Green sand is by far the most widespread molding method used in foundries for metal casting operations. The green sand process utilizes a mold made of compacted moist sand mixed with bonding agent bentonite. Bentonite is a type of clay when mixed with water and sand, and sticks to the sand particles as a tacky coating. This mixture is then filled around a wood or metal pattern and compacted by different methods (jolting, squeezing, air impact, and others). The tackiness ensures that sand particles aggregate and provide strength to the mold even when exposed to high temperatures.
This month, let’s learn all about bond usage in green sand systems and some effective ways to reduce it.
The clay level necessary to run a green sand system not only depends on making good molds, but also good castings, and to do so with the least amount of defects attributable to the sand. In addition, minimizing sand carryout to maintain return sand silo levels without adding excessive new material.
In my earlier posts, we have looked at ways to control sand compactability and how it is affected by process variables. The next important control variable in a green sand system is clay level. It is vital to understand the science behind clay for efficient production.
We told you how you can control the compactability of sand in our earlier blog. We are now back with tips to help you make better decisions during sand storage,transportation, testing, and handling.
What is Compactability?
Compactability relates to the reduction in volume of sand bonded with clay and water after undergoing compression applied by squeezing or compaction.
What is the ideal range for compactability?
Compactability should ideally lie in the range of 36-42.
Why is it important?
Compactability plays an important role in producing good quality molds and castings. It affects sand fill and mold density in the pockets of pattern. It also affects the integrity of mold edges and corners.