The Submerged Entry Nozzle (used for the nozzle between the tundish and the mold), the long nozzle (used for the nozzle between the ladle and the tundish) and the sliding nozzle are called the “three major pieces” of refractory materials for continuous casting. Refractory materials used in the final stage of the steelmaking process. They are different from other refractory materials in that they are mostly used as their own single components.
In the early stages of the introduction of the continuous casting method, fused quartz nozzles were used as continuous casting nozzle bricks based on the requirement of thermal shock resistance and the ability to be used without preheating. However, it has the disadvantage of extremely poor durability for steel types with high Mn content. Due to the development of steelmaking technology, which requires multi-furnace continuous casting and the production of clean steel, there is an urgent need to improve the durability of the nozzle. For this purpose, the highly durable Al2O3-C nozzle (AG quality nozzle) was developed and is still used as a mainstream nozzle brick to this day.
Continuous casting requirements for Al2O3-C Submerged Entry Nozzle In order to withstand the operating conditions of continuous casting steel, Al2O3-C (AG) quality refractory materials should have:
(1) It has good resistance to mold slag.
(2) It has excellent thermal shock resistance and can withstand severe thermal shock conditions at the beginning of steel casting.
(3) It has good corrosion resistance to molten steel.
(4) It has better resistance to oxidation and weakening during preheating and actual operation.
(5) Has sufficient mechanical strength.
Therefore, today, graphite and alumina are used as raw materials, phenolic resin is used as a binder, and antioxidants are added, followed by mixing, isostatic pressing (CIP) molding and firing, and mechanical processing to make long nozzles, integral stoppers and rods. Submerged Entry Nozzle.
This molding (CIP) method achieves the requirements of uniform internal structure and stable quality for large overall products.
For the Submerged Entry Nozzle, the lower part (the part in contact with the mold slag during actual operation) is usually covered with zirconium graphite (ZG) refractory material that has good resistance to the mold slag.
The development of continuous cast refractory products has introduced the isostatic pressing (CIP) molding process into the manufacturing of refractory materials. This is because:
(1) The length/diameter ratio of long nozzle bricks, immersed nozzle bricks and integral stopper rods is too large and cannot be pressed with ordinary double-sided hydraulic presses. Only by using isostatic pressure (CIP) can the pressure on the pressing surface be uniform. The volume density of each section of the brick is uniform.
(2) Isostatic pressing (CIP) can press corundum-graphite mud with high graphite content that is difficult to press and has low binder content and poor plasticity.
(3) Since long nozzle bricks, immersed nozzle bricks and integral plug rods are made of corundum-graphite material with high graphite content, only isostatic pressing (CIP) molding can avoid brick cracks and ensure brick quality.
The above-mentioned corundum-graphite mud material with high graphite content is mainly isostatically pressed using the wet bag method to form long nozzle bricks, immersed nozzle bricks and integral plug rods.
The entire forming process of long nozzle bricks, immersed nozzle and integral plug rods is divided into:
(1) Mold installation. The powder is put into a rubber mold, and when large parts are formed, the mold is placed in a support box.
(2) Close the mold. Seal the installed mold with a closing plug. In some cases, vacuum to remove part of the gas before sealing.
(3) Put it into a high-pressure container. Place the sealed mold together with the support box into a high-pressure container, and then fill the high-pressure container with liquid.
(4) Pressurize. After the high-pressure container is covered with a lid, the liquid and the mold are under pressure at the same time, and the powder is compressed by pressure from all directions to become a dense body.
(5) Take the mold. After the pressure of the liquid in the pressure vessel is removed, the air escapes from the pores of the green body and surrounds the green body. The rubber mold returns to its original shape. The green body can be taken out after taking out the support box. HYRE
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