RU2025202C1 - Method for preparing pouring ladle in the process of continuous steel casting - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: method involves applying 3-5 mm layer of refractory mixture on internal surface of ladle body; laying grog bricks in one layer with the thickness of 4-6 mm and applying refractory mixture to joint surfaces; heating ladle for 1-2 hours to 600-800 C; laying cob tar-dolomite bricks in one layer so that bricks are arranged in parallel annular row over ladle height and in two layers on its bottom without applying refractory mixture to brick joint surfaces; setting space between brick joints within the range of 0.001-0.003 of brick size; heating ladle to 400-500 C at heating rate of 10-20 C/min, then to 800-1000 C for 4-6 hours. Time between emptying and filling of ladle with liquid steel does not exceed 2-6 hours, with temperature of lining during this time being maintained within the range of 900-1000 C. Spaces between brick joints are filled with localized portions of tar-dolomite mixture (in powder fraction) or localized portions of thin strip of soft steel are inserted into these spaces. EFFECT: increased efficiency of method and high quality of product. 3 cl, 1 tbl

Description

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

Closest to the technical essence of the invention is a method of lining and operation of a casting ladle during continuous casting of steel, including subsequent laying along the height and bottom of the metal shell of the ladle with refractory bricks coated with a refractory mixture, heating the lining and maintaining its temperature. At the same time, the ladle is lined with three layers: heat-insulating in the form of sheet asbestos, reinforcing from burnt porous fireclay bricks, and a worker in the form of a ladle burnt fireclay bricks. Laying is carried out along a helix along the height of the bucket. After lining the ladle is heated to a temperature of ^about 900-1100 C and maintained at this temperature until the liner metal and filling it starts continuous steel casting process. After casting, the slag is removed from the ladle, the ladle is cooled, and the working layer of the lining is removed. After laying a new working layer of the lining, the bucket is heated and continued to operate in the process of continuous casting of steel.

 The disadvantage of this method is the low resistance of the casting ladle. This is due to the fact that the lining of the bucket is made of fired chamotte bricks using a refractory coating between them. Under these conditions, when a new lining is heated, deformation of the layers of bricks occurs with the formation of gaps between them. In addition, such a laying of a lining made of fired bricks requires compliance with their geometric dimensions of high accuracy. Fireclay bricks have a relatively low thermal conductivity, which leads to an increase in thermal stresses and deformations in bricks in excess of permissible values. Burnt bricks have considerable strength, as a result of which they cannot deform with respect to each other when shifting during masonry and heating layers of masonry bricks. In addition, chamotte bricks have low resistance to erosion by liquid steel and slag. The foregoing leads to the formation of cracks in the lining, burn-through of bricks with molten steel, which makes it impossible to re-operate the bucket without updating the lining and its repair.

 The technical effect when using the invention is to increase the durability of casting ladles during continuous casting of steel.

 The indicated technical effect is achieved by sequentially stacking along the height and bottom of the metal body of the bucket of refractory bricks with a coating of the refractory mixture, heating the lining and maintaining the temperature of the lining between emptying and pouring the steel of the bucket.

When lining, the inner surface of the bucket body is coated with a refractory mixture of 3 ... 5 mm thick, then one layer of fireclay brick is laid with the surfaces of the joints of bricks 4-6 mm thick and then the bucket is heated for 1 ... 2 hours to a temperature of 600 .. .800 ^о С. After this, unfired pecodolith bricks are laid dry without coating the surfaces of the brick joints in one layer with parallel ring layers along the height of the bucket and in two layers on its bottom. At the same time, at the junction of the bricks, a gap is set within 0.001 ... 0.003 of the size of the brick between the surfaces of the joints of bricks. Thereafter, the ladle heating to a temperature of 400 ... 500 ^{° C} at a speed of 10. ..20 dg / min, then - to a temperature of 800 ... 1000 ^{° C} for 4 ... 6 h period between successive emptying and. pouring molten steel ladle is set to 2 .... 6 hours and lining temperature during this period is maintained in the range 900 ... 1000 ° ^C.

 In addition, the gaps between the surfaces of the joints of the bricks are filled with local sections of the pecodolite mixture of the dust fraction or a thin strip of mild steel tape is installed in these gaps with local sections.

 An increase in the durability of casting ladles will occur as a result of laying the lining of unbaked pecodolite bricks dry without coating, with certain gaps between them. Under these conditions, the bricks are deformed relative to each other and their compaction due to expansion during heating due to the flexibility of the bricks in the unbaked state. Moreover, due to the increased thermal conductivity of pecodolith bricks compared with chamotte bricks, they quickly dry and heat under conditions of increased thermal insulation by chamotte masonry. The absence of refractory grease between the bricks ensures the absence of displacement of the annular layers of masonry relative to each other along the perimeter and height of the bucket. The optimum temperature regime for heating the brick lining provides the necessary conditions for hardening unfired bricks and their strength. The presence of gaps between the bricks within the necessary limits provides the conditions for permissible flow of liquid metal between the bricks with subsequent crystallization, which increases the resistance of the working surface of the masonry from pecodolith bricks. Under these conditions, with an allowable time between successive emptying and filling of each steel-pouring ladle, its multiple re-operation is ensured without destroying the pecodolith masonry of bricks.

 The range of thicknesses of the refractory coating of the inner surface of the metal body of the bucket within 3 ... 5 mm is explained by the laws of deformation of the body during operation of the bucket. At lower values, bricks of fireclay masonry may contact directly with the metal casing of the bucket, which leads to the destruction of the bricks. At large values, the refractory coating is overused, and its self-destruction and collapse are possible.

 The specified range is set in direct proportion to the inner diameter of the metal casing of the bucket at its upper level.

 The range of thicknesses of the layers of the refractory coating between the fireclay bricks within 4 ... 6 mm is explained by the patterns of deformation of the layers of the fireclay brick masonry along the perimeter and height of the bucket. At lower values, the necessary adhesion between the fireclay bricks will not be provided. At large values, bricks can be deformed relative to each other with the formation of gaps between them.

 The specified range is set in direct proportion to the diameter and height of the steel pouring ladle.

 The time range for heating the ladle after lining with fireclay bricks within 1 ... 2 hours is explained by the laws of drying and hardening of refractory coating. At lower values, the refractory coating will not reach the required hardness if the moisture is not completely removed from it. At high values, energy will be spent on heating the bucket without further improving the service properties of the chamotte lining of the bucket.

 The specified range is set in direct proportion to the capacity of the steel pouring ladle.

The heating range of the ladle with fireclay lining in the range of 600 ... 800 ^о С is explained by the laws of hardening and moisture removal from the refractory coating between the bricks and from the bricks themselves. At lower values, moisture will remain in the coating and bricks due to the hygroscopicity of these materials. At large values in the coating and bricks, temperature gradients and thermal stresses and deformations occur that exceed permissible values, which leads to failure of the fireclay lining.

 The specified range is set in direct proportion to the capacity of the steel pouring ladle.

 The laying of unbaked pecodolith bricks in one layer along the height of the bucket and in two layers on its bottom is explained by the laws of the action of liquid steel and its jet when filling the bucket on the surface of the refractory lining during successive emptying and filling with liquid steel under continuous casting with the "fusion melting" method successive change of steel casting ladles in a continuous casting plant.

 The range of gaps between pecodolite bricks at their joints within 0.001 ... 0.003 of the size of the brick between the surfaces of the joints of bricks is explained by the laws of expansion of bricks during their heating and operation. At lower values, deformation of the bricks will occur when they are heated above the permissible values, which will lead to the destruction of the bricks. In addition, liquid metal will not flow into such gaps. At large values, gaps between the bricks will be formed, exceeding the permissible values.

 The specified range is set in direct proportion to the size of the brick between the surfaces of the joints.

The range of preliminary heating of the bucket with pecodolite lining up to 400. ..500 ^о С is explained by the laws of coking pitch pitch in bricks. At lower values, the required strength of the coked refractory brick will not be provided. At large values, temperature gradients and thermal stresses will occur in the bricks material, exceeding the permissible values, leading to crack formation in the bricks.

 The specified range is set in direct proportion to the dimensions of the brick between the edges of the joint.

 The range of speeds for preheating a bucket with pecodolite lining within 10 ... 20 deg / min is explained by the laws of the pyrolysis process of coal tar pitch, which is part of pecodolite bricks. At lower values, the process of coking coal tar pitch in full will not occur, which will lead to a decrease in the strength of bricks. At large values, temperature gradients and thermal stresses will occur in the bricks material, exceeding the permissible values, leading to crack formation in the bricks.

 The specified range is set in inverse proportion to the dimensions of the brick.

The range of subsequent heating of the bucket with pecodolite lining up to 800 ... 1000 ^о С is explained by the laws of the complete removal of moisture from the bricks and their hardening. At lower values, moisture will not be completely removed from the material of the bricks, the bricks will not have the necessary strength. At high values, energy will be spent on heating the bucket without further improving the service properties of the pecodolite lining.

 The specified range is set in direct proportion to the capacity of the steel pouring ladle.

 The time range for subsequent heating of the bucket with pecodolomite lining within 4. ..6 h is explained by the laws of complete moisture removal from pecodolomite bricks, the acquisition of the necessary strength by them, and the complete end of deformation phenomena in bricks and in their annular layers along the perimeter and height of the bucket. At lower values, completely mutual deformation between the bricks in the annular layers will not occur, and the masonry as a whole will not reach the required strength. At high values, energy will be spent on heating the bucket without further improving the service properties of the pecodolite lining.

 The specified range is set in direct proportion to the capacity of the steel pouring ladle.

 The time interval between successive emptying and filling the ladle with liquid steel within 2 ... 6 hours is explained by the laws of cooling of the pecodolite lining after the end of the next process of continuous casting of steel. At large values in the material of the pecodolith bricks and in the joints between them, irreversible structural changes will occur that will lead to a decrease in the number of re-use of the bucket. At lower values, the time for preparing the bucket for the next use is reduced in excess of the permissible values.

 The specified range is set in direct proportion to the capacity of the steel pouring ladle.

The range of maintaining the temperature of the ladle lining between castings within 900 ... 1000 ^о С is explained by the laws of cooling the ladle lining and heat transfer through it. At lower values, gaps will form at the joints of the bricks. At high values, energy will be spent on heating the bucket without further improving its performance during repeated use.

 The specified range is set in direct proportion to the capacity of the steel pouring ladle.

 Analysis of scientific, technical and patent literature shows the lack of coincidence of the distinctive features of the proposed method with the signs of known technical solutions. Based on this, it is concluded that the claimed technical solution meets the criterion of "inventive step".

 An embodiment of the invention is given that does not exclude others within the scope of the claims.

 The method of lining and operation of the casting ladle during continuous casting of steel is as follows.

 PRI me R. In the process of lining the steel-pouring ladle, the refractory bricks are coated with the height and bottom of the metal case of the ladle and coated with the refractory mixture, then the lining is heated and the lining temperature is maintained between emptying and pouring the ladle steel.

When lining, the inner surface of the bucket body is coated with a refractory mixture in the form of a fireclay mortar mixed in water with a thickness of 3 ... 5 mm. Then they lay one layer of burnt bucket brick with coating of the surfaces of the joints of bricks with a thickness of 4 ... 6 mm. After that, the bucket with chamotte lining is heated with gas burners for 1 ... 2 hours to a temperature of 600. ..800 ^о С. Then unbaked pecodolith bricks are laid dry without coating the surfaces of the brick joints in one layer with parallel ring layers along the height of the bucket and in two layers on its bottom. The masonry, located along the height of the bucket, is laid around the perimeter on a two-layer brickwork on the bottom.

 At the junction of pecodolite bricks, a gap of 0.001 is set. ..0,003 the size of a brick between the surfaces of the joints. The gap is established by local backfilling with local areas between the mating surfaces of the bricks of the pecodolite mixture of the dust fraction. The same gaps in another embodiment form by installing local sections between the mating surfaces of bricks of individual pieces of thin strips of mild steel tape, for example 08Yu.

 At the same time, a gap of 20 ... 40 mm in direct proportion to the height of the bucket is left between the upper flange of the metal body of the bucket and the laying of bricks. This gap is filled with mullite mass, which makes it possible to expand the brickwork upwards when it is heated. The expansion of the ring masonry during heating in the transverse direction is compensated by the deformation of the bricks, which creates efforts to clamp the rings of bricks to the inner surface of the fireclay masonry and further to the bucket body. This leads to hardening of the joints of bricks and increase the service life of the entire lining, as well as to reduce the pressure of bricks on the bottom of the bucket due to the taper of the side walls of the bucket.

After laying the bricks is carried pekodolomitovyh heating the ladle by gas burners to a temperature of 400 ... 500 ^{° C} at a rate of 10 ... 20 ° C / min, and then - to a temperature of 800 ... 1000 ^{° C} for 4 ... 6 hours

 Then the ladle is filled with 3sp grade liquid steel from a steel casting unit, for example from a converter, and the process of continuous casting is started. In the process of filling the bucket with liquid steel, the latter penetrates into the existing gaps between the pecodolith bricks and, due to their increased thermal conductivity, hardens in the gaps. The latter is a condition for eliminating the penetration of steel further to fireclay bricks and, thereby, burn through the lining.

After continuous pouring and emptying of the ladle, slag is drained from it, the pouring nozzle is cleaned and the slide gate is routinely inspected. In this case, the period between successive emptying and filling the ladle with liquid steel is set to no more than 2 ... 6 hours, and the temperature of the lining during this period is maintained within 900 ... 1000 ^о С using gas burners under the covered ladle lid. After this time, the bucket is reused several times.

 The table shows examples of the method of lining and operation of the casting ladle during continuous casting of steel with various technological parameters.

 In the first example, due to the small gaps between the pecodolith bricks, steel does not flow in them, which leads to their mutual sintering and crack formation during deformation. The small thickness of the coating between the fireclay bricks does not provide their necessary adhesion. The small thickness of the coating of the inner surface of the bucket body leads to a violation of the continuity of fireclay bricks. Insufficient heating temperature of the lining leads to incomplete removal of the flags from it. A high heating rate leads to cracking in the lining. The above leads to a decrease in the durability of the bucket.

 In the fifth example, due to the large gaps between the pecodolith bricks, cracks are formed between them despite the flow of liquid steel in them. In combination with a large coating of chamotte bricks, this leads to burn-through of the lining and the bucket body. Increased heating of the lining for a long time leads to an excessive consumption of energy for heating the bucket.

 In the sixth example (prototype) due to the lack of lining of unfired bricks, laid dry without coating, the coating between the chamotte bricks is destroyed. Due to the low thermal conductivity of fireclay bricks, cracking occurs in them during heating and under the influence of liquid steel. At the same time, chamotte bricks have low resistance to erosion by liquid steel and slag. The foregoing leads to the destruction of the lining of the bucket and its quick exit from work, making the reuse of buckets impossible.

 In examples 2-4, due to the use of a lining made of unbaked pecodolite bricks, laid dry without coating with a certain gap of optimal size, the bricks are deformed relative to each other when they expand during heating, which ensures the necessary masonry density. In this case, the partial flow of liquid metal into the gaps between the bricks and its subsequent crystallization due to the relatively high thermal conductivity of the pecodolith bricks provides further lining compaction, which prevents the subsequent flow of metal to the fireclay bricks. The regulated heating of the lining and the sequence of changing the processes of emptying and pouring ladles with molten steel provide an increase in their durability, as well as conditions for reuse.

 The application of the proposed method allows to increase the resistance of steel casting ladles during continuous casting by the method of "melt to melt" from 5-10 to 40-50 heats. The economic effect is calculated in comparison with the base object, for which the method of lining and operation of casting ladles for continuous casting of steel used at the Novolipetsk Metallurgical Plant is accepted.

Claims (3)

1. METHOD FOR PREPARING A TILLING BUCKET AT CONTINUOUS CASTING OF STEEL, including sequential laying along the height and bottom of the metal casing of the bucket of refractory bricks with a coating of refractory mixture, heating the lining and maintaining the temperature of the lining between emptying and pouring the steel of the bucket, characterized in that refractory mixture with a thickness of 3-5 mm, then lay one layer of fireclay bricks with the coating of the surfaces of the joints of bricks with a thickness of 4-6 mm and then heat the bucket for 1 - 2 hours to a temperature of 600 - 800 ^o С, after which unbaked pecodolomite bricks are laid dry without coating the surfaces of the joints of bricks in one layer with parallel ring layers along the height of the bucket and in two layers on its bottom, while a gap is established at the joints of bricks within 0.001 - 0.003 of the size of the brick between the surfaces of the joints of bricks, after which the bucket is heated to a temperature of 400 - 500 ^o C at a speed of 10 - 20 deg / min, and then to a temperature of 800 - 1000 ^o C for 4 to 6 hours, and the period between successive emptying and AliViya ladle molten steel adjusted to 2 - 6 hours and lining temperature during this period is maintained in the range 900 - 1000 ^o C.  2. The method according to claim 1, characterized in that the gaps between the surfaces of the joints of the bricks are filled with local areas of the pecodolite mixture of the dust fraction.  3. The method according to claim 1, characterized in that in the gaps between the surfaces of the joints of the bricks, a thin strip of mild steel tape is installed in local areas.

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