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Manufacturing:
Metal Casting
Variation
of Green Sand Molding
High-Density
Molding (High Squeeze Pressure / Impact)
In recent years, the introduction
of high-pressure molding techniques has
greatly improved the standards of accuracy
and finish which can be achieved with certain
types of castings. Dramatic
changes have occurred in the foundry molding
system by increasing the capacity and ability
of the molding machines to produce molds.
This has been accomplished by more effective
use of large air cylinders, application
of electronics, use of hydraulics, and the
innovative use of an explosive-type method
of compacting the sand around the pattern,
referred to as impact molding.
In recent years high-pressure
or high-density molding has been widely
adapted for the casting of most metals.
High -pressure (high-density) molding has
virtually eliminated the past problems of
mold-wall movement. Mold-wall movement has
been markedly aggravated by the moisture
content of the molding sand, the density
of the molds, and the mold surface hardness.
High-pressure molding practices
have allowed lower moisture contents in
the molding sand, so that higher mold densities
can be achieved. Thus, castings having considerably
better dimensional accuracy are produced,
surface finish of the casting is improved,
and the castings more accurately reflect
pattern accuracy.
Advantages
- Most metals can be cast
by this process.
- Castings produced with
this method also demonstrate closer dimensional
tolerances, consistently uniform casting
weight, better surface finish, increased
productivity, and lower cost.
- Reduced feed metal
- Improved casting soundness
- Reduced cleaning costs
- Minimum setup for machining
because of casting dimensional accuracy.
Disadvantages
- Tighter quality controls
are required with this type of molding.
As a result, the foundry using high-pressure
(high-density) molding is generally accustomed
to more sophisticated equipment, maintenance,
and operating procedures.
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