Crucibles are used to melt and process materials at excessive temperatures. They are available in a variety of shapes and sizes, and are composed of materials that can withstand extremely high temperatures, such as alumina, silicon carbide, quartz, or water-cooled copper. They may be large vessels, built-in place liners for industrial iron or aluminum melting in primary production plants, metal casting foundries. Alternatively they may be of a much smaller size, for use in laboratory applications.
Crucibles are available in barrel-shaped, conical, and cylindrical designs. Barrel crucibles have an opening with a top outer diameter (OD) that is essentially the same as, or only slightly smaller, than the base or bottom OD. The sidewalls bulge out and produce a barrel shaped crucible. Conical or tapered crucibles have an opening with a top OD that tapers down to smaller base or bottom diameter. Typically, the sidewalls typically are straight sided. Cylindrical or straight walled crucibles have an opening with a top OD that is essentially the same as or only slightly smaller than the base or bottom OD The sidewalls are straight sided without any bulging out.
Wide-form and high-form crucibles are commonly available. Wide-form crucibles are low, shallow, or flat profile vessels with short walls compared to high-form crucibles. A wide-form crucible has a very wide opening with an OD that tapers down to a much smaller base-diameter. Typically, the sidewalls have a slight outward bow or bulge.
Unlike the wide form, high-form crucibles have high walls. High form crucibles have an opening with a top OD that tapers down to smaller base or bottom diameter. The sidewalls typically have a slight outward bow or bulge.
Crucibles for industrial and laboratory applications include skull melting crucibles and tongue-and-groove crucibles. Skull melting crucibles, otherwise known as melting hearths, have water or salt-cooled copper shells that maintain an unmelted skin. The unmelted layer contains the melt, which is heated by an arc, plasma, or electron beam. Tongue and groove crucibles are a modular crucible system that consists of a series of interlocking components that stack together to form a furnace lining. Tongue and groove crucibles may use a backup of ramming cement behind the crucible, but not within the interlocking grooves. The absence of refractory cement between the ceramic crucible portions improves lining life and quality of the melts quality.
When selecting crucibles, consideration should be given to the atmosphere (air, reducing, inert, vacuum); furnace type (VIM, VAR, induction, evaporator, CVD furnace, induction melter, electron beam melter, plasma arc melting furnace, or gas fired furnace); and application (aluminum melting, glass melting, iron and steel processing, foundry or metal casting, precious metal refining, red metal casting, reactive or titanium alloy handling, or analytical and laboratory processing).
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