Reverberatory furnace

A reverberatory furnace is a Four where the Chaleur is considered (reverberated) by the arch of the furnace. In this type of furnace, the fuel (coal, gas, fuel etc) is in theory flaring in a room different from that of the treated matters. These furnaces with the very old principle were the subject of improvement to the XVIIIe and 19th century in order to in particular improve the processes of metallurgical transformation. This technology makes it possible to increase the effectiveness of heating and thus to increase the temperature. One of the applications is the puddling of the cast iron which is the first great stage of the mass production of steel during the Industrial revolution. These furnaces were and are used in metallurgical industry, the cooking of the Céramique S and chemistry.

History

The term of furnace of reverberator is mentioned in the treaties of chemistry or sculpture of the 17th century to indicate a melting furnace enamels or to break up the substances into laboratory, and in which the flame is not applied directly to the product to heat but is reverberated by a vault.

Out of metallurgy, the reverberatory furnace such as we hear it today appears in Great Britain, and more precisely of the Wales and the England, in the last third of the 17th century. It is as of this moment characterized there by separation between heating and product to be heated and by a high chimney making it possible to activate the hearth by natural pulling. The privileged fuel is the Houille. It is used at the same time for the extractive metallurgy (reduction of the ores of Cuivre or lead, refining of siver-bearing lead) and to remelt the pig iron (in particular of old guns) to produce moulded objects.

It is used in France for the reduction of the Plomb as of the years 1730, probably with a heating with the Bois ; the temperatures lower than one obtains this manner undoubtedly explain than one did not then use it for the cast iron.

Starting from 1750, the reverberatory furnace is associated with the blast furnaces with coke to produce large castings (artillery, body of cylinders) in factories like Carron (Scotland) or Bersham (Wales). In 1775, the French Navy makes come a British ironmaster, William Wilkinson, to build a reverberatory furnace for the manufacture of cast iron artillery of fer : it will be the foundry of Indret. Furnaces of the same type are built thereafter with Ruelle, in Angoumois, and with the Creusot (Burgundy).

Use in the Metallurgy

The reverberatory furnace can be used for several type of operation as netting (solid matter heating like the Minerai S), reheating, fusion.

The reverberatory furnaces knew various forms. The first were an improvement of the shaft furnaces. They allowed the use of Combustible S as the Bois which produce flames. In the primitive reverberatory furnaces, the flames occupy all the cavity of the furnace and the matter to be heated is placed in the medium. The improvement of the reverberatory furnace consisted in separating fuels from the matters to heat and in particular to carry out heating on a side of the furnace. Thus, the fuels and the matters to be heated are separate. In addition to the improvement of heating, that avoids mixing the metal matters with fuels and thus to pollute or modify metal. The reverberatory furnace thus consists of a hearth where the fuel is flaring, and of a laboratory where one places metals or the ores.

Constitution of a reverberatory furnace of the XVIIIe XIXe century

A reverberatory furnace is consisted of the following elements:

the hearth:

*la grid on which are posed the solid fuels. This grid is absent if one uses gas or liquid fuels.

*Le ashtray in lower part of the grid to recover ashes.

*Le tisard: opening provided with a door allowing to place fuel on the grid.

the laboratory:

*L' furnace bridge sometimes called the bridge or the large furnace bridge (Grüner)

*Sole

*Porte or opening: provided with a removable wall, it makes it possible to introduce the metal matters. It also makes it possible to intervene on these matters (in the case of puddling for example).

evacuation of gases:

*Le crawling: drain located immediately after the laboratory allowing the circulation of gases.

*Le register: left valve which equips sometimes crawling it thus making it possible to control gas flow.

*La chimney: it allows the evacuation of gases. These dimensions are extremely important since they will condition “pulling”. The majority of the reverberatory furnaces generally not being equipped with apparatus of blowing, it is the pulling of the chimney which determines the effectiveness of the furnace. There can be a chimney by furnace but in the workshops comprising several furnaces, there can be a common chimney for the whole of the furnaces.

The heat created by combustion passes to the top of the furnace bridge, passes through the laboratory while following the vault and in continuation evacuated by crawling and the chimney.

The grid

The grid is present only in the furnaces using of solid fuels: coal, wood. It makes it possible to support fuel. Spacing of the bar and their forms allowing the flow of ashes in the lower part called the ashtray, where it will be easy to withdraw them. This space also allowing the air circulation.

The grids can be horizontal, tilted or with steps. The horizontal grid presents the great disadvantage of a discontinuous manual loading. It is necessary that the “driver” opens the old-fashioned one to charge the furnace. This opening involving a cooling of the furnace. Grüner mentions an experiment of comparison between the control of a furnace by various operators. The result shows a difference of 25% of fuel consumption between the various operators. The tilted grids or with steps can be fed automatically by a device placed outside the furnace allowing the flow of coal by gravity or the action of a person.

The furnace bridge

The furnace bridge is the low wall which separates the plate (thus matters to be treated) fuel. There exists sometimes a certain ambiguity on the exact definition of this part. Gaspard Monge in its work on the manufacture of the guns defines it as: “… the part of the furnace on which one poses the mass of metal” and not like separation. Grüner calls it in its metallurgy treaty the bridge or the large furnace bridge . The furnace bridge (or the small bridge ) being a small dam which separates the plate from crawling. This separation exists if the plate is concave and avoids thus that the molten metal runs out in crawling.

The furnace bridge is exposed to strong temperature, it is thus manufactured in refractory materials. It can be possibly to be equipped with means of cooling. Its height depends on its use. When one wants to protect metal from the flame and to thus avoid a chemical action which would modify its nature, it is built higher. But in against part, the furnace loses of its calorific effectiveness.

The plate

The plate is also manufactured out of refractory material. Its nature, its form, its dimensions depend closely on the use of the furnace.

For puddling, starting from 1818, the plate is made out of cast iron cools by a water circulation. It is covered with basic slag which improves, the refining of the cast iron.

The plate is punt when the furnace is only used for reheating. It is hollow (or concave) when the furnace is intended for the fusion of metal. The form can be rectangular, if the operator does not have an action to carry out during the heating or oval if it must intervene (case of the furnaces of puddling).

In certain cases, one uses the after-heat after the plate by equipping the furnace with other plates or while making pass flow in steam boilers.

Use in chemistry

The handbooks of chemistry of the XIXe century mention for experiments the use of reverberatory furnace of laboratory.

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