SU1764803A1 - Slag-forming mixture for protection of alloy against contact with atmosphere - Google Patents

Abstract

Slag-forming mixture for continuous casting of metals. Usage: in the processes of continuous and semi-continuous casting of copper and copper alloys. The essence of the invention: a slag-forming mixture containing, in wt.%: Silica 56, .. 64; sodium oxide 25 ... 30; boron oxide 11 ... 16. 4 tab.

Description

with

with

The invention relates to the field of metallurgy and can be used in the continuous casting of metals and alloys for protection against interaction with the atmosphere of air.

The purpose of the present invention is to eliminate folding in the corners of ingots and increase the productivity of continuous casting machines.

This goal is achieved by developing a composition of the slag-forming mixture, which allows you to limit heat loss from the metal mirror in the mold, while having a narrower melting range, optimal viscosity and thermal conductivity.

The fulfillment of these requirements is accomplished by increasing the content of silicon dioxide and decreasing the content of boron oxide. Content of components

wt.%: 56-64 S102, 25-30 Na20, 11-16 BaOz, while the ratio of the contents of sodium oxide to the content of boron a boron should be 1.7 ... 2.3.

The thermal conductivity of the proposed slag-forming mixture at the casting temperature of copper (1180-1160 ° C) is 2.01 W / m-K, while the mixture of the prototype, composition, wt.%: 48-52 SiOa, 8-10 Ma20, 38-40 VaOz, respectively, 2.17 W / mK. Using the calculated coefficients of heat conduction, mVJIAoSkreJozhg the rank of heat loss from the metal mirror in the mold (qi). When casting under a melting mixture, this value is determined by the formula (Shmrga L. Hardening and crystallization of steel castings. - M .; Metallurgists, 1985. - p. 227):

Vi o

4 00

about

with

qrtnbcv 1 - (tc / tn) 2

where tn is the surface temperature of the ingot, in the first approximation it can be taken equal to the crystallization temperature of the alloy;

Bc is the heat storage coefficient of the slag-forming mixture:

  s-y

where I, C, heat conductivity, heat capacity and density of the coating material.

All calculated and experimental data are given in Table. one.

The table shows that the amount of heat removed from the surface qi is minimal when using the proposed composition, which eliminates the formation of a hard crust on the metal mirror in the mold and thereby prevent the formation of torsions and the presence of slag inclusions on the ingot surface.

The most important characteristic of slag is the temperature range of its melting. Typically, the time for establishing a stationary thermal regime varies between 2 and 3 minutes, depending on the speed of pouring. A necessary condition for obtaining a high-quality ingot surface should be considered to be the melting and stabilization of slag properties. In this regard, the lower the melting point and the smaller the temperature range of melting, the greater the likelihood of obtaining a high-quality surface of the ingot. Below are experimental data on the temperature ranges of the melting mixture of the prototype and the proposed mixture:

MixtureTemperature

melting range, ° CX

prototype 830-900

offered 690-720

 The first figure is the beginning of softening the slag-forming mixture, the second is the end.

From the data presented it can be seen that the proposed mixture has the lowest melting range. This makes it possible to reduce the stabilization time of the mixture properties by a factor of 2–3 times and, therefore, shorten the length of the ingot, where there is the likelihood of winding and folding of the surface, all other equal technological conditions.

The properties of the slag-forming mixture make it possible to organize the process of heat removal from the ingot to the mold so as to reduce it in the upper part and increase the formation of a gas gap in the zone. In practice, when casting copper ingots (due to the very high thermal conductivity

Copper Yasi 376.8 W / mK) gas gap is formed at the very meniscus of the metal. In the case of casting under soot, the gap is filled with it, and under the slag-forming mixture - with liquid slag. Depending on the viscosity of the slag and the melting temperature range, it fills the gap to different depths.

To evaluate the effect of slag properties on heat flow, the average heat transfer coefficient from the ingot to the mold in the upper part was calculated depending on the gap size (Rutes VS, Askoldov VI. Theory of continuous casting. Technological bases. M .: Metallurgi, 1971, p. . 70):

a (

"1 Yazaz

+

Yasi

)

where "1 is the heat transfer coefficient from the mold wall to the water:

  V0,85 (1 + 1,011), - where tb is the temperature of the water in the crystallizer, tb 24 ° C;

, 825 m / s, about 3112,654 W / m2-K;

Phase 5s

-j, -j thermal resistance

Azaz ASI

air gap and the copper wall of the mold, respectively.

A decrease in the thermal conductivity of the slag-forming mixtures leads to a decrease in the coefficient a. The value of the coefficient is presented in Table. one.

The adhesion force acting on a non-metallic inclusion at the metal-slag interface can be determined by the formula (Schmga L. Hardening and crystallization of steel castings. - M .: Metallurgi, 1985, p. 227):

R Omet - shl S, N.,

where S is the area of the ejected particle, m2. Therefore, the less Omet - shl. the easier is the transition of inclusion from metal to slag, which is achieved by using the proposed mixture.

The viscosity of the slag and the temperature range of melting by filling the gas gap formed during solidification between the ingot and the crystallizer wall influence the average heat flux: q of the proposed mixture 101240 kJ / m2, of the prototype mixture 138546 kJ / m. As a result, during the casting of copper under the proposed mixture, the thermal stresses in the solid crust that is formed are lower and, therefore, less likely to form cracks.

In general, the quality of the ingot cast under the proposed mixture is higher (see Table 4).

To prepare the slag-forming mixture offered in the application, the following starting components are used:

1) quartzite natural deposits of the brand K-98-300 according to GOST 9854-81, ground, sifted through a sieve with a cell of 0.3 mm. Humidity is not higher than 0.5%;

2) drill technical No. 2840 according to GOST 8429-77, melted, ground and sifted through a sieve with a cell of 0.5 mm, the humidity is not higher than 0.5%. During casting due to thermal dissociation, the reaction proceeds

T 1000 ° C No. 2840 N320 + 2BaOz,

3) the missing amount of sodium oxide is introduced in the form of soda ash No. 2CO3 according to GOST 5100-73 with a humidity not higher than 1.0-1.5%. Soda, due to thermal dissociation in the presence of silicon oxide as a catalyst, is actively decomposed by the reaction

Si02 + T 1000 ° C

Na2SO3 Na20 + C02t

These components, prepared accordingly, are thoroughly mixed in a ratio, wt.%: Quartzite49-50

Soda ash 30-31 Borax melted 18-20 PRI me R. Under industrial conditions on a semicontinuous casting plant, ingots of copper grades M1 and M2 of rectangular section 600x200 mm, 5 m long were obtained in an amount of 20 pcs. and a round section with a diameter of 200 mm, a length of 1.4 m in an amount of 100 pcs. The proposed slag-forming mixture of composition 1–4 was used as a covering material (see Table 1).

For the basic technology adopted copper casting under a layer of calcined carbon black.

Due to the higher thermal conductivity of the proposed mixture, the casting speed was increased:

when casting ingots of rectangular section from 6.0-6.5 to 9-1 ohm / h;

when casting round ingots from 9 to 12 m / h.

This has led to an increase in the productivity of the casting plant. A similar effect is expected when using the continuous casting plant.

A great advantage has a mixture of the following composition, May. %: 56 Si02, 28№20, 16В2Оз

The proposed mixture can be used for casting copper alloys of the type BrX08, BrKd1, BrB2, etc., having a casting temperature close to the casting temperature of copper of 1180-1220 ° C.

By increasing the casting speed, reducing the cost of the coating material (in comparison with soot), and improving the quality of the ingots, an economic effect of 5.27 rubles was obtained. per 1 ton of copper ingots.

In tab. 2, 3 presents the properties of the proposed slag-forming mixture and a mixture of the prototype.

Claims (2)

Slag-forming mixture to protect the alloy from interaction with the atmosphere of air in continuous casting machines, containing silica, sodium oxides and boron, characterized in that, in order to improve the surface quality of the workpiece and increase the productivity of continuous casting machines, it contains these components in the following ratio, wt.%: Silica 56-64 Sodium oxide 25-30 Boron oxide11-16 moreover, the ratio of sodium oxide and boron oxide is 1.7-2.3. Interfacial Stmet - shl, N / m, and superficial sshl. N / m tension of mixtures Viscosity of slag-forming mixtures, Pa-s The presence of defects on the surface of the ingot 600x200 mm from copper M1 Note. 1. Defects were determined per 1 running meter of ingot taken from its middle. 2. The enterprise standard permits defects up to 3.0 mm in depth and up to 0.5 mm in diameter. table 2 Table 3 Table A