Battle A green sand caster shares how it reduced scrap by 70% with the use of a
sand cooler. MICHAEL MROCZEK, THOMAS WOZNIAK AND CARLOS CRESPO, WEIL MCLAIN, MICHIGAN CITY, INDIANA, STEPHEN NELTNER AND VIC LAFAY, S&B INDUSTRIAL MINERALS, CINCINNATI
cess, green compression strength increased more than 40%, the moisture content was reduced by 13% and the mulling efficiency significantly increased by 35%. The increment of mulling efficiency led to a reduced amount of active clay in the system and increased the permeability by 29%. Casting defects, such as sand inclusions, burn-on and leaks due to inclusions, were reduced. The company estimates a return on the investment in the sand cooler in three years.
Table 1. Sand Temperature Ranges vs. Sand Properties
Sand Temperature Sand Properties 100-120F (38-49C)
120-140F (49-60C) 140-160F (60-71C) Stable green sand properties.
Physical properties are diminished. Extra mulling may be required.
Physical properties are uncontrollable. High friable sand with weak strength properties.
Greater than 160F (71C) Water evaporates so quickly that mulling is not occurring due to clay not being wetted out or activated.
The Temperature’s Rising Weil McLain manufactures boiler
sections cast in green sand molds with cores made via the hotbox and coldbox processes. Te boiler sections are cast
in gray iron class 25 and subject to hydrostatic testing. Each section must meet the minimal wall thickness of 80% of the nominal value, so any deep surface defect or discon- tinuity that exceeds this requirement is a reason to scrap the casting. For instance, if the nominal wall thickness is 0.25 in., the maximum permissible
surface defect is 0.05 in. in non-critical areas. In critical areas, any surface discontinuity is unacceptable. The ferrous foundry produces castings ranging from 30 to 300
Fig. 2. A burn-on defect (shown) can result when too much mois- ture is in the sand.
Fig. 3. Sand inclusions appeared on this boiler section due to a cracked mold surface resulting from reduced green compression strength.
July 2011 MODERN CASTING | 33
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