US2085837A - Metallurgical furnace - Google Patents

Description

July 6, 1937.A J. THOMAS METALLURGICAL-FURNAGE Filed Jan. 20, 1934 2 Sheets-Sheet WILLIAM D'. THOMAS ATTO R N EYS July 6,- 1937.

. J. THOMAS I METALLURGICAL FURNACE Filed Jan. 20, 1954 2 Sheets-Sheet 2 rrr,

INVENTOR wlLu/Am 3. THOMAS .ATTORNEYS Patented July 6, 1937 .UNITED STATES METALLURGICAL FURNACE William J. Thomas, Great Falls, Mont., assignor to -Anaconda Copper Mining Company, New

York, N. Y.,

a corporation of Montana.l

Application January 20, 1934, Serial No. 707,452

from amongst those'substances capable of withstanding very high temperatures. Other considerations, however, also inuence the choice of the material to be used. For instance, a reverberatory furnace roof must be made from agood heat-insulating material, for otherwise great quantities of heat would be lost therethrough.

The material of the roof must be capable of withstanding the attack of corrosive substances which are carried in contact therewith by the gases passing through the furnace. The roof must be mechanically strong, and to be commercially successful the material from which it is constructed must be relatively inexpensive.

Hitherto the material most generally used for the construction of reverberatory furnace roofs has been silica, because more than other known material silica combines good heat-insulating properties, fair resistance to corrosion, and fair mechanical strength with relative cheapness.

It has long been known, however, that certain 35 more costly materials, while not generally possessing better Aheat-insulating properties, have Aconsiderably greater resistance -to corrosion and greater mechanical strength than has` silica. Magnesite, chrome, carborundum, and zirconia are a few of the materials which might be listed in this category.

A few experimenters, recognizing the chemical and mechanical advantages of such materials as magnesit, chrome, carborundum, and zirconia over silica, have constructed reverberatory furnaces using one of these materials for the roof, but invariably, except where the furnace was eX- tremely small, the increased cost of the special roof material has more than offset the chemical and mechanical advantages attained by its use.

I'have found by long experimentation that good results can be obtained by applying a lining of suitable refractory to the underside of a reverberatory furnace roof, the main body of -the roof being made of some comparatively inexpensive material. In this manner, a roof having such chemical and mechanical properties as are well adapted to resist the destructive actions of high temperature and contact with corrosive substances may be constructed at a comparatively 5 low cost.

' The development of a roof of this nature has ,been attended by many difficulties. The lining can not be made self-supporting in industrial practice, and it' must, therefore, be attached to 10 the main body of the roof in such a manner as to be supported thereby. 'Ihe means whereby the lining is attached to the main body ofthe roof should be suiiciently flexible to allowl fordiiierences in the thermal expansion of the lining 15 material and the material of the outer portion of the roof, yet it must be suiciently firm to supportthe lining in its proper position?vr result YI have accomplished in a numberfof ways.

The simplest and probably the leastlexpensive 20 method'fso'r this purpose comprises constructingv both the lining and the roof proper'of ordinary straight-sided or rectangular bricks, such as are obtainable upon the market in commercial quantities. The bricks used in the lining are com- 25 posed of the desired special refractory, and are laid in the form of an arch spanning the width of the furnace. Periodically, I lay bricks of the lining in such a manner that their longest dimension extends substantially vertically, while 30 the balance of thel bricks of the lining I lay with their longest dimension extending substantially horizontally. The bricks comprising the main body of the roof are then laid upon the upper side of the bricks of the lining in such a manner that the spaces between the upwardly extending bricks of the lining are lled with the bricks of the main body of the roof, and the main body of the roof is continued upwardly, in the usual manner, above the bricks comprising the lining, 40 until an arched roof of desired thickness and mechanical strength is obtained.

A procedure such as outlined above is entirely satisfactory for furnaces of small size, or in those cases where only a portion of the arched roof is to be lined with special refractory. In large furnaces, and in those where temperature variations are frequent and/or of considerable magnitude,

I prefer to use a series of bricks of such design that the lining and the main body of the roof are more completely interlocked. 'I'his may be accomplished by manufacturing the bricks of the main body of the roof in such a form that they are provided at one end (the end adjacent the lining) with protuberances which interlock with corresponding recesses in the bricks of the lining. By the use of such specially constructed interlocking bricks, I am enabled to attain a positive engagement of the lining with the main body of the roof, whereby the lining remains rmly yet iiexibly attached to the roof through even the most rigid and extreme` variation in temperature likely to be encountered in a reverberatory furnace.

For the purpose of 1r. ire adequately illustrating my invention, I will refe;` to my preferred practices, as illustrated in the accompanying drawings, in which Fig. l is a longitudinal sectional elevation of a reverberatory furnace of conventional design equipped with a roof embodying the invention;

Fig. 2 is a sectional elevation of the furnace taken substantiallyalong the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary plan cross-sectionV of the roof taken substantially along the line 3-3 `of Fig. 2;

Fig. 4 is a fragmentary longitudinal sectional elevation of a reverberatory furnace of conventional design equipped with a modification of the roof illustrated in Figs. 1 to 3;

Fig. 5 is a fragmentary plan cross-section of the roof taken substantially along the line 5-5 of Fig. 4;

Fig. 6 is a fragmentary longitudinal crosssection of a reverberatory furnace roof constructed from interlocking bricks of a preferred design;

Fig. 7 is a plan view of the underside of the roof section shown in Fig. 6; and

Fig. 8 is a transverse sectional elevation of a reverberatory furnace roof embodying a modification of my invention.

Figs. 1 and 2 show conventional cross-sections of a reverberatory furnace I0 having a floor II and a roof I2. The furnace is provided with side walls I3 and an end wall I4 having openings I5 and I5 therein through which fuel and air may I be admitted to a grate I1 on which combustion of the fuel takes place. The products of combustion pass upwardly from the grate and over a bridge wall I8, sweep the length of the furnace between theunder surface of the roof l2 and the upper surface or metal line 20 of the molten mass within the furnace, and pass out of the furnace through a flue 2|.

In this furnace the roof I2 is constructed according to the method of my invention. The main body 22 of the roof I2 is constructed of some comparatively inexpensive refractory, for example silica, and the lining 23 is constructed of a special refractory, for example magnesite, having desirable properties such as, for example, resistance to corrosion. The lining is bonded to the main body of the roof in a manner to be described.

For the purpose of simplicity in rendering the following disclosures, I shall assume that in the furnace the main body of the roof is constructed of silica bricks, and that the lining is constructed of magnesite bricks, but it will be understood that other types and combinations of materials may be employed in their stead.

Alternate magnesite bricks 24 are laid with one end lowermost and adjacent the interior of upwardly. Intervening magnesite bricks 25 are laid on their side, preferably, as shown in the drawings, with their surfaces of greatest area lying in substantially vertical planes. In this the furnace, and with the other end extending' manner spaces 26 are provided between the upwardly extending bricks 24.

On top of the magnesite bricks the silica bricks are laid in such a manner as to fill the spaces 26 and to build the main body of the roof 22 to the depth necessary to insure a proper degree of mechanical strength. The upwardly extending bricks 24 serve to bond the lining to the main body of the roof in a manner very similar to that whereby dowel pins may be used to join two boards together.

Fig. 3 shows a fragmentary sectional plan View taken substantially along the line 3 3 of Fig. 2. There the alternate magnesite bricks 24 are shown having the spaces therebetween filled with the silica bricks comprising the main body of the roof 22.

A modication of the above-described method of bonding the lining to the main body of the roof is shown in Figs. 4 and 5. Fig. 4 shows a fragmentary portion of a reverberatory furnace I0 with a iiue 2I for the escape -of the gaseous products of combustion. The roof' I2 of the furnace has bonded toits underside a lining 23.

In this modification two intervening magnesite bricks 25,'laid on their sides, are used between each alternate upwardly extending magnesite brick 24. A sectional plan view of this modification is shown in Fig. 5, taken substantially along the line 5 5 of Fig. 4, wherein the alternate bricks 24 are shown having the spaces therebetween lled with silica bricks comprising the main body of the roof 22.

A lining constructed as shown in Figs. 4 and 5 has the advantage of requiring a smaller 'quantity of special refractory than does the lining construction described in connection with Fig. 1, but it probably does notpossess as firm a bond between the lining and the main body of the roof.'

The roof I2 is built in the conventional arched form, and is supported in the usual way upon the side walls. As is customary in the art, the arch is restrained from flattening out by skewbacks 21 which may be held in place by buckstays and tie-rods (not shown). I have found that a reverberatory furnace roof constructed in this fashion and having a lining bonded to the underside thereof in the above-described manner is' very strong, and excellently withstands the corrosive action of hot furnace gases and other substances brought in contact'therewith by the hot furnace gases.

In one test, only a portion of the roof of a copper refining furnace was protected by a lining of magnesite bonded in the above described manner to the silica comprising the main body of the roof. The balance of the under-surface of the roof was silica. An expansion joint was provided between the portion of the roof which was lined with magnesite and the balance of the roof, partly to prevent uxing of the silica under-surface with the magnesite under-surface. After a forty-charge run thefurnace was shut down and, after cooling, the roof was inspected.

It was found that of a total magnesite surface area of 6,864 square inches, a spot of about 324 square inches, or 4.72% of the total magnesite area, had spalled to a depth of about three-quarters to one inch. At this spot, however, magnesite still remained to a depth of about 31/2 inches, or over '75% of the original 41/2 inches laid down. The balance of the magnesite lining was apparently unaected by spalling. The only other defect noted comprised a longitudinal slippage of a small portion of the lining. This portion had slipped downwardly to about an inch below the level it had originally occupied. I attribute these slippage conditions to the unequal thermal contraction of the magnesite and silica while the furnace was cooling to room temperature. Although close inspection of the roof was impossible during the operation of the furnace, the magnesite lining was visible through the charge doors, and throughout that period these conditions did not become apparent. Compared to the silica under-surface adjoining it, however, the magnesite was in excellent condition. While the silica showed very substantial signs of corrosion, and had deteriorated to a marked degree, the magnesite, with the exceptions above noted, was intact.

To produce an even firmer bond between the lining and the main body of the roof than is possible by the above methods of construction, I use a series of bricks of special design, as illustrated in Figs. 6 and '7. In this modification, the main body of the roof is constructed of alternately short and long silica bricks. The alternate long bricks 3i) extend below the intervening short bricks 3|. The alternate long bricks 30 are enlarged at their lower ends by protuberances 32, which t into corresponding recesses 33 in the alternate magnesite bricks 34 of the lining. The upper ends of the alternate bricks 3G of the lining are disposed adjacent the lower ends of the intervening bricks 3l of the main body of the roof, while their lower ends are adjacent the interior of the furnace. Intervening magnesite bricks 35 are provided to interlock with and to ll the spaces between alternate bricks 34 of the lining.

In this manner the alternate bricks 34 of the lining are held in place by the alternate bricks 3D of the main body of the roof. The intervening bricks 35 of the lining are in turn held in place by the alternate bricks 311 of the lining. This method of construction rmly bonds they lining to the main body of the roof by causing the former to actually interlock with the latter. Accordingly, slippage of the lining downwardly is impossible unless the bricks are broken.

Although I have shown specifically a series of interlocking bricks, the protuberances and recesses of which are providedby making the cross-sections thereof substantially trapezoidal in shape, or of such a shape as to be readily resolvable into two trapezoids (such as in the case of the alternate bricks 3f! of the lining), it will be understood that I do not limit myself to bricks having precisely this shape. Although I have herein described my preferred shape of interlocking bricks, other shapes having interlocking protuberances and recesses may be utilized.

I have found that within a reverberatory furnace, a focal point of corrosion appears to be at the line where the roof joins the side walls. Accordingly, it is sometimes possible to effect substantial diminution in the amount of corrosion that occurs, if corrosion-resisting refractory is placed along this line. Fig. 8 shows a transverse cross-section of an arched reverberatory furnace roof l2 having corrosion-resisting refractory 40 disposed on the underside of the roof and directly over the side walls I3. This corrosion-resisting refractory (for example, magnesite) may be continued inwardly toward the center of the arche-d roof l2 for any desired distance. Fig. 8 shows one extreme, with the corrosion-resisting refractory All extending inwardly only to the inner surface of the side wall I3. Fig. 2 shows the other extreme, where the magnesite has been carried inwardly from a point directly over each side wall to the center of the arch, thus completely lining the arch. It will be understood, however, that I do not limit myself to a type of construction wherein the lining is carried inwardly to a point directly over the side walls.

In constructing reverberatory furnace roofs in accordance with my invention, it is advisable to provide the customary cross-section expansion joints. Accor-ding to some present practices cross-section expansion joints are provided at intervals of approximately ten feet to take care of longitudinal expansion, the widths of opening o-f the joints being determined by the amount of expansion ofthe roof materials at the maximum furnace temperature. Lateral expansion is taken care of automatically by the rise and fall of the roof under the influence of heat at various temperatures, or mechanically by adjustment of the tie-rods .which support the buckstays.

By constructing a reverberatory furnace roof in accordance with my present invention, it is possible to attain the following advantages:

(a) The full strength and heat insulating properties of a heavy roof may be obtained without incurring the expense entailed by using the bricks of the lining for the full thickness of the roof.

(b) A- refractory surface capable of withstanding the corrosive action of hot furnace gases and fume is provided.

(c) The roof may be renewed in sections without loss of the remaining roof.

(d) Should the furnace lining be burned through to the main body of the roof, there still 'remains suflicient strength and thickness of the roof to permit completion of a reasonable furnace campaign before shutting down for repairs.

I claim:-

A reverb-eratory smelting furnace comprising side walls terminating in substantially horizontal upper bearing surfaces for at least a portion of their length, an arched roof bearing upon said upper horizontal surfaces, skewbacks on said horizontal surfaces for restraining flattening-out of the arched roof, and a lining of corrosiveresistant refractory material for the underside of said roof, said lining extending between the juncture of the inner side of the side walls and the roof and the skewbacks and being interposed between said horizontal surfaces of the side walls and at least a portion of the roof resting thereon.

WILLIAM J. THOMAS.

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