US3275309A - Apparatus for heating metal objects - Google Patents

Description

Sept. 27, 1966 L. WILSON ETAL APPARATUS FOR HEATING METAL OBJECTS 4 Sheets-Sheet 1 Filed April 8, 1964 M m E N M 0 wag W N r A 5 p Y B U Sept. 27, 1966 L. WILSON ETAL.

APPARATUS FOR HEATING METAL OBJECTS 2 +v w. h S ,r t e e h S 4 N w M Q Q A 6 w a l n p A w 1 INVENTORS. 45E W/L .SON PA UL E. BARE/V016 Sept. 37, 1966 L. WILSON ETAL 3,275,309

APPARATUS FOR HEATING METAL OBJECTS Filed April 8, 1964 4 Sheets-Sheet 5 M 7 v/ ML 67- A 39 i 2 j 40 Z j 1/ 38 INVENTORS. ZFE W/Z .S'O/V PAUL 1?. BAEENOK Wil 4 14 W *M ATTOE/VEKS.

l 1966 1... WILSON ETAL 3,275,309

APPARATUS FOR HEATING METAL OBJECTS Filed April 8, 1964 4 Sheets-Sheet 4 INVENTORS A [E W/L SON PA UL E. BAIQENOK M W, W AMA x4 4770/?)VEK5.

United States Patent 3,275,309 APPARATUS FOR HEATING METAL OBJECTS Lee Wilson, Rocky River, and Paul R. Barenok, North Olmsted, Ohio, assignors to Lee Wilson Engineering Company, Inc., Cleveland, Ohio, a corporation of Ohio Filed Apr. 8, 1964, Ser. No. 358,156 10 Claims. (Cl. 266-5) This invention relates to methods of and appartus for heating metal, and more particularly to improved furnace structures and procedures for heating strip metal in either tight or open coil form.

Although our invention is adapted for use in carrying out various metal heating operations it will be specifically illustrated and described herein in connection with the heat treating, for example annealing, of steel strip in coil form. Such annealing operations are now commonly carried out in bell type annealing furnaces with the strip either in tightly wound coils or in so-called open coils in which the laps are spaced apart. In the prior practice of both tight and open coil treatment of strip metal the coils are supported on a base structure and are enclosed in a bell shaped removable metal inner cover. This inner cover is made of relatively thin sheet metal, has a suitable sealing connection with the furnace base, and provides an enclosure for the coils being heated in which the desired protective or other type atmosphere may be maintained and in which such atmosphere maybe circulated to facilitate transfer of heat to and from the coils. A furnace bell unit, carrying suitable heating elements such as radiant combustion tubes, is placed over the inner cover and heat is applied for the desired length of time while the atmosphere within the inner cover is circulated. When heating is completed the furnace bell is removed but the inner cover must remain in place until cooling is completed to protect the charge.

In the Lee Wilson co-pending United States patent aplication Serial No. 271,413, filed April 8, 1963, now Patent No. 3,184,225, there is illustrated and described a regenerative furnace structure for heating coils of strip metal which incorporates the elements referred to above to- -gether with certain additional and novel features which increase the efficiency and reduce the cost as compared to previously proposed metal strip heating procedures. The apparatus illustrated and the procedures described herein incorporate some of the novel features of the said copending application but, as will be explained later, the present invention is adapted for use either in single unregenerative or double regenerative furnace structures and also includes novel and important improvements in strip coil heating methods and apparatus.

In the above described prior coil heating operations the cost of furnishing and maintaining the inner covers and of handling them during the operation of a furnace is very substantial. Accordingly it is one object of the present invention to provide a furnace structure for heating coils of strip metal, or other metal articles, within a protective or other type of special atmosphere wherein the use of inner covers is eliminated.

Other objects of our invention include the provision of a highly efficient furnace structure for heating coils of strip metal which is well adapted for single frunace installations and which also may readily be paired with a second furnace structure to provide a regenerative heating .arrangement whereby the desired treatment may be effected at very low cost and in a relatively short time for a given output. A further object of our invention is the provision of an improved method of and apparatus for transferring heat from a heat source to one or more coils of strip metal which achieves readily controlled, rapid and uniform heating and/ or cooling of the coil or coils.

The above and other objects of our invention will appear from the following description of one embodiment thereof, reference being had to the accompanying drawings in which:

FIGURE 1 is a plan view showing two of our improved furnaces arranged for regenerative heating, portions of the structure being broken away for clearness of illustration.

FIGURE 2 is a vertical cross-sectional view taken substantially on line 22 of FIGURE 1 on a slightly larger scale and showing the valves etc., in the'positions they assume when the charge in the right hand one of the pair of furnaces is being regeneratively preheated, and the charge in the left hand furnace is being cooled, by circulating, the total atmosphere in the two furnaces.

FIGURE 3 is an enlarged fragmentary cross sectional view taken substantially on line 3-3 of FIGURE 1 and illustrating the atmosphere distributing blades or vanes and the radiant heating tubes.

FIGURE 4 is an illustrative schematic view showing the double regenerative furnace arrangement of FIG- URES 1 and 2 with the valves, etc. in the positions they assume when the apparatus is being started up, the charge in left hand furnace being ready to be heated and the charge on the right hand frunace base being ready for preheating in the next operation.

FIGURE 5 is an illustrative schematic view similar to FIGURE 4 but showing the valves etc., in the positions they assume, after heating of the left hand charge is completed and during circulation of the total atmosphere between the two furnaces, the charge in the left hand furnace being cooled and the charge in the right hand furnace being regeneratively preheated by heat from the left hand furnace charge.

FIGURE 6 is an illustrative schematic view similar to FIGURES 4 and 5 but showing the valves etc., in the positions they assume when the atmosphere in the right hand furnace is being internally circulated over the heat source in the furnace bell to heat the charge and the charge in the left hand furnace is being cooled by circulation of the atmosphere through the furnace chamber and the external cooling means.

FIGURE 7 is a vertical cross sectional view of a single furnace incorporating our improved features and adapted for heating single open coils of strip metal.

As illustrated in the drawings our invention is incorporated in a double regenerative furnace installation particularly adapted for annealing tight wound coils of strip metal. One of the furnaces is seen on the left hand side of FIGURES 1 and 2 and is generally indicated at A and'the other furnace is seen on the right hand side of the views and is indicated at B. As the furnaces are substantially identical in form and general arrangement reference characters will be used in referring to similar parts. Thus, each furnace has a base structure 1 and a sealing trough 2 extends around the periphery thereof. Removable furnace bells, generally indicate-d at F and F respectively, are adapted to be supported on the bases 1 of furnaces A and B and each has a depending sealing flange 3 which forms a seal in association with a suitable sealing material it; in its trough 2 when the furnaces are in position on their ases.

A charge support 5 is supported on the base 1 and, as illustrated, includes a top plate 6 and a bottom plate 7 spaced apart by a plurality of radial ribs 8 whereby an atmosphere passage is provided between the plates 6 and 7. As illustrated in furnace B in FIGURES 1 and 2 the top plate 6 is imperforate while the bottom plate 7 has a central opening 9 which overlies a center opening 10 in the furnace base 1. In furnace A of FIGURES 1 and 2 vent or cooling holes 6 are shown at the centers of certain of the coils C. In some cases such holes may be desirable to permit limited flow of atmosphere over the exposed surface of plate 6 to prevent overheating thereof by direct radiation from the radiant heating tubes 12. Such holes would, of course, be placed at all locations on plate 6 where such cooling is desired. The charge in furnace A comprises a group of eight tight coils C of strip metal supported on the top plate 6 of the charge support with their axes vertical and in spaced apart relation to each other. In like manner the charge shown in furnace B comprises a similar group of coils C. It will be understood that the size and number of coils in any given charge may vary from one upwardly depend- 'ing on the size of the coils. Also as will be explained later, our apparatus may readily be adapted for heating "open coils of strip metal in apparatus such as is shown in FIGURE 7.

Supported in the upper portion of the furnace bells F and F, and extending radially inwardly through the side walls 11 thereof, are the hair pin shaped radiant combustion tubes generally indicated at 12. Each of these tubes has a lower inlet leg 13, a return bend portion 14 and an upper outlet leg 15. Fuel burners 16 are connected to the outer ends of the bottom legs 13 and upwardly the extending stacks 17 are adapted to carry away the products of combustion from the upper outlet legs of the combustion tubes 12. Suitable gas and air supply headers or manifolds 18 and 19 are connected to the burners 1 6 to supply the desired combustible mixture thereto and when the mixture burns in the tubes they are heated throughout the length of both legs in well known manner.

As best seen in FIGURE 3, the upper and lower legs 13 and 15 of the combustion tubes 12 are offset so that they do not lie directly one above the other and so that 'each leg has an unimpeded path for heat radiation directly downwardly to the charge in the furnace. The inner ends of combustion tubes 12 are supported by a ring member 20 which is in turn carried by rods 21. These rods extend upwardly to and are supported by transverse bars 22 which extend across but do not block the furnace inlet opening 23. As the tubes 12 extend transversely of the furnace chamber below the top wall 11' of the furnace bell (F or F) an atmosphere plenum chamber is provided betwen the top surfaces of tubes 12 and the inner surface of top wall 11'.

A plurality .of radially extending, circumferentially spaced inclined diffusing vanes or baflies, generally indicated at 25, extend transversely of the furnace bells and are supported at their outer ends at the side walls 11 of each of the furnace bells F and F. These vanes 25 are I supported at their inner ends on a center closure plate or disc 26 which is carried by the vertical bars 21 above the inner ends of the combustion tubes 12. In addition to serving as a support for the inner ends of the diffusion vanes or baflles 25 the disc 26 serves to block the passage of atmosphere downwardly into the furnace chamber through the generally circular opening defined by the inner ends of the radial combustion tubes 12.

As seen in FIGURE 1, the vanes 25 taper inwardly, being widest at their outer ends, and, as seen in FIGURE 3, each vane is provided at its upper edge with an upwardly extending flange 27 and at its lower edge with a downwardly extending flange 28. The main body portion 29 of each vane is inclined slightly to the horizontal and the vanes are disposed in to overlapping relation with each other so that atmosphere which enters the upper end of the furnace bells F or F through the inlet opening 23 can only exit therefrom by passing through the spaces between the edges of the vanes 25 in the general direction seen by the arrows in FIGURE 3.

By varying the vertical gap or spacing between the overlapping edges of adjacent vanes 25 the flow of atmosphere through the vanes may be so controlled and distributed that the desired flow over the radiant combustion tubes 12 will be obtained. Preferably, the vertical gap 30 betwen adjacent vanes 25 is greater at the outer edges of the vanes than at their inner edges. For example, if the vertical height of space 30 is about 2" at the outer ends of vanes 25 it could advantageously be about 1" at the inner ends thereof. This arrangement gives a uniform heating of the entire body of atmosphere flowing over the combustion tubes 12 because a relatively smaller volume will pass through the narrower portions of gaps 30 over the area adjacent the inner ends of the combustion tubes 12 where they are spaced much closer together than they are at their outer ends and where the heating area is accordingly more concentrated.

Referring now particularly to the right hand furnace B, an atmosphere outlet pipe or conduit 33 extends from the center furnace outlet opening 10 to the atmosphere circulating blower 34. A vertical pipe 35 extends upwardly from the outlet of the blower 34 to the horizontal return pipe 36 which connects to the furnace bell F at the top inlet opening 23. A main heat shut-off valve 37 (seen in closed position in FIGURE 2) is positioned in the vertical pipe 35 above the blower 34 and a cooler bypass pipe 38 extends from a point below valve 37 back to pipe 35 at a point above valve 37.

An atmosphere cooling unit, indicated at 39, is positioned in pipe 38 and is adapted to cool atmosphere flowing therethrough. This cooler unit may be of any suitable type, for example, a water or air cooled heat exchanger adapted to extract heat from the atmosphere which is by-passed from the pipe 35 through pipe 38 and returned back to the pipe 35 above the valve 37. A cooler shut-off valve 40 (seen in closed position in FIGURE 2) is located in the pipe 38 on the entering side of cooler 39, and, when this valve is closed, no atmosphere can flow through the cooler 39, In FIGURE 2 the pipe 38 and cooler 39 have been rotated counter clockwise from their true position seen in FIGURE 1 on to section line 2-2 of FIGURE 1 for clearness of illustration.

A regenerative flow connection pipe 41 leads olf from vertical pipe 35 below the valve 37 and the horizontal regenerative flow pipe 42 (FIGURE 1) is connected to pipe 41 through the vertical lift disc type valve generally indicated at V. This valve V includes a housing 43 (FIG- URE 2), a seating trough 44, a valve disc member 45 having a downwardly depending flange portion 46 adapted to have sealing engagement with a suitable sealing material in trough 44 when the valve is closed, and a vertically extending valve rod 47 which projects through and is movable in the gas tight bushing 48 in housing 43. A rack 49 at the upper end of rod 47 is adapted to be driven by suitable gears 50 which in turn are driven by the motor 51, thus lifting and lowering valve disc 45 be tween open and closed positions.

As seen in FIGURE 2 the valve disc 45 is in its upper or valve open position and there can be a free flow of atmosphere from the pipe 41 through the valve housing 43 and into the horizontal regenerative flow pipe 42. When the motor 51 is opera-ted to lower the valve rod 47 and valve disc 45 into the closed position (seen in phantom lines in FIGURE 2) the connection between the vertical pipe 35 and the regenerative flow pipe 42 is closed and there can be no flow through pipes 41 and 42.

In a manner similarto that just described in connection with furnace B, the left hand furnace A is also provided with an atmosphere outlet pipe or conduit 55 which extends to the blower 56, the outlet or which is connected to a vertical pipe 57 which in turn joins the horizontal return pipe 58 which connects to the top of the furnace bell F through its inlet opening 23.

A cooler by-pass pipe 61, similar to cooler by-pass pipe 38 of furnace B, extends around the main heat shutoff valve 37' (which is not seen in FIGURES 1 and 2 of the drawings but is shown in FIGURES 4-6) in vertical pipe 57 in the same manner as pipe 38 extends around the main heat shut-off valve 37 in vertical pipe 35 of furnace B. An atmosphere cooler unit 62 is interposed in pipe 61 and a shut-off valve 40 (see FIGURES 4-6), similar to valve 40 in pipe 38, is provided for preventing flow through the cooler unit 62 when such is not desired.

As the horizontal regenerative flow pipe 42 connects to the vertical pipe 57 at a point above a main heat shut-off valve 37 an atmosphere connection is provided between the furnaces A and B when the valve 37 is closed, valve V is open, and the valve 37 in vertical pipe 57 is also closed. This connection is from the bottom outlet opening in the base of furnace B through outlet pipe 33 and blower 34 to vertical pipe 35, then through the regenerative flow connecting pipe 41 and the valve V, to and through the horizontal regenerative flow pipe 42, and to and through vertical pipe 57 to horizontal return pipe 58 which in turn is connected to the top opening 23 in furnace bell F of furnace A.

A regenerative flow connecting pipe 59 extends from the vertical pipe 57 just above the outlet of the blower 56 and below the main heat shut-off valve 37. This pipe 59 extends to the housing of the disc type valve V which is similar in all respects to the previously described disc valve V and which controls the flow of atmosphere between the connecting pipe 59 and the horizontal regenerative flow pipe 60. As seen in FIGURES 1 and 2, pipe 60 is connected to the vertical pipe 35 above the heat shutoff valve 37 and thus the regenerative flow connections between the furnaces A and B are completed through pipe 36.

As illustrated in FIGURE 2, the connections between furnaces A and B are set for the regenerative heating operation and, when both blowers 34 and 56 are operating,

the valve 37 and its corresponding valve 37 are both closed, the valves V and V are both open, and the valve 40 in the cooler by-pass pipe 38 and its corresponding valve 40 in cooler by-pass pipe 61 are both closed, the atmosphere flow is downwardly out of furnace B through the center bottom opening 10, through pipe 33, blower 34,

pipe 35, pipe 41, valve V, pipe 42, pipe 57, and pipe 58 into the furnace bell F through its top center opening 23.

After the atmosphere has passed downwardly through the furnace chamber formed by the furnace bell F of furnace A it exits through the center outlet opening 10 and passes through pipe 55, blower 56, pipe 57, pipe 59,

valve V, pipe 60, and back to furnace bell F of furnace B through pipe 36 and top center opening 23.

Referring now to FIGURES 4, 5 and 6, the operation of the above described apparatus to anneal tight coils of strip steel will be explained. In FIGURE 4 the furnace bell F is in position on the base 1 of the left hand furnace A and the furnace bell F of furnace B has been removed from its base 1. The charge of coils supported on the coil support of furnace A is indicated at C while the charge of coils for furnace B is indicated at C. The main heat shut-off valve 37 of furnace A is open, the disc valves V and V are both closed, the cooler shut-off valve 40' is also closed, and blower 56 is operating while blower 34 is idle.

As shown in FIGURE 4 the apparatus may be deemed to be in its starting up condition. The charges C and C are both cold and the cycle of heating and cooling operations is just starting. As the blower 56 is operating and as the radiant tubes of furnace A have been fired, the circulation of heated atmosphere which is effected through furnace A by the blower 56 will rapidly and uniformly raise the temperature of the charge C to the desired point. As seen by the arrows in FIGURE 4, and is evident from the fact that the valves 40 and V are closed, the flow of atmosphere caused by blower 56 is entirely through the furnace A.

While the heating of charge C is going on the furnace bell F of furnace B is placed in position on its base 1 and, after the heating operation has been completed on charge C in furnace A, the heat shut- ofi valves 37 and 37 are both closed, the disc valves V and V are both opened,

and the cooler shut-off valves 40 and 40 are both closed. Now the valves, etc. are in the positions shown in FIG- URE 5 and when both blowers 34 and 56 are operated atmosphere will enter the top of furnace A through pipe 58, and will pass over the heated charge C therein and extract heat therefrom. The thus heated atmosphere will then move through pipe 55, blower 56, pipe 59, open disc valve V, pipe 60, the upper portion of pipe 35, and through the horizontal return pipe 36 into the furnace bell F. The blower 34 is effective to assist in moving the atmosphere downwardly through the furnace B where it preheats the cold charge C and exits through the pipe 33. From the blower 34 the atmosphere passes through pipes 35 and 41, open disc valve V, pipes 42 and 57, and backing into the top of'furnace A through horizontal return pipe 58.

As the entire volume of the atmosphere in both furnaces A and B circulates in the above described path the hot charge C in furnace A is cooled and the cold charge C in furnace B is preheated. This operation is continued until the temperatures of the charges C and C are substantially equalized. At this time the several valves of the apparatus are placed in the positions shown in FIG- URE 6, i.e., the heat shut-off valve 37 of furnace A is closed while the coresponding valve 37 of furnace B is open, the cooler shut-off valve 40 of furnace A is open while cooler shut-off valve 40 of furnace B is closed, and the disc valves V and V are both closed.

After the temperatures of the charges C and C have been equalized by the regenerative heat and cooling operation illustrated in FIGURE 5 it is desired to further reduce the temperature of the annealed charge C in furnace A down substantially to room temperature and to subject the charge C in furnace B to the desired annealing or other heat treatment. Accordingly, with the valves set as shown in FIGURE 6, with cooler 62 in operation to extract heat and reduce the temperature of atmosphere circulating therethrough, and with the combustion tubes in furnace bell F of furnace B fired, operation of the blower 56 will circulate the atmosphere of furnace A over the charge C and through the cooler 62 while operation of the blower 34 will independently circulate the atmosphere of furnace B rapidly over the combustion tubes and in heat transfer relationship with the charge C.

Thus the annealed charge C in furnace A may be rapidly cooled to a temperature at which the furnace bell F may be removed and the charge C taken away and a new charge placed on the base 1. While this is taking place the heating of the charge C in furnace B continues until the desired treatment is effected. By the time the heating of the charge C is completed in furnace B a new charge C will have been positioned on the base 1 of furnace A and its furnace bell F will have been replaced. Now, when the valves are set in the positions of FIGURE 5 and the blowers 34 and 56 are operated regenerative heating of the new charge C in furnace A will take place with concurrent cooling of the hot charge C in furnace B.

As has been previously indicated the furnace bells F and F are removable from the bases on which they are supported during a cycle of operation. As best seen in FIGURE 2, the furnace 'bell F and the horizontal return pipe 36 which is secured to the top wall 11 thereof are removable from the base 1 as a unit. Suitable lifting means,- not shown, is provided and, when the bell F is lifted vertically, the flange 3 will be lifted out of the sealing trough 2. To prevent leakage at the connection between the return pipe 36 and the top end of the vertical pipe 35 a similar seal arrangement is provided in which a trough 65 is carried by and extends around the upper end of pipe 35 and the lower end of pipe 36 is provided with a depending flange 66 which, when the bell F is positioned on the base 1, extends into trough 65 in sealing relation with a suitable sealing material 67 continued therein. A similar seal is provided between the horizontal return pipe 58 of furnace bell F and vertical pipe 57.

7 'These seals are not seen in FIGURES 1 and 2 but are schematically indicated at 65', 66' on FIGURES 46. The sealing trough and flange 65 and 66 are also schematically indicated on these figuresvas are the seals 2-3 between the furnace bells F and F and their respective bases 1.

By providing the external coolers 39 and 62, together with the regenerative heating and cooling connections which are illustrated in FIGURE 5, an extremely elficient operation, as far as fuel consumption is concerned, is obtained and, by virtue of the rapid final cooling which is effected by the external coolers, there is no delay or tying up of the furnace bases while waiting for a charge to cool thereon.

Because of the effective initial cooling of the charge and the rapid final cooling by the external cooler means, the necessity for inner covers, which in the prior practice were left in place over the charges after the furnace bells were removed in order to maintain the protective atmosphere around the charge during cooling, is completely eliminated;

FIGURE 7 is a vertical section view illustrating our invention as incorporated in a single furnace, as distinguished from the double regenerative arrangement of FIGURES 1 and 2, in which the charge support is arranged to receive an open coil of strip metal and to direct vthe flow of atmosphere through the spaces between the laps thereof. In this apparatus a furnace bell F" is removably supported on a base structure 70. The seal between the bell and the base, the arrangement of radiant heating tubes in the top portion of the furnace chamber and the means for diffusing and controlling the flow of atmosphere over the combustion tubes may be substantially the same as that previously described.

The base 70 is provided with a bottom outlet opening 71 from which an outlet pipe 72 leads to the inlet of a .blower 73. The outlet of blower 73 is connected to a vertical pipe 74 which is connected at its upper end, through a seal generally indicated at 75, to the horizontal return pipe 76. As the pipe 76 is integral with the furnace bell F", when the bell is lifted off from the base 70 the pipe 76 will also be removed and the connection between pipes 74 and 76 at the seal 75 will be broken. A main heat control valve 77 (shown in open position in FIGURE 7) is positioned in the pipe 74 and is adapted to regulate the flow of atmosphere therethrough. The cooler by-pass pipe 78 leads off from pipe 74 below the valve 77 and returns to pipe 74 above the valve 77. Interposed in pipe 78 is a cooler unit '79 (similar to cooler units 39 and 62 previously described) and the cooler flow control and shut-off valve 80 (shown in closed position) is inserted in pipe 78 ahead of the cooler unit 79.

The charge illustrated in FIGURE 7 is a single open coil C" in which the laps 81 of the strip metal are separated by gaps or spaces 82 thus providing passageways through which atmosphere may pass. The coil C is supported on a coil support and plenum unit generally indicated at P which includes a circular outer wall 83 and plurality of vertical radially extending coil supporting webs or flanges 84 extending inwardly therefrom. A center closure plate 85, slightly larger than the center opening in the coil C" is supported at the inner ends of the webs 84 and the outer periphery of coil C" rests upon an outer ring member 86 which is mounted at the upper edge of wall 83. An inclined or dished circular baffle plate 87 extends downwardly and inwardly from the top of ring 83 to the central opening in unit P which is defined by the inner ends of radial webs 84 and overlies, and is substantially the same size as, the bottom opening 71 in base 70.

In the operation of the single furnace unit of FIGURE 7, assuming that the main heat control valve 77 is open and cooler control valve 80 is closed as shown, and further assuming that the combustion tubes in the upper .portion of furnace bell F'" are fired and heated, when damage to the charge.

.of the valves 37 and 37' the blower 73 is operated atmosphere from the furnace chamber is drawn through outlet pipe 72, moved upwardly through pipe 74 and back into the center opening in the top wall of furnace bell F" through pipe 76. This atmosphere is distributed and diifused by the vanes in the top of bell F and passes over the radiant tubes and is heated thereby. As the center opening in open coil C" is closed by the baffle plate 85, and as the space at the outside of plenum P is closed by outer wall 83 thereof, all of the atmosphere which passes over the combustion tubes :must flow downwardly through the spaces 82 between the laps of the open coil C heating same by convection transfer of heat thereto. Radiant heat direct from the combustion tubes is also effective to heat the upper end of coil C" and the elevated temperature of this portion of the coil caused by such radiant heat transfer, will also transmit additional heat to the atmosphere as it enters the spaces between the laps of the coil.

After the desired heating operation has been completed the heat control valve 77 is closed and the cooler control valve 80 is opened and circulation of the atmosphere is continued until the temperature of the coil C is reduced to the desired value, it being understood that the time required for this to take place is greatly reduced by the cooling of the circulating atmosphere which is effected by the cooler unit 79.

As has been previously noted, our invention may also be incorporated in a single furnace designed for heating tight coils of strip metal. In such an embodiment the coil support would be similar to that shown in the furnaces of FIGURES 1 and 2 while the rest of the structure would be substantially identical with that of FIGURE 7.

In the operation of our furnaces, either single or regenerative, after a heating cycle has been performed and the charge is to be cooled by circulating the protective or other special atmosphere in the furnace chamber through the cooler by-pass pipe and cooler unit, it is important that the flow of the cool atmosphere into the heated furnace chamber be carefully regulated so that a sudden and severe pressure drop will not take place within the chamber with resulting forcing in of outside air through the seals between the furance bell and base and between the detachable pipe sections. Such inflow of air is of course extremely undesirable and might ruin the entire charge by oxidation.

The desired regulation may be accomplished, referring to FIGURE 7 for purposes of illustration, by gradually closing the main heat control valve 77 and simultaneously gradually opening of the cooler control valve 80 in such a manner that at first the circulating atmosphere is only slightly cooled. By regulating the rate of movement of these valves so that the cooling of the circulating gas is affected in such a manner that there is never a sufiicient pressure differential between the inside of the furnace bell F" and the outside thereof to force air in through the seals, the changeover from the circulation of heated atmosphere to the circulation of cooling atmosphere may be effected in a minimum time and without danger of This actuation of the valves 77 and 80 may be effected manually or by properly cou trolled power means which, for example, operates in response to the pressure differential between the inside and the outside of the furance bell F" and does not permit this differential to exceed a predetermined safe value.

The above type of control of the operation of the flow regulating valves may also be utilized in the regenerative apparatus of FIGURES 1 and 2 when the preheating cycle illustrated in FIGURE 5 is initiated. Thus the closing into their fully closed positions is preferably effected gradually so that the temperature of the atmosphere from bell F which enters bell F through return pipe 58 will not be so cool as to cause a dangerous pressure differential to occur between the inside and outside of hell F and, in like manner, so that the heated atmosphere from hell F that is conveyed to hell F for preheating purposes will not be so hot initially as to cause rapid expansion of the atmosphere in the bell P which might force atmosphere out through the seals thereof.

The atmosphere diffuser in the upper part of the furnace bells which, as illustrated, is made up of a plurality of radial vanes 25 (see bell F in FIGURE 2) serves to diffuse and distribute the atmosphere which enters the plenum or space in the top of the bell above the combustion tubes 12 through the inlet opening 23. This diffusion and distribution is important in that it permits the flow of atmosphere over the radial combustion tubes 1-2 to be so controlled that the tubes are uniformly cooled, thus preventing undesirable relatively hot and cool areas thereof. The arrangement of our apparatus, wherein the source of radiant heat (the tubes 12) is directly above the exposed upper ends of the coils to be heated, enables heat to be transferred to the end-s of the coils rapidly and efficiently by direct radiation. It is well understood in the coil heating art that heat applied to the ends of a coil is much more effective in raising the temperature of the entire mass of the coil than heat applied to the outside or inside cylindrical surfaces of the coil. This is because heat applied to the ends travels rapidly inwardly into the coil by conduction whereas the spaces and relatively poor contact between adjacent laps of a coil are a serious bar to the travel of heat radially from the inner or outer cylindrical surfaces of the coil.

Thus, by applying heat by direct radiation to the top end of the coil a rapid heat transfer is effected. As the radiant heat from the tubes 12 could raise the temperature of the top end of a coil to too high a value it is important that the flow of atmosphere, after it leaves the combustion tubes 12, be over and across the upper ends of the coils. This flow serves two purposes, i.e., heat is transferred to the atmosphere from the hot ends of the coils and the atmosphere serves to cool the upper ends of the coils and prevent possible overheating thereof.

As the hot atmosphere passes downward-1y in the furnace chamber F and then flows radially inwardly through the space between top and bottom plates 6 and 7 of the coil support heat is transferred from the atmosphere by convection to the top plate 6 and then by conduction to the bottom ends of the coils C for rapid travel upwardly into the body of the coil.

By the described arrangement of heating means, coil support means, and atmosphere flow control means a rapid and highly eflicient heating of a charge (as illustrated a coil or coils of strip metal) in a furnace chamber may be obtained. By far the largest proportion of the total heat transferred into the interior coils travels vertically up or down from the bottom or top ends of the coils which, as is well known, is the most efficient way to transfer heat to a coil .of strip material. The atmosphere flow control means of our apparatus provides effective protection for combusion tubes or other source of radiant heat and, by combining our efiicient heating with regenerative and/or direct atmosphere cooling it is possible to eliminate the use of inner covers with their accompanying expense, handling problems, etc.

Although we have illustrated and described in considerable detail certain particular embodiments of our invention it will be understood that variations and modifications may be made in the specific form and arrangement of the parts and elements which make up our improved heating apparatus and in the particular sequence and combinations of steps of our improved procedure. Accordingly, we do not wish to be limited to the apparatus and processes specifically illustrated and described herein but claim as our invention all embodiments thereof coming within the scope of the appended claims.

We claim:

1. Apparatus for heating metal objects including a base, a charge support on said base, a furnace bell on said base forming an enclosed furnace chamber therewith, said furnace bell having a top opening, said base having a bottom 10 opening and said charge support being adapted to support a charge in said furnace chamber, atmosphere circulating means connecting said bottom opening in said base and said top opening in said furnace bell, heating means supported in said furnace bell and extending transversely thereof, said heating means having a radiant heating surface area disposed for direct radiant heating of a charge on said charge support, and atmosphere diffusion means comprising a plurality of inwardly extending inclined vanes having their adjacent longitudinal edges spaced apart and .being supported by said furnace bell above said heating means on the side thereof opposite said radiant heating surface area.

2. Apparatus for heating metal objects as defined in claim 1 in which the heating means comprises a plurality of inwardly extending, spaced apart combustion tubes supported by said furnace bell above said charge support.

3. Apparatus for heating metal objects as defined in claim 2 in which said spaced apart longitudinal edges of said vanes provide atmosphere passages there'between and said atmosphere passages diminish in width from the outer to the inner ends of said vanes.

4. Apparatus for heating metal objects including a base, a charge support on said base, a furnace bell on said base forming a furnace chamber therewith and including a side wall and a top wall having a top atmosphere inlet opening, said base having a bottom atmosphere outlet opening and said charge support being adapted to support a charge above said base and to form a passage through which the atmosphere in said furnace chamber may pass from said furnace chamber to said bottom opening in said base, atmosphere circulating conduit means connecting said bottom opening in said base and said top opening in said furnace bell, blower means for circulating the furnace chamber atmosphere through said conduit and said furnace chamber, heating means in the upper portion of said furnace bell comprising a plurality of combustion tubes supported in said side wall of said furnace and extending transversely thereof and having inlet and outlet ends outside of said bell, said combustion tubes having their lower surfaces exposed for direct radiant heating of a charge on said charge support and having their upper surfaces disposed below said top wall of said furnace bell whereby an atmosphere plenum chamber is formed between said combustion tubes and said furnace bell top wall, and atmosphere diffusion means in said plenum chamber above said heating means comprising a plurality of radially inwardly extending inclined vanes supported at their outer ends on said side wall of said furnace bell and having their adjacent longitudinal edges vertically spaced apart to provide atmosphere passages therebetween.

5. Atmosphere for heating metal objects as defined in claim -4 in which said atmosphere passages between said adjacent longitudinal edges of said inclined vanes vary in width from the outer to the inner ends of said vanes.

6. Apparatus for heating metal objects as defined in claim 4 in which said vanes are positioned to direct substantially all of the atmosphere entering the furnace chamber through said top inlet opening to and over said combustion tubes.

7. Apparatus for heating metal objects as defined in claim 4 in which said charge support includes a charge supporting plate portion supported above said base and having its outer periphery spaced inwardly from said side wall of said furnace bell, said plate portion being disposed to direct the atmosphere circulated by said blower means inwardly to said bottom outlet opening below said plate portion and being provided with one or more vent holes positioned to permit limited flow of atmosphere therethrough for cooling an adjacent area of said plate portion which is not covered by the furnace charge and is therefore exposed to direct radiant heating from said heating means.

8. Apparatus for heating metal objects as defined in claim 4 including an atmosphere cooler by-pass pipe extending from said atmosphere circulating conduit at one point and rejoining said conduit at another point closer to said top opening than said one point, atmosphere cooling means on said cooler by-pass pipe, valve means in said atmosphere circulating conduit between said two points of connection of said cooling by-pass pipe thereto for controlling the flow of atmosphere through said conduit, valve means in said atmosphere cooling by-pass pipe for controlling the flow of said atmosphere therethrough, and means for operating said valve means whereby when said valve in said atmosphere circulating conduit is closed said valve in said atmosphere cooling by-pass pipe is opened and vice versa.

9. Apparatus for heating metal objects including two adjacently disposed furnace bases, two furnace bells adapted to be removably supported on said furnace bases to form enclosed furnace chambers therewith, each of said furnace bells having a top center opening, each of said furnace bases having a bottom center opening, atmosphere circulating conduits adapted to connect each of said bottom center openings in said furnace bases with the said top center opening in the furnace bell supported thereon, heating means supported in each of said furnace bells, atmosphere cooling by-pass pipes extending from one point on each of said atmosphere circulating conduits to a point thereon closer to the furnace bell top center opening with which the conduit is connected, a main heat shut-off valve ineach of said atmosphere circulating conduits between said points of connection of said atmosphere cooling by-pass pipes therewith, atmosphere cooling means in each of said atmosphere cooling by-pass pipes, a cooler flow shut-off valve in each of said atmosphere cooling by-pass pipes, regenerative flow connecting pipes extending from each of said atmosphere circulating conduits on one side of the said main heat shut-off valve therein to the other of said atmosphere circulating conduits on the heating of a charge in the furnace chamber, and each of said furnace bells includes atmosphere diffusion means extending transversely thereof above said combustion tubes and adapted to distribute and control the flow of atmosphere to and over said combustion tubes.

References Cited by the Examiner UNITED STATES PATENTS 2,093,381 9/1937 Mulford 266-5 2,161,162 6/1939 Harsch 266-5 2,222,244 11/1940 Simpson 263-36 2,477,796 8/ 1949 Germany 266-5 2,479,102 8/1949 Dailey 263-40 2,746,742 5/ 1956 Comley 266-5 2,752,148 6/1956 Kincaid et al. 266-5 3,032,326 5/1962 Hepburn 266-5 3,035,824 5/1962 Weaver 266-5 3,039,754 6/1962 Jones 266-5 3,065,117 11/1962 Brown et a1. 148-13 3,071,500 1/1963 Corbett et al 148-13 3,184,225 5/ 1965 Wilson 266-5 JOHN F. CAMPBELL, Primary Examiner.

DAVID L. RECK, Examiner. L. I. WESTFALL, R. O. DEAN, Assistant Examiners.

Claims (1)

1. APPARATUS FOR HEATING METAL OBJECTS INCLUDING A BASE, A CHARGE SUPPORT ON SAID BASE, A FURNACE BELT ON SAID BASE FORMING AN ENCLOSED FURNACE CHAMBER THEREWITH, SAID FURNACE BELL HAVING A TOP OPENING, SAID BASE HAVING A BOTTOM OPENING AND SAID CHARGE SUPPORT BEING ADAPTED TO SUPPORT A CHARGE IN SAID FURNACE CHAMBER, ATMOSPHERE CIRCULATING MEANS CONNECTING SAID BOTTOM OPENING IN SAID BASE AND SAID TOP OPENING IN SAID FURNACE BELL, HEATING MEANS SUPPORTED IN SAID FURNACE BELL AND EXTENDING TRANSVERSELY THEREOF, SAID HEATING MEANS HAVING A RADIANT HEATING SURFACE AREA DISPOSED FOR DIRECT RADIANT HEATING OF A CHARGE ON SAID CHARGE SUPPORT, AND ATMOSPHERE DIFFUSION MEANS COMPRISING A PLURALITY OF INWARDLY EXTENDING INCLINED VANES HAVING THEIR ADJACENT LONGITUDINAL EDGES SPACED APART AND BEING SUPPORTED BY SAID FURNACE BELL ABOVE SAID HEATING MEANS ON THE SIDE THEREOF OPPOSITE SAID RADIANT HEATING SURFACE AREA.

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