Is there any garbage in the precision casting shell?

Is there any garbage in the precision casting shell?

For most civilian products, the shell made with silica sol binder does not require further treatment. After the shell is dried, it only needs to undergo conventional dewaxing, roasting, and then pouring, and the entire casting process is basically completed. However, for products with high quality requirements, these alone are not enough. For example, for aerospace and automotive castings with high internal quality requirements, not only are appearance quality and dimensional accuracy required, but also corresponding requirements are put forward for internal metallurgical quality. At this time, requirements will also be placed on the garbage inside the mold shell. High quality castings generally do not allow defects such as inclusions and sand inclusions, and the mold shell has the conditions to form inclusions and sand inclusions. Therefore, garbage removal action must be carried out on the mold shell before pouring. Someone may say, isn't it just shell washing? It's so mysterious. That's not the case. Why wash the shell? What's inside the shell? You need to figure it out. Today, precision casting manufacturer Tianyao Metal will talk to you about the garbage in the mold shell?

Someone may say that there is sand and dust inside the shell. Not only these, but also the ash content of silica sol and wax, and possibly the surface layer flakes. So how did all of this come about? Sand and dust may come from wax, improper external operations, poor drying of the mold shell, and low local strength. It is mentioned that the water after cleaning each set of shell mold contains 0.5-0.6g of debris residue after filtration analysis. These debris are ash in wax and gel of ultrafine particles. These gel are silica sol gels. During dewaxing, most of the gel can be melted out with the wax, but a small part will stick to the shell wall. We often feel dust on the mold shell, which is the silica sol gel. Once poured and mixed with the metal liquid, it becomes an inclusion.

In addition, roasting furnaces are also a reason for generating waste. Due to the possibility of dust from insulation materials, refractory bricks, and shell fragments entering the shell, it is necessary to cover and protect the opening of the shell, such as the riser, during secondary roasting to ensure that garbage does not enter the shell. Based on the above reasons, we need to remove waste from the roasted shell. There are several cleaning methods here:

1. Blow with compressed air. For castings with simple shapes, compressed air blowing can be used. However, when blowing, try to keep the sprue cup down to ensure that dirt can be blown out. Secondly, it is necessary to ensure that the compressed air is dry, free of water and oil, as these can have side effects on the casting.

2. Cleaning. There is water for cleaning, and the cost of water is low. Some people also use alcohol, but the cost is a bit higher.

Try to use water as much as possible with compressed air. Turn down the compressed air and place it under the water surface, slightly foaming it to help improve the quality of shell cleaning. Secondly, it should be noted that some materials recommend using warm water at 50-60 ℃ for cleaning as much as possible. Because after cleaning the shell, the shell must go through a secondary roasting process. After the shell is soaked in warm water, it can naturally evaporate and disappear. However, after the shell is roasted with warm water, boiling water can cause shell peeling and damage.

Precision machining