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Manufacturing:
Metal Casting
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.
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