RU2365462C1 - Method of secondary cooling in course of continuous casting of metals (versions) - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: surface of the ingot drawn from the mould is cooled with air-water mixture obtained by spraying a flow of water containing surface-active agents. The oxygen content in the air-water mixture is 5-10%. The content of oxygen can be reduced by supplying carbon monoxide or nitrogen oxide or carbon dioxide or argon into the compressed air flow. Concentration of the surface-active agents in the water flow is 0.001-0.01% of the amount of the water supplied for the secondary cooling. The ingot surface minor radius can be cooled with air-water mixture containing argon and the major radius can be cooled with air-water mixture containing nitrogen. In the second version of the invention the ingot surface is cooled with air-gas mixture obtained by spraying the water flow with compressed carbon monoxide or nitrogen oxide or carbon dioxide or argon in any combinations. In the course of cooling the amount of sucked discharge air-water mixture is reduced to 20% of its nominal value.

EFFECT: increased output of the suitable metal because of reduced amount of the oxide scale forming on the ingot surface.

10 cl, 4 dwg, 3 tbl, 5 ex

Description

The invention relates to metallurgy, and more particularly to secondary cooling during continuous casting of metals.

During continuous casting, molten metal is fed into the mold of the continuous casting machine (MLNZ), an ingot (billet) is drawn from it, the ingot is moved to the secondary cooling hopper by means of supporting rollers with variable speed, the surface of the ingot is cooled with a water-air mixture sprayed by nozzles, and suction generated zone of secondary cooling of steam and remove condensed water. Known methods for the secondary cooling of continuously cast billets, including supplying a water-air mixture to an extruded ingot, differing in the modes of supplying a water-air mixture (SU 1196119, 1985.12.07, SU 1556810, 1990.04.15, RU 1110011, 1994.08.30, RU 2043843, 1995.09.20 and others, IPC B22D 11/124). A common disadvantage of the known methods of secondary cooling is the active formation of scale on the surface of the ingot due to the excess oxygen content in the water-air mixture, as well as the excessive intake of air from the atmosphere into the secondary cooling hopper when steam is removed from it. It is known that the total metal loss to scale during continuous casting of metal is 1-2% of the mass of liquid metal supplied to the mold.

In known operating continuous casting machines, for example continuous casting machine No. 2, Uralmashzavod, 1980, in order to maintain the crust of the ingot from expansion, the pitch of the supporting ingot during drawing of the rollers was reduced, which required a reduction in their diameter and the gap between them. This led to difficulties in removing the scale formed during the secondary cooling process through reduced gaps between the supporting rollers, while the gaps are clogged with scale, and this in turn leads to jamming of the supporting rollers and even to their breakdown. In addition, the scale accumulating in the gaps presses on the crust of the hardened ingot and breaks it, and a breakthrough of liquid metal to the surface of the ingot occurs, which leads to accidents.

To reduce the bending of long support rollers in subsequent continuous casting machine models, for example, continuous casting machine No. 5, Uralmashzavod, 1989, the supporting rollers are made integral and are supported by additional supports. This solution significantly complicates the design and does not exclude the breakthrough of liquid metal on the surface of the ingot under the influence of scale.

There is a method of protecting hot metal from oxidation, which consists in applying to its surface a composition that forms a protective film and contains an alkali metal silicate, an oxidation inhibitor, water and silicon dioxide (RU 9402755, 1996.05.20, IPC C21D 1/68). The disadvantage of this method is the need for the introduction of additional operations and, therefore, additional equipment in the process, which is difficult in the framework of existing industries. The creation of a new technological process and new equipment requires additional capital costs.

The closest analogue of the present invention in technical essence and the achieved effect is a method of secondary cooling during continuous casting of metals, which includes cooling the surface of the ingot with a water-air mixture containing surfactants (SU 1556810, IPC B22D 11/124, 1990,04.15). The addition of surfactants to the cooling water-air mixture allows to improve the quality of the ingots and simultaneously slightly reduce the activity of the formation of scale on the surface of the ingot, since the foam formed during the supply of the air-air mixture limits the flow of oxygen to its surface. However, this decrease in the scale formation activity is insignificant and the metal loss during continuous casting remains large. As the applicant knows, the task of combating the appearance of scale on the surface of the ingot during the continuous casting was not solved separately.

The technical task of the present invention is to reduce metal loss during continuous casting by reducing the formation of scale on the surface of the cooled ingot.

The problem is solved in the method of secondary cooling, including cooling the surface of the ingot drawn from the mold with a water-air mixture obtained by spraying a stream of water containing surfactants with a stream of compressed air, and suction of the spent water-air mixture, in which according to the invention cooling the surface of the ingot drawn from the mold carry out a water-air mixture having an oxygen concentration of 5-10%, which is obtained by supplying a stream of water before spraying into the compressed air stream of carbon monoxide or nitrogen, or carbon dioxide, or argon, while the concentration of surfactants in the water stream is 0.001-0.01% of the volume of water supplied for secondary cooling.

The water-air mixture may preferably contain, in volume parts:

air 0.8 carbon monoxide 0.2

or

air 0.7 nitrogen 0.3,

or

air 0.5 carbon dioxide 0.5.

In one embodiment of the method, the cooling of the surface of the ingot over a small radius is carried out with a water-air mixture obtained by supplying argon to the compressed air stream, and the cooling of the surface of the ingot over a large radius is carried out with a water-air mixture obtained by supplying nitrogen to the compressed air stream, while the air-water mixture supplied along a small radius, it may contain, in bulk parts:

air 0.88 argon 0.12

and the air-water mixture supplied over a large radius may contain, in volume parts:

air 0.67 nitrogen 0.33.

In the process of cooling, the suction capacity of the vapor-gas mixture formed during cooling is reduced to 55-20% of its nominal value.

The supply of carbon monoxide and / or nitrogen and / or carbon dioxide and / or argon to any compressed air stream in any combination of these can reduce the oxygen concentration in the resulting water-gas mixture from 21 to 5-10% and, together with the presence of surfactants, significantly reduce the activity of scale formation: from 1-2 to 0.5%. The indicated amounts of components of the water-gas mixture are optimal, but not limiting. The composition of a particular water-gas mixture is selected for a particular production, based on reasons of economy and / or safety. It is economically feasible to use gases, which are associated gases for this production, that is, gases obtained in other technological processes and which can be used to reduce the oxygen content in the air-water mixture without large capital expenditures. The security issue concerns mainly the use of argon because of its specific effect on the human body, therefore the use of argon in large quantities requires additional measures to ensure the tightness of the equipment.

Experimental data obtained under the conditions of OJSC Severstal showed that the content of surface-active substances (surfactants) in a water-gas mixture can be reduced by an order of magnitude compared to the closest analogue without compromising the process. Figure 1 shows the relationship between the lifetime of the foam bubble and the concentration of surfactants, and figure 2 shows the dependence of the reactivity of the foam (the possibility of re-foaming) on the concentration of surfactants. With a reactivity of less than 1, the foam is not re-formed; with a reactivity of 1 to 2, the foam is re-formed. The selected range of surfactant content (0.001-0.01%) in the water-gas mixture provides a screen effect of protecting the surface of the ingot from the formation of scale and avoids re-foaming of the suction water when it is cooled in the cooling tower.

The supply of various gas-gas mixtures over large and small radii allows using specific gravities of gases for better insulation of the surface of the ingot, therefore it is more advantageous to supply a mixture containing heavier gas (argon) from above (along a small radius) and a lighter gas below (along a large radius) (nitrogen).

As a result of the contact of the water-air mixture with the ingot, steam is formed during the cooling process. In the presence of a surfactant and the formation of a foam bag around the ingot, the vapor condenses, destroying the bubbles of the foam. At a surfactant concentration of 0.001-0.01%, the process of foam destruction and vapor condensation is optimal, that is, the amount of foam generated is sufficient to condense a larger amount of steam, therefore, the steam suction capacity can be reduced to 55-20% of its nominal value, and this leads to a decrease power consumption.

In a second embodiment of the invention, the surface of the ingot drawn from the mold is cooled by a water-gas mixture obtained by spraying a water stream with a stream of compressed carbon monoxide or nitrogen or carbon dioxide or argon, while the concentration of surfactants in the water stream is 0.001-0.01% from the volume of water supplied for secondary cooling.

The gas-gas mixture supplied over a small radius may contain argon, and the gas-water mixture supplied over a large radius may contain nitrogen.

In the second embodiment of the invention, the formation of scale occurs only due to the suction of air from the atmosphere, since the supply of air containing oxygen is excluded. However, this method is more expensive for the reasons mentioned above.

The invention is illustrated by examples with reference to the accompanying drawings, which schematically shows the following.

Figure 1 - the relationship between the amount of scale formed on the surface of the ingot and the oxygen content in the water-air mixture.

Figure 2 - the relationship between the concentration of surfactants and the average lifetime of the foam bubble.

Figure 3 - the relationship between the reactivity of the foam and the concentration of surfactants.

Figure 4 is a functional diagram of the cooling of the ingot.

The machine for continuous casting of billets (MLNZ) contains a mold 1 into which liquid metal 2 is fed, an ingot 3 (billet) is drawn from it. In the secondary cooling hopper 4, the ingot 3 is moved by means of variable speed supporting rollers 5, sections 1c-9c. The surface of the ingot 3 is cooled in sections 1c-9c by the air-water mixture sprayed by the nozzles in the area of the supporting rollers 5, the steam 6 formed in the secondary cooling zone is sucked off and condensed water is removed.

In the first embodiment (examples 1-3), the ingot was cooled with a water-air mixture with a low oxygen content, in the second embodiment it was cooled with pure nitrogen. The total volume of the water-air (water-gas) mixture in all examples was 1800 m ³ .

Example 1

366 tons of 08Yu steel were poured into the mold. The ingot with a size of 250 × 1540 mm was cooled by a water-air mixture containing 1440 m ^{3 of} air and 360 m ³ of carbon monoxide (0.8 and 0.2 volume parts, respectively), while the residual oxygen in the gas mixture was 5%. The concentration of surfactants in the water stream was 0.001% of the volume of water supplied for secondary cooling. The steam suction performance was 20% of the nominal value. The yield of metal was 365.085 tons, while the total amount of dross was 0.25% of the weight of the heat (0.915 tons).

The process modes are shown in table 1, which shows the speed of movement of the ingot in sections 1s-9s, the flow rates of water and air-water mixture supplied over a large radius R and a small radius r.

Example 2

372 tons of S235 steel were poured into the mold. The ingot with a size of 250 × 1540 mm was cooled by a water-air mixture containing 1260 m ^{3 of} air and 540 m ^{3 of} nitrogen (0.7 and 0.3 volume parts, respectively), while the residual oxygen in the gas mixture was 10%. The concentration of surfactants in the water stream was 0.005% of the volume of water supplied for secondary cooling. The steam suction performance was 40% of the nominal value. The yield of metal was 370.14 tons, while the total amount of dross was 0.5% by weight of the heat (1.86 tons).

The process modes are shown in table 2.

Example 3

371 tons of 10G2FB grade steel were poured into the mold. The ingot with a size of 250 × 1540 mm was cooled by a water-air mixture containing 900 m ^{3 of} air and 900 m ³ of carbon dioxide (0.5 and 0.5 volume parts, respectively), while the residual oxygen in the gas mixture was 10%. The concentration of surfactants in the water stream was 0.009% of the volume of water supplied for secondary cooling. The steam suction performance was 55% of the nominal value. The yield of metal was 369.145 tons, while the total amount of dross was 0.5% of the weight of the heat (1.855 tons).

The process modes are shown in table 3.

Example 4

366 tons of 08Yu steel were poured into the mold. The ingot with a size of 250 × 1540 mm was cooled over a large radius R with a water-air mixture containing 800 m ^{3 of} air and 100 m ^{3 of} argon (0.88 and 0.12 volume parts, respectively), and over a small radius r with a water-air mixture containing 600 m ³ air and 300 m ³ nitrogen (0.67 and 0.33 volume parts, respectively). The concentration of surfactants in the water stream was 0.001% of the volume of water supplied for secondary cooling. The steam suction performance was 20% of the nominal value. The yield of metal was 366.085 tons, while the total amount of dross was 0.25% of the weight of the heat (0.915 tons).

The process modes are similar to those shown in table 1.

Example 5

372 tons of S235 steel were poured into the mold. The ingot 250 × 1540 mm in size was cooled by a water-gas mixture containing 1800 m ^{3 of} nitrogen (pure nitrogen instead of air). The concentration of surfactants in the water stream was 0.005% of the volume of water supplied for secondary cooling. The steam suction performance was 40% of the nominal value. The yield of metal was 370.47 tons, while the total amount of scale was 0.45% of the weight of the heat (1.53 tons).

The process modes are similar to those shown in table 2.

From the above examples it follows that the method according to the present invention allows to increase the yield of metal by reducing the activity of scale formation during secondary cooling of the ingot by an average of 1.6%. In addition, the energy intensity of the process is reduced by a factor of two due to a decrease in steam suction performance.

Table 1 Speed m / min Butt ends cc ^* 1s water 2 centuries 3rd cc 4th cc 5c cc 6c cc 7c cc 8c cc 9c centuries l (p) r R r R r R r R r R r R r R r R r R 0.20 0.00 4.00 4.00 0.30 0.00 4.00 4.00 1,50 1,50 0.40 0.22 5.00 5.00 2,38 2,38 0.50 0.55 5.60 5.60 2,52 2,52 1,56 1,56 0.93 0.97 0.60 1.20 6.20 6.20 3.12 3.31 2.40 2.40 1.38 1.45 0.70 1.75 6.50 6.50 4.00 4.00 4.25 4.25 3.29 3.46 2.43 2.70 1.92 2.19 0.80 2.00 6.80 6.80 4.60 4.60 5.19 5.19 3.99 4.19 3.09 3.39 2.48 2.85 2.00 2.40 0.90 2.00 7.10 7.10 4.80 4.80 6.08 6.08 4.61 4.87 3.65 4.03 3.02 3.46 2,38 2.85 1.00 2.00 8.00 8.00 5.00 5.00 6.82 6.82 5.19 5.45 4.19 4.61 3.49 4.02 2.80 3.36 2,36 2.95 1.10 2.00 8.00 8.00 5.55 5.55 7.52 7.52 5.60 5.91 4.68 5.15 3.95 4.46 3.18 3.83 2.73 3.41 2,52 3.28 1.20 2.00 8.00 8.00 5.65 5.65 8.00 8.00 6.18 6.52 5.12 5.63 4.37 5.03 3,55 4.25 3.08 3.85 2.89 3.75 1.30 2.26 8.00 8.00 5.75 5.75 8.00 8.00 6.76 7.13 5.54 6.09 4.78 5.49 3.88 4.67 3.41 4.25 3.23 4.20 1.40 2.69 8.00 8.00 5.85 5.85 8.00 8.00 7.26 7.66 5.96 6.55 5.15 5.91 4.20 5.04 3.71 4.63 3,55 4.62 1,50 3.15 8.00 8.00 5.94 5.94 8.00 8.00 7.84 8.00 6.38 7.00 5.60 6.43 4.49 5.40 4.00 5.00 3.85 5.01 1,60 3.66 8.00 8.00 6.05 6.05 8.00 8.00 8.00 8.00 6.83 7.50 6.10 7.00 4.77 5.74 4.27 5.35 4.14 5.39 ^* - vv - water-air or water-gas mixture

table 2 Speed m / min Butt ends cc ^* 1s water 2nd cc 3rd cc 4th cc 5c cc 6c cc 7c cc 8c cc 9c centuries l (p) r R r R r R r R r R r R r R r R r R 0.10 0.00 4.0 4.0 0.20 0.00 4.0 4.0 0.30 0.00 4.0 4.0 0.40 0.00 5,0 5,0 2,38 2,38 0.50 0.00 5,6 5,6 2,52 2,52 1,56 1,56 0.83 0.87 0.60 1.10 6.2 6.2 3.13 3.13 2.40 2.40 0.87 0.91 0.70 1.20 6.5 6.5 3.30 3.30 2.62 2.62 0.96 1.01 0.64 0.70 0.80 1.30 6.8 6.8 3.40 3.40 2.70 2.70 1.42 1.49 0.68 0.74 0.64 0.74 0.90 1.40 7.1 7.1 3.46 3.46 2.76 2.76 186 1.95 0.96 1.05 0.67 0.77 0.56 0.67 1.00 1,50 7.1 7.1 3.56 3.56 2.90 2.90 2.26 2,37 1.24 1.36 0.91 1,04 0.69 0.83 0.56 0.70 1.10 1,50 7.1 7.1 3.65 3.65 3.36 3.36 2.64 2.77 1,50 1.65 1.14 1.32 0.90 1,08 0.68 0.86 1.20 1,50 7.1 7.1 3.89 3.89 3.75 3.75 3.00 3.15 1.74 1.92 1.37 1,57 1.10 1.32 0.87 1,08 1.30 1,50 7.1 7.1 4.15 4.15 4.18 4.18 3.34 3,51 1.99 2.19 1,59 1.83 1.29 1.55 1.05 1.31 1.40 1,50 7.1 7.1 4,59 4,59 4,54 4,54 3.64 3.82 2.21 2.43 1.80 2.07 1.48 1.77 1.22 1,52 1.88 2.44 1,50 1,50 7.1 7.1 4.74 4.74 4.92 4.92 3.94 4.14 2.42 2.66 1.99 2.29 1.65 1.99 1.39 1.73 2.18 2.84 1,60 1,50 7.1 7.1 5.00 5.00 5.26 5.26 4.20 4.41 2.62 2.88 1.19 2,51 1.83 2.19 1.55 1.94 2.48 3.23 ^* - vv - water-air or water-gas mixture

Table 3 Speed m / min Butt ends cc ^* 1s water 2 centuries 3rd cc 4th cc 5c cc 6c cc 7c cc 8c cc 9c centuries l (p) r R r R r R r R r R r R r R r R r R 0.10 0.00 4.0 4.0 0.20 0.00 4.0 4.0 0.30 0.00 4.0 4.0 0.40 0.00 5,0 5,0 2.27 2.27 0.50 0.00 5,6 5,6 2.40 2.40 1,04 1,04 0.60 1.10 6.2 6.2 2,53 2,53 1.80 1.80 0.64 0.67 0.70 1.20 6.5 6.5 2.68 2.68 1.80 1.80 0.64 0.67 0.80 1.30 6.8 6.8 2.75 2.75 1.80 1.80 0.64 0.67 0.64 0.70 0.90 1.40 7.1 7.1 2.80 2.80 1.80 1.80 0.66 0.69 0.64 0.70 1.00 1,50 7.1 7.1 2.88 2.88 1.80 1.80 0.94 0.98 0.64 0.70 1.10 1,50 7.1 7.1 2.95 2.95 1.80 1.80 1.21 1.27 0.70 0.77 0.64 0.74 0.56 0.67 1.20 1,50 7.1 7.1 3.15 3.15 1.85 1.85 1.45 1,52 0.91 1.00 0.64 0.74 0.56 0.67 0.56 0.70 1.30 1,50 7.1 7.1 3.36 3.36 2.12 2.12 1.71 1.79 1.13 1.24 0.79 0.91 0.59 0.71 0.56 0.70 1.40 1,50 7.1 7.1 3.61 3.61 2,36 2,36 1.94 1,04 1.34 1.47 0.98 1.12 0.75 0.90 0.56 0.70 0.96 1.25 1,50 1,50 7.1 7.1 3.83 3.83 2.60 2.60 2.17 2.28 1,54 1.70 1.16 1.34 0.91 1.09 0.71 0.88 1.00 1.30 1,60 1,50 7.1 7.1 4.04 4.04 2.82 2.82 2,38 2,50 1.74 1.91 1.34 1,54 1,07 1.29 0.85 1.06 1.27 1.65 ^* - vv - water-air or water-gas mixture

Claims (10)

1. The method of secondary cooling during continuous casting of metals, comprising cooling the surface of the ingot drawn from the mold with a water-air mixture obtained by spraying a stream of water containing surfactants with a stream of compressed air and suction of the spent water-air mixture, characterized in that cooling the surface of the bar drawn from the mold the ingot is carried out with a water-air mixture having an oxygen concentration of 5-10%, which is obtained by feeding a stream of water into the pot before spraying to compressed air, carbon monoxide, or nitrogen, or carbon dioxide, or argon, while the concentration of surfactants in the water stream is 0.001-0.01% of the volume supplied to the secondary cooling water. 2. The method according to claim 1, characterized in that the water-air mixture contains, ob.ch .:
Air 0.8 Carbon monoxide 0.2 3. The method according to claim 1, characterized in that the air-water mixture contains, in ob.ch .:
Air 0.7 Nitrogen 0.3 4. The method according to claim 1, characterized in that the water-air mixture contains, ob.ch .:
Air 0.5 Carbon dioxide 0.5 5. The method according to claim 1, characterized in that the cooling of the surface of the ingot along a small radius is carried out by a water-air mixture obtained by supplying argon to the compressed air stream, and the cooling of the surface of the ingot along a large radius is carried out by a water-air mixture obtained by feeding nitrogen into the stream of compressed air . 6. The method according to claim 5, characterized in that the air-water mixture supplied along a small radius contains, ob.ch .:
Air 0.88 Argon 0.12
and the air-water mixture supplied over a large radius contains, ob.ch .:
Air 0.67 Nitrogen 0.33 7. The method according to any one of claims 1 to 6, characterized in that during the cooling process, the suction of the spent water-air mixture is reduced to 55-20% of its nominal value. 8. A method of secondary cooling during continuous casting of metals, comprising cooling the surface of the ingot drawn from the crystallizer by a water-gas mixture obtained by spraying a stream of water containing surfactants with a stream of compressed gas, and suction of the spent water-gas mixture, characterized in that cooling the surface of the drawn from the ingot mold is carried out by a water-gas mixture obtained by spraying a stream of water with a stream of compressed carbon monoxide, or nitrogen, or carbon dioxide, or argon, while the concentration of surfactants in the water stream is 0.001-0.01% of the volume of water supplied for secondary cooling. 9. The method according to claim 8, characterized in that the water-gas mixture supplied to the surface of the ingot along a small radius contains argon, and the water-gas mixture supplied over a large radius contains nitrogen. 10. The method of claim 8 or 9, characterized in that during the cooling process, the suction of the spent water-gas mixture is reduced to 55-20% of its nominal value.

Images