Melting crucibles of glassy carbon SIGRADUR® are applied in the dental technology for melting noble metal and titanium alloys. SIGRADUR® melting crucibles are notable for the following properties:
- High thermal conductivity
- Much longer service time than graphite crucibles
- No adhesion of noble metal melts
- Resistance to thermal shock
- Suitability for all noble metal and titanium alloys
- Use in induction-heated casting centrifuges
- Generates a protective atmosphere over the metal melt
- No melting salt required
SIGRADUR® crucibles obviate the disadvantages of ceramic crucibles such as low thermal conductivity, adhesion of noble metal melts and the need for melting salt. With SIGRADUR® melting crucibles the heating and melting times are reduced. The electric heating coil of the melting unit can be operated at lower temperatures than those of traditional ceramic vessels. The time needed for each casting is thus reduced and the life of the crucibles extended. In addition, the absence of wetting eliminates the problems of material losses. SIGRADUR® glassy carbon crucibles have a much longer life than graphite crucibles. High purity, low specific surface and an isotropic structure cause a low and consistent oxidation generating a protective atmosphere over the metal melt. This low oxidation rate prevents the formation of an oxide layer on the molten metal. The melting powder or pellets usually required with ceramic crucibles are not necessary as the melt runs out freely without wetting the crucibles wall.
The casting obtained has a uniform and neat appearance. The metal-repellent properties of the crucible remain unchanged throughout the product life. With their extremely good resistance to thermal shock, SIGRADUR® crucibles don’t crack even if placed on cold surfaces when red-hot.
SIGRADUR® crucibles are also suitable for use in induction-heated casting centrifuges. Since glassy carbon crucibles - unlike ceramic crucibles - couple in the inductive field and reach the operating temperature within a minimum of time, the metal will melt quickly and evenly.
Extensive tests have shown SIGRADUR® crucibles to be well suited to the task of melting high-palladium alloys. The finished castings neither have cavities nor do they fade or flake after ceramic veneering.
SIGRADUR® is universally suitable for melting all palladium-based alloys and alloys with a reduced noble metal content. SIGRADUR® crucibles have also been employed for melting palladium-containing fused ceramic alloys with reduced noble metal content at temperatures around 1400°C.
SIGRADUR® crucibles should not be used for melting chromium-cobalt-molybdenum alloys (steel alloys).