Billet continuous casting parameters and tundish refractory configuration
A variety of refractory materials are needed in the production and use of the tundish, including castables, smears, dry materials, nozzles, slag retaining wall series, three continuous casting parts, etc. The main configuration of tundish refractories is shown in Table 1. , The main parameters of the continuous casting machine are shown in Table 2. (Picture 1: Picture 2)
Tundish refractory optimization
Refractory parameter optimization
The flow control method of the billet caster is stopper rod flow control. The original stopper rod head of the billet is obese and blunt. When the flow is controlled, the contact area with the steel flow and the bowl of the upper nozzle is large, and the amount of steel passing is the same. Under the conditions, the erosion rate is fast, and when the bag age increases, the steel loss control accident caused by the excessive erosion of the rod head is prone to occur. For this reason, the selection of stopper rods has been optimized. The stopper rod head has been improved to a thin and pointed head. The length of the stopper rod head has been increased by 20mm. The R value of the stopper rod head has been optimized to expand the effective flow control contact surface, increase the service life, and improve the uniform erosion. Improve the accuracy of flow control and ensure good flow control in the later stage . The process hole in the center of the stopper rod is extended to improve the thermal shock stability of the rod tip. The total length of the stopper rod is increased by 100mm to make the stopper rod higher than the tundish cover, which prevents the core of the stopper rod from being deformed by baking and the nut from loosening, reducing abnormal flow control. After optimization, the size of the stopper head and the upper nozzle are better matched, and the flow control is stable.
The inner diameter of the original billet nozzle is 30mm, and the amount of steel passing per unit time is large. When the drawing speed is low, the stopper rod is required to frequently participate in flow control. The number of punching rods increases, which is not conducive to the increase of the stopper rod life and is prone to stop pouring. The problem that the stopper cannot be stuck. However, after the inner diameter of the upper nozzle is reduced to a certain extent (such as 23mm), although the flow control problem is greatly improved, the problem of steel flow cannot keep up when replacing the immersion nozzle. After many trials and explorations, the inner diameter is 25mm. The upper nozzle is most conducive to steel flow control and stopper rod life improvement. See Table 3 for test tracking and comparison. (Picture 3)
Impact plate optimization
The impact plate is used in the tundish molten steel impact area to prevent leakage accidents at the bottom of the tundish. The size of the original impact board for billet is 480mm×480mm×60mm (length×width×thickness), the size is too small, the thickness is not enough, and the impact strength is not enough. When the long nozzle is not set up or the ladle is deflected, the steel flow is very easy to impact the area outside the impact plate, affecting the service life of the tundish, and in severe cases, it may cause a leakage accident at the bottom of the steel mouth of the tundish. For this reason, the impact plate was re-optimized and designed with a size of 700mm×550mm×100mm (length×width×thickness). In order to facilitate the embedment close to the overflow port, the corresponding area is designed as a small trapezoid, as shown in Figure 1. (Picture 4)
Refractory construction method optimization
Improvement of construction method of nozzle block
For the tundish constructed with smear material, in order to ensure the firmness of the placement of the runner block at the bottom, smear material will be filled around the runner block after installation. Since the spread material contains a lot of moisture, the nozzle block will absorb the moisture from the spread material. Before the steel is poured in the tundish, usually due to the short baking time or the insufficient baking temperature, the water in the runner block is not fully discharged. It is very easy to crack or burst when receiving the molten steel poured from the ladle. The occurrence of sinking causes the stopper rod to lose its flow control function or is severely scoured, which affects the increase in the number of continuous casting tundish continuous casting furnaces, and in severe cases, affects the smooth progress of continuous casting steel. Aiming at the above shortcomings, a new construction method of nozzle block brick was developed. Specifically: Before construction, the bottom of the tundish is reserved for the installation of nozzle block bricks. After the other parts of the bottom of the tundish are constructed with smear material, the nozzle block bricks are placed as required, and then filled with magnesia dry vibrating material. Use a small hammer to ram the dry vibrating material around the nozzle block. The main composition of dry vibrating material includes sintered magnesia particles of different sizes, fused magnesia fine powder, phenolic resin powder and a small amount of additives. The dry vibrating material does not contain moisture, and the nozzle base brick is not easy to crack when steel is poured; the filled dry vibrating material will not form a whole with the nozzle base brick and the permanent layer of the bottom of the ladle at high temperature, and it can be automatically separated when the tundish is overturned. Falling off; It can effectively prevent the tundish nozzle seat brick from cracking or bursting during the pouring process, which is conducive to the normal flow control effect of the stopper rod, and it also solves the problem of serious erosion of the stopper which affects the increase in the number of continuous casting furnaces; In addition, the nozzle block can be automatically separated and fallen off when the tundish is tipped after pouring.
Optimization of water inlet installation method
After the smear material for the working layer of the billet tundish is smeared, install the upper nozzle immediately. Since the smear contains a lot of moisture, the upper nozzle will absorb the moisture from the smear during subsequent construction and use. The upper nozzle is easy to produce after absorbing water and damp. Problems such as cracking affect the control of steel flow and even the direct production. For this reason, the installation method of the upper nozzle has been optimized. After the coating material of the working layer is wiped, it must be placed for 3~5h, and the upper nozzle shall be installed after the water has dried naturally.
Optimized use of refractory materials
Nozzle baking process optimization
The traditional billet nozzle baking device is a special roaster, the roaster flame surrounds the nozzle, and it is slowly baked and heated to the required temperature. The baking efficiency is low, and it is unfavorable to the bowl of the spout and the cladding. When the whole spout is roasted, accidents of the spout fracture due to collision with the roaster may occur. The billet runner baking is improved from external baking to exhausted internal baking. The flame is drawn from the bottom of the tundish, and the runner is baked from the inside to the outside. The baking device is simple, the operation is convenient, and the baking effect is better.
Tundish baking process optimization
The tundish baking time is generally long (average 5-7h), the stopper rod is over-baked, which reduces the life of the stopper rod. At the same time, the abnormal phenomenon of the nozzle sticking to the upper nozzle due to the over-baked stopper rod has occurred many times. Through series optimization and adjustment, the tundish baking time is 3～5h to meet the pouring conditions. For the tundish with a long baking time, the number of ovens or scrap must be limited. The curing standard is shown in Table 4. The flame requirements of the tundish barbecue process (low fire time: flame touches to the bottom of the bag; medium fire time: blue flame overflow The cover is about 500mm; the fire time: the blue flame overflows the cover about 300mm; the minimum abnormal time: cancel or reduce the medium fire time; the maximum abnormal time: increase the small and medium fire time).
Optimization of pouring opening and water exchange opening
Before the billet is poured, it is accustomed to repeatedly test the rod and test the rod, which is easy to damage the anti-oxidation coating on the surface of the stopper head. Some employees have the habit of punching the rod during the casting process, which can easily cause the zirconium bowl at the upper nozzle to crack and accelerate the wear Increase stopper accidents. For this reason, change the pouring operation mode. It is required to lightly bring the rod, do not jam the rod, and prohibit the punching rod. At the same time, it is required that the quick-change immersion nozzle does not jam the stopper rod, and the strip steel flow is required to change the nozzle, which is beneficial to reduce the plug head and The bowl of the upper nozzle is worn out.
Refractory technology optimizes the application effect
1) In 2018, the average package age of No. 2 and No. 3 units has increased compared with 2017. The package age of No. 3 unit has increased by 56.60%, and the maximum package age has been increased from 18 to 30.
2) Billet refractory accidents have been greatly reduced, and the planned casting stop rate for billet refractory due to full flow has increased from 85.72% in 2017 to 95.91% in 2018. The number of unplanned pouring stops due to refractory materials has been reduced from 14 in 2017 to 6 in 2018.
3) The tundish baking time is greatly reduced, from the original 5-7h to 3-5h.
The overall optimization design of billet refractories was carried out, and the standard of tundish refractory materials suitable for the continuous casting of Shaogang’s billet was determined and solidified. The construction method of billet refractories has been improved to solve the series of problems such as the sinking of the nozzle block and the cracking of the upper nozzle. The stability of the use process of the tundish refractory materials has been improved, and the use process of the billet refractory materials has been improved to improve the refractory materials. Service life.