Converter tapping seat brick and sleeve brick

The tapping hole of converter is the core channel for molten steel to flow into the ladle during the converter steelmaking process, and it is a key refractory component. Its main functions include steel slag separation, reduction of molten steel pollution and alloy element burnout, and promotion of deoxidation product floating through steel flow stirring [1] [5]. The tapping hole is composed of a tapping seat brick and a sleeve brick, and the sleeve brick is often assembled in the form of a steel pipe flange for easy installation [1] [3]. 
According to the forming method, it can be divided into machine-pressed production (high density and high strength) and isostatic pressing production (uniform structure). According to the structure, it can be divided into split type (easy to leak steel) and integral type (high safety). The main failure mechanisms involve high-temperature melting (1680-1710℃), molten steel erosion, and furnace gas oxidation. Measures to extend the life include high-pull carbon operation (end-point carbon mass fraction 0.07%-0.09%), tapping hole diameter expansion (155mm increased to 160mm), optimized refractory materials (MT-14A magnesia carbon bricks), and slag damming and slag hanging protection technology. Some companies have achieved breakthroughs in service life by improving the masonry process, such as Baosteel's 300t converter service life increased to 3200 furnaces, and Tangsteel's use of high-purity magnesia/graphite materials has resulted in a comprehensive service life of 380 furnaces for 3 converters [4]. The "sealed tapping method" developed by Japanese steel companies can reduce secondary oxidation of molten steel, and the lining repair material invented by Shandong Iron and Steel can increase the overall life to more than 370 furnaces.

Principle introduction

The tapping hole is the channel through which molten steel flows from the converter to the ladle, and it is one of the key refractory components of the converter. The tapping hole enables steel slag separation during the tapping process, reduces steel contamination caused by steel slag flowing into the ladle, and also reduces the loss of alloy elements; at the same time, the tapping hole steel flow strongly stirs the steel in the ladle, promoting the floating of inclusions and deoxidation products, which not only affects the production efficiency of steel smelting, but also affects the quality of the steel. Converter steelmaking enterprises at home and abroad place great importance on converter tapping-related technologies (tapping hole and slag retaining tapping process technologies).

Classification

Converter tapping holes can be divided into machine-pressed production and isostatic pressing production according to the forming method. The machine-pressed tapping holes have high bulk density and high strength; the isostatic pressing tapping holes have uniform structure and uniform internal stress distribution. From the structure, it can be divided into split type and integral type tapping holes. The split type tapping holes are easy to install, but because there are gaps in the product, steel leakage is likely to occur during use; the integral type tapping holes are heavy and inconvenient to install, but because the product is a whole, there are no gaps, so steel leakage is not easy to occur. The choice of which production method or structure of tapping hole should be comprehensively considered in terms of use and installation.

Structure

The tapping hole is generally composed of a tapping seat brick and a sleeve brick (also called a tube brick). 
1. Tapping seat brick: 
The tapping seat brick is the brick that is placed outside the sleeve brick. Its function is to protect the sleeve brick, and when the sleeve brick is replaced and drilled, the seat brick can support the converter brick, which is convenient for replacing the sleeve brick. Common seat bricks include pre-formed finished products and bricks directly built on site. The split and integral tapping seat bricks are pre-formed, so when they are built, they can be directly installed after being assembled with the sleeve brick, with fewer steel leakage channels and a high safety factor. Brick-built tapping seat bricks are generally built with working layer bricks inside the converter shell, and other places are built with permanent layer magnesia bricks on site, and the surrounding area is filled with ramming material, which has a relatively loose structure and many steel leakage channels, but the cost is relatively low. 
The prefabricated tapping seat bricks are generally square or round in shape, and the inner holes are all round. The size of the inner hole is 40~100mm larger than the outer diameter of the sleeve brick. 
2. Tapping hole sleeve brick: 
The tapping hole sleeve brick is the channel through which molten steel flows from the converter to the ladle. It is in direct contact with the molten steel, and its life directly affects the steelmaking rhythm of the converter. From the structure, the tapping hole sleeve bricks are divided into integral sleeve bricks (also called tapping hole tube bricks) and split sleeve bricks; the integral sleeve bricks are generally isostatically pressed, and the split sleeve bricks are machine-pressed. In order to facilitate installation on the converter, the tapping hole sleeve bricks are often assembled with steel pipes and flanges before use.

Failure principle

1. Oxidation of furnace gas: 
From the time the molten iron is charged into the converter to the blowing process, the tapping hole is in a high-temperature oxidizing atmosphere. The furnace gas generated during the blowing process contains a large amount of CO. When it is discharged from the tapping hole, a C-O reaction occurs, forming a decarburized layer on the inner wall surface of the tapping hole, directly causing damage to the tapping hole. 
2. Friction damage and mechanical scouring damage of molten steel and slag: 
During tapping, the tapping hole must withstand the huge pressure of the molten steel in the converter. At the same time, the molten steel and slag generate friction and scouring with the inner wall of the tapping hole when flowing out of the tapping hole, directly causing mechanical damage to the inner wall of the tapping hole. 
3. High-temperature melting of molten steel and slag: 
The tapping temperature is generally 1680~1710℃. Under the action of high-temperature molten steel, the material of the tapping hole will soften, its strength will be significantly reduced, and it may even melt, causing damage to the tapping hole.

Measures to improve the life of the tapping hole

Measures to improve the life of the tapping hole include: 
1. Hot replacement tapping hole process optimization: 
The main problems with the hot replacement process of converter tapping holes are: the tapping hole expansion time is long; the tapping hole is fixed by manual use of steel pipes; the tapping hole filling material is filled with a converter spray gun. To solve these problems, first, the drill bit of the expansion machine was optimized to shorten the drilling time and improve the drilling quality; second, a steel pipe was fixed on the inner wall when making the tapping hole sleeve brick to speed up the replacement time of the sleeve brick; finally, a special spray gun for the tapping hole was designed and used to improve the filling speed and quality. These measures greatly shortened the time to replace the tapping hole, ensured the temperature in the furnace and the hole shape of the tapping hole, thereby ensuring the sintering effect of the steel tapping filling material, and laid the foundation for improving the life of the tapping hole. 
2. Optimize the performance of the tapping hole inner filling material: 
Poor quality of the tapping hole filling material can easily lead to air gaps around the tapping hole sleeve brick, which accelerates the damage rate of the tapping hole. Through experiments, a special tapping hole filling material with high magnesium oxide content, good fluidity, and fine particle size is used to ensure that the gap between the tapping hole seat brick and the sleeve brick can be filled, sintered evenly, and have a good sintering effect. 
3. Lowering tapping temperature: 
The main measures to reduce the tapping temperature include implementing on-line and off-line baking of steel ladles, covering steel ladles and intermediate ladles for insulation, and using better insulation agents; continuous casting machines achieve full protection casting and low superheat casting. Through the above measures, the tapping temperature is reduced by an average of 15°C, reaching below 1690°C. The significant reduction in tapping temperature reduces the scouring and erosion of the tapping port by high-temperature molten steel and slag, effectively improving the service life of the tapping port. 
4. High carbon steelmaking technology: 
By promoting high carbon steelmaking technology, the oxidizing property of the end-point molten steel and slag is effectively reduced, and the oxidation and erosion of the tapping port by the molten steel and slag are reduced, creating conditions for improving the life of the tapping port. 
5. Tapping port slag blocking and slag hanging protection technology: 
After tapping, a slag stopper is used to block the tapping port to reduce the erosion and oxidation of the tapping port by furnace gas and slag during the smelting process. When tapping is about to end, a slag cone is used to block the tapping port to reduce the amount of slag and reduce the scouring and erosion of the tapping port by the slag. Promote the use of slag hanging protection technology. After splashing slag to protect the furnace, pour slag from the tapping side. When the slag passes through the tapping port, part of it adheres to form a slag hanging layer to protect the inner wall of the tapping port.

Tapping port maintenance

1) In the process of use, when uneven erosion of the splash slag layer occurs on the tapping side (such as pits around the tapping port and on the tapping surface, unevenness around the tapping port), change the previous model of simply relying on bag replacement time for repair and repair in a timely manner.

2) The standard is that the steel flow from the tapping is not scattered, no slag is produced, the steel control time is not more than 20 s, and the steel can be completely discharged; and the quality of each repair should reach more than 16h.

3) If the phenomenon of incomplete steel discharge occurs, the furnace must be shut down immediately for treatment.