Metals Conservation

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MetalcastingMetalcasting TechnologyTechnology

A brief historical perspectiveA brief historical perspective

Ralph E. NapolitanoRalph E. Napolitano

Department of Materials Science & EngineeringDepartment of Materials Science & EngineeringIowa State University Iowa State University

Ames, IowaAmes, Iowa

Metals Conservation Summer InstituteMetals Conservation Summer InstituteJune 1, 2005June 1, 2005

IOWA STATE UNIVERSITYMaterials Science & Engineering

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Metalcasting

Casting is an important method for reliable and reproducible production of net-shape metallic components of very intricate geometry.

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Early melting and casting

In mesopotamia, the melting and casting of copper began some time around 4000 BC and was followed by the casting of bronze and the introduction of the lost-wax process. By virtue of the well crafted products that resulted, the methods developed here spread rapidly through both east and west. With the development of smelting technology, the world was ready for the explosion of metalcasting.

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Eastern masters of clay molding

Chinese bronze vesselShang dynasty1000-1100 BCFreer Gallery of ArtWashington, DC

With very little evidence of an “incubation time”, Chinese casting emerges from about 1600 BC, with techniques much different from those used in the west.

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Cast iron giants

A better understanding of furnace bellows and control of heat permitted eastern artisans to work with cast iron, and they produced numerous monumental castings.

One of four cast-iron warriors guarding the 'Depository of Ancient Spirits' (Gu shen ku) of the Zhongyue Temple in Dengfeng, Henan (A.D. 1064).

The 'Eastern Iron Pagoda' of the Guangxiao Temple in Guangzhou, Guangdong (A.D. 967).

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The emergence of metalcasting methods

While simple cast copper objects date back as early as 4000 BC, it wasn’t until the 1600th century AD when melting of metals became a widely applied practice.

Significant Milestones

- open groove molds (clay or stone)-lost-wax molding (3000 BC)-Bivalve mold (cope and drag)-bivalve cored mold- piece molding- integral cast-on methods (700 BC)- casting and joining- sand casting (1500 AD)

- Guns, money, bells, and the press

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Bivalve castings

Appearing, perhaps, early in Egyptian castings,

cope and drag methods permitted more complex shapes than open molds, but was still restricted by convexity requirements.

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Casting with cores

Positioning of cores is critical, and incorporation of chaplets logically leads to integral cast-on methods.

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Piece-molds

Chinese bronze chiaChou dynastyBoston MFA

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Piece-molds

Large relief integrated into pattern for mold impression.

Fine detail carved directly into the accessible mold.

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Replication

Chou dynastyFreer GalleryWashington DC

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Lost-wax castings

BronzeTell Judeideh, Syria2900 BCBoston MFA

BronzeBenin, Nigeria1500-1700 BCBrooklyn Museum

GoldColumbiaMuseo del Oro(Bogota Colombia)

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Lost-wax castings

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Lost-foam process

Alfred Duca1960

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An advanced application

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Jet engine turbine blades

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Investment casting of single crystal parts

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Perhaps the most sophisticated castings ever made

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A challenge of scale

Turbines for power generation

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Novel casting methods

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Laser melting and cladding

X--Y Positioning Stage

Laser and Powder Delivery Nozzle

X

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Laser Engineered Net Shaping (LENS™)

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Localized alloying

12 mm

0% Cu 20% Cu

40% Cu 60% Cu 80% Cu 100% Cu

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Simulations

Simulation of laser welding

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Laser clad microstructure

50 µm

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Gas atomization

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Levitation melting

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Free-jet melt-spinning

Melt

Cu wheel(30 cm dia.)Extracted

ribbon

Melt pool

Chamber with controlled atmosphere

CCD Camera

Quartz crucible

Spinningdirection

Orifice(0.8 mm)

Free-jetmelt stream

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10 µm

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10 µm

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10 µm

(a)