Technical Analysis of Casting Mold Shell in Shell Baking Furnace

Before pouring the mold shell in the mold shell roasting furnace, preparation work should be done first. After dewaxing, the mold shell must be left to stand for more than 4 hours because the moisture content of the mold shell is high after dewaxing, and the room temperature strength cannot be improved. Secondly, it is necessary to carefully inspect the surface quality of the mold shell for cracks and damage. Defective mold shells should be repaired in a timely manner. After repair, it directly enters the shell baking process.
It is recommended to open the shell upwards and cover it with a dedicated lid as much as possible to prevent dust from the roasting furnace from entering the shell, which may affect the quality of the casting after pouring. Another point is that the shell cannot be stacked to avoid deformation of the formed shell and affecting the quality of the casting.
According to the quality requirements of castings, it may be necessary to clean some of the shell after roasting to remove sand, impurities, and dust inside the shell. It should be noted that the cleaning method for the mold casing.
Currently, there are two types of mold shell cleaning agents: water and alcohol. It is recommended to rinse with warm water at 50-60 ℃. The reason is that the water immediately evaporates after cleaning with warm water, causing less damage to the mold shell. When using cold water, water will seep into the crystallizer shell, and the secondary roasting of the crystallizer shell will cause water to boil and damage the crystallizer shell. Water washed templates should use air foaming as much as possible. The simple method is to fill the outer shell of the mold with water, reduce the pressure of compressed air, and then go deep into the water, relying on compressed air to foam. Alcohol can be used as much as possible with water to reduce cleaning costs. Alcohol will not damage the mold shell because of its strong volatility.
The calcined mold shell has a high temperature strength to resist the thermal shock of liquid metal. Pouring should be carried out in a red hot state. However, the thickness of the mold shell is relatively thin, and there is a significant difference from the external room temperature (even in hot summer, the on-site temperature cannot exceed 60 ℃). According to data statistics, after the crystallizer shell is taken out of the roasting furnace and left in the air for 1 minute, the temperature difference between the inner and outer layers of the crystallizer shell is 400 ℃. Therefore, it is necessary to ensure that pouring is completed within 20 seconds after removal from the furnace.
Currently, there are two popular pouring methods: shell pouring and subcontracting pouring. These two methods each have their own advantages and disadvantages. Due to the fact that the metal liquid is directly poured from the mold shell roasting furnace, there is no oxidation and high temperature in the metal liquid, which can avoid the defect of insufficient pouring. The disadvantage is that the mold shell should be poured as soon as possible after being taken out of the furnace, and the shell picker emphasizes coordination with the furnace platform; Subcontracting pouring is direct pouring without coordination, but the drawbacks are obvious: the mold shell temperature is difficult to control and is prone to secondary oxidation. It should be pointed out that the ladle must be preheated to 800-900 ℃ and thoroughly preheated before use.