The Shell Mold Process
Shell molding is a process for producing simple or complex near net shape castings, maintaining tight
tolerances and a high degree of dimensional stability.
The process begins with a precision-machined
pattern, which is heated and then covered with a fine resin sand mix. As the mix
polymerizes, excess sand is removed, leaving a hard, thin "shell" in the contour
of the pattern. The shell is ejected while still hot, and split into a cope and
drag. The two halves are pasted together to form a mold. If required, cores and
filters can be inserted before the halves are joined. Mold locators built into
the patterns minimize the probability of mismatch, or parting line
The resulting mold is then poured to your material specifications in a
non-conventional manner that helps assure:
• Precise temperature control
Cleaner metal with less oxide potential
• Reduced Metal Static Pressure
While much of our process is automated
to maximize productivity, exceptional quality requires special techniques. The molds are brought to the metal via conveyor, rather than
transporting metal to the molds. The two main advantages of this method are that
metal temperatures are maintained with extreme accuracy and metal turbulence is
minimized. Experienced hands ladle the metal directly from the melting furnace
into the molds with speed and artful precision. Hand pouring also minimizes the
distance from the ladle to the sprue, reducing the potential for oxides to enter
After cooling, the
castings are separated during the "shake out" process, and then cleaned. The
results are near net shape, semi-precision castings characterized by uniform
dimensional control and excellent surface finish, ready for the next step in the
Design Advantages of the Process
Because of the rigidity of
our molds and the positive cope and drag locators, we can provide a number of
advantages in the design of your product:
Tolerance Control: dimensional control on one half of the mold will typically be equal
to, or in some cases superior to, the investment casting process. Tolerances
across the parting line are superior to sand cast capabilities.
Concentricity and Location of Core to Mold Configurations: the
consistency of our castings is ideal for the tighter tolerances required by the
CNC Machining Centers. We specialize in multi-hole applications, such as
manifolds, where the concentricity requirements are beyond sand cast
Finish Requirements: casting accuracy allows for a reduction of up to 50% in finish
required on machine surfaces. In some cases, this eliminates roughing cuts and
reduces both casting weight and metal cost.
drafts (both I.D. and O.D.) of 1/2 degree are common in our pattern design.
Cores are often eliminated through our ability to "draw" deep holes. The
bushings illustrated here are made coreless.
Permanent Tooling: since our process is subject to heat, all of our tooling is fully
machined to exacting tolerances with high wear material such as continuous cast
iron or conductivity copper. High production parts are generally hard coated.
Tooling has produced hundreds of thousands of parts from a single
Competitive Pricing: our process is
the most productive method of manufacturing near net shape castings, competing
favorably with other processes and generally providing a superior
Call (281) 339-2700 or Email
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