Casting

The casting of gold and silver alloys is now carried out in a Vacuum Pressure Casting machine. The metal is melted in a graphite crucible that is heated by an induction coil. This is like a highly concentrated microwave oven. The hot mould with a perforated steel sleeve is placed in the lower chamber. The advantage over the older open centrifugal system is that VPC machines have a totally enclosed and controlled casting environment. This alone has resulted in significant improvements in the metal quality, as oxygen is no longer present during the casting cycle.

When the metal has reached the desired casting temperature, the operator will activate the casting sequence.

The casting chamber is flushed with helium to remove any erroneous gases that may be present. Then a vacuum is applied to the lower chamber, the stopper is lifted in the upper chamber, and gravity allows the metal to flow into the mould. This sequence is entirely controlled by preset programmes as the valve opening and closing times are very quick and critical. When the cycle has completed, the vacuum is released and the chamber opens, then the cast flask is removed, and quenched in water to reveal the cast tree.

Platinum casting is carried out in a centrifugal machine as this is a high temperature material, and the vacuum pressure casting machines cannot handle this material. Special ceramic crucibles are required, as graphite will burn up at these temperatures. This is very much a manual casting operation. The platinum is melted again by induction coil, and when it has almost melted the hot mould is brought from the furnace and placed into its cradle next to the crucible. As soon as the casting temperature is reached the operator lowers the induction coil and activates the spin cycle. With our machines this is manually controlled with regard to acceleration and speed so as to achieve the best possible result in terms of quality and surface finish. After casting the mould material is removed by quenching, high pressure water blasting, and finally by water and fine glass bead blasting, which removes 95% of the mould material. Finally the tree is pickled in hydrofluoric acid for total cleaning.

Occasionally we cast metal onto metal to create a bi-coloured ring or component. With the right design this can be done by casting the higher temperature item first and then attaching the second wax onto the first casting with feeds and then re-investing the structure. The second cast then fits to the first - there is a need though for some clever hidden overhangs or peg system to help key the two metals together permanently as no soldering is involved at all.

Nice combinations can be achieved, especially with contrasting metals, for example Platinum and 18ct Red gold, or 18ct Yellow and 18ct White gold.

We have also cast organic material direct to gold - in this case, pencil shavings.

We recently invested in a new casting machine with the ability to cast large items, such as this F1 Trophy component and the Arkenstone object that cast around 1kg of silver in one piece!

Larger cans have been specially made for us to be able to do this.

Specialist Platinum alloy casting for high tech industries including Scientific, Medical, Aeronautical, Automotive and Watch making.

One example - these tiny circular components measuring less than 10mm in diameter were designed for use in specialist medical measuring equipment.

Pure Platinum was specified as the right material, as the hostile working conditions involved high temperatures and the need for very accurate electronic monitoring.

We created the CAD model from the clients’ technical drawings and in this case we thought the parts would not replicate well enough from our usual rubber moulds. So we decided to have steel moulds made direct from our CAD files and produce the parts in plastic by injection moulding.

With careful control of the burnout cycle we successfully ‘lost wax cast’ batches of components in Pure Platinum.

We've worked closely with Hi Tech leading companies to cast various components including platinum probes to measure very high temperatures and pressures in jet engines, pure platinum probes in the development of marine speed testing equipment plus casting watch cases in non-magnetic platinum/rhuthenium.