polymorphic transitions (since in the range of low concentrations of MgFe ₂ O ₄ solid solutions do not undergo decomposition upon cooling), which significantly improves the thermal stability of the structure.

In addition, a small amount of Fe ₂ O ₃ does not lead to the formation of a large amount of Mg (Cr _1-x Fe _x ) ₂ O ₄ , prone to swelling and contributing to the destruction of the refractory.

List of sources of information

1. Technology of ceramics and refractories. Ed. P.P. Budnikova. Ed. lit. on construction. M. 1962. 707 p.

2. Plotnikov L.A. Refractories in the steel industry. M. Metallurgy. 1973. 273 p.

3. Zaitsev Yu.S., Filipiev OV, Zaitseva NN, Shevchenko V.I. and others. Cooled expansion and suspension arch of the open-hearth furnace. Application No. 95113545/02, publ. September 9, 1998.

4. P.V. Borisov, E.F. Goykolov, G.P. Gromakov. Laying open-hearth furnaces. M. Publishing House of Letters, on construction, architecture and building materials. 1962.p.160.

5. State diagrams of silicate systems. N.A. Toropov, V.P. Barzakovsky and other Handbook. T.1. Ed. “Science” 1969. p.822

6. I.F. Mikhailov Plastic refractory material. Patent for invention No. 2273618 according to the application No. 2004132518/20 (035212) dated 01.11.2004.

Claims (3)

1. A device for interfacing refractory bricks in a roof of an open-hearth furnace, comprising sealing plates in rows and between rows of bricks, characterized in that the sealing plates are made of plastic refractory material, the plates for interconnecting the rows have the form of a trapezoid, repeating the configuration of the arch, overlapped with each other and cover several bricks. 2. The device according to claim 1, characterized in that the sealing plates for installation between rows of bricks are made with the upper sides bent by 20-40 mm at right angles. 3. The device according to claim 1, characterized in that on the upper part of the sealing plate installed between the rows, a layer of non-drying adhesive coated with a protective removable film removed before installation is applied to fix the plate during assembly.