A Practical Review of Zircon and Fused Silica Mixed Slurry for Shell Making
In investment casting, zircon flour is widely used in primary slurry because of its good thermal stability, high refractoriness and reliable casting performance. However, zircon flour is also a relatively expensive raw material. For foundries that produce stainless steel and other precision castings, reducing shell-making cost without sacrificing surface quality is always an important topic.
A published production study tested the use of mixed slurry made with zircon flour and fused silica powder in silica sol shell-making. The study compared traditional 100% zircon flour primary slurry with mixed zircon and fused silica systems, especially 70% zircon flour + 30% fused silica powder and 50% zircon flour + 50% fused silica powder.
Why Fused Silica Powder Was Considered
Fused silica has several properties that make it interesting for investment casting shell systems. It has high SiO₂ purity, low thermal expansion and excellent thermal shock resistance. Compared with zircon, fused silica has a much lower density, which can also help reduce material weight in the slurry system.
The study noted that fused silica powder can improve shell collapsibility and make shell cleaning easier after casting. This is especially useful where foundries want to reduce cleaning difficulty while maintaining acceptable surface roughness and dimensional stability.
The Main Challenge: Density Difference
One technical challenge is that zircon flour and fused silica powder have very different densities. Zircon has a density of about 4.5 g/cm³, while fused silica is around 2.2 g/cm³. Without proper formulation and mixing, the two powders may separate in the slurry.
To solve this problem, the study used a special homogenizing additive. The additive helped combine the two different powders more evenly, improving slurry stability, flowability, coating performance and dispersion.
Production Trial Results
The first production trial used a mixed slurry containing zircon flour and fused silica powder. The slurry showed good flowability and smooth coating performance on wax patterns. It distributed evenly on the surface, with no obvious slurry accumulation. After sanding, the sand layer was also uniform.
The castings produced with mixed slurry showed good surface quality. The surface roughness and finish were comparable to castings made with traditional 100% zircon flour slurry. The study also reported stable dimensions and easier shell removal.
A second production trial used a 50% zircon flour + 50% fused silica powder primary slurry. This formulation was tested on stainless steel elbow flange castings and a pump body casting. The slurry remained workable after several days of slow stirring. After standing, the slurry showed sedimentation, but zircon flour and fused silica powder did not visibly separate, indicating that the homogenizing additive played an effective role.
The final castings passed dimensional inspection, and the surface roughness was good. According to the study, the casting surface quality reached or even exceeded the level of the 100% zircon flour slurry in the tested production conditions.
Cost Reduction Potential
One of the most important findings was cost reduction. Based on the 50% zircon flour + 50% fused silica powder system, the study reported that the cost of the primary refractory powder could be reduced by about 40%.
This does not mean every foundry can directly replace zircon flour by the same ratio. Slurry formulation, silica sol quality, powder particle size, homogenizing additive, mixer design, drying condition and casting material all influence the final result. However, the study shows that fused silica powder can be a practical option for foundries looking to reduce zircon consumption while keeping good casting quality.
Practical Points for Foundries
For foundries considering zircon and fused silica mixed slurry, several points should be reviewed carefully:
- The particle size of fused silica powder should match the slurry system.
- The density difference between zircon and fused silica must be controlled by proper formulation and mixing.
- A suitable homogenizing additive may be needed to prevent powder separation.
- Slurry viscosity and coating weight should be checked before production.
- Trial casting should be carried out before full production replacement.
- Surface roughness, dimensional accuracy and shell cleaning performance should be evaluated together.
What This Means for Fused Silica Buyers
For investment casting applications, fused silica powder is not only a cost-saving filler. It can also contribute to low thermal expansion, thermal shock resistance and easier shell removal. When used properly with zircon flour, it may help foundries build a more cost-effective shell system.
Chemsize supplies fused silica powder, flour, sand and grains for investment casting, refractory and other industrial applications. Particle size, purity, chemical composition and document support can be discussed according to the customer’s slurry system and production requirements.
Reference
Jing Zongliang, Wu Yaozu, Sun Xin. Application of the Zircon Powder, Fused Silica Powder Mixed Slurry to Investment Casting Production. Foundry, 2015, Vol. 64, No. 6, pp. 517–520.
This article is a technical review based on the above published production study. The discussion is provided for general reference only. Actual slurry performance may vary depending on zircon flour, fused silica powder particle size, silica sol system, additive selection, mixing equipment, drying conditions and casting process.