What is the Advantage and Disadvantage of tundish refractories

Refractory Lining of a Continuous Casting Tundish

Refractory Lining of a Continuous Casting Tundish

In the continuous casting (CC) of steels, tundish is a buffer refractory lined vessel which is located between the ladle and the CC mould. The tundish serves the purpose of a reservoir  and a distribution vessel. Over the years, there have been dramatic changes in CC tundish. From a mere reservoir and distribution vessel, the tundish today  is viewed as a steel refining vessel and a totally new field in the process of steel making technology has emerged which is known as tundish metallurgy. Tundish today also fulfills certain metallurgical functions such as feeding of the liquid steel to the mould at a controlled rate, and thermal and chemical homogenization etc. It also focus on the continuous improvement of many quality related parameters such as fluid dynamics, thermal insulation, inclusion floatation and removal, and hydrogen pickup etc.

Different refractories associated with tundish include tundish lining materials (both permanent and working lining), dams and weirs, impact pad, flow control system (monoblock stopper or slide gate), pouring stream protection between tundish and mould (shroud or submerged entry nozzle,SEN), tundish nozzle, and seating block. Dams and weirs are made of magnesite (MgO) boards or alumina (Al2O3) bricks. Liquid steel from tundish to mould is fed by nozzle submerged into molten steel in mould. SEN are to be resistant to corrosion and spalling, Nozzle clogging is also important. Isostatic pressed SEN with alumina graphite-fused silica are commonly used.

Fig 1 shows typical tundish along with its refractories.

Fig 1 Typical tundish along with its refractories

The refractory lining design and quality of refractories used for lining have major influence on the operational parameters of CC machines such as super heat requirements, speed of the machine, the phenomenon like initial cold running stopper, nozzle clogging, tundish through etc. Due to the temperature extremes involved, refractory linings of the tundish are to be designed to withstand thermal shock, prevent thermal loss, prevent oxidation, and resist erosion and corrosion while preventing the liquid steel getting contaminated with unwanted impurities. Selection of refractories for a tundish is also critical due to long casting sequence, faster tundish turnaround, higher campaign life, cleanliness of steel, and because tundish refractories constitute high specific costs in CC operation.

The tundish lining material has a direct influence on the quality of the liquid steel, since it is close to the solidification stage. Tundish working lining remains in contact with steel and erosion is initiated at the liquid steel-air interface with fluctuation of liquid steel level in the tundish. Different metallic oxides present in the liquid steel are the primary eroding agents for the tundish refractory lining. Slag coming in contact with tundish refractory during casting and the tundish covering powder are also responsible for the erosion. The starting point of erosion is the formation of &#;hair cracks&#; at the liquid steel-air interface due to thermal spalling. Penetration of liquid steel and slag takes place through these hair cracks and subsequently erosion occurs. Further, complex interactions at the refractory-liquid steel interface can also impair the steel quality due to the formation of inclusions. Lower erosion of working lining ensures less non-metallic inclusions in the steel.

The refractory lining of a tundish has a defined lifetime depending on the qualities of the lining and the types of tundish slag. Chemical reaction between the refractory working lining layer and the tundish slag is very important especially in the case where there is high sequence casting. The refractory working lining in the tundish is subject to different stresses resulting from the thermo-chemical load. The slag chemistry and slag viscosity play an important role in the wear of the refractory lining. In practice tundish slag composition varies widely even in the duration of a single sequence. Hence none of the refractory compositions gives good performance with all the types of the tundish slags normally encountered during operation.

It is desired that the tundish refractory lining fulfills a number of different functions which includes resistance against liquid steel (high solidus temperature), resistance against tundish slag, low heat conductivity (good thermal isolation properties), good stability (no erosion of refractory during casting), high resistance to thermal shock, chemical inertness, must be disposable after use, and reasonable in price.  Further tundish refractory lining is to have low oxygen potential, good mechanical resistance, low hydrogen pick up by steel, and easy deskulling.

There are several tundish refractory lining practices which are in use. These include (i) brick lining, (ii) gunnable lining, (iii) tundish board lining,  (iv) sprayable tundish lining, and (v) dry tundish lining. Each practice has its advantages and disadvantages both in terms of operations and impact on steel quality. These tundish lining practices are described below.

Brick lining

 Brick lining of tundish came into existence along with the introduction of CC technology for casting of liquid steels in s. This is basically an extension of ladle refractory practices to the tundish. In this type of lining, high alumina bricks are  normally used. The bricks are in direct contact with liquid steel, after preheating.

The advantages of this type of lining  are low risk of pickup of hydrogen by liquid steel, low inventory, no investment in specialized lining equipments, and low risk of lining wash out.

Disadvantages of brick lining are requirement of intensive curing, long tundish preparation time, high labour intensiveness, poor insulation, high thermal conductivity contributing to higher temperature loss, no possibility of cold start, chances of tundish through because of presence of weak joints, difficult stripping of used lining, and the requirement of large numbers of tundishes.

Gunnable lining

Gunnable linings in tundish was initially introduced by the Japanese steel industry for overcoming the problems of the brick lining. In this method the dry refractory powder of the right composition after fluidization is transferred and installed on the tundish wall by using a gunning machine to obtain a monolithic lining. Initially these were alumino-silicate based and later converted to basic type (magnesite based) to assist with metallurgical practice. Conventional tundish gunning materials are designed to have a low strength between deg C to deg C.

This feature assists in formation of a weak zone between the backup lining and the sintered zone, which in turn facilitates easy deskulling. One of the many disadvantages of tundish gunning material is the shrinkage at high temperature which deteriorates the performance of gunning material. A high shrinkage causes high stress and subsequent crack formations during operation whereas a low shrinkage can be a barrier for easy deskulling.

This type of lining  provides a monolithic joint free structure and relatively improved deskulling operations but little is gained with regards to the preheat times or heat losses because of the high density of the gunned linings. This type of lining has a tendency to crack and to spall during rapid preheating and hence the tundish with the gunnable linings cannot be subjected to cold start practices.

The advantages of gunnable lining are low risk of pickup of hydrogen by liquid steel, low inventory, no joints, less labour intensive, relatively easy installation in lesser time, and relatively less difficult to deskull.

Disadvantages of this type of lining are requirement of intensive curing, high wastage because of

rebound losses, poor insulation, no possibility of cold start, high risk of wash out, low thermal stability, dust problems, energy intensiveness, high costs, difficulties in applying variable thickness, and investment needed for gunning equipment.

Tundish board lining

Shortly after the introduction of continuous casting it was realized that some type of disposable lining was re­quired to reduce the refractory costs and improve thermal insulation. Bricks and conventional gunning products were unreliable and provided no ther­mal insulation. The introduction of low density, disposable, pre formed and pre cured tundish boards in mid s offered good thermal insulation and low re­fractory consumption. However the tundish board linings have the disadvantage of  higher man­power and time required for their preparation.

This lining with silica (SiO2) based boards has become popular in the areas where labour costs are low and application technologies are not readily available. The popularity of tundish board lining is also due to its low costs, no need of investment in equipment, and easy to deskull. The use of SiO2 based boards allows only cold start practice.  During s magnesite (MgO) based boards were introduced for fulfilling the requirement of pre-heatability for a hot start practice which is needed for low hydrogen considerations in the manufacture of high alloy quality steels. SiO2 based boards are used for mild steel and MgO boards for special steels and for steels with high calcium content. The reason being silica is attacked by lime, alumina and iron oxide present in the steel.

The advantages of the tundish board lining includes lesser tundish inventory, low hydrogen pick up in case of boards with hot start, uniform shape of the lining, no need for curing, good insulation, possibility of cold start and hence energy savings, easier deskulling, low requirement of energy, no investment needed in equipments, low risk of wash out, and better working environment.

The disadvantages of tundish board lining include presence of joints, sand backing, danger of hydrogen pick up in case of cold start, labour intensive, need of high inventory, problem of handling/breakage, and high cost in case of magnesite based boards.

Sprayable tundish lining

The sprayable tundish lining was first developed in and being used widely since later half of s. Presently it is being used in more than 50 % of tundishes around the world. This type of lining combines successfully many of the advantages of tundish board lining and gunnable lining, while eliminating the disadvantages like &#; joints, sand backing, rebound losses, dust problems, and poor insulation etc. The quality of lining is dependent on skill of the spray operative and the drying equipment.

In sprayable tundish lining a thick slurry of refractory materials is thoroughly mixed and is transported and deposited onto the tundish after atomizing with compressed air. The refractory materials used are mainly MgO and SiO2. The MgO content is usually in the range of 70 % to 90 % with balance percentage of SiO2. For longer duration of sequence casting higher amount of MgO along with higher thickness of the lining is needed. The lining operation can also be  carried out  with robotic application system.

Since homogeneous mixing is done in this lining before the product is applied, the incorporation of special chemical additives is possible which helps to improve thermal stability properties of the lining and  impart good flexibility. For chemical bonding in the sprayed mass, preheating at around deg C is needed.

Sprayable tundish lining has significant advantages of lower density of the lining and better control of the lining thickness when compared with the gunnable linings. In this type of lining normally fibres and other chemicals are added to the refractory mass. The lining is preheated in case of hot start tundish, or is allowed to cool to room temperature and taken as a cold start tundish. The lining integrity is to be ensured during curing and this requires deposit of the lining material on the tundish permanent lining after its temperature is lower than 100 deg C. Being a wet processes using up to 30 % water and  with the presence of hoses and spill-overs, the process creates occupational health and safety issues.

The advantages of sprayable tundish lining  includes low risk of hydrogen picking, absence of joints, lower inventory, lesser labour intensiveness, easy to deskull, good insulation properties, possibility of cold start, and controllable lining thickness.

Disadvantages of lining include requirement of investment in equipments, need of intensive curing, and moderate risk of wash out.

Dry tundish lining

Dry tundish lining was developed at the same time as sprayable tundish lining. However, the high price of phenolic resin powder and associated health and safety issues has resulted into dry tundish linings being used only in a handful of steel plants. Recently resin free binder systems (sodium silicate binder, or glucose binder) have elimi­nated any health and safety issues and in addition the second generation  of dry tundish products have been introduced with significantly reduced tundish prepara­tion time.

Dry tundish lining process differs from other lining processes since it is applied in a dry powder form and does not require the addition of water. Normally this lining makes use of a resinous bond. The added resin is activated by applying a small amount of heat. The forming of lining is carried out by using a former and feeding the dry powder in the gap between the permanent lining and the former. Special drying arrangement is required for drying this mass at around 300 deg C for 24 hours to develop polymerization of resin which gives strength to it.  For the activation of the resin to develop a bond hot air at around 400 deg C is needed.

The need of vibration of the dry powder depends upon the product being used. The dry tundish lining has relatively lower insulation because of its higher density. It needs service of the crane of the tundish bay for its installation. In case of dry lining since no water is used, there is no direct adhesion to the permanent tundish lining. This helps in good deskulling and prolongs life of tundish lining.

One advantage of dry tundish lining is that it ensures slow hydrogen pick up in the steel as it does not require water for application. Around 0.7- 0.9 ppm hydrogen pick up is reported as compared to 1.8 &#; 2.4 ppm in sprayable tundish lining. The smooth finish on a dry lining and abil­ity to consistently reproduce lining geometry offers improvements in steel quality and better erosion resistance resulting in the potential to increase sequence lengths. Since this type of   product is a free-flowing powder, in­stallation equipment is relatively sim­ple and easy to maintain. Other advantages of dry lining are a monolithic lining, lower inventory, less labour intensive, lower tundish preparation time, lower risk of wash out, easy to deskull since there is no direct adhesion to permanent lining,  environment friendly application, possibility of long sequence, and easy and quick installation.

Disadvantages of the lining include high investment needed, lower insulation and  dependence on shop crane.

With the reform and improvement of continuous casting technology and functional refractories, the most commonly used in our country is the zirconium sizing nozzle. According to the content of zirconia in the sizing nozzle, the zirconium sizing nozzle can be divided into ordinary type sizing water and zirconia type sizing water are two categories, ordinary sizing water The content of Zr02 in zirconium inlay is less than 85%; the content of Zr02 in zirconia type sizing nozzle is more than 85 %.

Due to the different production processes, the sound-through type sizing nozzle can be divided into four types: homogeneous sizing nozzle, direct compound sizing nozzle, vibration forming sizing refractory nozzle and inlaid sizing nozzle.

&#;Fully homogeneous sizing nozzle

The fully homogeneous sizing nozzle is mainly made of zirconia and a small amount of zircon in a certain proportion, mixed, molded, dried, and sintered at -°C. Since the content of zirconia is 60-90%, its advantages are good uniformity of composition and structure, high strength, high corrosion resistance, safe and reliable use, but the disadvantage is that the production cost is high and the life is short.

(2) Direct compound sizing nozzle

The body of the direct composite sizing nozzle is made of zircon, and the working surface of the nozzle sizing end is made of zircon and 72%-78% zirconia. The composite part of the body and the working surface is formed at the same time, in - &#;-time firing, the advantage of this nozzle is that it has good integrity, is not easy to fall off during use, and the production cost is much lower than that of a fully homogeneous sizing nozzle, but due to the martensitic transformation of zirconia and its accompanying volume Changes, it is easy to cause the nozzle to burst during use. Therefore, this kind of water must use stable zirconia as a raw material, but its content should not be too high. The expansion coefficients of zircon and zirconia are different, and it is easy to cause nozzle cracking when making the nozzle. In order to avoid this problem, it is necessary to minimize the difference between the expansion coefficients of the two. Therefore, the water sizing end working surface The content of zirconium oxide in the slab must be controlled at 70-80%, but this is not conducive to the improvement of the sizing water life.

sizing nozzle

&#; Vibration forming sizing nozzle

The vibration forming sizing refractory nozzle is composed of the nozzle body, the nozzle core and the iron shell. The nozzle body is made of high alumina material, and the nozzle core is made of zircon and zirconium oxide. The firing temperature is -°C. The nozzle adopts vibration and pressure to form the nozzle core, the high aluminum material and the iron sheet outer wall prepared in advance, and it can be dried after the molding without firing. The advantage of this kind of water is simple production and preparation process, lower production cost, but the disadvantage is that it is easy to cause leakage accidents after long-term use.

&#;Inlaid sizing nozzle

The body of the inlaid sizing nozzle is made of high-aluminum material, and the nozzle core is made of zircon and oxide compound. The two are made separately, and then the two are bonded together with fire clay. Therefore, if the water body and the water core are not well bonded, the water core will fall off after long-term use, which will cause the continuous casting production to not proceed normally, but the advantage of this nozzle is that the production cost is lower and the thermal shock is stable. The sex is better.

Common sizing nozzles are prone to problems such as diameter expansion and cracking during use, while zirconia sizing nozzles are widely used due to their good thermal shock resistance and corrosion resistance.

According to the gradual reduction of the particle size of the raw materials used, the zirconia type sizing nozzle can be divided into: coarse particle type sizing nozzle, fine particle type sizing refractory nozzle and ceramic type sizing nozzle.

(1) Coarse particle type sizing nozzle

The zirconia particles selected for the coarse-grained sizing nozzle are larger (up to 2mm), so the advantage of this nozzle is that it has good thermal shock resistance and is not easy to burst during use, but the disadvantage is that it has low compressive strength. The porosity is higher.

(2) Fine particle type sizing nozzle

The raw material particles of the fine-particle type sizing nozzle are relatively fine (particle size <50um), so the microstructure of the nozzle is relatively uniform. The advantage is lower apparent porosity, higher strength, and good corrosion resistance, but the disadvantage is heat resistance The seismic stability is poor, and the phenomenon of bursting occurs at the moment of pouring.

(3) Ceramic type sizing nozzle

The raw material particles used in the ceramic sizing nozzle are very fine (particle size <5um), so the strength of the nozzle is very high, the apparent porosity is very low (<5%), but its thermal shock resistance is poor, and the molding and firing The manufacturing process is more complicated, and it is prone to bursting during use.

zirconium sizing nozzle

Article Source:Classification of tundish sizing nozzle

Company name: Henan Changxing Refractory Materials Co.,Ltd

More refractory products:https://www.chinafirebrick.com/products/

Ladle Nozzle &Slide gate plate

Refractory Lining of a Continuous Casting Tundish

In the continuous casting (CC) of steels, tundish is a buffer refractory lined vessel which is located between the ladle and the CC mould. The tundish serves the purpose of a reservoir  and a distribution vessel. Over the years, there have been dramatic changes in CC tundish. From a mere reservoir and distribution vessel, the tundish today  is viewed as a steel refining vessel and a totally new field in the process of steel making technology has emerged which is known as tundish metallurgy. Tundish today also fulfills certain metallurgical functions such as feeding of the liquid steel to the mould at a controlled rate, and thermal and chemical homogenization etc. It also focus on the continuous improvement of many quality related parameters such as fluid dynamics, thermal insulation, inclusion floatation and removal, and hydrogen pickup etc.

Different refractories associated with tundish include tundish lining materials (both permanent and working lining), dams and weirs, impact pad, flow control system (monoblock stopper or slide gate), pouring stream protection between tundish and mould (shroud or submerged entry nozzle,SEN), tundish nozzle, and seating block. Dams and weirs are made of magnesite (MgO) boards or alumina (Al2O3) bricks. Liquid steel from tundish to mould is fed by nozzle submerged into molten steel in mould. SEN are to be resistant to corrosion and spalling, Nozzle clogging is also important. Isostatic pressed SEN with alumina graphite-fused silica are commonly used.

Fig 1 shows typical tundish along with its refractories.

Fig 1 Typical tundish along with its refractories

The refractory lining design and quality of refractories used for lining have major influence on the operational parameters of CC machines such as super heat requirements, speed of the machine, the phenomenon like initial cold running stopper, nozzle clogging, tundish through etc. Due to the temperature extremes involved, refractory linings of the tundish are to be designed to withstand thermal shock, prevent thermal loss, prevent oxidation, and resist erosion and corrosion while preventing the liquid steel getting contaminated with unwanted impurities. Selection of refractories for a tundish is also critical due to long casting sequence, faster tundish turnaround, higher campaign life, cleanliness of steel, and because tundish refractories constitute high specific costs in CC operation.

The tundish lining material has a direct influence on the quality of the liquid steel, since it is close to the solidification stage. Tundish working lining remains in contact with steel and erosion is initiated at the liquid steel-air interface with fluctuation of liquid steel level in the tundish. Different metallic oxides present in the liquid steel are the primary eroding agents for the tundish refractory lining. Slag coming in contact with tundish refractory during casting and the tundish covering powder are also responsible for the erosion. The starting point of erosion is the formation of &#;hair cracks&#; at the liquid steel-air interface due to thermal spalling. Penetration of liquid steel and slag takes place through these hair cracks and subsequently erosion occurs. Further, complex interactions at the refractory-liquid steel interface can also impair the steel quality due to the formation of inclusions. Lower erosion of working lining ensures less non-metallic inclusions in the steel.

The refractory lining of a tundish has a defined lifetime depending on the qualities of the lining and the types of tundish slag. Chemical reaction between the refractory working lining layer and the tundish slag is very important especially in the case where there is high sequence casting. The refractory working lining in the tundish is subject to different stresses resulting from the thermo-chemical load. The slag chemistry and slag viscosity play an important role in the wear of the refractory lining. In practice tundish slag composition varies widely even in the duration of a single sequence. Hence none of the refractory compositions gives good performance with all the types of the tundish slags normally encountered during operation.

It is desired that the tundish refractory lining fulfills a number of different functions which includes resistance against liquid steel (high solidus temperature), resistance against tundish slag, low heat conductivity (good thermal isolation properties), good stability (no erosion of refractory during casting), high resistance to thermal shock, chemical inertness, must be disposable after use, and reasonable in price.  Further tundish refractory lining is to have low oxygen potential, good mechanical resistance, low hydrogen pick up by steel, and easy deskulling.

There are several tundish refractory lining practices which are in use. These include (i) brick lining, (ii) gunnable lining, (iii) tundish board lining,  (iv) sprayable tundish lining, and (v) dry tundish lining. Each practice has its advantages and disadvantages both in terms of operations and impact on steel quality. These tundish lining practices are described below.

Brick lining

 Brick lining of tundish came into existence along with the introduction of CC technology for casting of liquid steels in s. This is basically an extension of ladle refractory practices to the tundish. In this type of lining, high alumina bricks are  normally used. The bricks are in direct contact with liquid steel, after preheating.

The advantages of this type of lining  are low risk of pickup of hydrogen by liquid steel, low inventory, no investment in specialized lining equipments, and low risk of lining wash out.

Disadvantages of brick lining are requirement of intensive curing, long tundish preparation time, high labour intensiveness, poor insulation, high thermal conductivity contributing to higher temperature loss, no possibility of cold start, chances of tundish through because of presence of weak joints, difficult stripping of used lining, and the requirement of large numbers of tundishes.

Gunnable lining

Gunnable linings in tundish was initially introduced by the Japanese steel industry for overcoming the problems of the brick lining. In this method the dry refractory powder of the right composition after fluidization is transferred and installed on the tundish wall by using a gunning machine to obtain a monolithic lining. Initially these were alumino-silicate based and later converted to basic type (magnesite based) to assist with metallurgical practice. Conventional tundish gunning materials are designed to have a low strength between deg C to deg C.

This feature assists in formation of a weak zone between the backup lining and the sintered zone, which in turn facilitates easy deskulling. One of the many disadvantages of tundish gunning material is the shrinkage at high temperature which deteriorates the performance of gunning material. A high shrinkage causes high stress and subsequent crack formations during operation whereas a low shrinkage can be a barrier for easy deskulling.

This type of lining  provides a monolithic joint free structure and relatively improved deskulling operations but little is gained with regards to the preheat times or heat losses because of the high density of the gunned linings. This type of lining has a tendency to crack and to spall during rapid preheating and hence the tundish with the gunnable linings cannot be subjected to cold start practices.

The advantages of gunnable lining are low risk of pickup of hydrogen by liquid steel, low inventory, no joints, less labour intensive, relatively easy installation in lesser time, and relatively less difficult to deskull.

Disadvantages of this type of lining are requirement of intensive curing, high wastage because of

rebound losses, poor insulation, no possibility of cold start, high risk of wash out, low thermal stability, dust problems, energy intensiveness, high costs, difficulties in applying variable thickness, and investment needed for gunning equipment.

Tundish board lining

Shortly after the introduction of continuous casting it was realized that some type of disposable lining was re­quired to reduce the refractory costs and improve thermal insulation. Bricks and conventional gunning products were unreliable and provided no ther­mal insulation. The introduction of low density, disposable, pre formed and pre cured tundish boards in mid s offered good thermal insulation and low re­fractory consumption. However the tundish board linings have the disadvantage of  higher man­power and time required for their preparation.

This lining with silica (SiO2) based boards has become popular in the areas where labour costs are low and application technologies are not readily available. The popularity of tundish board lining is also due to its low costs, no need of investment in equipment, and easy to deskull. The use of SiO2 based boards allows only cold start practice.  During s magnesite (MgO) based boards were introduced for fulfilling the requirement of pre-heatability for a hot start practice which is needed for low hydrogen considerations in the manufacture of high alloy quality steels. SiO2 based boards are used for mild steel and MgO boards for special steels and for steels with high calcium content. The reason being silica is attacked by lime, alumina and iron oxide present in the steel.

The advantages of the tundish board lining includes lesser tundish inventory, low hydrogen pick up in case of boards with hot start, uniform shape of the lining, no need for curing, good insulation, possibility of cold start and hence energy savings, easier deskulling, low requirement of energy, no investment needed in equipments, low risk of wash out, and better working environment.

The disadvantages of tundish board lining include presence of joints, sand backing, danger of hydrogen pick up in case of cold start, labour intensive, need of high inventory, problem of handling/breakage, and high cost in case of magnesite based boards.

Sprayable tundish lining

The sprayable tundish lining was first developed in and being used widely since later half of s. Presently it is being used in more than 50 % of tundishes around the world. This type of lining combines successfully many of the advantages of tundish board lining and gunnable lining, while eliminating the disadvantages like &#; joints, sand backing, rebound losses, dust problems, and poor insulation etc. The quality of lining is dependent on skill of the spray operative and the drying equipment.

In sprayable tundish lining a thick slurry of refractory materials is thoroughly mixed and is transported and deposited onto the tundish after atomizing with compressed air. The refractory materials used are mainly MgO and SiO2. The MgO content is usually in the range of 70 % to 90 % with balance percentage of SiO2. For longer duration of sequence casting higher amount of MgO along with higher thickness of the lining is needed. The lining operation can also be  carried out  with robotic application system.

Since homogeneous mixing is done in this lining before the product is applied, the incorporation of special chemical additives is possible which helps to improve thermal stability properties of the lining and  impart good flexibility. For chemical bonding in the sprayed mass, preheating at around deg C is needed.

Sprayable tundish lining has significant advantages of lower density of the lining and better control of the lining thickness when compared with the gunnable linings. In this type of lining normally fibres and other chemicals are added to the refractory mass. The lining is preheated in case of hot start tundish, or is allowed to cool to room temperature and taken as a cold start tundish. The lining integrity is to be ensured during curing and this requires deposit of the lining material on the tundish permanent lining after its temperature is lower than 100 deg C. Being a wet processes using up to 30 % water and  with the presence of hoses and spill-overs, the process creates occupational health and safety issues.

The advantages of sprayable tundish lining  includes low risk of hydrogen picking, absence of joints, lower inventory, lesser labour intensiveness, easy to deskull, good insulation properties, possibility of cold start, and controllable lining thickness.

Disadvantages of lining include requirement of investment in equipments, need of intensive curing, and moderate risk of wash out.

Dry tundish lining

Dry tundish lining was developed at the same time as sprayable tundish lining. However, the high price of phenolic resin powder and associated health and safety issues has resulted into dry tundish linings being used only in a handful of steel plants. Recently resin free binder systems (sodium silicate binder, or glucose binder) have elimi­nated any health and safety issues and in addition the second generation  of dry tundish products have been introduced with significantly reduced tundish prepara­tion time.

Dry tundish lining process differs from other lining processes since it is applied in a dry powder form and does not require the addition of water. Normally this lining makes use of a resinous bond. The added resin is activated by applying a small amount of heat. The forming of lining is carried out by using a former and feeding the dry powder in the gap between the permanent lining and the former. Special drying arrangement is required for drying this mass at around 300 deg C for 24 hours to develop polymerization of resin which gives strength to it.  For the activation of the resin to develop a bond hot air at around 400 deg C is needed.

For more information, please visit graphite electrode price.

The need of vibration of the dry powder depends upon the product being used. The dry tundish lining has relatively lower insulation because of its higher density. It needs service of the crane of the tundish bay for its installation. In case of dry lining since no water is used, there is no direct adhesion to the permanent tundish lining. This helps in good deskulling and prolongs life of tundish lining.

One advantage of dry tundish lining is that it ensures slow hydrogen pick up in the steel as it does not require water for application. Around 0.7- 0.9 ppm hydrogen pick up is reported as compared to 1.8 &#; 2.4 ppm in sprayable tundish lining. The smooth finish on a dry lining and abil­ity to consistently reproduce lining geometry offers improvements in steel quality and better erosion resistance resulting in the potential to increase sequence lengths. Since this type of   product is a free-flowing powder, in­stallation equipment is relatively sim­ple and easy to maintain. Other advantages of dry lining are a monolithic lining, lower inventory, less labour intensive, lower tundish preparation time, lower risk of wash out, easy to deskull since there is no direct adhesion to permanent lining,  environment friendly application, possibility of long sequence, and easy and quick installation.

Disadvantages of the lining include high investment needed, lower insulation and  dependence on shop crane.

With the reform and improvement of continuous casting technology and functional refractories, the most commonly used in our country is the zirconium sizing nozzle. According to the content of zirconia in the sizing nozzle, the zirconium sizing nozzle can be divided into ordinary type sizing water and zirconia type sizing water are two categories, ordinary sizing water The content of Zr02 in zirconium inlay is less than 85%; the content of Zr02 in zirconia type sizing nozzle is more than 85 %.

Due to the different production processes, the sound-through type sizing nozzle can be divided into four types: homogeneous sizing nozzle, direct compound sizing nozzle, vibration forming sizing refractory nozzle and inlaid sizing nozzle.

&#;Fully homogeneous sizing nozzle

The fully homogeneous sizing nozzle is mainly made of zirconia and a small amount of zircon in a certain proportion, mixed, molded, dried, and sintered at -°C. Since the content of zirconia is 60-90%, its advantages are good uniformity of composition and structure, high strength, high corrosion resistance, safe and reliable use, but the disadvantage is that the production cost is high and the life is short.

(2) Direct compound sizing nozzle

The body of the direct composite sizing nozzle is made of zircon, and the working surface of the nozzle sizing end is made of zircon and 72%-78% zirconia. The composite part of the body and the working surface is formed at the same time, in - &#;-time firing, the advantage of this nozzle is that it has good integrity, is not easy to fall off during use, and the production cost is much lower than that of a fully homogeneous sizing nozzle, but due to the martensitic transformation of zirconia and its accompanying volume Changes, it is easy to cause the nozzle to burst during use. Therefore, this kind of water must use stable zirconia as a raw material, but its content should not be too high. The expansion coefficients of zircon and zirconia are different, and it is easy to cause nozzle cracking when making the nozzle. In order to avoid this problem, it is necessary to minimize the difference between the expansion coefficients of the two. Therefore, the water sizing end working surface The content of zirconium oxide in the slab must be controlled at 70-80%, but this is not conducive to the improvement of the sizing water life.

sizing nozzle

&#; Vibration forming sizing nozzle

The vibration forming sizing refractory nozzle is composed of the nozzle body, the nozzle core and the iron shell. The nozzle body is made of high alumina material, and the nozzle core is made of zircon and zirconium oxide. The firing temperature is -°C. The nozzle adopts vibration and pressure to form the nozzle core, the high aluminum material and the iron sheet outer wall prepared in advance, and it can be dried after the molding without firing. The advantage of this kind of water is simple production and preparation process, lower production cost, but the disadvantage is that it is easy to cause leakage accidents after long-term use.

&#;Inlaid sizing nozzle

The body of the inlaid sizing nozzle is made of high-aluminum material, and the nozzle core is made of zircon and oxide compound. The two are made separately, and then the two are bonded together with fire clay. Therefore, if the water body and the water core are not well bonded, the water core will fall off after long-term use, which will cause the continuous casting production to not proceed normally, but the advantage of this nozzle is that the production cost is lower and the thermal shock is stable. The sex is better.

Common sizing nozzles are prone to problems such as diameter expansion and cracking during use, while zirconia sizing nozzles are widely used due to their good thermal shock resistance and corrosion resistance.

According to the gradual reduction of the particle size of the raw materials used, the zirconia type sizing nozzle can be divided into: coarse particle type sizing nozzle, fine particle type sizing refractory nozzle and ceramic type sizing nozzle.

(1) Coarse particle type sizing nozzle

The zirconia particles selected for the coarse-grained sizing nozzle are larger (up to 2mm), so the advantage of this nozzle is that it has good thermal shock resistance and is not easy to burst during use, but the disadvantage is that it has low compressive strength. The porosity is higher.

(2) Fine particle type sizing nozzle

The raw material particles of the fine-particle type sizing nozzle are relatively fine (particle size <50um), so the microstructure of the nozzle is relatively uniform. The advantage is lower apparent porosity, higher strength, and good corrosion resistance, but the disadvantage is heat resistance The seismic stability is poor, and the phenomenon of bursting occurs at the moment of pouring.

(3) Ceramic type sizing nozzle

The raw material particles used in the ceramic sizing nozzle are very fine (particle size <5um), so the strength of the nozzle is very high, the apparent porosity is very low (<5%), but its thermal shock resistance is poor, and the molding and firing The manufacturing process is more complicated, and it is prone to bursting during use.

zirconium sizing nozzle

Article Source:Classification of tundish sizing nozzle

Company name: Henan Changxing Refractory Materials Co.,Ltd

More refractory products:https://www.chinafirebrick.com/products/

Ladle Nozzle &Slide gate plate

Refractory Lining of a Continuous Casting Tundish

Classification of tundish sizing nozzle