RU2267469C1 - Raw mixture for refractory article production - Google Patents

Abstract

FIELD: refractory articles for manufacturing of ceramic units operating at 1800°C.

SUBSTANCE: claimed raw mixture contains (mass %): fused corundum of grade <0.05 mm 45-50; fused mullite of grade 0.4-1 mm 15-22; ethyl silicate 1-2: and additionally it contains fused corundum of grade 0.5-0.8 mm 20-25; fused mullite of grade 1.0-2.5 mm 5-8; and graphite 2-5. Method of present invention makes it possible to increase refractoriness up to 1900°C and simultaneously to decrease backing temperature to 1450-1550°C.

EFFECT: raw mixture for production of refractory articles with increased refractoriness.

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Description

The invention relates to the field of production of refractories and can be used for the manufacture of ceramic assemblies of high-temperature aggregates, refractories, operating at temperatures up to 1800 ° C in oxidizing and reducing environments, as well as insulators.

Known refractory mass (ed. St. USSR No. 1151529, class C 04 B 35/18, 33/22, 1985), including, wt.%:

electrocorundum fractions less than 0.05 mm 9-17 amorphous silica fractions less than 0.05 mm 3-4,6 mullite-corundum chamotte fraction less than 0.05 mm rest

The disadvantage of this mass is the low service temperature up to 1000 ° C and insufficient heat resistance, because products with high density and low porosity do not withstand temperature extremes and have a limited service life under “heating - cooling” conditions. The presence of a large amount of mullite-corundum fireclay, having a significant amount of impurities and glass phase, does not allow the product to work at temperatures above 1000 ° C. With an increase in the service temperature, the strength sharply decreases, and the products are destroyed.

The closest (prototype) is a raw material mixture for the manufacture of refractory products (av. St. USSR No. 1723070, class C 04 B 33/22, 1992), including, wt.%:

electrocorundum fractions less than 0.05 mm 15-20 high alumina chamotte with Al ₂ O ₃ content 68% or fused mullite fraction 0.4-1.0 mm 35-50 ethyl silicate 0.7-1.0 high-alumina fireclay with content Al ₂ O ₃ 68% or fused mullite fraction less than 0.05 mm Rest

The specified raw mix cannot be used for the manufacture of products operating at temperatures above 1600 ° C, due to the high content in it (about 80%) of high-alumina chamotte or fused mullite, which have a significant amount of impurities and glass phase, causing deformation of products at temperatures above 1500 ° C.

The disadvantage of the mixture is the need for high firing temperatures (1550-1580 ° C). Products operating in the temperature range 1200-1500 ° C have a low service life.

An object of the invention is to increase refractoriness while reducing the firing temperature and maintaining strength and heat resistance.

To solve this problem, the raw material mixture for the manufacture of refractory products, including electrocorundum fractions of less than 0.05 mm, fused mullite fraction 0.4-1 mm and ethyl silicate, additionally contains electrocorundum fraction 0.5-0.8 mm, fused mullite fraction 1, 0-2.5 mm and graphite in the following ratio of components, wt.%:

electrocorundum fractions less than 0.05 mm 45-50 electrocorundum fractions 0.5-0.8 mm 20-25 fused mullite fraction 0.4-1.0 mm 15-22 fused mullite fraction 1.0-2.5 mm 5-8 ethyl silicate 1-2 graphite 2-5

The increase in the composition of corundum material to a total of 70% is due to the fact that corundum contains Al ₂ O ₃ up to 99%, therefore it is more heat-resistant material than mullite, because its melting temperature is about 2050 ° С (for comparison, the melting temperature of fused mullite is 1810 ° С); therefore, the introduction of 45-50% corundum as a binding base and 20-25% in the form of a granular filler increases the fire resistance of the material to 1900 ° С.

When the content of the corundum fraction is less than 0.05 mm above 50%, the shrinkage of the material increases and the strength decreases, and when the content is less than 45%, the heat resistance decreases.

When the content of corundum fractions of 0.5-0.8 mm is more than 25%, the strength and heat resistance of the material decreases, when the content is less than 20%, the fire resistance decreases.

The introduction of 23-27% mullite into the material improves sintering and preserves the strength and heat resistance of the material. A mullite content of more than 27% reduces the refractoriness of the material, and a content of less than 23% reduces strength and heat resistance. In this case, the content of the fine mullite fraction of more than 22% requires an increase in the aqueous binder - corundum slip (electrocorundum fraction less than 0.05 mm), because fine grain absorbs more water, and this accordingly leads to an increase in shrinkage during firing and a decrease in heat resistance.

The content of the fine fraction of less than 15% reduces the sintering and strength of the material.

To preserve the heat resistance of the material with a general decrease in the amount of mullite, graphite is introduced into the material in an amount of 2-5 wt.%, Which, burning out at the firing temperature, leaves small closed pores in the material, contributing to an increase in heat resistance. Graphite is much lighter than corundum and mullite, so 2-5 wt.% Is a significant volumetric amount. A graphite content of less than 2% does not create a sufficient number of pores to maintain the heat resistance of the material, and a graphite content of more than 5% requires an increase in the aqueous binder — corundum slip, because graphite takes a large amount of water onto itself, and the mass becomes unstable.

The increase in the amount of ethyl silicate in comparison with the prototype is associated with an increase in the fine fraction in the material (graphite - by volume), for the wetting of which it is necessary. The introduction of ethyl silicate above 2% is impractical due to the fact that in this case all the pores of the granular aggregate are closed with ethyl silicate and there is not sufficient adhesion between the grain and the aqueous binder to form a homogeneous casting mass.

The manufacturing technology of products from the proposed raw mix is as follows.

First, corundum slip is prepared by wet grinding in ball mills with corundum lining and corundum grinding bodies, for which an appropriate amount of water and electrocorundum (No. 50, 63 or 80) are loaded into the mill and grinding is carried out for 36 months -48 hours to obtain a slip with a density of 2.7-3.0 g / cm ³ , pH 8-10, viscosity 4-9 ° E and the residue on a sieve 005-10%. Then, the prepared slip is mixed with a granular aggregate consisting of electrocorundum, mullite of various fractions and graphite, previously moistened with ethyl silicate, after which the injection mixture is poured into active (gypsum) forms and left in them until shaping. Then the finished product is removed from the mold and dried either in air at room temperature or in an oven at a temperature of 60-100 ° C. After drying, the products are fired in a tunnel gas furnace at a temperature of 1450-1550 ° C.

The proposed composition of the raw mix allows to increase refractoriness up to 1900 ° C while maintaining the strength and heat resistance of the material, as well as reduce the firing temperature to 1450-1500 ° C.

Products fired at a lower temperature, having initially lower density than sintered at a temperature of 1550-1580 ° C, will have greater heat resistance and resistance to temperature changes during operation.

From the proposed raw material mixture, products weighing from 0.5 to 25 kg of various designs, working in industrial conditions, are made.

Currently, when working in continuous furnaces for sintering tablets of nitride ceramics and hard alloys, technological equipment and parts of the furnace’s internal fittings made of molybdenum and tungsten are used, which intensively corrode under conditions of a humidified hydrogen atmosphere of the furnace (sintering of tablets), nitrogen saturated with carbon ( sintering of nitride ceramics) and in vacuum with excess carbon (sintering of hard alloys). In addition, at high temperatures (up to 1800 ° C), characteristic of these processes, molybdenum and tungsten recrystallize, which leads to catastrophic embrittlement, resizing of tool parts and distortion of their shape. The consumption of materials for the restoration of warped and burned-out parts only from vacuum remelting molybdenum is up to 1 ton per year.

The inventive raw material mixture is used for the manufacture of tooling and parts of the internal fittings of the furnace instead of existing expensive materials of molybdenum and tungsten.

In addition, electrical insulators were made from the raw material mixture (working temperature - 1200 ° C, have been working for 1.5 years and continue to work), a set of ceramic products working under load in the furnace during the firing of large products (working temperature -1260 ° C), lining for furnaces (working temperature up to 1600 ° C), burner stones for gas furnaces (working temperature 1600-1650 ° C), pallets for crucibles and crucibles for glass melting (working temperature 1500-1570 ° C), etc. All of them are tested and successfully work in industrial conditions.

Table 1 shows the compositions of the proposed and known masses, and in table 2 - comparative properties of these masses.

As can be seen from table 2, the proposed raw material mixture can increase refractoriness up to 1900 ° C compared with the prototype while maintaining strength properties, reduce the firing temperature of products to 1450-1500 ° C, increase the service life of products at temperatures of 1200-1500 ° C in 1, 5-2 times.

Table 1 The composition of the raw mix The content of components, wt.% Famous one 2 3 Outrageous values four 5 Electrocorundum fractions less than 0.05 mm 15-20 45 47 fifty 43 53 Fused mullite or high alumina chamotte with Al ₂ O ₃ content _of 68% fraction 0.4-1 mm 35-50 22 ^* 17 ^* 15 ^* 26 ^* 13 ^* Fused mullite or high alumina fireclay with Al ₂ O ₃ fractions of less than 0.05 mm rest Ethyl silicate 0.7-1.0 one 1,5 2 one one Electrocorundum fractions less than 0.5-0.8 mm 25 23 twenty 17 27 Fused mullite fraction 1.0-2.5 mm 5 8 8 eleven four Graphite 2 3,5 5 2 2 ^* only processed mullite

table 2 The properties Structure Famous one 2 3 Outrageous values four 5 Firing temperature, ° С 1550-1580 1450-1500 1450-1500 1450-1500 1450-1500 1450-1500 Open porosity 10-15 14-16 15-16 16-18 13-15 16-18 The apparent density, g / cm ³ 2.7 2.9 3,1 3.0 2.9 3.2 Compressive Strength, 20 ° С, MPa 250-320 240-320 240-320 250-310 250-320 240-280 Heat resistance, heat exchange 1000 ° С - water 20-25 20-25 20-25 20-23 20-25 15-17 Refractoriness, ° С 1600 1900 1900 1900 1700 1900 The number of working heat exchange at 1200-1500 ° С 890 more than 1600

Claims (1)

The raw material mixture for the manufacture of refractory products, including electrocorundum fractions of less than 0.05 mm, fused mullite fractions of 0.4-1 mm and ethyl silicate, characterized in that it additionally contains electrocorundum fractions of 0.5-0.8 mm, fused mullite fractions 1 , 0-2.5 mm and graphite in the following ratio of components, wt.%: Electrocorundum fractions less than 0.05 mm 45-50 Electrocorundum fractions 0.5-0.8 mm 20-25 Fused mullite fraction 0.4-1.0 mm 15-22 Fused mullite fraction 1.0-2.5 mm 5-8 Ethyl silicate 1-2 Graphite 2-5