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Development of high-life converter sliding plate slag-blocking taphole brick

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Table of Contents

Abstract: Many large and medium-sized converters in domestic steel plants adopt sliding plate slag-blocking tapping technology, and the supporting taphole bricks have become one of the factors affecting the development of sliding plate slag-blocking technology. This article analyzes the application of sliding plate slag-blocking taphole bricks, studies the causes of damage, and proposes optimization and improvement measures. The newly developed high-life sliding plate slag-blocking taphole brick has good application effects.

Keywords: converter; slide plate to retain slag; tap hole; lifespan; damage; improvement measures

1 Introduction

Reducing the amount of slag in converter tapping is an effective way to improve the cleanliness and quality of molten steel. The successful application of the converter slide plate (sliding nozzle) slag-blocking technology in many steel plants at home and abroad has verified that this technology is one of the most advanced converter tapping slag-blocking technologies in the world. In recent years, many large and medium-sized converters in domestic steel plants have gradually adopted the sliding plate slag-blocking steel tapping process.

The converter slide slag retaining system is mainly composed of gate valve mechanism, refractory material and supporting hydraulic station, and replacement mechanism, of which refractory material is the main consumable. The refractory material is mainly composed of sliding plate slag-blocking taphole bricks (referred to as taphole bricks), sliding plates and nozzle bricks. See Figures 1 and 2 for details. Slide gate plate bricks and nozzle bricks have a short lifespan and are frequently replaced. They are designed to be installed inside the gate valve mechanism and can be quickly disassembled and replaced with the gate valve mechanism. The tappet brick has a longer life than the sliding plate and nozzle brick. It is embedded inside the furnace body when installed. It is the channel for molten steel to flow from the converter to the ladle. It is also a key refractory component matched with the external gate valve mechanism, nozzle brick and sliding plate brick. The replacement of taphole bricks takes a long time, and their quality directly affects the smelting rhythm of the steel plant. It is one of the key factors affecting the development of the sliding plate slag retaining technology.

Figure 1 Overall structural configuration diagram of converter

Figure 2 Structural diagram of the converter slide plate slag retaining system

The sliding plate slag blocking taphole bricks produced by our company are basically divided into conventional converter sliding plate slag blocking taphole bricks and replaceable core structures, as shown in Figure 3 and Figure 4 respectively. It has been successfully used in many domestic steel plants such as Benxi Iron and Steel, Shougang Jingtang, Hebei Yongyang, Shaoguan Iron and Steel. This article analyzes the damage that occurs when the replaceable core slide plate slag blocking taphole brick is used, and proposes corresponding improvement measures, thereby increasing the service life of the slide plate slag blocking taphole brick.

Figure 3 Schematic diagram of conventional converter slide plate slag-blocking taphole brick

Figure 4 Schematic diagram of the replaceable core structure of the converter slide plate to retain the slag taphole bricks

2 Analysis of the causes of damage to the slag-blocking taphole brick of the converter slide

Statistics and analysis were made on the usage of taphole bricks of replaceable core converter slide plates produced by traditional methods. When the service life reaches more than 100 furnaces, the main factors affecting the life span are: the replacement core of the seat brick, the jacket of the seat brick, and the steel penetration and sintering in the gap between the nozzle bricks, resulting in the nozzle brick and replacement core being unable to be replaced. The edges of the outer shell of the seat bricks are severely powdered and peeled off, making them unable to be used continuously; the lifespans of the seat bricks and sleeve bricks cannot be synchronized, which limits the lifespan of the entire set of taphole bricks.

2.1 Steel penetration in the gap between the seat brick jacket and the replacement core

Take the replaceable core slide slag-blocking taphole brick of a domestic steel plant as an example. The expected service life of the taphole is 150 furnaces. When using 80 to 120 furnaces, the core of the seat brick will be replaced, the outer cover of the seat brick, and the gap between the nozzle bricks will be infiltrated and sintered (Figure 5). As a result, the replacement core and internal water inlet cannot be replaced, the taphole brick cannot be used anymore, and the machine is offline early.

Figure 5 Schematic diagram of taphole brick replacement system

The tappet seat brick jacket, seat brick replacement core, and inner nozzle brick are located outside the converter, close to the gate valve mechanism, and the temperature changes greatly. When the sliding plate of the gate valve mechanism is closed, it is violently impacted by molten steel and steel slag under the water hammer effect, so the erosion rate is much higher than other parts of the tap hole. Based on the need for rapid replacement of the replacement core at high temperatures, the replacement core is designed into a bowl shape with a narrow interior and a wide upper part, leaving a certain gap. Therefore, when the corrosion reaches a certain thickness, the gap is exposed, causing molten steel to penetrate, making the tapping port unusable.

2.2 The edge of the seat brick jacket is powdered and the replacement core is cracked

When the tappet seat brick jacket of a domestic 150 t converter was used for 100 to 150 furnaces, decarburization, powdering and peeling occurred on the outside of the seat brick jacket, as shown in Figure 6. The edge strength of the outer shell of the seat brick is very low and cannot cooperate with other parts, which limits the life of the tap hole.

Figure 6 Example of use in steel mills

The taphole brick is exposed to high-temperature oxidizing atmosphere for a long time and is prone to decarburization and strength reduction. The outside of the tapping port is located outside the furnace body. Intermittent tapping is in contact with molten steel, and the ambient temperature changes drastically, which can easily cause decarburization and peeling in this area. The inner nozzle brick and replacement core are replaced many times during use. During the replacement operation, they are squeezed and rotated, and external stress will aggravate the damage to the decarburized parts.

2.3 The service life of the seat brick jacket and sleeve bricks do not match

There are differences in application conditions between the taphole seat brick and the lower sleeve brick, and their service life is inconsistent. The joint between the taphole seat brick and the inner nozzle brick is easily eroded by molten steel, and the erosion rate is inconsistent with the sleeve brick, which limits the overall improvement of the life of the taphole brick.

3 improvement measures

3.1 Design optimization of seat brick jacket and replacement core

After research and analysis, there is room for optimization in the design size of the bowl-shaped replacement core, which can effectively curb the steel penetration that occurs when the taphole brick reaches a certain life span. This experiment designed replacement cores with different chamfer sizes (Table 1) to verify the application conditions.

Table 1 Replacement core chamfer size test mm

Plan number1*2*3*
Bowl-shaped replacement core chamfer R402510

An adjustment test was conducted on the chamfer R of the seat brick jacket and the bowl-shaped replacement core. The test results are: the chamfer R size is 40 mm, and the average furnace age when steel penetration occurs is 89 furnaces. The chamfer R size is 25 mm, and the service life is 144 furnaces when steel penetration occurs; the chamfer R size is 10 mm, and the tap hole life reaches 220 furnaces without steel penetration. As the chamfer size becomes smaller, the difficulty of on-site replacement increases significantly. Taking comprehensive considerations into account, it is optimal to set the chamfer R size of the bowl-shaped replacement core to 10 to 15 mm, as shown in Figure 7.

Figure 7 Schematic diagram of taphole seat brick and replacement core chamfer optimization

In order to solve the problem of local erosion rate differences, seat bricks with replacement cores were used to replace the original integral seat bricks. After a certain service life, replacing the replacement core can comprehensively improve the service life of the converter taphole brick.

3.2 Improvement of production process

The outer shell of the seat brick is a special product, and the outer edge is the weak link in the pressure. The outer edge of the seat brick jacket (see Figure 8) has harsh service conditions, causing its service life to be lower than other parts. Composite materials and regional focus pressure are used to increase the strength of this area. The overall steel tap is made of composite materials, the outer edge area is made of materials with good oxidation resistance, and the parts that contact molten steel are made of materials with strong slag resistance. Special tools are used to pre-pressure the outer edge area first, and then perform overall pressurization to increase the strength of the outer edge and other weak areas (see Figure 9), reduce porosity, and improve oxidation resistance.

During the use of the tap port, problems such as powdering and peeling of the upper edge of the outer cover of the seat brick frequently occur, causing the outer edge of the seat brick to peel off. The matching inner nozzle brick cannot be effectively installed, causing the tap port to be offline in advance. After on-site investigation, it was found that the edge of the tapping seat brick was relatively intact before the bowl brick was replaced, but there was oxidation and decarburization on the surface. During the process of replacing the bowl brick, the use of pneumatic picks and crowbars would cause the edge to fall off to varying degrees. However, the replacement of taphole components is performed at high temperatures and is difficult to change during on-site operations. Therefore, the edge strength must be strengthened through the production process to improve its applicability.

Figure 8 Diagram A of the weak area formed by the tapping seat brick

Figure 9 Schematic diagram B of the weak area formed by the tap hole seat brick

After analyzing the problems of powdering and peeling of the seat bricks, it was found that in the past, during the process of setting the steel hoops on the taphole seat bricks, the brick wall was cracked after the hoops were placed. Later, by improving the strength of the brick wall material, the crack situation after the hoop was greatly improved. During the forming process of the special-shaped taphole bricks of another manufacturer, due to structural reasons, local segregation and porous conditions occurred. After analysis, it is believed that the outer shell of the taphole seat brick is under uneven pressure, resulting in weak links. Simulation analysis of the outer shell molding of the tap hole seat brick is carried out, as shown in Figure 10. The thickness at A is about 40~55 mm, and the thickness at B is 135 mm. After the mud at A is compacted during molding, the pressure cannot be effectively transmitted to B, making B loose and low in strength.

Figure 10 Simulation diagram of tap hole seat brick forming and assembly

When pouring the mud into the molding, use a special tool to tamp Part B in advance, and at the same time increase the weight of the mud at Part B. As listed in Table 2, the strength of Part B is significantly improved after the improvement.

Table 2 Comparison of results after different molding methods kg

Pressure methodConventional pressurization methodmanual tampingspecial tool pressing
Product unit weight fluctuation range21.60~21.6821.62~21.7221.68~21.78

It was formed using manual tamping and tool pressing, and the product volume density and porosity indexes were analyzed. The data are listed in Table 3. The results show that the volume density and porosity of manually tamped products are slightly higher than conventional molding methods; the density of products pressed with tools is significantly improved.

Table 3 Effects of different pressing methods on product density and porosity

 Conventional pressurization methodmanual tampingspecial tool pressing
Average volume density/ (g·cm³)3.043.053.06
Average apparent porosity/%2.32.22.0

3.3 Improvement of raw materials

The production of taphole bricks usually uses large crystalline fused magnesia from southern Liaoning. However, after many trials and adjustments and improvements, it has been difficult to further improve the life of the taphole bricks. In 2019, large crystalline fused magnesia produced from the Kamado Mining Area in Tibet entered the market. The ore has a microcrystalline structure, a C/S ratio between 2.0 and 3.0, and an extremely low Fe₂O₃ content (≤0. 1%) Its composition and crystallization state of magnesia are significantly different from those of Liaonan magnesia. See Table 4, Figure 11 and Figure 12 for details. This test uses large crystalline fused magnesia produced in the Tibet mining area as the main raw material for taphole bricks.

Because the slag cannot penetrate through the magnesia particles into the interior of the magnesia carbon brick through the interior of the fused magnesia grains. The existence of super large grains and medium grain size magnesia particles on the hot surface effectively prevents the rapid penetration of slag on the hot surface, reduces the contact area between slag and magnesia, and reduces the dissolution rate of magnesia into slag.

Table 4 Comparison of the chemical composition of large crystalline magnesia in southern Liaoning and Tibet

raw material nameBurn reduction/%SiO₂/%Fe₂O₃/%Al₂O₃/%CaO/%MgO/%C/SBulk density/(g·cm-³)
Liaonan 98 large white crystalline magnesia0.10.470.510.150.7897.991.73.48
Tibet 98 large crystalline magnesia0.10.460.050.131.1898.082.63.50

Figure 11 98 white large crystalline magnesia in southern Liaoning (crystal particle size: 200~700μm)

Figure 12 98 large crystalline magnesia in Tibet mining area (crystal particle size: 700~2000 μm)

Table 5 lists the physical properties of taphole bricks using two different types of magnesia at room temperature, as well as the improvement data after process optimization. At Benxi Iron and Steel Company, by solving the problem of steel penetration and sintering, the average service life of the converter sliding plate slag blocking taphole brick was increased from the initial 82.26 furnaces to 168.86 furnaces. Through measures such as improving the production process and introducing high-performance raw materials, the average life of the tap port has reached 208.72 furnaces, and the maximum service life has reached 269 furnaces. The average life of the taphole has increased by 153.7% compared with the initial period. The application of Hebei Yongyang Iron and Steel Company shows that by adopting measures such as replacing core seat bricks and high-performance raw materials, the maximum furnace age of the taphole bricks has been increased from the original 300 furnaces to more than 540 furnaces, and the service life has been increased by 80%.

Using high-quality raw materials from Tibet, the structure of the taphole bricks was optimized and the production process was adjusted to develop a high-life sliding slag-blocking taphole brick. Compared with the previous taphole bricks, its service life has been greatly improved.

Table 5 Comparison of indicators of products produced by different magnesia and processes

Product CategoryAverage apparent porosity/%Average volume density/(g·cm³)Average compressive strength/MPa
Taphole bricks using large crystalline magnesia from Liaonan 2.3 3.04 38.4
Taphole bricks using large crystalline magnesia from Tibet2.13.0539.5
Taphole bricks adjusted using Tibetan large crystalline magnesia and pressurization process1.93.0642.1

4 Conclusion

(1) Strictly control the gap between the inner nozzle brick and the replacement core and the gap between the seat brick and the replacement core, which can effectively avoid steel penetration at the brick joints and improve the anti-seepage ability of the gaps.

(2) The use of replaceable core bricks can effectively improve the overall life of the sliding plate slag-blocking taphole bricks.

(3) Optimizing the size of the arc radius R of the replacement core can increase the effective thickness of the working layer of the replacement core and improve the life of the tap hole.

(4) Special tools are used to pre-press the edge of the seat brick, which can improve the edge strength of the seat brick, effectively solve the problem of edge cracking and powdering, and is more stable and safe than the manual method, significantly extending the life of the seat brick.

(5) The use of high-calcium and low-iron 98 large crystalline fused magnesia produced in the Kamado mining area in Tibet can improve the corrosion resistance of the taphole bricks and help extend the life of the taphole.

LMM YOTAI established in 2007. Our production technology comes from Japanese Yotai. As an experienced and international player in the refractories industry. We have succeeded in expanding both the breadth of its product range and the depth of its services. From raw material selection, refractory portofio & optimization, installation & services & recycle of used refractories on site to further reduce client’s Opex & Capex in refractory consumption per ton steel output, meanwhile improve product quality of client.

Our Product have been supplied to world’s top steel manufacturer Arcelormittal, TATA Steel, EZZ steel etc. We do OEM for Concast and Danieli for a long time

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