US3186698A - Heat treating apparatus - Google Patents

Description

June l, 1965 w. L. THOME HEAT TREATING APPARATUS Filed June 14. 1963 mrema&- WILLIAM I.. THOME.

KP O United States Patent O 3,186,698 HEAT TREATING APPARATUS William L. Theme, Toledo, Ohio, assignor to Milland- Ross Corporation, Toledo, Ohio, a corporation of Ohio Filed June 14, 1963, Ser. No. 288,@02 4 claims. (Ci. 266-3) This invention relates to improved heat treating apparatus. More particularly, the invention relates to an improved furnace for sequentially heating and cooling a moving strand of metal strip of indefinite length in a single vertical pass. More particularly, the invention relates to means to pressurize the uppermost extremity of such a furnace.

Iu U.S. Patent 3,021,236 to Beggs et al. there is described a method of, and apparatus for, sequentially heating and cooling a vertically disposed moving strand of metal strip of indefinite length. The teachings of this patent have particular value in the heat treating of such metals as brasses where the strip is preferably unsupported during the heating and cooling steps to avoid marring the surface thereof.

Because of the well known sensitivity of Copper and copper alloys to oxygen at elevated temperatures it is customary to arrange furnaces according to the aforesaid patent, when used in heating such metals, so that the strip passes vertically downwardly through the furnace, with the heating section of the furnace being disposed higher in elevation than the cooling section. An arrangement of this type is of particular value in the processing of oxygen-sensitive metals because it lends itself most Conveniently to the inclusion of a liquid seal at the bottom of the furnace. The purpose of the liquid seal is to seal the lowermost strip passage opening against the influx of air which would otherwise be caused by the draft producing effect of the furnace itself.

It has been found, however, that the provision of a liquid seal at the bottom of the furnace, alone, is not always suicient to limitair influx into the cooling section of the furnace to a rate sufliciently low to maintain the oxygen level of the cooling section atmosphere at an acceptably low value. In one known instance it was not possible to meet the furnace users requirement of cooling section atmosphere oxygen concentration of 50 parts per million maximum. In this instance it was concluded that the excessive oxygen concentraon of the cooling section atmosphere was due to air in filtration into the cooling section throughotherwise inconsequential furnace casing manufacturing flaws due to the negative pressure which existedin the cooling section. The negative pressure in the cooling section arose by virtue of the draft producing eifect of the furnace itself. r

In a furnace of the type described in the foregoing patent, of commercial size, and incorporating the latest design features, the draft producing eflect of the furnace may be of the order of magnitude of 0.5 inch Water column. Heretofore, the pressure of the furnace at the uppermost part of the heating section would be very close to atmospheric due to the fact that it was in communication-with the surroundings by way of the uppermost strip passage opening. This strip passage opening, of necessity, was of substantial size to provide sufi'icient pas'- sage clearance for the strip. Thus, in a prior art furnace wherein theupper heating section pressure Was very close to atmospheric, the pressure at the lower part of the cooling section Would he suflicient subatmospheric to cause a serious problem in meeting cooling section oxygen con centration requirements 'of the furnace user. It is, therefore, the object of this invention to provide' means for retarding the infiltration of air into a vertical furnace for heat treating a' downwardly moving'strand of ice metal strip. It is a further object of the invention to provide means to pressurize the upper, or heating, section of' such a furnace to the extent necessary to insure that the pressure in the lower, or cooling, section of the furnace will not be unduly subatmospheric.

For a further understanding of the invention, attention is directed to the following portion of the specification, to the drawing, and to the appended claims.

In the drawing:

FIG. 1 is a vertical sectional view of a furnace incorporating the present invention;

FIG. 2 is a fragmentary sectional view taken on line 2-2 of FIG. 1; and i FIG. 3 is a fragmentary sectional view, at an enlarged scale, taken on line 3-3 of FIG. l.

As shown in FIG. 1, there is provided a furnace, shown generally at 11, comprsing wall means 12 forming an upper section 13 and wall means 14 formng a lower section 15. A moving strand of metal strip S of indefinite length is caused to pass downwardly through furnace 11 by means comprsing an upper roller 16 and a lower roller 17. Strip S enters upper section 13 of fur-. nace 11 through an upper passage opening 18. From thence it passes into lower section 15 and it ultimately emerges from the lower section of the furnace through a lower passage opening 19. To prevent the natural stack action of furnace 11 from causing air to flow into the furnace through opening 19 it is customary to seal opening 19 by locating it downstream of, and at a higher elevation than, roller 17 and by submerging roller 17 in a body of an impervious fluent sealirg medium 21 such as water. It is to be noted, in passing, that in such a system sealing media 21 may be beneficially utilized to absorb some degree of heat from strip S.

During its passage through furnace 11 strip S is subjected to a metallurgical heat treatment, such as annealing in the case of brasses, by heating it in section 13 and then by cooling it in section 15. For reasons described in the aforesaid patent to Beggs et al., both the heating and cooling process are preferably predominently by convective heat transfer. Whether for heating or cooling, it has been found that optimum convective heat transfer rates are obta'ned when the heat transfer fluid is .directed against the strip in jets. Accordingly, heating section 13 is provided with jet convection heating means comprsing a blower 22 for circulating a compressible fluid. A heater 23 is provided for heating the compressible fluid circulated by blower 22. Conduit means 24 is provided for introducing the heated compressible fluid into heating section 13. A plurality of ported nozzle pipes 25 disp posed in vertical columns in section 13 on opposite sides of the strip as it passes therethrough are provided to cause the heated compressible fluid to flow toward strip S in jets having a Component of motion directed normally thereto. And a vertical riser 26 communicatng with conduit means 24 and with each of the nozzle pipes 25 in a column is provided to deliver compressible fluid from conduit means' i 23 -may be thought to be directly -fired and it is, for purposes of illustraton, provided with. fuel inlet means 28,

and combustion air inlet means 29. Totmaintain-the mass flow continuityof furnace 11 it Will be necessary to vent products of combustion therefrom at a rate equal to the rate at which products of combustion are introduced Paterted June 1, 1965 u '3 into the system by heater 23. UPPer passage opening 18 serves as convenient flue product eflluent and it is customarily so used in direct fired furnaces. Even in direct fired furnaces where passage 13 is used as a flue the fluid pressure drop across passage 18 will be very small in comparison to the magnitude of the furnace draftaction due to the fact that passage 18 will, of necessity, be relatively large in relationto the rate of flue product venting. Thus, the pressure drop of the flue products venting through passage 18 will be relatively small in comparison 'to the natural draft developed by furnace 11 near the bottom of cooling section 15. Hence, whether the heating section is directly fired or indirectly heated will be of little consequence in pressuring the iurnace to combat the infiltration of air.

In cooling section 15, as in heating section 13, the beat transfer step is again preferably by convecton from je-ts of compressible fluid directed toward moving strip S. Accordingly, cooling section 15 is provided with a blower 31 for circulating a compressible fluid. A cooler 32, such as an indirect cooler having a `coolant inlet 33 and a coolant outlet 34, is provided to cool the compressible fluid. The cooled compressible fluid is introduced into cooling section 15 by means of conduit 35 and is directed .toward the strip in jets by means of nozzle pipes 36 mounted in opposed vertical columns. A vertical riser 37 is provided to deliver compressible fluid from conduit means 3 to each of the nozzle pipes in a column Spent compressible cooling fluid -is collected in section 15 and is returned to blower 31 by means of conduit 38 for recirculation through the nozzle system. In order to pressurize the upper portion of sectont13 to overcome the subatmospheric pressure at the lower portion of section 15 due to the natural draft of furnace 11, there is provided wall means 41 defining a narrow throat 42 .intermediate upper roller 16 and upper passage openingls and in communication with upper passage ls. Associated With. throat 42 at a locus somewhat distant from the lowermost extremity thereof is jet nozzle means 43 adapted to inject compressible fluid downwardly into throat 42,. The injected compressible fluid may be allowed to vent with products of combustion but preferably ports 44 are provided so that compressible fluid may be withdrawn from throat 42 at a rate equal to the rate of injection.` Ports 44 are located intermediate the ends of throat 42 and it is pref erable that they be lower in elevation than jet nozzles 43 to safeguard against the influx of air into the heating system of section 13. The compressible fluid which is withdrawn from throat 42 through ports 44 is collected in a box 45 formed by wall means 46 with the lower part of wall means 41. The

' (AP will be a function of the pressure of the injected fluid collected in box 45 is delivered to a blower 47 by v means of a conduit 48 and is delivered, by means of a conduit 49, to a box 51 communicating' with jet nozzle means 43 and formed by wall means 52 with the upper portion of wallmeans 41.

The injection of compressible fluid into throat'42 and the subsequent emergence of the fluid in a direction less vertically downwardly than the direction of injection is effective' to 'establish a static pressure in throat 42by r virtue of the law of Conservation ofMomentum. According to this principle a moving fluid jet exerts a force when there is a change in its momentum, that is, a change in the product of its mass and its velocity. Since velocity is a vectorial quantity, a mere changein the direction jet (P the. total cross-section flow area of the jet or jets (A the angle of motion (6!) of the jet` with respect to the Vertical, and the cross-sectional flow area of the throat (A 'In such a system where the ratio of A zA is rel-atively small '(e.g., not in eXcess of 0.1) the actual attainable pressure build-up may be calculated fairly closely by the empirical formula:

From the foregoing formula it may be` seen that jets of small cross-sectional area (i.e., with r-atios of AJIAD of the order of 0.04, and With an angle 0 of the order of 30, it is possible to attain a value of AP of an order of magnitude of 0.5 in. w.c. with a reasonable jet pressure P of the order of 10 in. w.c. When throat 42 is pressurized to the extent of 0.5 in. w.c. a pressure substantially as high will be established in the upper portion of section 13 and the pressure in the lower portion of section 15 will not become subatmospheric in cases where furnace 11 is not of suificient height to establish a natural draft in excess 0.5 in. w.c. By keeping the pressure in the lower portion of section 15 at the value of atmospheric or slightly greater, or at least not significantly subatmospherc, it is possible to etfectively combat the infiltration of trace quantities of air into cooling section '13 and to. maintain lower levels of atmosphere oxygen concentration in accordance -with the desires of the furrace user. To attain` values of AP in accordance With the foregoing formula it is important that angle 6 be at least of the order of 30 and that jet .nozzle means 43 be located a distance above the. bottom of throat 42 at least of the order of twice the narrower width of throat 42. Otherwise, some of the injected fluid may pass directly into heating section 13 without undergong the change in direction needed to, establisha force by virtue of momcntjum change. p

` The best mode known to me to carry out this invention has been described above in terms sufliciently full, clear, concise, and exact as to enable any person skilled in the art to make and use the same. It is to bet understood, however, that other modes of practcing the invention can 'be made by a skilled artisan without departing from the, scope of the invention which is defined only by the ap pended claims. 3

I claim:

1. In heat treating furnace, apparatus comprising wall means forming a first treating section and a second treat- 'ing section communicating with the first treating section and disposed therebelow; roller means comprising an upper roller and a lower roller for passing a strand of i metal work of indefinite length into the furnace appaof a moving fluid jet, without any appreciable change in the magnitude of its velocity, will be effective to establish a .force by way of a change in momentum. i In the illustrated invention, then, there, will be a downwardly directd force established in throat 42 because of the fact that the velocity leaving throat 42` through ports 44 will have substantially no vertical downward Component of velocity whereas the fluid injected into .throat 42 through nozzle means 43 will have a very substantial vertical ratus through an upper` opening at an upper portion of the first treating chamber thence, sequentially, through the first treating section and 'the second treating section, and thence from the furnace apparatus through a lower opening at a lower portion of the second treating section; sealing means comprising a fluent impervious sealing medium to block the influx of' air into the furnace apparatus through the lower opening; the improvement comprising means for pressurizing the first treating section andcomprising, in combinat-ion: wall means defining a narrow strip passage throat intermediate the upper roller and the upper opening and in 'communication with the upper opening; and downwardly inclined jet nozzle means disposed at' an elevation' *intermediate the vertical extremities of the throat for injecting compressible fluid into the throat at a direction which has a substantial comt ponent of motion vertically downward. s

the threat at an angle from the vertical at least of the order of 30 and wherein the jet nezzle means is located a distance above the bottom of the threat at least of the order of twice the narrower width of the threat.

3. Apparatus according to claim 1 and further cemprisng means for withdrawing cempressible fluid from the threat and for recirculating the Withdrawn compressible fluid to the jet nezzle means.

4. Apparatus according te claim 3 Wherein the means fer Withdrawng compressible fluid from the threat comprises port means disposed at a locus intermediate the v than the jet nezzle means.

References cited by the Examner UNITED STATES PATENTS 1,890,065 12/32 Meehan 263-3 '2,799,605 7/57 Franck et al 148-156 X MORRIS O. WOLK; Pr'mary Examner.

Claims (1)

1. IN HEAT TREATING FURNACE APPARATUS COMPRISING WALL MEANS FORMING A FIRST TREATING SECTION AND A SECOND TREATING SECTION COMMUNICATING WITH THE FIRST TREATING SECTION AND DISPOSED THEREBELOW; ROLLER MEANS COMPRISING AN UPPER ROLLER AND A LOWER ROLLER FOR PASSING A STRAND OF METAL WORK OF INDEFINITE LENGTH INTO THE FURNACE APPARATUS THROUGH AN UPPER OPENING AT AN UPPER PORTION OF THE FIRST TREATING CHAMBER THENCE, SEQUENTIALLY, THROUGH THE FIRST TREATING SECTION AND THE SECOND TREATING SECTION, AND THENCE FROM THE FURNACE APPARATUS THROUGH A LOWER OPENING AT A LOWER PORTION OF THE SECOND TREATING SECTION; SEALING MEANS COMPRISING A FLUENT IMPREVIOUS SEALING MEDIUM TO BLOCK THE INFLUX OF AIR INTO THE FURNACE APPARATUS THROUGH THE LOWER OPENING; THE IMPROVEMENT COMPRISING MEANS FOR PRESSURIZING THE FIRST TREATING SECTION AND COMPRISING, IN COMBINATION: WALL MEMBER DEFINING A NARROW STRIP PASSAGE THROAT INTERMEDIATE THE UPPER

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