Improvement method for fire running in precision casting shell

Improvement method for fire running in precision casting shell

What is running fire in precision casting? As the name suggests, it is fire running out of the mold shell. The fire here refers to molten metal, which means that running fire is actually when the metal liquid runs out of the shell after being poured into it. What is the reason for this? It is obvious that the strength of the shell is not sufficient to resist the impact of molten metal on the shell, static pressure, and the test of high-temperature strength of the shell by high-temperature liquid metal. In other words, the high-temperature strength of the liquid metal is not enough. Today, precision casting manufacturer Tianyao Metal will talk to you about the improvement methods for mold shell fire.

When it comes to the strength of the shell, what is meaningful for the shell to escape fire is the wet strength and high temperature strength of the shell. Some people may think that the wet strength of the shell does not contribute much to the shell's fire resistance, or that it has little to do with it. This idea is incorrect, in fact, the strength of the shell is hereditary. The reason for saying this is because in fact, the better the wet strength, or the better the shell is dry, the better its wet strength can be, and its high-temperature strength can be guaranteed. This statement may not be correct, but it is indeed true. If the shell catches fire, it is definitely due to cracks in the shell, which may occur during the dewaxing and later pouring processes. Therefore, the reason for the fire may exist in the production, drying, and pouring processes of the shell.

A typical dewaxing process produces cracks (most likely due to poor drying). I think the first reason for this is poor drying. The humidity of the surface layer even reaches 80%, and the drying rate of this humidity is very slow. If we continue to operate according to the regular drying time, the drying will definitely not be in place, so it may be difficult to pass the dewaxing process. And several broken parts are all preventing free dewaxing. So, crack formation is inevitable, and the location of fracture is inside the mold shell, which can only be discovered after the casting is produced. This is a typical example of casting fire caused by low wet strength. Another point that needs to be explained to everyone is that the reason for the high humidity on the surface layer is for complex products, especially those with complex inner cavities. It is required that the drying inside and outside of the product should be consistent and uniform, to avoid shrinkage stress causing shell cracks. However, simple products do not necessarily need to be done that way, 50% humidity is sufficient.

The common way we run fire is directly from the outside, such as sometimes cracking from the four corners of the sprue after pouring. Generally speaking, it is caused by the insufficient thickness of the shell or the fire resistance of the shell refractory material. Sometimes it may also be caused by external forces, such as excessive force during the placement of the mold shell after pouring, causing the mold shell to catch fire from the bottom.

To sum up, there are two types of fire runaway. One is external fire runaway, which is often caused by insufficient thickness of the mold shell or insufficient fire resistance of the refractory material; One type is internal fire, often caused by defects in the shell making process, such as bridging or poor drying, which cannot be detected before pouring, leading to fire. The natural way to improve is to reasonably determine the number of shell layers based on the structure and size of the product. Shell production must strictly follow the process documents to ensure that the shell is dry and in place.

Precision machining