Sand casting is the most widely used metal-casting process to deliver cast products in a near net shape with or without internal passages. The process uses sand as the molding material and is versatile and cost-effective, even for low volume runs.
In the sand-casting process, a pattern of the desired finished part is constructed out of hardwood, urethane, metal or foam. Sand containing bonding materials, such as clay, is packed around the pattern to form the mold. The pattern is removed from the bonded sand, leaving a cavity in the mold that is the shape of the part. Internal passageways, including intricate structures, can be included in the mold by adding cores. Molten metal is poured into the cavity and the metal solidifies. The sand is removed through a shakeout process. The gates and risers (rigging) are removed, resulting in the desired part for finishing.
A simplified explanation of the process is such:
- Place a pattern in the sand to create a mold.
- Incorporate the pattern and sand in a gating system.
- Remove the pattern.
- Allow the metal to cool.
- Break away the sand mold and remove the casting.
There are two methods of sand casting, with the first being “green sand,” and the second being “air set.”
The “green sand” method
Despite its name, the color of the sand used in this method isn’t actually green. Rather, it refers to the fact that the sand is still in its wet, uncured state when the metal is poured in the mold. Additionally, it’s also not sand in the geological sense. It’s a mixture of materials that varies depending on the metal that is being poured.
The “air set” method
This method uses dry sand bonded with materials other than clay using a fast curing adhesive. Two types of molding sand are natural bonded (bank sand) and synthetic (lake sand); the latter is generally preferred due to its more consistent composition.
Sand casting capabilities
There are specific capabilities and advantages to using sand casting to produce parts and components, such as:
- Up to 12’ x 12’ x 15’ volume
- Ship weight up to 18,000 lbs
- Patternless molding technology
- Argon Oxygen Decarburization (AOD) technology
- NDT: Visual, Liquid Penetrant, Radiography, Magnetic Particle, Hydrostatic, CMM capability and Laser Scanning
- Tolerances: +/- 0.030” as cast
- Surface Finish: 150 – 250 RMS as cast
When to use sand castings
Sand casting is used to produce a variety of metal components with complex shapes. In general, sand casting is an ideal method when producing:
- Shaped or non-symmetrical parts
- Large parts – up to 15,000 lbs or more
- Parts that require internal structures
- Parts that require cast alloy materials that are not available in wrought form
Typical sand-casting products
There are a variety of products, both large and small, that are produced by sand casting, including:
- Pump and valve components
- Pump housings
- Aerospace HF and SPF forming dies
- Flow meters
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