What is running fire in precision casting

What is running fire in precision casting

Running fire generally occurs in sand casting. I checked the Investment Casting Manual and surprisingly, there was no defect of running fire. However, in both the "Handbook of Casting Defects and Countermeasures" and "Practical Investment Casting Technology" written by Jiang Buju, there are fire defects, both of which are listed under the details of investment casting defects. Today, precision casting manufacturer Tianyao Metal will talk to you about the reasons that cause overheating.

Running fire, as the name suggests, means the fire has come out. The fire here actually refers to high-temperature molten metal. Because the temperature of the molten metal is high, it is similar to fire in terms of color and temperature, so the term "running fire" has emerged. Since it can escape fire, it indicates that there is a channel for the shell to escape fire, which means that the strength of the shell is not enough, providing an opportunity for the metal liquid to escape. So, what are these channels and what are the reasons behind them?

1、 The lack of dryness or poor shell making operation in the holes or deep grooves of the product forms a bridge, resulting in insufficient high-temperature strength of the shell. Finally, under the action of high-temperature metal, the shell may crack or rupture, ultimately leading to the fact that the shell runs out and the casting is scrapped.

2、 During the process of dewaxing, transportation, or roasting, the formed shell of the product may crack due to collision, resulting in the shell catching fire and the casting being scrapped.

3、 The thickness design of the casting shell is insufficient, and the shell directly ruptures during the pouring of molten metal, forming a fire defect and causing the casting to be scrapped.

4、 The thermal shock resistance of the shell is poor, and it directly cracks during the pouring of the metal liquid, forming a fire defect. This phenomenon is often encountered in quartz shells.

In addition, it should be noted that there is a defect similar to fire running, which is that high-temperature metal liquid flows out of the shell during pouring, but only in small amounts. The shape of the casting is intact and can still be used after cleaning and polishing. We distinguish this defect from fire running and call it shell leakage. It is different from running fire in that the casting is not scrapped, it only requires additional cleaning and polishing efforts.

We can see from the above situations that there are multiple reasons for the occurrence of shell fire, including operational aspects, such as; The first and second situations mentioned above; There are design aspects, such as the third scenario; There are also details such as the quality of raw materials that we need to pay attention to in our daily work, so we must do a good job in these details to ensure the quality of the shell and reduce the occurrence of fire defects.

The fundamental way to improve the defect of running fire is to make the shell well and change bad operating habits, which will not be repeated here.

Precision machining