US2146432A - Annealing furnace - Google Patents

Description

Feb. 7, 1939. u. HUFF ANNEALING FURNACE Filed July 14, 1957 3 Sheets-Sheet l I .ZI.

INVENTOR. dwmd J fii f/ BY 5 Maw/4m ATTORNEYS.

Feh 7fl39 E. HUFF "2,146,432

ANNEALING FURNACE Filed July 14, 1957 s Sheets-Sheet 2 INVEN TOR.

BY @447 Md MW ATTORNEYS.

Feb. 7, 1939. E. l. HUFF 2,146,432

I ANNEALING FURNACE Fil ed Ju'ly14, 1957 :5 Sheets-Sheet s X g D IN VEN TOR. D zz l2 62am! W ATTORNEYS.

Patented Feb. 7, 1939 UNITED STATES ANNEALIN G FURNACE Edward I. Hufl', Reifl'ton, Pa., assignor to Hull Equipment Company, a corporation of Pennsylvanla Application July 14, 1937, Serial No. 153,585

This invention relates to the annealing of metal, and consists in an annealing furnace peculiarly adapted to the annealing of rolled steel strip. -Its objects are economy in structure and in operating cost, and excellence of product.

The invention is illustrated in the accompanying drawings. Fig. I is a view of a furnace of the invention in vertical section; Figs. II and III are views in horizontal section, on the planes indicated at IIII and III-III, Fig. I. Figs. IV and V are views, in vertical section and in plan from beneath, of the hood alone that forms part of the furnace assembly; Figs. VI and VII are views in plan from above and in vertical section of the pan that in the assembly rests upon the furnace hearth and immediately receives and carries the hood. Fig. VIII is a fragmentary view, corresponding to Fig. I, that illustrates an alternative arrangement in the matter of heat source. Fig. IX is a view that corresponds to Fig. III, of a furnace of more elaborate structure. In this drawing, to the left of the middle line, the hearth appears in plan, the outer walls of the furnace (which are removable) not being in place.

Conflning attention first to the simpler structure of Figs. I-VII, the furnace is of muflie type and includes an outer heat-insulating wall I and an inner heat-conducting mufiie'2. The muflie is thin-walled and made of metal. It is spaced from the outer wall, and the space C between is the combustion chamber, within which heataffording. flame may be developed. The space M within the muffie is the muffle chamber, within which the material to be treated is enclosed.

In modern practice ingots and billets of steel are reduced in continuous operation to highly attenuated strip of great and indefinite length.

- On completion of the rolling operation the strip is in the form of a compact spiral coil that may be handled as a unit, and in such form it may be, and it is desirable that it should be, subjected to the requisite annealing operation. The primary object of my invention is to accomplish the annealing of such a coil of strip steel, and to accomplish it in such manner that the quality of the annealed article shall be substantially uniform, throughout its extent.

'I'heoperation of annealing consists in heating the material to a peak temperature and cooling it again; and, while rate of heating, peak temperature, time at peak, and rate of cooling must (in order to attain desired results) conform to a certain standard, there is a margin of tolerance; and if throughout all its extent the strip in its treatment be brought within such margin, the product will be of uniform quality throughout. In the operation of the furnace of my invention the material is so brought Within the margin of tolerance, and the annealed product is of uniform and standard quality.

The muille 2 is of usual structure in that it consists of integral and imperforate side and top walls, is open at. the bottom, and is adapted to rest upon a horizontal base. It is unique,- in that it is of annular shape. It is shown in vertical section in Fig. IV, in plan from beneath in 1 Fig. V, and in plan from above in Fig. III; and it is shown in assembly in Fig. I, and there it is shown to contain and inclose the material S tobev treated. The furnace charge is here shown to consist of three superposed coils S of rolled strip. The proportioning of the muflie in height to the strip in breadth, and the piling of the coils of strip one upon another within the muille chamber, will be understood to be matters that admit of variation; and it will be understood that in these particulars the showing is exemplary merely. Ordinarily, rolled sheet rests flat within the annealing furnace; in the furnace of my invention it will be observed that the strip when under treatment stands upon edge.

The mufile in the assembly rests, as is usual, upon a pan 3, and the pan in turn lies horizontally upon the hearth 4 of the furnace. The pan is doubly flanged both at its inner and outer margins, and the lower edge of the hood engages the bottom of the pan between these pairs of flanges, and luting L is applied, as shown in Figs. I and II. An annular block 5, arranged within the doubly flanged margins of pan 3, may afford support for an annular stool 6, upon which the furnace charge S immediately rests.

The all-inclosing outer-wall of the furnace is, as has been said, formed esentially of heat-insulating material; and preferably it consists of a box-like structure, otherwise closed, but open at the bottom, applicable to and removable from the stationary and horizontally extending hearth 4. The walls of insulating material are built within a supporting shell of metal II, and this shell of metal, extended downwardly, may in the assembly enter a channel formed in the hearth for its reception, and luting may there be provided, as indicated at L Fig. I. In Fig.1 the frame of the box-like structure is shown to be provided with a perforate lug l2, for the attachment to it of raising and lowering mechanism.

The cross-sectional form of the box that forms the outer furnace wall is not of controlling importance. The square form shown in Fig. III is convenient.

When the movable parts of the furnace are assembled, the'outer furnace chamber includes the space 0 that surrounds the muiiie and this space is continuous over the top of the mui'lie with the central space D within the annulus of the muiile. The invention is achieved in effecting circulating of streams of hot gas upward over the outer wall of the muiile inward over the top, and downward through the central space within the annulus. This commonly is done by organizing, with the furnace assembly described, a plurality of bumers I that extend through the outer walls I and that deliver their flames at the base of the outer, muiiie-surrounding space C, and a flue 8 for the products of combustion that leads from the inner central space D through the furnace hearth. The tongues of flame that spring at the base of the mui'fle and at the outer periphery' thereof rise within space C, stream over the muille, and converge and form a stream that flows downward through the central space D to the flue 8. The lines of flow are indicated in Fig. I by arrowpoints. Preferably the line of direction in which the burners 1 project their flames are approximately tangent to the cylindrical outer surface of the muille 2. The outer wall I being of square cross-section, the number of burners 1 is conveniently four-one in each of the four walls.

The pan 3, flanged as has been described, may have its innermost flange extended downwardly at II, as well as upwardly, thus facilitating assembly, and rendering the assembly more secure.

It will be perceived that the tongues of flame swirl as they rise around the outer walls of the mume, and that they merge in the stream that flows downward through the space D toward the exit. The flame is hottest where it is most widely extended-over the outer surface of the muille; and as in its progress the temperature declines the stream is concentrated and flows in a passageway whose walls are wholly of heat-conducting material, carrying heat to the muille chamber, and more immediately to the inner portion of the coils of material within the chamber. Thus increase in heat-receptivity, or (more accurately speaking) the more complete taking up by the material of the heat as it is released, affords compensation for the diminution in rate of heat release; and in consequence the coils of material within the muille chamber are heated at approximately equal rate through exterior and interior surfaces, and are brought with substantial uniformity and with speed to the desired peak.

Further refinement is found in prolonging the flue 8 in a spiral beneath the floor of the furnace (cf. Figs. I and II). This spiral at its outer end communicates with a duct 9 that leads to a stack or other draft-maintaining structure. Heat loss through a furnace floor is in any case at a minimum; but by the provision of a flue 8 beneath the floor I achieve an actual input of heat, even through the floor, into the furnace chamber; and so, subjecting the coiled material peripherally centrally above and below to a condition of heat intake, I provide for the heating of the material with uniformity well within the margin of tolerance of which I have spoken.

The method of operation is essentially the method that is commonly practiced in furnaces of such sort. The pan 3 is brought to position upon hearth I; the block 5 is placed in the pan; the stool 8 is set on the block; and the furnace charge 8 is placed on the stool. The muffle 2 is then lowered to place, and when in place, resting at its edges in pan 3, the luting L is'attended to.

.That is to say, the munle may be lowered and sunk into previously prepared beds of luting; or the luting may be applied wholly or in part after the muilie has been lowered to place. The outer boxlike furnace part then is applied and brought to position on the hearth; and the luting 1.. is attended to. Connections are made for carrying fuel to the burners I; and, all being made ready. fuel is admitted and the burners lighted. The flames stream through the furnace and eflect the heating in the manner described. It will be understood that the supply of fuel and the conditions of draft may be regulated in well-known manner, to bring the material at desired speed to the desired peak temperature. The peak having been gained, and the peak temperature maintained for the desired length of time, cooling again at desired rate may be effected by radiation, accelerated if desired by circulation of air through the line of flame-flow, as the art well knows.

Indeed, in my structure, a counter circulation of cooling air is employed with advantage. That is to say, when the peak temperature has been gained and maintained for the desired length of time, the outer box-like furnace part is lifted from the hearth; the outer walls of the muflie 2 give up heat immediately to the outer air, and

hearth of the furnace is cooled with the walls of a the muflie, and a more uniform and gradual cooling of the charge is obtained.

I have described an installation in which the heating flame is projected directly into the outer chamber and caused to stream over the outer surface of the muille. The invention in broader aspect admits manifestly of indirect heating. It is essential to the invention that streams of heated gas flow in the outer chamber from the base of the muflle upward over the outer wall of the annular muffle, inward over the top wall, and downward over the inner wall; and, while under ordinary and usual conditions those streams of gas will be heated by the combustion of their component substances, they manifestly may be heated by causing them to flow over heated bodies. This is indicated in Fig. VIII, where a bank of combustion tubes 10 is shown, arranged at the base of the outer chamber C. From the fines in the hearth of the furnace, passages 'II (of which there may be a suitable number, of suitable size) open into the bottom of the space C between the outer wall of the furnace and the munie 2. The tubes 10 being hot, it is manifest that the body of air within the furnace will circulate. Streams of air will flow over the tubes 10 and will be heated; the heated air will flow over the walls of the muflle in the course indicated by the arrow points in Fig. I, and will impart heat. in the manner already described; and, upon descending through the inner space D and entering the underfloor flues 8, the air flows through passages ll into the bottom of outer space C. Thus, heated air is continuously circulated within the furnace, to heat the charge to desired temperature.

The furnace of Fig. IX will be understood with very little further explanation. In this case the outer furnace walls l2 are so enlarged as to receive an extended muiile 22; within which may 7 be arranged a multiplicity of such units as the single unit shown in the other figures of the drawings. The extended mullie 22 is but a plurality of mufiles 2 merged into'one, and provided with a plurality of passageways D that severally are continued in flues 8 in the hearth. In such case there is a plurality of blocks carrying each a stool, and each stool carrying one or more coils, as has already been explained. A single muiile 22 overarches and incloses all the pans with their bur- .den's. There is a single external flame space into which the combustible mixture is delivered, and within which the flame is developed. The mufiie is so particularly shaped that in the assembly there is a passageway D descending through each stool with its burden of coiled material. With this modification in organization, the operation is essentially that already described. Ihe flames spring at the base of the muffle on its outer side and rise around the mufile, to flow over its top and descend through the passageways within the coils to the multiplicity of fines in the hearth. These dues are here shown to lead to headers 80, and from the headers flues 8| rise in the side walls l2. These flues 8|, so situated, tend to reduce heat loss through the walls l2.

The furnace is of simple construction, easy to be operated, readily responsive to the demands of the metallurgist, and affords aheat supply so distributed as to afford, with material shaped and disposed as specified, a product of uniform quality.

I claim as my invention:

1. An annealing furnace for an annular body including a hearth in which is formed a spiral flue with central intake and peripheral delivery, an outer inclosing furnace wall of heat-insulating material removably borne by the hearth, an inner inufiie of heat-conducting material and of annular shape and consisting of continuous and imperforate inner and outer side walls and a top wall continuous with the inner-and outer side walls, and open at the bottom, removably-borne by the hearth within the outer wall and when in '5 place spaced from the outer wall, the centre of the annulus in open communication with the spiral flue at the intake end, and adapted when in place to enclose a charge of material resting on the hearth and a plurality of burners extendin; through the outer furnace wall at the base thereof and at intervals around the circumferential extent of the wall and adapted when the parts are assembled to deliver flamesto the space between the outer furnace wall and the mufile wall, whereby such flames springing at the base of the mufile and at the outer periphery thereof flow upward over the surface of the muflle and converge and descend through the centre of the annulus and thence to the spiral fine in the hearth.

2. An annealing furnace for an annular body including a hearth in which is formed a spiral fiue with central intake and peripheral delivery, an outer inclosing furnace wall of heat-insulating material removably borne by the hearth, an inner inclosing muflie wall of heat-conducting material and of annular shape and consisting of continuous and imperfcrate inner and outer side walls and a top wall continuous with the inner and outer side walls, and open at the bottom, removably borne by the hearth within the outer wall and when in place spaced from the outer wall, the centre of the annulus in open communication with the spiral fine at the intake end, and adapted when in place to enclose a charge of material resting on the hearth, and a plurality of burners extending through the outer furnace wall at the base thereof and at intervals around the circum ferential extent of the furnace and in tangential direction with respect to the said muffle wall of annular shape and adapted when the parts are assembled to deliver flames to the space between the outer furnace wall and the muflle wall, whereby such flames springing at the base of the mufile and at the periphery thereof flow upward over the surface of the muflie and converge and descend through the centre of the annulus and thence to-the spiral flue in the hearth.

EDWARD I. HUFF.

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