How efficiently can a crucible be used in the heating furnaces?
The pot or the vessel that holds the metal while melting it in the furnace is called the crucible. This crucible is generally made out of the silicon carbide or clay graphite. There are different shaped crucibles in the market that are designed as per the requirements of the applications they are used in. The main type of the crucible is the bulge shaped crucible. This resembles the shape of a barrel. The middle part of this type of crucible that is wider than the top and bottom part is called the bilge. It has a maximum diameter of the entire crucible. The top part has a lesser diameter and the bottom part has a much lesser diameter.
The next important shape of the crucible is that of an inverted A shape. In this type of furnace the crucible has a narrow bottom and a wider top. This crucible has straight ends that bend outwards and the diameter of the crucible increases from base to the top continuously. It is much easier to manufacture an inverted A shaped crucible than the bilge shaped crucible. It implies from this that the cost f the inverted A shaped crucible is lower than the bilge shaped crucible and also the capacity of the inverted A shaped crucible is lesser than the bilge shaped crucible. These two shapes can be manufactured using the silicon carbide or the clay graphite.
Crucibles are designed in such a way that they are able to withstand extremely high temperatures of the molten metal. For this the main thing that is to be considered is the materials that are used in the making of the crucible must have the melting point more than that of the metals that are melted in the crucible. The raw materials used in the construction of the crucible must be in a good state and have an excellent strength even in white hot state. Mostly we find the clay graphite or most importantly silicon carbide used in the making of the crucibles. This is because the melting points of the silicon carbide and the clay graphite are relatively higher than most of the metals.
To melt metals like zinc and aluminium, the crucible made out of steel is appropriate. This is because the melting point of Aluminium and Zinc is relatively lower than that of steel. Once these crucibles made from steel are being used for the melting purposes of metals, then gradually scaling occurs on the walls of the crucible. These flakes of steel get mixed up with the molten metal and thus pollute the metal. In order to prevent the inner surface of the steel crucible is coated with a material that prevents the steel crucible from scaling and thus protects the molten material from getting polluted by the steel. Such steel crucibles that have been coated with a protective layer to prevent the molten metal formed inside from getting polluted from the steel cases, is considered suitable for carrying out the heating process as this is free from contamination and the steel scales do not cause any serious problem.
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