University of Minnesota
Minnesota Technical Assistance Program
http://www.mntap.umn.edu
612.624.1300

Energy Efficiency Opportunities for Metal Casters

Melting is the most energy-intensive operation in metal casting facilities, accounting for about 55% of the total energy use in foundries. Opportunities exist to increase energy efficiency and productivity through technology upgrades and process changes. With today’s energy prices, impressive energy savings do not always require major capital investments in new equipment.

Inefficiencies in melting may be found in stack losses, inaccuracies in temperature measurement, conduction and radiation losses, poorly-fitting charge well covers and doors, temperature imbalance when adding cold metal to the charge and improper handling procedures. Process heating and compressed air systems are two areas that may hold efficiency improvement opportunities.

Process Heating

Melting and molten metal holding technologies comprise a large portion of energy consumption in the primary metals industry.  Fuel-fired melting system opportunities from MnTAP’s experience includes:

  • Insulation integrity and maintenance
  • Proper metal furnace charging and fluxing procedures
  • Process flow optimization
  • Ladle preheating
  • Burner tuning
  • Furnace and ladle covers
  • Waste heat recovery technologies like recuperative and regenerative heat exchangers or combined heat and power applications

When considering new furnaces or ovens, it is important to note that there are a number of types of melting furnaces on the market and each have differing degrees of efficiency that can affect the degree of metal loss and thermal efficiencies.

Furnace type

Gas

Electric

Melt loss

Thermal efficiency

Thermal efficiency rating

Crucible (gas)

x

 

4-6%

7-19%

Poor

Cupola

x

 

3-12%

40-50%

Good

Reverberatory

x

 

3-7%

30-45%

Fair to good

Rotary

x

 

-

35%

Fair

Stack melter

x

 

1-2%

40-45%

Good

Direct arc

 

x

5-8%

35-45%

Fair to good

Induction

 

x

0.75(aluminum)-3%

50-76%

Good to excellent

Reverberatory

 

x

1-3%

59-76%

Excellent

 

Electric melting has some overall advantages in thermal efficiencies and in lower metal melt loss. Combustion inefficiencies, exhaust waste heat loss, and combustion and oxidation contaminants in the form of dross and slag metal melt loss can contribute to fuel-fired furnace lesser efficiencies. Nonetheless, fuel-fired furnace equipment operations can effectively employ a variety of procedures and methodologies that can lead to some significant energy savings estimates.

Resources

Compressed Air

Compressed air is a very expensive and energy-intensive utility commonly used for air tools and control valves, as well as occasionally for drives, media blasting, cooling, and blow-offs. Common improvements include repairing leaks in piping and equipment, reducing the compressor output pressure, using a cold-air intake, setting up remote air receivers, correcting large system pressure drops, controlling the loading pattern of the compressed air system, and reducing inappropriate uses such as process cooling and cleaning. More costly solutions include properly sizing and distribution of the compressed air system, improving sequencing controls, and installing variable speed compressors to handle variable loads.

Resources

  • MnTAP Fact Sheet: Air Compressor Energy-Saving Tips. This fact sheet will help you calculate operating costs, understand your system and identify easy-to-implement energy efficiency strategies for your compressed air system.
  • DOE Tool: AirMaster+ Software. This assessment and analysis software package helps maximize the efficiency and performance of compressed air systems through improved operations and maintenance practices.
  • MnTAP Source Article: Top Compressed Air Energy Saving Options (2006). Compressed air assessments reveal that facilities have common opportunities for energy efficiency improvements: storage, sequencing, and removing inappropriate uses.

Energy Case Studies

To learn more about energy-efficient metal casting technologies, visit the Department of Energy (DOE) Industrial Technologies Program’s Web site. The ITP has sponsored many collaborative R&D projects for the metal casting industry; many of which have produced technologies that are now commercially available. Other projects focused on identifying emerging technologies.

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