US3424444A - Bell furnaces for heat-treating coiled strip metal and the like - Google Patents

Description

Jan. 28. 1969 J. R. GUINGAND BELL FURNACES FOR HEAT'TREATING COILED STRIP METAL AND THE LIKE Filed April 29. 1966 Sheet Jan. 28, 1969 J. R. GUINGAND 'BELL FURNACES FOR HEAT 3,424,444 TREATING COILED STRIP METAL AND THE LIKE Shet Filed A rii 29. 1966 ILED' J. R. GUINGAND BELL FURNACES Jan. 28. 1969 FOR HEAT-TREATING CO STRIP METAL AND THE LIKE "Sheet Filed April 29, 1966 United States Patent 16 Claims ABSTRACT OF THE DISCLOSURE An apparatus for cooling an atmosphere gas circulating, in response to a recycling fan, between a base and a protective cover of a heating bell furnace used for heat-treating products such as spools of strip-metal. The apparatus includes at least one atmosphere gas heat exchanger having at least one gas inlet located beneath said cover in a position where an overpressure prevails, and at least one gas outlet likewise located beneath said cover in a position where a negative relative pressure prevails, the gas flow through said heat exchanger being effected by said single fan, a gas duct element being retractable into said base mechanically associated with said inlet.

The heat treatment of coiled strip metal (hereinafter referred to as strip) under the controlled atmosphere of bell furnaces is usually slowed down by the lengthy period during which the spools into which the strip is coiled are allowed to cool.

It has already been proposed, for this cooling phase, to draw off the atmosphere gas by means of fans, to cause it to flow through one or more cooling heat-exchangers and to re-introduce it beneath the protective cover once it has been cooled. In addition to the special atmosphere-circulating fans in the heat exchangers, each spool-supporting base is equipped with a fan which causes the atmosphere gas to circulate beneath the cover itself, especially during the heating period.

It is the principal object of the present invention to provide a simplified apparatus of this kind, wherein the fan equipping each base is used to cause part of the atmosphere gas to circulate through at least one cooling heatexchanger.

In accordance with the present invention, the intake and outlet points and their locations are so devised that the intake point into the heat-exchanger are located in a part of said base whereat the atmosphere gas is at overpressure and the return-flow outlet from said exchanger in a part of the base whereat the atmosphere gas is at lower pressure.

In one specific form of embodiment of the invention, said inlet into the heat-exchanger isassociated with an obturator which is retractable in order not to hinder ventilation during the heating phase. Said obturator surmounts a profiled duct which improves the intake when the obturator is lifted. The cold-gas return flow outlet is formed by an oblong nozzle fitted with deflectors.

Since such bases are generally circular, it will be advantageous to observe flow symmetry by arranging said inflow and outflow and heat exchangers in a suitable number of diametrically opposed pairs, whereby there is provided a simplified and efficient apparatus requiring only one fan and only one motor usable for two purposes.

In accordance with another improvement provided by this invention, it will be of advantage to incorporate a leakproof valve in a heat-exchanger exit pipe providing return passage to the base of the furnace, and to locate this valve as close as possible to said base.

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During the process of heating a charge (usually consisting of spools of strip from a rolling-mill), the mixture of water and soluble oil used for the rolling and retained on the strip by surface tension evaporates and produces vapors liable to condense at the bottom of the heat exchanger, even if the precaution is taken to render the exchanger inoperative by shutting off the flow of cooling fluid, and even if the tanks surrounding the exchanger and containing said fluid are drained.

When the exchanger is rendered operative for the phase of accelerated cooling of the charge, this condensed water evaporates once more inside the exchanger and is carried along in the form of vapor by the atmosphere gas as the latter is recycled. This vapor can deteriorate the charge by producing thereon, in the case of a ferrous metal for instance, an undesirable blue oxide film.

In accordance with yet another improvement, there is provided, immediately upstream of said valve, a pipe for continuously bleeding the heat exchanger and which is efl ective in counterstreaming into said exchanger a proportion of atmosphere gaswhich circulates through the exchanger during the charge heating phase, this circulation being made possible by the fact that said obturator is by design not leakproof.

These provisions are effective in preventing the formation of oxide as previously mentioned.

The description which follows with reference to the accompanying non-limitative exemplary drawings will give a clear understanding of how the invention can be carried into practice and will disclose other advantageous features thereof.

In the drawings:

FIG. 1 shows fragmentally with cutaway a base of a furnace for heat-treating strip spools, said base being equipped with a single fan and with means for establishing at will a bypassed flow of atmosphere gas through accelerated-cooling heat exchangers.

FIG. 2 is a plan view corresponding to FIG. 1.

FIG. 3 is a detail side elevation view of the inlet and outlet of a heat exchanger.

FIG. 4 shows on an enlarged scale the leakproofing means used for the operating rod of an inlet obturator.

FIG. 5 is a detail view on an enlarged scale of means for detecting water in a heat exchanger.

FIG. 6 is a fragmental sectional view with cutaway of a heat-treatment furnace base portion at the location of the bleed pipe, and of the furnace inlet located between the ditfuser blades; and

FIG. 7 is a corresponding sectional view showing the location of said bleed pipe and the disposition of the isolating valve.

The form of embodiment shown in FIG. 1 includes a base 1 of refractory material mounted on a support 2 fabricated from metal girders and supported in turn on posts 3. Upon this refractory base may be placed a heating bell (not shown), inside which the junction between said base and the lower frusto-conical portion 5 of a protective cover is rendered leakproof by means of a ring of sand 4. Inside said cover portion 5 is arranged a charge-carrying plate 6 on which rests the charge proper 7, consisting of stacked strip-spools of which the turns, though normally tightly wound thereon, may alternatively be loose, but through which an inner passage or chimney 8 is formed in all cases.

Plate 6 rests upon the blades 9 of a diffuser bounding a central area in which rotates a centrifugal fan wheel 10 mounted on a shaft 11 carried in a sealed bearing 12, the opposite external end of shaft 11 supporting thereon pulleys 13 which are rotated through the medium of belts 14 by the drive pulleys 15 of an electric motor 16.

The blades 9 additionally rest on a plate 17 designed to reinforce the top of refractory base 1.

Plate 17 is formed with an upturned flared rim 18 which leaves clear an annular slit 19 for impelling therethrough the atmosphere gas trapped beneath cover 5, which gas is sucked by fan 10 into passage 8 and impelled between blades 9 towards said annular slit 19.

This constitutes the classic process whereby the controlled atmosphere is swirled about the charge, not only during the heating periods but also during the dwelling and cooling periods.

Formed in base 1, between two blades 9, is a lined passageway 20 which communicates with a suitably bent conduit 21 extending into a tube coil 22 which is submerged in water contained in a cooling tank 23 fitted with inlet and outlet water pipes 24 and 25. The exit from tube coil 22 extends upwardly through a pipe 26 into a further pasageway 27 formed in base 1 and projects upwardly therefrom in the form of a flattened nozzle 28 which may be made co-extensive with rim 18 and cover portion 5, up to the upper end-section of the latter.

Slidable through the liner of passageway 20 is a cylindrical obturator body 29 formed with a port 30 therein and a flat cap 31 and, internally, with a deflector 32 facing port 30, Which port is directed towards the center of the blading. Cylindrical body 29 is connected through struts 33 to an operating rod 34 which passes through the bend in pipe 21 via a leaktight gland 35 and is connected to the rod 36 of a hydraulic jack 37 mounted on the associated post 3.

Similarly, flared nozzle 28 has, positioned in the center thereof, a pair of symmetrical deflectors 38 (see FIG. 3) for distributing the gas flow through the gap between the periphery of charge 7 and the inner wall of protective cover 5.

As shown in FIG. 4, rod 34 extends through a bushing 39 having therein a guide 41 formed with grooves 40, which guide 41 creates pressure losses required to protect a plastic leakproof gland 42 therebelow made of graphite-bearing asbestos which is compressed by a plug 43 screwed over the bushing through which said rod extends. In order to provide additional protection, a pressurizing pipe stub 44 has a port between gland 42 and guide 41.

For safety reasons, provision is made at the lowermost point on the last turn of tube coil 22 for a drain 45 on to which a plug 46 is sealingly screwed over a rubber gasket. Said drain communicates with a suitably bent dip-tube 47 which passes through the opposite wall of the tube coil and extends, as a safety measure, up to a burner which heats a warning bi-metallic strip. Similar drains, devoid of a warning device, are provided at the lowermost points of the other turns.

Preferably, the system hereinbefore described includes diametrically opposed pairs of cooling means, this uniform layout ensuring that the general pattern of flow of the atmosphere gas beneath the cover 5, in response to the single fan 10, is not disturbed.

During the periods when the charge 7 is heated, the obturating flat caps 31 are applied flush with plate 17, obtuators 29 being retracted into the base. Thus, the flow of atmosphere gas is normal and the cooling coils 22 are isolated and inoperative.

During the cooling period, responsively to jacks 37, the corresponding obturators 31 are raised. The blowing force of fan 10, in conjunction with the fact that lined passageway 20 is located in a zone of overpressure and nozzle 28 in zone where a lesser pressure prevails in the general pattern of flow of atmosphere gas beneath cover 5, causes active circulation of part of the atmosphere gas through the corresponding heat-exchanger coil 22.

This results in a speeded-up cooling of the atmosphere gas, and hence of the charge 7, with no expenditure other than the circulating water in tanks 23.

Should water form by condensation in the cooling circuit, it will collect at the lowermost point of coil 22 and block pipe 47, the burner of which Will consequently go out. Said bi-metallic strip then closes a set of warning contacts or operates any other convenient safety device.

As may be seen in FIG. 7, the outlet pipe 26 from the cooling heat exchanger is disposed as near as possible to refractory base 1, with a leaktight closable isolation valve 50. A bleed pipe 51, has a nozzle 52 which opens into pipe 26 upstream of valve 50 and is adapted to deliver thereinto a flow of atmosphere gas. Pipe 51 is bent so as to pass through refractory base 1 and plate 17 and it terminates between blades 9 at a point where there prevails a gas pressure higher than that prevailing outside the diffuser 18. Pipe 51 is open at all times.

The system hereinbefore described operates in the following manner:

During the heating of charge 7, fan 10 draws the atmosphere gas through the central chimney 8 in the charge and impels it beneath cover 5 to annular slit 19. Obturator 29 is closed, but not leaktightly. Gas bled through pipe 51 is delivered through nozzle 52 into conduit 26. This bleed prevents atmosphere gas from stagnating inside an inoperative cooling heat-exchanger, for such stagnation could cause any steam and soluble oil vapor included in the gas to condense. Valve 50 is closed. This being so, notwithstanding the leak through obturator 29 when same is closed, the heat exchanger cannot operate as a condenser since its walls, heated thus, cannot act as a source of cold or as a condensation trap.

During the forced cooling of the charge, valve 50 is open and obturator 29 is likewise open. This heat exchanger is rendered operative. Fan 10 delivers atmosphere gas thereinto but this gas encounters no liquid condensation in the exchanger and cannot therefore carry with it an unduly large detrimental proportion of steam, whereby oxidation of the charge is avoided, as would otherwise unfailingly occur during the accelerated cooling period.

Circulation of the atmosphere gas through the heat exchanger during this accelerated cooling period is in no way hindered by the small flow of counter-streamed bleed gas continuing to escape through nozzle 52.

It goes without saying that many changes and substitutions may be made to the specific form of embodiment hereinbefore described. Thus, the heat exchangers could include means other than the coil referred to hereinabove, and could comprise, for instance, multiple clustered tubes of the single or dual flow type and, possibly also, water tubes. Such individual heat exchangers could furthermore be positioned vertically and, instead of being associated to an inlet and an outlet each, could be connected to sets of inlets and outlets. Similarly, a cooling jacket could be used to protect the sealing gland used for the obturator actuating rod. Moreover, flow and temperature measuring instruments could be provided on each circuit.

Lastly, it is to be noted that whilst it is useful to cause a high proportion of the total recycled gas to pass through the cooling heat exchanger or exchangers, fixed gas intakes and outlets would produce a very substantial reduction in the fiow during the heating process, whereas, in the subject apparatus of this invention, the use of thenretracted mobile inlets and outlets averts hindrance to recirculation during the heating process.

The apparatus hereinbefore described thus enables any proportion of the recirculating atmosphere gas to be bypassed through the cooling heat-exchanger or exchangers; indeed, it would be possible to cause virtually the entire output from the single centrifugal blower to be flowed through such cooling heat-exchanger(s).

What I claim is:

1. In a heating bell furnace having a base on .which products to be heat-treated are supported, a protective cover enclosing said products, and a recycling fan below said base for circulating an atmosphere gas in the furnace between the center and the periphery thereof via a passageway beneath said base, an improvement comprising means for selectively cooling said atmosphere gas including at least one heat exchanger for cooling said atmosphere gas, sa-id exchanger having at least one gas inlet located beneath said cover at a location where an overpressure prevails and at least one gas outlet also located beneath said cover at a location where a negative relative pressure prevails whereby a natural flow of gas through said exchanger tends to :be produced, said flow of gas through said exchanger being supplemented by said fan, and a gas duct element retractable in said base and associated with said inlet to selectively direct the circulating gas to said inlet.

2. An improvement as claimed in claim 1 wherein said retractable gas duct element comprises an obturator for blocking said inlet.

3. An improvement as claimed in claim 2 wherein said retractable element includes a profiled duct for improving gas flow.

4. An improvement as claimed in claim 1 comprising an actuating rod connected to said retractable element to operate the same.

5. An improvement as claimed in claim 1, comprising a flattened nozzle at said heat exchanger outlet.

6. An improvement as claimed in claim 5 comprising deflector means facing said flattened nozzle for the deflection of gas discharged therefrom.

7. An improvement as claimed in claim 1 wherein said fan includes a fan wheel and a diffuser comprising radial blades extending from said fan wheel, said diffuser having a frusto-conical rim spaced from the protective cover, said inlet being located between the blades at the exit of the diffuser, and said outlet is located between said rim and said protective cover.

8. An improvement as claimed in claim 7 in which a plurality of heat exchangers are provided, each having an associated inlet and outlet in diametrically opposed relation with the inlet and outlet of another heat exchanger at the periphery of said base.

9. An improvement as claimed in claim 1 wherein said heat exchanger comprises a tank of circulating water and a coil submerged in the water in said tank, said coil being connected to said inlet and outlet.

10. An improvement as claimed in claim 9 comprising a condensation detector means at the lowermost point of said coil.

11. An improvement as claimed in claim 1 comprising an actuating rod connected to said retractable element to operate the same, said inlet having a wall with a leakproof guide therein for said rod, said guide comprising a gland housing with an intermediate pressurizing port therein.

12. An improvement as claimed in claim 1 comprising a leakproof sealing valve controlling said outlet.

13. An improvement as claimed in claim 11 wherein said sealing valve is located beneath said base in immediate proximity thereto.

14. An improvement as claimed in claim 11 comprising a nozzle located upstream of said sealing valve to continuously inject bled ofl gas into the heat exchanger in countercurrent with the flow of gas to said outlet:

15. An improvement as claimed in claim 14 comprising means for conveying the bled gas to said nozzle from a point within the furnace where an overpressure prevails.

16. An improvement as claimed in claim 14 wherein said fan includes a fan wheel and a diffuser comprising radial blades extending from said fan Wheel, said diffuser having a frusto-conical rim spaced from the protective cover, said inlet being located between the blades at the exit of the diffuser, and said outlet is located between said rim and said protective cover and means for conveying the bled gas to said nozzle from a point located between the blades of said diffuser.

References Cited UNITED STATES PATENTS 1,938,306 12/1933 Webb 266-5 2,325,677 8/1943 Hoak 266-5 2,477,796 8/1949 Germany 266-5 3,035,824 5/1962 Weaver 263-40 3,169,158 2/1965 Wigg 266-5 3,309,073 3/1967 Guingand 266-5 3,294,596 12/1966 Daubersy 266-5 XR 3,302,939 2/ 1967 Scharbrough 266-5 FOREIGN PATENTS 930,063 7/ 1963 Great Britain.

WILLIAM J. STEPHENSON, Primary Examiner. R. S. ANNEAR, Assistant Examiner.

U.S. Cl. X.R. 263-40; -107

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