DE2444794A1 - Continuous casting of steel - using steam-cooling instead of water to increase prodn., or reduce size of casting machine - Google Patents

Abstract

Cooling the billet in a continuous casting plant in which wet steam is used for extracting heat from the continuous billet, by being projected against the outside surfaces of the billet by nozzles. The water content of the wet stream is pref. adjusted to ca. 20% by the injection of water and the outlet velocity of the wet steam through the nozzles is pref. ca. 200 m/s. The cooled steam is pref. fed into both a compressor in the circuit and also into a turbine driving the compressor, the turbine being followed by a condenser which provides water for adjusting the water content of the wet steam. The casting machines can be shorter and of lower height, or the output of existing machines can be increased.

Description

Method for cooling that produced in a continuous steel caster Strands The invention relates to a method for cooling the in a steel continuous casting plant generated strand, in which the strand heat extracting medium means Nozzles is directed against the strand outer sides.

Cast steel strands exist at the exit from the lower collar of the Mold made of a relatively thin, already solidified shell and a still molten shell Core.

It is therefore necessary to use strands of larger formats, in particular Slabs should be cooled as intensively as possible, because the strand only after it has been completely reached can leave the continuous caster in a completely solidified state.

The faster the strand solidifies, the shorter the continuous caster can be can be built or the higher can the line speed with the same length of the system to get voted. The cooling of the strand is of particular importance here the areas in which the shell is still relatively thin because of the heat of solidification of the liquid core heats the shell. In contrast, the surface temperature increases of the strand behind the swamp tip, i.e. in the already solidified area, is essential faster.

The surface temperature of the strand is at the mold exit about 1,2000 C; in the area of the sump tip, the surface temperature is around 8000 C. A large part of the amount of heat contained in the strand is caused by radiation released to the environment. Another part of this amount of heat comes from touch discharged with the usually water-cooled support rollers. Another part of the Heat is added by spraying cooling water onto the strand. Here Efforts have been made to achieve a uniform nozzle design and arrangement by means of a special nozzle configuration and to produce effective cooling, with the even distribution of the cooling water Naturally, limits are set by the necessary support rollers for the strand.

It has now been found that the with the help of sprayed water generated cooling effect is much less than previously assumed, and accordingly, the effort required for this is out of proportion to the success stands. So one has apparently no decisive factor since the amount of cooling water supplied Influence on the cooling effect had originally with 2 1 water / kg steel and a larger amount of cooling water in many cases to 1, or even to 0.5 1 reduced. By far the largest part of the heat contained in the strand is despite the spray cooling dissipated by radiation and heat transfer to the support rollers.

The invention is based on the object of the previously known cooling method to improve, because it is possible with intensified cooling, the continuous caster to shorten or, with the same overall length, higher production output through enlargement the strand speed achieve. To solve the above The object of the invention is to use the above-mentioned method as a cooling medium Use wet steam.

The low cooling effect when water is sprayed onto the cast strand is due to the Leidenfrost1 see phrinoma. This is that at the points of contact of the water droplets hitting the strand A layer of vapor forms, which has an insulating effect that hinders further heat transfer caused. In contrast, with steam cooling with wet steam, the water droplets are in the steam considerably smaller than in spray water and close to the evaporation temperature preheated.

In addition, their impact speed is much greater than this can be achieved when spraying water. For these reasons, almost everything works water contained in the wet steam is converted into steam and thereby removes heat of evaporation from the strand, while with the previous spraying of water, by far the largest part of the water after relatively little heating takes place from the strand.

According to an advantageous proposal of the invention, the water content of the wet steam can be set to approx. 20 lSo. Perner can use the wet steam with a Nozzle exit speed of approx. 200 m / s directed towards the outside of the strand will. The ratios mentioned are achieved by setting the steam pressure accordingly and temperature can be achieved with simple cylindrical pipe sockets as nozzles.

In the computational investigation of the cooling conditions on a Steel slab 2 m wide and 0.25 m thick, which is placed on an arch system with a Casting speed Vg = 1 m / min. is poured, the following values result: Of course Casted amount of steel approx. 220 t.

With the usual spray water cooling, with one liter of cooling water per kilogram of steel used is based on experience based formula the sump tip - beginning of the fully solidified slab section - 32 m behind the mold exit. H. the transition of the Arch in the further horizontal part, at the top of the swamp, must be the arch system have a radius of 20 m.

l for cooling by means of steam instead of water spray cooling 18 nozzles each with a 2 cm diameter between each 2 support rollers at intervals of 0.3 up to 0.5 m on 16 m strand length from the mold. The cooling steam is said to be wet steam with x = 80. Steam content; the pressure in front of the nozzles is 1.5 ata. The hourly amount of steam In this example, the result is the same amount of spray water as 220,000 1. This was chosen so that the comparison between the two types of cooling is clear will.

Assuming that all of the wet steam is on impact converts the hot strand into saturated or superheated steam, results in the calculation a reduction of the casting radius from 20 to 15m. So the casting machine is rebuilding 25% lower and shorter. The smaller overall height and the resulting lower Ferrostatic pressure gives a lighter construction in addition to the smaller one Length of spray water pumps and fans for extracting steam from the casting chamber omitted.

If no appropriate steam is available, the cooling steam be circulated.

An apparatus for performing the method is shown in the figure shown schematically.

1 is a continuous casting machine surrounded by a housing in the usual manner. Nozzles 3 are arranged between the support rollers indicated at 2, through which the wet steam is fed and directed against the cast strand (not shown). The saturated one Steam is for the greater part, e.g. 80 o, fed to a compressor 4, which turns it on the pressure required at the nozzles 3 of e.g.

1.5 sta compressed. The (still) saturated steam enters a mixer 5, where it is converted into wet steam of e.g. x = 0.8 by adding water, the is fed to the nozzles 3 again.

A smaller part of the saturated steam produced during cooling, e.g. 20 @, is passed from the continuous caster through a turbine C, which produces the Compressor 4 drives. The steam reaches a condenser behind the Ikirbine 6 7 and is then available as busatz water for Hischer 5. To promote the condensate to the mixer 5 is used by a pump 8. If necessary, additional water is required can be taken from line 9. The arrangement is supplemented by a data memory 10, from which steam is withdrawn when the continuous caster starts up. Through this arrangement the hot strand provides its own even and intensive cooling.

Claims (6)

Claims 1. Process for cooling the strand produced in a continuous caster, in which the medium extracting heat from the strand is directed against the outside of the strand by means of nozzles is passed, characterized in that wet steam is used as the cooling medium. 2. The method according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the water content of the wet steam can be reduced to approx. 20% is set. 3. The method according to claims 1 and 2, d a d u r c h g e k e n n z e i c h n e t, da, the wet steam with a nozzle exit speed of approx. 200 m / s against the outer sides of the strand. 4. The method according to claims 1 to 3, d a d u r c h g e k e n nz e i c h n e t that when a compressor is switched on, the cooling steam in the circuit to be led. 5. The method according to claims 1, 2 and 4, characterized in that that the drive energy of the compressor with the activation of a steam turbine and a condenser is obtained from the excess steam. 6. The method according to claims 1, 2 and 5, characterized in that that the condensate of the turbine steam again as injection water to generate the wet cooling steam 5 is used. L e r s e i t e