RAUTOMEAD TECHNOLOGY FOR UPWARDS CONTINUOUS CASTING OF COPPER ALLOYS Paper given by Brain Frame, MD Rautomead at teh IWCC technical Seminar, Santiago, Chile, March 2013

1. RAUTOMEAD TECHNOLOGY FOR UPWARDS CONTINUOUS CASTING OF
COPPER ALLOYS
BACKGROUND
Rautomead Ltd was formed in 1978, and is based in Dundee, Scotland, approximately 1
hour drive north of Edinburgh. Since the company’s foundation in 1978, Rautomead has
specialised in continuous casting technology for non-ferrous metals. Over that period,
close to 350 systems have been built and installed at customer sites in 45 countries
around the world. Although a large portion of these installations have been of the
horizontal, or even vertically-downward, mode (which are all still available and being
developed), the core of Rautomead business over the last 20 years or so has been in the
area of vertically upwards continuous casting.
Rautomead plants are being successfully applied to production of oxygen-free copper, a
wide range of copper-based alloys, precious metals and zinc. Forms include wire rod,
straight length bars, flats and hollow sections. As stated previously, according to material
and section, the casting process selected may be vertical upwards, vertical downwards or
horizontal. The machines may be used either as integrated melting, holding and casting
machines, or may be arranged to be fed with pre-alloyed molten metal.
RAUTOMEAD PROPRIETARY TECHNOLOGY – key components of Rautomead
capability
Most modern continuous casting systems use electric induction heating and rammed
ceramic lined furnaces to melt, hold and cast the metals. By contrast, the Rautomead
system is based on electric resistance heating of its furnaces, with graphite containment
crucibles, graphite heating elements and also graphite casting dies. Each technology has
its own characteristics, advantages and disadvantages and each has applications where it
is in particularly well-suited.
Graphite Crucibles
Furnace crucibles are machined from extruded or vibration-moulded solid blocks to a
variety of designs for either vertical or horizontal casting. Sacrificial linings are used to
protect exposed surfaces from oxidation. The naturally reducing effect of the graphite
material assists in ensuring the full de-oxidation of copper and avoids contact with and
contamination of the melt by refractory particles.
In Rautomead’s oxygen-free copper and high copper alloy casting systems, crucibles are
machined to create two separate, but linked chambers for maximum exposure of the
copper to a carbon environment and to ensure a steady flow of metal through the system
and consistent alloy chemistry.
Graphite Heating Elements
The good electrical conductivity of graphite enables this material to be used as heating
elements in a low voltage resistance furnace heating system. Secondary power is fed to
water-cooled graphite busbars and to a chain of accurately rated heating elements which
surround the crucible. The heat is fed to the metal in the crucible by radiation and
convection and all at low voltage (typically 40 V). The arrangement is not only thermally
efficient, but also very safe in operation.
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2. Graphite Casting Dies
Available in a variety of sizes according to casting requirements, graphite casting dies
utilise a range of graphite “recipes” to optimise performance aspects, such as die life and
as-cast surface finish, dependant on the material being cast.
Still Metal Bath
Whereas induction heating tends to create an electromagnetic stirring effect in the molten
metal, resistance heating in the Rautomead system delivers the energy through the walls
of the graphite crucible and ensures a still metal bath. This avoids any metal turbulence in
proximity to the casting die and has special advantages in melting and casting alloys
prone to slag formation, including Cu-Mg.
Oxygen Reduction
To achieve an adequate casting die life and thus an economically viable performance, it is
necessary that oxygen must be reduced to extremely low levels (normally less than
10ppm). From a normal grade A cathode oxygen content of 60-80ppm, Rautomead
graphite technology can reduce this to the 2-5ppm levels over a period of 2-3 hours. This
oxygen reduction is achieved by exposing the copper to graphite at five specific stages of
the process:
•
graphite pellet metal cover over melting chamber
•
graphite sacrificial lining of upper part of melting chamber
•
graphite walls of crucible
•
graphite filter bed fitted in the casting chamber
•
graphite flake cover over casting chamber
This multi-stage exposure to carbon is conducive to rapid oxygen reduction and contrasts
with induction heated systems, where users rely only on a charcoal or reducing gas cover
over the melt to remove the oxygen.
PRODUCTION OF COPPER ALLOYS
Rautomead supplied its first two continuous casting machines for production of Cu-Mg
wire rod in 1990. These were 8 strand horizontal machines built to produce a range of
Cu-Mg alloys from 0.2% to 0.5% Mg for trolley wire applications. Cathode and elemental
Mg were added direct to the graphite crucible in accurately measured proportions. Cast
diameter was 19mm and 28mm. Production speed was relatively low at around
30kg/strand/hour, but rod quality was sound and consistent, both in terms of alloy
composition and physical properties. These machines are still in use today.
The upwards vertical adaptation of the Rautomead continuous casting process was
developed in the early 1990s, initially to produce oxygen-free copper rod, but latterly
adapted to produce copper alloys, including Cu Mg. The vertically cast rod presents
greatly superior structural symmetry compared with horizontally cast rod, where the latter
tends to lean forward owing to the uneven effects of gravity around the circumference of
the solidifying metal.
Casting speeds of around 100 kg/hour are achievable in production of 28mm diameter rod
in Cu-Mg – a three-fold increase from horizontal casting. Time taken to change casting
dies was also reduced and made significantly safer than in the horizontal process.
Rautomead’s first upwards vertical casting machine for Cu-Mg production was supplied in
1997, since when this has become something of an industry-standard specification in
contact wire applications for high speed rail. Around 20 machines of this type have been
supplied to customers globally over recent years.
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3. Current Technology
The Rautomead model RS 3000/5-Cu-Mg copper-magnesium wire rod casting machine
comprises a single, integrated graphite melting/holding and casting furnace. The machine
is equipped with automatic cathode feed and weighing and casts five strands up to 34mm
diameter vertically upwards. Rods are guided over the machine and down to form layerwound coils. The process is largely automatic in operation with all key production
parameters constantly monitored and alarmed. In the event of mains power failures the
casting dies are automatically lifted from the crucible and the machine is made safe.
Nominal output is 500 kg per hour. an automatic cathode feed and weighing system and
casts 5 strands at up to 34mm diameter into coils to produce around 500 kg per hour.
Crucible holding capacity is approximately 2,500 kg.
Developments in Copper Alloying Capability
Although CuMg for high speed rail applications has been very much the “star performer”
for Rautomead over the last few years (with around 20 customer installations now in place
throughout Europe and, more recently, China), Rautomead has not rested on its laurels.
Still very much with a firm eye on the areas of copper and copper alloys, innovation, and
product and process development are key drivers of Rautomead business strategy, and
much of this development activity has been focussed on projects to expand the capability
of Rautomead technology toward the production of a wider range of copper alloys.
Although generally driven by some level of customer involvement, whether a direct
request, which may lead to a formal business relationship/agreement internal
development, or a general “it would be good if….” conversation, notes of interest in
developing alloys are usually based on a desire to provide performance improvements in
areas such as strength, corrosion resistance, conductivity, wear resistance, machinability,
and even colour. These performance improvements result in areas of reduced weight,
longer product and process runs, and hence improved cost benefits.
Today, Rautomead vertically upwards continuous casting technology provides a capability
for a range of copper based alloys, ranging from brasses and bronzes through to copper
tin/silver/magnesium. These are used to serve a number of industrial applications from
building and construction, electro-discharge machining (EDM) and automotive. However,
as a very small fish in a very large, changing, and at times aggressive pond, Rautomead
has to continue to expand its capabilities.
Current development activities are all about either improving the performance of existing
capabilities, extending scope of existing capabilities, or indeed developing new
capabilities. Again, these projects are pursued via a number of avenues, ranging from a
“go-it alone” by Rautomead, in conjunction with UK universities, by loose co-operative
arrangements with both existing and potential customers, as well as upstream and
downstream process providers, all the way to formal co-development projects with product
providers.
Some examples of such activities include:
•
the provision to produce lower and tighter tolerance bands of copper magnesium
(CuMg) for automotive cable harness applications
•
the provision of DHP copper tube casting capability as a starting process for both
water and ACR tube production,
•
the provision of a capability to continuously cast CuCrZr material
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4. •
the ability to re-melt and cast Sudronic needles, as used in tin can manufacturing
•
vertical upwards casting of aluminium bronze rod, for welding applications
•
Autofeeding of cored wire alloying material, in order to improve process efficiency
and reduce operating costs
•
In-process monitoring of alloy composition, as a means of in-line process control
•
Grain refining (by a number of methods) as a means to improve product quality
and reduce downstream processing requirements
As a result of these activities, Rautomead has also developed and created an
additional dedicated R&D production machine at its facility in Dundee, to be used in
conjunction with existing development facilities. This has been designed specifically
to further expansion of the Rautomead in-house capability in terms of alloying,
process controls and dimensions of material cast. Development of this machine has
in itself resulted in a specific Rautomead product offering, as some customer express
a demand to carry out in-house casting developments. However, the machine itself is
seen as a key component in allowing Rautomead to pursue its objective of becoming
a leading provider of continuous casting technology well into the 21st century.
Thank you.
Rautomead Limited
Nobel Road,
Wester Gourdie Industrial Estate
Dundee DD2 4UH
U.K.
tel. + 44 1382 622341
fax. + 44 1382 622941
email. sales@rautomead.com
www.rautomead.com
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