US2169621A - Method and apparatus for annealing metal charges - Google Patents

Description

Aug. 15, 1939 J. R. TAYLOR 2,169,621

METHOD AND APPARATUS FOR ANNEALING METAL cameras Filed Oct. 9, 1.937 3 Sheets-Sheet 1 N M flylNVENToR.

1L2 ATTORNEYS.

5, 1939 J. R. TAYLOR 2,169,621

METHOD AND APPARATUS FOR ANNEALING METAL CHARGES ALL; A TTORNEYS.

Aug. 15; 1939 J. R. TAYLOR METHOD AND APPARATUS FOR ANNEALING METAL CHARGES Filed Oct. 9, 1937 3 Sheets-Sheet 5 INVENTOR.- ;Z%s@ 44;, ATTORNEYS.

Patented .Aug. 15, 1939 UNITED STATES PATENT oFF cE METHOD AND APPARATUS FOR ANNEALING METAL CHARGES John R. Taylor, Natrona, Pa., assignor to Allegheny Steel Company, a corporation of Pennsylvania Application October 9, 1937, Serial No. 168,233

9 Claims.

My present invention relates to the art of annealing charges of metal articles, for example, metal sheets, and more particularly concerns a procedure and an apparatus whereby such charges can be uniformly annealed or heat treated in a reduced period of time.

to as the inner cover, and a removable refrectory heat-insulating cover is placed over the inner cover and spaced therefrom. This refractory heat-insulating cover will be herein after referred to as the outer cover. Ordinarily, means is provided in the outer cover for applying heat between the outer and inner covers for the purpose of bringing the charge to annealing tempe'rature and inasmuch as it is the outer cover which must be removed from time to time, certain disadvantages have resulted which are well recognizedin this industry. For example, the outer covers have generally been heavy and cumbersome as well as expensive, requiring heavy and hazardous crane lifting. In moving the outer cover it has always been necessary to disconnect the gas lines associated therewith and this has resulted indifiiculty and delay.

In prior furnaces constructed. along the foregoing lines it has been found that relatively poor fuel economy is secured and that it has been impossible actually to secure uniform annealing or heating. Tests made with thermo-couples inserted at various locations in the metal charge have shown temperature variations as great as 50 to 60 degrees F. and due to the natural propensity ofheat to rise rapidly, the top of the charge is usually hotter than other portions thereof and if the annealing time is prolonged to raise the most difliculty accessible parts of the charge to the desired temperature, then some portions of-the charge are always found to be over-anhealed. If this is not done then some portions will be over-annealed and some under-annealed.

Other disadvantages are recognized, such as lack of satisfactory flatness where metal sheets or the like are annealed and the liability to explosion dueto, the disturbing of,the gas con.- nections.

It is accordingly one of the objects of w my present invention to carry out annealing under such cqnditions as I? av d t e i i mt es and disadvantages hitherto encountered and to accomplish annealing operations in a reduced period of time with greatly enhanced effectiveness.

' Another object of my invention resides in annealing stacks of sheets or other metal articles with a condition of uniformity of temperature throughout the charge not heretofore obtainable and t the same time to accomplish this in a shorter period of time and with greater fuel economy as compared with prior practice.

Other and ancillary objects and advantages reside in the provision of an outer furnace cover which is light and easy to handle and which is free from obstructing connections of any sort; the production of a furnace wherein the base is permanent and is provided with permanent gas connections, thereby eliminating those hazards and inconveniences resulting from the use of portable gas connections, andin general the provision of a new procedure and a new furnace as well as certain d tails thereof which will accom-. plish the objec and advantages herein outlined. In the accompanying drawings, wherein like numerals designate corresponding parts:

Figure 1 is a transverse section through a furnace embodying the present invention;

Fig. 2 is a view partly in section and partly in perspective of a furnace essentially the same as Fig. 1 but provided with vent'stacks;

Fig. 3 is a perspective view of the heating system of Figs. 1 and 2; and

Fig. 4 is a fragmentary modified heating system.

I have discovered that a much improved annealing furnace and procedure can be produced by applying a gaseous heating medium through the base of the furnace and transmitting heat by conduction first to the bottom of the charge while the heating medium is' at its maximum temperature. Then the heating medium is caused to pass between the inner and outer covers and to impart heat to the sides and top of the charge perspective view of a but out of direct contact with the charge, thus resulting in new qualities of uniformity of annealing and reduction of the duration of the annealing cycle.

One mode of constructing a furnace to satisfy these requirements is illustrated in Figures 1 and 3am! in those figures it will be apparent that the furnace consists of three main parts, a base'lll, an outer cover H and an inner cover l2. The base I0 is built up of suitable refractories l3 within a structural steel shell M, the base resting upon a concrete or other flooring ii. To this shell suitable structural steel beams I6 dered) insulating refractory H, such as Sil-ocel, and this arrangement, I have found, cuts down heat losses due to radiation and at the same time allows for expansion.

Passing transversely through the refractory base It is a series of tubes l8 through which heatingmedium is passed. Each tube I8 is made up of a refractory material having a high rate of heat transfer, such as carborundum, and is preferably composed of a number of sections suitably secured together to form a closed heating tube or conduit. These tubes or conduits may, however, be made of any other satisfactory material of high heat transfer properties which will withstand the temperatures and other conditions of operation and suitable metals or alloys may be used for this purpose.

From Figure 1 especially it will be apparent that the tubes I! extend from one side of the base nearly to the opposite side and that they terminate in upwardly extending elbow portions I9 which communicate with the space or chamber 23 between outer cover II and inner cover II. From Fig. 3 in particular, it will be understood that adjacent tubes are oppositely disposed, that is, the tubes i3 alternately start at opposite sides of the base. andaiternately discharge via the upwardly extending elbow-portions is into the space 20 but at opposite sides of the furnace. The tubes 18 are alternately fired from opposite sides of the base and for this purpose I provide a manifold 2| alongeach side provided with retractible gas burners 22 in the usual manner understood in this art.

It will be further noted from Figure 1 that superjacent. the tubes l8 there are two courses of refractory 23 and 24 forming a central raised or pier portion for the base Ill. The inner cover I! rests in depressions or recesses 25 at either sideof the central pier and a suitable seal is made, as by sand 26, to exclude air in known manner, Likewise, the upper outer edges of the base i0-are cut away as at 21 and the spaces thereby produced are filled with sand go for making a seal with thedownwardly extending flanges 29 of the outer cover H. Ihave found, however, that due to the porosity of all refrac' torles some leakage of air or gas inevitably infiltrates within inner cover' I! particularly while the charge is cooling, since the lowering of the temperature creates a sucking effect probably due to the formation of a partial vacuum within the cover which draws in air. This'is objectionable in connection with the inner cover since air or oxygen finding its way thereinto will cause oxida tion and discoloration of the hot metal charge. To prevent the inherent porosity of the refractory materials-from enabling air or the like to gain access within the inner cover I provide the metal plate 30 which effectively seals the chambers within the covers from such effect. This metal plate 30 is shaped as shown in section in Figure 1 and is composed of any suitable metal which will withstand the conditions of operation of the furnace and which is impervious or substantially impervious to the passage of air or gases therethrcugh except, of course, that the plate is provided with rows of apertures 3i in each side thereof in order not to interfere with 'the'upwardly extending tube elbow p rtions l9 which discharge heating medium (hot gases) between the two covers.

As stated, the inner metal cover l2 rests within the recesses or depressions 25 in the base ill. The plate 30 is shaped to correspond to these recesses and a sand seal or other suitable seal is provided at such points. Thus heating medium discharged from elbows I9 is maintained out of direct contact with the charge of metal 32 without objectionably impeding or obstructing the transmission of heat from ,the medium to the charge. The presence of the inner cover permits removal of the outer cover after heating is discontinued and thus enables one outer cover to be used with a plurality of bases asls understood in this art.

Outer cover II is madeof suitable refractory material 33 with an arched roof 34 disposed within a structural metal shell 35, the arched roof 34 being provided with one or more vents 36 so that the heating medium may pass therethrough after it has carried out its purpose of heating the charge 32. It will be noted that the removable cover is of comparatively light weight and great portability, particularly as compared with prior art outer covers, and this not only cuts down the cost of these removable covers and'reduces crane lifting operations to a minimum but makes it easy to utilize a single removable cover 'for a plurality of permanent stationary bases.

At the same time the removable cover has no fuel or other connections and hence the removal thereof is greatly facilitated.

A relatively thick metal plate 31 which may be, for example, in the neighborhood of 1 inches thick-is placed upon that portion of metal plate 30 which rests upon the refractories 23, 24 and it is this thick plate 31 which receives the charge of material as is apparent.

It is recognized by annealers that the central lower portion of the charge, particularly when the charge consistsof flat sheets, is the most difficult, to heat and that ideal conditions would result if this portion of the charge were a few 1 degrees hotter than the balance of the charge and could be heated first to the required temperature since it is relatively inaccessible to the heating medium. The relative inaccessibility of such to the heating medium ordinarily results in under-annealing this portion of the charge and if the armeallng temperature is so high or the annealing period so prolonged as to bring this porton up to proper temperature then the top and sides of the charge are inevitably overannealed. This inaccessible charge portion is demarked by the line indicated at 33. It will be understood from Fig. 1 in view of the arrows placed thereon that as heating medium is passed through tubes l8 its first and full effect thereof is transmitted to this inaccessible charge portion 38 through the refractories and metal forming the pier and the effect of this is to bring the inaccessible charge portion up to temperature first and rapidly while the heating medium is at its highest temperature. This heating effect substantially occurs through conduction, as will be understood.

Due to the fact that alternate heating tubes are oppositely fired, the temperature of the bottom of the charge is readily equalized. After the heating medium passes through the tubes it turns up wardly through the tube elbows i9 and passes into the chamber 20 between the covers ii and i2. As it passes through this chamber it is deflected to the top of the charge by the arched roof and eventually passes from the furnace via vent 36 but during this. passage. through the chamber 20 it transmits heat both to the inner cover I! and toing of the sides and top of the charge and causes quick and deep penetration of the heat to the interior of the charge. This I have found gives an unusual uniformity of heating and annealing and tests made by me in this connection have shown -a maximum diflerential of not over about 20 degre'es F. between various portions of the charge as compared with common 50-60 degree F. differences'in prior practice. Thus, even on the basis of uniformity of heating alone, my present invention is a great improvement over prior practice.

By permitting fresh air at room temperature to pass through the tubes I8 I have also found that I can cool the charge uniformly and in a materially reduced period of time, thus cutting down the entire annealing cycle involving the heating and cooling operations. To do this I may retract the burners whichare ordinarily spring pressed toward the open tube ends in conven-- tional manner and the conditions are such that this will cause fresh air to be sucked into the tubes l8 and into chamber 20 and if I so desire I may enhance this effect by admitting such air under forced draft, but in the-latter case retracting of the burners is not required.

I have further discovered that this construction and procedure for carrying out annealing gives me at least a 20 to 60 per cent better fuel, economy. For example, where in a conventional annealing furnace I have found that approximately 1576 cubic feet of gas'were required per net ton of charge, under the same conditions my annealing furnace consumed approximately only 1194 cubic feet of gas per net ton of charge, an improvement of the order of per cent. In operating a furnace in accordance with my present invention I-have found that the firing time and the heat treating cycle are reduced at least 10 to 50 per cent as compared with prior operations in conventiona furnaces. Where the charge consists of fiat metal sheets, plates or the like the annealedproduct produced by me in accordance with this invention is characterized by much impr d flatness in contradistinction to prior practice ficient in that quality due to distortion, warping etc., which may be explained at least in part by the non-uniform annealing thereof. r

While in Figures 1 and 3 I have illustrated a preferred form of the present invention which is eminently satisfactory, Imay make certain vari ations thereof such as indicated in Figure 2. In the latter figure the parts are substantially the same as in Figs. 1 and 3, as indicated by the use of corresponding numerals, but in the form of the invention illustrated in Figure 2 I have employed auxiliary chimneys or stacks 33, the lower ends of which respectively communicate with the elbow' portions IQ of tubes I. As will be understood from Fig. 2, each chimney or stack 39 is composed of an upper cylindrical portion formed of refractory or metal of suitable composition and a lower somewhat bell-shaped portion so as to fit over the elbow portions l9 aforesaid. Suitable braces or supports 40 are provided to maintain chimneys or stacks 39 inproper association I with the remainder of the structure and these chimneys or stacks extend through the roof of here the annealed sheets or plates are dethe furnace, as shown, and exhaust to the atmos- 'phere. In utilizing this form of the invention the heating medium, such as hot gases, passes as before, through tubes I8 and elbows l9 but then instead of discharging into the space 20 between In order to-prevent the natural propensity of heat to rise to carry off the heating medium too rapidly for efficient operation, I provide each chimney or stack 39 with a core-buster which is made up of a chain or the like 4! to which are afixed in spaced relationship a series of discs or the like 42 which are composed of suitable refractory or metal and which have a maximum diameter somewhat less than the internal diameter of the chimneys or stacks. Thus the upward flow of heat is retarded and checked to that extent found necessary or desirable to make the most efiicient use of the heating medium for this purpose. In such case it is not necessary to provide vents in the arched roof of the furnace, as shown at 38 in Fig. 1, and where the bell-shaped lower ends of the chimneys or stacks 39 meet the elbows IS a suitable sealing is effected, such as by sand or any other recognized sealing medium.

I am not limited to the precise arrangement of tubes l8 as utilized in Figures 1 to 3, inclusive, because I have found that I can vary the arrangement and disposition of such tubes without loss in effectiveness and under some conditions, i. e.,

.for some types of metal charges, even improved results are secured by such tube variation. In Figure 4 the gas manifolds 2| are provided with the retractable burners 22 as before and tubes l8 are alternately fired from opposite sides of the .base but each tube l8, instead of terminating adjacent the opposite side of the base in which it is located, returns to the same side and there discharges via upwardly extending elbows l9 either into the space 20 (as per Fig. 1) or into the chimneys or stacks 33 (as per Fig. 2). While in Fig. 4 I have shown the tubes I8- as being U- shaped, they may be provided with any type of return bend, such as a horse-shoe bend, a hairpin bend or any other suitable arrangement and if I so desire I may provide each tube with multiple bends making them S-shaped or any other form, depending upon the resultsto be accomplished in a given case and the termini of such tubes may be at the same or the opposite side as the starting points thereof.

While I have particlularly described the invention in connection with a charge of metal sheets, this is for exemplary purposes only, and it is to be understood that the furnace and the procedure herein described and claimed is equally applicable to the treatment of all ferrous and non-ferrous materials in any form whatsoever. Among these forms I have found that the invention is suitable for the heat treatment or annealing of sheets, plates, strips, bars, rods, coils, castings and various miscellaneous shapes.

Other and further modifications, omissions, substitutions and alterations may be made in my present invention, as will be understood by those skilled in this art, and all such are deemed to be a part of my present invention and are intended to be covered by the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patout is: a

1. Apparatus for uniformly and rapidly annealing a charge of metal sheets comprising a base, a removable heat-insulating cover and an air-excluding cover within and spaced from said heat-insulating cover, a metal sealing plate disposed upon said base and upon which said air; excluding cover rests, and means for sealing said covers to exclude air from within them, said base being provided with heating ducts which terminate in elbow portions disposed between said covers.

2. An annealing furnace comprising a refractory base traversed by tubular heating ducts composed of material having a high rate of heat transfer, a removable heat-insulating cover and an inner spaced air-excluding cover, a sealing plate disposed upon said base and upon which said air-excluding cover rests, a seal between said heat-insulating cover and said base and between said air-excluding cover and said plate, means for passing heating gases through said base ducts and thence upwardly between said covers and means for venting the spent gases to the atmosphere.

3. A method of annealing a metal charge on a pier confined and sealed within an inner cover which is enclosed within a spaced outer cover comprising the steps of conducting heating gases across the bottom of the metal charge below the pier to first raise the temperature of the bottom of .the charge, then -"causing the heating gases to pass upwardly between said covers to raise the temperature of the top and sides of the charge and finally venting the heating gases through the outer cover to the atmosphere, the bottom of the charge being thus heated by conduction and the remainder of the charge by combined conduction and radiation, the charge being at all times maintained out of direct contact with said heating gases. l t

4. A method of annealing as defined by claim wherein a thick metal plate is disposed upon the central portion of the sealing plate to provide a support for a metal charge and to transmit heat received by the sealing plate to the bottom of said charge.

7. An annealing furnace as defined by claim 2 wherein the sealing plate is provided with troughlike portions in which the inner cover rests and in which a sealing medium is disposed.

8. A method of annealing as defined by claim 3 wherein the heating gases originate as a plurality of distinct and substantially parallelgaseou's streams disposed along each side of the charge, the streams on one side of the charge traveling initially in a. direction opposite to the streams on the other side.

\9. In an annealing furnace of the character described, a refractory base, a series of heating ducts passing in a generally horizontal direction through such base and composed of material having a high rate of heat transfer and a metal sealing plate disposed upon said refractory base and adapted to prevent the passage of air upwardly through said base due to the inherent porosity of the refractory material of the base,

the said sealing plate being provided with trough- 35 shaped portions corresponding to recesses in said base and having a relatively thick metal plate disposed thereupon between said trough-shaped portions for supporting and transmitting heat to JOHN R. TAYLOR.

a charge of metal adapted to be disposed there-

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