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Copper alloys in investment casting technology

January 2015
Metalurgija 54(1):293-296

Authors:

Jerzy Zych

AGH University of Krakow

Aldona Garbacz-Klempka

AGH University of Krakow

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This paper presents research results in the field of casting technology of copper and copper alloys using the invest-ment casting technology, both from historical as well as modern technology perspective. The analysis of exemplary elements of the old casting moulds is included, as well as the Bronze Age casts. The chemical content of various copper alloys was determined and the application of lost wax method was confirmed in the Bronze Age workshop. At present, investment casting method is used for manufacturing high-quality casts, especially products for power engineering that is why it demands respecting very rigorous technological requirements. The casts were character-ised based on microstructure research, chemical composition and conductivity in relation to oxygen content.

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293

METALURGIJA 54 (2015) 1, 293-296

S. RZADKOSZ, J. ZYCH, A. GARBACZ-KLEMPKA, M. KRANC, J. KOZANA,

M. PIĘKOŚ, J. KOLCZYK, Ł. JAMROZOWICZ, T. STOLARCZYK

COPPER ALLOYS IN INVESTMENT CASTING TECHNOLOGY

Received – Prispjelo: 2014-04-29

Accepted – Prihvaćeno: 2014-09-10

Professional Paper – Strukovni rad

ISSN 0543-5846

METABK 54(1) 293-296 (2015)

UDC – UDK 669.3:621.7467:930.26.669=111

S. Rzadkosz, J. Zych, A. Garbacz-Klempka, J. Kozana, M. Piękoś, J.

Kolczyk, Ł. Jamrozowicz, AGH - University of Science and Technol-

ogy, Faculty of Foundry Engineering, Krakow, Poland

M. Kranc, Foundry Research Institute, Krakow, Poland

T. Stolarczyk, Copper Museum in Legnica, Poland

This paper presents research results in the field of casting technology of copper and copper alloys using the invest-

ment casting technology, both from historical as well as modern technology perspective. The analysis of exemplary

elements of the old casting moulds is included, as well as the Bronze Age casts. The chemical content of various

copper alloys was determined and the application of lost wax method was confirmed in the Bronze Age workshop.

At present, investment casting method is used for manufacturing high-quality casts, especially products for power

engineering that is why it demands respecting very rigorous technological requirements. The casts were character-

ised based on microstructure research, chemical composition and conductivity in relation to oxygen content.

Keywords: copper alloys, investment casting technology, ceramic forms, casting defects, archaeometallurgy

INTRODUCTION

Historically, investment casting technology was

mainly used for casting: tools, weapons and ornaments.

Nowadays, this technology is employed in many impor-

tant manufacturing sectors, both industrial and artistic.

The propagation of the metal usage skills and cast

production is connected with the technology of creating

models, moulds and casts. Archaeol ogical studies con-

firm the knowledge of alloy preparation and the appli-

cation of advanced methods of mould making [1-8].

The wax model method, based on melting the wax be-

fore the mould is cast, ensures smoothness and preci-

sion of the model reproduction as well as thin wall of

the cast. Wax model was covered with many layers of

clay, dried and fired in the proper temperature to ensure

refractoriness and mould durability. In the Bronze Age,

with the investment casting technology arms and orna-

ments were produced. The fact, that this method was

used is attested to, i.a, by the discovery of ceramic

moulds workshop (Grzybiany-Legnica, Poland), des-

tined for manufacturing precise casts of bracelets and

necklaces made from copper alloys [9]. The research

conducted confirmed the characteristic content of the

alloys (Table 1) and the usage of multilayer ceramic

casting moulds (Figure 1a).

The moulds were made from sand mixture of vary-

ing grain, clay and materials of organic origin (Figure

1b), and next they were subjected to drying and firing

process, leaving the porosities for letting the gasses es-

cape form the mould.

Table 1 Chemical compositions of copper alloys

from Grzybiany-Legnica (Poland) / wt.%

No Concentration / wt. %

Cu Sn Pb As Sb Fe Ni

300-78 65,82 19,13 3,92 2,24 2,44 4,01 1,05

001-72 77,17 20,84 0,32 1,68 0,06 0,41 0,14

047-10 46,81 0,00 38,83 0,39 4,18 5,21 1,00

Figure 1 Microscopic picture of archaeological ceramic mould

from the Bronze Age, Grzybiany-Legnica (Poland)

Figure 2 Ceramic casting mould from the Bronze Age,

Grzybiany-Legnica (Poland), radioscopic image

a b

For achieving better durability the moulds were cov-

ered by external protective and strengthening layer. De-

fectoscope research of archaeological ceramic moulds

led to the discovery of a cavity in the shape of an oval,

bracelet together with a gating system, which is directed

294 METALURGIJA 54 (2015) 1, 293-296

S. RZADKOSZ et al.: COPPER ALLOYS IN INVESTMENT CASTING TECHNOLOGY

perpendicularly to the surface of the cast (Figure 2). In

Figure 2b the circular cross section of the channels of

the mould cavity can be seen.

Reproducing the surface relief precisely was the de-

cisive factor behind applying this technique in sculpture

and jewellery workshops. At the end of the 19th century

the investment casting method was already used in den-

tistry prosthetics [2].

Nowadays this method makes it possible to make

unique artistic pieces from alloys of copper with tin,

zinc, lead and also from copper and silver, and also to

manufacture both big and very small, precisely cast ma-

chine and equipment parts. With the development of

many branches of the world’s economy, the demand for

specialist machine parts increases. These elements are

often difficult to make by subtractive manufacturing be-

cause of their complex shapes, strongly developed area

or special requirements connected with their physio-

chemical and functional properties, and also the special

quality of their surface. To manufacture these products

precise casting technologies are used, according to the

investment casting method [10-14]. It is especially

common in armaments and aviation sectors, for mining

and automotive, power engineering, construction and

also in medicine for implant production and in jewel-

lery.

melting temperature, low flowing power, significant

casting shrinkage, surface tension and viscosity. Other

property, adverse from the viewpoint of casting technol-

ogy, is high solubility of oxygen and hydrogen in cop-

per, and, thus, the possibility of creating gas porosity.

The difficulties of copper casting process in many cases

direct our attention to the investment casting method,

especially in special casts technology for power engi-

neering. The reason of using copper in power engineer-

ing is the fact, that pure copper is characterised by the

highest, apart from silver, electrical conductivity. Elec-

trical conductivity of copper depends, first of all, on its

very high purity, from metallic impurities as well as ox-

ides and gasses. These high quality standards and also

low casting properties allow, with the application of in-

vestment casting method, to manufacture high-quality

sub-assemblies of of power engineering machines, such

as windings, primary rods, high conductivity connec-

tors free from porosity.[8-12]

RESEARCH METHODOLOGY

The elements analysed, belonging to the precision

casting where the investment technology was used, are

primary windings for transformers used in power engi-

neering. For their manufacturing, because of demands

for high physio-chemical properties and surface quality,

investment casting technology is applied. It is essential

to observe a rigorous technological regime at every

stage of the process, beginning with using high quality

wax mixtures, ceramic materials, stock materials, melt-

ing procedures, copper refining and casting [15-20].

Figure 3 Contemporary ceramic moulds for manufacturing

casts: a) industrial, and b) artistic

This technology is used to manufacture turbine

blades (Figure 3a), surgical instruments, endoprosthet-

ics, artistic casts (Figure 3b), and also casts made from

alloys with special properties.

Technological process of investment casting con-

sists of several stages:

- preparing wax models and assembling them in

model sets,

- preparing the ceramic mass and applying it in suc-

cessive layers,

- melting the wax in an autoclave and holding the

moulds within the proper range of temperatures,

- pouring molten metal into the casts, knocking the

casts off and cleaning the casts.

Modern copper and copper alloys casting encoun-

ters many technical limitations. The reason of limited

use of copper for cast manufacturing are the problems

resulting from its low casting properties which are high

Figure 4 Exemplary wax models for primary winding casts

As part of the research, a set of wax models was

made (Figure 4), in a metal die, and next layers of ce-

ramic mass were applied, dried intensively within the

proper range of temperatures. The application of suc-

cessive layers of ceramic mass by immersing in a rotat-

ing bath volume in a mixer, was conducted several

times to obtain a durable shell. After drying, the ceram-

ic moulds were placed in an autoclave to melt and re-

295

METALURGIJA 54 (2015) 1, 293-296

S. RZADKOSZ et al.: COPPER ALLOYS IN INVESTMENT CASTING TECHNOLOGY

move the wax, and then they were heated in a tunnel

kiln before being filled with molten metal.

Melting of the metal stock was conducted in an in-

duction furnace, using high conductivity copper and

pure copper MOK1 cathode, in a chamotte graphite cru-

cible with protective coating and a layer of charcoal.

Refining of the metal bath was conducted with the use

of synthetic slags.

A series of melts was conducted: melting under the

protective layer of charcoal, refining slag for removing

non-metal inclusions, de-oxidation with the help of

CuP10 and others, using the copper-based metal stock,

in the temperature 1 150 ºC ÷ 1 180 ºC. Liquid metal

was cast into ceramic moulds, held in 850 ºC for 6 hours

and, directly before casting, cooled down to 650 ºC.

Apart from industrial casts of power engineering

windings, also some samples were cast for researching

copper quality from the perspective of microstructure

and impurities, as well as electrical conductivity.

RESULTS ANALYSIS

To make casts of high quality it is crucial to keep the

bath purity at a proper level, most of all, keeping the

content of oxygen and hydrogen low. Hydrogen, creat-

ing gas porosity, significantly decreases active cross-

section of the cast, and, in the microstructure, an active

oxygen admixture causes precipitation of large oxygen

eutectic zones at the copper grain boundaries, which

very strongly decrease electrical conductivity of the

casts.

55 ÷ 1 870 ppm. The presence of this kind of impurities

leads to changes in the microstructure. There are oxy-

gen eutectic precipitates visible in Figure 6b.

The oxygen presence in copper influences directly

electrical conductivity of the material. Depending on

the oxygen content in copper, in the range of 50 ÷

300 ppm electrical conductivity changes 48 ÷ 57 MS.

The results obtained show unequivocally that the oxy-

gen content present in the copper, even below 300 ppm

will significantly lower the properties of the manufac-

tured casts for the power engineering.

CONCLUSIONS

In spite of the fact, that investment casting technol-

ogy was already used in the Bronze Age, nowadays, es-

pecially when manufacturing high-quality casts for, i.a.

power engineering, it demands respecting very rigorous

technological requirements. Properly chosen parame-

ters at every stage of the technological process ensure

creating the cast with the highest functional properties.

Special attention should be paid to the metal bath

quality, especially its hydrogen content, solid inclusions

and especially oxygen. The research provided an oppor-

tunity to evaluate the quality of the casts from the per-

spective of gas porosity, the kind of microstructure and

the influence of oxygen on the lowering of electrical

conductivity of the copper casts manufactured with in-

vestment technology.

Acknowledgment

This research the Bronze Age workshop was con-

ducted within the project of Ministry of Culture and Na-

tional Heritage, National Heritage Institute (MKiDN,

1879/13) “Grzybiany, the lakeside settlement from the

Late Bronze and Early Iron Age”, Copper Museum in

Legnica.

REFERENCES

[1] Z. Górny, Non-ferrous metals and their casting alloys –

melting, casting, structures and properties, Krakow 1995.

Figure 5 Gas porosity in the copper cast section, made by

using the investment technology

The presence of gas porosities in the structure of the

cast (Figure 5), as well as non-metallic inclusions, di-

rectly influences the properties.

A significant hydrogen content causes the increase

of porosity, which decreases physio-chemical proper-

ties, this is lowering the density, thermal and electrical

conductivity as well as mechanical properties, resulting

in the lowering of the properties of the cast. Proper con-

ducting of the copper melt and application of the meas-

ures preventing hydrogen solution in copper still can

lead to the solving of excess amount of oxygen.

Research of slag and de-oxidation formulas allowed

to analyse the efficiency of the latter as well as asses the

influence of oxygen in the copper on electrical con-

ductivity. The samples of de-oxidised copper showed

varied content of the oxygen, in the range of

Figure 6 Copper microstructure with the oxygen content

of a) 150 ppm, b) 1 000 ppm, magnification 200 x

a b

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[2] Z. Górny, J. Sobczak, Modern casting materials based on

non-ferrous metals, Krakow, 2001.

[3] K. Dies, Copper and copper alloys in technique, Springer

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Note: The responsible translator for English language is A. Hardek,

AGH - University of Science and Technology, Krakow, Poland

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Streszczenie Technologia wytapianych modeli należy do najstarszych technologii odlewniczych. Historycznie służyła do odlewania narzędzi, broni i ozdób. Model wykonany z wosku pszczelego oblepiano gliną suszono i wypalano. Otrzymywano odlewy o dużej gładkości powierzchni, dokładności i precyzji wykonania ornamentu. Metodą tą odlewano niewielkie kilkugramowe odlewy jak i wielkogabarytowe pomniki. Współcześnie ta technologia jest wykorzystywana w wielu ważnych gałęziach produkcji zarówno artystycznej, jak i przemysłowej. Szczególnie w przemyśle zbrojeniowym, lotniczym, motoryzacyjnym, energetycznym, budowlanym, a nawet kosmicznym. W pracy przedstawiono wyniki badań i eksperymentów, prowadzonych w zakresie technologii odlewnictwa miedzi i stopów miedzi z zastosowaniem metody wytapianych modeli, zarówno w aspekcie historycznym, jak i współczesnej praktyki przemysłowej. Przykładowo przedstawiono analizę wybranych elementów dawnych technologii, form i odlewów wytworzonych w epoce brązu oraz wyniki badań dotyczące aktualnie produkowanych odlewów dla branży energetycznej. Jakość odlewów została oceniona na podstawie przeprowadzonych badań z zakresu mikrostruktury, składu chemicznego, przewodności elektrycznej i zawartości tlenu. Słowa kluczowe: innowacyjne materiały i technologie odlewnicze, metalografia, wady odlewów, technologia wytapianych modeli, stopy miedzi. Investment Casting Technology Applied to Copper Alloys Abstract Investment casting technology belongs to the oldest casting techniques. Historically, it was used for casting tools, weapons and ornaments. A model, made from beeswax, was covered in loam, dried and fired. The casts obtained were characterised by high surface smoothness, accuracy and precision of its ornaments. This method was used for relatively small casts as well as for big monuments. Nowadays, this technology is used in many fields of manufacturing, both artistic and industrial, especially in armaments, aviation, automotive, power, construction and even space industry. This work presents the results of research and experiments conducted in the field of casting technology of copper and copper alloys, applying the investment casting method, both in its historical aspect and modern industrial practice. An exemplary analysis was presented of the chosen elements of the old technologies, moulds and casts, as well as the results of casts made currently for the power industry. The casts quality was evaluated based on the research of their microstructure, chemical composition, electrical conductivity and oxygen content.

Rheological properties of ceramic slurries with colloidal binders used in the investment casting technology

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Jan 2013

The article presents results of analyses of ceramic slurries made using materials currently tested in this technology, i.e.: colloidal silica (Ludox AM and Ludox SK) as a binder and Al 2 O 3 as the ceramic matrix material. To characterise the binder, the size of colloidal binder particles, the Zeta potential and the binder pH were determined. Rheological properties were studied for slurries whose proportion of the (technologically justifi ed) solid phase amounted to: 73; 74; 75 %. The impact of the solid phase proportion on the thickness of subsequent coats applied to the wax model, the dynamic viscosity and the density was determined. Research also included the impact of the size of matrix grains and the temperature on the above properties.

Production Technology, Physical, Mechanical and Performance Characteristics of Cu-Zr-Y-Mo Finely-Dispersed Microlayer Composite Materials

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Full-text available

Apr 2007

The production of Cu-Zr-Y-Mo Finely-Dispersed (FD) microlayer composite materials for electrical contacts by the method of electron-beam evaporation and layer-by-layer condensation from the vapor phase is described and the chemical composition, structure, density, electrical conductivity, hardness, and main mechanical characteristics of the materials in the temperature range from 290 to 1070 K are studied.

Influence of refining operations on a structure and properties of copper and its selected alloys

Article

Jan 2009

The analysis of the refining effwctiveness of the liquid copper and selected copper alloys by various micro additions and special refining substances - was performed. Examinations of an influence of purifying, modifying and deoxidation operations performed in a metal bath on the properties of ceratin selected alloys based on copper matrix - were made. Refining substances, protecting-purifying slag, deoxidation and modifying substances containing micro additions of such elements as: zirconium, boron, phosphor, sodium, lithium, or their compounds introduced in orfder to change micro structures and properties of alloys, were applied in examinations. A special attention was directed to macro and micro structures of alloys, thier tensile and elongation strength and hot-cracks sensitivity. Refining effects were estimated by comparing the effectiveness of micro structure changes with property changes of copper and its selected alloys from the group of tin bronzes.

Copper and bronze during the Eneolithic and Early Bronze Age: A metallographic examination of axes from the Northalpine region

Article

Jul 2006
ARCHAEOMETRY

This paper presents the results of a metallographic examination of Eneolithic and Early Bronze Age axes from the Northalpine region of central Europe. During this period, different types of copper were in use: arsenical copper, Fahlerz copper and tin bronze. We examine if and to what extent the different properties of the metals used were known to prehistoric metalworkers and actively manipulated in the production of the axes. The development of methods of casting and smithing is discussed. Both aspects contribute to our understanding of the nature of prehistoric technological change. During the Early Bronze Age of the Northalpine region, different traditions of early metallurgy can be identified, which differ in their use of Fahlerz copper, their attitude towards tin alloying and the use made of tin bronze in the production of the axes. These traditions can only be adequately described by reference to both composition—that is, access to different types of copper as well as tin—and knowledge of the production techniques provided by metallographic data.

Copper and copper alloys in technique