Advantages crucible furnaces consist in, that with them simple to operate and easy to maintain them. Moreover, initial capital investments in them are not too great. Crucible furnaces used in the aluminum foundries, which produce castings from aluminum alloys and various small batches. Crucible furnace can operate with virtually any type of cast aluminum alloys. The melting process is performed directly in the crucible, and, if necessary, Aluminum alloy change occurs quickly and easily.
aluminum melting crucible furnaces speed
crucible furnaces, which are used in the aluminum casting plants - plants for the production of aluminum cast products and components - as melting units, to have a volume 1000 kilograms (stationary) or even up to 1500 kg (tiltable). full speed aluminum melting crucible furnaces with electric heating is about 250 kilograms per hour. a melting crucible furnace rate, burners which heat - gas or liquid fuel, reaches 400 kilograms per hour.
Principle crucible furnace
Figure 1 shows the principle of a crucible furnace, which is heated by gas burners. Combustion gas occurs inside the furnace - between the outer wall of the crucible and furnace lining, and the combustion products go directly into the chimney. Therefore, neither the aluminum melt, neither the workplace is contaminated with combustion products of gas (or liquid fuel). Crucible furnace provided with pivoting lids for reducing radiation energy loss from the aluminum melt at a shutter operation.
Nowadays still apply - all less – crucible furnaces, in which the flue gases exit through the crucible edge of the chimney. The drawback of these furnaces is, that the flue gases are brought into contact with the aluminum melt. This adversely affects the quality of the melt, and also worsens the working conditions at the workplace.
On the image 2 shows a crucible tiltable electric resistance furnace, which is provided with a turning mechanism and a hydraulic system. A thermocouple is placed inside the furnace bath in a graphite protective casing (visible at the top right). A thermocouple is used to measure and control the temperature of aluminum melt. Crucible furnace with a gas or fuel heating generally have a similar construction.
Energy consumption in the crucible furnaces
Energy consumption crucible furnaces for gas or liquid fuel per ton of the molten aluminum does not depend only on the construction of the furnace and crucible size. Other important factors are the dimensions accurate matching crucible furnace body, correct setting of the burner and crucible material condition.
In gas burners unheated gas depending on the crucible size consume about 130-150 cubic meters of gas to melt 1 ton of aluminum at a temperature 720 degrees Celcius. Schematic crucible furnace similar problem requires supply of electric energy in an amount of about 400 kilowatt-hours.
Gas and electric crucible furnaces
In addition to these factors, important parameter is the time, which is necessary to melt the fully loaded crucible furnace. for instance, preheated gas crucible furnace capacity 350 kilograms of molten aluminum and "swamp" about 20 % It takes about 85 minutes to, to melt a full load charge. Crucible furnace capacity 800 kilograms required for a complete melting of the charge about 130 minutes. Application of cold - not heated - crucible furnace can increase the melting duration at 50 %. Electric crucible furnaces require twice as much time to complete the melting cycle, than coreless furnace gas or liquid fuel,.
Large crucible furnaces
Large crucible furnaces (more than one ton of aluminum) are becoming less economical, in comparison with other types of melting furnaces. This is mainly due to the relatively high specific energy consumption, as well as a large amount of manual labor when loading the aluminum charge. Moreover, This charge shall only be completely dry, since moisture in the charge can lead to explosions and the threat to the life of the working-casters. This requires additional costs for sorting and preparing the charge.
A source: foundry-planet.com