US2086970A - Annealing method and furnace therefor - Google Patents

Description

July 13, 1937. WILSON ANNEALING METHOD AND FURNACE THEREFOR 2 Sheets-Sheet 1 2 Sheets-Sheet 2 L. WILSON ANNEALING METHOD AND FURNACE THEREFOR Filed Feb. 23, 1955 r 1 /n I I Q/ AVr/QAAAAM 9 Jul 13, 1937.

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AM. (0 II Patented July 13, 1937 UNITED STATES ANNEALING METHOD AND FURNACE THEREFOR v Lee Wilson, Cleveland, Ohio Application February 23, 1935, sci-taint. -7,905

6 Claims.

This invention relates to annealing furnaces of the general type described in my U. S. Patent No. 1,952,402 and, specifically, to improvements in the construction of the furnace disclosed in said patent, and a new method of annealing adapted to be practiced with the aid of such improved furnace construction.

In the use of the furnace described in the patent before mentioned; I have discovered that the heat exchange tubes or mullies'which con- ;vey the hot gases of combustion along the side walls of the furnacecover, and which are made of heat resistant alloy in order to stand up under the extreme conditions oftemperature to which they aresubject, exhibit a considerabletendency to expand and even to elongate permanently. If these tubes are fixed at both ends, therefore, objectionable stresses will .be intro 'duced in the operation of the furnace. One object of the present invention, therefore, is to provide a furnace in which the heat exchange tubes are fixed at one end only, the other end being permitted to "float, and at the same time, toprovide a gas-tight connection between the 5 floating end and the furnace wall.

Certain difflculties were experienced with the furnace roof, furthermore, because of the passage therethrough of the outlets for the spent heating gases. A further object of the invention, therefore, is to provide a furnace having outlets forthe spent gases extending outwardly of the side walls and then upwardly thereof.

It has also been observed that in annealing stacks of-sheets of different heights, the rates. at which the temperatures of the various "portions of the stack rise are not entirely uniform. Another object of this invention, therefore, is to provide a method and means whereby uniform heating of stacks of various heights may be obtained. In this connection, I also provide a method and means whereby the desired uniformity of heating along the length of the stack may likewise be obtained.

Other objects and advantages of the invention will be pointed out in the following detailed description and the novel features ,thereof will be specifically set forth in the appended claims. for a complete understanding of the invention, in connection with the accompanying drawings illustrating a present preferred embodiment. In the drawings Figure 1 is a view partly in plan with a portion thereof shown in horizontal section, cer-, tain parts being omitted for clearness;

Reference is made to said description- Figure 2 is a side elevation with a'portion in I vertical section;

Figure 3 isa transverse sectional view taken along the line IIIIII of Figure 1; and

Figure 4 is an end elevation, Referring now in detail to the drawings, the furnace of my invention comprises a base Ill and a cover II. The base includes a structural frame I2 having a refractory hearth-I3 supported thereon. A sheet metal channel. I 4 extends around the edge of the hearth and is adapted to receive a depending flange I5 carried on the lower edges of the side walls of the cover I l, to provide a fluid seal by virtue of sealing fluid contained in the channel I4. The side walls of the cover II, indicated at I6, are composed of refractory material assembled within a structural frame IT. A roof [8' is formed by "a refractory arch sprung from the side walls I6, and a layer of insulating material I9 is superposed on the arch. End walls20 similar in character to the side walls I6 complete the enclosure provided by the cover II in cooperation with the base I 0. The hearth I3 carries a flat supporting plate 2|, conveniently a steel plate, which is adapted to-re'ceive the charge of material to betreated, indicated as a stack 22 of ,steel sheets. The cover ll, of course, is'lifted from the base I0 while the furnace is being charged. An inner cover 23 is first disposed over the charge. The lower edges of the cover cooperate with a groove or-recess 23a formed in the hearth I3 and adapted to be filled with sand, whereby to seal the interior ofthe' inner cover from the space out side it. The cover 23 comprises simply an open bottomed metallic shell, the top being formed by a flat plate with suitable bracing members attached thereto. When the charge 22 and the cover 23 have been placed in position, the cover H is lowered onto the base Ill. This operation is facilitated by guide pins 23- secured to and extending upwardly from the base I0 .and guide rings 23" secured to the lower edges of the cover II and adapted to slide down over the pins 23. 7

Referring again to'the construction of the .cover I l, the side walls I6 thereof are provided with a plurality of heat exchange tubes 24. Only a few of these are shown in the drawings, but there isa, continuous series of them on both sides of the cover. Although these tubes are shown vertical, they may be disposed in any convenient relation to the axes of the cover. The tubes'Zl, are reentrant, having generally a U-shape, the

lower ends being embedded in the refractory forming the side walls. The middle portions of the tubes extend upwardly of the side walls I6 and the upperends extend outwardly thereof through openings 25 which are larger than the tubes themselves. The tubes are thus fixed'only at their lower ends, the upper ends being permitted to float so that expansion of the tubes on heating, or permanent elongation thereof after considerable use, will not subject the tubes to any stress. Top lines 25 are connected to the upper ends ofthe tubes 24 to carry the spent heating gases upwardly of the furnace.

In order to seal the joints between the upper ends of the tubes 24 and the opening 25, I provide the lines 26 with L-shaped sleeves 21. The lower ends of the sleeve extend into the refractory side wall l6 and entirely enclose the outer ends of the holes 25. The upper ends of the sleeves are provided with sealing cups 28 adapted to contain sealing fluid. Sealing bells 29 carried on the flues 26 project dovmwardly into the cups 28 and the sealing fluid contained therein. Free expansion of the tubes 24 and the flues 26 is thus permitted, while the interior of the furnace is completelysealed from the atmosphere surrounding it. e

- The tubes 24 are disposed, as stated, along the side walls of the furnace cover, but preferably not on the ends, and, when combustion gases are passed through the tubes, the furnace charge is heated by convection and radiation to the anhealing temperature. Currents of hot gases are set up within the cover and these currents generally rise in the space between the'sides of the cover II and the inner cover 23, sweep over the top of the cover 23 and diverge toward the ends thereof from which they descend in the space between the ends of the inner cover and the cover II and then return to the lower portion of the space occupied by the tubes 24. The tubes may,

alternatively, extend inwardly of the end walls and along the. side walls, generally horizontally, by merely increasing the length of the elbows thereof to approximately the length of the cover.

Combustion gases for heating the interior of the furnace cover by passage through the tubes 24 are delivered to the latter by burners 30 projecting into the lower ends of the tubes. Air for combustion is delivered to the burners through manifolds 3|, by manifolds 32 extending along the lower edges of the side walls of the cover Individual valves 304; control the volume of air delivered to the burners from the manifolds. The lower ends of the tubes 24 are open for the induction of secondary air.

The manifolds 3| and 32 extend around one end of the cover as shown in Figure 4, and connect with Ts 33 and 34. The horizontal branchesof the Ts are connected to the manifolds by slip joints 35, which permit the manifolds to be moved laterally of the Ts without breaking the connection therebetween. Fexible hose connections may be used instead of the slip joints. The vertical'branch of the T 33 is connected to the discharge port of a blower 36 mounted on the end of the cover and adapted to be driven by a motor 3|- similarly mounted. -A gate valve 38 controls the volumeof air delivered to the manifolds 3| by the blower 34. This arrangement is provided for artificial cooling of the furnace as will be explained later. The T 34 is tapped into the 'T 33 above the valve 38 for supplying air to the burners during firing. Individual valves 39 in the horizontal branches of the T 34 permit the distribution of air blast between the two sides of the furnace and, therefore, the rates of combustion on such sides, to be varied. The vertical branch offthe T 34 includes a valve 34a.

The manifolds 3| and 32 are adjustably supported on brackets 40 extending outwardly from the side walls of the cover Clamping bolts extend through suitable holes in lugs depending from the manifold and slots in.the brackets, whereby the manifolds 3| and hence the burners 30, may be adjusted toward or away from the side walls. l6. This adjustment permits the hot spo or zone of maximum temperature of the combustion gases to be shifted along the tubes 24. With the burners in their extreme in position, the point of maximum combustion rate is obviously farther up the tubes 24 than when the burners are in their extreme outposition.. Be-

tween these two extremes, considerable latitude is afforded for placing the hot spot at the proper level, depending on the height of the stack 22, to supply the heat absorbedby the base plate and to insure that all portions along the height of the stack will have their temperature increased at substantially the samerate, whereby uniformity of heating and annealing is obtained.

The fuel supply for the burners 3|) includes gas manifolds 4| having individual valved connections 42 to the burners 30. The manifolds 4| are suspended on the manifolds 3| by these connections and move therewith. The manifolds 4| are connected to a T 43 through slip joints 44 and regulators 45, the latter serving. to maintain a constant pressure in the manifolds. The slip connections, of course, permit lateral adjustment of the manifolds. The T 43 is connected to a source of gaseous fuel by any convenient means such as a flexible hose line. Although the furnace disclosed herein is shown as adapted for gaseous fuel, the construction may be modified to burn other types of fuel such as liquid fuel.

By manipulating the valves controlling the supply of fuel to the individual burners, it is possible to vary the rate of combustion along the length of the side walls of the furnace. Considerable heat is absorbed by the ends of the sheets in the stack from the gaseous currents descending thereover as above explained, and I therefore prefer to adjust the fuel valves of the burners adja'cent the ends of the cover to supply less fuel to the burners than supplied by the valves of the burners toward the middle of the side walls. Overheating and welding of the sheets adjacent the ends isthus avoided, and uniformity of annealing assured. It is. sometimes desirable to cool the charge after annealing at a rate greater than that caused by natural radiation. To this end, valve 34a is closed and valve 38 opened, reversing their relacover to be observed when the latter is placed on the hearth or base. Conduits such as that indicated at 41, permit the introduction of an at- 2,086,970 portions of the charge is made possible with a resulting uniformity in the product, which is greatly to be desired. The proper adjustment of the points of maximum temperature may be easily obtained. as regards both the height and the length of the charge. The heat exchange tubes or muflles are mounted with one end floating to prevent stressing the latter as a result of expansion and contraction,

spirit of the invention or the scope of the follow;

ing claims.

I claim:

1. A furnace comprising a hearth, side and end walls and a roof, manifolds extending along the side walls for supplying an element of com bustion toburners spaced along said side walls, a

connection adjacent one of the end walls 'to a source of said element, and extensible joints between said'connections and said manifolds.

2. In a method of heating a furnace chamber to treat a'charge of material therein, the steps including introducing combustion gases into the chamber, confining them out of direct contact with said material,- and moving the point of delivery of the gases to vary the location of the hottest zone produced thereby.

.3. In a method of annealing in a liftable, openbottomed furnace chamber having side and end walls, to treat uniformly a charge of material therein, the steps including supplying combustion gases to the chamber at spaced points along the side walls, confining the gases out of contact with the material, and supplying a greater quantity of such gases per unit length of side wall to the middle portion thereof than to the portions adjacent the end walls.

4. In'a method of annealing in a liftable, openbottomed furnace chamber having side and end walls, to treat uniformly a charge of material therein,-the steps including supplying combusbut a perfect seal is maintained at all times to tion gases to the chamber at spaced points along y the side walls, and restricting the supply of such gases adjacent the end walls.

5. In a method of heating a charge of material 'in a chamber, the steps including introducing combustion gases into the chamber adjacent the bottom of the charge, confining them out of direct contact with said charge while conducting them upwardly alongside the charge, and shifting the point of delivery of said gases and, therefore, the point of maximum combustion rate, vertically of the charge to cause uniform heating of the material throughout the height of the charge. 1

6. An annealing furnace comprising a base adapted to receive a charge of material, a cover adapted to be positioned on the base to enclose the charge, heat-exchange tubes extending through the side wall of the cover adjacent the base, upwardly along the side wall, and outward--

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