pressing applications, you don’t want the casting to bend, or it will produce a leak.” Gray iron’s superior heat conductiv-
ity vs. steel and ductile iron makes it an attractive material for brake compo- nents, such as rotors and brake drums, as well as cookware and ingot molds (Table 6). “Thermal conductivity is one of the
sterling aspects of [gray iron],” said David Neil, president of iron caster ATI Casting Service, La Porte, Ind. “Gray iron is still a good choice for heavy industry engine blocks because of its strength and thermal conductivity.”
More Where That Came From Rowe Foundry has been produc-
Fig. 3. With several automotive applications converting from iron to lighter weight alloys, aluminum casting has shown a marked growth in shipments in the U.S.
Table 3. Property Comparison for ADI Grades (ASTM A897) Grade
Tensile Strength
1 2 3 4 5
Yield Strength
140 ksi (966 MPa) 110 ksi (759 MPa) 165 ksi (1,139 MPa) 130 ksi (897 MPa) 190 ksi (1,311 MPa) 160 ksi (1,104 MPa) 220 ksi (1,518 MPa) 180 ksi (1,242 MPa) 240 ksi (1,656 MPa) 210 ksi (1,449 MPa)
ing counterweights in gray iron for decades. The complexity of the cast- ings have changed, said Glenn Kue- hnel, plant manager, but the material choice has not. “Twenty years ago, counterweights
% Brinell
Elongation Hardness 11 10 7 5 3
302 340 387 418 460
Fracture Toughness (
ksi-sq.in./MPa-sq. m)
100/109 78/85 55/60 48/52 40/44
Table 4. Relative Damping Capacities of Some Common Structural Alloys
Material
Gray iron, coarse fl ake Gray iron, fi ne fl ake Malleable iron Ductile iron Pure iron
Eutectoid steel White iron Aluminum
Relative damping capacity
100-500 20-100 8-15 5-20 5 4
2-4 0.4
Source: ASM Handbook Vol. 15 Casting
were just large pieces of rectangu- lar metal, and at the same time, we could cast-in lifting devices for ease of assembly,” he said. “As that market progressed, gray iron became even more of a desired material. Now, counterweights are much more a part of the machine from a cosmetic and functionality standpoint.” Gray iron’s cost, combined with its
ease of production, has kept it tops for counterweights, Kuehnel said. Accord- ing to several metalcasters, gray iron is simpler to produce than ductile iron, CGI or ADI, and that simplicity can be attractive for straightforward, non- safety-related applications. According to Peaslee, the chemis-
try for gray iron does not require as much control as other ferrous met- als. In other words, the material can fall within a wider range while still meeting mechanical requirements. “Gray iron is fl exible,” Peaslee said.
“Ductile iron has a smaller range, and CGI has a much smaller range to fall
Table 5. Property Comparisons for CGI Grades (ASTM A842) Grade
Min. Tensile Strength
This gray iron casting serves as the main body for a hydraulic valve on a Bobcat.
30 METAL CASTING DESIGN AND PURCHASING
250 300 350 400 450
36.2 ksi (250 MPa) 43.5 ksi (300 MPa) 50.7 ksi (350 MPa) 58.0 ksi (400 MPa) 65.2 ksi (450 MPa)
Min. 0.2% Yield Strength
25.3 ksi (175 MPa) 30.4 ksi (210 MPa) 35.5 ksi (245 MPa) 40.6 ksi (280 MPa) 45.6 ksi (315 MPa)
% Elongation (in 50 mm)
3.0 1.5 1.0 1.0 1.0
Brinell
Hardness 179 max 143-207 163-229 197-255 207-269
SEPTEMBER/OCTOBER 2010
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