COPPER-BASE
CASTING PROCESS CAPABILITY Copper-based alloys are cast commer- cially via the following methods: • Green sand. • Nobake sand. • Permanent mold. • Investment. • Lost foam. • Shell mold. • Centrifugal. • Plaster mold.
DESIGN CONSIDERATIONS • The copper family offers the designer a wide range of choices since several alloys may be suitable candidates for any given application, de- pending on design loads and corrosiveness of the environment.
• From a metallurgical standpoint, many cast copper alloys are single phase solid solutions, in which the alloying elements, such as zinc, tin and nickel, are substituted for copper. As the alloy content increases, a second phase may form. For instance, when zinc content is increased in brass, a hard second phase forms with the copper-rich matrix. This phase can impair room temperature ductility but increase elevated temperature ductility.
• Thick to thin sections can cause solidifi cation problems, particularly in the most common copper alloys such as red brasses, tin bronzes and yellow brasses due to their medium to wide freezing ranges. These alloys do not solidify directionally. Rather, pockets of metal through- out the casting solidify at the same time and pull from surrounding liquid areas. To counteract the solidifi ca- tion issues, metalcasters may use molding tools, such as chills, but these add cost. The best option is a sound casting design without abrupt changes from thick to thin sections.
PROCESS CONSIDERATIONS • Copper alloys exhibit good ma- chinability. Leaded copper alloys are free-cutting at high machining speeds, and many unleaded alloys are readily machinable at recom- mended feeds and speeds with proper tooling.
• Good surface fi nish and high tolerance control leads to ease in post-casting processing. Many cast copper alloys are polished to a high luster, and plating, soldering, brazing and welding are routinely performed.
Copper castings, such as this piston, are used in plumbing due to their good corrosion resistance, which leads to increased fl ow capacity.
This mixing valve body (above) and water meter housing were cast using the lead-free copper alloy C89836.
Typical Mechanical Properties of Common Alloys* Alloy
Ultimate Strength (ksi)
Copper
Beryllium Copper Red Brass
Semi-Red Brass Yellow Brass
Manganese Bronze Tin Bronze
Aluminum Bronze Copper Nickel
28 80
36-38 34-38 34-52 69-120 27-48 77-102 70
Yield Strength (ksi)
4 40
15-16.5 14-14.9 12-18
26-69 14-24 28-43 40
Elongation %
45 20
30-34 27-37 35-50 16-37 20-43 11-40 25
* Ranges refl ect different casting processes and heat treatment conditions.
Hardness Bhn
40 150
55-65 55-58 46-77
88-235 55-80
125-195 140
Jul/Aug 2012 | METAL CASTING DESIGN & PURCHASING | 35
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