Advanced know-how ensures quality precious metals

Advanced conti-cast expertise, utilising a naturally oxygen-reducing graphite crucible and safe, low voltage resistance heating produces the very highest quality precious metals products.

Since the introduction of its very first precious metals continuous casting machines in the early 1980s, Dundee-based Rautomead International has become world-renowned for the design, development and delivery of compact, convenient and highly versatile casting technology for a whole range of precious metals applications.

These applications include the production of bullion coins and medals, jewellery, dental alloys, electronics, brazing alloys and sputtering targets.

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

Considerable flexibility - with ten integrated casting and melting models available - in both vertical and horizontal casting formats - Rautomead today can offer technology for a variety of applications and production capacities.

Power outputs range from 15kVA to 105kVA, melt rates range from 30kg to 390kg per hour; whilst the ability to produce semi finished rod products from 2mm - 100mm diameter and metal strip from 5mm - 400mm wide, ensures that virtually all precious metal production requirements can be easily fulfilled.

For small volume producers, machines are available with crucible capacities of as little as 0.5 litres, with volumes increasing to around 80-litres for those with larger requirements.

The continuous casting process - technology is a key factor when considering the alternative types of continuous casting precious metals machinery available, and the resistance-heated graphite furnace method offered by Rautomead clearly provides significant, highly proven advantages over the induction-heated, ceramic lined furnaces of other companies.

Graphite crucible - 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.

Resistance heated - melting is achieved via Rautomead'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 the heating elements are protected from oxidation in an inert nitrogen gas atmosphere.

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

It is this combination of features - gained over 25 years of continuous casting expertise - that is at the very heart of the Rautomead process.

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

Cost-effective tooling - as the precious metals industry often produces relatively small quantities of valuable materials in a wide range of sizes and alloys, tooling changes can sometimes prove to be an expensive feature of the casting process.

With this in mind, Rautomead has endeavoured, wherever possible, to keep tooling costs to a minimum by ensuring that tooling used on newly developed machines is compatible and interchangeable with that used on earlier Rautomead models.

Other technical features - a gas bubbling facility fitted at the base of the Rautomead crucible permits inert gas to be bubbled through the molten metal.

When melting and alloying virgin metals, it is recommended that the molten charge is gas bubbled to ensure full and homogenous alloying of the charge before casting.

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

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

Designed to offer optimum performance and operational simplicity, Rautomead precious metals machines feature easy to read eye level controls, enhanced operational maintenance, impressive safety features and a highly efficient cooling system.

A quartz window enables checks to be made for metals leakage without the need to open the tap hole - and, therefore, avoid the ingress of oxygen.

Whilst an optional tilt mechanism provides easy drainage.

Consistent production parameters - precise withdrawal parameters can be set and changed by the operator at the push of a button.

Pre-set programmes, according to material and cast shape, can be recalled from the memory to ensure repeatable consistent production parameters from cast to cast.

A PLC control system records all the key parameters of production, and depending upon the model selected, production trends can be viewed on screen over a pre-determined period.

Using an RS 232 connection, this information can also be downloaded to the customer's own computer system for quality control record keeping and subsequent analysis.

Two modes of operation - as an additional user benefit, Rautomead precious metals casting machines can be operated in either continuous or "discrete" modes.

For continuous operation, gold or silver is added in small quantities every ten minutes, allowing production to continue as long as material is regularly 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 commencement 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.

In this "stand-by" mode, the machine may then be left either overnight or over a weekend until the next working day, when production can recommence within thirty minutes.

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

Considerable precious metals casting expertise - Rautomead International offers a comprehensive range of continuous casting machines suitable for precious metals production.

Already the American Eagle, the Canadian Maple Leaf and the British Britannia coins are all produced using metals processed via Rautomead equipment.

Whilst the medals proudly received by gold and silver-winning athletes at recent Olympic Games also resulted from precious metal strip cast through Rautomead machines.

Other recent contracts of note include the supply of continuous casting technology to the South African Rand Refinery - makers of the world-renowned Krugerrand, and a new Rautomead casting line for the Royal Canadian Mint in Ottawa.

Two continuous casting machines have also been supplied to a precious metals casting specialist in Algeria for the production of gold and silver alloys.

As testimony to the success of Rautomead's continuous casting technology, there are now over two hundred and fifty of the company's continuous casting installations in operation around the world.

Rautomead offers proven, well-established technology that is supported by a comprehensive service package that includes trial and demonstration facilities, pre-shipment testing, installation, commissioning and engineer training.

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