Table 1. Comparison of the Capabilities of Various Sand Casting Processes Process
Low Wall Thickness
Green Sand-Horizontal Green Sand-Vertical Air-Set/Nobake
CO2 Gas-Hardened/Coldbox Shell
0.25 0.25
0.1875 0.1875 0.1563
framing around each mold. Vertically parted molding machines are usually integrated into a highly automated casting line, which is characterized by minimal manual involvement in the areas of molten metal handling, pour-
Extreme Low Wall Thickness
0.1 0.1
0.125 0.1
0.02
Typical Low Weight (lbs.)
1 1
0.5 0.5 0.1
Typical High Weight (lbs.)
200 100 150
200 25
ing and cleaning operations. Size and shape-wise, the green sand
casting process has almost no limit. Typical green sand castings range from several ounces to 500 lbs., but green sand castings as large as 7,000 lbs.
Extreme Low Weight (lbs.)
0.25 0.25 0.2 0.2
0.05
Extreme High Weight (lbs.)
1,000 1,000
100,000+ 100,000+ 50
Typical Thick Section (in.)
0.5
0.375 0.5 0.5
0.25
have been made. Nobake’s size range is similar to green sand, but it is often the process of choice for very large castings weighing more than 100,000 lbs., due to its mold strength. When the binder and catalyst are
mixed with sand in nobake molding, a strong, brick-like mold is formed. Te rigid walls of a nobake mold can with- stand the pressure of a large amount of metal and have less chance of breaking than green sand. Te choice between green sand molding and nobake sand casting is fairly straightforward if the casting job will be high volume (green sand) or large in size (nobake). But for those parts that fall in between, the choice is not so simple.
Cost Factors For many applications, green
sand casting is the most cost-effec- tive of all metal forming operations, and the process can be used to pro- duce a wide range of casting sizes in almost all casting alloys. While the process has been automated in many facilities for high volume work, it is economical for short runs and prototype work, as well. Production rates often are increased by produc- ing multiple parts in a single mold. Sometimes, completely different parts are poured in the same mold. While the green sand process is
Nobake molding is used for castings that range between a few ounces and more than 100,000 lbs. The process offers good surface finish and tight tolerances.
34 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2014
one of the most economical metal manufacturing methods, when an ap- plication requires the process to reach beyond its normal capabilities, it can become more expensive. For instance, if a part requires tighter tolerances or a smoother surface finish, nobake sand casting can deliver better results. Te rigidity of a cured sand mold allows for tighter dimensional tolerances than green sand. Te hardness of the mold also translates to a smoother mold surface and casting finish. Unfinished nobake molded castings
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