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| Crucibles and Moulds for the Dental Laboratory | ||||||||
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GlossaryIndex:
Airbubbles in metal.. show that gas has been desolved during melting. Too long or too high heating of the metal leads to an exaggerated casting temperature. This has been experienced sometimes when shifting to Ceramed crucibles, because they heat up faster and the casting procedure might have to be redeveloped.Biosil..is a special alloy from Degussa, known for its tendency to slag formation. This reduces your crucible life (< 10 casts ). Therefore, this alloy should rather be worked under reducing conditions like open flame, protective gas or vacuum. Slag formation is independent of crucible material or coating.Casting machinesCasting machines are distinguished by..
Crucibles have different requirements for different systems. Ceramed crucibles are specially designed for these requirements. Coating of Ceramed cruciblesCeramed crucibles are coated with a fine powder, which is infiltrated in the inner wall. It is hardly wetted by metal melts and does not react with the metal. The porosity of the crucible is closed, therefore the melt does not stick to the wall. This special coating is the major reason for the durability of the crucibles. There is no harm for man or environment.DEGUSSA MotocastFor DEGUSSA Motocast machines moulds with a slot must be used. This is thought to prevent a backfiring of the flame during heat-up. Additionally, the cast channel can be heated up easier.EngobeEngobe is a fine coating of clay, comparable to a glaze (a coating of glass). An engobe is porous, whereas a glaze is water-tight. The inner coating of Ceramed crucibles is sometimes called engobe, even if it is not an engobe in a strict sense. Engobes are used for coloring or smoothing surfaces, the effect of the Ceramed coating is completely different.Glassy Carbon (Sigradur)Graphite crucibles have a crystalline structure, glassy carbon is amorphous. This leads to different properties: low burn-off and hardly any carbonizing with Sigradur. Production of Sigradur is complicated, therefore the price is rather high. The customer has to find out the cost-benefit ratio for his application.Graphite qualitiesThe selection of the just the right graphite from more than 500 different qualities is crucial for the quality of the crucible. Ceramed uses the highest quality available, resulting in a very low burn-off. Nevertheless, the properties may vary over the cross section of the graphite block, so do not judge the quality by one single crucible. In addition, your handling is very influencing.See Protection cap LiabilityCeramed is liable within set conditions for personal or material damage, caused by faulty products. Wrong application is not insured.Melting powders.... are fluxing agents to dissolve oxide layers on molten metals. Melting powders attack the crucible and "soften" it. Therefore: Lowest consumption only when necessary for metals with very high tendency for oxidation. Just pit ontop of the melt, never into the empty crucible.Melt-through of cruciblesThe crucible is not designed for long thermal load above 1300° C. Nevertheless, metals with melting points up to 1470° C can be melted, because melting is fast and the crucible temperature is well below the temperature of the metal. If you stop the casting procedure, you have to cast the metal - or you risk your crucible, Another reason for melt-through is excessive use of melting powder.Protection cap of graphite cruciblesThis cap has been proposed by our customers and has proven in many laboratories. The cap protects the rim of the crucible, that has the largest burn - down. Whenever possible, the cap is put onto the crucible, the rim is protected against oxygen and the life - span of the crucible is extended. Just order under protection cap.Safety of Ceramed cruciblesCeramed crucibles are safe. In over ten years of use, no damages or accidents have been reported, where the material, the form or the coating of the Ceramed crucibles has caused damage to casting machines, to the metals or to people.Slag formationSlag is the reaction product of metal and oxygen. By deairing, vacuum or a reducing atmosphere, slag formation is avoided. Different alloys have a very different reaction tendency. Slag is rather low-weight and stays in the crucible, reacting with and sticking to the ceramic wall. The longer the melting time, the more slag is formed. Therefore, melting should happen very fast. Highly ductile slags like from Pd - base - alloys are transformed into brittle, glassy slags by melting powder. Slags can be very viscous, so sometimes the metal cannot be cast.Tubular cruciblesA tubular crucible is the typical crucible used in resistance heated machines (Heraeus CLG 77, CLG 2002, Degussa TS 1-3). This crucibles are designed for high thermal resistance by using up to 80% alumina. High purity raw materials help avoiding impurities in the melt. |
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Ceramed GmbH Adam-Krafft-Strasse 4, D - 94315 Straubing |