As detailed by THORS in their article “Green Sand Clay Level 101”, controlling green sand clay levels is essential for efficient metal casting production. Clay acts as a bonding agent that holds sand grains together during compaction, with sodium (Western) bentonite being the preferred choice in iron foundries. Various tests, such as AFS clay and methylene blue (MB) clay tests, help foundries measure the clay’s effectiveness in binding and moisture absorption. Understanding these clay levels ensures better sand bonding, ultimately improving mold quality and reducing casting defects.
The AFS clay test measures total water-absorbing materials in the sand system, including both active and inactive clay, coal dust, and other fines. This test involves dissolving dried molding sand in water, allowing heavier particles to settle, and siphoning off suspended fines. The remaining sand is dried, and its weight loss is recorded as AFS clay. However, only active clay contributes to the sand’s bonding strength.
The Methylene Blue (MB) clay test further refines this analysis by determining the base-exchange capacity of bentonite. This test measures the amount of active clay present by titrating a sample with methylene blue solution. Active clay, which absorbs moisture and strengthens the mold, plays a critical role in maintaining casting integrity.
Two other essential terms, Available Bond (AB) and Working Bond (WB), describe the bonding state of the sand. AB is derived from green compression strength and moisture content, indicating the presence of moisture-absorbing materials, including active clay. WB, on the other hand, represents the actual amount of clay that produces bonding strength. Foundries often estimate muller efficiency by calculating the ratio of WB to AB, with higher values indicating better clay utilization.
Since compactability and moisture levels fluctuate throughout the sand system, consistent monitoring is crucial to maintaining quality. By optimizing clay levels, foundries can improve mold strength, reduce casting defects, and enhance overall production efficiency.
Click here to learn more about Plymouth Foundry’s services.
Article with all rights reserved, courtesy of THORS.