copper-based alloys in fuel-fired furnaces, roller-formed silicon car- bide crucibles perform better due to higher thermal shock resistance. In other furnace types, crucibles often are selected because of their high density. Less dense and more porous crucibles may allow erosion. Carbon and ceramic-bonded clay


Melting and holding practices involving metal temperatures also must be taken into consideration when selecting a crucible.


may not be available at all times or be prohibitively expensive at certain times or levels. In this case, it may be par- ticularly important to select an energy efficient crucible.


Types of Metal Melted or Held A detailed catalog of the met-


als to be melted will help establish the maximum temperature the crucible must support and define how the metal will interact with the crucible material chemically and physically. It also will be a key factor in determining what the optimal crucible should offer. In melting


graphite and silicon carbide crucibles are widely used for aluminum alloys, copper-based alloys, nickel alloys, pre- cious metals and zinc alloys. Crucibles also are used in melting cast iron. As a group, these metals represent temperatures from 750F-2,912F (400C-1600C). While some crucible types support metal temperatures encompassing a broad spectrum of metals, it is often necessary to select crucibles targeted to specific metals or alloys and with more limited operating temperature ranges. Selecting such crucibles can be preferable because they offer impor- tant performance characteristics. For


36 | MODERN CASTING May 2012


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