RU2172726C1 - Method of manufacturing refractory products from chromium oxide - Google Patents

Abstract

FIELD: refractories industry, more particularly manufacture of chromium oxide refractories for lining of glassmaking furnaces. SUBSTANCE: as blend is being prepared, magnesium oxide and silica- containing component present in alkali-free grade E glass are added to finely dispersed fraction of chromium oxide refractory; the whole is mixed, and molding mixture is made by addion of phosphate binder and finely dispersed fraction to granular fraction of chromium oxide refractory; mixture is granulated by rubbing through sieves, poured into mold, subjected to vibrooscillations, and pressure is applied at value which does not exceed ultimate strength of grain of chromium-containing refractory, and products are dried and fired. EFFECT: improved property and lower dispersions of operating characteristics. 2 tbl, 2 ex

Description

 The invention relates to the refractory industry and can be used for the manufacture of chromoxide refractories used for lining glass melting furnaces.

 Chromium oxide is a refractory material with high chemical resistance to alkali free glass melts.

The widespread use of chromium oxide refractories is constrained by the difficulties encountered in the development of technology for producing high-density chromoxide large-sized products. According to published data, the porosity of chromium oxide samples calcined in air at 1750 ^o C is 38.6% (A.I. Leonov - Izvestiya AN SSSR, Inorganic Materials 1966, v. 2, No. 12, p. 2168-2174).

 A common technological technique used to increase the sintering of oxides is the introduction of small additives into the charge and the use of various gaseous media. Moreover, the amount of added additives ranges from fractions of a percent to several percent. From a technological point of view, experimental confirmation of the assessment of the quality of the added additive and the parameters of technological operations for the formation of physical and mechanical properties is necessary.

 A known mixture for the manufacture of refractory products, including chromium oxide, titanium dioxide, magnesium oxide, characterized in that, in order to increase strength and glass resistance, reduce wettability by the melt, it additionally contains clay in the following ratio of these components, wt.%: 89-97 chromium oxide, 1 to 5 titanium dioxide, 0.1 to 1 magnesium oxide, 1 to 5 clay (ed. certificate No. 442175, USSR, Bulletin No. 33, 1974).

 The known solution allows to obtain chromoxide samples with porosity of the order of 15-18%.

 A disadvantage of the known charge is the use of finely dispersed components, which, as a result of sintering, lead to significant (10-12%) shrinkage deformations and an increase in waste of scarce materials during machining.

 The closest to the claimed object for the technical problem being solved - the prototype - is a method of manufacturing chromoxide products from granular masses.

The method consists of two stages. At the first stage, briquettes were obtained by mixing OHP grade chromium oxide with a combined additive containing 3.5% TiO ₂ , 4% Chas-Yar clay and 0.5% MgO, the mixture was moistened in a 1.5% sulfate-alcohol mash mixer, pressed briquettes at P _beats = 500 - 600 kgf / cm ² , dried and calcined in an oxidizing medium at 1650 ^o C.

Burnt briquettes were crushed, crushed and dispersed into fractions (mm) 2 - 1; 1 - 0.5; 0.5 to 0.09; <0.09. To obtain products, the mass was prepared in a mixer with zeta blades, with fractions of 1-2 mm - 24%, 0.5-1 mm - 22.6%; 0.5-0.09 mm - 24.6%; <0.09 mm - 38.4%, moistened with 1.5% sulfate-alcohol mash until a moisture content of 1.5-2% was reached, pressed and sintered in an oxidizing medium at 1650 ^o C (E.V. Degtyareva, I.I. .Kabakova, Ya.Z. Shapiro, A.I. Portnova, N.M. Kvasman. Publishing House "Metallurgy", "Refractories", 1977, N 12, p. 31-35).

 The known method allows to reduce shrinkage deformation, since linear shrinkage does not exceed 5.3%.

The disadvantage of this method is the uncertainty in the content of the glass-forming additive, since in the Yar clay, depending on the grade, the spread in the content of the glass-forming components is quite high (SiO ₂ from 49.4 to 78.3%), which can significantly affect the sintering kinetics and formation of properties.

 In addition, it is rather difficult to achieve a uniform distribution of the clay additive, since depending on the particle size and pore size, it can accumulate in local areas, which leads to uneven structural characteristics and chemical composition, which is what determines the increased (8.2-11.9 %) open porosity, shrinkage and a significant dispersion of operational characteristics from average values.

 The authors' task is to develop a method for producing chromoxide refractories that ensures the achievement of the goal - improving quality while reducing the dispersion of operational characteristics.

This goal is achieved in contrast to the known method in that at the stage of preparation of the charge, magnesium oxide and a silica-containing component are introduced as a complex additive contained in alkali-free glass of grade E, composition, wt.%: SiO ₂ 54.0, Al ₂ O ₃ 14 5, MgO 4.0-4.5, CaO 16.5-18.0, B ₂ O ₃ 8.0-10.0, F 0.2-1.0, mixed with co-grinding to obtain a fine fraction molding mixture is prepared by introducing a phosphate binder and a finely divided fraction into the granular fraction of a chromium-containing refractory, the mixture is granulated by wiping through sieves , fall asleep in the mold, subjected to vibrations, apply a pressure not exceeding the tensile strength of the granular fraction of the chromium-containing refractory, the products are dried and fired.

The technical essence of the proposed method is as follows:
- the introduction of magnesium oxide and a silica-containing component in the form of alkali-free glass of grade E with fixed values of oxides of silicon, aluminum, magnesium, calcium, boron and fluorine allows you to objectively control the quantitative composition of the introduced impurities and their influence on the compaction processes and the formation of physical and mechanical properties in the absence of alkaline oxides;
- mixing chromium oxide and a complex additive during co-grinding allows you to get a mixture with a uniform distribution of components per unit volume with high surface energy of dispersed particles, stimulating surface and volume diffusion during compaction, as well as the formation of solid solutions with chromium oxide that are resistant to aggressive environments ;
- obtaining a molding mixture from the calculated amount of the granular fraction of the chromoxide refractory and the finely dispersed complex component allows us to obtain a given composition of the chromoxide refractory and aims to reduce volume shrinkage effects when compacting the finely dispersed component in the border regions of coarse particles and, as practice shows, it becomes possible to reduce the deformation of the products and reduce machining is minimized, and for a large product range exclude it, which increases the yield of the finished product and reduces the cost per unit;
- the maintenance of the phosphate binder is determined by its high adhesive ability to the chromoxide material and due to the large curvature of the pores in the coarse-grained material and the capillary effect of the channels of the communicating pores, it is energetically advantageous at the initial moment to adsorb the binder in the open volumes of coarse-grained particles and subsequent coating of the dispersed component on them, which during sintering leads to the closure of open pores;
- aluminum and calcium oxides present in alkali-free glass E form a phosphorus-containing binder AlPO ₄ orthophosphate and Ca ₂ P ₂ O ₇ pyrophosphate, the structural features of the phases of which are characteristic of chemical compounds with increased sintering reactivity;
- wiping the moldable mixture through sieves provides for obtaining spheroid-like particles of different fractions, which contribute to a denser packing of the material when filling the molds;
- the application of vibration makes it possible to obtain the maximum possible bulk density of the backfill for a given conglomerated system and, together with the applied pressing pressure, to achieve an increased density of raw material, which makes it possible to produce dense and undeformed products during sintering due to low volumetric shrinkage;
- the formation of raw material at specific pressures below the tensile strength of chromium oxide refractory eliminates the destruction of coarse-grained particles and thereby reduces shrinkage, maintains the specified polycrystalline structure that regulates the physicomechanical, thermophysical properties and corrosion resistance in alkali-free glass.

 Examples of implementation.

 Example 1

 1. Raw materials and supplies.

 1.1. Chromium oxide metallurgical grade ОХМ-1, GOST 2912-79.

 1.2. Scrap of products made of chromoxide material after service in furnaces.

 1.3. Titanium dioxide, GOST 9808-84.

 1.4. Alkaline-free glass grade E (industrial waste).

 1.5. Thermophosphoric acid TU 113-08-5015182-105-95.

 2. Preparation of raw materials.

 2.1. Scrap of chromoxide refractories is thoroughly cleaned of impurities and large inclusions and crushed into pieces of 150-200 mm. Scrap grinding was carried out on a KID-300 brand crusher.

 The crushed material was passed through an EVS-B-3650 magnetic separator to separate iron and dispersed on a vibrating screen, taking fractions of 0.6-2 mm. The glass break was ground and a 0.6 mm fraction was taken.

 2.2. For the manufacture of finely dispersed components, fractions of ground scrap of products and glass, which passed through a 0.6 mm sieve, were selected.

The ratio of components for the manufacture of finely divided mixture was, wt.%:
Chromium Oxide (OXM) - 72
Chromium oxide scrap - 16
Titanium dioxide - 11.8
Croup of glass E - 0.2
The components were loaded into a CBM 45/100 brand vibratory mill and milled for 40 minutes. The dispersion of the particles of the mixture was 1 to 3 microns. The resulting dispersed charge was packaged in a sealed container and transferred to the operation of preparing the molding mixture.

 3. Preparation of the molding sand.

3.1. The molding mixture was prepared from the calculated content of the components, wt.%:
Shredded scrap chromium refractories,
fractions - 2 + 0.6 mm - 55
fine mixture <3 microns - 45
phosphoric acid, Y = 1.45 g / cm ³ (in excess of 100%) - 5
3.2. The mixture was prepared in a mixer with Z-shaped blades.

 Initially, the crushed scrap of chromoxide refractory fractions of 2-0.6 mm and half of the calculated amount of phosphoric acid were loaded with constant stirring for 5 minutes.

 The finely dispersed mixture was introduced in portions (10-15% of the calculated) with constant stirring and was moistened with the remaining amount of acid. The total mixing time was 20-25 minutes. The moisture content of the molding mixture was 4 wt.%.

 3.3. The prepared mass was unloaded on a sieve with a mesh size of 3-5 mm and thoroughly wiped.

 4. Molding products.

4.1. The mold thoroughly cleaned and lubricated with machine oil was mounted on a vibrating platform. The molding material was weighed on a platform scale in order to obtain a beam measuring 630x320x83-85 mm. After filling the mold, vibrations were applied for 5-10 seconds, then a pressure of 700-800 kg / cm ^{2 was} applied with the upper punch and the process was conducted with constant vibration until the punch was set to a predetermined level. The entire molding process was 40-50 seconds. After molding, the products were measured, weighed to determine volumetric weight
5. Drying products.

5.1. The products were dried in an electric double-chamber dryer at a temperature of 70-100 ^o C for the time necessary to achieve a moisture content of 0.2-0.3%.

 6. Firing products.

6.1. Products were fired in a gas flame furnace. Products were loaded into the muffle for protection against the torch at a temperature of 1580 ± 20 ^o C.

 6.2. Sintered products were controlled by weight and size to determine the density. Samples from different points of the volume (3-4 samples) were cut from the timber to determine the composition, physicomechanical properties, and stability in the E glass melt by standard methods.

 The results of the determinations are presented in the table.

 Example 2

When implementing example 2, the entire sequence and parameters of the process operations of example 1 were duplicated. The exception is the composition of the mixture to obtain a refractory containing 96% Cr ₂ O ₃ and 2% TiO ₂ . The content of components in the charge was, wt.%:
chromium oxide (OXM-1) - 80
chromoxide scrap grits - 15
titanium dioxide powder - 4
glass pellet E - 0.5
These tables show that the proposed method for producing refractories from chromium oxide allows the manufacture of products with improved technological and operational characteristics compared with the values obtained on products manufactured in a known manner, which confirms the high quality of refractories, which determines the competitiveness of imported analogues.

 Practical implementation of the proposed method confirms that the proposed solution allows to effectively implement the battle of products that have been in use, or the marriage of products after annealing and leads to the rational use of expensive raw materials and reduces financial costs for manufacturing a unit of production.

 The inventive method is carried out on standard industrial equipment with safety measures for staff and the environment, is objectively controlled in the manufacture of industrial batches of products of a given composition. The proposed method was implemented in the manufacture of 50 tons of refractories for lining a glass furnace at the Norilsk Mining and Metallurgical Combine.

Claims (1)

 A method of manufacturing refractory products from chromium oxide, including the preparation of a mixture containing chromium oxide, titanium oxide, magnesium oxide and a silica-containing component, crushing, grinding, sieving into granular and finely dispersed fractions, obtaining a molding mixture, pressing, calcining in a gaseous medium at 1650 ° C characterized in that at the stage of preparation of the charge, magnesium oxide and a silica-containing component are introduced into the finely divided fraction in the form of a complex additive contained in alkali-free glass of grade E, they are mixed together m grinding, a molding mixture is made by introducing a phosphate binder and a finely divided fraction into the granular fraction of a chromium-containing refractory, the mixture is granulated by rubbing through sieves, put into a mold, subjected to vibrations, apply a pressure not exceeding the tensile strength of the granular fraction of a chromium-containing refractory before firing the product is dried.

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