This gray iron turbo bear- ing housing incorporates an intricate water jacket core that was designed into an exist- ing bearing housing.
Gray Iron’s New Role in
Manufacturing
Gray iron may face conversions to aluminum and ductile iron, but for many applications, it is still a perfect fi t.
Shannon Wetzel, Senior Editor H
istorically, gray iron has been the king of casting, but advances in other met- als, such as aluminum and ductile iron, have chipped
away at its market share. Thirty years ago, the U.S. casting industry produced 10 million tons of gray iron, compared to 3 million tons of ductile iron. By 2008, production for both materials were even at around 4.1 million tons. Aluminum has grown from 700,000 tons in 1980 to more than 2 million tons by 2007. Overall, ductile iron and aluminum have been trending upward and gray iron downward (Figs. 1-3). Forecasting fi rm Stratecasts Inc., Ft. Myers, Fla., does not predict the gray iron casting industry will ever again exceed 4.2 million tons in a year. Sales for ductile iron, however, are forecast to exceed gray iron by $2.4 billion in 2016, making it the number one cast ferrous metal in total revenue.
“In the larger casting world, people
have pretty much switched from gray iron to ductile iron,” said Chris Atkin, president of gray and ductile iron metalcaster Willman Industries, Cedar Grove, Wis. But gray iron still holds a place within
the casting industry, according to several metalcasters and their customers. “Gray iron will always have a mar-
ket because of its cost effectiveness and the properties needed by specifi c appli- cations,” said Robert Peaslee, president of gray and ductile iron metalcaster Manitowoc Grey Iron Foundry Inc., Manitowoc, Wis. Aluminum can lighten the weight of
a part—important for automotive mak- ers. Ductile iron brings strength on par with steel. But for many applications, only the talents of gray iron fi t the bill.
Keeping a Lid on Cost, Vibrations One of the greatest advantages gray
Table 1. Property Comparisons for Gray Iron Classes Property
Class 25 (as-cast)
Brinell Hardness
Tensile Strength (min.) Modulus of Elasticity Tensile Poisson’s Ratio
Compression Poisson’s Ratio 187 20 ksi
iron has over other materials is its cost. It is less expensive to produce than steel, ductile iron, austempered ductile iron (ADI) and compacted graphite iron (CGI). “Because it’s a lower cost material
than ductile or ADI, we use gray iron in structural engine components where gray iron is suffi cient,” said Ron Wall- ing, technical advisor for engine maker Cummins Inc., Columbus, Ind. “Gray iron is typically our fi rst choice, but as engines have higher loads or higher power requirements, they drive us toward higher strength CGI.” When high strength is not a require-
ment (gray iron’s tensile strength upper limits are around 45,000 psi, while duc- tile iron’s ranges between 60,000 and 100,000 psi), gray iron is typically the most economical material (Tables 1-3). Gray iron’s mechanical properties
also lend the material to certain appli- cations. By nature, gray iron dampens
Class 30 (as-cast)
207 30 ksi Compression-to-Tensile Strength Ratio 3.68 28 METAL CASTING DESIGN AND PURCHASING
0.19 0.28 3.84
Class 30
(annealed) 109
30 ksi
0.21 0.26 4.05
Class 35 (as-cast)
212 35 ksi
0.22 0.28 3.63
Class 40 (as-cast)
235 40 ksi
16.6 Msi (114 GPa) 17.0 Msi (117 GPa) 14.5 Msi (100 GPa) 18.0 Msi (124 GPa) 18.2 Msi (126 GPa) 0.29 0.27
0.24 0.23 3.71
SEPTEMBER/OCTOBER 2010
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