The Capacity of Crucible Steel Furnaces

Compartments

• The average crucible furnace has up to 50 crucibles in the melting chamber that can be used in a single heating event. The chamber is divided into eight different compartments -- two on the end that can hold eight crucibles each and six in between holding six crucibles each. Although the furnace has a total capacity of 52 crucibles, only 50 are used during any single event since the remaining space is needed for the heating runner cups. Smaller furnace designs featuring 30 crucibles or slightly larger ones with 60 are also available from certain manufacturers.

Output

• The production capacity of a 50-pot crucible furnace is limited to approximately one heating event every four hours. This equates to six events in a 24-hour period and 30 events per work week if the furnace is run continuously. Each crucible can hold about 102 pounds of material. It must all be well-packed and fitted with a clay cover to maximize the heat's effect. The average resulting output comes to roughly 74 tons of material per week or 3,552 tons over a 1-year span. The heating time and individual crucible capacity is the same for 30- and 60-pot furnace models.

Cost Vs. Capacity

• Standard 50-pot crucible furnaces operating at full capacity year-round require inexpensive weekly maintenance, including coke bed renewals and re-patching of the interior silica bricks. More significant repairs, however, such as a total rebuild of the melting chamber, can be expected about every six months with an average outlay of $350 per repair. Fuel costs must also be considered. Furnaces that use oil require approximately 87 pounds of fuel for every 100 pounds of material being melted, while coal furnaces use anywhere from 40 to 60 pounds of coal for the same amount of material. Costs will vary based on the market prices of coal and oil.

Other Considerations

• A crucible furnace is so productive in generating small castings because the molten metal goes right from the crucible to the mold, with no intermediate pouring ladle in which the metal will start to cool. However, it should be noted that crucible furnaces can't oxidize or refine the metals being melted. In addition, the capacities outlined above are measured averages, but may vary depending on the furnace model and material being melted. While a furnace may be capable of achieving greater outputs than those referenced in sections 1 through 3, overrunning the furnace may result in greater maintenance, fuel and repair costs.