US1843099A - Ingot reheating furnace - Google Patents

Description

Jan. 26, 1932. r. c. SIEMENS INGOT REHEATING FURNACE Filed Nov. 3. 1927 4 Sheets-Sheet 1 Z172 V617 for fav-f.

Jan. 26, 1932. F. c. SIEMENS INGOT REHEATING FURNACE Filed Nov. 3. 1927 4 Sheets--Sheel 2 THT/*611 faz" yal? Jan. 26, 1932. F, C, SIEMENS 1,843,099

' INGOT REHEATING FURNACE Filed Nov. 5, 1927 4 Sheets-Sheet 3 dm W N @d Jan. 26, 1932. E slEMENs 1,843,099

INGOT REHEATING FURNACE Filed Nov. s. 1927 v 4 sheets-sheet 4 Patented Jan. 26,1932

UNITED sTaTEsl V FRIEDRICH CARI. SIEMENS, or BERLIN, GERMANY INGOT' REHEATING FURNACE Application led November-3, 1927, Serial No.

u My invention relates to improvements in lngot reheating furnaces which are also called continuous furnaces, that is, in such furnaces as are used in rolling mill work for 5 the purpose of bringing the iron and steel lngots that are to be rolled to the requisite .hightemperature at which rolling is possible. These furnaces are of elongated form and 'of considerable length. At one end there J is a door through which the cold ingots are introduced into the furnace. In the furnace there are usually water-cooled rails, upon which the ingots are placed. By repeatedly introducing fresh ingots, the ingots already 5 located upon the'rails are pushed farther into and through the furnace, so that this part of the furnace or sometimes the entire furnace is described as a-push furnace. At the other end of the furnace is provided the fire, the flame of which traverses the entire length of the furnace in counter-current to theingots travelling through the latter, while the waste gases escape through flues, which are provided at the charging end of the furnace7 and which lead to the furnace chimney.

These furnaces are known in two constructional forms. In one constructional form there. is connected with the rails of the push furnace a comparatively short hearth, on to l` which the ingots fall from the rails, to attain here the required rolling or welding temperature. In order that the ingots may be uniformly heated and softened, the ingots are rolled by-hand on this hearth, so that this J part of the hearth has received the name of rolling hearth or welding hearth. The ingots, after being completely heated to the Welding tem erature, and so to speak softened throug Tout, that is, until the correct l rolling temperature has been reached in the interior thereof, are then withdrawn through doors provided at the side of the furnace, to be introduced between the rollers. In the second constructional form of these furnaces, the rails extend throughout the entire furnace and incline obliquely downwards at the further end, so that the ingots, after bein brought to the requisite rolling tempera'ure, then slide out of the furnace over this inclined plane, on to a live 'roller'gear 230,822, and in Germany November 20, 1926.

bed', for example, which feeds the ingots to the rollers. These furnaces are therefore called push-through furnaces, because the ingots are pushed forward throughout their entire path through the furnace by the fresh ingots subsequently introduced from time to time.

Hence in both these constructional forms provision must be made at the end of the furnace opposite to the charging end to eny sure that there is here a sufliciently high hearth temperature to bring the ingots to welding heat or rolling temperature and soften them right through, so that they are at a uniform rolling temperature right to the interior. Since these furnaces require very considerable quantities of heat, and, particularly in the so-called roller or welding hearth, that is, in the hottest part of the furnace, in which the ingots have to acquire ultimately the final temperature, amounting to welding heat, have to be very highly heated, efforts have for a long time been made to utilize for these furnaces the regenerative principle, which is ver advantageous for the attaining of such hig temperatures. This, however, gave rise to the great difliculty that this principle does not admit of being directly adapted to the operation of such a roller and push furnace, because the material to be heated namely the ingots, have always had to travel through the furnace from one end to the other in a const-ant direction, whereas it is known that in a regenerative furnace the direction of the flame is so controlled at definite intervals that it travels sometimes in one direction and sometimes in the opposite direction through the furnace, for example in the case of a Siemens-Martin or open hearth furnace, from the left-hand burner head to the right, and back from the right-hand burner head to the left. The solution of this problem of transferring the regenerative principle to thea ingot reheating furnaces hereinbefore described has been given in my United States specification No. 1,017,181. This solution is based upon the fact that for the roller hearth or hottest part of the furnace I utilized a regenerative flame moving to and fro, and of this flame I deflected a part, which traversedthe push hearth in a constant direction, f opposite to the direction of movement of the ingots. I thereby obtained for the roller or welding hearth, that is, the hottest part of the furnace, an exceedingly powerful heating, owing to the regenerative flame here moving to and fro, and for the push hearth, in which the ingots introduced cold have to be gradually heated up to a moderately high temperature, an' opposite flame, accompanying the movement of the ingots and gradually cooling down on the in ots, so that in this way for both parts of the urnace the appropriate heat treatment is obtained.

It has now been ascertained from experiments carried out during the last few years that 'the roller or welding hearth does not play the important part that people felt constrained to assign to it in the past. While the roller hearth was formerly given a not inconsiderable length, for the purpose of exposing the ingots that fell out of the push hearth, or from the rails of the push hearth, to the utmost heating for a rather considerable time, it has now been ascertained that this construction of the furnace rested upon an erroneous assumption, and also had a. number of disadvantages, inasmuch as the lengthy action of an exceedingly high temperature upon the ingots naturally resulted in a con-- siderable burning away and consequent loss of material. It has at last been recognized by further investi ation of the method of working of these urnaces that it would be very much more advantageous to extend the push hearth to as great a length as possible, so that the ingots, in the push hearth, are a1- ready brought to a temperature which is as near as possible to the ultimate welding or rolling temperature to be attained, and are then exposed, upon a comparatively short roller hearth for only a short time, to a particularly high temperature in such a way that the flame in the roller hearth merely has to soften completely ingots that are a1- ready very highly heated, that is, to convert them linto such a condition that they are ready for rolling. The heating arrangements of the 4furnacemust therefore be arranged in accordance with this discovery. The object of he present invention is to solve this probein.

In my prior specification No. 1,017 ,181, as already remarked, I have provided the hottest part of the furnace, that is, the roller or welding hearth, with a reversing regenerative furnace, one part of which I split off as a flame of constant direction for the push hearth. The remaining part of the regenerative flame of the hottest part of the furnace therefore went intov the regenerators for the purposey of heating them up. This yielded in the roller or welding hearth and hottest part of the furnace an exceedin ly sharp and hot flame, the energy of which ar exceeded the degree of heating necessary for the preparation of the ingots. Since, moreover, a division of the flame was merely effected by the draft in the furnace, that is, by the action of the colder part of the furnace, namely the push hearth and the chimney connected therewith, this division of the flame was very diflicult to regulate. Consequently the gradual heating of the ingots in the push hearth was not always attained in thesame desirable manner. Now'it is clear that the charge, that is, the capacity of the furnace, or the quantity of ingots passing through the furnace per unit of time, per hour, or per working shift for example, and raised to the welding temperature, is essentially dependent upon the uniform heating and also upon the length of the furnace, so that the regulating of the heating arrangements of the furnace throughout its entire length is of considerable importance. Now in order to solve the problem hereinbefore set forth, I therefore arrange a plurality of burners or pairs of burners on the furnace, and to these burners I supply through suitable pipes the air preheated in the regenerators while I supply the gas to these burners through pipes in such a manner that-by means of the selected gas supply at each burner a flame is produced, which flows longitudinally through the furnace in a direction opposite to the direction of movement of the ingots, While for heating up the regenerators, part of the preheated air mixed with gas is char ed directly into the regenerators. I prefera ly arrange the various burner positions i'n such a manner that one burner position provides the roller or welding hearth or hottest part of the furnace, while at the point of division between the roller and push hearth, or at the corresponding position in push-through furnaces, I arrange a further burner position, and even additional. burner positions according to the length of the furnace in the further course of the push hearth, in the manner contemplated.

The flames produced in the usual regenerative furnace by employing highly preheated air, or it may be also highly'preheated gas, are as is known very hot, but also comparatively short. On this ground, according to my invention, I employ a plurality of burner positions orflames, the number of which is determinedaccording to the length of the furnace and the charge desired. Thus I regulate the supply of gas to the individual burner positions, in such a way that at each burner position the flame requisite for, this partv of the furnace, or for the regenerators according"A to their quantity of heat, is obtained. y v

In the accompanying Ydrawings I have illustrated my invention in various constructional forms Figurel shows in longitudinal section an Figure 3 is a section on the line 3-3 in Fi l 1 v n I t Figure 3a shows a section 1n the line Figure'4 shows in longitudinal section an ingot reheating furnace according to the invention as a push-through furnace.

Figure 5 isa section on the line 5 5 in Fig. 4,

Figure 6 is a horizontal section of Fig. 4 on the line 6 6. y

Figure 7 is a sectional elevation on the line 7-7 in Fig. 4, and

Figure 8 illustrates on an enlarged scale the end wall and the construction of the burnerat the head of the furnace shown in Fig. 4.

The arrows in the accompanying drawings indicate the paths of the air, gas and combustion products.

The furnace a illustrated in Figs. 1 to 3a shows the usual elongated form with watercooled rails b, upon which the ingots which are here not illustrated, are conveyed through the furnace. Underneath the elongated furnace are located regenerators c for the prevheating of the combustion air, which ascends through shafts d arranged at the sides of the furnace. To each air shaft d is connected a passage e,"which is connected with a rearwardly extendingpassage f, into which a gasthe furnace head a burner or burner slot z',

through which the flame produced by the combination of the gas flowing out of the nozzles k with the ascending air enters the furnace.

For the purpose of obtaining a uniform heating of theV furnace and of the ingots throughout their entire breadth, a plurality of gas nozzles h, as shown in Figs. 2 and 3,

is here provided, to which there then correspond an equal number of comparatively narrow burner mouths or iiame slots z', so that here it is not a single flame that enters the furnace but a group of llames, seven in the.

present case, which distribute themselves uniformlyl over the entire breadth of the furnace so that within the furnace at this point a uniformly high temperature prevails, and the ends of the ingots are as highly heated as their central parts. With the flames issuing through [theburner slots z', the hottest part a1 of the furnace, the so-called roller or welding hearth, is here heated'. This hottest part of the furnace, or welding or roller hearth, has' here, as will be seen from Fig. l, a comparatively small expansion opposite to the actual push hearth a2, the length of which is determined by the cooled slide-ways or rails b. At a3 is indicated on one side of the furnace a door through which the ingots, after being softened through, that is, when they have attained the required rolling temperature, are withdrawn from the furnace, to pass into the rolling mill.

With the air passage e is connected inside the furnace arch a horizontally extending air passage 7c, which, as shown in Figs. 2 and 3, is subdivided into a plurality of small ducts. Into these air ducts k there open at suitable points further rows of gas nozzles h1 and k2, with gas-supply pipes g1 and g2, and further burner slots il, 2, the arch bemg so recessed at the inlet point as toI produce here further burner positions for the furnace, as shown in Figs. l and 3.

The number and position of these burner points or of the further gas nozzles h1 and k2 is determined according to the length of the furnace and the various requirements.Y In the constructional example of an ingot re- -heating furnace here illustrated, according to Figure l, two such burner positions are provided, of which one, g1, h1, is located rather towards the end of the push hearth, While the other is located somewhat more towards the charging end, so that the desired high preheating of the ingots can be reliably attained within the push hearth a2.

The design or formation of the burners in a furnace may be carried out in any desired manner, for example in the furnace according to Figure 1, one of the push hearth burners is constructed according to Figure 3, and the other according to Figure 5, which will be hereinafter described. It will obviously be possible to construct all the burners of the push hearth according to Figure 3 or according to Figure 5.

The removal of the waste gases of all the burners is preferably effected near the charging aperture of the furnace through Hues or passages a4 provided at this point in any desired manner, leading to a chimney, not shown.

In Figures 4 to 8 the invention isillustrated as applied to a so-called push-through furnace. y

The elongated furnace am is here open not merely at the charging end but also at the opposite end, the so-called discharge end, or. else is provided with doors that can easily be opened. The slide-rails blo here extend throughout the entire furnace, and at the discharge end are inclined downwards, so that the ingots pushed through the furnace slide obliqucly downwards and pass over an which is indicated at 611.. Thisro ler gear bed then conveys the ingots automatically to the rolling inill, not shown. Underneath the furnace are again fairanged regenerators 01 serving for the prehating ofthe combustion p air, each of theseregenerators being connected by an ascending shaft d10 (compare Figures 6 and 7 with a passage e1o Vwhich is here horizontal. The horizontal passage vc1" is open at the bottom in the centre, as shown in Fig. 7, and is here connected with the burner slots '7110, which open obliquely into the furnace, the hottest part of which is at this position. For the formation ofthe flames for the hottest part ofthe furnace a gas supply g1 is provided externally, from which there start a number of nozzle tubes 1h10, corresponding to the number of burner m-ouths or slots 10, the said nozzle tubes, as will be seen from Figures 4 and 8, being in alignment with 'the burner slots 10, and opening at the point of connection between the air passage c1 and the burner slots 10, so that here, as in the case of the constructional form of Figs. 1 to 3, a plurality of Iiames is produced, which heat the furnace in its hottest part and at this point bring the already preheated ingots to welding heat.

In order to heat up alternatel generators 01 for the prelieating o the coinbustion air in the furnaces there is provided above the horizontal passage 61 a gas supply 01 which comprises a change-over valve 011, with which are connected two tubes 021, passing one to each side, as shownmore particularly in Fig. 7. These tubes 021 open intochambers 011,' which have slots 011 on their under sides. According to the position ofl the valve 011, gas iiows either throughv the left hand or the right hand tube 021 into the corresponding chamber 031 and throu h the slots 011 into one or other of the sha s d1", A

leading to the regenerator that is to be heated up. The gas issuing from the chamber o31 mixes with the hot combustion air introduced into-the horizontal passage-e1 from the'other regenerator .and accordingly forms a flame,

. quisite temperature.

which liows into the regenerator 01 to be heated up, and brings the latter to the re. It is preferable in this constructional form to lill up not only the regenerator but also the shaft d1 connected with it with bricks in the manner usual in regenerators, so that there may be no waste ear bed,

of the fgrnacel with burner mouths 1:21 upderl neath t e rai S451". The suppl o vgas takes place at this point according to Fig. 5, in .such a manner that above the structure containing the passage c1 is located a gas supply pipe g21 which is preferably equi ped with a regulating valve, not shown. Iprom the gas supply pipe g21 there lead downwards nozzle pipes g1, which, at the level of the burner slots 1511, Vopen into the air passages c11, so that here again, on both sides ofthe furnace, flames areproduced, which enter the furnace underneath the rails b and accordingly play round the ingots on the underV side.

At the discharging end of the furnace, as

will be evident from Figs. 4 and 8, the brickwork which serves for the formation of the burner slots or mouths i1. and for the lower closure of the air passage c1 must be supported by a special bearing construction,

y which consists essentially of T-beams or the from time to time, which normally leads to the stoppage of the furnace. In `order to obviate this disadvantage the girder construction is made in the manner shown in Figsnt and 8, whereby the result is obtained that the burnt parts of this girder construction can be changed and replaced `by 4nesh undamaged girders even while-fiile going on, that is, without haviiiggtoi thev furnace. As the drawings` `shw,'the

brickwork of thefurnace head and thlhurner wall11is supported underneath for theinost Part by a plate p, which is supported atthree' points by girders p1,v which in their turn restV upon supporting plates or the like, here indicated at p2, lfitted to the sides of the furnace, so that the girders extend over.the entire breadth of the furnace head and/can be changed simply by being drawn out and'introduced sideways. The` part of the brickwork q' which .is most exposed to burning is supported according to the invention b a plurality of girders r (Fig. 8), which, e lthe aforementioned girders, on both sides ofthe furnace head by plates r1 there provided, which are here only indicated diagrammatically. The girders r are protected from the furnace chamber by a vrtically positioned T-bar r1, and are furtherV more connected with angle irons r, so that within the supporting structure cavities are here produced, which can be utilized for the cooling, by passing either air or cooling water through them, for the purpose of prolonging the lifelof thesupporting structure. If -in spite of this a part of this supporting structure burns away, it will be understood from the explanation already givcn that this can be remedied by simply withdrawing the burntv girder laterally and introducing a fresh one.

What I claim is 1. In a furnace for heating ingots having an elongated hearth and slide Irails for supporting ingots arranged inside said hearth, the combination comprising a plurality of regenerators for preheating combustion air, air shafts extending vertically from said regenerators, an air passage connected to the aforesaid vertically extending air shafts so vas to place said shafts in open communication with one another, a burner wall having a plurality of burner slots therein in direct open communication with the said air passage and with the hearth, burner nozzles in open communication with said air passage, on the side thereof remote from the burner slots and directed towards the said burner slots, and a gas supply pipe connected to said burner-nozzles for supplying gas to the nozzles, an air duct communicating with said air passage and with the interior of the hearthl intermediate the ends thereof and gas supply means connected to said duct, as and for the purposes set forth.

2. In a furnace for heating ingots having an elongated hearth and slide rails for supporting ingots arranged inside said hearth, the combination comprising a plurality of regenerators for preheating combustion air, air shafts extending vertically from said regenair, air shafts extending vertically from said regenerators, an air passage connected to the aforesaid vertically extending air shafts so as to place said shafts in open communication with one another, a burner wall arranged over said slideway and having a plurality of burner slots therein in direct open communication with said air passage and with the hearth, burner nozzles in open communication with said air passage, on the side thereof remote from the burner slots and directed towards the said burner slots, and a gas supply pipe connected to said burner nozzles for supplying gas to the nozzles, a horizontal air duct communicating with said air passage, descending air shafts in communication with said air duct intermediate the ends of the hearth and having their lower ends in open communication with the side portions of the furnace vunderneath said slide rails, gas supply pipes connected to said descending air shafts at the lower ends thereof, as and for the purposes set forth.

In testimony whereof I have signed my name to this specification.

FRIEDRICH CARL SIEMENS.

erators, an air passage connected to the aforesaid vertically extending alr shafts so as to place said shafts in open communication with one another, a burner wall having a plurality of burner slots therein in direct open communication with the said air passage and with the hearth, burner nozzles in open communication with said air passage, on the side thereof remote from the burner slots and directed towards the said burner slots, and a gas supply pipe connected to said burner nozzles for supplying gas to the nozzles, an air duct communicating with said air passage, a plurality of burner 'slots in open communication with said air duct and with the interior of the hearth. said burner slots being spaced longitudinally of the hearth intermediate. the ends thereof, and burner nozzles in open communication with said air'duct on the side thereof remote from the burner slots and directed towards said slots, and gas supply pipes Jconnected to said burner nozzles, as and for the purposes set forth. v

3. In a furnace for heating ingots having an elongated hearth and slide rails for supporting ingots arranged inside said hearth throughout the entire length thereof, an inclined slideway at one end of said furnace for discharging the ingots therefrom, a plurality of regenerators ,for preheating combustion

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