Why do silica sol precision castings in production need to clamp iron?

With the introduction of silica sol shell production technology in my country, the production of silica sol precision castings in my country has developed rapidly. In view of the development of the forging industry in recent years, the competition in the same industry has become more and more fierce. There are comparisons in many aspects such as raw materials, equipment, and technology, and customers have higher and higher requirements for casting quality. Ningbo Zhiye Machinery Parts Co., Ltd. specializes in the production of precision castings made of various carbon steel, alloy steel, stainless steel and other materials.

There are many reasons for iron inclusion in castings, which can be analyzed from three aspects: welding, shell making, and casting. Among the three, shell making is the key. Let’s first analyze the reasons for iron inclusion in terms of shell making:

1. Improper preparation of raw materials: A large amount of gas is generated by a chemical reaction in the surface layer slurry, which will adhere to the wax parts along with the paint. In addition, if the slurry is too thick, its fluidity will be reduced, and some grooves and corners of the wax parts will not be covered, leaving air holes, and iron beans will appear after casting.

2. The correct selection of the number of sand grains: the casting structure is complex, with deep and narrow gaps or holes, because the sand is too thick, so that these places are blocked, resulting in insufficient dipping, resulting in the shell not dense, and some shells Thinner, less strength.

Corresponding measures: During the processing of silica sol precision casting, before soaking the slurry, blow off the floating sand on the upper layer with an air gun, and then pass the silica sol once before soaking the slurry, which can enhance the fluidity of the slurry and avoid clogging . After floating sand, the operator can use a thin rod to pass through a round hole and pile sand in the gap, which is also helpful for the subsequent soaking and sanding. In addition, for deep hole products, it is possible to fill the hole with grout and sand after the third layer, so as to avoid iron leakage on the inner wall of the deep hole.

3. If the mold shell is dry and impermeable, it will directly lead to a sharp drop in the strength of the shell. And the reason is that the temperature and humidity in the workshop are not good, which makes the drying time insufficient.

Corresponding measures: control the temperature and humidity in the workshop, and adjust according to the actual situation.

Next, let’s talk about welding. It will not directly lead to iron inclusion in the product, but due to the unreasonable welding process, it will increase the difficulty of the shell-making operation, and then the iron inclusion rate of the product will increase. Usually, many factories use a wax to maximize profits. The rod will be full of products. Although the yield is high, if the product is too dense, the slurry cannot enter. The shell between the gate and the wax rod is not thick enough and has no certain strength. There will be iron leakage, so the gap between products must be scientifically arranged.

Secondly, for products with deep holes and grooves, the complicated side of the silica sol precision casting must face up or face away from the wax stick, so as to facilitate draining, blowing, and drying. Shell workers work on a piece-rate wage system. They cannot waste too much time and energy on a series of products. For them, the more they do in the same time, the more they get. Therefore, we should also improve the welding method. , so as to help them reduce the difficulty of operation, improve work efficiency and ensure product quality.

To sum up, iron inclusion defects in castings are mainly found in welding, shell making, and casting. As long as these three are well controlled, most iron inclusion problems can be resolved.