Raw mixture for refractory article production

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.

2 tbl

 

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

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

oxide particles less than 0.05 mm9-17
amorphous silica particles less than 0.05 mm3-4,6
malacology the clay fraction less than 0.05 mmrest

The disadvantage of this mass is a low temperature service up to 1000°and insufficient heat resistance, because the products having high density and low porosity, can not withstand temperature changes and have a limited lifetime in terms of "heating - cooling". The presence of a large number mullitokorundovye chamotte having a significant amount of impurities and glass rim, it is not possible to operate the product at temperatures above 1000°C. When the temperature service is sharply reduced strength, and the product dissolved.

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

the oxide fraction less than 0.05 mm15-20
high alumina fireclay with the content of Al2About3
68% or fused mullite fraction of 0.4-1.0 mm35-50
ethyl silicate0,7-1,0
high-alumina clay content
Al2About368% or fused mullite faction
less than 0.05 mmRest

Specified raw mixture may not be used for the manufacture of products, operating at temperatures above 1600°With, due to the high content (about 80%) high alumina fireclay or fused mullite, having a significant amount of impurities and glass rim, causing deformation of workpieces at temperatures above 1500°C.

The disadvantage of the mixture is the necessity of using high temperature firing (1550-1580°). Products operating in the temperature range of 1200-1500°have low life.

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

To solve this problem sireva the mixture for the manufacture of refractory products, including oxide particles less than 0.05 mm, fused mullite fraction of 0.4-1 mm and ethyl silicate, further comprises the oxide fraction 0.5-0.8 mm, fused mullite fraction of 1.0-2.5 mm graphite in the following ratio, wt.%:

oxide particles less than 0.05 mm45-50
the oxide fraction 0.5-0.8 mm20-25
fused mullite fraction of 0.4-1.0 mm15-22
fused mullite fraction of 1.0-2.5 mm5-8
ethyl silicate1-2
graphite2-5

The increase in the material composition of corundum total of up to 70% due to the fact that the oxide contains Al2About3up to 99%, and is therefore more heat resistant material than the mullite as its melting temperature is about 2050°With (for comparison, the melting point of fused mullite 1810°C), so the introduction of 45-50% alumina binder basics and 20-25% in the form of a granular filler provides increased fire resistance of the material to 1900°C.

When the content of corundum particles less than 0.05 mm greater than 50% increases the shrinkage of the material and decreases the strength, when the content is less than 45% reduced the resistance.

When the content of the oxide fractions of 0.5-0.8 mm more than 25% of snige the camping strength and temperature resistant material, when the content is less than 20% decreases the resistance.

Introduction to material 23-27% of mullite improves the sintering and retains strength and heat resistance of the material. The content of the mullite more than 27% reduces the resistance of the material and content of less than 23% reduces the strength and heat resistance. The content of the fine fraction of mullite more than 22% requires an increase in water bundles - corundum slip (oxide fractions less than 0.05 mm), because of small grain absorbs more water, and this accordingly leads to an increase in shrinkage during firing and reduction of heat resistance.

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

To maintain thermal stability of the material in a General reduction in the number of mullite in the material injected graphite in the amount of 2-5 wt.%, which, burn out at a temperature of burning leaves in the material of the fine closed pores, contributing to the increase in heat resistance. Graphite is much lighter than corundum and mullite, therefore, 2-5 wt.% - this is a significant volume number. The graphite content of less than 2% does not create a sufficient number of pores to maintain the heat resistance material, and a graphite content of more than 5% requires an increase in the water chords - corundum slip, because graphite takes large amounts of water, and the mixture is nepronicaemoj.

The increase in the number of ethylsilicate is compared to the prototype associated with an increase in fine material fraction (graphite - by volume), for wetting which he needed. The introduction of the ethyl silicate above 2% is impractical due to the fact that in this case all the pores of the granular filler is closed by ethyl silicate and between the grain and the water bond is not created sufficient adhesion to form a homogeneous casting mass.

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

First wet grinding in ball mills with corundum lining and corundum grinding bodies prepare corundum slip, which in the mill loads the appropriate amount of water and oxide (No. 50, 63 or 80) and in the presence of specially selected electrolyte is phosphoric acid are grinding within 36-48 hours to obtain a slurry density of 2.7-3.0 g/cm3pH 8-10, viscosity 4-9°E and residue on the sieve 005-10%. Then, the prepared slurry is mixed with a granular filler consisting of oxide, mullite different factions and graphite, pre-moistened with ethyl silicate, and then molding the mixture is then poured into active (gypsum) forms and leave them in to shape. Then the finished product is extracted from the mold and dried either in air at room temperature or in a drying Cabinet at a temperature of 60-100°C. after drying, the product is fired in a tunnel furnace at t is mperature 1450-1550° C.

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

Products, baked at a lower temperature, having initially less density than sintered at a temperature of 1550-1580°will have greater thermal stability and resistance to temperature changes during operation.

Of the proposed raw mix produced products weighing from 0.5 to 25 kg of various designs, working in an industrial environment.

Currently, when working in the through-type furnaces for sintering tablets nitride ceramics and carbide used industrial equipment and parts of the inner valve of the furnace, is made from molybdenum and tungsten, which are intensively corrode under conditions of moist hydrogen atmosphere furnace (sintering of pellets), nitrogen-rich carbon nitride sintering of ceramics) and in vacuum with an excess of carbon (sintering carbide). In addition, at high temperatures (up to 1800° (C)characteristic of these processes, molybdenum and tungsten recrystallized, which leads to catastrophic embrittlement, change the dimensions of the parts snap and distortion of their shape. The consumption of materials for recovery warped and burnt de the Aley only from molybdenum vacuum melting is up to 1 ton per year.

The inventive feed mixture used for manufacturing tooling and parts of the inner valve of the furnace to replace the existing expensive materials molybdenum and tungsten.

In addition, from a raw mixture were made electroisolator (operating temperature - 1200°S, have been working for 1.5 years and continue to work), a set of ceramic products working under load in the furnace for roasting large items (operating temperature -1260° (C)lining for furnaces (operating temperature up to 1600° (C), the burner stones for gas furnaces (operating temperature 1600-1650° (C)the pallets for the crucibles, and the crucibles for melting glass (operating temperature 1500-1570°C) etc. they are All tested and work successfully in an industrial environment.

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

As can be seen from table 2, the proposed raw mixture can improve the resistance to 1900°compared with the prototype while maintaining strength properties, to reduce the firing temperature of the products to 1450-1500°to increase the service life of the products at temperatures of 1200-1500°1.5-2 times.

Table 1
The composition of the raw mixContaining the s components, wt.%
Known123Transcendent values
45
Oxide particles less than 0.05 mm15-204547504353
Fused mullite or alumina fireclay with the content of Al2About368% fraction of 0.4-1 mm35-5022*17*15*26*13*
Fused mullite or alumina fireclay with the content of Al2About3fractions less than 0.05 mmrest
Ethyl silicate0,7-1,011,5211
Oxide particles less than 0.5-0.8 mm2523201727
Fused mullite fraction of 1.0-2.5 mm588114
Graphite 23,5522
*only fused mullite

Table 2
PropertiesComposition
Known123Transcendent values
45
Firing temperature, °1550-15801450-15001450-15001450-15001450-15001450-1500
The open porosity10-1514-1615-1616-1813-1516-18
Apparent density, g/cm32,72,93,13,02,93,2
Compressive strength, 20°C, MPa250-320240-320240-320250-310250-320240-280
The resistance to thermal cycles 1000° - water20-2520-2520-2520-2320-2515-17
The resistance, °160 19001900190017001900
The number of working shifts at 1200-1500°890more than 1,600

Raw mix for the production of refractory products, including oxide particles less than 0.05 mm, fused mullite fraction of 0.4-1 mm and ethyl silicate, characterized in that it further comprises the oxide fraction 0.5-0.8 mm, fused mullite fraction of 1.0-2.5 mm graphite in the following ratio, wt.%:

Oxide particles less than 0.05 mm45-50
The oxide fraction 0.5-0.8 mm20-25
Fused mullite fraction of 0.4-1.0 mm15-22
Fused mullite fraction of 1.0-2.5 mm5-8
Ethyl silicate1-2
Graphite2-5



 

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2 tbl

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