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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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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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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 layer-wound 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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• 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