US2218354A - Method and apparatus for annealing strip - Google Patents

Description

Oct. 15, 1940. J D, KELLER 2,218,354

METHOD AND APPARATUS FOR ANNEALING STRIP Filed March 13, 1939 3 Sheets-Sheet l Fig. l

I INVENTOR John 0. Keller- Oct. 15, 1940. J. D. KELLER 2,218,354

METHOD AND APPARATUS FOR-ANNEALING STRIP FiledMarch 13, 1939 3 Sheets-Sheet 2 if /7 J8 INVENTOR John D. Keller Oct. 15. 194 J. D. KELLER METHOD AND APPARATUS FOR ANNEALING STRIP Filed March 13, 1959 5 Sheets-Sheet 3 I l l I I I I I I I I I II NN INVENTOR John 0. Keller Patented @et. 3%. 39 I Q WTHOD AND $2.5?ARATKJS F$ ANNEAHNG S'ERKP John D. Keller, Pittsburgh, Ea, assignor to The Wean Engineering Company, liner, Warren, Ohio, a corporation of Ohio Application March 13, 1939, serial No. 261.51%

8 Glaizns.

This invention relates to the metallurgical processing of rolled metal and, in particular, to material in strip form, such as cold rolled steel strip.

a Rolled material has been annealed heretofore in the form of coils or stacks of sheets by the use of conventional annealing boxes and furnaces or in cover type furnaces. In either case, the process is slow because of the time required to 10 bring the material up to the desired temperature. A further objection is that the characteristics of the finished product are not uniform because all portions of the mass are not raised to exactly the same temperature. The long time required for annealing under the conventional practice makes the cost thereof high because the annealing facilities necessary for a substantial capacity represent a large investment.

I have invented a novel method and apparatus for annealing strip which overcome the aforementioned objections and are characterized by other novel features and advantages. In a preferred embodiment and practice of the invention, I provide an elongated heating chamber having a muiile extending therethrough, and pass the strip progressively through the muflie in strand form, while applying heat to the exterior of the muiile. I also provide cooling chutes or ducts through.- which the strip is led after passing through the mume, whereby it is gradually reduced to atmospheric temperature. I maintain a non-oxidizing atmosphere in the mufile and cooling chutes to protect the material from oxidation during treatment. Other novel features and advantages of the invention will become apparent in the course of the following detailed description and explanation which refers to the accompanying drawings illustrating the embodiment and practice outlined above. In the draw- 40 ings Fig. 1 is a vertical central section through the heating chamber and cooling ducts constituting a complete annealing apparatus embodying my invention;

Fig. 2 is a sectional view taken along the plane of line IIII of Fig. 1;

Fig. 3 is a partial sectional view taken along the line IIl--II[ of Fig. 1;

Fig. 4 is a sectional view taken along the plane of line IV--IV of Fig. 3; r

Fig. 5 is a sectional view taken along the plane of line VV of Fig. 2; and

Fig. 6 is a sectional view taken along the plane of line VI-VI of Fig. 2.

Referring now in detail to the drawings, the

apparatus which I prefer for annealing strip in accordance with the invention includes a heating chamber Ill. The heating chamber it, in the preferred construction, is disposed with its greatest dimension substantially vertical and is 5 carried on any suitable supporting framework 4!. It may conveniently be built up of retractory or refractory-insulating brick i2 within a suitable enclosure formed by sheathing plates l3 and structural frame members such as may be 10 needed to sustain it. Bailies or cross walls M divide the chamber into a plurality of zones lia, 55b, 550. In these zones, the rough heating of the strip is accomplished. A final heating and temperature-regulating zone l5d above the zones 35 55a, i517 and H50, or beyond them in the direction in which the strip moves, effects the heating of the strip to the desired final temperature and insures the temperature of the strip being uniform across its width. A cross wall it separates the zone 1511 from the zones therebelow.

Mumes 16 extend upwardly through the heating chamber in side by side relation and have supporting flanges Ilia secured thereto. The muflies are long, flat, tubes of suitable metal, 25 preferably heat-resistant alloy and are supported. on beams ltb, with their lower ends free to move vertically and laterally between angle bars "5. While I have shown two such muiiies, it will be apparent that the number and width of the muf- 30 fies will be determined by the width of the strip to be treated. The zones iSa, I51) and 15c are provided with burners l1 adapted to circulate hot combustion gases around the muflies whereby to heat .the portions thereof'located in the several 3| zones. These burners are supplied with air and combustible such as fuel gas under a slight pressure and in such a ratio as to'provide a luminous flame adapted to heat the mufile to a temperature of about 1600 F. The combustion gases deliv-' o ered by such burners are of a reducing character. This, together with the fact that the gases do not impinge directly on the muflles but circle therearound, precludes rapid deterioration of the portions of the muiiles in the lower zones. 4

The combustion gases pass upwardly around the muflles through the-slots in the cross walls or positive pressure at any point in the chamber l0.

The uppermost zone |5d of the chamber I is defined by converging side walls 20 and is provided, adjacent the bottom thereof, with a plurality of burners 2|. Fuel is supplied to the burners 2| from manifolds 22. Preferably a substantially perfect fuel air mixture is delivered to the manifolds from any suitable mixer, to cause complete combustion with a blue flame. Refractory baffles 23 extend the width of the zone |d in front of the burners 2| for the purpose of directing the flames therefrom upwardly along the converging side walls 20. The burners 2| may be so adjusted, individually or in groups, by suitable control valves 2|a, as to produce the desired temperature at each point along the width of the muflles IS, the average temperature of the portion of the muflle in the zone |5d being only slightly higher than the desired final temperature of the strip, and usually from 1300 to 1500 F. Preferably the flow of gas-air mixture to the manifolds 22 is regulated by an automatic temperature controlling device effective to maintain constant the temperature of the strip at the top of zone I511. The heating of the muffles in the zone |5d is effected principally by radiation, the heat of the combustion gases being absorbed by the refractory brick composing the wall and then radiated to the muflies. The combustion gases are deflected by the baiiles 23 and prevented from coming in contact with the mufiie until they reach the top of the zone, where, as waste gases, they finally flow through exhaust ducts 24 to the stack. By means of dampers 24a in the fiues leading from these ducts to the stack, the pressure in zone |5d may be maintained nearly atmosphgric, independent of the pressure or draft in the lower zones.

One end wall of the chamber I0 is provided with a slot 25 extending the full height thereof, to permit the sidewise removal of the muflles I6. A closure 26 which may conveniently be made in sections, normally overlies the slot 25. As shown in Fig. 6, refractory blocks 2'! are laid on the cross walls I4, bridging the slot therein, after the muflies have been placed. The top and bottom of the chamber In and the topmost cross wall l4 are provided with slots 28 extending laterally and intersecting the slot 25. Removable closures 29 are disposed in these slots.

The mufiles l6 extend upwardly from the heating chamber In through a seal 30 to an initial cooling chamber 3|. The chamber 3| communicates with a series of cooling chutes or ducts 32, 33 and 34, through which strip is adapted to pass successively after emerging from the muilles. Guide drums 35 and 36 are disposed in the chamber 3|, the former cooperating with a similar drum 31 below the chamber II) to guide thestrip S progressively through the muflles. The drums 35 and 36 may be of any suitable material and, if desired, may be provided with scrapers (not shown) to remove any accretions which might be picked up therefrom by the strip and cause scratches in the surface of portions of 'the strip subsequently traversing the drums. The drums may be of a heat-resistant alloy such as Nichrome with a highly polished surface so that the strip will not adhere thereto. Alternatively, the drums may be of material which is softer than the strip being treated, such as copper or Monel metal. The strip may be fed from coils suitably supported, around the drum 31 and thence upwardly through the muilles, by tension applied to the strip by means at the exit end of the apparatus.

The strip ascending through the heating chamber is quickly heated to the desired maximum temperature and then enters the initial cooling chamber 3|. The drums 35 and 36 are provided with shrouds or jackets 38 of thermal insulation to prevent excessively rapid cooling of the strip which would cause it to buckle. The walls of the chamber 3| and the several cooling ducts are subjected to atmospheric cooling and the strip gradually loses heat to the walls as it traverses its path, being guided therein by drums 39 and 40 at the opposite ends of the several chutes or ducts and a similar drum 4| at the exit end of the apparatus. The chamber 3| and the cooling ducts are composed of sheet metal supported by a suitable framework. The ducts are provided with baffles 42 to limit the circulationof the atmosphere contained therein, and withinsulation 42a to prevent too rapid loss of heat from the outer edges of the strip. This atmosphere is preferably a non-oxidizing gas supplied through inlets 43 and 44 whence it flows downwardly through the chamber 3|, the muflies l6 and the cooling ducts, thereby preventing oxidation of the strip being treated. The downflowing gas carries away any vapors evolved from oil left on the strip from the rolling process. Sealing rolls 45 at the entrance and exit ends of the apparatus prevent excessive loss of the protective atmosphere at these points.

After passing over the drums 35 and 36 in the chamber 3|, the strip passes between cooling tubes 46 of hairpin or V-shape disposed with their vertex upward and located at about the middle of the strip S. Any suitable cooling fluid may be circulated through the tubes 45 to absorb heat from the strip. Because of the shape and arrangement of the tubes, the advancing strip is cooled first at the center thereof and then progressively toward each edge. This prevents buckling which might result from an attempt to cool the strip across its entire width at one point along its path. A shroud or jacket 41 of thermal insulation is disposed above the tubes 46 of the upper set, to prevent excessive cooling of the strip before it passes between these tubes. After passing between the sets of tubes 46, the strip continues through the chutes or ducts 32, 33 and 34, thereby losing additional heat to the walls thereof and eventually cooling to a temperature at which atmospheric oxidation does not proceed rapidly, by the time it reaches the lower end of the chute 34. On emerging from the latter, the strip may be drawn-around the drum 4| to a coiling device or may be advanced in strand form for further processing such as coating, stamping, or the like. If the strip is coiled, the coiler will provide the tension necessary to advance the strip through the heating and cooling chambers. Otherwise, this tension may be applied by suitable pinch rolls adjacent the guide drum 4|.

The cooling apparatus described above is disclosed and claimed in Wean Patent 2,199,472 and Wean et a1. Patent 2,205,915 granted on applications copending herewith.

It will be apparent from the foregoing description that the invention provides a relatively simple, yet highly effective method and apparatus for annealing strip, which are not subject to the objections to the conventional annealing practice. According to the invention, each unit length of strip is subjected to precisely the same in the finished product is assured. The apparatus may be operated, furthermore, at relatively high speed as the heating and cooling of the strip may be effected fairly rapidly since it is handled in single thickness or strand form at all times. It will also be evident that the cost of the apparatus disclosed is less than that of conventional annealing equipment of the same capacity.

Among other advantages may be mentioned the fact that since the muflles are suspended from their upper ends, they are maintained straight by their own weight. The increased life of the muflies resulting from the non-oxidizing character of the flame in the lower zones and the fairly uniform and relatively low temperature therein and the fact that the heating to the maximum temperature in the topmost zone is effected largely by radiation and with little or no direct impingement of the gases on the muflles, have already been pointed out. The burners of the several zones can be regulated for the greatest economy at any particular operating rate. The mufiles can be removed sidewise from the heating chamber so that no extra head room is required. The two muffies shown, furthermore, can be replaced by other muflles of different widths depending on the width of strip to be handled.

Although I have illustrated and described herein but a preferred embodiment and practice of the invention, it will be understood that changes in the construction and operation disclosed may be made without departing from the spirit of the invention or the scope of the appended claims. A single mufile, for example, may be used to treat wide strip, instead of the two muflies shown.

I claim:

1. Apparatus for treating strip comprisingan elongated, vertical heating chamber, a muiile suspended therein, means for guiding strip through the mufiie, and transverse baflies dividing said chamber into successive zones, the topmost zone having walls converging toward said mufile, burners in said topmost zone, and means deflecting combustion gases flowing upwardly from said burners toward said walls whereby the walls radiate heat to said mufile.

2. Apparatus for treating strip comprising an elongated heating chamber, a muiile extending therethrough, means for guiding strip through the muifie, means dividing said chamber into a plurality of zones, burners positioned to deliver combustion gases circumferentially of the muffle in the initial zones, and a plurality of independently controlled burners in the final zone spaced apart across the width of the mufiie.

3. In a method of treating strip, the steps including drawing the strip upwardly through a substantially vertical muflie, heating the lower portion of the muffle substantially exclusively by convection to a temperature below the desired maximum temperature to which the strip is to be heated, maintaining a reducing atmosphere about the lower portion of said mufile, and heating the upper portion of the muflle substantially to said desired maximum temperature, substantially exclusively by radiation, and maintaining the temperature of the strip substantially uniform across the width thereof as it traverses said upper portion.

4. Apparatus for treating strip comprising an elongated, vertical heating chamber, a mufile therein and extending substantially the full height thereof, means suspending the muiile from its upper end for sidewise movement, means for guiding strip through the mufile, means for heating said mufile, and a slot in a side wall of said chamber having a removable closure, Whereby said muflle may be removed sidewise from the chamber in one piece.

5. In a method of heating a tall, vertical muflie through which strip is drawn for annealing, the steps including discharging into a muffleenclosing chamber, at points spaced along its length, along a circumferential path around it, combustion gases in a state of freedom for direct contact with the muilie, and substantially confining said gases against unrestrained upward flow under natural draft, thereby defining zones of substantially constant gas pressure and causing repeated circumfiuence of the mufiie by said gases.

6. Apparatus for treating strip comprising an elongated heating chamber, a mufile extending therethrough, means dividing the chamber into successive zones, means forguiding strip through the muilie, means for heating the portions of the muffle in the initial zones including burners firing into the chamber circumferentially of the muffle, and means for heating the portion of the muilie in the final zone including burners distributed across the width of the chamber and firing toward the muffle, and means directing the combustion gases flowing from said lastmentioned burners longitudinally of the mufile.

7. Apparatus for treating strip comprising an elongated, vertical heating chamber, a mufiie depending through said chamber, means for guiding strip through said muflle in strand form, means supporting said muflle substantially exclusively from the upper end thereof, whereby the weight of the muflie keeps it in tension and prevents buckling, and means effective to confine the lower end of the muille against horizontal movement in one direction while permitting movement thereof vertically and horizontally in a direction at right angles to said first-mentioned direction.

8. Apparatus for treating strip comprising an elongated, vertical heating chamber, a mufile suspended therein, means for guiding strip through the mufile, burners positioned adjacent the muffle firing into the space between the muflle and the chamber wall, combustion gases free for direct contact with the former, so as to circulate a heating flame around the mufile, burners positioned near the exit end of the muflie adapted to heat the chamber wall to radiant temperature whereby the exit end of the muffle is heated principally by radiation, said last-mentioned burners being spaced across the width of the muifie, and means for separately controlling them whereby the temperatures at points spaced across the width of the muiile may be maintained at the desired value.

JOHN D. KELLER.

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