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Areverberatory furnace is ametallurgical or processfurnace that isolates the material being processed from contact with thefuel, but not from contact withcombustiongases. The termreverberation is used here in a generic sense ofrebounding orreflecting, not in theacoustic sense ofechoing.
Chemistry determines the optimum relationship between the fuel and the material, among other variables. The reverberatory furnace can be contrasted on the one hand with theblast furnace, in which fuel and material are mixed in a single chamber, and, on the other hand, withcrucible,muffling, orretort furnaces, in which the subject material is isolated from the fuel and all of the products of combustion including gases and flying ash. There are, however, a great many furnace designs, and the terminology of metallurgy has not been very consistently defined, so it is difficult to categorically contradict other views.
The applications of these devices fall into two general categories, metallurgical melting furnaces, and lower temperature processing furnaces typically used for metallic ores and other minerals.
A reverberatory furnace is at a disadvantage from the standpoint of efficiency compared to a blast furnace due to the separation of the burning fuel and the subject material, and it is necessary to effectively utilize both reflectedradiant heat and direct contact with theexhaust gases (convection) to maximizeheat transfer. Historically these furnaces have used solid fuel, andbituminous coal has proven to be the best choice. The brightly visible flames, due to the substantial volatile component, give more radiant heat transfer thananthracite coal orcharcoal.
Contact with the products of combustion, which may add undesirable elements to the subject material, is used to advantage in some processes. Control of the fuel/air balance can alter the exhaust gas chemistry toward either anoxidizing or a reducing mixture, and thus alter the chemistry of the material being processed. For example,cast iron can bepuddled in an oxidizing atmosphere to convert it to the lower-carbonmild steel orbar iron. The Siemens-Martin oven inopen hearth steelmaking is also a reverberatory furnace.
Reverberatory furnaces (in this context, usually calledair furnaces) were formerly also used for melting brass,bronze, andpig iron forfoundry work. They were also, for the first 75 years of the 20th century, the dominant smelting furnace used in copper production, treating either roasted calcine or raw copper sulfide concentrate.[1] While they have been supplanted in this role, first byflash furnaces and more recently also by the Ausmelt[1] andISASMELT furnaces,[2] they are very effective at producing slags with low copper losses.[1]
The first reverberatory furnaces were perhaps in the medieval period, and were used for meltingbronze for casting bells. The earliest known detailed description was provided by Biringuccio.[3] They were first applied to smelting metals in the late 17th century. SirClement Clerke and his son Talbot built cupolas or reverberatory furnaces in theAvon Gorge belowBristol in about 1678. In 1687, while obstructed from smelting lead (by litigation), they moved on to copper. In the following decades, reverberatory furnaces were widely adopted for smelting these metals and also tin. They had the advantage over older methods that the fuel was mineral coal, not charcoal or 'white coal' (chopped dried wood).
In the 1690s, they (or associates) applied the reverberatory furnace (in this case known as an air furnace) to melting pig iron forfoundry purposes. This was used atCoalbrookdale and various other places, but became obsolete at the end of the 18th century with the introduction of the foundrycupola furnace, which was a kind of small blast furnace, and a quite different species from the reverberatory furnace.[citation needed]
Thepuddling furnace, introduced byHenry Cort in the 1780s to replace the olderfinery process, was also a variety of reverberatory furnace.[citation needed]
Reverberatory furnaces were introduced toChile around 1830 byCharles Saint Lambert.[4] This revolutionized Chilean copper mining to such degree that the country came to supply 19% of the copper produced worldwide in the 19th century.[5][6][7] By 1872 there were one hundred "smelting works" in Chile.[8] Competition stemming from newprocessing techniques pushed Chilean copper production in the late 19th century back to represent 6% of the worldwide production, reaching a low of 4.3% in 1914.[9][10]
Reverberatory furnaces are widely used to melt secondaryaluminium scrap for eventual use by die-casting industries.[11]
The simplest reverberatory furnace is nothing more than a steel box lined withaluminarefractory brick with aflue at one end and a vertically lifting door at the other. Conventionaloil orgas burners are placed usually on either side of the furnace to heat the brick and the eventual bath of molten metal is then poured into acasting machine to produceingots.[11]
