RU2289493C1 - Heat insulation mixture - Google Patents

Abstract

FIELD: ferrous metallurgy, namely warming surface of melt steel and cast iron in ladle during casting or transporting.

SUBSTANCE: mixture contains, mass %: field spar -amazonite, 65 -70; ground coke, 20 - 25; aluminum powder, 9 - 11. Fraction size of mixture is no more than 3 mm at next relation of fractions, mass %: fraction 3 -2mm, 1 - 5; fraction 2 - 1 mm, 88 - 95; fraction 1 - 0.1 mm, 5 - 6.

EFFECT: possibility for providing desired heat insulation properties of mixture for period from starting casting process till ending transportation of ladle, elimination of volatile matters separation, lowered exhaust of combustion products to atmosphere.

2 cl, 1 tbl, 1 ex

Description

The invention relates to ferrous metallurgy, in particular to the insulation of the surface of liquid steel and cast iron in the ladle during casting or transportation.

Known heat-insulating mixture for casting steel (Auth. St. USSR No. 582054, IPC B 22 D 27/00, B 22 D 7/10, publ. In BI No. 44, 1977). The mixture contains a carbon-containing substance, which is used as sawdust, as well as expanded perlite. Sawdust is a waste of woodworking, perlite is a silicate component of volcanic glass. Its expansion occurs when heated due to the removal of chemically bound water from its composition. Expanded perlite is a heat-insulating material and in a mixture with sawdust due to their combustion provides thermal insulation of the steel surface.

However, this heat insulating mixture has the following disadvantage:

- after complete combustion of the sawdust, which occurs within a few minutes, the heat-insulating properties of the mixture sharply decrease, the expanded perlite remaining in the mixture due to contact with molten steel melts and loses its heat-insulating properties.

For this reason, such a mixture cannot be used to insulate the surface of molten steel or cast iron in the ladle during casting or transportation, where it is necessary to maintain a high temperature of the molten metal for a long time.

Also known is a mixture for thermal insulation of metal during casting of steel (Auth. St. USSR No. 833367, IPC B 22 D 7/10, published in BI No. 20, 1981). The mixture also contains a carbon-containing additive and expanded perlite. As a carbon-containing additive, the mixture contains amorphous graphite and thermoanthracite. Moreover, the grain size of thermoanthracite is 0.2-0.4 parts of the grain size of expanded perlite, which ensures uniform distribution of thermoanthracite in the mixture.

Due to the use of graphite and thermoanthracite as a carbon-containing additive, their combustion is slower compared to, for example, sawdust, and the gases emitted during combustion protect the perlite from melting and maintain it in the expanded state throughout the entire combustion period.

Thus, the heat-insulating properties of the mixture are maintained throughout the entire combustion period of the mixture. Moreover, the duration of this period is insufficient for the time from filling the bucket to its pouring and transportation.

This is one of the disadvantages of the insulating mixture.

Another disadvantage of the mixture is the deficiency of amorphous graphite and thermoanthracite. In addition, when using the mixture, the release of volatile and combustion products pollutes the air atmosphere, especially due to the combustion of thermoanthracite.

An object of the invention is to provide the required heat-insulating properties of the mixture for the period from the start of casting to the end of transportation of the ladle with the exception of the release of volatiles and a decrease in the release of combustion products into the atmosphere.

The problem is solved in that the insulating mixture includes carbon and silicate components and aluminum powder. As a silicate component, a variety of feldspar is used - amazonite, and as a carbon component - ground coke, in the following ratio of components, wt.%:

Feldspar (Amazonite) 65-70 Ground coke 20-25 Aluminum powder 9-11

The size of the mixture fraction is not more than 3 mm in the following ratio of fractions, wt.%:

3-2 mm fraction 1-5 Fraction 2-1 mm 88-95 Fraction 1-0.1 mm 5-6

The composition of the heat-insulating mixture includes the following components: feldspar (amazonite), ground coke and aluminum powder.

Their purpose in the mixture is as follows.

Feldspar is a raw material for the production of silicate melts, in particular various types of glass.

The composition of feldspar includes: SiO ₂ , AlO ₃ , K ₂ O, Na ₂ O and Fe ₂ O ₃ .

As practice shows, to obtain a viscosity with the possibility of the formation of a porous structure, the content of K ₂ O and Na ₂ O is required in the range of 8.5–10.2%, which is ensured by the content of feldspar (amazonite) in the range of 65-70%.

When the content of feldspar-amazonite in the mixture is less than 65%, the melt viscosity is high, which leads to uneven spreading of the mixture over the entire surface, and which prevents the formation of the porous structure of the mixture, and hence reduces its heat-insulating ability.

If the content of feldspar-amazonite in the mixture is more than 70%, the melt viscosity is too low, which will lead to the elimination of pores and, consequently, to a decrease in the heat-insulating ability.

Thus, the optimal limits of the content in the mixture of feldspar-amazonite are the limits of 65-70 wt.%.

Coke is the main combustible material in blast furnace and steelmaking, as well as the carbon-containing component of many heat-insulating materials in metallurgy.

The advantage of coke in comparison with other carbon-containing additives, for example wood sawdust and coal, is that during its combustion, when used in heat-insulating mixtures, no volatile substances polluting the air are released.

Its purpose in the mixture is to provide heat-insulating ability before burning, and then to prevent the metal from cooling during combustion.

At coke costs of less than 20%, the heat generated is not enough to prevent the cooling of liquid metal.

At expenses of more than 25% in the mixture, delamination of the mixture and loss of heat-insulating ability are possible.

Based on the above, the optimal limits for the coke content in the mixture are 20-25%.

Aluminum powder is the third component of the insulating mixture.

Aluminum powder is usually used in the composition of exothermic slag-forming mixtures used in steelmaking.

Aluminum powder is introduced into the composition of the heat-insulating mixture as a fuel of exothermic reactions. The oxidizing agents of this reaction are iron oxides contained in feldspar (amazonite) and coke ash as a result of its combustion, as well as iron oxides contained in non-metallic inclusions of metal melt.

The content of aluminum powder in the insulating mixture is taken in the range of 9-11 wt.%.

As practice shows, when the content of aluminum powder in the mixture is less than 9%, the heating of the mixture due to the exothermic reaction is insignificant, and therefore, in the process of coke burning and after its combustion, this heat will not be enough to prevent cooling of the liquid metal.

If the mixture contains aluminum powder in an amount of more than 11%, the mixture may overheat and reduce its heat-insulating ability. In addition, at such costs of aluminum powder, an intense heat of the refractory lining of the steel pouring ladle in the neck area (in the zone of the slag belt) is possible. Therefore, the optimum content of aluminum powder in the mixture is a content of 9-11%.

To ensure the flowability of the inventive mixture, the size of its fraction should be in the range of 0.1-3 mm.

When the size of the fraction of the components of the mixture is less than 0.1 mm, aggregation of particles into large granules is possible with an equilibrium moisture content of the mixture of about 2%, which does not ensure uniform dispersion of the mixture.

When the size of the mixture fraction is larger than 3 mm, delamination of the mixture is possible, which leads to its uneven distribution over the surface of the metal melt.

The content in the mixture fraction of 3-2 mm less than 1% leads to an increase in its density, caking and reduce its flowability.

In a mixture with a fraction content of 3–2 mm greater than 5%, the porosity of the mixture increases, but an uneven distribution of aluminum powder is observed, which leads to a slowdown in the exothermic reaction.

When the content of the fraction of 2-1 mm in the mixture is less than 88%, its porosity also increases, leading to uneven distribution of aluminum powder, which also leads to a slowdown in the exothermic reaction.

The content of the fraction of 2-1 mm in the mixture of more than 95% leads to an increase in the density of the mixture and poor mixing with other components and especially with ground coke, which reduces the heat-insulating properties of the mixture.

When the content of the fraction of 1-0.1 mm in the mixture is less than 5%, the porosity of the mixture increases, which leads to a deterioration in the mixing of the mixture with coke and aluminum powder, which also reduces the quality of the mixture.

The content in the mixture of a fraction of 1-0.1 mm more than 6% leads to an increase in the density of the mixture, which also reduces its quality.

Concrete example

In the steelmaking shop of OJSC Magnitogorsk Iron and Steel Works, experiments were carried out on the use of heat-insulating mixtures in steel-pouring ladles with a nominal capacity of 175 tons for the smelting of steel grade St3sp. Conducted 18 swimming trunks - swimming trunks No. 93777 ÷ 93794.

In the experiments used a heat-insulating mixture in accordance with the prototype and the inventive mixture.

In the composition of the claimed mixture used the following materials:

- dry ground coke according to STP 101-68-98;

- feldspar (amazonite) of the Vishnevogorsk deposit according to TU 5726-96;

- secondary passivated aluminum powder of grade APV-P according to TU 1790-99.

In the experiments used the following mixtures:

Table Composition number The content of components, wt.% Feldspar Ground coke Aluminum powder one 65 25 10 2 67 22 eleven 3 70 twenty 10

The following results were obtained: the temperature difference during casting in continuous casting machines (continuous casting machines) was when using a heat-insulating mixture according to the prototype 14.7 ° C, the inventive heat-insulating mixture (compositions 1, 2, 3) was 12 ° C, which is 23% lower .

Claims (2)

1. The heat-insulating mixture, including the carbon and silicate components, aluminum powder, characterized in that it contains feldspar - amazonite as the silicate component, and ground coke as the carbon component in the following ratio, wt.%: Feldspar - Amazonite 65-70 Ground coke 20-25 Aluminum powder 9-11 2. The mixture according to claim 1, characterized in that the size of the fraction of the mixture is not more than 3 mm in the following ratio of fractions, wt.%: 3-2 mm 1-5 2-1 mm 88-95 1-0.1 mm 5-6