US 1476142 A
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Dec. 4 1923. 1,476,142
G. D. BRADSHAW FURNACE Filed June 9, 1921 2 Sheets-Shet i Dec. 4,1923." a
G. D BRADSHAW FUHNACE I Filed June 9', 192].
2 Sheats-$heet 2 6 atures,
ne tel/athlete G- D. ERAD$HAWf0E MTTSBURGH. PENmYLVAL-TA.
Application filed 311E9 9.
To all whom it may concern:
Be it known that I, Guam D. Bnaosnmv, a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and a State of Pennsylvania, have inventeo certain new and useful Improvements in Furnaces, of which the following is a specification. I
This invention relates to furnaoes which 1e are used for heating metal vbillets or for other similar purposes, and it has for one object a method of operating such furnaces in order to increase the capacity and the efiiciency of the furnaceaand a urther ob- '15 ject is to produce suitable apparatus for carrying out the improved method.
It has been customary in operating continuous billet furnaces to pass the billets in at one end of the furnace and take them out so at the other end of the furnace, and also to pass the hot gases,'which are intended to heat the billets, in at one end of the furnace and out at the other end, usually in a direction opposite to that of the movement of the '25 billets. If the billets and gas move in the same directionfrom one end of the furnace to the other the hot ases will first come in. contact with the cold hillets and will impart heat rapidly thereto according to the lawof so the transference of heat by gases t0 solids,
35 the furnace, much of the heat having been extracted from the gases and the temperature of the billets having been materially increased, the temperature of the two substances rapidly approximate each other. and
v to the rate of heating is very materially reduced. Also in such a case, in order to heat the billets sufficiently it is necessary to pass the gas oil from the furnace at an extremely high temperature and hence the capacity of 4.5 the furnace is materially decreased and com-,
plex recuperating mechanism is necessaryin order to maintain a reasonable etliciency. On the other hand if the gases and billets move in opposite directions from one end of the so furnace to the other the hot gases entering the furnace come in contact with the hot billets, and as" the temperature of the gases decreases the temperature of the billets like-- wise decreases, and the difference in temperalthough increasing somewhat towards the gas exit, does not become very 1921. Serial Ho. 78,1tti.
li t. Hence, as a consequence of the la I eating, the heat is not transmitted from gases to the billets ata very high rate, a d the capacity of the furnace is this limited..-
I have found that a materially capacity and etliciency is arrived .i maintained by a combination of these to methods of associating the gases and hill In order to transmit to the billets the heat of the gases at acaoaximum rate I pass a por tion of the hot gases in at the end of the furnace where the billets enter, the
and the billets moving thus in the some direction. At the same time, in order to raise the temperature of the billets to the quired amount most efficiently, it also pass hot ases into the end of the furnace from which the billets are removed, so that the heated billets come in contact with gases at the highest temperature. I then pass the hot gases, coming from both ends of the furnace, out of the furnace at some point intermediate the two ends. By this method heat is passed to the billets at a much greater rate from the gases moving in the direction as the billets than isthe case with the gases moving in the opposite direction,
and at the same time. by passing some gas -1X1 at-the end where the hot billets are re moved, the temperature of the billets is raised to the desired point with less gas and more cfiiciently than when all of the gas and. the billets pass continuously in the direction.
Of the accompanying drawings is a central sectional view, more or less diagrammatioot a furnace and its attachments, which embodies the features of my inven tion: and Fig.2 is a similar view of a modified form of apparatus which may be used in carrying out ,my method.
Referring to Fig. 1 the billets 4 to be heated are passed into the heating chamber 5 of the furnacenthrough an opening 6, at, what may be called for convenience, the rear end thereof; being mounted on skid pipes 7 which are kept sulhciently cool in any suitable or ordinary manner. The billets are passed intothe furnace in any suitable or ordinary manner and are pushed towards ice the forward end of the furnace bymeane oil V cm.
billets in this instance many he in all respects substantially similer'to the ordinary memo .ulation ofbillets in on ordinary continuous the pipe 12 which is connected with any suitable source of gas supply. The burned gases from the burner pass into the furnace and over the billets moving counter to the billets for e material distance, and they'are then passed out of the furnace in any suitable manner such as by means of the conduit 13, which is intermediate the two ends of the furnace. At the same time hot gases are generated in the gas burner 14, in the rear of the furnace, the burner being supplied by air and combustible gases from the respective pipes 15 and 16. The hot gases from'the burner 14. pass in the same direc tion as the billets for amaterial distance and then are also passed out of the furnace in any suitable manner. In this instance I have indicated the exit for these gases also as the conduit 13, the flowof the gases} throughout the system being indicated by the arrows. It is to be understood. that the exact location of the conduit 13 is not a necessary feature of my invention, nor is it necessary that the two streams of hot gases coming from opposite directions shall pass out of the same conduit.
- The hot gases after leaving the heating chamber of the furnace may be transmitted to any suitable heat utilizing device, or directly to the chimney 17 of the furnace as is ordinary, or as may he desired. I prefer to pass the gases to some form of recuperetor 18, or to some other heat economizing apparatus, so that more heat mhy be extracted the gases before they are passed to the chimney. By means of the recuperstor the air for the burners may be heated; and, if desired at times, a portion of the hot air may be passed directly to the chimney through the valve 19 and the pipe 20.
Without desiring to enter into any strict mathematical demonstration of the differences between the results obtained by my method and those ordinarily obtained, attention is called to the following suggestions as a basis for the alleged differences:
Assuming; the law of heating involved to be as the fourth power of the difi'erences in the temperatures it is evident that e slight increase in this difference will" reduce it material increase in the rate of eating, so
that a. slight increase only will substentielly increase the cepacity of the furnace. if, for instance, the diilerence is only two per cent, the increased rate 'will be over eight per cent. This, however, is assuming that the difference is uniform throughout. practice this will not be true and the increased heating will be equal to the mean of the of the billets and also the temperatures of the ases to be unchanged, it is evident that the ot gases enteringin the rear and coming in contact with the cold billets will have an enormously greater temperature than the billets, and the dili'eren es in temperatures will be enormously greater than the dilferences with the old method, as with the old method the coolest gas is in contact with the coldest billets. At the same time the differences in the front of the furnace will be substantially the same in the two cases. The counter. currents of gases, 3. distance away from the front end, will be even nearer the temperature of the billets by my method than by the old method, as the temperature of the billets necessarily will be higher due to the effect of the gases entering from the rear, so that in this regard there is a slight loss by my method. That this is true is evidenced by the fact that, with equal amounts of gases in the two cases, the stream from the front must be much slower than by the old method, as only a portion of the gases enters at this point; end, hence, by my method the gases which enter at the front will be materially longer in contact with the billets, thus necessarily more nearl approaching the temperature of the billets. But the difference in temperature between the billets and the gases entering at the reer end, and until the gas outlet is reached, is so much greeter than by the old method that the decrease in difference near the other 1 end is much more than offset. Alsoit is evident that the amount of increase in difference will depend upon' the position of the outlet or inlet, the relative amount of gases entering the inlets, the totalamount of ases entering, and the rate of movement of the billets as well as the maximum temperatures of the gases and the billets if changes therein the exact proportions or arrangements in these regards are not to be considered as essentiel to the invention in general which i: have made.
In reference to the relative results of the old method and my method we may consider llfi a are made. Hence it is to be understood that the following: If the rate of outflow of the gases and the rate of movement of the .billetsare unchanged, by my method, as more heat is imparted to the billets in the same time, the maximum temperature of the billets will be increased and the tem erature of the outgoing gases decreased. 0wever, by increasing the rate of movement of the billets, and thus increasing the capacity of the furnace,the maximum'temperature of the 'billets may be reduced to the normal amount. But it will be found that the outlet temperature of the uses will then be decreased still, more. as t e difference in temperatures will be increased due to the cooler. billets. As a consequence the rate of flow of the gases may be increased and this allows a further increase in the movement of the billets, so that with a given size of furnace the capacity thereof may be, for these reasons, materially increased. Or if it is desired, the gases may be passed from the furnace at a lower temperature and the comp-lica-tion's of the recuperating system may be simplified.
In the modified form of apparatus indicated by Fig. 2, the billets are moved along the upper skids 21 towards the center of the furnace, and, at some suitable point, are dropped on to the lower skids 22, and the gases pass out from the heating chamber through the space 23 between the adjacent ends of the rows of billets, as indicated. In this case a secondpusher 24 may be used in order to move forwardly the billets on the lower skids. The general-method carried out by this apparatus is substantially the same as the method carried out by the apparatus indicated by Fig. 1.
I claim as my invention:
1. A method of heating articles consistin in passing articles through an elongate heating chamber by moving them from one end. to the other, by passing hot gases in at' both ends ofsaid chamber at points adj acent the entrance and the exit of said articles, and in passing said gases out of said chamber intermediate the points of entrance thereof.
2. In a continuous heating furnace a heating chamber, means for paming articles to be heated in oneend of said chamber and out of the other end thereof, means for passing hot gases into said chamber at both ends thereof, and means for )assing the said hot gases out of said cham r at some point intermediate the ends of said chamber.-
3. A method of heating articles consisting in moving a row of articles in contact with streams of hot gases, the streams passing from both ends of the row of articles towards the central portion of the row.
4. A method of heating articles consistin in moving them in contact with a stream 0' hot gases moving in the 'same direction as the articles, and then-in moving the articles in contact with a stream'of hot gases moving in a direction opposite to the direction of movement of the articles.
.In testimony whereof, I hereunto set my hand.
GRANT D. BRADSHAW.