Getting Ideas for Energy Management Opportunities
Commonly, sand is mixed with an oil or chemical binder to make cores, which are then placed into a mould cavity to form the interior surface of the casting. Once the casting is made, the sand cores are removed, and the sand, which contains binder, is frequently mixed with the mould sand. The contaminated sand must be discarded. The disposal issue is very serious, and the CFA has succeeded in helping the foundry industry obtain permission to dispose of the sand in landfills, where it is used as a day cover.
Sand reclamation
As sand reclamation is becoming more common, it puts greater demand on the correct cooling of hot sand. That may be done in rotating coolers, with water used as the cooling medium. The temperature is controlled to within ±2–3°C. The close temperature control is especially critical for the nobake process, or core or mould making. There, too low a temperature delays the binder-setting reaction, and if it is too high it may harden in the box and not strip out.
The customary one-time use of the core sand and its disposal is expensive. A large foundry in Quebec installed a sand reclamation system, which recycles over 90% of the volume of the “contaminated” sand. Binder-contaminated sand is collected in a hopper and augered to a heating bed, from which it enters a fluidized-bed reactor, maintained at 677°C. The heat comes from submerged burner tubes. The clean sand is then cooled down to ambient temperature in a fluidized bed cooling chamber. Cooling is provided by an air-to-water exchanger. The foundry claims that the thermally reclaimed sand has better characteristics than new sand. Up to 100% of the reclaimed sand can be reused. According to the 1999 news release, the recycling of 1 t of sand used 31 m3 natural gas and 28 kWh of electricity; total savings were about 90% and the payback was just under two years.
A similar system for thermal reclamation of furan-binder based, nobake mould and core sand was installed by an Ontario foundry, which can recycle up to 98% of the sand.
Improving process controls in the mullers helps produce well-mixed, uniform, good-quality moulding sand. This, in turn, will generate fewer broken moulds, sand holes and casting repairs, and less burned-on sand and scrap, all of which needlessly consume additional energy.
Other EMOs
Housekeeping
- Limit your sand disposal expense – rather than using costly landfill, negotiate disposal through your local asphalt-making company.
- Switch off the sand system equipment when not in use.
- Power-up and power-down the sand system equipment in production sequence, not all at once, when parts of it are not yet (or no longer) needed.
- Pay proper attention to the classification of the reclaimed sand in order to maintain mould and core quality.
Low cost
- To reduce sand mould defects and improve sand consistency and uniformity, consider using an automatic sand tester at the mullers to test for compactibility, strength and moisture, and to govern the muller operation and sand composition (e.g., Hartley™).
Retrofit; high cost
- Consider installation of a thermal reclamation system (e.g., Thermfire™ type using turbulent flow precipitators); only about 2% of make-up sand is required after the reclamation.
- Mullers use some of the largest and hardest-working electric motors in the foundry. In large foundries, consider staging of mullers’ production – use one for steady, continuous production and the other to cover the peak demand periods. Alter them to ensure their even wear and tear.
- Consider replacing the energy and maintenance intensive pneumatic conveying of sand with belt or bucket conveyors.