US2926902A - Heat-treating furnace - Google Patents

Description

March 1, 1960 2 w. ROTH ETAL 2,926,902

HEAT TREATING FURNACE Filed Jan. 27, 1956 6 Sheets-Sheet 1 March 1, 1960 w. ROTH ETAL 2,926,902

HEAT TREATING FURNACE March 1, 1960 w. ROTH ETAL 2,926,902

HEAT TREATING FURNACE Filed Jan. 27, 1956 s Sheets-Sheet 4 Fig.4.

March 1, 1960 w. ROTH ETAL HEAT TREATING FURNACE Filed Jan. 27, 1956 6 Sheets-Sheet 5 Fig. 6.

Mai-ch l, 1960 w. ROTH ETAL HEAT TREATING'F'URNACE a Sheets-Sheet 6 Filed Jangz'r, 1956 Fig. 7.

HEAT-TREATING FURNACE Willard Roth, Meadville, and Thomas L. Case, West Mead Township, Crawford County, Pa., assignors, by mesne assignments, to Sunbeam Equipment Corporation, a corporation of Delaware Application January 27, 1956, Serial No. 561,780

7 Claims. (Cl. 266-3) Our invention relates generally to temperature treatment chambers, and it has more particular relation to a furnace for the heat-treatment of a'strip of aluminum or the like, which is continuously passing through the furnace. The furnace or other chamber may consist of either one, and preferably both, of two parts, namely a first part which acts as a heat-exchanger for heating (or cooling) the strip, soon after it enters the furnace, until the strip reaches a predetermined desired temperature, and a second part for soaking the strip at substantially this predetermined temperature for a predetermined length of time, which is determined by the length of the strip which is included in the soaking-chamber at any moment, and the velocity of the strip.

When the strip is aluminum, it is desirable to soak the strip at a temperature which is of the order of 975 F., more or less, in a heat-treatment soaking-chamber in which the temperature of the strip is maintained constant within extremely close limits, such as from 2 to F. Usually, the aluminum strip enters the furnace at a temperature which is not quite as high as the desired heattreatment or soakingtemperature, and in this case the furnace is provided with a special heating-section wherein the temperature of the strip is raised as quickly as possible to the desired soaking-temperature.

There are problems which have had to be solved in both parts of the furnace.

The strip to be temperature-treated does not need to be aluminum, and it could conceivably require refrigeration, rather than heating, with respect to the temperature of the ambient atmosphere outside of the chamber. In its most general sense, therefore, our invention may be regarded as being a heat-exchanging device, or a temperature-holding device, or both, without limitation as to whether the holding-temperature is above or below that of the ambient atmosphere, although the invention was particularly designed for the heat-treatment of an aluminum strip, and our description will be directed more particularly to the embodiment of our invention in the form of a furnace rather than a refrigerator.

The main features of our invention will be pointed out more particularly hereinafter. Two alternative forms of embodiment are shown in the drawings, wherein- Figure .1 is a vertical longitudinal sectional view of a vertical three-pass aluminum-strip furnace, on the sectionplane I--I of Fig. 2;

Fig.2 is a view, partly in side-elevation, and partly in verticalsection on a plane indicated by the line I II-I in Fig. 1;

Fig. 3 is a front elcvational view of the upper part of the furnace of Figs. 1 and 2, aswould be seen from the plane III--III in Fig. 2;

Figs. 4 and 5 are sectional views on the planes IV-IV and V-V, respectively, as indicated in Figs. 2 and 3; and

Figs. 6 and 7 are sectional views, similar to Figs. 1 and 2, showing a somewhat modified form of construction, in the form of a vertical twelve-pass aluminum-strip furnace, the sectional planes being indicated by the lines ice VI-VI of Fig. 7 and VII-VII of Fig. 6, respectively.

The furnace which is shown in Figs. 1 to 5 has a tall heat-insulated furnace-housing 10 which is. supported on a base-framework 11, and which is free to expand and contract vertically between suitable vertical guides 12. The housing 10, in this form of construction, has an entryslit 13 which is located at the top, and an egress-slit 14 which is located at the bottom, the housing being otherwise as gas-tight as it can conveniently be made.

The furnace is provided with a means for guiding a longitudinally moving strip 15 in one or more long substantially unsupported vertical spans or passes, as the strip moves through the furnace from the entry-slit 13 to the egress-slit 14. In Fig. 1, three passes of the strip are shown, as provided by a lower roll or roller 16 between the first and second passes, and an upper roll or roller 17 between the second and third passes. The two rollers 16 and 17 may be driven by suitably controlled motors 16' and 17', as shown in Fig. 2. Both rollers are journally supported outside of the furnace, where accurate alignment may be more easily maintained, out of the heat of the furnace, by means of bearings 18.

In the illustrated form of embodiment, as shown in Figs. 1 and 2, both of the rollers 16 and 17 are removable for repair and replacement. To this end, their bearings 18 are carried by pivoted arms 19 which are counterweighted at 20, as shown in Fig. 1. In order to prevent any substantial chimney-action within the furnace-housing, the roll-shafts are sealed reasonably tightly through spring-loaded friction-sealing means 22 (Fig. l). The rolls can be removed from the furnace through movable or removable insulated plugs 23 and 24 in the bottom and top, respectively, of the furnace-housing 10. The bottom roller 16 may be used as a tension-adjuster roller, which can move slightly up and down to control the tension of the strip when the strip is being initially heated, and the variation in the'length of the strip can be communicated to a suitable control or indicating device 25 which is attached to the counterweight 20 of this lower roller 16.

The aluminum strip 15 will usually enter the entry-slit 13 of the furnace-housing 10 in Fig. 1 at a certain temperature, say 925 or 950 R, which is a little below the intended soaking-temperature, which is usually 975 F. During the first 15% (more or less) of the strip-travel in the furnace, the strip is heated so as to bring it up precisely to the desired soaking-temperature. Our furnace is a recirculating convection-heating furnace, and so this initial heating of the strip, to bring it fully up to temperature, is accomplished by means of a narrow elongated vertically disposed heat-exchanging passageway 30 (Fig. l), which is suspended within the furnace close to the entry-slit 13, so that the first span or pass of the strip passes approximately centrally through this passageway, the walls of the passageway being closely spaced from the side surfaces and the edges of the strip 15.

We provide a gas-recirculating system for maintaining a supply of gas at a temperature which is hotter than the entrance-temperature of the strip (assuming that the strip is to be heated), and we supply this gas through a suitable inlet-duct or ducts 32 (Fig. 2) to a plenum chamber 33 (Fig. 1) at the top of the heating-passageway 30. In the particular form of embodiment of the invention which'is shown in Fig. 1, the hot gas in the plenum chamber 33 is divided into two parts. Approximately half of the gas is bled off at the top and fed diagonally V passages 35 which are disposed on the opposite sides of the heating-passageway 30. From these two hot-gas passages 35, we admit a plurality of pairs of equal and opposite downwardly directed streams 36 of gas which superimpose, on the respective longitudinally moving heat-exchanging streams 34, substantially equal and opposit'erlateral converging movements of said gas, which impinge upon the opposite surfaces of the strip 15, at each of a plurality of levels in the vertical path of the strip as it passes downwardly through the heating-passageway 30.

The purposes of the laterally impinging streams 36 is mainly to provide a centering force for holding the strip 15 approximately in the center of the long narrow heating-passageway 30. There may bemany reasons which might tendto cause, or contribute to, the flappingor decentering of the strip as it passes through thenarrow heat-exchanging passageway 30. For one thing, the length ofthe unsupported span ofthe-strip l ,-is fairly great,

being of the order of seventy feet, in thefurnace'whichis shown in Fig. 1, so that a relatively slight disturbance may induce or initiate flapping or lateral movement of such a long strip. In the second place, the longitudinal or vertical velocity of the two streams 34 of the hot gas is quite high, being, for example, of the order of from 100 to 200 feet per second (more or less) in the furnace of Fig. l, and the laws of gas-flow may contribute toward the creation of sensible laterally-applied strip moving forces at such velocities. In the third place, the strip itself is not absolutely uniform in width or in gauge or in flatness, being subject to certain random warpings which may contribute considerably toward the initiation of a deleterious flapping or decentering of the strip, if this decentering tendency were not overcome by the centering action which is obtained by the laterally impinging gas-movements 36, preferably arranged in equal and opposite pairs, so that, if the strip became decentered or off-centered, the strip would get further away from one lateral stream and closer to the other lateral stream, thus resulting in a centering action, because the impinging force of each lateral stream diminishes as the strip gets further away from the stream-source.

We are not limited, of course, to the particular means which is shown in Fig. l for producing these laterallydirected strip-centering gas-movements 36 at one or more points or levels within the strip-heating passageway 39. Besides the strip-centering action of the lateral streams or gas-movements 36 within the narrow heating-passageway 30, these lateral streams are also useful in causing the hot gas to impinge in good heat-exchanging relation to the surfaces of the strip 15, increasing the turbulence of .the gas within the heating-passageway 30, thus increasing the rate of heat-exchange between the gas and the strip.

The major portion or volume of the space within the furnace-rousing 10 of Fig. 1 is a heat-soaking space, which is entered by the strip 15 as it emerges from the bottom of the heating-passageway 30 at the desired temperature at which the strip is to be soaked or held, for a matter of four minutes, or whatever other time is prescribed by the metallurgists for the heat-treatment of the aluminum strip. In the furnace which is shown in Fig. 1, it was specified, by the aluminum-strip manufacturer, that the strip should be held at a constant soaking-temperature within suchnarrow temperature-limits that it at first seemed impossible to satisfy such strict conditions.

These strict soaking-temperature limits (amounting to something like i2 or 33 F.) are met inour present invention by Providing a long open ended-tubular heatinsulat'ed, bafiie 40, which is disposed in a substantially vertical position within the heat-insulated; furnace-housing 10, in closely spaced relation to the four side walls of the housing. Within this bafiie 40 are disposedthe lower portion of the first span or pass of the strip 15 (after it leaves the heatingepassageway30), and all of the, second and third spans or passes of said strip. The lower roller 16 is disposed below the bottom open end of the bafile 40, and the upper roller 17 is dispo'sed above the upper open end of said baffie 44), while the emerging portion of the strip 15 extends down below the lower end of the bafile, and comes out of the egress-slit 14 in the housing it The hot emerges from the bottom of the narrow heating-passageway 30 at a temperature which is approximately the same as the desired soaking-temperature of the strip, within the previously specified narrow limits. It is necessary to provide a means for guiding this exitgas, which leaves the heating-passageway 3% so that most of this exit-gas travels longitudinally in slow-moving temperature-soaking streams 41 on opposite sides of the remaining portions of the entire length of the strip within the temperature-soaking space within-the baffle 48, In the form of invention shown in Fig. 1 this temperature-soaking gas-flow, between the first and second passesof the strip 15, is secured by means of a partition 42 (Fig. 1), which is suspended from the lower inner edge of the hot-gas passage 35 of the heating-passageway 3%.

As a result of the foregoing construction, one strean'i 41A of the exit-gas leaves the heating-passageway 30 in the space between the adjacent side-wall of the baffle 49 and the nearby surface of the first pass of the-strip 15, as shown'in Fig. 1. This stream 41A thus passes downwardly to the space 43 below the open bottom end of the bafiie 40. A second stream 41B of this'exibgas'fiows downwardly from the heating-passageway 30 between the other side of the first pass of the strip 15 and the partition 42, discharging at or near the lower open end of the baffle 40. From the lower end of the bafiie 4-0, in the space 43 therebelow, the-hot gas spreads out across the entire area ofthe bottom portion of the furnacehousing 10, and passes. up in four upwardly moving streams 41C, to 41F on opposite sides of the second and third passes of the striplS, discharging therefrom in the space 44 above of the open top'end of the baflie 462.

According to our invention, as large a portion of the hot gas as may be necessary is diverted from the bottom space 43, below the bafile 40,and is caused to flow in vertically moving temperature-buffering streams 45 outside of the bathe 44), in the spaces between the baffle and the four side-walls of the'furnace-housing 10. These bufiering streams 45' thus act as heat-buffers between the outside wall-surfaces of the hot-tubular heat-insulated bathe and the inside wall-surfaces of the relatively cool heat-insulated furnace-housing 10. It is not practical to hold the temperature of these buffering streams con stant within anything approaching the narrow limits which are required of the temperature-soaking space inside of the bathe 40, but the provision of these heat-buffering streams 45 makes it practically feasible to maintain the required extremely close temperature tolerances for the soaking-temperature of the strip 15.

It is usually desirable for the temperature-soaking streams 41 of the constant-temperature gas to flow at a much more moderate rate than the rate of flow in the heating-passageway 30. This is because of the desirability of heating the strip to the desired soaking-temperature as quickly, or in as short a length of strip, as is reasonably possible, in order to keep the size of the furnace within reasonable limits. The slower gas-flow velocities are obtained in the temperature-soaking streams 41 by reason of the fact that the cross-sectional areas of said temperature-soakin'g streams are greater than the cross-sectional areas of the heating-streams 34 within the narrow heatingpassageway. 30.

The various passages andgasflow spaces are designed so that the proper v distribution of-gas-flow takes place within the-insulated bathe 40, as-above described, ,It is generally desirable to provide various dampers '48 by which the division of the gas-flow streams may be more accurately controlled or regulated.

The circulated gas is withdrawn from the furnace at any convenient point, preferably at some point outside of the tubular baffle 40. In the form of embodiment of the invention which is shown in Fig. 2, this exit-point for the circulated gas is provided at a point, in the furnacehousing 10, which is a small distance below the inlet-duct 32, as indicated by the outlet-duct 52. The gas which is withdrawn from the furnace through the outlet-duct or ducts 52 passes first through a heater-section or sections 53, and next through a blower or blowers 54, from which the gas is discharged to the previously mentioned inlet duct 32, through which the gas is recirculated through the furnace. The heater-section 53 is shown, in Fig. 2, as comprising a plurality of fuel-consuming burners 55 which discharge their combustion-gases into the gas-recirculating system for heating the recirculated gas of the furnace. It will be understood, of course, that, in the broader aspects of our invention, any other form of heating-means may be used for heating the recirculated gas.

As shown in Fig. 2, we also provide an exhaust-duct 56 which leads off from the outlet end of the blower 54, having a damper 57 which may be opened wide for purging-purposes, when first starting up the furnace, so as to exhaust any gas which may be trapped within the furnace.

In the form of furnace which is shown in Figs. 1 and 2, the heat-treated strip, which leaves the furnace through the egress-slit 14, passes immediately into a quenching means, which is shown as comprising a plurality of waterspray nozzles 58 and a water-quench tank 59.

Depending from the bottom of the furnace-housing 10, and enclosing the egressing strip 15, we preferably provide a substantially gas-tight duct 61, the lower end of which is immersed within the water in the quench-tank 59, thus providing an exhaust-chamber which hermetically joins the quench-tank 59 to the bottom of the furnace-housing 10. We also preferably provide a means for exhausting the space in this exhaust-chamber above the quench-tank, as by means of an exhaust-pipe 62 (Fig. 2), from which gas is gently exhausted by means ofan exhaust-blower 63. The rate at which gas is exhausted can be suitably adjusted by many convenient means, as by means of a large exhaust-damper 64 (Fig. 2), which bypasses a small exhaust-damper 65. The larger exhaust-damper 64 will usually be open during the initial heating-up period of the furnace; but once the furnace has been suitably heated, this large exhaust-damper 64 will normally be closed, and the small exhaust-damper 65 will be open or partially open.

The exhaust-blower 63 provides a slight suction for withdrawing steam from the exhaust-chamber over the quench-tank 5!, thus preventing said steam" from entering the furnace. At the same time, the exhaust-blower 63 gently exhausts the gas-space within the furnace, for providing an exit for the gaseous-combustion products of the burners 55, and also for controlling or limiting the amount of gas-movement into or out of the furnace at the point of strip-entry 13, thus combatting a slight tendency for hot gas to leak out of the furnace at the entry-slit 13, in the particular furnace-design which is shown in Figs. 1 and 2.

It will be understood, of course, that our furnace can be embodied in a large variety of designs. For example, as shown in Fig. 6, the strip 15 may enter at the bottom of the furnace-housing 10, through an entry-slit 73 and sealing rolls 74. Also, a large number of vertical passes of the strip may be used in the furnace. Thus, twelve strip-passes may be used, and the entire first two passes may be used for strip-heating, while the last ten passes are used for strip-soaking. It will be noted, in the form of invention shown in Figs. 6 and 7, that the hot-gas inletduct 32 is provided so as to feed into two plenum chambers 33A and 3313 at the tops of the first two passes, re

. 6 spectively,so that the strip-heating streams of longitudinally moving gas will flow downwardly along the opposite surfaces of the strip, at each of these first two passes, so that the gas flows counter to the movement of the strip in the first pass, and in the same direction as the movement of the strip in the second pass. The rate of longitudinal gas-flow of the strip-heating gases, in the narrow heating-passageways 30A and 308 in Fig. 6, is so many times greater than the rate of movement of the strip, that it makes relatively little difference whether the gas-flow is with, or counter to, the direction of movement of the strip.

In Fig. 6, also, all of the gas from the plenum chambers 33A and 33B flows downwardly in equal strip-heating streams along the opposite surfaces ,of the respective passes of the strip 15. The effect of lateral converging streams or gas-movements 36 is obtained, in Fig. 6, by means of Venturi surfaces or louvers 79 which are provided in the side-walls of the narrow heating- passageways 30A and 30B.

Other innovations are also illustrated in Figs. 6 and 7, including the use of diagrammatically indicated radiant tube heaters or electric resistance heaters 85, in place of the gas burners 55, and the omission of the pivoted roller supporting arms 19, the quenching-means 5859, and other parts which were shown in Figs. 1 and 2.

We wish it to be understood that the foregoing and many other changes may be made, in the way of the substitution of equivalents, the omission of unneeded parts, or the addition of various supplementary or auxiliary parts, including pressure and temperature regulators and gauges, air-filters, and many other practical details which will be readily understood by those skilled in the art.

We claim as our invention:

1. A heat-treating furnace comprising a thermally insulated furnace housing, means for guiding a strip to be treated to move longitudinally in a vertical direction through the furnace housing, a thermally insulated baffle surrounding the strip within the furnace housing, means for introducing gas to flow through the baffle and from the baffle through the space between the baffle and the furnace housing, and means for controlling the flow of gas to the space between the bafile and the furnace housing to maintain the strip at a desired temperature within the bafiie.

2. A heat-treating furnace comprising a thermally insulated furnace housing, means for guiding a strip to be treated to move longitudinally in a vertical direction through the furnace housing, a thermally insulated bafile surrounding the strip within the furnace housing, an elongated vertical heat-exchange passage through which the strip passes, means for directing streams of gas through said passage on opposite sides of the strip in heat-exchange relation with the strip, said gas discharging from the passage to flow through the bafiie and from the baffle through the space between the baflle and the furnace housing, and means for controlling the flow of gas to the space between the bafile and the furnace housing to maintain the strip at a desired temperature within the bafile.

3. A heat treating furnace comprising a thermally insulated furnace housing, means for guiding a strip to be treated to move longitudinally through the furnace housing in a plurality of vertical passes, a thermally insulated bafile surrounding the strip within the furnace housing, means for introducing gas to flow downward through the baffle and back upward through the baffle and through the space between the baflle and the furnace housing, and means for controlling the division of said upward flowing gas between the baffle and said space to maintain the strip at a desired temperature within the baflie.

4. A heat-treating furnace comprising a thermally insulated furnace housing, means for guiding a strip to be treated to move longitudinally through the furnace housing in a plurality of vertical passes, a thermally insulated baflle surrounding the strip within the furnace housing, an elongated vertical heat-exchange passage through which space to maintain the strip at a desired temperature within the baffle.

5. A heat-treating furnace comprising a thermallyinsulated furnace housing, means for guiding a strip to be treated to move longitudinally through the furnace housing in a plurality of vertical passes, a thermally insulated baflie surrounding thestrip within the furnace housing, an elongated vertical heataexchange passage through which an initial portion ,of the strip passes, means for directing streams of gas through said passage on opposite sides of the strip in heat-exchange relation with the strip, means for directing substantially equal and oppositely directed streams, of gas against opposite sides of the strip within the passage, all of said gas discharging into said battle to flow downward through the baflle and back upward through the baffie and through the space between the baflie and the furnace housing, and means for controlling the division of said upward flowing gas between the baifie and said space to maintain the strip at a desired temperature within the baffle.

6. A heat-insulated chamber having a housing. which has slits for the entry and egress of a strip and which is otherwise substantially gas-tight; an open-ended tubular heat-insulated baffle disposed in a substantially vertical position within said housing in closely spaced relation to the side walls of the housing; a means for guiding a longitudinally moving strip in at least one long substantially unsupported vertical span within said baflle; at least one narrow elongated vertically disposed heat-exchanging passageway surrounding the initial portions of the entire length of the strip within said chamber, the walls of the passageway being closely spaced from the side'surfaces and the edges of the strip; a means for maintaining a supply of a gas at a temperature other than the entrancetemperature of said strip and for causing two substantially equal heat-exchanging streams of said gas to flow longitudinally along the respective surfaces of said strip in said passageway; the velocity of said heat-exchanging streams of gas, the length of the unsupported'span of the strip, and the uneven Warpings of the strip being in combination great enough to tend to cause a deleterious amount of decentering of said strip as it moves through said passageway; a means for superimposing, on the respective longitudinally moving heat-exchanging streams, a plurality of lateral converging movements of said gas, impinging upon the opposite surfaces of the strip, whereby to provide stripcentering forces within said passageway; and a means for guiding the exit-gas which leaves the passageway or passageways, so. that most :of. said exitrgas travels ,longitudi-..

continues. its movement through the ,chamber.

7. A heat-insulated chamberhaving a housing with a temperaturerholding vspaeegtherein, said housing. having slits for thetentryt-and egress of a strip and beingotherwise substantially gas-tight; an open-ended tubular heatinsulated ba'ffie disposed, inya substantially vertical position Within said housing vin closely spaced relation to the side walls of the housing; a means for guidinga longitudinallymoving strip-in at least one long substantially unsupported vertical span within said bafl le, said strip entering said.temperature-holding space at an entrancetemperature other than theambient atmosphere outside of said chamber; a means. for maintaining a supply of a gas atsubstantially ,said ,entrancertemperature: of the strip; anda means for guiding said gas so thatrmost of said gas. travels longitudinally .in temperature-soaking streams on opposite sides. of thestrip insaid temperature.- holding space, and so thata portion of said gas flows in vertically moving temperature-butfering streams outside of-saidbafilein the spaces 'betweenthe baffie and the side-walls ofthe. housing, thedivision of saidgas between said temperature-soaking streams. and. said temperature-buifering streamsbeing, such as to maintain the temperature of .thestrip withindesirably narrow limits as the strip moves through the temperatureeholding space,

References Cited in the file. of this patent UNITEDSTAT-ES PATENTS i 339,219 Scott Apr. 6, 1886 2,009,856 Otis July 30, 1935 2,023,285 Otis Dec. 3, 1935 2,144,919 Gautreau F,.Jan. 24, 1939 2,191,133. Pearson ..Feb.. 20,.1940 2,199,472- Wean May 7, 1940 2,206,734 Stassinet July, 2, 1940 2,415,856 Somes Feb. 18, 1947 2,462,202 Kniveton .,Feb. 22, 1949' 2,534,973 Ipsen Dec. 19, 1950 2,594,876 Cope Apr. 29,, 1952 2,658,742 Suter Nov. 10, 1953 2,693,353 Vaughn Nov. 2, 1954 2,706,110 Noss Apr. 12, 1955

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