RU2851397C1 - Refractory magnesia-alumina shotcrete concrete for lining metallurgical units and method for its application - Google Patents

Abstract

FIELD: ferrous metallurgy.

SUBSTANCE: invention relates to the refractory industry, can be used for the production of refractory material intended for creating lining of metallurgical units and repairing linings of such units, including steel ladles, converters, vacuum units, electric arc furnaces. Refractory magnesia-alumina shotcrete for lining metallurgical units contains a mixture of a magnesia component with a particle size of up to 5 mm in an amount of 30-70 mas.% and a high-alumina component in an amount of 30-70 mas.%. magnesia component represents a periclase composition shotcrete mass containing, mas.%: fractionated granular and fine-dispersed periclase 75-95, functional additives and plasticisers 0.1-3.0, inorganic binder 1-10. high-alumina component contains, mas.%: high-alumina cement 1-20, clay 1-10, high-alumina composition aggregate based on aluminium oxide with a content of up to 98% and a particle size of up to 12 mm – the remainder. Method for applying magnesia-alumina shotcrete of the specified composition includes obtaining a mixture of a magnesia component with a particle size of up to 5 mm in an amount of 30-70 mas.% and a high-alumina component in an amount of 30-70 mas.%, feeding into the spray nozzle of a shotcreting unit with simultaneous addition of water into said nozzle.

EFFECT: creation of shotcrete having high adhesion and combining the advantages of periclase and high-alumina shotcrete masses.

5 cl, 1 dwg, 3 tbl, 1 ex

Description

The invention relates to ferrous metallurgy, including the refractory industry, and can be used for the production of refractory material intended for creating linings for metallurgical units and repairing linings of such units, including steel-pouring ladles, converters, vacuum degassers, and electric arc steel-smelting furnaces.

In this area, the technical problem is associated with the need to create refractory materials that are resistant to elevated temperatures, have high adhesion to the main lining and, when applied locally, allow for the restoration of areas damaged during operation, and, when applied on a large scale, create a protective coating that allows for an extension of the service life of the main lining.

The characteristic features of the chemical composition of known materials possessing the above properties are that they belong predominantly to the class of either magnesia materials (for example, magnesia shotcrete masses) or to the class of high-alumina materials (refractory concretes).

A refractory gunning mass is known for lining metallurgical units, which consists of 11-18% periclase of fraction 3-1 mm, 60-65% periclase of fraction 1-0 mm, 12-21% periclase of fraction less than 0.09 mm, 1.4-2.0% magnesium sulfate, 0.7-2.5% bentonite of fraction up to 0.5 mm, 0.9-3.5% burnable additive of fraction 3-0 mm and 1.8-3.0% sodium metasilicate (RU 2155733 from 06.10.98, IPC С04В 35/66).

Disadvantages of the well-known refractory gunite mixture include the use of a large amount of fine periclase (60-65% of the 1-0 mm fraction and 12-21% of the <0.09 mm fraction) with a relatively small amount of the coarser 3-1 mm fraction (maximum 18%). This leads to increased water consumption during gunning and, consequently, increased shrinkage and crack formation, resulting in lining cracking and damage to its integrity during application, drying, or operation of metallurgical units. The strength characteristics of this mixture at elevated temperatures do not meet the service conditions of metallurgical units.

The absence of requirements for the density of the periclase used does not guarantee the absence of shrinkage of the shotcrete layer during service, and the adhesion of the layer during service will be impaired (the shotcrete layer will peel off from the main lining).

Also known is a refractory gunning mass, including a granular periclase filler, dispersed periclase and a binder, containing periclase with a particle size of no more than 4 mm and a density of at least 3.25 g/ ^cm3 as a granular periclase filler, and a mixture of inorganic and ceramic components as a binder, wherein the ratio of inorganic components to ceramic components is 1.5-2.9, with the following ratio of components, wt. %: said granular periclase 48-75, dispersed periclase 18-33, said binder 7-19 (RU 2596233 C1 dated 16.06.2015, IPC C04B 35/66).

The disadvantages of the well-known refractory gunite mass include the insufficient size of the periclase filler, which in some cases does not allow for the required density to be achieved during application, which subsequently negatively affects the performance characteristics of the material.

A known gunite mass includes periclase powder with a grain size of up to 2 mm, high-alumina cement and grade 180 wood flour (author's certificate SU 1616881 dated 12.01.1989, IPC С04В 35/68, 35/04).

The specified technical solution was selected as the closest analogue (prototype).

According to GOST 28874-2004, refractory concrete mass consists of filler, refractory cement, liquid and, where necessary, additives, ready for use.

Thus, the shotcrete mass according to patent document SU 161881 is shotcrete concrete, since it contains the above-mentioned components.

The use of this gunning mixture exhibits some disadvantages. Specifically, the insufficient size of the periclase filler (up to 2 mm) and the lack of coarse-grained high-alumina filler prevent the formation of a durable refractory coating on the lining surface due to the sintering of coarse-grained components and the formation of a coating framework. The inclusion of wood flour in the gunning mixture to impart thermal insulation properties to the coating after heat treatment results in increased open porosity in the material due to the combustion of wood flour components at high temperatures. This reduces the density and mechanical strength of the coating, which negatively impacts the performance of the refractory and leads to a reduction in its durability. In general, the ratio of the magnesia component (periclase powder) and the high-alumina component (high-alumina cement), the presence of wood flour in the composition of the material, does not lead to the desired result - the unification of the scope of application of shotcrete for the repair of the lining of a number of heating units.

The technical problem solved by the proposed invention consists in expanding the arsenal of means for a similar purpose by creating a shotcrete concrete that has high adhesion and combines the advantages of single-component periclase shotcrete masses applied using shotcrete machines that do not require a special nozzle design for feeding a liquid binder, and the advantages of high-alumina refractory concretes that have a high application density and strength at high temperatures, ensuring resistance to high temperatures, as well as resistance to the effects of molten metal and slag with an increase in the period between repairs and while maintaining the application method, characterized by ease of use.

The essence of the proposed invention.

Refractory magnesia-alumina shotcrete for lining metallurgical units contains a mixture of a magnesia component with a size of 0.1-5 mm in an amount of 30-70 wt.% and a high-alumina component in an amount of 30-70 wt.%. The magnesia component is a shotcrete mass of periclase composition with the following composition of components, wt. %: fractionated granular and finely dispersed periclase 85-95, functional additives and plasticizers 0.1-5.0,

inorganic binder 0.1-10. The high-alumina component has the following ratio of components, wt.%: high-alumina cement 1-20, clay 1-10, high-alumina filler based on aluminum oxide with a content of up to 98% and a size of up to 12 mm - the rest.

Corundum and/or tabular alumina and/or mullite and/or high-alumina chamotte and/or calcined bauxite are used as a filler for a high-alumina composition based on aluminum oxide.

The high performance properties of shotcrete, namely resistance to high temperatures and the effects of molten metal and slag, are achieved through the combination of magnesia and high-alumina components and the formation of aluminum-magnesium spinel at high temperatures due to the sintering of the magnesia and high-alumina components in the shotcrete.

As a magnesia component of 30-70 wt.%, it is possible to use a ready-made periclase gunning mass with an MgO content of 80-95 wt.% (per calcined substance), consisting of sintered periclase with a size of 0.1-5.0 mm and an inorganic binder, and/or separately powders of fused and/or sintered periclase of the specified MgO content and size, inorganic binders 0.1-10 wt.%, functional additives 0.1-5 wt.%.

Fractionated periclase refers to material with a particle size of 0.1–5.0 mm, pre-divided into two or more fractions with any interval within the particle size range up to 5 mm, for example, fractions of 0–1 mm, 1–3 mm, and 3–5 mm. Fine periclase refers to ground periclase powder with a particle size of less than 0.09 mm or less than 0.063 mm.

As a high-alumina component of 30-70 wt.% it is possible to use ready-made refractory concrete mixtures with an Al ₂ O ₃ content of 50-98 wt.% (per calcined substance) based on fused and / or sintered high-alumina refractory filler, fractionated and finely dispersed with a size of up to 12 mm, high-alumina cement, and / or separately fractionated and / or finely dispersed corundum, mullite, high-alumina chamotte, tabular alumina with the specified Al ₂ O ₃ content, including high-alumina cements of 0.1-10 wt.%, functional additives of 0.1-5 wt.%. Understanding the property of fractionation and fineness of high-alumina filler is similar to the approach to this property for periclase, but with an increase in the fraction to 12 mm.

The use of high-alumina cement in the composition of shotcrete, which contains calcium aluminates, determines the strength properties of the shotcrete coating both immediately after its application due to the reaction of hydraulic hardening of the material, which occurs in the thickness of the applied shotcrete concrete on the surface of the repaired lining, and at high temperatures due to the high refractoriness of the cement, up to the service temperature of the repaired lining at 1580-1750°C.

An increase in the density of the shotcrete coating from the proposed shotcrete concrete is achieved due to the bimodal distribution of the particles of the components used by size, with the first maximum in the range of up to 5 mm, due to the distribution of particles within the magnesite component with a size of up to 5 mm, and the second maximum in the range of up to 12 mm, due to the distribution of particles within the high-alumina component.

An example of a bimodal distribution of particles of granular filler of shotcrete can be schematically taken as the graph shown in the figure, where the maximum at point A corresponds to the magnesite component, B to the high-alumina component (see figure illustrating the bimodal distribution of particles of shotcrete).

The use of sodium salts of orthophosphoric acid and magnesium sulfate as an inorganic binder, which determine the adhesive properties of the material during shotcreting, contribute to the gain in strength in the temperature range up to 1000

With heating of the lining, as well as the gain in strength due to sintering during operation at temperatures in the range from 1580 to 1750°C.

The use of sodium salts of polymethylene naphthalene sulfonic acids and technical lignosulfonates as a functional additive helps reduce the water consumption of the material during the shotcrete process, and helps form the rheological properties of the shotcrete after mixing it with water in the shotcrete machine. This, in combination, ensures uniform application of the shotcrete to the lining surface, reduces rebound due to reduced water consumption, reduces porosity, and increases the density and strength of the coating.

The use of a high-alumina component, which is based on materials with a higher true density compared to sintered and/or fused periclase, also influences the increase in density.

In order to achieve the specified technical result, a method for applying magnesia-alumina shotcrete is proposed, according to which a pre-prepared mixture of a magnesia component and a high-alumina component, having the content and composition disclosed above, is fed into a spray nozzle of a shotcrete installation with the simultaneous addition of water to said nozzle.

Furthermore, an advantage of the proposed method for applying shotcrete is the ability to pre-mix the periclase and high-alumina components at the manufacturer or metallurgical plant, creating a ready-to-use mixture. According to this method, the prepared mixture of these components is fed via compressed air from the receiving hopper of the shotcrete machine into the nozzle of the shotcrete machine. Water is added to the nozzle to moisten the refractory mass to 10-20% by weight. The shotcrete is then ejected from the nozzle onto the surface of the cooled or heated lining, where the material hardens and forms a durable refractory coating.

An example of the invention implementation is given below.

Shotcrete was used to repair the lining of numerous steel-pouring ladles at Converter Shop No. 2 of Novolipetsk Steel (hereinafter referred to as KS-2 NLMK) using the shotcrete method.

To carry out repairs using shotcrete, steel-pouring ladles were used that had been taken out of service for scheduled intermediate repairs (first and subsequent) of the working layer of the lining, when the residual thickness of the working layer of the lining of the bottom and/or walls in the “slag belt” zone reached 75 to 80 mm.

The selection of a ladle for repair using shotcrete was carried out after cooling of its lining, based on the results of a visual inspection and scanning of the working layer of the lining, made after the ladle was taken out of operation, while the selection of ladles with the following defects of the working layer was not allowed:

- the presence of any transverse and longitudinal cracks;

- the presence of open horizontal and vertical masonry joints with a thickness of more than 2 mm.

The preparation and application of shotcrete was carried out directly in the NLMK KC-2 workshop using a shotcrete unit as follows:

- dry initial components (periclase component and high-alumina component) were poured into a container in the form of a metal box using a measuring container (a 10-liter bucket) from big-bag containers in a ratio of 55% to 45% (including a different ratio reflected in Table 3 below) and mixed for 3-10 minutes;

The prepared dry concrete shotcrete mix was poured into the receiving hopper of a Meyko Piccola shotcrete machine, which simultaneously loaded and delivered the prepared concrete mix through a feed hose to a spray nozzle, where it was mixed with water from the workshop's water supply. The moisture content of the shotcrete mixture when mixed with water was 18%.

- spraying of shotcrete was carried out with compressed air (pressure
0.6 MPa) with its moistening at the nozzle outlet with water (with a flow rate of 2 to
8 l/min);

- application of shotcrete was carried out continuously “from bottom to top” along the height of the lining of the ladle walls;

- by regulating the water flow, we achieved a minimum amount of “rebound” and the absence of cases of sliding or peeling of the shotcrete coating;

- the thickness of the applied layer of shotcrete ranged from 20 to 50 mm and varied depending on the thickness of the residual layer of brick lining of the walls and the zone of its application (“battle” area, “subslag” zone, etc.).

After applying the repair coating, the ladle was kept in natural conditions for at least 4 hours.

Drying and heating of the lining was carried out according to the current schedules for drying and heating of linings with a monolithic bottom.

The bucket was put into operation after the first intermediate repair and the bucket operation process was carried out according to the current technology.

When, during operation of the ladles after intermediate repairs, the residual thickness of the working layer of the lining of the bottom and/or walls in the “slag belt” zone reached 75 to 80 mm and the wall lining in the “metal zone” was in a satisfactory condition, the second and subsequent intermediate repairs of the working layer of the lining were carried out using shotcrete.

In the above example, a material with a chemical composition of up to 5 mm, indicated in Table 1, was used as the periclase component.

Table 1

Name of material Chemical composition in wt.% Fe ₂ O ₃ SiO ₂ CaO MgO Magnesia
component 1.30 7.00 1.96 88.2

The high-alumina component was a material with a chemical composition of 12 mm in size, as indicated in Table 2.

Table 2

Name of material Chemical composition in wt.% SiO ₂ Al ₂ O ₃ CaO MgO High alumina component 1.68 93.7 3.04 0.90

Below in Table 3 is presented the chemical composition of the obtained shotcrete for various ratios of magnesia (MC) and high-alumina component (HAC), with a description of the result of application in the repair of the lining of KC-2 steel-pouring ladles.

Table 3

Sample number Ratio of VGK/MK Analysis results in wt.% (for calcined substance) Description of the result of application Fe ₂ O ₃ SiO ₂ Al ₂ O ₃ CaO MgO Na ₂ O P ₂ O ₅ K ₂ O C p.p.p.* No. 1 45:55 0.66 3.29 38.8 2.62 47.9 0.083 0.54 1.46 0.107 0.64 Excellent: even application, strong and dense coverage, increased durability of 28-35 layers No. 2 45:55 00.64 33.39 338.9 22.66 447.4 00,058 00.54 11.46 00,101 00.55 No. 3 45:55 00.65 33.49 335.0 22.60 449.7 00,072 00.59 11.41 00,091 00.33 No. 4 30:70 00.53 22.47 226.1 11.8 662.4 00,084 00.59 11.96 00,112 00.69 Good: even application, strong and dense coverage, increased durability of 28-30 layers No. 5 70:30 0.84 55.13 660.8 33.98 224.9 00,042 00.32 00.69 00,065 00.31 Good: even application, strong and dense coverage, increased durability of 25-30 layers

* relative change in mass loss on ignition according to GOST 2642.2.

Samples No. 1-3 characterize the serial use of shotcrete, where the ratio of magnesia to high-alumina components is on average 45:55. For this composition (samples No. 1-3), the presence of aluminum oxide in the shotcrete composition of approximately 35-40 wt.% is due to the use of a high-alumina component, including fractionated granular and finely dispersed high-alumina filler based on aluminum oxide, clay, and high-alumina cement.

The use of fused corundum and/or tabular alumina and/or mullite and/or high-alumina chamotte and/or calcined bauxite in the high-alumina filler component, either individually or in combination, ensures the high refractory properties of shotcrete due to the high refractoriness of each of these materials. These materials, combined with periclase, form the coating "skeleton," which is maintained at lining operating temperatures ranging from 1580 to 1750°C.

The presence of magnesium oxide (approximately 50% by weight) is due to the use of periclase in the magnesite component. The presence of silicon dioxide and iron oxide reflects the use of clay and indirectly determines the presence of impurities in the high-alumina and magnesite components. Calcium oxide is due to the use of high-alumina cement, alkali oxides and carbon are a consequence of the use of functional additives and plasticizers, and phosphorus oxide is an inorganic phosphate binder.

Shotcrete prepared with an average high-alumina to magnesia ratio of 45:55, as well as with a VGK/MK ratio of 70:30 and VGK/MK ratio of 30:70, yields satisfactory results, ensuring uniform application of the shotcrete and sufficient strength and density of the finished coating, both after application and during drying, as well as at high temperatures during operation. A durable and dense shotcrete coating extends the period between repairs for steel ladle linings, increasing their durability by an average of 30 heats.

Exceeding the specified ratio of high-alumina/magnesium component in the direction of increasing the proportion of the high-alumina component to more than 70 wt.% and decreasing the proportion of the magnesite component to less than 30 wt.% worsens the application of shotcrete to the lining; the application becomes uneven, and cases of the shotcrete coating slipping from the surface of the lining are observed.

Reducing the high-alumina component to less than 30% by weight and increasing the magnesite component to more than 70% by weight ensures uniform application, but the strength and density of the gunned coating decrease, which does not provide the required increase in durability—at least 30 heats. A repaired layer with a given high-alumina/magnesium ratio provides an increase in lining durability for 15-25 heats, which is not cost-effective due to the high cost of materials used for the repair.

The durability of the lining of steel ladles, thanks to the implementation of technology using shotcrete at NLMK KC-2, increased by 30 heats and amounted to an average of 115-125 heats.

Comparing the proposed shotcrete made from magnesite and high-alumina components with the prototype described in patent document SU 1616881, the advantages of the proposed concrete include minimal rebound during application, which is virtually nonexistent and amounts to no more than 5% (compared to 16.5-18% for the prototype). Flaking and crumbling during drying, which are common with the prototype, are not observed with the proposed shotcrete. Another advantage of the proposed concrete is its low impregnation with molten metal and slag, due to the absence of open pores in the shotcrete coating, which form in the prototype due to the combustion of wood flour when the lining is heated to 1300-1400 ^° C and during operation.

Based on the above, the proposed refractory shotcrete expands the range of similar products by achieving its intended purpose of ensuring the resistance of metallurgical unit linings to high temperatures and exposure to molten metal and slag. This is confirmed by a significant increase in the number of heats by 25-30%, leading to an extended period between repairs. Furthermore, the lining application method using the proposed shotcrete is also designed to achieve this result while maintaining ease of use.

Claims (14)

1. Refractory magnesia-alumina shotcrete for lining metallurgical units, containing a mixture a magnesite component with a particle size of 0.1-5 mm in an amount of 30-70 wt.% and a high-alumina component in an amount of 30-70 wt.%, wherein the magnesite component is a gunite mass of periclase composition with the following composition of components, wt.%: fractionated granular and finely dispersed periclase 85-95, functional additives and plasticizers 0.1-5.0, inorganic binder 0.1-10, The high-alumina component has the following ratio of components, wt.%: high alumina cement 1-20, clay 1-10, high-alumina filler based on aluminum oxide with a content of up to 98% and a size of up to 12 mm - the rest. 2. Shotcrete according to paragraph 1, characterized in that sodium salts of orthophosphoric acid and/or magnesium sulfate are used as the inorganic binder. 3. Shotcrete according to paragraph 1 or 2, characterized in that sodium salts of polymethylene naphthalene sulfonic acids and technical lignosulfonates are used as functional additives and plasticizers. 4. Shotcrete according to any one of paragraphs 1-3, characterized in that corundum and/or tabular alumina and/or mullite and/or high-alumina chamotte and/or calcined bauxite are used as a filler of high-alumina composition based on aluminum oxide. 5. A method for applying magnesia-alumina shotcrete for lining metallurgical units, which includes obtaining magnesia-alumina shotcrete according to claim 1, consisting of a mixture of a magnesia component with a size of 0.1-5 mm in an amount of 30-70 wt.% and a high-alumina component in an amount of 30-70 wt.%, and feeding it into a spray nozzle of a shotcrete unit with the simultaneous addition of water to said nozzle for application as a refractory lining of metallurgical units.