Getting Ideas for Energy Management Opportunities
Whatever methods are used for cleaning of the castings, such as shot-blast in abrasive cleaning, grinding wheels, electric-arc cutoff torches, etc., they should be examined for energy-saving opportunities in general, based on proper operating practices and equipment maintenance.
Electrohydraulic cleaning
The shakeout is a major source of dust in a foundry and is a very energy (or labour) intensive operation. The use of electrohydraulic cleaning addresses these two aspects in an imaginative way. The castings are immersed in a water tank, and a high-voltage discharge between the casting and the submerged electrode produces a shock wave. The shock wave strips the sand from the casting. The cleaning is done in seconds and uses very little energy. No dust collection system is required which, in turn, reduces the amount of ventilation make-up air. In addition, the hot castings warm the water. After treatment, the heat from the water can be used elsewhere in the foundry. In addition, the need for shot-blast operations may be reduced or even eliminated. On the other hand, of course, water management and wet sand reclamation must be adequately addressed.
Mechanical grit blasting
Cleaning of castings down to the bare metal surface, suitable for further treatment, is normally done by grit blasting using compressed air. To accelerate the grit by compressed air is energy inefficient and expensive due to the high cost of compressed air. A foundry in the Netherlands uses the grit-blasting method, where the grit is accelerated by mechanical paddle wheels instead of compressed air. The energy is therefore used more efficiently. Energy savings on cleaning of 120 000 m2 of cast surface amounted to 1 000 000 kWh/y and 120 000 m3/y of natural gas. The payback was 2.1 years.
Housekeeping
- Apply preventive maintenance to the casting cleaning equipment and tools.
Low cost
- For cutting work, consider switching from electric arc-air torch to gas-oxygen torch.
- For cutting work, consider switching from high-pressure MAPP gas to low-pressure bulk natural gas, supplemented with oxygen.
- Consider using trimming dies for high production runs of non-ferrous castings.
- Consider using hydraulic wedges for breaking off the risers and runners.
Retrofit; high cost
- Instead of sand or grit blasting for cleaning permanent moulds, consider using “dry ice” pellets of solid carbon dioxide (CO2); the technique also works well for general preparation of surfaces for painting. Obviously, only the blasted-off impurities need to be dealt with, not the sand or shot.