Sand Reclamation System Lowers Core Sand Costs.

When Western Steel Casting Co., Seattle, was looking at a large casting project with tight margins on the bottom line, it examined how to trim costs in core production. The foundry decided one way was to use its Rotary Sand Reclaimer from Roberts Sinto Corp., Lansing, Michigan, to further refine reclaimed sand for use in core production.

Drawing a connection between clean sand and clean castings, the foundry felt that by lowering clay content to the right specifications, good core sand could be produced from reclaimed sand. Recovery of usable silica sand from reclamation for mold production exceeds 90% for the foundry. For facing mold sand, the reclaimed sand is re-bonded with 5.4% clay and 2.85% water, providing excellent mechanical properties with high permeability. No new sand is added to the facing sand or backing sand mixtures for mold production.

For reclamation of facing molding sand, the batches of sand to be reclaimed are circulated four times through the reclaimer cell in order to obtain the desired 0.5% clay content. The reclaimer cell already has passed more than 12,000 tons of sand to manufacture more than 3000 tons of sand used to date. The base sand is 6.0% total clay for mold facing sand. Through experimentation, the foundry found that an additional two passes through the cell reduces the clay down to 0.15%, which makes it usable for core sand production.

The firm decided to test the new process on a mooring bollard, a low-alloy steel casting in the 3000-4000 lb weight range that is used on docks to secure ships' mooring lines.

The firm normally runs about 0.8% of binder for cores due to the efficiency of the mixer. The first cores were made with 1% binder, but this will drop to 0.85% binder in the future. The process results in cores produced with good scratch hardness, high strength and excellent permeability. The reclaimer does not degrade the sand, so the process continually operates at 55-57 AFS fineness.

The firm now is producing castings weighing 3500 lb with an excellent surface finish using reclaimed sand cores.

The foundry's president, Bob Alexander, says, "We are very excited about the success of this process because we believe the savings in core sand on this project are going to amount to over $17,000 to the bottom line of the job. We do not have to purchase new sand for these cores."

The firm plans to use reclaimed core sand for other casting projects. It installed an additional 80-ton sand tank and now transfers the reclaimed sand into separate silos for facing sand and core sand.