The main material used for the manufacturing of crucibles is ceramic. This has the unpleasant characteristic of a high sensitivity against themal fluctuations occuring for example at the melting of Platinum alloys. Due to this other products on market have to be preheated. This means prior to use the crucible has to be heated up slowly on a temperature of 900 ° C – 1000 ° C. Afterwards the preheated crucible has to be placed in the casting machine. After the casting again these crucibles have to be cooled down slowly in an oven. Foir this also see the remarks at the end of the text.
Not with our crucibles!!
Please fill our crucibles in cold condition. Means at room temperature.
Melt the metal in the crucible as fast as possible and cast it.
Let the crucible cool down to room temperature before you use it again.
With our crucibles the coolig down in an oven is not necessary.
Another advantage is the energy-save-effect. Because of the slightl thinner wall thickness and the different grain-building of our crucibles the induction energy produced by the casting machine can get through the crucibles and transfered to the metal easier. So less energy will be absorbed by the crucible and your casting machine can be operated with a lower power level –means less enery expenditure- to reach the same melting capacity. This also leads to a longer life of your casting machine.
Surely you know the problem. After the crucible is used there is a certain quantity of precious metal –especially Platinum- in the crucible. This is really melted inside the ceramic. This is bonding capital. After the refinery this capital comes back to your company, but it is not possible to prevent a certain loss. After many tests we managed to reduce even the attachement of the precious metal in the crucible to a minimum.
To reach a life of the crucible as long as possible let them cool down to room temperature after each casting. Then you can use it significant longer than the other crucibles on market.
Mechanical destruction by thermal shock
During the melting process the metal expands stronger than the ceramic. Metal dices and casting parts can wedge in the crucible. (Picture 3).
During the heating process this leads to a characteristic destruction of the crucible. Outwarding from a central preassure point, fine cuts like a spider web are leading to the outside. (Picture 1).
Often a hole arises because of the strong preassure. The resulting hole is a cone. Beginning from the inside of the crucible and getting bigger and bigger to the the outside. (Picture 2 and 4).
A wedgeing of the metal has to be avoided.
The metal has to be loose in the crucible. It need enough place to expand during the heating phase.
Destruction by thermal overtaxing (vitrification)
Vitrification occurs when the applied temperature is too high for the silica, or the time the crucible is kept under high temperature is too long. When a crucible vitrifies a change of the structure is the consequence. The crucible is loosing ist high themal shock resistance.
Mainly a vitrification can be identificated by the darkening of the ceramic.
At this place often a tansparence can be seen.
In extreme cases the ceramic is getting soft and gets out of shape.