CHOOSING
BETWEEN GREEN SAND, NOBAKE
Navigate the differences in capabilities and cost factors between green sand and nobake molding processes to ease your sourcing decision.
O AN MCDP STAFF REPORT
pting for a sand casting process over permanent mold, diecasting, or investment casting is step one in sourcing a casting. But sand casting encom- passes several methods, each of which carries its own advantages and disadvantages. T e two most common processes used are green sand and nobake molding, and sourcing between the two is not always cut and dry.
Forty-two precent of North American metalcasters employ the green sand molding process. Its popularity stems from its aff ordability, ability to be used for most metals and fl exibility for low to high volume production. Green sand molding does not hold the tightest tolerances or achieve the fi nest
surface fi nish of all the casting processes; however, in general, it meets most of the qualifi cations desired to produce a high quality casting with a good fi nish. Nobake sand casting, which is utilized by 40% of North American metalcasters, also is known for its versatility. Virtually all metals can be cast via nobake mold- ing, a wide range of sizes can be produced, and the rigid mold walls provide good dimensional tolerances and control. Although it is one of the most popular molding systems, nobake sand casting
production has not been automated to the same extent for high volume production. Up to 500 molds per hour can be made on green sand lines, compared to 20-30 molds per hour in nobake. Automated green sand molding lines use metal pattern equipment to withstand the high pressure, high density molding method of the high volume machines. T is
normally results in a well compacted mold that yields better surface fi nishes, casting dimensions and tolerances than other green sand molding methods. Typical nobake casting produc-
tion ranges from low to medium volumes. Nobake sand molds are produced using a chemical binder and catalyst to cure and harden them. Due to the curing time re- quired for the chemicals to harden the mold, as well as the methods to distribute the sand on the pattern, the high production rates achievable with green sand are not possible. T e highest level of green sand au-
tomation is found in vertically parted green sand casting, where the parting line between the two mold haves runs vertically rather than horizontally. With a production rate up to 500 molds per hour, these lines produce molds without fl asks, thus eliminating the cost to produce and maintain the
Sept/Oct 2014 | METAL CASTING DESIGN & PURCHASING | 33
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