This issue will discuss the most common problem in the lost-wax investment casting process for shell making—the problem of succulent defects in the shell.

2. Cause: The coating surface is detached or peeled off, a

3. Specific reasons and possible improvements:

(1) The front and back coatings are not firmly connected, mainly in the following aspects:

① The sand material contains too much powder, resulting in the coating being coated with powder after the slurry is applied, effectively isolating the adhesion between the sand and the slurry;

The powder content needs to be controlled according to industry standards (generally ≤0.03%). Speaking of powder content, several aspects should be considered when designing equipment: no powder should be generated, and dust removal is required. Dust collector sand, ground sand and workshop corner sand cannot be used. ② Excessively large or small differences in the particle size of the sand between the front and back layers result in poor joint strength. This difference in particle size prevents the front and back layers from effectively fitting together, reducing strength and increasing the risk of peeling. The sand selection for each layer of shell construction should refer to industry standards and be considered in conjunction with the casting structure.

③ The coating layer between the front and back layers is too thin or too thick, resulting in insufficient strength. The viscosity of each coating layer is crucial; using the same coating or sand for each layer is a taboo. While a thin coating layer is easy to understand, a thick coating layer can lead to low strength for three main reasons: It prevents the coating from drying and hardening effectively; it prevents effective slurry control, leading to coating accumulation; and it makes it difficult for the coating to flow into the gaps between the previous layer's sand particles. ④ The coating deteriorates and the strength is insufficient. The coating maintenance is critical. ⑤ Water glass shell making: Insufficient hardening and drying; The silica sol shell mold is not effectively dried. ⑥ The shell floating sand is not processed. ⑦ The silica sol shell is over-dried, and the coating cannot effectively coat the previous layer. It is recommended to add a pre-wetting process.

(2) The coating strength is insufficient, and it falls off or glass or collapses during dewaxing. Pay attention to several key points: Drying and hardening are very important, coating quality control is very important, and special product shell making operation details are very important. Pay attention to several key points of dewaxing: Dewaxing increases pressure quickly and releases pressure slowly. After dewaxing, the mold needs to be fully dried before firing. Casting process design is very important: It is easy to remove wax so that the overall force of the dewaxing mold is small. The process design is easy to control slurry, sprinkle sand, and dry to ensure the quality of the mold. Attention should be paid to firing: It is best to fire the mold according to the drying, firing, and insulation stages to avoid the mold directly entering the temperature environment required by the process for firing. Core: Avoid rapid heating of the mold. Improve formwork strength: Consider formwork strengthening technology (wet strength, high temperature strength)。

I am Venda from China, and I have been working in the investment casting industry for over 20 years. I am eager to discuss the problems and improvement methods encountered in the precision casting process with teachers and experts from the global precision casting industry. My contact information is WhatsApp/WeChat: +8618562112686