401 History of Metal Casting Early Lost Wax PDF

8/9/2019 401 History of Metal Casting Early Lost Wax PDF

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History of Metal Casting

A quick run around the world of

ancient lost wax casting



Copper

• Copper has a history ofuse that is at least 10,000years old

• A copper pendant was

found in northern Iraqthat dates to 8,700 BC• Gold and meteoric (not

smelted) iron were theonly metals used byhumans before copper

• It is believed that copperwas first



History of copper metallurgy:

• Earliest use of copper wasin cold working

• Between 5,000-6,000 BC,people began using copperore by heating (annealing)and hammering.

• Then they discovered howto process copper orethrough smelting

• Finally they developed lostwax casting technology

A corroded copper ingot from Zakros,Crete, shaped in the form of an animalskin typical for that era.



Copper Ore

• Malachite, a form ofcopper carbonate,was often used for

gemstones inantiquity and formsof copper ore havebeen used in beadseven in Paleolithictimes.



Mining Copper

• It was not untilaround 3,000 BCthat people began

to figure out howto smelt theimpurities out of

copper and thenbegin casting theminto other forms.

Chalcolithic copper mine in Timna Valley,Negev Desert, Israel.



• Ötzi the Iceman, amale dated from3300 –3200 BC,was found with anaxe with a copper

head 99.7% pure;high levels ofarsenic in his hair

suggest hisinvolvement incopper smelting.



Different types of copper orewere found above or below thewater table, due to the leachingaction of water.



Copper facts:• Is very soft, highly ductile (flexible) and an excellent

electric and thermal conductor• It is one of only three metallic elements that is not

silver/grey in color (gold and osium)• When placed against a second metallic element

galvanic corrosion will occur• Copper can be found as either native copper or as part

of minerals. Native copper is a polycrystal, with the

largest described single crystal measuring4.4×3.2×3.2 cm.

• The largest mass of elemental copper weighed 420tonnes and was found in 1857 on the KeweenawPeninsula in Michigan, US. There are many examples ofcopper-containing minerals: chalcopyrite andchalcocite are copper sulfides, azurite and malachiteare copper carbonates and cuprite is a copper oxide.

•Copper is present in the Earth's crust at aconcentration of about 50 parts per million (ppm), andis also synthesized in massive stars

• 90% of all copper mined was unearthed after the year1900

• Unlike other metals, it does not dissolve inhydrochloric. Nitric acid will replace it.



• The Statue of Libertyis the largest copper

statue in the world

• Its green color iscaused by the

reaction of thecopper with the airwhich creates a layer

of verdigris or coppercarbonate.



Difficulties in casting copper

• Pure copper is very difficult to cast, it is prone to surface cracking, highlyporous and tends to develop internal cavities. It picks up gas easily whenliquid.

• Copper has a narrow freezing range (50 degrees C between liquidus andsolidous)

• The casting characteristics of copper can be improved by the addition ofeven small amounts of elements including beryllium, silicon, nickel, tin,zinc, chromium and silver.

• Copper should be melted under a floating flux cover to prevent bothoxidation and the pickup of hydrogen from moisture in the atmosphere. Inthe case of copper, crushed graphite should cover the melt.

• When the molten metal reaches 1260oC, either calcium boride or lithiumshould be plunged into the molten bath to deoxidize the melt. The metalshould then be poured without removing the floating cover (this acts todegas the metal).



Smelting

Copper sulphide ores are heated in contact with air first.) At this temperature the metal, nowliquid, flows to the bottom of the furnace, and the remaining matter (slag) floats to the top,

whence it is removed. (Slag usually includes large amounts of silicon and related material andproduces waste heaps of glass-like or cinder-like material.) Although this sounds straightforward, inantiquity, and especially before the invention of a bellows, it was difficult to attain the necessarytemperature, and the extraction of copper from slag was in fact a difficult, messy, and extremelylabor-intensive project.Smelting produces a blob of metal (called bloom) prepared for the next step. In the case of copper,that step is often casting. Iron has a higher melting point than copper, but below its melting point

can still become spongy and amenable to treatment by hot hammering (forging), which helps toextract some of the remaining impurities.

Ellery Frahm experiments conducted in Cyprus. She is a ResearchFellow at the Department of Archaeology, University of Sheffield

Smelting is the basic process bywhich one produces workablemetal from metal ores. Theminerals in copper ores arereduced to copper through mixingcarbon with the ore and heating

the combination to about 1,100°C.(This can be done directly withcopper oxide ores.



SmeltingSmelting is the process of

heating raw ore to the pointthat the impurities areseparated from metal.

To smelt copper, the ore wascrushed and placed into a clay

crucible over a charcoal fire.Since bellows were a laterinvention, bamboo canes tippedwith clay were used to increasethe temperature of the fire.

At these temperatures, arelatively small amount of orewill be produced and can beseen in small shiny needles or“prills” of pure copper.



Dancing Girl Of Mohenjodaro, Indus

Valley Civilization

• 4500 years oldand 4” tall (10.8

cm

• Found in 1926from a brokendown house onthe "ninth lane" inMohenjo-daro



Lost wax infographic:



Casting in India•

Wax pattern is made outof beeswax and tree resin• Pattern is covered withclay obtained from riverbanks and then allowed todry for 3-4 weeks. Then the

pattern is bound with wire.• The wax is then melted outof the mold over a fire madefrom cow dung• An alloy of copper (84%Cu, 14% Zn, 2% Sn) is melted

in a crucible furnace usingwood charcoal and coal as afuel. Hand bellows are usedto force air into the fire. Themold is pre-heated as wellthen the casting is poured.



Metal Casting in Foumban,

Cameroon, Africa • Wax is applied to clay

core.

• Clay is applied aroundwax

• Wax gates are applied to

form• Clay mold applied to

entire casting• Mold is placed inside kiln

and wax is melted out,then bronze is poured

into mold• Casting is refined with

files and chisels.

Images and research of the next several pageswere created by Dr. Carol Ventura, Professor of

Art at Appalachian Center for Crafts, TennesseeTechnical University



Putuench Ismaila

• Often the coresare highly detailed

• Then wax isapplied over thesurface andrefined before

covered with theouter mold

Putuench

Ismaila who

was also

pictured inthe last slide

with his

work.

Contact him for purchase of his workby writing: Putuench Ismaila at B.P.

10, Foumban, Cameroon



Ashanti Lost Wax Castingin Krofofrom, Ghana –

wax working• Wax is soften over fire•

Then applied to amold and trimmedwith a knife

• Details are added• Then soldered in place

with a knife• Next they are formed

with a modeling tool•

Wax is rolled out intoa string to create thehair and ears

• Alternatively wax ispressed into aplaster/cement moldas a basis for asculpture



Ashanti Lost Wax Casting in

Krofofrom, Ghana - moldmaking • Charcoal is

pulverized andsifted then mixedwith clay andwater to form aslip which ispainted over thewax pattern

• Next a thickerlayer of clay isapplied to thepattern

• Then palm fibersare separatedand mixed in withclay, water andcharcoal dust

• Sand is alsomixed in



Ashanti Lost Wax Casting - kiln • The clay, sand,

palm fibermixture isapplied to thepattern. Ashallowdepression is leftat the top.

• A cup or crucibleis also formed.

• Scraps of brassare cut down andweighed

• The metal isplaced into thecrucible and thetwo sections are joined

• The molds arethen placedinside a kiln,metal side down.

• An electricblower is movedto each hole toevenly increase

the heat to thecharcoal fire.photographs, and research by Carol Ventura



Ashanti Lost Wax Casting - melting

• After a few hoursthe kiln wall is tornout and the moldsare removed andinverted so that themolten metal willflow from the

crucible into themold.

• Water is used tocool the kiln so thefoundry worker cansafely removemore molds

• A bannana stemdipped in clay isused to chill a crackin the mold

• After the moldshave cooled, theyare broken open toreveal the castings



Ashanti Lost Wax Casting - finishing

• The molds andcores arehammered awayfrom the castingsand then the gatesare clipped off

• The gates and flawsin the casting areremoved andsmoothed withgrinders (note thelack of propersafety gear).

• The casting is thenpolished usingcrushed lemonsand a wire brush(the acid in thelemon helps toremoved theoxides).



Ashanti Lost Wax Casting – alternate process • In an alternate

approach used by

the same foundrythe same type ofmolds are used,without thereservoir crucible

• A crucible of metalis placed into asquare brick furnacethat and filled withcharcoal. An

electric blower isused to increase thetemperature

• Plastic is placed onthe fire to increasethe temperature

• The foundryworkers know thatthe metal is readywhen blue smoke

comes from thecrucible (caused byzinc)

• The patterns arethen poured fromthe crucible, whichin this case wasmade from arefrigerator motorhousing



Foundries still continue to use claybased lost wax molds

Brass Baron Foundry



Other early casting techniques

• Not all earlycasting techniquesinvolved lost wax

• Many culturesused two partimpression molds,

which were thenbound togetherbefore pouring



Multi-sectional clay molds from China



Stone mold with a clay core

• Stone molds were alsooften used. Theseusually employedlimestone or dolemite

which is easily carved.• Frequently these molds

used clay cores.• These molds were re-

usable for a few casts, ifthe metal caster washighly skilled



Bronze Molds from Britian

• Finally, bronzemolds were alsoused which were

re-usuable• This allowed for

steps towardsmass production

• These molds musthave perfect draft

401 History of Metal Casting Early Lost Wax PDF

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