within in order to be a good part.” The simplicity of the metal also
means more metal casters pour it. “Another way gray iron is attrac-
tive is by how easily it is to find a supplier,” Kuehnel said. “There is a large range of suppliers domestically, which gives you a lot of flexibility.” On the same token, the simplicity
of producing gray iron castings has been a main reason for a significant amount of tonnage moving to foreign casting suppliers. “You can get all kinds of contami-
nants in gray iron, and it still will be okay, unless you are using more specific alloys,” Peaslee said. “Within a five-year span in the mid-1990s, a lot of gray iron was gone [offshore]. The good news is that purchasers of gray iron castings have mostly only good gray iron suppliers left in the U.S. to pick from.”
Making Cost Compromises According to Stratecasts, while gray
iron likely will continue to see annual down trends in the motor vehicle, household appliances and electric
Table 6. Thermal Conductivity Values for Various Gray Irons Compared with Those for Steels and Other Irons
Metal
Steels 1020 4135
Gray Irons 3.5% C, 2.25% Si, 4.25% Carbon equivalent (CE) 3.93% C, 1.4% Si, 4.4% CE 3.16% C, 1.54% Si, 3.67% CE
Ductile Irons Ferritic, 2.35% Si Pearlitic, alloyed
Source: ASM Handbook Vol. 15 Casting
machinery markets, other market sec- tors have reached the point where conversion from gray iron to other metals or materials is minor. Others in the industry see further conversions in the years ahead. As much as cost can be an advan-
tage for gray iron, some engineers and purchasers are comfortable opt- ing for the more expensive ductile iron, even where gray iron would
suffice. Jeff Sugarman, domestic casting buyer for valve maker Henry Pratt, Aurora, Ill., said he’s leaning toward staying away from keeping gray iron and ductile iron material in stock to reduce inventory. “Many of our products have dual
design purposes for class 150 lb. and 300 lb., in which case the ductile iron material will work in both ap- plications, but the Class 40 gray iron
Thermal conductivity at indicated mean temperature (W/m x K) 200F (95C) 400F (205C) 800F (425C)
51.9 43.3
57.1 55.4 46.7
41.5 26
48.5 41.5
51.9 51.9 n/a
38.1 27.7
41.5 38.1
n/a
46.7 41.5
32.9 n/a
September/OctOber 2010
metal caSting DeSign anD purchaSing
31
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