SU789219A1 - Heat insulation mixture for continuous casting of metals - Google Patents

Description

.1 The invention relates to ferrous metallurgy, in particular, to the composition of l mixtures for isolating a metal mirror in tundishes during continuous casting of steel. When casting on continuous casting machines (MNLE), the metal from the casting ladle is first fed into the tundish and then fed to the mold. At present, a typical steel casting technology on a continuous casting machine is a smelting melt casting method, in which the residence time of the metal in the tundish is usually 4-5 hours. A necessary element of this technology is the insulation of the metal mirror in the tundish various mixtures and materials whose application is aimed at reducing heat losses; the surface of the metal is the prevention of its oxidation by the oxygen of the air and the exception of sticking to the stopper formed around it by a slag-metal crust. Known telpoisolating mixture containing expanded perlite (base and amorphous graphite in the amount of 1020 vol.%. Expanded perlite of the most well-known deposits (for example, Aragatskoye, Arm nska SSR) with a volume weight of 0.06-0.11 t / m at room temperature characterized by a very low thermal conductivity (0.050, 08 w / m “hail) 11- However, due to the low melting temperature (11201350 ° C) when in contact with a liquid metal, its particles melt and sinter, as a result of which the thermal conductivity of perlite increases dramatically and its use It is impractical to heat the insulator under such conditions. To prevent the melting of the perlite, it is mixed with amorphous graphite. The graphite particles are placed on the surface of the pearlite grains to form a refractory protective layer that prevents the perlite grain from heating to high temperatures and, therefore, from melting. The latter contributes to maintaining the required; insulation properties1 of the mixture for 1.5-2.5 hours, i.e., a period of time usually sufficient to complete the formation ingots of the most common weights. An increase in the content of graphite in the mixture, including the complete replacement of perlite with graphite, is accompanied by a continuous decrease in the thermal conductivity of the mixture during operating temperatures (improving its heat insulating properties) and, accordingly, makes it possible to use it for a longer time under high impact conditions. temperatures. However, in the known mixture the content of graphite is limited to 35-65 weight. %, equivalent to 10-20 vol. % This is due to the fact that with an increase in the composition of the mixture for casting ingots of graphite content beyond the specified limits, a significant carburization of the upper (subprofit) part of the ingot is observed, leading to the development of subdued segregation and an increase in head trimming. Thus, despite the whole range of positive properties of the known mixture — the possibility of eliminating the oxidation of a metal by atmospheric oxygen, maintaining high thermal insulation properties for a relatively long period (up to 2.5 hours), its use for insulating a metal mirror in an intermediate ladle was It is impractical because the duration of the serial casting (4-5 hours) significantly exceeds the period of preservation by the mixture of the required thermal insulation properties. In addition, it should be taken into account that the temperature of the metal in the tundish is noticeable (by 30–70 s higher than the average temperature of the metal in the mold during the casting and crystallization of the ingot. As the lead of the mixture thermal conductivity coefficient increases, the effect of using the known mixture under these conditions (to isolate the metal mirror in the tundish); he. The purpose of the invention is to stabilize the casting process, reduce metal loss and increase the durability of the lining of the ladle. Avlennoi purpose. Achieved by the fact that the mixture contains components in the following amounts, wt.%: Amorphous graphite 71-85 Perlite expanded The remaining increase in the content of graphite to 71g85 wt.%, against 35-65 wt.% in the known mixture provides more even protection of grains perlite from melting and, consequently, the possibility of using the mixture under the conditions of exposure to molten metal for a longer time, filling the pores between the particles of perlite, as a result of which the conservative and radiation components of heat transfer are reduced at high temperatures, which reduces the effective thermal conductivity of the mixture and, therefore, improves its thermal insulating properties, and also improves the insulation of the metal from oxidation by oxygen of air, as the amount of carbon monoxide increases per unit time. Increasing the carbon content in the composition of the mixture under the conditions of its use for warming the metal mirror in the tundish does not lead to the negative consequences (excessive carburization) that occur in the case of using such a mixture for casting ingots. Even assuming that all carbon. Of the mixture is completely converted to metal,. then, with a typical mixture consumption of 0.05 kg / t and a maximum content of graphite in it of 85%, the concentration of carbon in cast steel increases by no more than 0.004 abs. %, which is significantly lower than the analysis error. When using the mixture to isolate the metal mirror in the tundish, carbon passes into the metal gradually and is evenly distributed in it, while in the casting of ingots, local and, therefore, higher carbon enrichment of individual sections of the ingot is observed. A further increase in the content of graphite in the mixture, despite the possibility of improving its thermal insulation properties, is impractical because some of the operational properties of the mixture deteriorate (increased clodiness, complication of the mixture from mixing units, etc.), and the ability of the mixture to spread freely decreases. over the metal mirror, which is important in connection with the large sizes of tundishes. Laboratory and Proiz. water experiments showed that by. For these reasons, the content of graphite in the mixture used under these conditions is limited to 85%. The lower limit on the content of graphite in the mixture is determined on the basis of ensuring the POSSIBILITY of its stay on the metal for a long period of time (4-5 hours) .. When the carbon content is less than 70%, the mixture loses its heat-insulating properties after 1.5- 2.5 h. In order to more significantly reduce the tendency of the mixture to melt when exposed to high temperatures and to ensure that it can be used under conditions of long-term thermal effects of the molten metal, it is advisable to use the varieties of perlite available in the USSR that differ from those usually used by higher melting temperatures and bulk density. For example, perlite of the Transcarpathian deposit has a melting point

1400-1430 C and the volume weight of 0.120, 25 t / m, while for the widespread perlite of the Aragats deposit these indicators. significantly lower and constitute, respectively, 0.06-0.11 t / m and 11201350 ° C.

Since an increase in the content of fine fractions of perlite in the mixture increases its fusibility, it is limited. It was established experimentally that the content of the fraction less than 0.1 Mm should not exceed 5%.

The proposed mixture is a more effective material for insulating a metal mirror in a tundish, since, compared with the known, it has better heat insulating properties, characterized by the possibility of using it in contact with a liquid metal for a longer period of time, it better isolates the metal from the effects of oxygen, provides the possibility of reducing the temperature of the metal at the outlet and, accordingly, accelerating the smelting, and also prevents the formation of walling in the ladle, the removal of s leads to the destruction of the lining of the tundish.

Mixture consumption depending on. the size of the ladle and the number of bottled bottoms in the series, as well as their weight is 0.03-0.05 kg / ton of steel. .

Example 1. When casting melts from steelmaking aggregates of small capacity (50-100 tons) for a long-term billet up to 150x150 mm in size, a mixture of the following composition is used,%: amorphous graphite 71, expanded perlite 22. The content of the fine fraction perlite can be close to the IMM to the upper limit (4.5-5%), and the melting temperature and the volume weight of the perlite used are respectively 0.12-0.15 t / m.

The mixture consumption in this case is 0.03 kg / ton steel.

Example 2. In the case of casting of bottoms from medium-capacity aggregates (150-200 tons), a mixture of j%: amorphous graphite 78 and perlite is used for large varietal billets up to 300x300 mm in size, as well as for large sheet sizes (up to 300x1900 mm). expanded 22. The content of fine fraction perlite is limited to 3-4%, while the volume weight of perlite is 0.18-0.20 t / m, and the melting point is 1410-1415 ° C. The mixture consumption in this case increases to 0.04 kg / ton.

PRI me R 3. When using

5 mixtures under more severe conditions, for example, when casting melts of greater weight (300-350 tons), a mixture is used on billets with an average cross section of Csortov 250x250 mm and sheet 150x1600 mm)

0 including,%: amorphous graphite 85 and expanded perlite 15. In this case, the content of fine fraction perlite should not exceed 1.5-2%, and the melting temperature and volume weight should be maximum (1430 C and 0 , 25 t / m). The mixture consumption is increased to 0.05 kg / ton.

 The mixture sits on the mirror.

0 metal in the tundish after filling it by 2/3 Or to a predetermined height. It can be made by mechanically mixing components in paddle or propeller mixers. The mixture should be packaged in plastic packaging.

When testing the proposed and iz-. A well-known mixture revealed that the mixture being described is characterized by higher efficiency.

For the test, the mixtures listed in Table 2 were taken. one.

Table 1

Known dare on pearlite Aragats field 50

The mixture on the perlite of the Transcarpathian mine 50 is known.

We offer a mixture with graphite content at the lower limit of 71

50 1250 0.08 1.5

50 1430 0.25 1.5

29 1430 0.25 1.5

The same with the content of graphite on the average limit78

The same with the content of graphite on the upper limit85.

Mixture different from the proposed lower content of graphite66

The same, characterized with a higher content of graphite 95

A mixture characterized by the use of perlite with a lower melting point 78

A mixture characterized by the use of perlite with a lower bulk density78

A mixture characterized with a high content of fine fractions 78

These mixtures are tested in laboratory conditions (the value of the coefficient of thermal conductivity at temperature and the duration of the mixture in the unmelted state are determined), as well as in the casting of x) The initial thickness of the layer is 75 mm;

Continued table. one

22 1430 0.25 1.5

15 1420 0.25 1.5

34 1430 0.25 1.5

1430 0.25 1.5

22 1380 0.25 15

22 1420 0.15 1.5

22 1430 0.5 10.0

mental heats (at the same time, the change in the layer thickness in time and the ability of the mixture after entering to spread on the metal mirror) are recorded. The test results are given in table. 2

table 2

The obtained data testify both about the validity of the chosen limits of the content of the components of the mixture, and its higher efficiency compared to the known one;

Claims (1)

1. USSR author's certificate 348288, cl. On 22 D 27/04, 1970.