Processes

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Sand Casting

Sand casting is the process of producing metal parts from a cavity created in a sand mold.  The technique of molding sand around a pattern generates this cavity.  Here at Marlborough Foundry, we use two types of molding sand: Green Sand and No-Bake Sand.

Green Sand Molding


Castings with Pattern equipment

Green Sand Molding is a process that takes sand (combined with clay and water as a binding agent) and rams or squeezes the mixture around the pattern equipment.  Once the pattern is removed, the cavity is filled with molten aluminum.  The heat from the aluminum will drive out the moisture that holds the mold together. After the metal has solidified, the sand can be broken apart easily in the knockout process.

 

 

No-Bake Sand Molding


No-Bake Sand Molding requires a chemical binder to hold the sand together.  This type of system allows for the production of more complicated castings.  Castings that are selected for this process usually are extremely large castings, require deep pockets, or limited draft situations.  Another important feature to No-Bake Sand Molding is that there are no products of combustion incorporated in the material. Consequently, castings that require a high level of x-ray quality can be produced on a regular basis.

DESIGN CONSIDERATIONS FOR SAND CASTINGS

  • Basic Linear Tolerance up through 6 in. (150mm): +/- .030 in. (.8mm)
  • Additional tolerance for each inch greater than 6 in. (150mm): +/-.003 in. (.08mm)
  • Machining Allowance: .125 in. (3mm) with a .060 in. (1.5mm) minimum
  • Draft angle: 2 degrees.
  • Surface Finish: 200 to 400 RMS.
  • Wall Thickness: .100 in. (2.5mm) minimum