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.

Types of 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.

Shapes

Barrel-shaped 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 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.

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.

Specifications

When selecting crucibles, consideration should be given to atmosphere type, furnace type, and application.

Atmosphere Type

Air / oxidizing - Furnace or thermal processing system employing an air or oxidizing atmosphere. Crucibles should be chosen that are resistant to oxidization or burn-up at the end-use temperature. Graphite or refractory metal crucibles may burn up if used at high temperature in an oxidizing atmosphere. 

Inert - Furnace or thermal processing system employing an inert gas such as argon as an atmosphere or shielding blanket.  

Reducing - Furnace or thermal processing system employing a reducing  gas such as hydrogen an atmosphere. Crucibles should be chosen without constituents that can be reduced at the end-use temperature. Iron oxides or silica could be reduced to iron or silicon under high temperature, reducing conditions. 

Vacuum - Furnace or thermal processing system employing a vacuum as an atmosphere. Crucibles should be chosen that do not consist of volatile or high vapor pressure components at the end-use temperature. 

Furnace Type

• VIM
• VAR
• Induction
• Evaporator
• CVD furnace
• Induction melter
• Electron beam melter
• Plasma arc melting furnace
• Gas fired furnace

Applications

Aluminum melting - Refractory ceramic materials and components suitable for use in aluminum smelting, melting and casting operations such as thermocouple protection tubes, combustion gas heaters tubes and die casting stalks or sleeves. 

Ceramics / glass manufacturing - Ceramics, refractories or crucible with resistance to molten glass or compatible with ceramics and glasses during firing, calcining or fusing in a kiln or furnace. 

Foundry or metal casting - Ceramic and refractory crucibles, tubes, stoppers, liners, spouts, permanent molds, thermocouple protection tubes, combustion gas heater tubes, submersible heater tubes, die casting stalks / sleeves and other furnace components used in foundries for melting and casting aluminum, steel, copper alloys or other metals. 

Iron and steel melting - Refractory ceramic materials and components suitable for use in iron and steel smelting, melting and casting operations.

Precious / red metal refining - Crucibles suitable for melting, alloying or refining precious or red metals. Red metals include copper, brass, bronze and other copper alloys. Precious metals include silver, gold, platinum  and palladium. 

Reactive or titanium alloy handling - Crucible or other refractory products designed for melting, processing or casting reactive metals such titanium, zirconium or hafnium, which tend to dissolve or react with most crucible and mold materials. Copper cooled crucible or coatings of yttria-ceria layers are often used in titanium melting applications. 

Standards

ISO 1772 - Laboratory crucibles in porcelain and silica

JIS R 2701 - Graphite crucible and its accessories

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