It takes a lot of energy to melt metal for sand casting, and this is not the only component of a foundry’s environmental footprint. Along with energy, foundries consume sand and water, and can produce a lot of waste. This blog looks at the tools, practices and technologies being used to make sand casting as sustainable as possible.

Consumption and Waste in Sand Casting

The process of making parts by sand casting begins with mold production. In sand casting, the mold is made of sand, which is broken apart to release the cast metal part. This means a new mold is produced for every part produced, making mold production a major activity within the foundry.

In parallel, metal is melted in a furnace, held at temperature, then poured into the mold. Melting takes a lot of energy, even for low melting point, non-ferrous alloys like aluminum. Contamination in the metal rises to the top of the material and is removed as “slag.” Cooling systems may be used to accelerate solidification and control metal temperature.

After casting, the channels that fed metal into the mold – the runners, risers and gates – are cut away. These can often be remelted. The same applies to any parts found to have casting defects. A metric used to measure yield is “Operational Material Efficiency” (OME), defined as the ratio of weight melted to weight shipped.

Tools, Practices and Technologies for Improving Sustainability

Sustainability and waste reduction are closely related, and leading foundries have always been very focused on the latter. When taking a sustainability perspective, things that reduce the environmental footprint of the sand casting process include:

• Implement measurement systems
• Maximize energy efficiency
• Reuse materials
• Design optimization

Here’s a closer look at each.

Implement Measurement Systems

Many foundries are implementing management systems that meet the ISO 14001 and ISO 500001 standards for environmental and energy management. Measurement is a big component of these, because it lets managers identify and prioritize problems and opportunities.

Maximize Energy Efficiency

Melting and holding metal at temperature are the biggest uses of energy. Consumption can be reduced through a combination of lean manufacturing practices and new technology.

Applying Lean principles can eliminate delays that require metal to be held at temperature. In addition, modern induction furnaces are extremely efficient, converting up to 75% of the energy consumed into heat.

Heat recovery systems can capture heat that would otherwise be lost to the atmosphere. One example is to pre-heat ambient air in winter as it’s drawn into the building HVAC system. Water used for cooling is another source of thermal energy.

Reuse Materials

Sand reclamation is possible in most sand casting foundries as an alternative to sending it to landfill. Sand used for molds is broken apart mechanically and then subjected to either wet or thermal treatment. These remove resins and prepare the sand to be resin coated again.

A small proportion of sand is unsuitable for reuse, often because the particles are too small. Many foundries have found beneficial reuse applications such as selling it to cement manufacturers.

Design Optimization

Part geometry and metal feeding system design have an impact on foundry sustainability. Minimizing metal consumption reduces energy usage, and this can be realized by designing to avoid defects, and making the feeder system as compact as possible. In addition, any actions taken to improve OME will also reduce resource consumption.

Responsible Environmental Stewardship

Sand casting is, arguably, a very sustainable process: producing near-net shape parts is inherently more efficient than machining to remove excess material. In addition, any waste material resulting from set-up, the molding process itself, or quality defects is easily recycled. (Waste segregation is important when a foundry handles a mix of alloys.)

A large proportion of the sand used to create the molds is also recycled, reducing resource consumption and the volume of waste sent to landfill.

Elsewhere in the process, foundry managers focus on measurement, especially of energy consumption, as a way to identify further cost and waste reduction opportunities.

As a global leader in casting, Impro is aware of the potential environmental impacts of the process and is continuously striving to find and make improvements. If you would like to learn more, please contact us.