Shell molding
April 8th, 2008
Shell molding is also similar to sand molding except that a mixture of sand and 3-6% resin holds the grains together. Set-up and production of shell mold patterns takes weeks, after which an output of 5-50 pieces/hr-mold is attainable. Aluminium and magnesium products average about 13.5 kg as a normal limit, but it is possible to cast items in the 45-90 kg range. Shell mold walling varies from 3-10 mm thick, depending on the forming time of the resin.
There are a dozen different stages in shell mold processing that include:
- Initially preparing a metal-matched plate
- Mixing resin and sand
- Heating pattern, usually to between 505-550 K
- Inverting the pattern (the sand is at one end of a box and the pattern at the other, and the box is inverted for a time determined by the desired thickness of the mill)
- Curing shell and baking it
- Removing investment
- Inserting cores
- Repeating for other half
- Assembling mold
- Pouring mold
- Removing casting
- Cleaning and trimming.
The sand-resin mix can be recycled by burning off the resin at high temperatures.
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