Preparation before pouring precision casting shell

Preparation before pouring precision casting shell

After the dewaxing of the investment casting shell is completed, it is ready for pouring. Firstly, the mold shell must be left to stand for at least 4 hours after dewaxing, as the moisture content of the mold shell after dewaxing is relatively high 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. If any problems are found with the mold shell, they should be repaired in a timely manner. After the repair is completed, the mold shell baking process should be directly carried out. Mold shell roasting prevents dust from entering the mold shell, which in turn affects the quality of the castings after pouring. Also, the mold shell cannot be stacked to avoid causing deformation of the mold shell and affecting the quality of the casting.

According to the quality requirements of castings, some of the mold shells may need to be cleaned after baking to remove sand particles, impurities, and dust from the mold shells. It is important to note the method of cleaning the mold shell. There are currently two types of mold shell cleaning agents I have seen: water and alcohol. It is recommended to use warm water at 50-60 ℃ for water, as the water immediately evaporates after cleaning with warm water, causing minimal damage to the mold shell. When using cold water, water seeps into the mold shell, and the second roasting of the mold shell can cause water boiling and damage to the mold shell. Try to use air foaming for washing the mold shell. The simple method is to fill the mold shell with water, reduce the pressure of compressed air, and then go deep underwater, relying on compressed air to foam. Alcohol should be used in conjunction with water as much as possible to reduce cleaning costs. Alcohol, due to its strong volatility, will not cause damage to the mold shell.

The precision casting mold shell has high-temperature strength that is resistant to the thermal shock of molten metal after being baked. Pour in a red hot state. However, due to the relatively thin thickness of the mold shell and the significant difference from the external room temperature (even in hot summer, the on-site temperature does not exceed 60 ℃). According to data statistics, the temperature difference between the inner and outer layers of the mold shell after being exposed to air for 1 minute after coming out of the calcination furnace is 400 ℃. Therefore, it is necessary to ensure that the pouring is completed within 20 seconds after removal from the furnace.

There are currently two popular pouring methods: shell casting and subcontracting casting. These two methods each have their own advantages and disadvantages. Shell casting, due to the direct pouring of the metal liquid from the furnace, the metal liquid does not oxidize and the temperature is high, which can avoid insufficient casting defects. The disadvantage is that the mold shell needs to 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 does not require coordination and can be poured directly, but its drawbacks are obvious: the mold shell temperature is difficult to control and is prone to secondary oxidation. It should be pointed out that the subcontracting pouring package must be preheated to 800-900 ℃ and preheated thoroughly before use.

Actually, every product is composed of one detail at a time. Every detail needs attention. Only by cultivating the habit of being careful and serious can we truly do our work well and benefit from it for a lifetime.

Precision machining