Refractories for Tundish
As a transitional device between the ladle and the crystallizer during the continuous casting process, the tundish is not only a storage and distributor?for molten steel, but also a refining container for molten steel. It is used to stabilize the steel flow and reduce the impact of the steel flow on the billet shell in the crystallizer. Ensuring that the molten steel has a reasonable flow field and a suitably long residence time in the tundish to ensure uniform temperature of the molten steel and the separation and floating of non-metallic impurities, as well as ensuring the cleanliness of the molten steel and continuous pouring of multiple furnaces, which is an important link in improving steel quality and continuous casting efficiency.
The main tasks of the tundish are:
(1)Divert molten steel. The multi-stream continuous casting machine distributes molten steel to various crystallizers through the tundish.
(2)Steady flow. Reduce the static pressure of molten steel, maintain a stable liquid level in the tundish, and smoothly inject molten steel into the crystallizer.
(3)Store molten steel. When replacing the ladle in continuous pouring of multiple furnaces, the pulling speed is not reduced to create conditions for continuous pouring of multiple furnaces.
(4)Purify molten steel. During a long pouring time, the temperature of the molten steel is basically kept constant, which promotes the further floating of inclusions in the molten steel, prevent contact between the molten steel and the air, and avoid?oxygen and nitrogen absorption.
Refractories used in the tundish can be functionally classified into three categories:
The first category?is lining material, which mainly consists of insulation layer, permanent layer and working layer.
The second category is flow stabilizing components, including slag weir, slag baffle, impact pad, etc.
The third category is the flow control part, which is divided into stopper rod, sliding nozzle, sizing nozzle and submerged?entry nozzle.For billet continuous casting, the core of high-efficiency continuous casting is high casting speed, which requires that the continuous operation rate and pouring speed of the continuous casting machine should be improved as far as possible on the basis of the molten steel quality meeting the requirements, so as to achieve high billet temperature and billet quality.?These technical indicators put forward two requirements for the tundish refractories, one is high performance, and the other is long service life.
The composition of refractories?for the inner lining of the tundish generally includes the following parts:
(1) Insulation layer(10～30mm),this layer is next to the tundish steel shell and is usually uses asbestos panels, insulating bricks or lightweight castables. The best effect is aluminum silicate fiber felt, which has low thermal conductivity and is easy to build.
(2)Permanent layer (100～200mm),this layer is in contact with the insulation layer, and generally uses clay bricks. The overall?permanent lining is the most common, and the castables are generally high-aluminum or mullite self-flowing castables.
(3)Working layer(20～50mm),this layer is in contact with molten steel and is a key?part.Insulation boards?or coatings are commonly used now. The insulation board is generally made of silicon, magnesium, or magnesium olivine.?The coating is made of magnesium, magnesium chromium, and magnesium calcium. The coating shall be mechanically sprayed or manually applied.
(4)Well block,it is embedded at the bottom of the tundish, used to install the nozzle of tundish , usually made of high aluminum material.
(5)Tundish bottom working layer,the material of the bottom of the tundish is basically the same as that of the working layer. The bottom is easily damaged by the impact of molten steel and requires corrosion resistance and wear resistance. Generally, high alumina bricks or dense high alumina bricks and aluminum chromium bricks are used, as well as specially made large high-strength tar magnesium bricks. The molten steel impact part is reinforced with zircon bricks or precast blocks.
(6)The cover covers the tundish to insulate and prevent molten steel from splashing. The cover is made of clay or high-aluminum castables.
(7)Slag baffle(Weir),the baffle is built in the tundish and can be a single or a double. The material of the baffle(weir) is generally casted with refractory castables, such as high-alumina, aluminum-magnesium or magnesium, etc., which are made into precast blocks through curing, demoulding, baking and other processes.Magnesium baffles are widely used because they have good corrosion resistance, high refractory resistance, and can effectively reduce the oxygen content brought into the molten steel. Their purpose is to retain molten slag. In order to improve the cleanliness of molten steel, a molten steel filter can also be arranged on the baffle.
The End.