How to control the casting of fused bricks

How to control the casting of fused bricks？

The melt of fused zirconium corundum bricks during casting must not only ensure good fluidity, but also avoid overheating, because overheating will promote the melt to absorb gas, and the shrinkage rate after casting into the mold will increase accordingly. Shrinkage and cracking will also occur. Therefore, when the melt temperature is too high, let it stay in the furnace for a few minutes to more than ten minutes, or when casting, adjust the melt flow rate to allow it to reach a suitable temperature. Before taking out the melt, the liquid outlet and discharge nozzle need to be cleaned, and the cooling and power supply of the furnace shell must be stopped. When casting, tilt the furnace body so that the melt flows out from the liquid outlet, passes through the trough, and is cast into the prefabricated and installed refractory mold. Start with thick, powerful streams and then inject the model with long, thin streams. Until the upper riser is filled, taking a square brick with a length × width of 600mm × 300mm and a thickness of 200mm as an example, the casting time is 30-40s, while a square brick with a thickness of 250mm is 40-50s.

The casting speed and casting time vary depending on the mold material and mold size. Too fast a pouring speed will cause material accumulation in the model, and cracking will occur in the future. Too slow a pouring speed will cause corrugated knots on the surface of the fused bricks and a decrease in density. The melt cast into the mold gradually cools and condenses, turning into a crystallized entity. Crystallization first starts on the wall of the casting mold and gradually expands to the inside of the fused brick. Because the volume of the crystal is smaller than the volume of the liquid, shrinkage holes are formed during casting, which greatly changes the volume of the fused brick. Fused zirconium corundum brick The volume change is as high as about 30%. Generally, shrinkage cavities are distributed in the upper half of the brick, that is, under the casting port, accounting for about 1/3-1/4 of the thickness of the fused brick.

 

In order to reduce the volume of shrinkage cavities and increase the fine area of AZS bricks, in the casting process, the casting method with a riser is often used, that is, an extended casting cap (funnel-shaped) is added to the upper part of the mold casting opening to store the melt. body to add the filling amount of melt in the mold. The liquid melt enters the brick body through the riser and fills the shrinkage cavities. After 2-3 minutes, the skin is formed, and the remaining melt is extruded through a connected riser; if the melt does not completely separate from the riser, it is extruded again after 4-5 minutes. The casting mold for fused bricks is assembled from cast iron plates (heat-treated) or graphite rectangular plates with a thickness of 50mm. In-mold dimensions depend on melt crystallization effects. The dimensions of the standard square brick mold are increased by 2%.

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