Carbolite Cupellation Furnace

Presman Mastermelt Ltd

A specially designed cupellation furnace from Carbolite has enabled Presman Mastermelt Ltd to increase the productivity and consistency of precious metal assaying operations at its premises in the City of London while reducing energy costs and the need for repeat processes to confirm results. Established over 50 years ago, the Presman Mastermelt Group is one of the largest UK companies involved in the recycling of precious metals. At its premises in Hatton Garden, London, it evaluates the gold, silver, platinum and palladium content of scrap and residues from a variety of sources in order to determine its value. Assaying by cupellation — the ISO11426:199 the standard method used by UK assay offices and a quantitative reference method laid down by the International Hallmarking Convention— involves heating samples to closely controlled temperatures, which separates any precious metals from base metals that might be present. The process is based on the principle that precious metals do not oxidise or react chemically, unlike base metals, which burn off or form separate slags. The company previously used two cupellation furnaces at its London premises, but these were relatively slow to heat up to the 1100°C required, temperature control was unreliable and thermal insulation was unsatisfactory, resulting in high energy costs. The single Carbolite furnace chosen to replace them has reduced the heat- up time to two hours, and also has a seven-day programmer that automatically switches the equipment on at 7am each working day so that it is ready to be used when staff arrive. Silicon carbide heating elements mounted above and below the work chamber provide even heating of the cupels that contain the samples. Rapid heat transfer and even temperature within the chamber are further improved by passing incoming air over the lower elements before it enters the chamber and so pre-heating it. The speed and reliability of the new furnace enable Presman Mastermelt to quickly inform customers of the value of their material, with both parties having complete confidence in the validity of the assay.

Low thermal mass insulation is included to reduce energy usage, and the work chamber is lined with silicon carbide tiles, which withstand the corrosive lead fumes emitted during the cupellation process. Fumes are extracted through an insulated chimney and pass into the existing exhaust system at the premises. A removable container below the chimney collects any condensed lead, which is used as part of the cupellation procedure. The position of the existing exhaust system, the size of a door opening into the assay laboratory and the fact that the laboratory is on the third floor of the building meant none of the 4 standard sizes of cupellation furnace could be used and required the furnace to be manufactured to specific dimensions and delivered in two sections for final assembly in the laboratory. Overall dimensions of the floor- standing unit are 1718mm high x 750mm wide x 1140mm deep.

 FOR FURTHER INFORMATION CONTACT

Carbolite

110 South Second Street

Watertown, WI 53094

920-262-0240

sales@carbolite-usa.com