Reverberatory furnace

“ Modern Reverberatory Practice.—The requirements for the successful operation of the reverberatory furnace, and the methods for ensuring its efficient working which have just been reviewed, involve the application of the following principles, which are the essential factors in modern reverberatory smelting practice:—
1. The grade of the furnace products is controlled at the roasters. 2. The melting must be as rapid as possible. 3. The employment of very large furnaces. 4. The use of a heated matte-pool in the furnace. 5. The charging of hot calcines. ”

“ The construction of these furnaces demands no other attention than to give to the sole or laboratory the suitable size, and so to proportion to this the grate and the chimney that the heating may be effected with the greatest economy.
The reverberatory furnace is always employed to roast the ores of precious metals, and especially those for amalgamation; as the latter often contain arsenic, antimony, and other volatile substances, they must be disposed of in a peculiar manner. ”

“ The reverberatory is essentially the furnace for the smelting of fine material, as the comparatively still atmosphere, the absence of blast, and the opportunities for settling prevent the heavy losses by dust which necessarily accrue with the other types of smelting furnace. The atmosphere of the furnace is practically neutral, it therefore exercises little influence on the reactions taking place in the charge, and the reverberatory is, in consequence, mainly a melting furnace. ”

“ The furnace is fired with coal on a grated hearth, built at the lower end; it is more economical both in fuel and in labour than an ordinary reverberatory furnace.
The Thwaite-Denny Revolving Furnace.—This new type of furnace, which is fired with gaseous fuel, is stated to combine the advantages of the Stetefeldt, the Howell-White, and the Brückner. ”

“ As the iron melts it runs out through a tap hole and spout at the bottom of the furnace, to be poured into the moulds by means of clay-lined ladles. The air furnace is a reverberatory furnace like that used for puddling (fig. 14) , but larger, and in it the pigs of iron, lying on the bottom or hearth, are melted down by the flame from the coal which burns in the firebox. The iron is then held molten till it has grown hot enough for casting and till enough of its carbon has been burnt away to leave just the carbon-content desired, and it is then tapped out and poured into the moulds. ”

“ Steel rivets should be heated in the hearth of a reverberatory furnace so arranged that the flame shall play over the top of the rivets, and should be heated uniformly throughout the entire length of the rivet to a cherry red. Particular attention must be given to the thickness of the fire in which they are heated. ”

“ The furnaces, ovens, or kilns in which porcelain is fired are always of the reverberatory type; that is to say, the fuel is burned in a separate chamber or fireplace, and the products of combustion pass over or among the ware that is being fired. Such furnaces differ on the one hand from the arrangement in a blast furnace, or that often used in the burning of bricks, where the fuel is mixed with the material to be heated, and on the other hand from the muffle-stove, where the object exposed to the heat is protected from the direct flame by the box of fireclay or iron in which it is placed. ”

“ MM. Dufrénoy and Beaumont consider the smelting of lead ore by the reverberatory furnace as practised in Derbyshire, as probably preferable to that with the slag hearth as carried on in Brittany; a process which seldom gives uniform products, while it occasions a more considerable waste of lead, and consumption of fuel. ”

“ The iron to be heated was placed upon the sand bottom a, and the flame from the fuel in the fire-box passed over it, not only heating the metal directly but the roof and side walls and bottom of the heating chamber also, which, as was said when this form of furnace was first introduced, "reverberated" more heat upon the metal; hence the name "reverberatory furnace" often applied to such structures. The walls, roof, fire-bridge, and chimney-flue are built of very refractory ”

“ A blast-furnace, once lit, remains burning till the end of its existence. I got inside her, and was delighted to satisfy a deep-seated curiosity: we crawled in the cinder notch. The hearth of the furnace lay six or eight feet below the brick flooring, and the effect of standing inside, with the fourteen round blowpipe holes admitting a little sunlight, was like being in a round ship's cabin, with fourteen portholes, except that the hollow furnace shot up to dark distances that the light didn't penetrate. ”

“ We now turn to consider, very briefly, the general design and arrangement of some typical glass-melting furnaces. The oldest and simplest form of furnace is, in effect, simply a box built of fire-brick, in the centre of which stands the crucible, while a fire of wood or coal is placed upon either side. To attain any great degree of heat by such means, however, the size of the box or chamber and especially of the grates in which the fires are maintained must be properly proportioned both to the dimensions of the crucible and to each other. ”

“ These small furnaces are frequently arranged for direct coal firing, but regenerative gas-fired furnaces are also employed. The empty crucible, having first been gradually dried and heated to a bright red heat in a subsidiary furnace, is taken up by means of massive iron tongs and introduced into the previously heated furnace, the temperature of which is then gradually raised. When a suitable temperature for the fusion of the particular glass in question has been attained, the mixture of raw materials is introduced in comparatively small quantities at a time. ”

“ Temperatures sufficiently high for all glass-melting purposes can be attained by both means.
In both systems of furnace, heated gas and heated air are admitted to the furnace by separate fire-brick flues or passages, air and gas being allowed to mix just before they enter the furnace chamber proper. The economy and efficiency of the furnace depend to a very great extent upon the manner in which this mixing is accomplished. ”

“ The tank furnace utilises the heat of the flame more efficiently, as the glass is exposed to the heat in a basin whose surface covers the entire area of the furnace, while in a pot furnace there is much vacant, unused space. ”

“ The heat that the worker about these furnaces must face may be divided in general into two classes: there is first that heat due to the flame and hot gases that the blast in the furnaces forces out onto a man's body and face. In the majority of furnaces Page 193 this is by far the most discomforting, and care must be taken to fend it and turn it behind a suitable shield. The second class is the radiant heat, discharged as light from the glowing interior of the furnace. ”

“ All modern tank furnaces work on the principle of the155 recovery of heat from the heated products of combustion as they leave the furnace, and the return of this heat to the furnace by utilising it to pre-heat the incoming gas and air ”

“ His efforts to procure a means of making his fire burn under his little dump of ore led him first into the science which has attained a new importance in very recent times, pneumatics. The first American furnaces were blown by the ordinary leather bellows, or by a contrivance they had which was called a "blowing tub," or by a very ancient machine known as a "trompe" in which water running through a wooden pipe was very ingeniously made to furnish air to a furnace. It is when the means are small that ingenuity is actually shown. ”

“ Herder is always telling us how much better the glass business is than the steel business," said Mrs. Farrell. "You'll have to get used to that." She gave everybody a smoothing-out smile.
It was fun when you could pick up "dope" in the course of a morning's sweat. I learned one Sunday a few pointers about judging conditions through the peepholes. If there is a lot of movement, your furnace is O.K. If the cinder begins to settle into the tuyère, your furnace is cold. If she looks reddish, cold; blue, O.K. Don't be fooled by different colored glasses in the peepholes. ”

“ This opening serves for the introduction of the glass-mixture, for the removal of the melted glass and as a source of heat for the processes of manipulation.
The Venetian furnaces in the island of Murano are small low structures heated with wood. The heat passes from the melting furnace into the annealing kiln. In Germany, Austria and the United States, gas furnaces are generally used. In England directly-heated coal furnaces are still in common use, which in many cases are stoked by mechanical feeders. ”

“ The first-helper gives her that, passing up and down every few minutes to look through the peepholes in her furnace-doors. He puts his glasses down on his nose, inspects the brew, and notices if her stomach's in good shape. If the bricks get as red as the gas flame, she's burning the living lining out of her. But he keeps the gas blowing in her ends, as hot as she'll stand it without a holler. On [Pg 34] either end the gas, and on top of it the air. The first-helper, who is cook of the furnace, makes a proper mixture out of them. ”

“ Each is charged with its covered pot full of blistered steel with coal to match. Their lidded mouths dull the roaring sound of the terrible combustion, but the furnace-men show by their looks the intensity of the heat. The pouring-off sight is really thrilling. When the lid is removed from each furnace, and the pot of molten metal lifted out by a pair of long-handled tongs with rounded jaws, even a spectator must have steady nerves to look at it. ”

“ Herb looked interested.
"Of course, on the open-hearth you pick them up with a tongs, when they're red-hot, and cool them in water."
Herb nodded.
"So there are always halves of test-ingots on the floor, cold. On the blast-furnace the stove-tender pours the test and knocks it out of the mould. Iron breaks easier than steel, so he never bothers to cool the ingot, but breaks it red-hot. Last Wednesday I wander up from the stoves when the furnace is ready to tap. ”

“ The blowing furnaces have, however, somewhat larger side-openings, and the gas, instead of being introduced at the ends, is burned directly under the openings, or blow-holes. The furnace simply provides an intensely hot chamber for controlling the temperature of the glass under manipulation. On each side of the furnace, and directly in front of the blow-holes, there is a wide platform built over a cellar, or pit, perhaps ten feet deep. ”

“ I do not know that cast-iron furnaces are more liable to be overheated than others, and you cannot "burn the air" with them if they are, unless you burn the furnace too. You may fill a room with air, every mouthful of which has been passed between red-hot iron plates, not over half an inch apart, and I do not suppose the essential properties of the air will be perceptibly changed, or hurt for breathing when properly cooled. ”

“ In pot furnaces, however, in which the more refractory kinds of glass are to be melted, it is generally considered desirable that the flame should be made to play69 about the pots in such a way as to heat the lower parts of the pots most strongly. In connection with the question of the uniformity of heat distribution in a gas-fired furnace it must further be borne in mind that in the case of regenerative furnaces the direction of the flame is reversed every time the valves are thrown over, and in practice this is done about once every half-hour ”

“ In short the electric furnaces can be used to improve the molten product of the Bessemer converter and open-hearth furnace, essentially because their atmosphere is free from sulphur and oxygen, and because they can therefore remove sulphur, iron oxide and mechanically suspended slag, more thoroughly than is possible in these older furnaces. They make a better though a dearer steel. ”

“ In a more refined furnace, the chamber itself is double, and the flame, after playing around the crucible in the inside of the chamber, is made to pass through the space between the outer and inner chamber before passing to the chimney or cone. We need not give any greater attention to these primitive furnaces, since they are practically obsolete at the present time. In modern furnaces the process of combustion is carried on in two distinct stages ”

“ There seems to be something innately picturesque about all furnaces and those who work about them. Whether it is the Rembrandt effects produced by the strong light and shade, or whether it is that the necessary use of the long iron instruments, such as all furnace workers employ, compels a certain dignity and grace of poise and action, we know not ”

“ They should never rest directly upon the sole of the furnace, but must have their bottom freely played upon by the flame, as well as the sides and top. The degree of heat is regulated by openings in the arch, or upon the long sides of the furnace, which lead to the chimney; as also by the greater or less quantity of air admitted below the grate, as in glass-house furnaces. ”

“ A.--It has already been stated that furnace bars should not much exceed six feet in length, as it is difficult to manage long furnaces; but it is a frequent practice to make the furnaces long and narrow, the consequence of which is, that it is impossible to fire them effectually at the after end, especially upon long voyages and in stormy weather, and air escapes into the flues at the after end of the bars, whereby the efficacy of the boiler is diminished. ”