RU2720413C1 - Method for bottom blowing of liquid metal in ladle - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy and can be used for bottom blowing of liquid metal by gas in ladle using two tuyeres in one socket unit. Blowing is performed through one tuyere at that working surface of one tuyere is processed with oxygen, through which blowing is performed at the following melting.EFFECT: invention increases service life of the device for bottom blowing of liquid metal when melting steels with low content of non-metallic inclusions.1 cl, 1 dwg

Description

The invention relates to metallurgy and can be used in baking steel by bottom blowing a liquid metal with an inert gas

Steel smelting using bottom purging of liquid metal with gas in the ladle is as follows. Each melting of liquid metal is smelted in a steel-smelting unit (electric arc furnace, converter, open-hearth furnace) and poured into a steel-pouring ladle, in the bottom of which a lance is installed, usually with slotted channels for supplying inert gas to the liquid metal. Inert gas, rising in the liquid metal from the bottom of the bucket upwards, produces its mixing. This allows you to get the finished metal with the required parameters for chemical composition, temperature, content of harmful gases and non-metallic inclusions. The finished liquid metal is poured from the ladle into the molds or on the UNRS with obtaining the necessary rolling billets. The next smelting metal is poured into the empty ladle and the steelmaking process is repeated.

This process is provided only with reliable operation of the lance. However, after casting the metal from the ladle, a layer of slag and metal remains on the working surface of the tuyere, which penetrate the slotted channels to various depths, solidify there and partially or completely clog them. The channels are cleaned with a stream of oxygen supplied through a steel pipe (Patent RU No. 2294968 C21C 5/48 of July 27, 2005). At the same time, significant removal of the lance refractory material from the working surface occurs, and the lance length decreases. The lance can be reduced only to the minimum permissible length. After that, it is replaced with a new one. The resource (duration) of the lance operation is estimated by the number of heats that was carried out with its application before replacing it with a new lance. Therefore, cleaning, as a rule, is carried out according to the best option. First of all, they clean those slotted channels that are clogged to a shallow depth. In most cases, they are enough to supply the right amount of inert gas. This significantly reduces the removal of refractory material from the working surface of the lance.

However, in some steels, for example, in tool, bearing, etc., the content of non-metallic inclusions should be very low. This is achieved by the most intense inert gas purge in the bucket. Therefore, when smelting such steels with an oxygen stream, all slotted channels must be guaranteed to be cleaned, which accordingly sharply increases the wear of the lance. The lance operation time can be reduced by half. To change the lance, the steel pouring ladle is taken out of operation for several days to cool it, remove the worn out lance, install a new lance and then heat the ladle. This complicates the technology of steel production and increases the cost of its production.

Known patent RU No. 173109 V22D 41/58 from 08/09/2016, in which the lance has an increased length and, as a result, its working end faces under the working surface of the bottom of the bucket. An increase in the length of the lance increases its service life. However, the extension of the lance is only possible by a small amount, because part of the lance, which protrudes significantly above the working surface of the bottom of the bucket, is chipped off due to high thermal stresses. The disadvantage of such a lance is a short service life with more intensive oxygen treatment in the production of steels with a low content of non-metallic inclusion.

Known patent RU No. 134090 V22D 41/58 of 08/08/2013, in which two tuyeres are installed in one socket unit, while the working surfaces of these tuyeres are shifted in height relative to each other by 20-150 mm. Moreover, the working surface of the first tuyere is located at the level of the working surface of the nesting unit, and the working surface of the second tuyere is 20-150 mm below the level of the working surface of the nesting block. On the working surface of the second lance to the height of the level of the working surface of the nest block is refractory material without channels for the passage of gas.

The specified design works as follows. At the beginning of operation, gas is supplied only through the first lance (the working surface of which is at the level of the working surface of the nesting block). When cleaning with oxygen after casting each melt, refractory material is removed from the working surfaces of both tuyeres. After working out the working surface of the nesting unit to the level of the working surface of the second lance, the gas supply is switched off through the first lance and gas is blown through the second lance. If the first lance is operable, gas is not disconnected from it and the metal is blown through simultaneously with two lances: the first and second.

Thus, with this method of using a device for purging liquid metal of gases in a bucket, the duration of two tuyeres is equal to the duration of one tuyere, including the smelting of steels with a low content of non-metallic inclusions. This is a disadvantage of this method.

A known method of purging liquid metal, application RU No. 2017137557/02 (062218) (adopted as a prototype), in which inert gas is supplied simultaneously through two or more lances. This achieves a high intensity of mixing of the metal, but the duration of the service life used for this purge device is equal to the service life of the purge device with one lance. This is a disadvantage of this method of purging liquid metal.

The task to which the proposed technical solution is directed is to increase the service life of the device for bottom purging of liquid metal with gas in a ladle during the smelting of steels with a low content of non-metallic inclusions.

In the proposed method of using a device for bottom blowing liquid metal with gas in a ladle, including bottom blowing liquid metal with gas in a ladle using two or more tuyeres in one socket unit and treating the working surfaces of the tuyeres with oxygen, the bottom blowing of liquid metal of each melting is performed through one of the tuyeres , and with this, the working surface of one lance is treated with oxygen, through which the bottom blowing of the liquid metal of the next melting will be carried out.

The proposed method for the use of devices for bottom purging of liquid metal with gas in a bucket is presented using an example of a device with two tuyeres. Liquid metal is smelted in a steelmaking unit. The resulting melting of molten metal is poured into a steel pouring ladle, in the lining of the bottom 1 of which there is a device for purging molten metal with gas in a ladle, drawing. The device consists of two tuyeres 5 (A and B) installed in one socket unit 2. The tuyeres have slotted channels 7 for supplying gas from gas supply tubes 3 to the working surface 8 and further to the molten metal 10.

After casting the metal of the previous melting on the working surface of the lining of the bottom of the bucket, on the working surface of the nesting block and on the working surfaces of the tuyeres, there are frozen slag and metal 9 residues. In most cases, while still in a liquid state, they flow into all or only some of the slotted channels tuyeres A and B to various depths, solidifying there, and clog them. Therefore, before pouring the next smelting metal from the steelmaking unit into the bucket on the working surface, for example, tuyeres B, the remains of slag and metal are removed by the flow of gaseous oxygen supplied from the steel pipe. In this case, the remains of slag and metal on the working surface of the lance And are not removed. On lance B (drawing), dashed lines show the place where the solidified slag and metal were located until they were removed with oxygen. The lance working surface was also in place of the lower dashed line 8 before the oxygen treatment: After oxygen treatment, it sank to the place of the solid line 8. The distance between the dashed and solid lines 8 is the tuyere wear due to one oxygen treatment (after one melting). About the same tuyere wear occurs after each subsequent melting. In order to prevent accidental flow of liquid metal through the lining, the total wear of the plugs should not be lower than line 6, the level of which is determined in practice. After that, the worn lance is replaced with a new one. The number of heats after which the working surface of the lance drops to line 6 characterizes the longevity of the lance (lance resistance).

In the smelting of steels with a low content of non-metallic inclusions, the gas flow through the liquid metal should be the most intense, which is ensured only after all slit channels are completely free of slag and metal. This is achieved only by removing the lining from the working surface of the lance to a considerable height. The lance resistance with this technology is reduced to two times compared with the technology of smelting other steels.

In the proposed method, in the newly lined bucket, the levels of the working surfaces of the tuyeres, the working surface of the nesting block and the working surface of the lining of the bottom of the bucket are approximately in the same plane, within the deviations that a specific technological process allows. After filling the bucket with liquid metal, it is purged with inert gas only through one of the tuyeres. After casting metal from the ladle, a layer of solidified slag and metal residues forms on the working surface of both tuyeres. Partially, they are also located in slotted channels and clog them. Therefore, the working surface of one of the tuyeres, through which it is planned to purge the liquid metal of the next heat, for example, tuyeres B, as indicated in the drawing, is cleaned with oxygen of metal and slag residues. Clogged slotted channels open. In this case, the lance is shortened by the amount of oxygen removed refractory material on its working surface.

Then the next metal melting is poured into the steel pouring ladle from the steelmaking unit (second melting). Inert gas is blown through a lance in which the slotted channels are cleaned. In this case, it is tuyere B. After casting the metal of the second heat, oxygen again cleans the working surface of one of the tuyeres. This should preferably be a lance that was not used to purge the metal of the previous heat. In this case, it is lance A, because she is longer. As a result of its cleaning after casting the second heat, the length of both tuyeres again becomes approximately the same. When gas is blown through subsequent melts, the lances are also used alternately, so that their lengths differ by a minimum value.

In the attached technology, there can be various options for the priority of using tuyeres for supplying inert gas to liquid metal, depending also on the number of them in the socket unit. For instance:

1. The number of tuyeres in the nest block is two, A and B:

- on one heat, gas is supplied through lance B, and on subsequent heat through lance A or vice versa;

- on two consecutive heats, gas is supplied through lance A, and on the next two heats through lance B or vice versa;

- on one heat, gas is supplied through lance B, and on the next two heats through lance A or vice versa;

2. The number of tuyeres in the nest block is three or more:

Any of the possible tuyere sequence options can be applied.

In all of the above options, after casting metal from a ladle with oxygen, the slag and metal residues are cleaned of the working surface of the lance that will be used in the next heat.

Options for applying the priority are determined by the conditions of the technological process of smelting at a particular enterprise. The most important condition for choosing the sequence of application of tuyeres is to ensure the minimum difference in their length. In the event that one lance is much longer than the other, then its lateral surface is in contact with the liquid metal, which can lead to chipping of its upper part.

Thus, the proposed method provides the duration of the device for bottom purging of liquid metal with gas in the bucket equal to the sum of the duration of all tuyeres included in it.

An example of a specific implementation.

The proposed method was used in the production of electric steel, for example, tool and ball bearing grades. The nesting block with two tuyeres was installed in the bottom of a steel-pouring ladle with a capacity of 150 tons. Two identical cone-shaped tuyeres had the following dimensions: height 450 mm, diameter of the bases — lower 189 mm — upper (working) 110 mm. The nesting block had the shape of a flattened ellipse with overall dimensions in the cross section of 500 and 360 mm and a height of 510 mm.

The indicated nesting block was installed in the bottom of the newly lined bucket. After heating the bucket, liquid metal was poured into it from the electric arc furnace (first melting). In the course of melting, the metal was purged through one lance, conventionally designated A. The metal was cast on a continuous steel casting plant. After metal casting and slag discharge at the bottom of the bucket, incl. and on the working surface of the tuyeres there remained a layer of solidified slag and metal 3–15 mm thick. This layer blocked the outgoing ends of the slotted channels. We remove it with the help of gaseous oxygen on the working surface of only one lance, conventionally designated B. Through this lance, a second-molten liquid metal was purged. After its casting, the working surface of lance A was again cleaned and, using it, the liquid metal was purged of the next third melting.

Thus, during the operation of the bucket, both lances were used alternately for purging the liquid metal with argon, and at the same time they were cleaned of residual slag and metal alternately. The duration of the bucket using this technology until it was stopped for repair to replace blowing tuyeres was more than 35 heats. When using one lance, the bucket was stopped for repair after 17-20 heats.

Claims (1)

A method for purging liquid metal with gas in a ladle, including bottom purging of liquid metal with gas in a ladle using two tuyeres in one socket unit and treating the working surfaces of tuyeres with oxygen, characterized in that the bottom purging of liquid metal with each melting is carried out through one of the tuyeres and with oxygen process the working surface of one lance, through which the bottom blowing of the liquid metal of the next heat will be carried out.

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