The surface detachment of investment casting parts is caused by insufficient adhesive strength on the surface or damage by external forces. Let's take a look at two key factors: insufficient self adhesive strength and external force damage. So what factors are strongly related to these two factors, specifically as follows:
1. In terms of coating viscosity for castings, the coating is used to bond sand particles, while achieving the adhesion of two coatings and sand particles. The low viscosity of the coating results in insufficient strength of the thin coating and high maintenance viscosity of the coating, resulting in poor strength due to drying or hardening after the coating. The coating temperature is too low, causing the previous layer of coating to cool and cause coating cracks to fall off.
2. In terms of coating performance for investment castings, the unqualified powder, binder, and additives themselves cause strength failure; The coating preparation time is too short and not fully recovered; Failure to standardize maintenance of coatings resulting in coating failure or uneven coating; Poor flowability of coatings; Adding a lot of foreign substances to strengthen or improve other issues in the coating, resulting in poor stability of the coating; Coating additives can accelerate the deterioration of coatings by feeling that the addition is not quantified or standardized; The preparation of coatings is not standardized according to specifications, which is very arbitrary, and the performance of coatings such as powder to liquid ratio is not up to standard. In fact, the preparation of coatings is also meticulous; The changes in coating environment have a significant impact on coating performance.
3. In terms of adhesive and sand application, the coating is too thin due to prolonged slurry control time; Short slurry control time, poor coating accumulation and drying; Poor sanding and insufficient coating strength.
4. In terms of metal casting parts drying, the drying time is too long, too dry, or too short; Inappropriate drying wind speed and temperature.
5. In terms of sand material, the sand material has a high powder content, and during the sanding process, the dust first adheres to the coating, making it too dry and poor for sanding; The improper particle size of the sand material results in inadequate adhesive strength of the coating.
6. In terms of casting process design, poor dewaxing causes deformation of the dewaxing mold shell due to expansion and stress, which can lead to cracking and detachment in severe cases; The tree string process is not suitable, and the eccentric force during the shell making process causes the mold shell to crack and the coating to fall off.
7. In terms of investment casting component structure, the product structure is flat, and the coating separates from the wax mold surface, causing coating bulging or cracking, leading to severe detachment.
8. After the casting is dewaxed, there is too much residual water in the mold shell, which is directly baked in the furnace, causing rapid vaporization of water and damaging the coating; Generally, after dewaxing, the mold shell needs to be stored for a period of time before being baked and poured.
9. The baking of the mold shell of the casting should avoid rapid heating to prevent the mold shell from rapidly expanding and causing deformation of the coating, which can lead to cracking and detachment in severe cases.
10. Is there any force on the coating during the shell making process. Drying, vibration, collision, and other factors such as sanding machines and floating sand buckets can cause coating detachment.
Investment casting ( As well as known precision casting and lost wax casting) is a very complex engineering project with many influencing factors, involving various professional fields.
We are a manufacturer providing investment casting services. We hope that the internal surface detachment of the mold shell we share will be helpful to investment casting practitioners. If you have any problems, please email us. We will respond with ideas, analysis, or solutions based on our work experience.
Email: boah@sczyltd.com
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