RU2369463C1 - Heat insulating mixture - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: heat insulating mixture contains, wt %: feldspar in kind of amazon-stone 45-46, milled coke 15-18, aluminium powder 6-8, and rice husks 22-30.

EFFECT: reduced wear of refractory of ladle in point of its contact with heat insulating mixture at transporting and tapping.

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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 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 provides thermal insulation of the steel surface.

However, this heat-insulating mixture has the following disadvantage: - after complete combustion of the sawdust, which takes several minutes, the heat-insulating properties of the mixture sharply decrease, the expanded perlite remaining in the mixture melts due to contact with molten steel and loses its heat-insulating properties.

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

Also known is an insulating mixture for casting steel, which is the closest analogue of the claimed invention (RF patent No. 2289493, IPC B22D 7/00, publ. 20.12.2005 in Bull. No. 35). The heat-insulating mixture includes feldspar (amazonite), ground coke and aluminum powder.

However, the disadvantage of this mixture is that during the period of transportation and casting of metal with direct contact of the mixture with the refractory lining of the bucket, its erosion wear occurs. The magnitude of the wear of the lining of the bucket is 2.3-3.1 mm / heat.

An object of the invention is to reduce the wear of the refractory lining of the bucket in place of its contact with the insulating mixture during transportation and casting in continuous casting machines to 2.1-2.2 mm / smelting.

The problem is solved in that the heat-insulating mixture, including feldspar (amazonite), ground coke and aluminum powder, additionally contains rice husk, in the following ratio, wt.%:

Feldspar (Amazonite) 45-56 Ground coke 15-18 Aluminum powder 6-8 Rice husk 22-30

The preparation of a heat-insulating mixture with the addition of rice husks does not differ from the preparation of a conventional heat-insulating mixture.

Rice husk (sometimes called rice husk) is a waste from rice processing.

The particle size of the rice husk during the preparation of the insulating mixture, as a rule, does not exceed 3 mm, which corresponds to the largest size of the fractions of the other components of the mixture and therefore ensures good flowability of the mixture when it fills the melt surface in the ladle.

A characteristic feature of rice husk is the chemical composition of its ash, which contains, wt.%: SiO ₂ 90,7-92,4; (CaO + MgO) 3.3-4.2; Al ₂ O ₃ 3.3-3.6; (FeO + Fe ₂ O ₃ ) 1.0-1.5.

The high content of SiO ₂ in the ash provides its practically unchanging viscosity with decreasing temperature during casting and transportation. As a result of this, the heat-insulating properties of the mixture practically do not change, this does not lead to a decrease in the temperature drop of the molten metal during transportation and casting in the continuous casting machine by more than 11-12 ° C, which reduces wear on the refractory lining of the bucket.

When the rice husk consumption is less than 22%, the formation of a melt in the contact zone of the heat insulating mixture with molten metal of the required viscosity is not provided and the required heat insulating ability of the mixture is not ensured, which leads to increased wear of the refractory lining.

With the consumption of rice husk more than 30%, intense burning of the heat-insulating mixture in the initial period is observed, which also reduces its heat-insulating ability and leads to increased wear of the refractory lining.

Thus, the optimal consumption limits of rice husks in the mixture is a consumption of 22-30%.

If the ratio of rice husk to coke is less than 1.2, intensive burning of the mixture in the initial period is possible, which reduces its heat-insulating ability and leads to increased wear of the refractory lining.

When the ratio of rice husk to coke content is more than 2.0, the burning intensity of the mixture increases, which also reduces its heat-insulating ability and increases the wear of the refractory lining.

Thus, the optimal limit for the ratio of the content of rice husk and coke is 1.2-2.0.

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 24 swimming trunks - swimming trunks No. 570410 ÷ 570434.

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;

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

- rice husk PAM-73.

Rice husk ash contains more than 90% SiO ₂ (in our particular case, 90.7 ... 92.4% SiO ₂ ).

It is known from practice that rice husk provides thermal insulation of steel in ladles during transportation and casting.

Silica (SiO ₂ ) ash has an amorphous or vitreous state, and individual grains of this silica are surrounded by a “coke” shell formed as a result of coking of the organic component of the rice husk at the boundary - molten metal - backfill. The access of oxygen is excluded from the atmosphere due to the upper insulating layer of the backfill, the access of oxygen from the molten metal is also excluded, since the contact layer of the backfill - metal - consists of silica particles enclosed in coke shells forming a continuous coke shell.

The resistance of coke shells is sufficient for the transportation and pouring of liquid metal.

The diffusion (penetration) of silica enclosed in coke shells into the ladle lining slows down, which reduces the penetration of SiO ₂ ash into the lining, resulting in reduced wear of the lining.

In the experiments used the following mixtures:

Composition number The content of components, wt.% Feldspar Ground coke Aluminum powder Rice husk one 45 eighteen 7 thirty 2 47 17 8 thirty 3 55 fifteen 8 22

The following results were obtained: wear of the refractory lining of the bucket at the place of its contact with the heat-insulating mixture during transportation and casting in continuous casting machines amounted to 2.3-3.1 mm / melt, the inventive heat-insulating mixture when using the heat-insulating mixture (compositions 1, 2 , 3) - 2.1-2.2 mm / smelting, which is 20.4% lower.

Claims (1)

The heat-insulating mixture, including feldspar in the form of amazonite, ground coke and aluminum powder, characterized in that it additionally contains rice husk in the following ratio of components, wt.%:
Feldspar in the form of amazonite 45-56 Ground coke 15-18 Aluminum powder 6-8 Rice husk 22-30