07/07/2025
Product Features
Kyanite-Based Foundry Material: Seven Distinct Advantages
1. In-Situ Expansion Effect
The mineral composition of kyanite-based coatings mainly includes kyanite, zircon kyanite, sillimanite, and andalusite, with the addition of other mineral materials and a small amount of chemical additives. The core theory relies on the irreversible transformation of kyanite group minerals into mullite and cristobalite under high temperatures (1100°C–1500°C), resulting in volumetric expansion. This counters the shrinkage effect caused by suspended minerals and organic compounds in aggregates and additives during high-temperature casting, ensuring a consistent coating thickness from ambient to high temperatures. This "in-situ expansion effect" helps maintain the dimensional stability of the casting.
2. Carbon Adsorption Effect
During high-temperature casting, kyanite transforms into mullite and cristobalite—an initial phase known in mineralogy as *primary mullitization*. At this stage, cristobalite exists in a liquid phase and reacts with auxiliary elements in the aggregates and carbon monoxide generated from the pyrolysis of the lost foam, forming mullite- and silicon carbide-based minerals. This is referred to as *secondary mineralization* in mineralogy. The transformation causes the coating to change from white to black post-pouring and effectively mitigates the common problem of carbon pickup in lost foam casting.
3. Excellent High-Temperature Strength
Mullite crystals typically form in needle-like or elongated shapes. In the original coating stage, the crystal axes of kyanite minerals are multi-directional in three dimensions. The mullite crystals formed through two stages of mullitization also inherit this multidirectional structure. As a result, the coating behaves like a resilient "mineral wool blanket" under high temperatures, offering excellent strength and thermal shock resistance.
4. Good Shell Removal Performance
Due to the irreversible transformation of kyanite into mullite at high temperatures (the in-situ effect), the coating no longer changes in volume. In contrast, the casting shrinks from molten to solid state, creating gaps and shear stress between the coating and the casting, which naturally facilitates shell removal.
5. High Permeability
The kyanite-based coating from Tongbai Mountain contains 97% natural minerals and only 3% organic content. It exhibits a high water absorption ratio (approx. 10:8). During application and drying at room temperature, large volumes of steam escape, forming air channels that act as effective vacuum exhaust pathways during high-temperature casting, ensuring excellent gas permeability.
6. Applicable for Double Coating
Thanks to its excellent high-temperature strength, the coating does not need to be thick. A total coating thickness of just 1.5 mm achieved through two applications is sufficient, reducing labor and material costs.
7. Eco-Friendly
All mineral components of the kyanite coating are stable silicates that are non-toxic. The amount of chemical and organic additives is minimal, resulting in low toxicity and minimal corrosion risk. The transformation of kyanite into mullite during contact with molten iron absorbs substantial heat energy without re-releasing it at room temperature. As a result, the casting workshop is cooler compared to those using conventional coatings, creating a safer and more comfortable work environment.
