The metal is usually introduced into a flask at a temperature of several hundred degrees using two different processes, traditional centrifugal casting or modern vacuum casting. In each case, the material to be cast has to be heated and melted.
A temperature-resistant graphite or ceramic melting pot is filled, for example, with a gold alloy. The metal can now be heated and liquefied in different ways depending on the type of system. Centrifugal casting, as the name suggests, uses a centrifuge. The hot flask, inside which there is now space for the liquid metal after the wax has been melted out, is placed on the arm of the centrifuge. Once the centrifugal process is started, the melt flows into the flask, e.g. by tilting, while the centrifuge immediately starts rotating. In induction-heated centrifuges, the coil moves down, the material rises due to the acceleration of the rotating arm and shoots through a lateral opening on the pot into the horizontally lying flask.
Vacuum casting, which has been practised at our company since its very early years, is carried out using melting pots that have an opening at the bottom. This is sealed with a sealing rod during the melting process. The flask to be filled is then placed underneath this hole in the so-called barrel. Lifting the sealing rod once the casting temperature is reached therefore opens the melting pot and the hot melt can enter the flask from here. Just as the rotation ensures that the metal jet accelerates and the metal is compressed overall with centrifugal casting, additional forces are required here too. In the case of vacuum casting, the inflowing melt is also sucked into the flask by a previously built up vacuum. Further compression can be achieved under certain circumstances by pressing it out of the melting chamber with overpressure or also by incipient vibration.
There are again many sources of error during the actual casting processes. Gas and solidification pores in the finished casting must be mentioned, to name just two problems. Gas pores are created by the melt’s high gas solubility in its liquid state. Solidification pores, on the other hand, form when the hot melt cools down in the flask. This error will occur if the cooling conditions are not optimal due to an incorrectly selected casting or flask temperature or, for example, an incorrect sprue technique. The quality of the alloys, investments and other auxiliary and operating materials used is also important. The whole range of errors is so extensive and so complex that it is the subject of extensive scientific essays, seminars and books.