US2417063A - Rotating annular hearth annealing furnace - Google Patents

Description

March 11, 1947. V o. P. COOPER 2,417,063

ROTATING ANNULAR HEARTH ANNEALING FURNACE Fi led Au 5, 1943 2 Sheets-Sheet 2 R O T N E V m Dal/i0 Cooper 56 4.5 58 A We 4 915 44 Patented Mar. 11, 1947 UNITED STATES PATENT OFFICE ROTATING 'ANNULAR HEARTH ANNEALING FURNACE David P. CoopenYoungstown, Ohio, assignor, by

mesne assignments, to The Cold Metal Products Company, Youngstown, Ohio, a corporation of Ohio Application August 5, 1943, Serial No. 497,523

7 Claims.

. 1 a This invention relates to the art of annealing and, in particular, to the annealing of metal strip in coils. Specifically, it involves a novel furnace construction whereby the desired treat- I ment may be carried out rapidly and efficiently.

In the annealing of coils of strip as practiced heretofore, the coils are usually stacked up on a base to a height several times their diameter,

on elevated supports and subject them to heating from the bottom, sides and top. I also limit the height of the coils, when disposed on their sides with their axis vertical, to a value less than the diameter of the coil. This facilitates rapid penetration of the heat into the interior of the coil from the edges of the successive turns thereof and avoids the existence of marked differences in temperature between different portions of the coil.

My invention contemplates a novel form of annealing furnace including a circular hearth mounted for progressive movement through a heating chamber which is circular in plan. The hearth has elevated supports spaced circumferentially thereof adapted to receive enclosures for the coils of material te be annealed and I provide means for supplying a protective atmosphere to each enclosure continuously during its travel through the heating chamber. The heating chamber is provided with burners spaced circumferentially thereof and they are fired in such a manner as to provide several distinct zones in the complete circumference of the heating chamber, such as a preheating zone, a rapid heating and soaking zone, slow cooling zone and a rapid cooling zone.

Further objects, advantages and novel features of the invention will become apparent from the following detailed description and explanation which refer tothe accompanying drawings the preferred mode of procedure. In the drawings: i Figure 1 is a partial transverse section through the heating chamber and hearth showing the manner of supporting and driving the latter and the means for supplying a protective atmosphere to the coil enclosures disposed thereon;

Figure 2 is a horizontal sectional view, largely diagrammatic, taken on the plane of line 11-11- ofFigure 1, showing the hearth and the enclosures. thereon in plan; and

Figure 3 is a partial sectional view similarto Figure 2,showing a, portion thereof'to enlarged scale.

Referring now in detail to the drawings, the apparatus of my invention which is preferably employed for carry out the procedure thereof comprises a circular hearth Ill and a heating chamber H circular in plan concentric therewith. The heating chamber is composed of side walls l2 and I3 and a roof [4 built up of refractory brick and assembled within a suitable binding. The furnace binding includes buckstays l5, posts l5a,circumferential channels l6- and I1 and a sheathing of metal plate I8. Burners I9 extend into ports 20 formed in the side walls l2 and I3 and spaced circumferentially thereof, The center lines of the several burners are designated IS in Figure 2. The several burners are controlled in any suitable manner to provide a plurality of successive heating and cooling zones hereinafter referred to in greater detail.

l The hearth l0 comprises a plurality of segmental base plates 2l secured to spaced circular beams 22. The beams 22 have a bottomplate The hearth and heating chamber have cooperating baille flanges 3ll thereon. Thebase plates 2| have sealing channels 3| formed on the'edges thereof and sealing flanges 32 extend downwardly from the lower edges of the side walls l2 and I3 into these channels. The heating chamber is thus effectively sealed at all points between its two open ends.

through the heating chamber The hearth l includes a layer 88 of refractory brick on which piers 84 are laid up in spaced relation circumferentially of the hearth. A charge support in theform of a base 85 is disposed on each set of piers 84 and is adapted to receive a charge of material to be annealed, e. g., a coil 88 of metal strip. A cover 81 is disposed over the coil or coils on each base 85, thereby providing a, complete enclosure or retort'therefor. A sealing channel 88 is formed on the periphery of the base 85 and is adapted to receive the lower edge of the cover 81. It will be noted that the bases 85 are disposed at a level above that of the burners i9. The purpose and effect of this relative disposition will be referred to later.

It is desirable to maintain a protective atmosphere surrounding material being annealed, to prevent atmospheric oxidation thereof at elevated temperatures.

I accordingly provide means for supplying such atmosphere to each coil enclosure or retort continuously throughout its travel I provide an annular channel 89 extending around the furnace under the hearth Ill, having spaced flanges 40 and adapted to be partly filled with sealing fluid as shown in Figure 1, thus 'forming continuous gas-supply chambers 4| and 42. Pipe connections 43 and 44 extend from these chambers to-any convenient source of the gas to be used as the atmosphere in the coil enclosures.

In order to convey the desired gas atmosphere to the individual coil enclosures, I provide pipe connections 45 for each enclosure extending vertically through the hearth and the base 85. A transfer valve 45 is inserted in each piping connection and branches extending downwardly therefrom communicate respectively with the chambers 4| and 42. Thus by shifting the valve 46, one or the other of two special atmosphere gases may be supplied to the interior of the coil enclosures. Since the channel 39 and the chambers 4| and 42 are continuous the coilenclosures are maintained in communication with the gas supply throughout their travel around the full circle of the hearth. Vent pipes 48 extend upwardly through the hearth and the bases 35 and have valves .49 at the lower end thereof. The pipes 48 and valves 49 permit the coil enclosures to be purged of atmospheric air as the specialatmosphere gas is admitted.

The method of operation may best be explained by reference to Figure 2. If the hearth I0 is assumed to rotate in the direction indicated by the arrow 50, the portion of the travel of the hearth adjacent the end ,of the heating chamber may be considered the charging zone, as indicated by a legend on the drawing. a While a given charge support is in this zone, the coil or coils constituting the charge to be annealed may be placed thereon and a cover 81 disposed thereover. The valve 46 of the retort or enclosure in question is then opened to admit the special atmosphere, after opening the valve 49 to permit the esiape of atmospheric air trapped in the enclosure. The hearth is driven at a speed such that it makes a complete revolution in a matter of forty-eight hours orso. There is thus ample time to attend to the necessary preliminaries after depositing and enclosing the charge and before the sealed retort reaches the entering end 5| of the heating chamber. After the retort or enclosure has been thoroughly purged of atmospheric air, the valve 48 is closed. The valve 45 however is left open to maintain the retort in communication with the source of protective atmosphere.

charge when deposited on its supporting base, to

. a value less than its maximum diameter and preferably to a value about sixty per cent and not more than seventy-five per cent of the maximum diameter. This limits the thickness of metal through which heat must flow in the direction in which the mass is most easily penetrable, i. e., parallel to the axis of the coil. The charge, of course, maybe composed'of one or more coils but in either case, the ratio between the height of the charge and its maximum diameter as given above should be maintained-for best results.

The burners nearest the entering end of the heating chamber are fired in such a manner as -to maintain a preheating zone extending over sible, with due regard for the danger ,of damaging the retorts by burning or the like.

From-v the preheating zone, the retort passes into and through a rapid heating and soaking zone extending over about half the circumferential length of the heating chamber as indicated by a legend in Figure 2. In this zone, the burners l8 are adjusted to fire so as to cause the temperature of the charge to rise as rapidly as possibl to the desired maximum after which sufficient time is permitted for the temperature of the charge to equalize throughout the mass thereof without further increase. The rate of heating attainable in-both the preheating zone and the rapid heating zone is high because the combustion gases from the burners l9 have access to the retort at the bottom, the sides and on top thereof. This fact, together with the limitation on the height of the coil or coils, causes the heat-to flow into the central parts of the coil very rapidly from the edges of the successive turns thereof. The rate of heat in flow in this direction is much greater than that which takes place radially or normal to the successive turns of the coil.

After the charge has been brought to the desired maximum temperature and the temperatures of all portions thereof equalized, the heating stage of the annealing cycle has been completed and the charge is ready for gradual cooling. To this end, I maintain in the remainder of the circumferential length of the heating chamber II, a slow cooling zone and a, rapid erses the final or rapid cooling zone, by blowing cooling zone as indicated by legends in Figure 2. In the slow cooling zone, the burners I9 are adjusted to supply a very small amount of heat, i. e., less than that necessary to maintain the temperature of the charge against decrease by natural radiation.- As a result, the temperature of the charge decreases at a relatively low rate while it traverses the slow cooling zone. I effect a more rapid cooling of the charge while it trav- By'the time the charge reaches the exit end 52 of the furnace chamber it has been cooled below the temperature at which atmosheric oxifor supporting charges of material to be andation proceeds rapidly. The valve 46 may there-- fore be moved to closed position and the cover 31 removed. The charge is then lifted off by appropriate means while its support is traveling through the unloading zone indicated by a legend in Figure 2. When the charge has been removed,

the supporting base is ready to receive another,

coil of material to be annealed and the entire cycl is then repeated.

It will be understood that the travel of the hearth is preferably continuous so that fully annealed charges are'being delivered from the exit end 52 of the furnace in a steady stream while coils of strip to be annealed are being disposed successively on the charge supports as they traverse the charging zone. In a particular operation carried out according to my invention, the charges are heated to a temperature of about 1350 F. in the rapid heating and soaking zone, are cooled to about 1250 F. in the slow cooling zone and are finally cooled to about 500 F. or below in the rapid cooling" zone. It will be understood, however. that the temperature limits in various portions of the hearth travel .may be varied widely, depending on the characteristics desired in the fully annealed product.

It will be apparent from the 'foregoingdescription that my invention is characterized by important advantages over the practice previously followed in annealing strip and the apparatus available therefor; In theflrst place, by supporting the charges in elevated position and 'flring combustion gases beneath them as well as around the sides and over the top, I am able to eifect the heating of the charge at a rate considerably greater than that achieved heretofore V by supplying heat only or principally to the sides of the charge. My invention also makes itpossible to maintain-more nearly a uniform temperature throughout the charge because the height of the latter is less than the coil diameter and, since th heat flows readily into the coil from the exposed edges of the strip, both of which are subjected to heating, there can be no substantial difference between the temperatures on the interior of the coil and those on the exterior thereof. My invention also possesses the advantage that gas for maintaining a special atmosphere around the charge may be supplied continuously throughout the annealing cycle, even though the charge is moving constantly.

Although I have illustrated and described but a preferred embodiment and practice of my invention; it will be recognized that changes in the construction and procedure disclosed may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim: 4

1. An annealing furnace comprising a'chamber which is circular in plan, a circular hearth mounted for traveling movement through the chamber, burners in the chamber adjacent ,the level' of said hearth, and charge-supporting means spaced circumferentially around said hearth and positioned above the level of said burners, whereby heat is supplied to charges on said supports from the bottom as well as the sides and top thereof.

v is circular in plan, a circular hearth mounted for healed in circumferentially spaced relation around the hearth, atmosphere-supply pipes extending upwardly through said hearth and said supporting means, an annular gas chamber below said'hearth open at one side, a liquid seal for the open side of the gas chamber and connections extending from said pipes through said seal into the gas chamber.

3. A furnace comprising an elongated chamber, a hearth mounted for traveling through the chamber, means for supporting charges of material to be annealed in. spaced relation along said hearth, atmosphere-supply pipes extending upwardly through said hearth, a gas chamber below said hearth open at one side, a liquid seal for'the open side of the gas chamber and connections extending from said pipes through said seal into the gas chamber. x

4. .A furnace for annealing flat-rolled meta stock or the like comprising a chamber which is circular in plan, a circular hearth mounted for traveling movement through the chamber, charge enclosures spaced circumferentially around the hearth, an annular gas chamber below .said hearth open at one side, a liquid seal for saidopen side and pipe connections extending from the -intion of the hearth, an annular gas chamber below-- said hearth open at one side, a liquid seal for the open sideof saidgas-chamber and atmospheresupply pipes extending downwardly through the hearth and through said seal into the gas chamber.

6. An annealing furnace comprising a circular rotating hearth having charge supports spaced therearound, a heating chamber overlying a portion of the hearth, concentric annular gas chambers below said hearth open on one side, a liquid seal for the open sides of said gas chambers, at mosphere-supply pipes extending through the hearth with branches projecting through said seal into said gas chambers, respectively. and a transfer valve between each pipe and its branches. '7. An annealing furnace comprising a circular rotating hearth having charge supports spaced therearound, a heating chamber overlying a portion of the hearth, an annular gas chamber Resonances crrap The following references are of record in the file 01 this patent:

UNITED STATES PATENTS Number Name Date 1,638,908 Baker Aug. 16, 1927 1,843,336 Pike et al. Feb. 2, 1932 1,854,850 Linkenauger Apr. 19, 932 1,903,909 Cope et al. Apr. 18, 1933 2,074,662 McLay Mar. 23, 1937 699,528 Hunt'et a1 May 6, 1902 2,201,308 Edge May 21, 1940 1,825,790 Hansen Oct. 6, 1931

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