Green Sand Molding
Green sand is by far the most diversified molding method used in current metalcasting operations. The green sand process utilizes a mold made of compressed or compacted moist sand packed around a wood or metal pattern. The term “green” denotes the presence of moisture in the molding sand, and indicates that the mold is not baked or dried.
Process
The mold material consists of silica sand mixed with a suitable bonding agent (usually clay) and moisture. To produce the mold a flask, usually a metal frame, (although wood may be used for some processes and types of castings), is placed over the pattern to produce a cavity representing one half of the casting. Compaction is achieved by either jolting or squeezing the mold. The other half of the mold is produced in like manner and the two flasks are positioned together to form the complete mold.
If the casting has hollow sections, a core consisting of hardened sand (baked or chemically hardened) is used. Cores are located in pockets formed by projections on the pattern equipment to produce coreprints. Should extra support for the core be required, chaplets or spacers are properly positioned to maintain the required dimension. These will fuse with the molten metal when the casting is poured.
Green sand is the best known of all the sandcasting methods, as the molds may be poured without further conditioning. This type of molding is most adaptable to light, bench molding for medium-sized castings or for use with production molding machines.
Variations of Green Sand Molding
- High-Density Molding (High Squeeze Pressures, Impact)
- Flaskless Molding
- Tight-Flask Molding
- Skin-Dried
- Dry Sand Molding
Advantages
- Most ferrous / non-ferrous metals can be used.
- Low Pattern & Material costs.
- Almost no limit on size, shape or weight of part.
- Adaptable to large or small quantities
- Used best for light, bench molding for medium-sized castings or for use with production molding machines.
Disadvantages
- Low design complexity.
- Lower dimensional accuracy.
Original Source: http://www.engineershandbook.com/MfgMethods/greensandmolding.htm
