As outlined by THORS in their article “Reducing Bond Usage in Green Sand Systems,” bond usage in green sand casting is essential for maintaining mold integrity and ensuring high-quality castings. However, excessive bond consumption can increase costs and reduce system efficiency. Bond, primarily clay, is added to replace inactivated materials due to metal heat, compensate for material lost during processing, and bond new sand grains.
Key Factors Affecting Bond Usage
- Materials:
The type of clay used plays a significant role in bond performance.- Western Bentonite (Sodium Ion): More durable and less prone to heat-induced deactivation.
- Southern Bentonite (Calcium Ion): Requires higher replacement due to more rapid inactivation.
Other additives, such as sea coal and cellulose, can interfere with strength development. To minimize bond usage, it’s recommended to reduce unnecessary additives and use western bentonite.
- Additionally, higher metal temperatures increase bond inactivation, requiring more replacement clay.
- System Design:
Effective system design can reduce bond losses:- Sand Cooling: Return sand above 130°F loses more bonding material during handling.
- Silo Capacity: Smaller silos reduce clay activation time, leading to increased clay additions.
- Bond Addition Location: Adding bond before the return sand silos allows more time for clay activation, reducing the required bond levels.
- Dust Collection: Excessive dust collection removes active bonding material. Recycling dust collection materials can help reduce losses.
- Shakeout System: Inadequate shakeout can lead to sand losses, increasing the need for new sand and additional bond.
- Operation:
Operational parameters directly influence bond usage:- Sand-to-Metal Ratio: A low ratio increases the clay level required to achieve green strength.
- Compactability: High compactability set points lead to lower green compression strength, prompting increased clay additions.
- Sand Carryout: Deep pockets and hard molds increase the amount of sand carried out with the casting, necessitating more new sand and additional bond.
- Silo Maintenance: Buildup on silo walls reduces capacity, shortening the activation time for clay and leading to higher bond usage.
Conclusion
By optimizing material selection, improving system design, and refining operational practices, foundries can reduce bond usage without compromising mold integrity. Techniques such as using larger silos, recycling dust collection material, and ensuring effective shakeout can significantly improve efficiency.
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Article with all rights reserved, courtesy of thors.com.