US2509209A - Annealing furnace - Google Patents

Description

May .J, 1950 \A. J; CASTLE ANNEALING FURNACE 5 Sheets-Sheet 1 Filed Aug. 25. 1944 Ma? 30, 1950 A. J. cAs'rLE l 2,509,209

ANNEALING FURNACE Filed Aug. 25. 1944 5 Sheets-Sheet 2 May 30, 1950 A. J. CASTLE 2,509,209

ANNEALING FURNACE Filed Aug. 25. 1944 5 Sheets-Sheet 3 A. J. CASTLE NNEALING FURNACE May 30, 1950 5 Sheets-Sheet 5 Fgled Aug. 25. 1944 Patented May 30, 1.950

ANNEALING remmen Alfred J. Castle, Chicago, Ill., assigner to Inland Steel Company, a corporation of Delaware Application August 25, 1944, Serial No. 551,207

lIv'his invention relates to an annealing furnace. In the operation of open fired annealing furnaces for the handling of iron and steel products, such particularly as cold and tin mill products, it was heretofore necessary to fire g the furnaces slowly in order to procure uniform temperatures from top to bottom of the material being annealed y (which material will sometimes be referred to and these products were placed in stacks whichreached from the platform well toward the roof of the furnace. Furthermore the products were covered by metal hoods or covers which were sealed against air at theiredges by the use of sand or other material.

The furnaces were proportioned so that the walls were as close las practicable to the covers and these walls were lined with refractory material which, during operation of the furnace, radiated land reflected radiant heat. The proportions of the furnaces, however, differed somewhat, depending on the shape and character of the products to be annealed therein.

The furnaces have been red in different manners. In vone type the flame was directed vertically near a side wall of the furnace. In another type of furnace the flame was directedy horizontally beneath the platform. This method does not permit faster firing, however. When horizontally ring, a reducing or incompletely consumed gas was necessarily used to avoid overheating the platform itself. It was the general practice, due to inadequacy of the furnaces, to use heavy covers over the annealing material to avoid local overheating if the furnace was to be fired at its maximum rate. Ihese heavy covers delayed heat transfer and slowed down the annealing process.

Furnaces were also heated by internally fired tubes, this type being known as the radiant tube annealing furnace. In the radiant tube furnaces firing was slow because the top temperature within the tube was limited, by the characteristics of the metal of the tube, to 1600? to about 1800 F.

It was characteristic of the past processes that the top temperature of the material would tend to become unduly high before the bottom had reached the minimum annealing temperature. Therefore, firing was slowed after the peak per- 2 claims. (ci. 26a-2s) 2 missible temperature had been reached in the top material, and the work held in the furnace to obtain temperature equilibrium throughout. This, of course, slowed down the output of the furnace.

In the present apparatus and method the structure `of the furnace is basically the same as in previous open fired furnaces but means are pro- A vided in the side walls for breaking up convection currents and directing a greater proportion of the heat to the lower portion of the products being annealed. By correlating the position of the flame with respect to the wall and a heat' deflecting baille, and the relative size and position of theplatform cover and furnace walls, it has been found possible under plant operating conditions to maintain a temperature difference between the top and bottom of the material undergoing annealing to as little at 50-60 and with the lowest temperature at or above the minimum annealing temperature, and to maintain this relationship during the annealing operation while firing at a rate such that the time required for annealing is substantially reduced. Firing at an increased rate permits improved combustion with a higher combustion temperature. The higher firing rate also increases the lvelocity of the combustion gases. Heat transfer from these gases is improved with the increase in velocity. This is particularly true at the bottom of the furnace where increased heat transfer is especially desirable. It has likewise been possible to eliminate the heavy covers in cases where formerly they were required in the cold mill furnaces, and to substitute therefor covers only about`1/4 inch in thickness.

As a result of all of these factors, the'output of the cold mill furnaces has been multiplied as much as four to six times. For example, in a furnace Where the former output was approximately 1K2 ton per hour, the introduction of the present changes produced an output of as much A as 2 to 3 tons per hour.

In the tin mill furnaces firing was usually perpendicular and light covers were normally employed. In these furnaces, however, the output has been also greatly increased by the present invention, for example, from 1.4 tons per hour t0 3 tons per hour, using the same sized coils in each y case.

In its preferred form, the present invention comprises a vertically directed flame which impinges upon an inclined baille of refractory material having a, heat deflecting surface directing a substantial portion of the heat from the side wall to the cover. The particular angle depends upon the proportions of the furnace and the position and volume of the material being annealed.

The baffles establish a substantial radiating firing, and the reduction in available space, allincrease the velocity of the combustion gases, and the baiiies direct these toward the portion of the work where they are `most needed.

The invention is illustrated in the drawings in which Figure 1 is a view taken along -line I-I of Fig. 2 and showing an end elevation in section of a typical cold strip mill annealing furnace; Figure 2 is a longitudinal sectional elevation through the furnace; Figure 3 is a sectional end elevation of a typical tin mill furnace; Figure 4 is a longitudinal sectional elevation taken along the line l-I in Figure 3; and Figure 5 is an end elevation in section of a modined form4 of baille for a cold strip mill.

The figures are drawn to scale, the distance from the center of the platformin Figure 1 tol the inside of the side wall of the furnace being 6 ft. 6 inches at the farthest point. The over-all length of the furnace frominside wall to inside wall is 18 ft. 5 inches, as shown in Figure 2. The furnace shown in Figure 3 has an interior attheV widest point of 14 ft. 11/2 inches, and, as shown in Figure 4, has an over-all inside length of 26 ft. 11/2 inches, representing the longest dimension on the inside of the roof.

The furnace I 0 shown in Figure 1 comprises refractory side walls Il and a refractory roof I3. A series of burners i5 is arranged at the base of the wall Il and are spaced 9 inches apart from center to center. A bame i6 runs from one end of the vwall Il to the other and has a face I1 inclined inwardly in an upward direction at a sharp angle from the vertical. The face of the baille is approximately 19% inches in a straight line and is then slightly curved as indicated. The upper portion of the baille is inclined downwardly in an inward direction to form the face I8. As shown, the angle is approximately 28 from the vertical. The upper face I8 is sloped at about 20 from the horizontal. The burners are separated by the transverse walls 20 into 'groups of three.

The material to be annealed which will here be designated as the work 25, is mounted upon a platform 26 and covered by a metal cover 21. As already explained, this cover may be very thin, for example, inch plate. The platform itself comprises the central work carrying area 28 which is surrounded -by a tr0ugh429 bounded on the outside by the flange 30. The lower edges 3l of the cover extend into the trough 29 and are sealed by sand 32. The platform is carried on a frame which in turn is mounted on any suitable carriage such as the wheels 33 .operating on the truck 3l. Products of combustion are removed from the furnace through a chimney I 2.

In operation of the structure the work is mounted on the platform 26 covered by the cover 21 and sealed with sand 32.V It is then run into the furnace and the door closed. The burners, which customarily burn hydrocarbon vapor or liquid, are lighted and fired with a hot 0r oxi- 4 dizing flame. lThe length of the flame is such that little, if any, of it extends beyond the end of the baiile, but the convection currents which would otherwise tend to flow upwardly along the walls Il are broken up and some of the convection heat diverted to the covers and the material thereunder. vMore important. however, as the bames become hot, the radiant heat therefrom is deflected and concentrated on the lower portions of the covers directly above the platform. Whatever may be the theoretical operation of the bafile, however, in actual practice ithas produced remarkable uniformity 0f product and greatly reduced the temperature difference between the top and bottom of the work. This is illustrated by the following typical runs in furnaces ccnstructed as showninFigures l'and 2:

181,840 lbs. of strip Vwere charged in the vfurnace and temperature recordings were taken at the following points:

ga) 6 inches above the bottom at the front.'

b) 6 inches above the bottom at tne back.

gd) Top front.

e) 18 inches above the bottom' at the back.

(f) 18 inches above the bottom at the front. A (y) Fumaoe temperature taken at the usual roof position.

H51- (0) (b) (C) (6)' (e) (l) (a) 22--. 105 105 250 l225'1115 180 -000 070 4. 215 2:10 230 320 200 250 050 E y 1,0m 5 305 435 505 500 350 300 1,050 1090 510 510 040 710 470 500 12000 650 020 770 850 580'010 1,120 1,150 500 705 805 055 710 735 1.180 ,1,210 020 000 1,000 1,025 810 550 1,215 1,20 10 1,005 1,010 1,100 1,100 035 935 1,205 17 1,320 1g 1,105 1,120 1,100 1,170 1,045 1,040 1,320

1,310' g1) 1,170 1,150 1,215 1,220 1,115 1,120 H320 0 22 1,220 1,225 1,240 1,200 1,105 1,175 1,300 z, 1,300 24---,--- 1,255 1,250 1,245 1,270 1,205 1,215 ,1,300 25 1,215 1.285 Fce.oif 70. 1,230 1,250 1,240 1,220 1,220 1,240 0 1,255 1,255 1,230 1,205 1,230 1,255 1,2111; 30 1,205 1,240 1,200'1,z15 1,220 1,240 11100 Fce.on 21 1,250 22.. 1,240 1,215 1,100 1,240 Lm 1,235 1,270

.ture readings were made at the following points:

b Right center' 6 inches above the bottom. c Right front 18 inches above the bottom. d) Center 18 inches above the bottom.

e) Top back.

(o Lett iront 6 inches above the bottom.

Top iront.

Furnacetempexature.

Hrs. (a) (b) (d) (D (a) m5 210 350 205 1,080 340 340 540 470 Lm() 455 460 650 010 l, 540 550 750 730 1,100 6%) 6m 810 810 1,12) 700 710 900 910 1,120 800 810 960 970 1,160 880 890 l, 0m 1, 020 l, 170 950 060 1,060 1,070 1,180 l, 010 1, 010 l, 090 l, l, i90 1,000 1,070 1,140 1,155 1,260 1, lm 1, 130 l, m0 1, 210 1, 310 l, 166 1, 175 1, 2m 1, 235 1, 280 1,205 1,205 1,225 1,240 1,280

The output was 2.89 tons per hour.

In the structures shown in Figures 3 and 4 the .proportions of the furnace and the proportions of the baille are somewhat different. There, the furnace lila is provided with side walls I Ia, the ceiling 13a, burners 15a and bailles 18a. Inthis case the angle of the lower face Ila of the baille is approximately 45 and the lower edge of this face is slightly above the edge of the platform 26a. Furthermore the upper face 18a is level, and a vertical partial forward face 40 is provided between the inclined face I'Ia and the upper face IBa. A rather elongated vertical face 4I is provided immediately adjacent and above the burner. The combustion gases pass upwardly to the roof of the furnace, downwardly between the covers 21a, and out through lthe nue 42 at the base of the structure. Because of this path of the gases it is possible to locate the baille at a somewhat higher position with respect to the platform than is the case in the cold mill furnaces.

As will be readily understood, the exact proportions and location of the baille will depend upon the burner, the way it is operated, the size and shape of the furnace, and the character of the work to be annealed. In all cases these are correlated to produce Y a substantially uniform temperature from top to bottom of the Work.

The following are typical runs with and without bafe in a tin mill annealing process, in furnaces constructed as shown in Figures 3 and 4. In these operations the platform carried ten covers which were numbered from the door toward the rear of the furnace. The covers were mounted in pairs, the left-hand cover in the first pair toward the door being numbered 1, and the second member of that pair, 2. This numbering system was repeated until the last pair at the rear of the furnace was numbered 9 at the left, and 10 at the right. The thermocouple readings are indicated in each table. Furnace temperature is'taken inv the customary location at the top of the furnace. The other column headings indicate by the number the particular cover concerned and the initial B indicates that the thermocouple was at the bottom of the cover, and the initial T indicates that the temperature was taken at the top of the cover.

Without baffle normal operation 140,690 lbs. of metal were charged. The operation required 40 hours and the output was 1.7 tons per hour.

In another operation 133.120 lbs. of metal were charged and annealed, the time required being 40 hours and the output 1.7 tons hour.

The operating figures are as follows:

H12. Tg 10-11 1-'1 0-11v 1B 2-'1 1,000 190 170 100 "180 1,210 100 240 100 100 200 1,2110 200 210 210 250 aso 1,310 310 5m 380 350 520- 1,290 430 `660 500 450 650 1,280 530 780 620 550 750 1,300 6K) 860 720 630 810 1,310 700 930 810 700 880 1,300 750 980 880 770 930 1,300 .810 1,020 900 8m 900 1,240 soo 1,000 00o 210 1,000 1,220 200 1,020 1,020 000 1,010 1,22) 930 1,100 1,030 920 1,020 1,270 950 1,080 1,030 9N 1,080

1,280 970 l, 120 I1,070 960 1,060 1,260 940 1,090 1,040 940 1,02) 1,260 9,10 1,040 1,000 000 980 1, 260 A. 930 1, 050 l, 010 921 990 1,260 920 1,040 1,010 910 O 1,260 92) 1,050. 1,020 910 980 In contrast the following operations lwere carried out with the baflle's shown in the drawings.

134,510 lbs. of metal were annealed, the time required' being 22,hours and the output 3 tons per hour.

Fee.

Hrs. Temp. 10-B 5-B 1-13` 7-T 2-T 1,220 230 200 190 250 Z50 1,390 380 310 270 420 380 1,430 550 460 390 620 540 1,470 720 620 540 800 Y 690' 1, 440 860 750 680 910 820 l, 440 960 870 800 1,000 920 1,430 1,040 970 910 1,060 1,000 1,450 1,090 1,040 090 1,110 1,170 1,450 l. l, 100 1,060 1, 150 l, 120 1,390 1,170 1, l, 110 1, 190 l, 170

, m 1,180 l, l, 140 1, 200 1,190

In another operation 155,160 lbs. of metal were charged to a bafiie furnace and annealed, the time required'being 18 hours and the output being 4.3

In another operation 138,690 lbs. of metal were annealed in 24 hours, the output being 2.8 tons per hour. The following are the temperature recordings: i

In a simuar operation, 134,020 ibs. 0f metal were charged and annealed in 22 hours, the output being 2.8 tons per hour. The following are Part of the saving in time produced by the new furnace is due to increased efficiency of heat distribution. Some of, the improvement in time is4 due to the fact `that the furnaces may be fired l5 increased to 1400-1750 lbs. per square inch per at a faster rate. In the tin mili accurate gas zo consumption figures are maintained and with the old type furnaces without the baii'ie, the average consumption is 2679 cubic feet of gas per ton of metal annealed. With the bames, the average consumption is approximately 2370 cubic feet per ton. On the basis of an average time of 40 hours for the former process, the firing rate was approximately 67 cubic feet per hour per ton, whereas with the new process on the basis of an average of 24 hours treatment, the firing rate would be 100 cubic feet of gas per ton per hour. It is thus apparent that the. firing rate is approximately 50% greater than before but the total'consumption is approximately 11.5% less.

In the modified form shown` in Figure 5, theA l Ib and a refractory roof 13b. The series of burn-K..`

ers 15b is arranged at the base of the wall I I and spaced 9 inches apart from center to center. Thebaille 16h runs from one end of the wall ll to the o other and has a face I'Ib inclined inwardly in an upward direction at a sharp angle from the vertical. The face of the baille is approximately l5 inches in a straight line. The upper portion of the baille is -horizontal and forms the face [8b 45( -approximately 9 inches in width. The vertical mately 4 inches, and this is accomplished at the upper side by the vertical face 5I approximately 4%/2 inches in height, and the horizontal face 52 approximately 4 inches in Width. The platform 2Gb, upon which the work lib is mounted, has its upper edge 54 approximately 2 inches above and 4 inches inside the corner 50 of the baille.

It will be observed that thelhexact size, angle, and disposition of the baille varies`in the dierent furnaces shown. In all cases the size, shape and position of the baille is correlated to the size, shape and position of the platform and of the work thereon to produce substantially uniform annealing temperatures under full firing operation. It

- will also be observed that the baiiles, platforms,

and the work, may be considered to bound or define the combustion zone of limited area. The .gases impinge upon the bames before they are completely consumed. They are then deflected toward the platform and the work. Ihe platforms and the work thereon thus enter into the structure of the furnace in order to obtain maximum efficiency.

One of the improved results in the operation vof the` new furnaces is that strip in coil form may be coiled considerably tighter than was heretofore the case. This not only permits a greater volume of material to be treated at one time but the tighter windingof the coils establishes better heat transfer. It is also advantageous in the later handling of the strip.` It has been discovered that previously the maximum tension usable was 700-1050lbs. per square inch per inch of width, depending upon the ltype of treatment and the type of material employed. This has now been inch of width.

The term "sheet metal is used herein to cover thin metal whether technically in strip or sheets.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

What I claim as new, and desire to secure by Letters Patent, is:

1. In an annealing furnace for sheet metal y products having side walls and a closed roof of refractory material, a platform within the furnace for the dispositionof the material to be annealed, burner means arranged adjacent the sides of the platform, and a downwardly facing refractory baille above but adjacent the platform and projecting inwardly from a side wall, said baille having an upwardly and inwardly inclined sidesurface and an upwardly and outwardly into Aa idsidewallbi bo th furnace Illb is provided with refractory side walls c ed p surf ce sa e ng a ve e bame and said burner means being located at the base of said haine and being substantially the sole l heating means for the furnace.

A2. An annealing furnace for sheet metal products having side walls and a closed roof of refractory material, a movable car adapted to be arranged within said furnace below the bottoms of said side walls, a platform on said car for the disposition oi' the material to be annealed, burner means arranged adjacent and below said platform, and a downwardly facing refractory baille adjacent the platform and above the burner means and projecting inwardly from a side wall, said refractory baffle being located below said side wall with the burner means locatedat the base of said refractory baille and being substantially the sole heating means for the furnace, the baille having an upwardly and inwardly inclined side surface and an upwardly and outwardly inclined top surface.

ALFRED J. CASTLE.

REFERENCES crrnn The following references are of record in the file of this patent:

y UNITED STATES PATENTS Number

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