US2763582A

US2763582A - Apparatus and method of producing protective combustion atmospheres

Info

Publication number: US2763582A
Application number: US474462A
Authority: US
Inventors: Frank A Rusciano
Original assignee: Metallurgical Processes Co
Current assignee: Metallurgical Processes Co
Priority date: 1954-12-10
Filing date: 1954-12-10
Publication date: 1956-09-18
Anticipated expiration: 1973-09-18

Description

Sem.. M8. 1956 F. A. RUSCIANO 2,763,582

APPARATUS AND METHOD oF PRODUCING PROTECTIVE COMBUSTION ATMOSPHERES Filed Dec. 1o, 1954 a sheets-snaai 1 J7 Vj f7 j jf .INI/ENTOR.

PARUSQANO Sept.. l, 1956 F. A. RusclANO 2,763,582

APPARATUS AND METHOD 0F PRODUCTNG PROTECTIVE coMBUsTToN ATMosPHEREs Filed Dec. lO, 1954 3 Sheets-Sheet 2 i441' A |1 V INVENTOR. F.A .RUSClANO ATTORNEY A. RusclANo 2,763,582

mpi. 18, 1956 F APPARATUS AND METHOD OF PRODUCING PROTECTIVE COMBUSTION ATMOSPHERES 3 Sheets-Sheet 3 Filed DeC. 10, 1954 amil] if fz INVENTOR. F. A.RUSCIANO W MM AT ORNIEY Unit States atent O APPARATUS AND METHOD F PRODUCING PRO- TECTIV E COMBUSTION ATMOSPHERES Frank A. Rusciano, New York, N. Y., assignor to Metallurgical Processes Co., Newark, N. J., a corporation of New Jersey Application December 10, 1954, Serial No. 474,462

Claims. (Cl. 14S-16.5)

This invention relates to an industrial furnace for the scale-free heating of metal in the products of reaction of air and the fuel which serves as the principal heating medium of the furnace. It is particularly suitable for operation with oil fuel but is not limited thereto and may be utilized either for neutral heating of metal or for carburization.

The invention utilizes the principles set forth in the copending application of H. I. Ness et al., Serial No. 255,774, filed November l0, 1951, and entitled Two Stage Combustion Furnace, that is, a mixture of fuel and air having a deficiency of air of approximately 50% is reacted to substantial completion and the stabilized products of the reaction are utilized as the protective atmosphere and as a source of heat for the work in the work heating chamber, these products then being vented to a second combustion chamber, which is isolated from but disposed in heat transfer relation to the work cham* ber, wherein they are mixed with air in an amount substantially equal to said deficiency and burned to completion, thereby providing additional heat to the work chamber.

in order to produce the work protecting atmosphere from the air deficient air-fuel mixture, it is necessary to supply external heat to the constituents in order to increase the reaction temperature thereof substantially above the normal temperatures of these reactions, since this latter temperature is not suicient to carry the reactions to completion. When employing a gaseous fuel this additional heat energy may be obtained by ring the mixture into contact with a hot surface, such as the arch, of the work heating chamber. However, when employ ing oil fuel, the problem is greatly increased due `to the slow cracking rate of the oil and its tendency to form soot when an effort is made to burn it with any appreciable deficiency of oxygen.

One of the objects of the present invention is, therefore, to provide a furnace of the two stage combustion type in which oil may be satisfactorily employed as the fuel.

Another object is to provide a two stage combustion furnace having a high heat transfer efficiency from the secondary reaction products to the work.

A further object is to provide such a furnace in which the primary reactions are completed with great rapidity and without the formation of soot.

A still further object is to enable air-fuel mixtures having an air deficiency in excess of 50% to be employed in the primary reactions whereby work chamber atmospheres which are non-decarburizing or even carburizing may be produced.

Another object is to provide a reaction chamber for a two stage combustion furnace in which the primary reactions may be effected at high temperatures and which will have a long commercial life.

Still another object is to provide a two stage combustion furnace of high operating eiciency and low cost.

Other objects and advantages will hereinafter appear.

In accordance with the present invention I provide a furnace having a work heating chamber and a secondary combustion chamber partitioned from the work heating chamber by a wall of good heat conductivity. In the specific embodiment shown the secondary combustion chamber is disposed above the Work chamber between spaced refractory arches. The atmosphere employed in the work chamber is produced by the thermal reactiort of fuel and air. When a non-scaling atmosphere is de` sired, the ratio of fuel and air should be such as to pro-4 duce, when the reactions are carried to completion and stabilized, reaction products in which the sum of the CO2/CO and the H2O/Hz ratios is substantially equal to 1. In the case of gaseous fuel this ratio summation is obtained with approximately 52% of the air required for complete combustion. With fuel oil, in which the ratio of contained carbon to hydrogen is somewhat higher, the non-scaling products may be obtained with an air deficiency of from 40% to 42%. As previously indicated, these rich fuel-air mixtures are not completely reactable by the exothermic heat of combustion alone and must be further energized endothermically. In the case of oil fuel this endothermic energy must be applied at a relatively high temperature and at a high rate so as to vaporize the oil and crack it completely down into its constituents, hydrogen and nascent carbon, in an extremely short interval, so that all of the carbon will have an opportunity to combine with the meager oxygen supply. When the cracking is extended over a longer period, the lighter constituents crack first and use up the oxygen in forming `CO2 and H2O. The later formed nascent car bon must either react endothermically with the CO2 and H2O to form CO or deposit out as soot. Once this soot has formed it is substantially inactive with respect to the gaseous products. However, if the cracking of the heavy constituents of the oil can be effected substantially simul` taneously with the lighter constituents by means of rapidly absorbed heat from an external source, the thermal reactions may be completed and stabilized with the proper CO2/CO and H2O/H2 ratios without appreciable soot formation and the resulting atmosphere supplied to the work chamber will be clear. When it is desired to produce a work chamber atmosphere which is not only nonscaling but non-decarburizing, that is, having a carbon potential in balance with the steel to be heated or, if desired, carburizing to the steel, it is necessary to employ a greater air deficiency to the fuel thus requiring the application of a greater amount of externally applied heat to properly effect the reactions.

The furnace of the present invention provides one or more primary reaction chambers for carrying out the reactions by Whic-h the Work chamber atmosphere is produced. These primary reaction chambers are shown in the form of segmented arched tubes extending through the secondary combustion chamber in a maner to rapidly transmit the heat generated in this combustion chamber to the reacting air-fuel mixture. The primary reaction tubes are in direct communication with the Work chamber to supply the reacted products thereto, these products after passing through the work chamber being inspirated into the secondary `combustion chamber with additional air to form the combustible medium therein. Since about 25% or less of the available heat of the fuel is released in the primary combustion, and since the resulting products are substantially at the work chamber temperature when introduced into the secondary combustion chamber, the secondary combustion occurs at a rapid rate and va high temperature. Therefore, by producing this combustion in suitable heat transfer `relation to the primary combustion tubes, a rapid and etiicient heating of the latter occurs. The use of a number of relatively small primary reaction tubes also enhances the rapid heat transfer to the primary mixture and the use of arched tubes provides an extremely hot arched refractory surface against which the primary mixture and the reacting products are brought into scrubbing relation to further enhance the heat transfer.

The invention will best be understood by reference to the accompanying drawings in which:

Fig. l is vertical longitudinal sectional view of a furnace embodying the present invention;

y Fig. 2 is a vertical transverse sectional view of the furnace taken on the line 2--2 of Fig. l

Fig. 3 is a horizontal sectional view of the furnace taken on the line 3 3 of Fig. 1;

Fig. 4 is a fragmentary view, partly in section on the line 4--4 of Fig. 3;

Fig. 5 is a vertical sectional view corresponding to Fig. 2 but showing a modified arrangement;

Fig. 6 is a fragmentary vertical 'longitudinal sectional View corresponding generally to Fig. l showing a modified slot venting arrangement; and

Fig. 7 is a sectional view on the line '7-7 of Fig. 6.

- Referring first to Figs. l and 2, the furnace structure therein shown is composed of an outer metal shell 10 supported by suitable structural steel elements 11, the remainder of the furnace contained within said shell being composed entirely of built-up ceramic refractory. The furnace includes a work heating chamber 12, a combustion chamber 13 disposed over the heating chamber, and a series of combustion tubes 14 extending through the combustion chamber 13 and in communication with the work heating chamber.

The work chamber 12 is defined by a floor 15,

side walls

16 and 17, rear wall 18, front wall 19 containing a work opening 21 closed by a door 22, and an arched roof 23. The combustion chamber 13 is defined by the arch 23, side and end walls 16 to 19, and an arched roof 24. The combustion tubes 14 are composed of assembled short arc-shaped sections of a high temperature refractory, such as silicon carbide, having interlocking annual tongue and grove end formations whereby relatively long tubes having a wide span may be fabricated and held in close fitting engagement without exerting excessive pressure on the

abutment blocks

25, 26 disposed at opposite ends of the assembly and supported by the

side walls

16 and 17; respectively. The arched formation of the tube assemblies, in addition to providing long span strength, eliminates the necessity for complicated resilient abutments, such as are required to compensate for the expansion of the tubes in the case of straight horizontal sectional tubes.

Burner blocks 27 are disposed in alignment with the openings in the abutment blocks 25, suitable burners 28 as oil, from a manifold 29 and air by conduit 31. The abutments 26 which terminate the opposite end of tubes 14 have an elbow passageway therein aligning with vertical tube sections 32 which directs the products of combustion from the tubes into a bifurcated block 33 (Fig. 4) having a pair of spaced entrance ports 34 wherebyto obtain a more even distribution of the products in the work chamber 12.

As previously explained, the air-fuel mixture introduced through the burners 28 is highly deficient in oxygen, amounting in the case of oil to 58% to 60% of the aeration required for complete combustion. This mixture, when reacted to completion, will produce reaction products which are neutra-l to steel and thus may be supplied to the work chamber as a protective atmosphere. The volume of such products must be suicient to maintain the work chamber full at a slight positive pressure at all times, that is, when the door 22 is either open or shut, so as to prevent entrance of air into the furnace. In a furnace of the nature shown, having a relatively large door opening, it may be necessary to provide of the order of one hundred volumetric changes in the work chamber atmosphere per hour. rIlhis large volume of partially combusted gas has a very large unused B. t. u. content, as stated, only about one-quarter of the available heat of the fuel being released in the primary reactions. The amount of heat so released from the fuel in the reactions in tubes 14 is insufficient to supply the required heating temperature and rate to the work in the chamber 12. Furthermore, particularly in the case of oil fuel, the unassisted reaction temperature of this rich mixture is insucient to crack down the oil and cornpletely react the carbon and hydrogen constituents thereof with the available air, with the result that large deposits of soot are formed and a considerable proportion of the hydrocarbons remain undissociated. Any unburned carbon or hydrocarbon eiectively reduces the fuel to air ratio which in turn increases the CO2/CO and H2O/H2 ratios of the resulting products and, further, any deposited carbon effectively decreases the C/Hz ratio of the fuel which, with a given percent aeration, further increases the CO2/CO and H2O/H2 ratios of the resulting products. As a consequence, the desired neutral atmosphere is not obtained.

Both of the above difficulties, i. e., low temperature and low heating rate in the work chamber and incomplete reaction of the rich mixture in the combustion tubes 14 are yovercome `by releasing the latent heat in the work chamber atmosphere by the further and complete combustion thereof With additional air in the combustion chamber 13. For this purpose the chamber 12 is provided with Vent ports 35 disposed adjacent the oor 15 in the side wall 16 and similar ports 36 disposed in the end wall 18. These ports communicate with vertical ues 37 (for ports 35) 'and 38 v(for ports 36) extending upwardly through the side and end walls and terminating at their upper ends in

ports

39 and 40, respectively, opening into the combustion chamber 13. Supplemental air for cornbustion of the gases vented from the work chamber is provided by nozzles 41 (for ports 39) and 42 (for ports 48). A further function o-f the

nozzles

41 and 42 is to provide a suctional effect in the flues 37 and 38 to enable fa controlled ow of the primary combustion prodv ucts through the work chamber and to enable a large l these flues any air or products of combustion of the furbeing associated therewith and supplied with a fuel, such nace gases with air entering through the open door.

As will be noted, the air nozzles 42 tand 46 tire directly beneath the tubes 14 so that the secondary combustion occurs largely in the space between the tubes yand the arch partition 23. Consequently the partition 23, which is composed of thin interlocking waffle type blocks of a refractory having high heat conductivity, such as silicon carbide, yare highly heated and convey this heat to the work chamber 12. In addition the combustion gases pass upwardly over and around the tubes 14, to the combustion chamber vents 50, thereby rapidly heating these tubes. The nozzles 41 in the side wall 16 are disposed to each side of tubes 14 at the burner ends thereof so as to tire therebetween and between the tubes and the side walls and thus to supplement the heat input to the primary mixture at the point where it enters the tubes 14. Ey virtue of this arrangement the incoming air-fuel mixture is heated very rapidly to a high temperature, thus quickly vaporizing and cracking the oil and thereby facilitating its reaction with the meager oxygen supply available to it. The normal combustion temperature of :an air deficient mixture which is capable ofproducing a non-scaling 'atinosphere in the work chamber is of the order of 2l00 F., whereas the temperature which must be attained in the combustion chamber 13 in order to produce sucient heat in the tubes 14 to drive the reactions to completion whereby to prevent soot deposition and obtain 'a clear atmosphere is, with light fuel oils, of the order of 2500 F. With heavier oils it is necessary to obtain even higher primary reaction temperatures. The heat absorbed by the primary reaction products in tubes 14 in addition to promoting these reactions is carried into the work :chamber to increase the heating temperature and rate of the work.

Reference was made to the provision of the vents 43 in the door opening arch to prevent influx of air into the furnace upon opening of the door 2.2. To further prevent sueh influx along the floor or hearth of the furnace l provide a series of vents, such as Sl, in the door sill 52, each vent 5l having a suction producing air nozzle 53 firing into a conduit 54 beneath the furnace. The nozzle 53 is supplied with a valve 55 which may be opened in any suitable manner upon opening of the door Z2 -as by a door extension arm to supply air to the nozzle 53 and thus divert into the vents 51 air attempting to enter the furnace at the hearth level.

Air for the

secondary air jets

41, 42 and 46, is provided, from any convenient source under suitable pressure by vertical conduits 5d extending downwardly to the respective nozzles from above the furnace. The supply manifolds 57 for the conduits S6 are shown extending above the vents dii ot' the combustion chamber 13 whereby tof preheat the secondary air. The primary air for burners 2d may also be similarly supplied with preheated air.

lt will be appreciated that the Volume of atmosphere supplied to the chamber i2 rnust be suicient to keep the furnace under slight pressure with the door open whether the furnace be on full fire or on control. lt is desirable, therefore, in the design of the furnace to control the design variables, such as door size, radiation losses, the height of arch 235, and its heat conductive capacity, and the like, so that when the furnace is on control the volume or' atmosphere necessary to maintain the furnace full a all times will not be. greater, upon combustion thereof in chamber i3, than that required to maintain the tubes i4 at the necessary temperature and to supply the normal radiation losses from the furnace. Additional heat maybe supplied to chamber i3 by a series of burners, auch: as shown at which tire into the arch chamber i3 under the control of a suitable pyrometer. These burners are provided in case it is desired to operate the furnace under conditions different from those for which the furnace is previously designed and in which the secondary reactions are insullieient by themselves 'to maintain the tube i4 up to the required reaction temperature. Any suitable arrangement may be provided, of course, for varying the amount of the air-fuel mixture supplied to both the burners 2d 'and 53 depending upon the open. or closed condition of the door 22 and the distribution of the air supply to the

nozzles

41, 42 and 46, may be varied depending upon these same conditions. Thus with the air-fuel mixture supplied to burners 23 adjusted to a. value suflicient to mia-intein the furnace full with `the door open, the air induction nozzles 46 may be provided with. all ora relatively large proportion of the total secondary air required to complete the combustion of the furnace chamber gases so as to Ainduce la `propofrtionately largel share of the furnace chamber gases through the vents 44 to keep the door slot 2@ full against influx of air through the door opening. With the door closed fa different distribution of the secondary air to nozzles 4l, 42 `and 46` .may be provided to produce the best heating condition in the secondary combustion chamber 13 and uniformity of the atmosphere distribution in the work chamber l2. ,lt may also be desirable to reduce the air-fuel mixture to the primary reaction burners 28 when the door is closed,

since under this condition le'ss atmosphere is normally reiii! 6 quired to maintain the desired low positive pressure in the heating chamber.

In the present embodiment all of the secondary ai'r is shown as being supplied by the' induction nozzles 4.1, 42, and 46 associated with the work chamber vents 35, 38 and 44. However, it is to be understood that a portion of this secondary air may be supplied to chamber 13 by inlets which are not in inductive relation to the work chamber vents, as disclosed in my copending application Serial No. 429,493, tiled and entitled Method of Venting Controlled Atmosphere Furnaces.

In the foregoing description reference has been made only to the use of the air-fuel mixtures in the primary reaction tubes 14 which Iproduce non-scaling reaction products, that is, products which have CO2/CO and H2O/H2 ratios the summation of which is one. It is to be understood, however, that the tubes 14 may also be employed as endothermic cracking units for producing furnace atmospheres which are non-deca'rburi'zing or, if desired, earburizing in nature. With richer mixtures of this nature it will, of course, be necessary lto supply a larger proportion of secondary air to complete their com bustion in the secondary combustion chamber 13 with a corresponding greater heat release in this chamber. Irrespective of whether endothermic or rich exothern'iic reactions are employed for producing the work chamber atmosphere, the primary heat for eifecting these reactions and for heating the work is obtained 'from the secondary combustion of the primary products. The burners 58, which utilize a fully combustible air-fuel mixture, are of a supplemental nature to give greater latitude in the operation of the furnace under varying conditions and in many instances need not be utilized.

As previously stated, with the use of light fuel oils it is necessary to maintain the 'reaction tubes 14 at ternpcratures of the order of 2500 F. in order to obtain a sufciently rapid and complete reaction to prevent soot deposition and resulting cloudy furnace atmosphere. When the work temperatures are also high, of theV order of 2300 F. to 2400" F., this presents no particular problem due to the normal temperature differential existing between the work chamber and the secondary combustion chamber. Under some conditions, however, when the furnace is operated at lower work temperatures and the work is retained in the furnace for appreciable periods after it is up to temperature, overheating may occur. If the door is maintained closed during this soaking period, the amount of atmosphere required to maintain the work chamber full will be greatly reduced and the volume of mixture supplied to burners 28 may be reduced sufciently to maintain the desired temperature in work chamber 12, that is, to obtain a balance between the heat generated and the furnace radiation losses. When it is necessary to maintain a relatively large volume of atmosphere to a work chamber operating at a temperature of, said, around 2000 F., a more serious problem is involved. As will be evident, the tube 14 serves as a very effective heat transfer agent between the secondary combustion chamber and the work chamber by conveying the heat produced by the secondary combustion to the primary reaction products Which enter the Work chamber 12 at the stated reaction temperature of 2500" F. or higher. This feature is highly advantageous in the rapid heating of the work but makes it difficult to maintain a wide temperature differential between the secondary combustion chamber and the work chamber, and in some eases, where low temperature operation is required, may necessitate the use of a heavy arch 23 of good insulating mate# rial, rather than the thin conductive arch disclosed, so as to obtain the heating of the work chamber primarily by the hot primary reaction products entering through the inlets 34. In Fig. 5 I have shown a modified arr`angement which also is effective to enable lower Work cham ber temperatures to be obtained. Thisiform is Partien- ".7 larly suitable when non-decarburizing or carburizing atmospheres are required.

The `construction of Fig. differs from the form previously described in the' provision of a special block 69 forming a part of the outlet portion of the tube 14, this block having an air cooled nozzle or tube 61 extending therethrough and projecting into the tube 14. The tube 61 is connected by a conduit 62 to a source of gaseous fuel under suitable pressure and by conduit 63 to a source of air for the cooling jacket thereof. The nozzle 61 is provided with a restricted outlet port arranged to discharge a stream of gaseous fuel into the tube 14 in a direction contra to the flow of reaction products through .the tube. In this figure I have also shown the arch 23 as composed of a heavy section of a refractory having good insulating characteristics, although it is to be understood that the nozzle 61 may be used advantageously with the thin arch structure of Fig. 2. As will presently appear, the arrangement of Fig. 5 permits a lower temperature to be maintained in the secondary combustion chamber and also effectively reduces the temperature of the primary reaction products entering the work chamber.

Let it be assumed by way of example that it is desired to produce a neutral atmosphere in the work chamber resulting primarily from the reactions of a fuel oil and air. In the absence of the gaseous fuel inlet 61 it would be necessary to employ about 58% aeration of the oil fuel to produce this atmosphere with a relatively high temperature in the combustion chamber 13 to effect the reactions, In the modification of Fig. 5, however, it is contemplated that a portion of the fuel will be supplied by nozzles 61 in the form of a gas with all of the air supplied through the burners 28. Thus with a portion of the fuel supplied as a gas, the quantity of oil supplied to the burners 28 may be `correspondingly reduced, resulting in an effectively greater percent aeration at the burners 28. The air-oil mixture supplied to burners 28 may be one that is cleanly combustible, that is, combustible without carbon deposition. An air-oil mixture having about 70% aeration will meet this condition. This means that approximately 85% of the fuel will be supplied, as oil, through the burners 28 and 15% as gas through the nozzles 61. The normal unassisted combustion temperature of such an air-oil mixture will be of the order of 2300 F. to 2400 F., and this mixture, therefore, will be burned cleanly, that is, with all of the carbon combined with oxygen in the form of CO or CO2, before coming in contact with the gaseous fuel entered through the nozzles 61. This initial combustion will be accelerated by the tubes 14 which, due to the external heat of the secondary combustion in the chamber 13, are maintained at or above the primary combustion temperature so that at least a portion of the heat required for cracking down the oil is obtained from the secondary combustion without, however, the necessity of maintaining a high heat head in the secondary combustion chamber. As the primary combustion products come into contact with the raw gas adjacent the nozzle 61, they are reacted therewith. The tendency of the gas to form soot is very low, as compared with oil, and with the relatively small proportion of gas employed, these subsequent reactions may be completed under the stimulus of the hot primary reaction products and of the external heat applied to the tube 14, without soot formation. However, since these reactions are endothermic, they absorb heat from the primary reaction products, thereby lowering the temperature thereof prior to entry into the work chamber and thus enabling a work chamber temperature to be maintained which is substantially below the primary reaction temperature.

In case a carburizing or non-decarburizing atmosphere is desired, the amount of gas supplied by the nozzle 61 may be increased sufficiently to produce the required atmosphere. Due to the location of the nozzle 61 adjacent the discharge end of the tube 14, the cracking of a portion of the greatly increased gas supply required for carburizing may be delayed until the products enter the work chamber, thereby greatly increasing the carburizing potency of the products.

In Figs. 6 and 7 I have shown an added feature provided for the purpose of improving the slot venting at the door 22. A combustion chamber 66, disposed beneath the door slot 21, has an inlet passageway 67 for the primary combustion products extending from the entrance block 33 to a burner ring 68 positioned in the end of the combustion chamber 66, so that during normal operation of the furnace the rich primary products will ow into chamber 66. The chamber 66 extends through the full width of the slot 21 and has a series of openings 69 extending upwardly to the slot opening substantially beneath the slot vents 43, whereby a `circulation of the primary products is produced through the passageway 67, chamber 66, openings 69 and vents 43, under the suctional effect of the nozzles 46, thus producing a curtain of such products across the door opening. With the door closed any air seepage into the furnace about the door opening will combust with this atmosphere curtain and the products thereof will be drawn directly into the vents 43, thus precluding any seepage of cold air along the floor of the furnace towards the work.

An air jet nozzle 71 is also positioned to discharge into the burner ring 68 during the time the door 22 is open. For this purpose the air supply line 72 is provided with a normally closed valve 73 adapted to be opened by the arm 74 whenever the door 22 is raised. The suction produced by the nozzle 71 draws an increased quantity of the primary products through the passageway 67 and supplies sufficient air for complete combustion thereof in the combustion chamber 66, the resulting products serving as a gas curtain across the slot 21 to prevent entrance of air through the door. Since this curtain is composed of completely burned gases it is substantially non-reactive with the external air which comes into contact therewith. Some combustion will occur between the curtain and the furnace atmosphere gases at the inner face of the curtain but since there is no free oxygen in the gas curtain this reaction will be of a greatly reduced intensity compared to the reactions which take place when the rich furnace atmosphere is brought into direct contact with the eX- ternal air. The arrangement of Figs. 6 and 7 results in much greater clarity through the slot and less danger of flame flare-out through the door opening. It also reduces the door slot temperature thereby improving the loading and unloading conditions of the furnace. It is to be understood that the combustion chamber 66 may be used independently of or in conjunction with the door sill vent S1.

It is evident that the invention is susceptible to numerous variations and embodiments without departing from the essential attributes thereof, and I contemplate all such modifications as coming within the scope of the appended claims.

What I claim is:

l. A furnace for the scale-free heating of work cornprising a work heating chamber for the work to be heated, a roof for said chamber, a combustion chamber disposed over said heating chamber with said roof forming a common partition between said work heating chamber and said 'combustion chamber, a primary reaction chamber disposed within said combustion chamber, means for supplying a mixture of fuel and air, having a predetermined deficiency of air, to said reaction chamber, a conduit extending from said reaction chamber to said work heating chamber, by which the products of the thermal reaction of said fuel-air mixture may be conducted into said work chamber, said furnace having a plurality of exhaust passageways extending from said work heating chamber to said combustion chamber, by which said reaction products may be conducted from said work heating chamber into said combustion chamber, means for supplying air to said combustion chamber in an amount substantially equal to said deficiency, for completing the combustion of said reaction products in said combustion chamber and venting means for said combustion chamber for the products of said last combustion.

2. A furnace constructed in accordance with claim 1 in which said roof is composed of a plurality of thin arcuate interlocking ceramic tile sections forming a continuous arch.

3. A furnace constructed in accordance with claim 1 in which said reaction chamber comprises a refractory tube extending across said combustion chamber.

4. A furnace constructed in accordance with claim 1 in which said reaction chamber comprises an arched ceramic tube extending across said combustion chamber.

5. A furnace constructed in accordance with claim 1 in which said reaction chamber consists of an arched tube composed of a pluraltiy of interlocking arcuate tubular sections of ceramic refractory, and said means for supplying a mixture of fuel and air to said reaction chamber comprises a burner disposed in said one end of said tube.

6. A furnace constructed in accordance With claim 3 in which said exhaust passageways extend into said combustion chamber beneath said tubes and in which said venting means for said combustion chamber is disposed above said tubes.

7. A furnace for the heating of metal comprising a work heating chamber having an opening for the insertion of work, a roof for said chamber, a combustion chamber disposed over said heating chamber and separated therefrom by said roof, a plurality of spaced parallel conduits extending across said combustion charnber, each of said conduits having a passageway extending from one end thereof into said work heating chamber, a burner extending into the opposite end of said conduit, said furnace having a plurality of exhaust flues extending trom said work heating chamber into said combustion chamber, and venting means for said combustion chamber.

8. A furnace constructed in accordance with claim 7, in which said conduits are composed of a plurality of interlocking arcuate tubular sections forming continuous arched tubes extending across said combustion chamber, abutment blocks at opposite sides of said combustion chamber for supporting said arched tubes, said blocks having openings therethrough forming a continuation of said tubes, and a burner block in alignment with one of said abutment blocks of each tube into which said burner extends.

9. A furnace constructed in accordance with claim 7, in which said exhaust tiues enter into said combustion chamber beneath said conduits and said venting means are disposed above said conduits.

10. A furnace constructed in accordance with claim 7, in which each of said passageways extending from said conduit into the work heating chamber is divided to form a plurality of spaced openings into said work heating chamber.

l1. A furnace constructed in accordance with claim 7, having means extending into said conduits adjacent to said passageways for the introduction of a hydrocarbon fuel therein.

12. A furnace for the heating of metal comprising a work heating chamber having an opening for the insertion of work to be heated, a gas generating chamber having a passageway extending into said work heating chamber, a combustion chamber surrounding said gas generating chamber, means for supplying a combustible mixture of fuel and air to said combustion chamber, means for supplying a mixture of fuel and air to said gas generating chamber at a point remote from said passageway and separate means for supplying a hydrocarbon fuel to said gas generating chamber at a point adjacent to said passageway.

13. A furnace constructed in accordance with claim 12, in which said means for supplying a combustible mix-v ture of fuel and air to said combustion chamber includes means for withdrawing from said work heating chamber the gas generated in said gas generating chamber and conducting the same into said combustion chamber.

14. A furnace constructed in accordance with claim l2, in which said gas generating chamber is composed of a plurality of conduits extending across said combustion chamber, said mixture of fuel and air being supplied to one end of each of said conduits and said hydrocarbon fuel being supplied to the opposite end of said conduits.

15. A furnace for the scale-free heating of work comprising a work heating chamber having a passageway for the entrance of work into said chamber, means for producing a combustible atmosphere for said work heat ing chamber composed of the thermally reacted products of a mixture of fuel and air, having a large deficiency of air for complete combustion, a combustion chamber, means for supplying fuel and air in a combustible ratio to said combustion chamber for combustion therein, means forming conduits extending from said combustion chamber into said passageway at one side thereof for the passage of the products of said combustion from said combustion chamber into said passageway, means forming vent flues disposed at the opposite side of said passageway for the conduction of gases away from said passageway, and suction means for said ilues for drawing the products of said combustion across said passageway and into said tlues.

16. A furnace constructed in accordance with claim 15 and having a door normally closing said passageway and means operated concurrently with the opening of said door for controlling the supply of air to said combustion chamber.

17. A furnace constructed in accordance with claim 15, having a second combustion chamber, means for conducting said combustible atmosphere from said work heating chamber to said second combustion chamber, and means for supplying air to said second combustion chamber for reaction with said combustible atmosphere therein.

18. A furnace constructed in accordance with claim 17 in which said means for producing a combustible atmosphere comprises a reaction chamber disposed in heat transfer relation to said second combustion chamber, means for introducing a mixture of fuel and air into said reaction chamber and means for conducting the products of said reaction to said work chamber and to said rstmentioned combustion chamber.

19. The method of producing a heating and non-scaling atmosphere for metal contained in a furnace heating chamber which comprises mixing a fuel and air in combustible proportions, thermally reacting said mixture, sup plying supplemental heat to raise the reaction temperature of said mixture to above the normal combustion temperature thereof to accelerate said reactions, permitting said reactions to continue to substantial completion and there after endothermically reacting an unreacted hydrocarbon fuel with the heated products of said reaction to decrease the temperature thereof and increase the carbon and hydrogen content thereof, and passing the resulting hot products about the metal to be heated.

20. The method of heating and carburizing ferrous metal contained in a heating chamber comprising mix ing fuel and air in a proportion which upon thermal reaction thereof will produce reaction products which are non-carburizing in nature, adding heat to said mixture to cause thermal reaction thereof at a temperature above the desired carburi'zing temperature of the metal, whereby to accelerate and complete said reactions, thereafter adding an unreacted hydrocarbon fuel to said heated products for endothermic reaction therwith whereby to reduce the temperature thereof, said unreacted hydrocarbon being added in sufficient quantity to render said products L 1 1 earburizing in nature, and passing said last-mentioned 1,851,831 products about the metal to efect heating and carburiz- 2,233,474 ation thereof. y

References Cited in the file of this patent 5 241,471

UNITED STATES PATENTS 1,195,641 lBatehell et a1 Aug. 22, 1916 12 Hayes Mar. 29, 1932 Dreein Mar. 4, 1941 FOREIGN PATENTS Great Britain Oct. 22, 1925

Claims

19. THE METHOD OF PRODUCING A HEATING AND NON-SCALING ATMOSPHERE FOR METAL CONTAINED IN AFURNACE HEATING CHAMBER WHICH COMPRISES MIXING A FUEL AND AIR IN COMBUSTIBLE PROPORTIONS, THERMALLY REACTING SAID MIXTURE, SUPPLYING SUPPLEMENTAL HEAT TO RAISE THE REACTION TEMPERATURE OF SAID MIXTURE TO ABOVE THE NORMAL COMBUSTION TEMPERATURE THEREOF TO ACCELERATE SAID REACTIONS, PERMITTING SAID REACTIONS TO CONTINUE TO SUBSTANTIAL COMPLETION AND THERE-