As a transition device between the ladle and the crystallizer during the continuous casting process, the tundish is not only a storage and distributor of molten steel, but also a refining container for molten steel. It is used to stabilize the steel flow and reduce the scouring of the steel flow on the shell in the crystallizer; it makes the molten steel have a reasonable flow field and a suitable long residence time in the tundish to ensure the uniform temperature of the molten steel and the separation and floating of non-metallic impurities, to ensure the cleanliness of the molten steel and continuous casting of multiple furnaces, which is an important link to improve the quality of steel and continuous casting efficiency.
The refractory bricks for tundish can be divided into three categories from the functional point of view: the first category is the lining material, which is mainly composed of the heat insulation layer, the permanent layer and the working layer; the second category is the flow stabilizing parts, including slag weir, slag plate, impact plate, etc.; the third category is the flow control part, which is divided into stopper rod, sliding nozzle, sizing nozzle and intrusive nozzle, etc. For small billet continuous casting, the core of efficient continuous casting is high casting speed. This requires that on the basis of the molten steel quality meeting the requirements, the continuous operation rate of the continuous casting machine and the steel pouring speed should be improved as much as possible to achieve high billet temperature and billet quality. These technical indicators put forward two requirements for the refractories of the tundish, one is high performance and the other is long life.
The refractory material composition of the tundish lining generally includes the following parts:
(1) Insulation layer (10-30mm), which is close to the tundish steel shell and usually uses asbestos board, insulation brick or lightweight castable. The best effect is aluminum silicate fiber board, which has low thermal conductivity and is easy to lay.
(2) Permanent layer (100-200mm), which is in contact with the insulation layer and is generally made of clay bricks. The integral permanent lining is the most common, and the castable is generally a high-aluminum or mullite self-flowing castable.
(3) Working layer (20-50mm), which is in contact with the molten steel and is a key part. Insulation boards or coatings are now commonly used. Insulation boards are generally made of silicon, magnesium, or forsterite; coatings are made of magnesium, magnesium-chromium, or magnesium-calcium. Coatings are applied mechanically or manually.
(4) Seat bricks, which are embedded in the bottom of the tundish and used to install the tundish water inlet. They are usually made of high-aluminum. (5) The bottom of the tundish, whose material is basically the same as the working layer. The working layer of the bottom of the tundish is easily damaged by the impact of molten steel and requires corrosion resistance and wear resistance. Generally, high-aluminum bricks or dense high-aluminum refractory bricks and aluminum-chromium bricks are used, and special large blocks of high-strength tar magnesium bricks are also used. Zircon bricks or prefabricated blocks are used to strengthen the impact area of molten steel.
(6) The cover covers the tundish and can play a role in heat preservation and molten steel splashing. The material used is clay or high-aluminum castables as the cover.
(7) Slag retaining wall (weir), which is built in the tundish and can be a single wall or a double wall. The material of the slag retaining wall is usually high-aluminum brick, which can also be made into prefabricated blocks. Its purpose is to block. In order to improve the cleanliness of molten steel, a molten steel filter can also be set on the slag retaining wall.
Magnesia-chrome brick is a refractory material with excellent erosion resistance and is suitable for tundishes with high molten steel temperatures. However, magnesia-chrome refractory bricks have poor thermal shock resistance, are prone to cracks, and are expensive. High-aluminum bricks: High-aluminum bricks are a common refractory material with good high temperature resistance and thermal shock resistance. However, high-aluminum bricks have poor erosion resistance and are suitable for tundishes with low molten steel temperatures. Zircon bricks: Zircon bricks are a refractory material with excellent erosion resistance and high temperature resistance, suitable for tundishes with high molten steel temperatures. However, zircon bricks are expensive and difficult to construct. Silicon carbide bricks: Silicon carbide bricks are a refractory material with excellent erosion resistance and high temperature resistance, suitable for tundishes with high molten steel temperatures. However, silicon carbide bricks have poor thermal shock resistance and are prone to cracks.
