RU2370340C1 - Heat insulating mixture - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to iron and steel metallurgy. Heat insulating mixture contains, wt %: feldspar - amazon-stone 61-69, ground coke 20-25, chaff of aluminium chips 10-15.

EFFECT: reduced temperature drop of metal at transporting and casting in machines for continuous casting; reduced prime cost of mixture.

1 tbl, 1 ex

Description

The invention relates to ferrous metallurgy, in particular to warming the surface of liquid steel in a ladle during transportation and casting.

Known heat-insulating mixture for casting steel (ed. Certificate. USSR No. 582054, IPC B22D 27/00, B22D 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 - woodworking waste, perlite - silicate component - 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 provide 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 in the ladle during transportation and casting, where it is necessary to maintain a high temperature of the molten metal for a long time.

Also known is a heat-insulating mixture for heat insulation of metal during casting (ed. Certificate. USSR No. 833367, IPC B22D 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, and 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 in the mixture, 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 transportation and casting.

This is one of the disadvantages of the insulating mixture.

Another disadvantage of the mixture is the deficiency of amorphous graphite and thermoanthracite.

Also known is a heat-insulating mixture, which is the closest analogue of the claimed invention (RF patent No. 2289493, IPC B22D 7/00, publ. 12/20/2005, Bull. No. 35). The mixture includes feldspar (amazonite), ground coke and aluminum powder.

However, this mixture also has the following disadvantages:

- aluminum powder significantly increases the cost of the mixture and makes it practically unprofitable;

- in industrial production, in the preparation of mixtures, aluminum powder requires special conditions of storage, transportation and use due to its increased explosion hazard.

The given heat-insulating mixture after complete combustion of the aluminum powder, which occurs within a few minutes, sharply reduces its heat-insulating properties and does not fully fulfill the role of heat insulation for the period of transportation and casting of steel.

For this reason, such a heat insulating mixture is not effective enough and at the same time has a high cost.

An object of the invention is to reduce the cost of the insulating mixture while maintaining the required insulating properties for the entire period of transportation and casting, improving working conditions and safety when manufacturing the mixture and feeding it into the bucket.

The problem is solved in that the insulating mixture includes carbon, silicate and aluminum components. As an aluminum component, it contains screenings of aluminum chips in the following ratio of components, wt.%:

Feldspar (Amazonite) 61-69 Ground coke 20-25 Screenings of aluminum chips 10-15.

The ratio of the screening content of aluminum chips to ground coke is 0.40-0.75.

The particle size of the screenings of aluminum chips used in the preparation of the insulating mixture is 3-1 mm, i.e. does not exceed 3 mm and therefore provides good flowability of the mixture when it fills the surface of the melt in the bucket.

As practice shows, when the content of screenings of aluminum chips in the mixture is less than 10%, its heating due to the exothermic reaction is negligible, while the heat from the combustion of coke during the entire period of transportation and casting is also not enough to prevent cooling of the liquid metal.

When the content of the screenings of aluminum chips in the mixture is more than 15%, the mixture may overheat and reduce its heat-insulating ability. In addition, at such costs of aluminum shavings, intense heat of the refractory lining of the steel pouring ladle in the contact zone with the heat-insulating mixture is possible.

Therefore, the optimum content of aluminum chips is the content of 10-15%.

In the course of an exothermic reaction, in addition to the fuel of this reaction, which are the screenings of aluminum chips, an oxidizing agent is also necessary - iron oxides. The oxidizing agent in an exothermic reaction at its beginning is feldspar (amazonite) containing iron oxides, and coke ash containing iron oxides, as well as non-metallic inclusions in steel containing iron oxides.

When the ratio of the screenings of aluminum shavings to ground coke is less than 0.40, the iron oxides in the ash of ground coke are not enough for an exothermic reaction to occur, which leads to a decrease in the heat-insulating properties of the mixture.

When the ratio of the screenings of aluminum shavings to ground coke is more than 0.75, the exothermic reaction proceeds intensively in the initial period and slows down by the end of the transportation and casting period, which also leads to a decrease in the heat-insulating properties of the mixture.

Thus, the optimal ratio of the screening content of aluminum chips to ground coke is 0.40-0.75.

Concrete example

In the steelmaking workshop 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 grades St3sp, S275JR and other grades. A total of 126 heats were bottled - heats No. 452132 ÷ 452258.

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:

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

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

- screenings of aluminum chips according to TU 1781-001-78530992.

In the experiments used the following mixtures:

Composition number The content of components, wt.% The ratio of screenings of aluminum shavings to ground coke Feldspar (Amazonite) Ground coke Screenings of aluminum chips one 61 25 fourteen 0.56 2 65 twenty fifteen 0.75 3 69 21 10 0.48 four 65 22 13 0.59

The following results were obtained: the temperature difference of the metal during transportation and casting in continuous casting machines (CCM) was when using a heat-insulating mixture of the prototype 12.3 ° C, the inventive heat-insulating mixture (compositions 1, 2, 3, 4) - 11.7 ° C, which is 4.9% lower. The cost of 1 ton of the inventive insulating mixture decreased by 15% compared with the prototype. The explosion hazard of the mixture is completely eliminated compared to the prototype.

Claims (1)

The heat-insulating mixture, including feldspar-amazonite, ground coke and an aluminum component, characterized in that it contains screenings of aluminum shavings as an aluminum component in the following ratio, wt.%:
Amazonite Feldspar 61-69 Ground coke 20-25 Screenings of aluminum chips 10-15