System Reclaims Lost Foam Sand Cost Effectively.

Lost foam casting has been a key manufacturing technology for Saturn Corp., Spring Hill, Tennessee. Pouring aluminum castings using the lost foam process results in organic compounds from the vaporized Styrofoam patterns in the sand. The gradual accumulation of these materials causes the sand to become sticky, reduces flowability and eventually causes sand compaction defects. Saturn uses 460 grade, subangular unbonded silica sand and relies on loss on ignition (LOI) tests to determine the amount of foam residue on the sand as a measure of the need for reclamation. The sand system averages 0.04% LOI, and the reclaimed sand has less than 0.01% LOI (with Saturn's operating specification being at or below 0.1%).

In 1999, Saturn brought online two new Calcifire thermal sand reclamation systems, manufactured by Dependable Foundry Equipment Co., Tualatin, Oregon. The 4-ton/hr and 2 ton/hr sand reclamation systems each include a 17-ton silo, screw feed auger, the reclaimer, a high-temperature cooler/classifier and a DFT dense-phase sand transporter.

Two systems process sand for a cylinder head cast line and a cylinder block cast line. In each system, a 40-ton blended sand silo receives sand from the shakeout, the thermal reclaimer and the new sand silo.

New sand is metered into each blended sand silo in 280-lb batches (one for every 20 compacted flasks). On average, makeup of sand is 89% shakeout sand, 10% reclaimed sand and 1% new sand. The three sands are blended into a homogenous mix by silo anti-segregation tubes, and fluidization takes place in a cooler/classifier downstream from each silo.

Each sand system diverts a minimum of 10% shakeout sand through its respective sand reclamation system. Sand to be reclaimed is stored in a 17-ton silo and screw-fed into the reclaimer at a rate of 4 tons/hr for the cylinder block line and 2 tons/hr for the cylinder head sand system. Sand usage requires almost 24 hr/ day operation of both reclaimers.

The reclaimer itself has processing parameters of 1300-1500F (704-815C) with a full hour of sand residence time. The gas supply is modulated by a feedback system that reacts to the actual temperature of the sand in the calcining zone. The fluidization air is supplied by a dedicated blower and moves the sand through the full-area-utilization steel hearth to the exit weir. A static bed of sand serves as insulation.

The new refractoryless system runs unattended and is shut down each time the foundry shuts down for more than a day. This saves the foundry $274,000 for each periodically required replacement of the refractory lining in the old system.

In addition, Saturn feeds the exhaust from the reclamation unit into the shakeout ventilation system to assist with keeping VOCs in suspension. This results in less use of duct burners, a natural gas savings of $42,000/yr and a cost avoidance of more than $108,000 for an additional dust collector.