US2329211A

US2329211A - Continuous heating furnace and method of operating the same

Info

Publication number: US2329211A
Application number: US337987A
Authority: US
Inventors: William A Morton
Original assignee: Amsler Morton Co
Current assignee: Amsler Morton Co
Priority date: 1940-05-31
Filing date: 1940-05-31
Publication date: 1943-09-14
Anticipated expiration: 1960-09-14

Description

Sept. 14, 1943. w. A. MoRToN 2,329,211

CONTINUOUS HEATING FURNACE AND METHOD 0E OPERATING THE SAME Filed May 31, 1940 4 Sheets-Sheet l il J7 34.22

, BY f LZORNELYC( I Sept. 14, 1943. w. A. M-oRroN 2,329,211

CONTINUOUS HEATING FURNACE AND METHOD OF OPERATING THEYSAME Filed May 31, 1940 4 sheets-sheet 2 w ATTORNEY Sept. 1 4, 1943. w. A MoRToN 2,329,211

CONTINUOUS HEATING FURNACE AND METHOD OF OPERATING THE SAME Filed May 31, 1940 4 Sheets-Sheet 3 f fffff 57 ATTORNEY Sept 14, 1943- 'I w. A. MoR'roN 2,329,211

CONTIYNUOUS HEATING FURNACE AND METHOD` OF 'OPERATING THE SAME Filed May 51, 1940 4 sheets-sheet 4 f5" .7 Q 34 I i j Qa Z5 .55

t i ATTORNEY Patented Sept. A14, 1943 CONTINUOUS HEATING FURNACE AND METHOD OF OPERATING THE SAME William A. Morton, Mount Lebanon Township,

Allegheny County, Pa., assignor'to The Amsler- .Morton Company, Pittsburgh, Pa., a corporation of Pennsylvania Application May 31, 1940, Serial No. 337,987

49 Claims.

` This invention relates generally to heating furnaces and more particularly to heating furnaces of the type wherein articles are heated as they are continuously moved therethrough, and the method of operating the same.

In the steel industry a continuous type heating furnace is employed for heating billets, ingots.,

blooms,4 slabs, rails and the like, to a predetermined temperature, preparatory tO rolling or per- I forming lother operations thereon.

This type of furnace may be made up 'of two chambers, namely a heating chamber and the extension or preheating chamber.

The furnace chamber generally extends to the charging end of the furnace for the waste gases which preheat the steel. 'I'hs preheating operationis a direct function of the rate of ring in the main heating chamber and it is not independent thereof and can therefore not be controlled'r The material to be heated continuously passes from the charging end of the furnace, then through the preheating chamber, then through the heating chamber, and 4across the soaking chamber, by which time it is uniformly heated and discharged from the other en d of the furnace.

It has been customary to fire this character of furnace by direct radiation from the flames adjacent the articles at one or more positions throughout the furnace, but it is impractical, to control the atmosphere with this method of firing. High-carbon and alloy steels are principally affected and decarburization takes place.

Variationsl in furnace temperature and undesirable furnace atmosphere conditions tend to break the original scale of oxidation from vthe surface of the material and an undesirable tight thin secondary scale forms thereon. Conditions'of this character in heating create surface defects in the steel when Worked. Again heating by direct radiationfrom flames adjacent the 'steel produces streaked heating in the steel Which'is detrimental when rolling.

1n one direct radiation type heating furnace the flames are produced from burners adjacent.

the discharge end (Patents. 1,789,966; 1,912,933,

and 1,944,729) and flow over thesteel inthe opposite direction of its travel for, the full length of the furnace. The hottest portion of the flames are adjacent the soaking hearth and the cool' gases are discharged adjacent the steel charging to vary the rate of production-and maintain the desired critical final steel temperature. This ob.-

viously creates thetendency of over-heating the steel. This is especially'true if there is any interruption or change of the speed of travel of the steel moving through the furnace. The rate "of heat exchange at the charging end of the fur'- nace is low and is dependent-upon the fixed or permissible rate of firing the heating chamber.

In view of the fact that the hottest ame is ad' jacent the dischargeend it is impossible to employ more than of the available preheated air from the high temperature waste heat gases and thus the furnace operation is ineiiici'ent. Each of these factors interferes with the heating of the steel and especially high carbon and alloy steels. y

When the burners delivering a direct radiation type heating flame are placed adjacent both -the discharging and the charging end .of the furnace (Patents 1,476,142; 2,133,673, and 2,157,221) and the waste gases are roved adjacent the center of the furnace chamber, the efliciency is increased somewhat by reason of the fact that there is a greater heat exchange at the charging end than in the type of furnace referred to above. However it is impossible to control the furnace at- .mosphere in the preferred manner. The' discharge end of this type of furnace is heated by and break away and produce an undesirable con-` direct radiation, making it difficult to control and equalize the temperature across the steel when it is discharged, resulting in local overheating and producing some of the difliculties asdescribed above. f

In both of these methods of heating by a direct radiating llame, cold air is drawn i-nto the furnace at the discharge end. Thisair chills the steel causing the heavy original scale to contract A third type of furnace, which employs a direct l the furnaceatmosphereor to separately control end. With this type of furnace' it, is dilcult to maintain the desired temperature of the steel be fore itis discharged and also virtually impossible the critical temperature of the steel when discharged. i The burner'of `another type of furnace is posi- -tioned so that the flame' directly im'pinges the steel at an angle and is divided, the smaller porvtion traveling with the steel across the soaking hearth and the larger portion traveling'against the movement of the steel to the charging end. (Patent 2,056,904.) Since the gases are withdrawn from the furnace at both ends, the atmosphere ofthe furnace may be controlled t some degree. However the directI impingement of the fiame on the steel limits the ring temperature and streaked heatingl is pronounced. All of the other disadvantages mentioned above are also present to a degree.

The principal object of this invention is the vprovision of an improved character of furnace and the method of operating the same to overcome these objectionable features and characfteristics.

Another object is the provision of a method for uniformly 'beating the steel by diffused radiation ring.

Another object is the provision for local regulation of the temperature of the steel on the soaking hearth independently of the principal firing of the heating chamber. This method of operation maintains the steel on the soaking hearth at its -proper rolling temperature while the fuel supplied to the heating chamber is varied or .completely shut off. This is exceptionally advantageous during periods in which the mill is shut down' temporarily for repairs or changes of mill rolls.-

Another object 'is the provision for automatically controlling thetemperature of the steel as it is discharged regardless of the rate of production, or the rate of firing of the heating chamber, or during mill delays.

Another object is to provide for an automatic control system which regulates the temperature and furnace atmosphere conditions during normal operation, and during mill delays or reduced rates of production automatically stops the ring of the principal burners for the heating chamber and transfers the fuel to the auxiliary burners for holding the steel on the soaking hearth at rolling temperature during such delays, at any selected rate of ring.

Another object is the provision of a method for controlling the rate of heating of the steel g in the furnace in proportion to the rate of production ,without endangering Ithe k thermal or physical characteristics of the steel in the criti-.

cal heating range. l

Another object is to provide a supplementary chamber for preheating sensitive high carbon and alloy steels at a predetermined rate prior to their entry into the main heating temperature. I

Another object is to pass the steel through a furnace in which the atmosphere adjacent the steel is a non-oxidizing atmosphere, differing from the normal uncombined combustibles.

Another object is the provision for an improved character of ring llame which enables control of the furnace atmosphere and the use of a higher than normal percentage of -the waste heat recovery and which also enables one to vary the position of the maximum thermal input within the furnace.

Another object is to combine the ow of all the gases of combustion as they pass over the steel on the soaking hearth to obtain a diffusion of the total heat of the names, to thereby equalivze the temperature along the steel.

VAnother object is the provision for introducing and withdrawing the heating medium at the same end of the furnace.

Another object is the provision for introducing i and withdrawing the heating medium at both ends of the furnace.

Another object is the provision of means for controlling the percentage of inp ut and withdrawal of the heating'medium adjacent each end of the furnace.

Other objects and advantages appear in the of a furnace red with three ames, two of which are redirected.

Fig. 3 is a sectional view taken longitudinally of a furnace fired with three principal flames,

whereingonly the soaking chamber flame is re directed and two independent ames are provided for preheating. l

Fig. 4 is a sectional view taken longitudinally of a furnacefired with two flames, the flame supplying heat to the soaking chamber being redirected.

Fig. 5-is a sectional view taken longitudinally of the furnace having a sloping hearth and fired with opposed redirected flames, the main furnace chamber ilame normally supplying approximately of the heat delivered to the furnace.

Fig. 6 is a sectional view of a furnace having' a sloping hearth similar to that shown in Fig. 5 and which is provided with a preheating chamber.

Fig. 'I is a diagrammatic view illustrating the circuits for automatically controlling the temperature of the air and fuel delivered to a furnace such as that illustrated in the previous iigures, and the furnace pressure control for the same. The outline of the furnace used to illustratezthese controls is taken on the line 1 1 of Fig.

Fig. 8 is a graph illustrating the temperature characteristics of the furnace disclosed herein which includes the preheated air delivered to the furnace, the furnace temperature, and the temperature of the steel as it passes therethrough.

Referring to Fig.. 1, the furnace illustrated therein comprises three principal elements. the main heating chamber III, the soaking hearth II in one end of the main heating chamber, and the preheating chamber I2, Water cooled skids I3 extend through the preheating and heating chambers for supporting the material Il to be heated which is charged through the opening I5 and is shoved in the usual manner, through the preheating chamber, the heating chamber and over the soaking hearth, from whence it is discharged through the opening I6. The soaking .hearth Il is a solid hearth. The openings I5 and I6 are closed with suitable doors.

The main heating chamber I0 is divided by the steel charge Il into upper and lower independent chambers II and I8. The chamber I1 above the steel is formed by the enclosing roof structure I9. The height of these chambers may be determined by the formula governing the expansion of gases from 60 F. to 2500* F. with the assumption that the average furnace temperature will reach the latter amount, and thus by employing the proper firing rate, the furnace pressure is maintained constant.

The roof structure above the soaking hearth II may also be determined in the same manner.

The preheating chamber Il is likewise divided by the `steel charge Il into the upper and lower independent chambers 20 and 2|. Each of these chambers connect with the independent chainbers I1 and I8 of the main heating chamber and thus form continuous upper and lower independent chambers in these two sections of the furnace.

The lower chamber I8 is below the plane of the hearth and is enclosed by the sub-floor 22 and the continuous outside walls 23, which carry the outer skids I3, andwhich extend from the intermediate transverse wall 24 adjacent the soaking hearth II to the charging end of the preheating chamber I2 as indicated at 25.

The rear wall 26 ofy the furnace, through which the preheating chamber I2 opens, is provided with two rows of

burners

21 and 28 for firing the chambers I1 and I8 respectively. The burners are supplied with fuel transmitted through the conduits 30 and with preheated air transmitted through the conduits 3I and 32. Burners are provided between the Walls 23 and the side walls of the vfurnace as shown in Fig.'7. However a portion of the ames of these burners may pass upwardly over the ends of the steel to the chamber I1.

The soaking hearth II is locally heated as desired bya flame issuing from the row of burners 33 in the front Wall 34 of the furnace. Ordi-v narily these burners are operated onlyduring mill delays, during which time the preheated air and fuel -are transferred from the

burners

21 and 28 to the burners 33 which are described below in relation with the furnace control and operation.

It will be noted that each vof the burners 21,

steel on the soaking hearth II and is discharged at the front of the furnace. 'Ihe paths of the gases are indicated in each of theA views by dotted lines.

Flues 35 are positioned just inside the charging opening I5 fordrawing off the

main portion

28 and 33 are substantially horizontally disposed and that they are spaced further from the plane of the hearth than they are from the rcof or the floor. The reason for this arrangement is to provide a flame that travels outwardly in a path substantially 'parallel with the steel until its velocity is reduced to such an extent that the draft, which is induced in the vicinity of each burner, redirects the path. of movement of the products of combustion. Combustion is substantially complete in each flame before it is redirected by the draft forces and the hottest part of the flame does not impinge directly on the steel. Thus the products of combustion of each ame blanket the steel on its return path of movement to the ues. In this manner the atmosphere surrounding the steel may be controlled to prevent local overheating, excess oxidation and decarburization f the steel.

The hottest portion of the llame is along the. initial path of projection. Thus the .steel is heated by radiation from this portion of the ame and by convection from the products of combustion passing back over the steel. The radiant heat energy reflected` from the roof and directly effective from the flame must pass through the products of combustion owing back over the steel. The radiant heat energy is thus diffused as it passes through the products of combustion, thereby uniformly heating the steel laterally across the furnace, and the detrimental effects of direct heating from initial flame combustion are eliminated. Again the eiliciency of the heat exchange is increased by the extension of the flame length and the location of the area of the highest rate of heating may be accurately controlled.

This method of heating utilizes direct radiation and in addition direct convection in combination to accelerate the normal heating rate of the products of combustion fromV the upper chambers I1 and all of the products of combustion from the lower chamber I8. These waste gases are selectively drawn through the independent upper and lower lchambers 20 and 2I of the preheating chamber I2 in their travel to the flues 35 and thus regulably preheat the steel to any desired temperature for delivery into the heating chamber. If this chamber were not added at the rear of the furnace the gases would pass directly from the chambers I1 and I8 to the vertical flues 35 which direct them through the horizontal flue 36, the recuperator 31 or other heat absorbing device, to themain flue 38, from whence they are ordinarily directed to a stack. If desired the gases may be carrled'directly to the stack and the air preheater'omitted.

I'hat portion of the products of combustion from the burner 21 which flows over the steel on the soaking hearth II is drawn down past the steel discharge opening I6 into the flues 39 where they may be discharged directly to the short. damper controlled auxiliary stack 40.

During mill delays when the firing is instantaneously switched from the

burners

21 and 28 at the rear of the furnace to the burners 33 at the front of the furnace the flames project over the soaking hearth and when their velocity is diminished the products of combustion are redirected back over the steel, as described above, and are discharged down past the steel discharge opening VI6 through the flues 39 to the stack 40 as described above.

The

flues

35 and 39, 'which direct the gases from the plane of the hearth, may in each case be a single flue or may comprise a plurality of smaller flues, depending upon the character of the furnace structure. In the latter case they usually open into a single connecting flue 36 at their lower ends.

The flues or outlets are thus positioned in the vicinity of the burners and the gases discharged from the furnace chambers pass both the charging and discharging openings I5 and I6, thus carrying away any cold air that may lter into the furnace and preventing its access to the hot steel on the hearth even when the doors are open.l

The steel is thus protected from cold air and is blanketed by the products of combustion. This avoids surface temperature variations which would tend to break the original scale of oxidation from the surface of the steel and'thereby avoids the formation of the thin tight secondary scale which is highly objectionable. 'I'he removal of the heavy scale deposited on the hearth, which would necessitate shutting down the furnace is also avoided.

This character cf flame provides uniform heating of the steel and permits accurate control of the heating cycle.

The flue 35 may be controlled by the damper 4I which in turn may be operated by the servomotor 42. The flue 39 is likewise controlled by the damper 43 operated by the servomotor 44. The main' flue 38 which leads to the stack is controlled by thedamper 45 operated by the servornotor 48.

The rate of preheating the steel may be controlled by damper 4| to regulate the quantity of waste heat leaving the charging end of the furnace. y

A pyrometer 41 is placed in the flue 39 for registering the temperature of the gases flowing off the steel in the soaking hearth.

In Fig. 2 a greater portion of the gases passing from the lower independent heating chamber I8 are carried off by the flue 48 in the center of the furnace, which is controlledby the damper 50 operated by the servomotor I, to the horizontal flue 36. The balance of the products of combustion of the flame issuing from the burner 28 passes back along the steel through the lower preheating chamber 2| and is discharged out the flues 35, thus forming a thinner layer of waste gas which prevents the flames from coming directly in contact with the steel.

The preheating chamber I2 in Fig. 2 is much .the same as in Fig. 1.

The flues 39 carrying the gases over the soaking hearth Il are connected with the horizontal flue 38. In order to prevent uncontrolled migration of lthe gases, -which might upset the firing conditions therein, the dampers may be regulated to produce a draft of .04 inch of water in the

flues

35 and 48 and a draft of .06 inch of water in the flue 39.

In Fig. 3 the independent chambers 20 and 2I of the preheating chamber I2 are fired directly by the upper and lower rows of burners 52 and 53, respectively, which control the rate at which it is desired to preheat the steel prior to delivery in the mainv heating chamber. The products of combustion from the llames of these burners pass into the main heating chambers I1 and I8, because combustion is substantially complete when these flames pass into the main heating chambers and their products of combustion blanket the steel from initial flames of combustion in chambers I1 and I8 to produce substantially the same effect as that obtainable with the structure illustrated in Fig. l,

The hottest part of the flames issuing from the

main burners

21 and 28 is thus prevented from heating the steel by direct radiation. The preheated steel is thus subjected to diffused radiant heat energy from the furnace surfaces and the llames in both the upper and lower chambers. When combustion of the arnes from the

burners

21 and 28 ls substantially complete the products of combustion from both the preheating burners and the main burners combine and equalize in temperature as they continue to` blanket the steel with an inert atmosphere of uniform temperature until it is discharged.

In the case of the structure illustrated ln Fig.'

3 any cold air that may filter into the furnace through the charging opening I5 aids in supporting the combustion of the preheating flames and the free oxygen ls substantially all consumed before the gases pass out of the preheating chamber. Thus the infiltration of the cold air does not have an opportunity to injure the heated steel which is not at a critical temperature adjacent the point of entry andsuch air is usable in this design of furnace.

The hot gases of combustion from the lower preheating chamber 2I form a protective layer between the steel and flames from the burners 28 in the chamber I8. The products of combustion of the flames issuing from the burners 28 mix with the products of combustion from the preheating chamber 2l and pass down nues 48 out of the chamber I8. Gases from the chamber I1 travel along, blanketing the steel over the soaking hearth and finally pass down outlets 39. All flues or outlets are provided with independent damper control as described above and are further subject to common damper regulation by furnace pressure control.

The heat delivered to the soaking hearth from the redirected flames of the burners 33 is preferablyA applied only during mill delay or interruption of normal operation. .At the time of interruption the heat will be automatically turned on by means of the control system which is herein described. The burners 33 may or may not be used at any time, depending upon the changing conditions within the furnace, but these burners are always subject to independent automatic control when desired.

As previously described the flames from the .burners 33 must pass through the previously produced blanketing gases to the steel and as the forward velocity of thev flame diminishes the llame is returned by draft in the flue 39 and the gases therefrom mingle with the other products of combustion and travel down past the discharge opening I6 through the flue 39, the horizontal flue 36, to the recuperator.

The furnace illustrated in Fig 4 is not provided with a preheating chamber I2 nor a lower heating chamber I8. However the

burners

21 and 33 function in the same manner as that just described in'connection with Fig. 3. This view illustrates some of the details of an actual furnace structure of the charging and fired type, whereas the previous views are relatively diagrammatic. K

A portion of the gases flowing through the horizontal flue 36 are drawn up the passageway 49 through the floor 22 and pass over the ends of the steel into chamber I0 to form a blanketing protection through which the radiant heat from the ame issuing from the burners 21 must pass to heat the steel. These gases are drawn off at the rear of the furnace through the flues 35 which in this instance pass directly to the stack 38. Thus the same effect is produced in this furnace as that described in relation to the previous furnaces.

In Figs. 5 and 6 a sloping hearth is provided for receiving. cylindrically shaped articles I4 wich are to be heated. These articles are charged through the rear opening I5 and are progressively rolled down the hearth manually. Entrance to the furnace chamber is gained through the doors along the side walls. The

steel ls discharged laterally through the openthe radiant heat of 2,329,211 steel and is discharged through the flues 35 while the remaining portion ows over the soaking hearth Il and out the ues 39 to the auxiliary stack 40. The roof I9 being substantially horizontal is economical to construct and becauseof the sloping hearth the heating chamber l progressively increases in volume towards the front of the furnace. The roof over the lower end of the hearth Il is also horizontal and the connecting roof, which slopes from one roof level to the other, restricts the inner end of the heating chamber I0. The slope of the connecting roof thus aids in redirecting the flame from the burner 21 by the restriction. The blanketing gases traveling back up over the steel are discharged downwardly through the flue 35 tol the recuperator 31.

The slope of the hearth enlarges the volume of the chamber over the soaking hearth Il toward the front of the furnace, thus aiding in redirecting the flame from the burner 33 during mill delays, and causing the burned gases to travel down over the steel on the hearth and thus blanket it from direct radiation. These gases are 'discharged through the flue 39 to the auxiliary stack 49.

The quantity of gas passed out the stack 40, during normal operations when the burners 33 are shut down, will .be merely suicient to provide a. measure of the final heated temperature of the steel prior to` discharge Whichhas not been pro-` nace shown in Fig. 6 is desired to provide the largest chamber for approximately 60% of the V)furnace length at the front of the furnace and the smallest chamber for approximately 40% of the furnace *for the smallest chamber which in this instance is the preheating chamber I2.` In each instance the recuperator 31 is connected to vided for in this manner for this or any other the outlets of the chamber containing the largest ring proportion, which. in Fig. 6 is the preheating chamber l2 and is connected through the flue 39 to the recuperator in the same manner a that described in relation to Figs. 1 and 2.

In both of these structures the steel is protected by the blanketingv layer of products of combustion and any infiltration of cold air at the charging or discharging openings is carried along with Waste heat gases and cannot produce any detrimental effect on the steel.

Fig. '7 is a diagrammatic view showing the automatic control circuits for operating anyone of the above described furnaces. lined is shown as a plan view of the hearth shown in the furnace of Fig. 2 which is representative of each of the furnace structures comprising this invention. Independent preheating burners 52 and 53 are employed only in the furnace shown in Fig 3. These preheating burnersfor all practical purposes may be fed by branch lines from the main burners and therefore may be considered auxiliary to the main burners 21 and/.28 insofar as the controls are concerned. It may or may not be desirable to provide the preheating burners with preheated air and to avoid perplexity Vthey are not illustrated in Fig. '7.

60 represents the blower for delivering air to the recuperator 31 where it is preheated and di- The furnace outrected to the

burners

21 and 28 or to the burners 33. A Venturi tube 6|` is inserted in the blower inlet which is controlled by the damper 62 operated by the servo motor 63.

`The fuel is supplied through the conduit 64 and its flo'w is controlled by the regulating valve 6,5 which is operated by the motor 66. When the fuel passes from the valve 65 it must flow through an orice plate 61 and then continuesthrough the supply conduit to the

burners

21 and 28 or to the burners 33. Each of these sets of burners is provided with a hand-operated valveli for independently adjusting the flow of fuel to each of the burners. The ow of fuel .may be read by the meter 69.

The burners are preferably of the induction type and the preheated air in the common ducts while it is induced it is also proportioned by the orifice 61'in the fuel line to the other diaphragm of the air-fuel regulator and register the quantity of fuel delivered to the furnace. The quantities of air and fuel are thus kept proportional by means of this vratio regulator control which is operated by differential pressures created by the flow of air and the quantity of fuel is maintained proportional. The quantity of air is previously determined by the temperature of the furnace.

The temperature of the gases being discharged from the furnace through the flue 39 has a direct relation to the temperature of the steel on the soaking hearth which the gases have just passed over, Whether these gases are coming from the main burners 21 during normal operation or from the burners 33 during mill delays. furnace temperature is approximately 2500 F.

.the steel on the soaking hearth will be approximately 200 F. less. This difference may vary slightly but for purpose of control the waste gases always bear a direct relation'to the steel temperature whereby the furnace control system may be accurately operated. Y

The temperature ofthe gases discharged from the furnace is measured by the pyrometer 41 and registered in the recording potentiometer temperature control 13. This control in turn operates the servo motor 63 for opening and closing the damper 62 and thereby regulates the amount of air delivered to the furnace for controlling the temperature.

Any change in the quantity of air delivered to the recuperator is registered as differential pressures in the air-fuel regulator 1I which actuates the ratio control 14 for automatically main- '.taining a predetermined ratio of air and fuel When the In order to maintain the furnace at a predetermined pressure an atmosphere connection in the furnace is made through the conduit 16 to the pressure regulator 11 for carrying pressure impulses thereto. These impulses are relayed through the furnace pressure control device which opens a high pressure valve in lines 18 to open ports in the opposite ends of the fluid operator motor 46 for regulating the main damper 45 in the flue 38 leading to the stack. The furnace pressure regulation is supplemented by al sible and practical for the first time in continuous furnace practice.

During normal mill operation the potentiometer temperature control 13 of the furnace control regulates the flow of air delivered to the fur- -v nace and the regulator 1I proportions th'e flow of fuel with the quantity of air being delivered to the furnace. The air and fuel lines are each provided with the Y connections 8D and 8|, respectively, for conducting the air and fuel to one of two branch lines. One branch line connects with the

main burners

21 and 28, and the pre- Vheating burners, if any, for normal operation of Th'e other branch line connects the furnace.' with the burners 33 for operation delays.

Each of these branch lines is controlled by a solenoid operated valve which preferably has a spring return action for closing the valve. This arrangement provides a safety feature in case of a power failure. The valves 82 and 83, in air and fuel branch lines respectively, control the lines leading to the main burners at the rear of th'e furnace and are electrically energized through the common return wire 84 and the control wire 85. The

valves

86 and 81, in the air and fuel branch lines respectively, control the lines leading to the mill delay burners at the front of the' furnace and are electrically energized through the common return wire 84 and the control wire 88. These control wires are connected with' the selection switch 90 which in turn is operated by the servo motor 63. The switch 90 is provided with electrical energy from any suitable source such as indicated by the wires Si.

The switch 90 selectivelyenergizes either set of valves for controlling the normal operating

main burners

21 and 28 or the mill delay burners 33. This selection is determined automatically by the temperature of the furnace. The furnace controls are adjusted to provide the proper firing during mill conditions for th'e desired rate of reduction.

With this adjustment normal operation of the furnace is automatically continued by moving the steel therethrough at the chosen predetermined rate of speed. If hot steel is `not taken from the furnace at the normal rate, by feeding cold steel thereto, the furnace temperature will quickly rise. This rise in temperature isiimmediately registered by the pyrometers 41 in the potentiometer temperature control 13 which energizes thel servo motor 63 to reduce the quantity of air delivered to the furnace. The reduction of air thus automatically reduces the quantity of fuel through the regulator 1l and the air fuel ratio control 14. As the quantity of heat energy delivered to'the furnace is reduced, the furnace temperature falls to normal.

If no steel is taken from the furnace the temperature rises very fast and initiates the automatic operation just described. When the potentiometer control 13 reduces the quantity of air delivered to thefurnace to a predetermined amount, such Aas 50%, then the servo motor 63 throws the switch -90, thereby selectively changing the firing from normal operation at the rear of the furnace to the mill delay burners 33 at the front of the furnace by deenergizing and closing the air and fuel valves 82 and 83 and energizing and opening the air and

fuel valves

86 and 81.

The waste gases from the redirected ames of the mill delay burners 33 continue to control the temperature of the steel on the soaking hearth il and the automatic controls continue to function in the same manner. The fuel consumption during mill delays is naturally materially less than that required for normal furnace operation because the small amount of steel on the soaking hearth is all that is maintained at rolling temperature. Again this steel is not o verh'eated and is always ready for use.

When mill operations are resumed, hot steel is discharged from the soaking hearth and cold steel is charged into the rear of the furnace, the gases discharged through the ues 39 become cooler because the furnace temperature drops due to increased absorption o'f heat by the cooler steel moved onto the soaking hearth and. into 'the furnace. The pyrometer 41 then actuates lthe potentiometer temperature control 13 which in turn energizes the ser'vo motor 63 for operating the damper 62 to increase the quantity of 'air delivered to the furnace. The air-fuel ratio regulator 1l and the control 14 are operated by the change in the quantity of air delivered to increase the quantity of fuel delivered to the furnace. When the quantity of air delivered to the furnace reaches a predetermined amount the servo motor 63 actuates the selectionsswitch 90 which deenergizes the

valves

86 and 81, causing them to close and energize the valves 82 and 83, causing them to open and thereby transfer the firing from the front to the rear of the furnace. Thus the furnace has been restored to normal 'operation' for continued mill production.

The selection switch 90, which controls the transfer of firing from normal operation to mill delay operation, maybe designed to operate the transfer valves in the branch lines when 50% ofv the normal amount of air is delivered to the furnace as stated above. being made from mill delay operation to normal operation of the furnace this selection switch 90 maybe made to operate when the quantity of air delivered to the furnace reaches 40%, 50% or 60% as desired. This adjustment is advantageous in the control system as different fuels and different characters of furnaces may require faster or slower pick up to aeturn them to normal operation.

When the transfer is Again the

transfer valvesy

82, 83, 8B and 81 may be arranged to proportion the quantity of air and fuel between the rear and front of the furnace, in which case the

burners

21, 28 and 33 Will all be firing at the same time and a greater differential will be provided between the complete transfer of the firing from one end of the furnace to the other.

This automatic control system may be applied to furnaces of this type other than that disclosed herein. However it is particularly advantageous for use with these furnace structures.

If it be necessary to turn off the burners in the preheating and main heating chambers because the mill is shut down for roll change or repairs, the steel on the soaking hearth may thus be kept at rolling temperature automatically by means of this control system which mechanically transfers the firing operation froml the main burners to the mill delay burners 33. When the mill is again ready for hot steel the furnace is prepared todeliver it immediately from the soaking hearth and the burners in the main furnace and the preheating chamber automatically resume operation inlmresponse to initiation of cold steel charging creating a Vfuel demand. This represents ay material advance in the continuous furnace art.

The graph illustrated in Fig. 8 shows the temperature conditions throughoutthe continuous furnaces disclosed above. The upper curve FI represents the temperature of the furnace throughout its length when it is being used for low carbon steel. F2 represents the temperature of the furnace when heating alloy or high carbon steels. The respective temperature of the low carbon and high carbon steels as they pass through the furnace under these conditions is represented by the curves SI and S2. Obviously more low carbon steel may be heated, but high carbon steel may be heated under the particular conditions or safe controlled rates of temperature acceleration in the same furnace safely for the first time.

' The temperature of an ordinary continuous type of furnace such as that found in the prior art is illustrated as curve F3 in Fig. 8. In such continuous type furnaces the temperature within `the main heating chamber is highest between the center of the chamber and a soaking chamber, whereas in this improved furnace with above disclosed method of firing the same, the highest temperature is vadjacent the charging end of the main heating chamber and the temperature gradually diminishes to the discharge end of the furnace, thereby providing a preferred state of thermal equilibrium, in that the gases, steel` and `furnace parts are substantially uniform across the furnace. In ordinary continuous type furnaces these temperature conditions are not attained. e

If the preheating chamber beeliminated these curves start at the charging end of the heating chamber but they assume substantially the same character as that illustrated. `If the preheating chamber and the main heating chamber are shut down because of the interruption of mill operations the furnace remains closed and the steel ceases to move therethrough. The temperature of these chambers and the steel therein slowly lowers while the temperature of the steel in the soaking chamber is maintained at the proper amount. After many hours under these conditions there is a* uniform gradation in the steeltemperature from the inlet end of the soaking chamber to the charging door I5.

The supplementary preheating chamber may or may not be used. depending upon the type of steel or rate of production desired. It is obvious however that when -a high rate of production is desired from low carbon steels, the supplementary chamber may be operated at a very high temperature, thereby increasing the temperature of the steel prior to its entry into the main heating chamber. In the case of special steels requiring a controlled preheating cycle, the rate of temperature rise in the steel may be controlled independently of the rate of `firing in the heating zone. The prior art does not disclose furnaces which have this function. In Patent No. 2,157,221, of which the present inventor t is a co-"patentee, the center outlet prevents the gases of the preliminary burner from protecting the steel Iand also prevents regulation of the bottom heating chamber independently of the top chamber. I prefer to use a substantial portion of the heating cycle for preheating but generally this will be less than half or the furnace investment will be improperly distributed.

I claim: f

1. The method of heating billets and the like in a continuous furnace which comprises causing heating flames which produce radiant heat en ergy to travel from both ends of the furnace and toward each other in lines substantially parallel to the path of the billets, interposing between the billets and the heating iiames a blanketing layer of non-oxidizing gases through which the radiant heat energy passes to heat the billets and withdrawing the non-oxidizing gases after they have passed over the billets about to be discharged.

2. The method of heating billets and the like in a continuousfurnace which comprises causing heating flames to travel from both ends of the fur- .nace and toward each other in lines substantially tially parallel to the path of the billets, interposing between the billets and the heating names a blanketing layer of non-oxidizing products of Combustion originating from the heating flames and withdrawing the non-oxidizing gases after they have passed over the billets about to be discharged.

4. The method of heating billets and the like in a. continuous furnace which comprises causing heating flames to travel in lines substantially parallel to the path of the billets and above and below the same, and interposing between the billets and the heating flames blanketing layers of vnon-oxidizing products of combustion originate ingfrom theheating flames. l

5. The method 0f heating billets andthe like in a continuous furnace which comprises causing heating flames to travel from both ends of the furnace and toward each other in lines substantially parallel to the path ofthe billets and redirecting the non-oxidizing products of combustion of the flames from they/discharge end to for heating travel between the billets and the heating flames to provide a blanket heat energy of the heating flames travels to heat the billets.

6. The method of heating billets and the like in a continuous furnace which comprises causing heating flames to travel in lines substantially parallel to the path of the billets and above and below the same and redirecting the non-oxidizing products of combustion from said flames to travel between the billets and the heating flames to provide blankets above and below the billets through which the radiant heat energy of the heating flames travels to heat the billets.

'7. The method of firing a continuous furnace billets and the like which comprises causing heating flames which produce radiant heat energy to travel in the direction of the travel of the billets in the furnace, dividing the non-oxidizing products heating flames and controlling the division of the products to cause a portion of the products to travel with the billets and in contact therewith toward the discharge end of the furnace to blanket the same and redirecting another portion to travel in the reverse direction between the parent flames and the billets to form a blanket through which the radiant heat of the flames passes to heat the billets by regulating the withdrawal of the products from both ends of the furnace.

8. The method of firing a continuous furnace for heating billets and the like which comprises causing heating flames to travel above and below the billets in the direction of their travel in the furnace, dividing the non-oxidizing products of combustion from the heating flames and causing portions of the products to travel with the billets and redirecting other portions to travel in the reverse direction between the parent flames of' the billets to form blankets above and below the billets through which flames passes to heat the billets.

9. The methods of firing a continuous furnace for heating billets and the like which comprises causing heating flames to travel with the billets to preheat the same before their entry into the heating chamber of the furnace, causing other heating flames to travel with the billets as they travel in the heating chamber while interposing the non-oxidizing products of combustion of the preheating flames between the second mentioned flames and the billets to provide a blanket through which the radiant heat energy passes from the second mentioned flames to heat the billets.

10'. The method of firing a continuousV furnace for heating billets and the like which comprises causing heating flames above and below the same to preheat the billets `before their entry into the heating chamber of the furnace, causing other heating flames. to travel with the billets both above and below the same as they travel in the heating chamber while interposing the non-o products of combustion of the preheating flames between the second mentioned flamesand the billets to provide a blanket through which the radiant heat energy passes from the second mentioned flames to heat the billets.

1l. The method of firinga continuous furnace for heating billets and the like which comprises causing heating flames to travel in the direction of the travel of the billets in the furnace, dividing the non-oxidizing products of combustion of combustion from the to travel with the billets through which the radiant the radiant heat of the in contact with the from the heating flames and causing a portion of the products to travel with the billetsand in contact therewith toward the discharge end of the furnace and redirecting another portion to travel in the reverse direction between the parent flames and the billets to form a blanket through which the radiant heat of the flames passes to heat the billets, causing additional flames to travel in the opposite direction to the above mentioned flames, and redirecting the nonoxidizing products of combustion of the last mentioned flames to travel with the billets to provide a blanket through which the radiant heat energy of the last mentioned flames pass 4to soak the billets.

l2. The method of firing a continuous furnace for heating billets and the like which comprises causing heating flames to travel with the billets to preheat the same before their entry into the heating chamber of the furnace, causing other heating flames to travel with `the billets as they travel in the heating chamber while interposing the non-oxidizing products of combustion of the preheating flames between the second mentioned flames and the billets to provide a blanket through which the radiant heat energy passes from the billets, causing additional flames to travel in the opposite direction to the second mentioned flames, and vredirecting the non-oxidizing products of. combustion of the last mentioned flames to travel with the billets to provide a blanket through which the radiant heat energy of the last mentioned flames pass to soak the billets.

13. The `method of controlling the operation of a continuous furnace for heating billets and theA like which comprises regulating the intensity of heat supplied to the furnace in response to variations in the temperature of the discharged gases in the flue after they have flowed off the heated billets at the discharge end of the furnace.

14. The method of controlling the operation of a continuous furnace for heating billets and the like, which comprises regulating the quantities of fuel and air supplied to the furnace in response to variations in the temperature of the discharged gases in the flue after they have flowed off the heated billets at the discharge end of the furnace.

l5. The method of controlling the operation of a continuous furnace for heating billets and the like, which comprises regulating the intensity of heat supplied to the furnace in response to variations in the temperature of the products of combustion in the flue after'they have passed heated billets at the discharge end of the furnace.

16'. The method of controlling the operation of 'a continuous furnace for heating billets and the like by combined fuel and air which comprises regulating the supply of one of the heating elements in response to variations in the temperature of the products of combustion in the flue after they have passed in contact with the heated billets at the discharge end of the furnace, and regulating the supply of the other heating element in response to the supply of the first mentioned heating element.

17. The method of controlling the operation of a continuous furnace for heating billets and the like and which is arranged to be fired at both ends which comprises regulating the quantities of heat supplied to either end in response to the temperature of the products of combustion in the iliue .after they have passed in contact with second mentioned flames to heat the ment- 'of the 'travel in the v while asaazaii the the heatedbillets at the discharge end of furnace.

18. The method of controlling the operation of a continuous furnace for heating billets and the like and which is arranged for firing adjacent'both ends which comprises during normal operation heating the billets by tiring adjacent the charging end of the furnace, and, during a temporary cessation of travel of the billetswithin the furnace, maintaining the heat of the billets adjacent the discharge end of the furnace by ring adjacent the discharge end.

19. The method of controlling the operation a continuous furnace for heating billets and th like and which is' arranged for firing at both ends, which comprises during normal operation heating the billets by ilring adjacent the charg- `nace having a preheating portion, a main heat- A Aingl portion and a soaking hearth, which comprises causing 'heating llames to travel in the direction ofy the movement of the-billets and above and xbelow the same to preheat the same as they -pass through the preheating portion. causing heating llames to travel with the billets in the main heating portion and above and below the same to heat the preheated billets, and

'saturating the heatedbillets with heat'from that portionof the products of combustion ofthe Y heating flames above the billets while the billets ing end of the furnace.. and, during a temporary cessation of travel of the billets within the furnace, maintaining the heat of the billets adjacent the discharge end of the furnace by firing ladjacent the discharge end. and regulating the quantity of firing vin either instance in response tothe temperature of the products of combustion passed in contact with the heated billets adjacent the discharge end of the furnace.

20. The method of controlling the operation of a continuous furnace for heating billets and.

the like and which is arranged for ring at either end. which comprises during normal operation heating the billets vby firing adjacent the charging end of the furnace, and in case of a tempothe billets in the main heating portion to heat are passed over the soaking hearth.-

25. The method of heating .billets and the i like while passing them through a continuous furnace having a preheating portion, a main heating portion and a soaking hearth, which com-- prises` causing heating flamesto travel in the direction of the movement of the billets to preheat the same as they pass through the preheat-l ing portion, causing heating dames to travel with the preheated billets. saturating the heated` billets with heat from the products of combustion of the preheating and heating flames while the vbillets are passed over the'A soaking hearth, and regulating the temperature of the soaked billets Aby the temperature of' the saturating products rary cessation of travel of the'billets in the furnace as the furnace temperature tends to rise above a predetermined degree-switchingthe iiring to the discharge end of the furnace, and upon resumption of travel of the billets again switch- .ing the firing to the charging end of the furnace. 2l. The method ofheating billets and the like hile passing them through a continuous furnace-having a preheating portion and a main heating portion, which comprises causing heating ilamesto travel in the direction of the movement or the billets to preheat the billets1as they passthroughthe preheating portion, and causing heating names tol travel in the same 'direction to heat the preheated billets as they'pass through the main heating portion.

22. The method of heating billets .and the like whiley passing them through a continuous' furnace having 'heating portion,- which comprises causing heata preheating portion and a main prises causing heating flames to travel in the direction of the movement of the billets to preheat the same as they pass through the. preheating porti0`n, 2ausingheatingA flames to travel with'A ,the billets in the main heating portion to heat the preheated billets, and saturating the' heated billets with heat from the products of combustion of' the preheating andv heating flames` while the billets arepassed over the soakix'ig hearth.'

24. The method of heating billets and the like passing them through acontinuous' furportion, a main heat-A ling. portionand a soaking hearth, which com- .0f combustion billets.

26. In a continuous furnace for heating bilu lets and the like and through which the billets are caused to pass from the charging end to the discharge end, means vfor introducing heating llames at the charging en'd of the'furnace which vtravel in the, same direction as the 'billets for preheating the same, and means for introducing additional heating flames in-the same direction y as the preheating flames for heating the preheated billets to an elevated temperature.

27. In a continuous furnace for heating billets and the like and .through which the billets are caused to pass from 'the charging end to the discharge end, means for introducing heating llames above and below the billets at the' charging end of vthe furnace which travel in the same direc- 'tion as' the. billets for preheating the same, and

means forintroducing additional heating flames above an'd below the billets and in the same direction as the preheating llames for heating the preheated billets to an elevated temperature.v .28. In a continuousfurnace for heating billets and the'like and through which the billets are same direction above and. below liu caused to pass fromI the charging end to the discharge end, means for introducing heating llames at the charging end of the'furnace which travel in thesame direction as the billets for preheating the same, means for introducingv additional heating ames in the same direction' as the preheating ames for heating the preheated billets j' to an elevated temperature, a soaking hearthover which the billets travel before theyare discharged from the furnace, andl means for withdrawing the products of combustion of said llames over thebiilets on the soaking hearth fand discharging them from the furnace.

29. Ina continuous .furnace for heating billets andthe like and through which the' billetsare caused to pass from the charging end to the discharge' end, means 'forl introducing heating names above and below the billets at the charging end ofthe furnacewhich travelfin the same direction as lthe billets fo'r preheating the same, means for i introducing additional4 heating' amesabove and below the billets and in the same direction as the after they' have traveled over the adjacent the discharge end of 'ing' thebillets, means preheating flames for heating the preheated bi1- lets to an elevated temperature, a soaking hearth. over which the billets travel before they are discharged from the furnace, means for withdraw'-A ing the. products `of combustion of the upper flames over the billets on the soaking hearth and discharging them from the furnace, and means for independently withdrawing the' products of combustion of the lower flames ahead-of the soaking hearth.

30. In a continuous furnace for heating billets and the like. and through which the billets are caused to pass from the charging end to the discharge end, means for introducing heating flames at the charging end of the furnace which travel in the same direction as the billets for preheating the same, means for introducing additional heating flames inthe same direction as the preheating flames for heating the preheated billets to an elevated temperature, a soaking hearth. over which the billets travel .before they are discharged from the furnace, means for withdrawing the products of combustion of said flames over the billets on the soaking hearth and discharging them from the furnace, and means responsive to the temperature of the products vof combustion passing from the soaking hearth for controlling the final heated temperature of the billets.

31. 1n a continuous furnace-for heating muets and the like and through whichthe billets are caused to pass from the charging end to the discharging end, means for introducing flames and. withdrawingthe products of combustion thereof adjacent the discharge end of the furnace, and means forintroducing other flames and Withdrawing thevproducts of combustion thereof ad'- jacent the charging end of the furnace.

. 32.' In a continuous furnace for heating billets s and the like and through which the billets are caused to pass from the chargingend to the discharging end, meansfor introducing fla-mes and withdrawing the products of combustion .thereof adjacent the discharge end ofthe furnace, and

and the like,

means for withdrawing the products Vof combustion of said heating flames adjacent the discharge end of the furnace.-

35. In a continuousfurnace for heating billets Athe combinationl of an 'elongated chamber through which the billets pass from the charging end to the discharge end, means for introducing heating haines into the furnace,.a flue for withdrawing the products of combustion adjacent the discharge end of the furnace, and pyrometric means in said flue responsive to variations in temperature in the withdrawn products after they have entered the'ilue and arranged to regulate said flame introducing means.

36. In a continuous furnace for heating billets and the like, the combination of a furnace chamber having a soaking hearth adjacent the dis; charge end over which the billets pass, means for heating said billets as they pass through said chamber, an outlet adjacent the discharge end of the furnace for conducting the products' of combustion after they have passed over the billets on the soaking hearth, heat responsive means in 1 said outlet for controlling the heat supplied to the furnace chamber to regulate the temperature of the billets on the soaking hearth.

37. I n a continuous furnace for heating billets and the like, the combination of afurnac'e chamber through which the billets pass from the` charging end to the discharge end and having a soaking hearth adjacent the latter end, means for heating the furnace chamber from adjacent the charging end during normal operation, means` Y forA heating the billets on the soaking hearth during a cessation of the billets in the furnace, an

outlet adjacent the discharge end of the. furnacechamber for conducting the products of combustion after they have passed over the billets on thesoaking hearth, heat responsive means in said outlet for controlling the heat delivered to the furnace to regulate the temperature of the billets on the soaking hearth, and means for semeans for introducing other flames and withdrawing' a portion of the products of combustion thereof adjacent the charging end4 of the furnace and withdrawing the remainder of said products the furnace.

-33. In a continuous furnace for heating billets andthe like, the combination of a main heating chamber, a preheating chamber connected to the main heating chamber, a hearth extending from the charging end of the preheating chamber through the main heating chamber for supportfor introducing heating flames at 'the charging end of the vp reheatng chamber. andseparate means for introducing heating flames at the charging end of the main heating chamber, and outlet means for withdrawing the products of combustion of said heating- .charging end to the flames adjacent to the discharge endvof the fur 3 4. In a continuous furnace for heating billets and thelike. the combination of a main heating chamber having a soaking hearth adjacent the discharge end, a preheating chamber connected to the other end of the main heating chamber, a hearth extending from the `charging end of lthe preheating chamber through the main heating ,chamber forsupporting the billets, means forinlectively transferring the application of the heat .to a selected end of the furnace when the quantity of heat delivered to the furnace reaches a predetermined rate of ilow.

38. The method of consisting of the products of comlmstion of saidheating flames.

39; In a continuous furnace for heating billets and the like, the combination vof. a furnace chamber through which the billets trave1 from the discharging end, burners at the charging endof. troducing heating flames to heat the billets as they' enter thel furnaceA chamber, burners at the discharge end of the furnace chamber for in inducing heating names to mak the muets before they leave the furnace chamber, an outlet for the discharge of products of combustion from the.

furnacev chamber, -and means responsive to the temperature of the products of combustion in said outlet for regulating said heating names.

troducing heating flames at the charging end of of the main heating chamber and at the charge end of the main chamber, and

and separate means for outlet they enter the'furnace chamber,

40. In'al continuous furnace for heating billets and the like. the combination of a'furnace cham ber through which the billets travel from the charging end tothe discharging burners at. the charging end of the furnace chamber for introducing heating flames to heat the billets as heating billets and the like' which comprises causing heating flames to travel burners at discharge end of the furnace chamber for introducing heating flames to vsoak the billets before4 they leave the furnace chamber, and means for withdrawing products of combustion adjacent the discharge end.

4l. In a continuous furnace for heating billets and the like, the combination of a furnace chamber through which the billets travel from the charging end to thev discharge end, burners at both ends of the furnace chamber for introducing heating ames in lines substantially parallel to the path ,ofl the billets, means for maintaining a flow of non-oxidizing gases between the heating flames and the billets, and a flue at the end of the furnace for withdrawing the nonoxidizing gases flowing over the billets about to be discharged.

42. In a continuous furnace for heating billets and the like, the combinationof a furnace chamber through which the billets travel from the charging endto the discharge end, burners at both ends of the furnace chamber for introducing heating flames in lines substantially parallel to the path of the billets, means for maintaining av blanketing layer of non-oxidizing products of combustion between the heating flames and the billets, and a flue at the end of the furnace for withdrawingthe non-oxidizing products of combustion flowing over the billets about to be discharged.

43. In a continuous furnace for heatingbillets and the like, the combination of a furnace chamber through which the billets travel from the charging end to the discharge end, burners at both ends of the furnace chamber'for introducing heatingilames in lines substantiallyparallel tothe keting layer of the non-oxidizing products of combustion, originating from the heating flames,

between the billets and the heating flames, and a flue at the end of the furnace for withdrawing the non-oxidizing products of combustion flowing over the billets about to be discharged.

44. The method of heating billets and the like in a continuous furnace, which comprises causing heating flames to travel, in lines substantially parallel with the travel of the billets, from both the charging end and discharging end of the furnace, interposing a blanket of Vnon-oxiding gases between` the billets and the flames traveling from the charging end of the furnace, and reversing the direction of travel of the products of combustion ofthe flames traveling from the discharge end of ythefurnace to inter-pose a blanket of non-oxidizing gases between the billets and said last mentioned names. v

45. The method of heating steel billets to roll- 11:18temperaturewhichcomprlsestliesteell throughaheatedfurnacea,thenheat v ing'the steel from above during the nal portion of its travel through the furnace over a solid xefractory hearth, and heating the hearth from below by passing thewastegases from the furnaceincontactwlththeundersideofthehearth.

46.Inacontinuousfurnaceforheatingbillcts and the like and through which the billets are caused to pass from the charging end to the discharge end, means for introducing v heating flames at the charging end of the furnace which., travel in the same direction as the billets for heating the same, a soaking hearth in the furnace over which the billets pass before they leave the furnace, a gravity discharge slope at the'end of the hearth down which the billets slide as they 47. In a continuous furnace for heating billets and the like and through which the billets are caused to pass from the charging end to the discharge end, means for introducing heating flames atthe charging end of the furnace which travel in the same direction as the billets for heating the same, heat exchange means below said furnace, a soaking hearth in the furnace over which the billets pass before they leave the furnace, said hearth also forming the top wall of the heat exchange means, and ues at the discharge end of the furnace for withdrawing the products of combustion of said flames over the billets on the soaking hearth and directing them to the heat exchange means under the hearth.

48. In a continuous furnace for heating billets and the like and through which the billets are caused to pus from the charging end to the discharge end, means for introducing heating flames above and below the billets at the charging end of the furnace which travel in thesame direction as the billets for heating the same, heat exchange means below said furnace having a stack flue connection, a soaking hearth in the furnace over which the billets pass b efore theyleave the furnace, flues at the discharge end of the furnace for withdrawing the products of combustion of said flames over the billets on the soaking hearth, ilues ahead of the soaking hearth for independently withdrawing the products of combustion of the flames below the billets, both of said flues directing the products of combustion to said heat exchange means, and damper means in all of said ilues for separately regulating the draft therein.

49. 'Ihe method of operating a continuous furnace for heating billets and the like which combillets at both ends of the furnace to provide a Vgreater 'quantity of lgasesilowing over the billets atthechargingendthanatthedischargeend sothat the surface temperature of the billets does not exceedthetemperatureofthebodyofthe -billetsatthetimeoftheirdischarsefromthe -furnace.

WILLIAM A. NORTON.