Continuous casters process precious metals

With ten integrated casting and melting models available - in vertical and horizontal configurations - precious metal continuous casting machines offer a range of production capacities.

Since the launch of its very first precious metals continuous casting machines in the early 1980s, Rautomead has become world-renowned for the design, development and delivery of compact, convenient, highly versatile casting technologies.

Of particular note are Rautomead's highly robust continuous casting solutions for the processing of gold and silver alloys for various jewellery applications.

Embracing the hallmarks of Rautomead's advanced casting expertise, using a naturally oxygen-reducing graphite crucible and safe, low voltage resistance heating, all models in the Rautomead precious metals range are designed for the production of the very highest quality continuous cast, semi-finished gold and silver-based alloy products.

With ten integrated casting and melting models available - in both vertical and horizontal casting configurations - Rautomead offers technology for a range of applications and production capacities.

Power outputs range from 15kVA to 105kVA, melt rates range from 30kg to 700kg (Ag)/h; whilst the ability to produce semi-finished rod products from 2-10mm diameter and flats from 5-400mm wide ensures all applications can be easily fulfilled.

Horizontal casting machines are normally specified for rods and flats and vertical machines for hollow sections, where a low tolerance of concentricity (better than 2%) is achieveable.

For those many smaller volume producers, Rautomead also offers machines with crucible capacities of as little as 0.5 litres, with volumes increasing to 80 litres for those with larger requirements.

* The Rautomead graphite crucible - technology is key when considering the alternative types of precious metals continuous casting solutions available and the resistance-heated graphite crucible offered by Rautomead provides significant, measurable advantages over the purchase of induction-heated, ceramic-lined furnaces.

* Submerged casting die - during the Rautomead casting process, the metal charge is melted and held in a solid graphite crucible, a naturally oxygen-reducing environment that is conducive to the production of metallurgically clean cast products, without inclusions, voids or other internal defects.

The crucible is fed from above and discharged through a submerged casting die at its base.

A graphite baffle plate may be used to prevent cold metal dropping to the bottom of the crucible.

The machines are designed to be self-draining to avoid residues of valuable materials at the end of a production run.

* Resistance heating technology - in the Rautomead system, melting is achieved via the company's world-renowned resistance heating technology, a method that operates at inherently safe low voltages and is exceptionally simple to operate and maintain.

In the Rautomead process, the graphite crucible and heating elements are protected from oxidation in an inert gas atmosphere.

Furnace temperature is automatically controlled within a tolerance of +/-2 deg C, using a thermocouple located at the crucible and a hinged lid is provided to close the crucible when it is not being charged.

The result is a reliable, high quality and sound cast semi-finished product, de-gassed and without porosity or inclusions for the highest yield down-stream processing.

* Highly cost-effective tooling - the very nature of the precious metals industry dictates that relatively small quantities of valuable materials are frequently produced in a wide range of sizes and alloys, a fact that can make tooling changes an expensive aspect of the casting process.

To keep tooling costs down to a minimum, Rautomead has ensured that, wherever possible, tooling used on newly developed machines is compatible and interchangeable with that used on earlier models.

* Technical innovations - a gas bubbling device fitted to the base of the Rautomead crucible permits inert gas to be bubbled through the molten metal, ensuring full and homogenous alloying of the charge prior to casting, particularly when melting and alloying virgin metals.

Thermocouples fitted in the casting die monitor temperature at the pre-determined point of solidification and warn of any anomaly.

Casting dies are made in high-density graphite, with multi-channel water-cooled copper alloy cooling plates and cast strip is withdrawn through an arrangement of twin articulated pinch rolls, driven by computer-controlled AC servo geared motor.

A quartz sightglass window is available to check for metals leakage, without the need to open the tap hole, thus avoiding the ingress of oxygen.

* Continuous or 'discrete' operation - fully PLC controlled, with quality control downloads available to the user's computer system, an additional benefit of Rautomead precious metals technology is the flexibility of either continuous or 'discreet' operation.

For continuous operation, gold or silver is added in small quantities at approx.

ten minute intervals, allowing production to continue as long as required.

In 'discrete' mode, the machine is operated on a batch basis, where the charge is made up of the constituent elements in heat-weighed proportions prior to the start of production.

At the end of the working day, production can then be halted, leaving the strips in the casting dies, molten metal in the crucible and the temperature reduced to just over the liquidus.

Production can then recommence within 30 minutes when required.

Metal can also be left to solidify and go cold in the crucible, in the event of power failure, without damage to the machine.

Rautomead offers a comprehensive range of continuous-horizontal and continuous-vertical casting machines for the production of the highest quality jewellery alloys.

The American Eagle, Canadian Maple Leaf, Krugerrand and Britannia coins are all produced using precious metals processed using Rautomead technology and the medals received by 'gold' and 'silver' winning athletes at the 2000 Olympic Games in Sydney were made from strip cast through Rautomead machines.

Rautomead technology is used by the South African Rand Refinery and the Royal Canadian Mint.

* Precious metals casting expertise - available on line - the full range of Rautomead precious metals continuous casting technologies - complete with comprehensive specifications and literature downloads - can be viewed on the Rautomead Web site.

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