US2261702A - Annealing furnace - Google Patents

Description

K. TAMELE ET Al.`

ANNEALING FURNA CE Filed April 30, 1940 2 Sheets-*Sheet l vENToRs WITNESSES:

ATTORNEY Nov. 4, 19417.

K. TAMELE ETAL ANNEALING EURNACE F-i'led April 30, 1940 2 Sheets-Sheet 2 INVENTORS WITNEssEs:v

ATTORNEY Patented Nov. 4, 1941 ANNEAmNc. FURNACE Karl Tamele, Berlin-Schmargendorf, and Alois Schmitt, Berlin-Charlottenburg, Germany, assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 30, 1940, Serial No. 332,494

In Germany February 9, 1939 (ci. zest-s) Claims.

'Ihis invention relates more particularly to a furnace through which metal strip is continuously fed for heat treatment while enveloped by a special or controlled gaseous atmosphere of any desired composition.

An object 'of our invention is to provide a furnace in which continuously-fed strip can be uniformly annealed without distortion or any significant surface contamination.

A further object of our invention is to construct a furnace of the type mentioned which will occupy relatively little floor space, and to this end the furnace is built high in a vertical `direction, that is, the furnace is of a tower type with a long relatively-narrow, ,vertically-extending chamber in which the strip is first conducted upward from an entrance at the bottom of the furnace, reversed by a guide roller atA the Atop of the furnace, and then conducted downward to an exit also at the bottom of the furnace.

In accordance with our invention, the furnace comprises a heating or annealing zone at the top of the furnace, a heating intermediate zone below the heating zone and in which strip on its way to the heating zone absorbs heat from strip coming from the annealing zone, the latter being thereby cooled, and a bottom or lower fzone in I deemed gas-now booster means, these being dis' which the entering strip may be initially preheated and the leaving strip cooled. Thiscycle is carried out with provisions for maintaining the strip nat and. for preventing distortion such as might occur if any of the heat-treatments on'the strip weredrastically non-uniform on one o f its sides as compared to the other.

To assure uniform and constantly satisfactory amiealing, the 'strip is, in accordance with our invention, Vat all times uniformly heated or cooled on both of its sides as it passes through the successive heat-treating zones. In furtherance of uniform heat-treatment of the strip, the gaseous atmosphere enveloping it is circulated completely about the strip, preferably moving longitudinally of the strip and enveloping both` its sides and edges.

In accordance with the invention, the protective atmosphere enveloping the strip also acts in the additional capacity of a heatexchange medium for cooling the portions of the stripcoming from the heating zone of the furnace, and preheating the portions going to that zone. Consequently, the gaseous atmosphere is, in the main,.passed longitudinally ofthe strip, and, in the preferred embodiment,`is recirculated in a path -which has a portion for cooling the recirculated gas. Therefore, the gas-now channels correspond with the channels in the lfurnace through which the strip passes, but certain booster means for causing or aiding the gasflow is employed disposed in short branch conduits paralleling the gas-ilow channels.

Preferably the atmosphere is admitted to the furnace, or distributed therein, or both, on both sides of the strip by an expedientwhich involves having all gas exit and entrance openings directed toward the rim edge of the strip and extending beyond both sides of these edges. In

other obvious embodiments, nozzles, or tubes having gas-distributing means, may project and advance the gas in a direction longitudinal of the strip. Additionally the gas-flow is preferably regulatable, and valves, dampers, pet-cocks, baffles, or other such -expedients may be provided posed in bypass conduits which are located approximately at the center of the lowermost zone of the furnace, with .the intake and discharge ends of the booster means spaced apart-slightly in the direction of gas-flow. In order to prevent `a direct short circuit between the outlets or discharge of the gas-flow booster means and its intake or inlet gas-now, air-flow restriction means or curtains are provided in the gas-now channels between the inlets and outlets so that Such gas-flow booster means and restrictive curtains are provided in both the strip-ascending channel and strip-descending channel of the furnace, and are, therefore, located on opposite sides of the gas-recirculating system. This disposition, together with the exhaust and admission 'of the gas from and on both sides of the strip, has the,

advantage that the pressure of the gas can be comparatively small so that the gas losses are reduced, but, the pressure is nevertheless suf-V ficient to prevent infiltration into the furnace of air or other obnoxious gases.

One ofthe primary purposes of our invention is to provide a furnace which will heat-treat strip uniformly on all its surfaces and, nevertheless, be economical and eflicient. To this end the intermediate heat-exchange zone has provisions whereby the hot descending strip heats the cool ascending strip `by radiation. This is accomplished by having the two strips move in oppositeV directions in close proximity to each other and with one face or side oi' the descending strip facing one face'or side of the ascending strip.

ascending strip so that this last side is thereby heated. Consequently, both sides of the ascendlng strip and the descending strip are heated an'd cooled, respectively, so that neither will have any appreciable tendency to distort or warp.-

To achieve also in the top heating zone of the furnace a uniform heating of the strip, heating means are disposed on both sides of the strip, the heating means having umts between which the strip moves.

Many other purposes and features of our invention not particularly described or mentioned above will be apparent from the following descirption thereof, taken in conjunction with the drawings, in which:

Figures la and lb are to be vertically juxtaposed with Fig. la on top, and together represent a vertical cross-sectional view of a preferred embodiment of our invention.

Figs. 2a and 2b are similarly to be vertically juxtaposed, and together represent a vertical cross-sectional view, with some parts in elevation and the metal strip omitted for clarity of illustration, of our furnace at right angles to that of Fig. 1 and taken substantially on the line II-II of Fig. 1.

Fig. 3 represents a vertical cross-'sectional view of a portion of a furnace substantially along the line III- HI of Fig. 1b.

Fig. 4 is an enlargedhorizontal cross-sectional view through the heating zone of the furnace taken substantially along the line IV-IV of Fig. la, and v Fig. 5 is a vertical cross-sectional view of part lof a modified furnace indicating a partition in atmosphere through the furnace, preferably in a recirculating path with a major part of the atmosphere recirculating in the lower section 1. Controlled atmosphere may be admitted to the furnace through an inlet pipe I0.

The entire furnace is supported in any suitable manner and is preferably encased in a gas-tight metallic shell having suitable gas seals such as I I and I3 where the diilerent sections or parts of the furnace abut. 'I'hese latter features are com- Amon to furnaces employing a controlled gaseous through an opening I6, into an inlet channel I1 the intermediate zone for dividing it into gas channels.

A furnace in accordance with our invention is designed to occupy little room horizontally and it is, therefore, extended, or elongated, vertically. The furnace in its entirety is represented by the numeral I and is divided into a number of vertically contiguous and communicating sections comprising an upper section 3, an intermediate section 5, and a lower section 1.

'I'he upper section 3 comprises the heating or annealing zone of the furnace and includes suit' able non-metallic heat-insulating and refractory side walls and a. similar top wall, the top wall preferably comprising a. removable covering 3.

The intermediate section 5 comprlsesa heatexchange zone where the ascending strip is exposed to the descending strip for heat-exchange between the two. This section also has heatinsulated walls which need not be as thick as those -of the heating section.

The lower section is also a heat-exchange section by which heat from the descending strip is transferred to the ascending strip, preferably by the recirculation of the controlled atmosphere permeating the furnace. The upper part of Rthis lower section can be insulated while the lower v part comprises exposed metal whereby recirculating atmosphere can be better cooled for cooling the strip; although the lowermost section at-its bottom where the strip leaves it may be provided with a length of' a 'water-cooled jacket for furat the bottom of the lower zone 1 which, in general, consists of sheet metal. 'Ihe strip I5 passes about a guide roller I8 and continues upwardly through the lower section 1, through the intermediate section 5, and the heating section 3, at the top of which it is reversed by a roller 2l, and then comes down the other side of the heating section 3, the intermediate section 5 and the lower section 1, in succession, being guided by suitable rollers as, for example, the roller 23 at the bottom of the lintermediate section and the roller 25 below the strip outletl 21 at the bottom of the lower section 1. The arrows at the strip indicate its direction of movement which can be accomplished in any suitable manner as, for example, by making the roller 25 a driving roller, assisted, if necessary, by the roller 2I which also can be power-driven in suitable synchronized speed relation tothe roller 25. It may thus be observed that the stripin the nirnace goes up one side of it through the respective zones and then is reversed in the top of ,the heating chamber 3 to go down the respective zones in the reverse sequence. i

The heating section is insulated from the intermediate section by non-metallic refractory tile, or the like, 3I and `33 arranged to provide slots through which the strip passes, the tile extending between two end walls of the furnace, and the intermediate tile 33 further acting as a support for a partition 35 extending up into the heating section between the strip portions and supporting heating units 31 for heating one side or face of the ascending and descending strip portions. Heating units 39 are suitably supported on two side walls of the furnace opposite the transversely-extending partition 35 so that the strip portions are necessarily heated on both of their sides.

,The major portion of the gas circulation is accomplished in the lower, section 1, and to this end a closed partition 4I, paralleling the strip and extending between two end walls, divides the lower section into an ascending channel'and a descending channel. The partition 4I terminates `somewhat'. short of the boi-,tom of the section 1 A transverse bar 49 between the lower section- 1 and the intermediate section 5 is spaced somewhat above the top of the partition 4I to provide a suitable top cross channel for the other tiun of the recirculating gases, and the edge walls assumaY of the furnace may be also provided with cli nels l' to enlarge the gas-tum passage.

In the middle part 53 of the lower section 1 an air-now producing means is provided and to this end the partition 4 I which otherwise extends intermediate section 5 has no partition between the ascendingand` de-V scending strip. Accordingly,the ascending strip is directly exposed to radiationfrom the descend- Y in fairly close proximity to the sides of the strip j sides. Blowers 65 are disposed in these conduits,

preferably of the centrifugal type. As may be seen in Figs; 1b and 3, the outlets 61 and 61 of the branch conduits il and 5I' are spaced somewhat from the inlets 69'and 59', respectively, the spacing being in the direction of gas ilow, but

' counter to the direction of movement of the strip. Preferably,.the blowers are driven by direct current motors whose speed can be regulated.

The bilateral arrangement of the blowers on both edges of the ascending strip and correspondingly on the descending strip offers the advantage that the strip is uniformly cooled. In this same connection, gas inlets and the gas outlets Y for each of the branch conduits are so designed A that they span and 'extend beyond the rim or edge of the strip on both sides.

In order to prevent a direct ow of gaseous atmosphere from the outlets to the inlets of the branch conduits, a gas-flow restrictive means or resistance is provided in the form of rollers 1I which are covered by asbestos cloth, and may have additional shields 13 over them to further restrict the air iiow directly through the central section 53. l

Accordingly, it may be observed that in operation of the furnace thus far described, the conduits 53 and 63' force the gas upwardly along the descending portion of the strip while the conduits 6I and 6I force the gas downwardly in the ascending portion of the' strip, the recirculating air turning at the channel 434 and gas passages 41 in the lower part of the lsection,'|, and at the channel 5| and the gas passage between the top of the partition I3 and cross bar 49, at. the top is heated on both its sides, the one side byexposure t0 the radiation from the descending strip and contact with the gases between the strips,A

which in oneembodiment ing strip so that the former will befurther preheated and the latter cooled. In this intermediate section 5 a further vcooling device 8|.is pro.- vided on theside of the descending strip opposite to the ascending strip. 'I'his device 8l consists of a tube system which may be connected by aA pipe 82 to the pressure side of a branch conduit as, for examplefthe'conduit 63 whosel associated motor is suitably adjusted to run, therefore, at

a slightly higher speed than the other motors. Protective atmosphere is, accordingly, conveyed through the tube system 8l and can discharge at the bottom of the intermediate section 5 at an outlet 95 located at the side of the ascendingV strip which is not exposed to the descending strip.

Consequently, both sides of the descending strip are cooled, the side facing the ascending strip being cooled by radiation and by. contact with the turbulent gaseous atmosphere between the twoV Y strips andthe other side cooled bythe tube e system 8l. In the same way the ascending strip and the other side by heated gases flowing from the outlet l85.

lIn the modification shown in Fig. 5, the intermediate section 5 is providedl'with a central parofthe lower section 1. However, there is suflicient space between the cross bar 49 and the side walls of the furnace to provide slots through which the strip passes, and to permit a fraction of the`recirculating gases to lenter into the upper sections of the furnace, corresponding slots beingV also provided between the tile 3l and the intermediate tile A33 separating the intermediate section 5 from the heating section 3. Accordingly,

the entire furnace will be permeated by the protective atmosphere. It may be preferable to restrict the openings I E and 21 in order to permit only a slight leakage of the protective atmos.

tition 89 and in this case the gas will have con- .ilned recirculating paths through the upper section of the furnace, as well as through the lower section 1.

Accordingly,'it may be-seen that we have prof vided a furnace in which the strip is heat-treated uniformly on both its sides and while enveloped by a gaseous atmosphere. Moreover,r we have-V created a furnace in which the heat is utilized to its maximum extent; being taken'fromthe portions of the strip already heated and transferred to portions of the stripto be heated.

We claim as our invention:

1. An elongated vertical furnace of the\ type described for `the heat-treatment of metal strip while enveloped by a controlled gaseous atmosphere and continuously fed through said furnace. v

said furnace comprising vertically contiguous and communicating sections including, an insulated upper section comprising a heating zone closed at the top' and having heating'means therein, and

a lower furnace section comprising a zone 'forl cooling the descending strip and preheating the' ascending strip, means for directing said strip up a side of said sections, reversing it in the upper portion of said heating section, and then directing it back down another side of saidsections opposite the rst said side whereby the strip in the furnace takes the general form, in effect, of an inverted U, partition means in. said sections for forming gas passages completely about the portion -of the strip inthe lower section 1 is necessarily preheated to some extent, and the descending strip cooled.

Further heat exchange is provided for in the ascending strip and about the` descending strip, said partition means terminating in said heating section short of the bend of said strip and means for circulating controlled atmosphere lthrough .said passages along the length ofv said strip.

l2. An lelongated vertical furnace of the type described for the heat-treatment of metal strip while enveloped by a controlledgaseous atmosphere and continuously fed through said furnace, said furnace comprising vertically contiguous and communicating sections including, an insulated upper section comprising a heating zone closed at the top and having heating means therein, and a lower furnace section comprising a zone for cooling the descending strip and preheating the ascending strip, means for directing said strip up a side of said sections, reversing it in the upper portion of -said heating section, and then directing it back down another side of said sections opposite the first said side whereby the strip in the furnace takes the general form, in effect, of aninverted U, partition means forming gas passages paralleling said ascending strip and said descending strip, and means for circulatingr controlled atmosphere through said passages, comprising blower and branch conduit means. for the said gas passages, having an inlet'opening and an outlet opening spaced from said inlet opening in a 'direction longitudinally of the strip, and means for increasing the gas-flow resistance of the direct passage along said strip between said inlet and outlet openings.

3. The structure of claim 2 in which said inlet and outlet openings are edgewise of said strip and each extends beyond both sides of the edges of said strip.

4. An elongated vertical furnace of the type described for the heat-treatment of metal strip while enveloped by a controlled gaseous atmosphere and continuously fed through said furnace, said furnace comprising vertically contiguous and communicating sections including, an insulated upper section comprising aheating zone closed at the top and having heating means therein,an insulated intermediate section comprising a heat-exchange zone, and a lower section having an entrance and-exit for said strip, means u for directing said strip up a side of said sections,

reversing it in the upper portion of said heating' section, and then directing it back down another side of said sections opposite the rst said side whereby the strip in the furnace takes the general form, in effect, of an inverted U, and means for circulating controlled atmosphere in said furnace longitudinally of the strip and completely enveloping it, said last means including branch conduits with blower means having entrance and discharge openings in said lower section spaced respectively in a direction opposite to that of the movement of said strip.

5. The structure of claim 4 including gas-flow restrictive means within said furnace between said openings.

6,. An elongated vertical furnace of the type described for the heat-treatment of metal strip while enveloped by a controlled gaseous atmosphere and continuously fed through said furnace, said furnace comprising vertically contiguous and, communicating sections including an insulated upper section comprising a heating zone closed at the top and having heating means therein, an insulated intermediatesection comprising a heat-exchange zone, and a lower. section having an entrance and exit for said strip, means for directing said strip up a side of said sections, reversing it in the upper portion oi said heating section, and then directing it to each other for heat-exchange whereby the ascending strip is preheated, and the descending strip cooled, said intermediate section including cooling means on the side of said descending strip away from said ascending strip, and preheating means on the side of said ascending strip away from said descending strip.

7. An elongated vertical furnace of the type described for, the heat-treatment of metal strip while enveloped by a controlled gaseous atmosphere and continuously fed through said furnace, said furnace comprising vertically contiguous and communicating sections including, an insulated upper section comprising a heating zone closed at the top and having heating means therein, an insulated intermediate section comprising a heat-exchange zone, and a lower section having an entrance andexit for said strip, means for directing said strip upl a side of said sections, reversing it in the upper portion of said heating section, and then directing 'it back down another side of said sections opposite the first said side whereby the strip in the furnace takes the general form, in effect, of an inverted U, means in said lower section including a blower for circulating controlled atmosphere in gas-paths substantiallyr for the heat-treatment of metal strip while en-f veloped by a controlled gaseous atmosphere and continuously fed through said furnace, said furnace comprising a strip heating section, and a heat-exchange section, means for ldirecting strip to be heated along aside of said vheatexchange section and heated strip along the opposite side of said heat-exchange section in'such manner that the strip to be heated and the heated strip move in opposite directions with their large sides facing for heat exchange, heating`4 means in said heat exchange section for heating the other large side of said strip to be heated, and cooling means in said heat-exchange section for cooling the other large side of said heated strip.

9. A furnace for the heat-treatment of metal strip while enveloped by a gaseous atmosphere, said furnace comprising an elongated passageway closely encompassing said strip, means for moving said strip through said passageway, means for permeating said passageway with a gaseous atmosphere, and gas-moving means comprising a gas-conduit means having an inlet and an outlet in and along said pasageway intermediate the ends of said passageway, said inlet being relatively closely. spaced from said outlet with respect to the distancexbetween the ends of said passageway, said gas-moving means end section comprising a heating zone closed at one vand and having heating means therein, a second section adjacent said end section, means for directing said strip along a side of said sections, reversing it in said heating zone, and then directing it back along another side of said sections opposite the rst saidy side, and means for recirculating controlled atmosphere for enveloping said strip, the last saidV means comprising a pair of enlarged gas-reversing passages spaced along said sections and spanning said sides. the last said means further comprising gas-propelling means between said passages and comprising a branch conduit having an inlet and an outlet spaced longitudinally of said strip.

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