US2509856A - Heating apparatus - Google Patents

Description

E. BLAHA HEATING APPARATUS May 30, 1950 5 Sheets-Sheet l db/2b BY d ATTORNEY INVENT M Filed April` 18 1946 May 30, 1950 E. BLAHA HEATING APPARATUS 5 Sheets-Sheet 2 INVENTOR WM BY Filed April 18 1946 May 30, 1950 E. BLAHA .HEATING APPARATUS 5 Sheets-Sheet 3 Filed April 18, 1946 May 30, 1950 E. BLAHA HEATING APPARATUS 5 Sheets-Sheet 4 Filed April 18, 1946 l IN V EN TUR.

Patented May 30, 1950 UNITED STATES HEATING APPARATUS Emil Blaha, Cheltenham, Pa., assignor to Selas Corporation of America, Philadelphia, Pa., a corporation of Pennsylvania Application April 18, 1946, Serial No, 663,158

(Cl. :Z-142) 18 Claims.

My invention relates to heating apparatus, such as furnaces, kilns, and ovens, for example. While the principles of the invention may be employed for a Variety of heating purposes, both industrial and otherwise, the improvements disclosed herein are especially useful in those heating applications in which consideration must be given to the character of the atmosphere enveloping the Work being heated, especially the presence of objectionable and undesirable constituents in the gases forming such Work enveloping atmosphere.

In view of the fact that the character of the atmosphere enveloping the Work often is an important factor in many heating operations it has usually been the practice in such cases, when a combustible gas mixture is utilized as a source of heat, to employ internally fired heat radiating muffles or tubes to keep the work or goods out of physical contact with the high temperature heating gases consisting of heated products of combustion. In this Way the heating chamber is fired to an elevated temperature by heat radiated from the exterior surfaces of the muiiles, and a gaseous atmosphere is provided which is of such a character that it will contribute to produce the desired end result in the goods or Work being fired.

Such heating practices have been followed, for example, in the firing of articles to produce glazed or glass-like surfaces, as in the glost firing of ceramic Ware and in vitreous enamelling. This is so because the high temperature heated products of combustion usually contain harmful constituents, such as sulphur dioxide and sulphuric acid fumes, for example, which adversely affect the glazed surfaces produced on articles when such heated gases freely circulate in the atmosphere enveloping the Work.

In accordance With the present invention, it is proposed to heat Work to high temperatures in heating chambers by radiant heat in such a manner that the character of the atmosphere enveloping the Work may be accurately determined While projecting such radiant heat from a plurality of heat radiating regions which are heated to incandescense by a high temperature gaseous heat producing medium exposed to the chamber atmosphere. I accomplish this by Withdrawing exteriorly of the heating chamber the gaseous heat producing medium before such medium can pass into the heating chamber and become an active component of the chamber atmosphere.

In order to produce high radiant heating temperatures, the heat radiating regions are preferably heated to incandescence by combustion of a combustible gas mixture effected at vicinities or zones adjacent to such regions and in open communication with the heating chamber. The heated gases generated and developed at the combustion vicinities or zones adjacent to the heat radiating regions may be Withdrawn therefrom at such a rate that the chamber atmosphere is substantially free of objectionable and undesirable components. Thus, in practicing the invention to produce glazed or glass-like surfaces on articles, the heated products of combustion may be withdrawn exteriorly of the chamber at such a rate from the combustion vicinities that the chamber atmosphere is impoverished in sulphur impurities to such a degree that the glazed or glass-like surfaces produced are smooth and lus- 0 trous and free of surface defects.

By effecting combustion of the gas mixture at vicinities or zones adjacent to heat radiating regions to heat such regions to incandescence, such combustion vicinities or zones being in open communication With the heating chamber, radiant heat is projected from the regions Without the necessity of shielding the work or goods from the combustion zones by a heat transfer Wall or barrier like a mule. In this Way radiant heat transfer may be accomplished at the highest possible temperature from the heat radiating regions which are heated to a high incandescent condition and openly exposed to the heating chamber at the surfaces adjacent to which burning of the gas mixture is accomplished.

In the embodiment of the invention disclosed herein the heated gases generated and developed at the combustion zones or vicinities are Withdrawn and diverted therefrom, without becoming an active component of the chamber atmosphere, by producing a suction effect adjacent to the combustion vicinities. Such suction effect may be produced by an exhaust blower to cause withdrawal of the high temperature heated gases exteriorly of the heating chamber through a path of ow which is in heat exchange relation with a Wall of the heating chamber. To promote further the radiant heating of Work in the heating chamber, the path of ow through which the diverted heated gases pass exteriorly of the heating chamber may be formed of refractory ma terial which is heated to incandescense and from the outer surfaces of which heat is radiated to the interior of the heating chamber.

The suction effect produced adjacent to the combustion vicinities may be adjusted to effect withdrawal of the heated gases from the vicinities at such a rate that heated gases can pass substantially by diffusion only from the combustion vicinities into the chamber atmosphere. Under such conditions the gases at the boundaries or interfaces between the heated gases formed at the combustion vicinities and the chamber atr mosphere may be maintained practically quiescent.

heating chamber may be slightly below tlfle=pressure of the surroundings and negative due to-y the suction effect produced adjacent to the vicini-,-

ties at which combustion is accomplished. Such suction effect may be utilized to draw into the heating chamber an essential gas which con- U tributes to the end result desired when rlring Work at high; temperatures. In the ring of articles to produce glazed or glass-like surfaces thereon, for example, the negative pressure of the heating chamber may be utilized to draw'essential air into the chamber which purges the gases in the chamber and contributesv to the production of high quality glazed surfaces onY Work.

Further, in a continuous tunnel type furnace or kiln having preheating and cooling zones a-t the opposite ends of a high temperature firing zone embodying the invention, theessential air may be drawn into the high temperaturezone through the cooling zone into which thework passesafter being red to the desiredhigh temperature. l'n this way, theheatedworkincooling gives up heat to essentialair in thecooling zone, and suchpreheated air. is then introduced.

into the nring zone to effectpurging of the gases therein.

Due to the suction effect produced adjacent to the vicinities at. which combustion. is accom.- plished,.there. will always bea tendency. for gases of the chamberv atmosphere to be drawn eXteriorly of the kiln or furnace along with the diverted heated products of combustion .before such heatedY products can become an active. component of the furnace atmosphere. Suitable control.

provisions may be providedto. control thein.- ow ofv essential air into the heatingk chamber, the rate of Withdrawal of the heated products of combustion, and the pressure and rate at which the combustible gasV mixture issupplied tothe vicinities at which combustion is accomplished.

Some or all of these variable factors may be controlled, for example, responsive to a temperature condition affected by the temperature maintained in the heating chamber.

rhe novel features which I believe to be characteristic of my inventionare set forthwith particularity in the claims. The invention, both as to organization and method, together With the objects and advantages thereof, will be better understood by reference to the follow-ing description taken in connection with the accompanying drawings, of which:

Figs. 1 and 2 are longitudinal horizontal and vertical sectional views, respectively, illustrating more or less diagrammatically a preheating zone and a portion of an intermediate high temperature firing zone of a continuous tunnel kiln emfoodying the invention;

Figs. 1A and 2A are longitudinal horizontal and vertical sectional views, respectively, diagrammatically illustrating another portion of the intermediate high temperature firing zone and cooling zone of the kiln shown in Figs. 1 and 2;

Fig. 3 is an enlarged transverse vertical sectional view, taken at line 3 3 of Fig. 1, to illustrate the high temperature firing zone more clearly;

Fig. 4 is an enlarged fragmentary transverse vertical sectional View, taken at line 6 4 of Fig. 5, to illustrate details of the high temperature firing zone;

Fig. 5 is an enlarged fragmentary longitudinal sectional view, taken at line 5-5 of Fig. 1, to illustrate more clearly the side walls of adjacent portions of the preheating andV high temperature firing zone, respectively;

Fig. 6 is an enlarged fragmentary horizontal sectional view, taken at line iof Fig. 3, to illustrate more clearly the burners and iiues tvs therefore embodied in the high temperature firing zone;

Fig. 7 is an enlarged front View of a refractory shape, partly broken away and in section, to illustrate details of the burners embodied in the high temperature firing zone;

Fig. S'is an exploded perspective View of the refractory shape of Fig. 7;

'Fig 9 is an enlarged transverse vertical sectionalvievv, taken at line l-S of Fig. 1, to illustrate the preheating zone more clearly;

Fig. l0 is an enlarged transverse vertical sectional view, taken at line IQ--lgoi Fig, 1A, t0 illustrate details of iirst and second portions'of.: the cooling zone of the continuoustunnel kiln;

Fig. 1l is an enlarged vertical sectional View.v taken-at line ll-H of Fig. 1A, to..illustrate more.

clearly the final and last portioniof the cooling;v

zone;

Fig. 12 is a horizontal plan View of the continuous tunnel kiln of Figs. 1 to 11 and controlA revisions for the kiln; and.

Fig. 13 is a View diagrammatically illustrating the operating conditions existing; at the combustion vicinities adjacent to the refractory lined heat radiating regions distributed-along the ,high` temperature firing zone.

In the drawings the instant inventionhas been. shown in connection with a continuous tunnel kiln lil through which goods or wares may be.

moved successively through a preheating zoneY or section I5, a high temperature firing zone-or section I l5 and a cooling zone or` sectionv l1. It is to be understood that the kiln I4=is only illustrative of one manner of practicing the invention for producing glazed or glass-like surfaces on articles, and that the improvements disclosed herein may be embodied in other forms of heating apparatus.

VThe goods or wares to betreated are loaded'on is carried by a metallic underframe, extends` through an opening orslot formed inthe bottom wall ofthe kiln chamber. In this way narrow gaps 23 are formed between the sides of the refractory' bcdy portions of the cars I8 andthe side walls of the slot, the lower ends orjeachare closed and sealed at Zi by flanges whichextend downwardly frcm the, sides of the4 cars I.8-int0 troughs adapted to contain sander likematerial.4 Duringoperationof the kiln iii, the car-s I8 moving through the kiln chamber are4 in abuttingrelation and the gaps Z'sare effectively sealedat the lower ends thereof longitudinally of the` kiln,` as just explained, so` as to minimize leakage of. air into the kiln chamber.

After the goods or wares to be treated are loaded on the cars i8, such cars are moved in succession onto a transfer track 25, as best shown in Fig. l, on which the cars .pass into a side entranceV vestibule 2S having a normally closedslidingdoor 2l. of the preheating zone i 5, and vestibule propeller, mechanism '2i-l of any Well known type, having a reciprocatory pusher member 29, may be provided Y The vestibule 2B is located at the inlet endj from the cooling zone l' of the kiln chamber pass into an exit vestibule 3l] from which the cars are moved through a normally closed sliding door 3| onto a transfer track 32.

Ihe sides of the kiln I4 are provided with suitable supporting framework 33 connected at the upper ends by cross rods 34. The framework 33 extends the full length of the kiln and includes metallic side walls 35 forming an outer shell for the kiln i4. As best shown in Fig. 3, the refractory kiln structure providing the high temperature ring zone or section l5, which is disposed within the framework 33 and outer metallic side walls 35, includes spaced apart side walls 36, a roof 3l, and a bottom 38 having the slot or opening therein through which the refractory body portions of the cars i3 project, as previously explained.

In the refractory side walls 36 of the high temperature firing zone or section I 6 are mounted or l incorporated gas-fired radiant heaters or burners 4U each having a cavity 4! at an inner face thereof opening into the kiln chamber. Each radiant heater comprises a molded block 42 of ceramic material having a central passage within which is disposed a tube or sleeve 43 of refractory material. As best shown in Figs. 3 and 6, the tubes or sleeves 43 extend rearwardly from the block 42 through wells or openings 44 formed in the outer portions of the refractory side walls 36. outer ends of the tubes 43 may be connected by suitable flexible connections to apertured brackets 45 xed to the casing 35, as seen in Fig. 3. The tubes or sleeves 553 may also be spring-biased at the brackets in any suitable manner (not shown), so as to cause the rear enlarged portion of each tube to t snugly in position at the rear face of the block 42 with which it is associated.

The heater tubes 43 are connected by pipes 46 to short horizontal manifolds 47 which in turn are connected by conduits 43 to larger vertically disposed headers 49. The combustible gas mixture is delivered to the headers i9 from a suitable source of supply in any desired manner. In the conduits 48 are connected manually operable Valves 5D to control the pressure and rate at which the gas mixture is supplied to each horizontal manifold 42, and in the pipe connectionsI 45 are provided manually operable valves 5l for individually controlling the support of the gas mixture to each radiant heater 45.

The inner end of each tube or sleeve 43 adjacent to the heater cavity 4l is internally threaded to receive an exteriorly threaded part of a gas distributor tip 52 formed of refractory material. The gas mixture in the tubes 43 is subdivided into a plurality of gas streams by a plurality of slots or channels 53 formed about the periphery of and extending lengthwise of the narrow part of the distributor tip 52. The outlet ends of the channels 53 at the underside of the enlarged end of the tips 52 flare outwardly toward the inner Wall surfaces 5d of the heater cavities 4l.

The gas mixture is discharged from the outlet ends of the channels 53 at the undersides of the enlarged ends of the tips 52, and it is at these regions that the iiames are produced and maintained. The individual flames produced at the tips 52 nare outwardly and project into the cavities or spaces 4l alongside of the outwardly flaring wall surfaces 54. The gas flames maintained at the tips 52 effect such heating of the inner wall surfaces 54 that the latter are heated to incandescence.

The extreme The gas mixture introduced into the spaces or cavities 4l is subjected to the intense radiant heat of the inner wall surfaces 54, so that substantially complete burning of the gas mixture may be accomplished in the spaces or cavities before the heated gases pass from the open ends of the spaces 4l. By providing the radiant heaters 45 a large fraction of the heat developed and generated in the spaces 4| is converted to radiant heat which is projected from the highly incandescent wall surfaces 54 into the interior of the high temperature firingzone i6 to effect heating of the goods or wares passing therethrough on the cars i8.

The heated gases generated and developed at the vicinities of the radiant heaters All pass into spaced apart vertical ues 55 in the refractory side walls 36, as will be explained more fully hereinafter. As shown in Fig. 5, the lower ends of the vertical ues 55 communicate with horizontal ues 56 provided in the firing zone at the bottom parts of the refractory side walls 36. The ends of the horizontal flues 56 terminating at the juncture of the firing zone I6 and cooling zone il are closed, and the opposite ends terminating at the juncture of the firing zone I5 and preheating zone l5 communicate with the horizontal transverse passages 5l formed in the bottom parts of a pilaster 58.

As shown in Fig. 5, the lower ends of vertical iues 53, which are offset laterally with respect to the horizontal flues 55 in the firing zonet i8, communicate with the transverse passages 5l. Each side of the refractory kiln structure at the pilaster 58 is formed with openings or passages E@ at different levels which communicate with the vertical iiues 5 and through which heated gases may flow into horizontal heat transfer flues el' extending lengthwise of the preheating zone i5 at each side wall of the kiln chamber from the pilaster 58 to the entrance vestibule 26. The horizontal flues 6i extending lengthwise of the preheating zone l5 and into which the heated gases pass through the openings G0 from the vertical iiues 53 are disposed one above the other in the refractory side walls of the kiln, as shown in Fig. 9.

The horizontal ues 6l comprise a plurality of rows of refractory shapes or tiles 62 in abutting relation and secured together, as by a high-temperature cement, for example. The refractory shapes 62 are U-shaped in section and disposed one above the other so that the longer closed sides thereof are substantially in alignment to provide heat radiating surfaces at the side walls of the kiln chamber substantially coextensive in height with the maximum vertical loading of the goods or wares on the cars i8. The shorter legs of the refractory shapes 62 cooperate with refractory brick of the kiln structure to form the longitudinally extending passages or flues 5l. The refractory shapes 62 are preferably formed of a refractory material having good thermal conducting properties, such as silicon carbide, for example, to promote heat transfer from the heated gases through the inside walls of the flues 6l to the goods or Wares passing through the preheating section l5.

The fiues 6| in the preheating zone l5 communicate with vertical nues t3 and 64 formed in lthe kiln side walls adjacent to the entrance vestibule 26, as best shown in Fig. 1. To the upper ends of the vertical hues 53 and 6d :are connected ducts 65 and 66, as shown in Fig. 9, which in turn are connected by a duct 61 to the inlet of1-'an-.exhaustblower which may befdriven-.in anyssuitablewma-nner, asby` an electric motor, forv example..

ItY will no wbe seenthat-l the residual heat inv the-heated .gases passinginto-.the horizontal flues- Eil' of the preheating zonek i5 is effectively-utilized to effect preheatingofrthe goods rnoving'through'-` such zone lto `the high temperature firing zone iii, and that theg-ases are thereafter discharged eX- teriorlyrofthe kiln lilby the exhaust blower t3;

After the goods or-wares are treatedinthehighte-mperature ringzone iii, suchgoods then pass intothe-coolingzene l? inwhich the teinperature of the goods is gradually reduced. As show-n*inthegleft--handV part'of Fig. l0,- the porti-on ofthecooling zone l'tiinmediately adjacent to theV lringjzone l5- is` formed with relatively thick refractory sidewalls ,6% spacedi'rom the metallic side walls 350ithe outer-casing to provide ver ticallyextending passages l'otherebetween. At

theiirst portion ofthe cooling zoneV adjacent toV the ring zone It, the bottom edges of the metallic side walls 35yterminate a short distance from the eXtreme lower ends of the kiln side walls Gto provideopenngs l i through which air from the surroundings may pass upwardly through the passages lil. Heat is given up, by the refractory side walls li to the air passing upwardly through the passages, 70 thereby promoting natural draft circulation ofj air over the outer surfaces of the kiln side wall', as indicatedby the arrows inthe l'eft hand partA of Fig. l0, to effect initial cooling of the, treated goods passing from the firing zone I6.

Thesecond orintermediate portion of the cool-V ing zone, Il isA shown in the right hand part of Fig. 4and diiTers from the lrst portion justV described in that vertical passages 'l2 are formed within the refractory side walls 13. The thickness of the refractory side wall separating the kiln chamber and each passagefl is considerably lessin thesecond or intermediate portion o the cooling zone il then in the rst portion thereof, sothatthe temperature o the goodslwill berreduced furtherin the secondI` portion by the natural draft circulation or air which entersthe lower endsofY thepassages at inlets l;

As shown in Fig. 11, the inalandlast portion of the cooling zoneil' is formed by hollow metallic shells l5 and 'l defining the roofand sideV walls, respectively, of the kiln chamber at the exit end thereof. Airl to effect the linalvcooling of the goods Vor wares may be circulated through the shells l5 and lo in counterlow toV themovef ment of the goods-toward tlfiegexit4 vestibule Sil, asshown in Figs, 1A,V andll. Thismay be accomplishedg byintroducing air'. into,v the ,shell l5;-`

through. suitable openings4 (not shown) formed in the 4elidtlfiereofV adjacent, to the .exit vestilmle 362. Ainrnay alsobe introduced into the shells 'lthrough suitable conduit connections T: pro

vided at the bottom partsthereoiadiacent to. the.

exit vestibule 3G. The cooling air is withdrawnV from thel shellsA T5. andy le; at. regions`A removed from the exitgvestibule 3D, through conduits` l8r, wandte, whichfare connected by. a conduit Si to the inlet of an exhaust blower 32, as showninA Fig, 11.

Bypreviding the cooling zone il justdescribed; the temperature of the treatedgoods can bereducedin several stages without adverselyaffecting;the1goods, sothat. the goods willbe at adesired low.. temperature upon reaching theexit vestibule Silgto be discharged-fromthe kiln l 4.

lt: has been explainedabove-Ythatvthe. radiantY heaters` le in they high temperatureiiiringv zoneL i@ are heatedto a high incandescent temperature by a gaseous heat producingmedium. ByV ac-` complishinga largeopart and preferablysubstantially alloi the combustion of thegasmixture in the vVicintes or spaces l'adjacent to the Wall surfacesl. of the .radiant heaters 4,0., extremely. high combustion. temperatures are developeditol heat-the wallzsurfacesto a highly radiantV condition. In this manner a large proportion or fraction. of the. heat. developed and. generated rin,

the*spacesiil-:isrconverted to radiant hea*U which is projected from the highly incandescent wall surfacesi; into the interior of the^ highitempera-A tureringzone Sto effect heating of thegoods.`

or wares passing therethrough onthe carsi..

In accordance with the present invention,l in order toV control the character of the atmosphere inthe high temperature firing zone I8', the heatedY gasesgenerated anddeveloped in the combustion.

spaces-.or vicinities di are withdrawn exteriorly ci the. kiln it before sucnheated gases-can become anactive component of the atmosphere enf.

veloping the work in the high temperature firing,

zone. in the embodiment of the invention dis? closed herein, this is accomplishedby positioning` the open endof @ach combustion spaceV orA cavity di a-platey ephavingan openingtherein of approximately the same size as the. cavity opening,y Each plate 83 is spaced .a short dSIancelip ai formed at the; front face of the.

withdraw gases from the horizontal flues' 6l inthe preheating zone l5 and the latter arear-Y ranged to receive heated gases from the horlzontal nues 5ev in the firing zone I6, asuction effect may be produced in thehorizontal flues-V and vertical ues 5f which.is reflected. back to the gaps 85.` The plate 83 of eaehradiant heater im is positioned relatively close to the forward edge of the lip Sil; dening theextreme open end of the cavity 4l, sothat restricted out.

lets are provided by the gaps 8,5 at which Yregions the suction effect produced by the blower 6,8 is irubensiiied` in a manner similarl to the suction effect produced at the nozzle of a vaccum cleaner. Y Since the blocks 52 are subjected to, elevated,l temperatures as high as 2800 F; and higher at thelinner faces thereof; the plates 83 must not only-withstand thermal Vshock but provision must be made for holding such plates accurately in i position under all or" the operating conditions ofthe kiln it.

To this end each refractory blockAZ is con. structed in sucha manner thatv the plate 83 associated therewitl-rforms a rigidly held part of the block. As shown mostclearly in Fig. 8, each,

lock comprisesv a refractory Shape having slots orchannels te'extending lengthwise of the shape. at the cut-away corners thereof. TheslotsorV channels are rnoreor less U-shaped incross. section and formed with outwardly Haring Side walls to receive tie rods 81 having enlarged end portions 88. The slots are deeper at the front and rear ends than at the intermediate portion, as shown in Figs. '7 and 8, to receive the enlarged ends 88 of the tie rods 8l.

The tie rods 8l, which are more or less triangular-shaped in section, are rmly secured in position in the slots 86, as by high-temperature cement, for example. When the tie rods are secured in position, the refractory Shape and tie rods embodied therein form the rectangularshaped block 42 having smooth outer surfaces at the four sides thereof to facilitate mounting each such block in the side walls 3E of the high temperature firing zone I6.

The enlarged forward ends 88 0f the tie rods 8l are notched at the inner faces thereof, as indicated at 89, to receive the cut-away corners of the apertured plate 83. The notches 89 accurately position the plates B3 a fixed distance from the lips or raised portions 84 at the front faces of the burner blocks 632, the plates being secured in position in any suitable manner, as by high-temperature cement.

As seen in Figs. and 6, the radiant heaters 40 are in spaced apart relation in the side walls 3B and arranged in vertical rows. The refractory blocks 42 are mounted at the inner portions of the refractory side walls 35 between vertical rows of refractory blocks Sil which are of less depth than the blocks e2, as best shown in Fig. 6. Refractory plates e! are arranged between adjacent vertical rows of radiant heaters d, the outer vertical edge portions of which bear against the plates S3 fixed to the refractory blocks 42. The refractory plates Si are disposed one above the other in vertical rows and cooperate with the refractory blocks 9o to form vertically extending spaces between adjacent vertical rows of radiant burners dil.

The refractory plates Sl are T-shaped in section, as shown in Fig. 6, and the blocks B0 are formed with relatively deep slots to receive the rearwardly extending legs 92 of such plates. In this manner the vertical spaces in front of the blocks 90 are divided to form two manifolds or flues 55 each of which communicates with the gaps 85 in one vertical row of radiant heaters ell. Thus, for each vertical row of radiant heaters di), the heated gases generated and developed in the spaces or cavities @l can be withdrawn through the gaps 35 into the vertical nues 55 provided at both sides of the heaters.

By producing a suction effect in the vertical nues 55 in the firing Zone I6 which is intensified at the gaps 85, the pressure at the gaps is below and negative with respect to the pressure prevailling in the combustion spaces or vicinities lll of the radiant heaters d. By providing any well known control provisions, such as a damper $3 in the conduit 6l which is connected to the inlet of the exhaust blower 68, as shown in Fig. 9, the suction effect produced at the gaps 85 may be adjusted and controlled. Hence, substantially all or any desired fraction of the heated gases generated in the Combustion spaces al can be eifectively withdrawn from said spaces and diverted through the gaps, as diagrammatically indicated by the arrows F in Fig. 13, before such gases can pass from the combustion spaces 4l through the open ends thereof and become an active component or constituent of the atmosphere in the firing zone IB.

The suction effect produced at the gaps 85 of the radiant heaters lill is related to the pressure at which the gas mixture is supplied to the heaters and the lengths of the individual flames produced in the combustion spaces 4 l. In the operation of the radiant heaters llt, as indicated more or less diagrammatically in Fig. 13, the inner cones of different size fiames A1, A2, and A3 always extend more or less along an axis B alongside of the inner wall surface 54. Irrespective of the lengths of the flames, the inner cones thereof will always be out of contact with the wall surface 54.

When the radiant heaters Ml are being operated at low capacity and the flames are relatively small, the suction effect produced at the gaps is correspondingly adjusted so as to avoid pulling the flames from the wall surface 515 and reducing the effectiveness of the flames in heating the refractory linings of the heaters to a high incandescent temperature. When the pressure at which the gas mixture is supplied to the radiant heaters is increased, the suction effect produced at the gaps 85 may also be correspondingly increased.

In radiant heaters of the type illustrated, there is a tendency for the individual fiames to bend inwardly toward the axes of the heaters in a manner similar to the bending of the ribs of an umbrella when it is fully opened. It has been found that the suction effect produced at the gaps 85, which completely encircles the open ends of the combustion spaces 4l, tends to overcome such lifting of the individual flames from the wall surfaces 5i and promote uniform incandescent heating of the wall surfaces. It has also been observed that when the radiant heaters it are being operated at less than maximum capacity, the areas of the wall surfaces 5i heated to incandescence increases when the suction effect is produced at the gaps t5 to withdraw and divert heated gases into the vertical fines 55.

The gas mixture supplied to the radiant heaters lli may be a complete mixture in which all of the combustion supporting gas, such as air, for example, is supplied with the combustible gas to effect substantially complete combustion of the latter in the combustion spaces or Vicinities ill. Under these conditions the suction effect produced at the gaps B5 may be regulated to withdraw and divert through the gaps substantially all of the heated gases generated and developed in the combustion spaces, so as to maintain the regions at the open ends of the spaces ll! practically quiescent. When such operation of the radiant heaters fifi is effected, no blast of heated gases can be felt by the hand when it is momentarily placed over the open ends of the combustion spaces lil. When the suction effect produced at the gaps 35 is regulated so as to maintain the gases immediateiy in front of the open combustion spaces practically quiescent, heated gases can pass substantially by diffusion only from the spaces 4l into the interior of the high temperature firing zone I The suction effect produced at the gaps t5 also may be regulated to minimize the ow of the` the'fopen ends 'ofthespacesfil ,pass toward `the gaps :andV ow therethrough, alongY .with the .diverted "heated gases, .in al common stream into the verticalflues .-5. .It is to be understood that there will aiwaysubewa tendency for-gases inthe atmosphere-of the nrin'g zone I6 to'bedrawn into Y'the open ends of the spaces-4l due tothe .suction 4effect "producedfatv the gaps. :When a complete gas mixture is supplied to the radiant heaters 4G, the 'suction yeffect Ais "preferably properly related to the gas pressure delivery .pressure tof eiect substantially complete vcombustion ofr-thergas mixture in the spaces or vicinities 4I of the radiant heatersr.

firing the ,highy'temperature zone I6, the gas fmixturesupplied to the radiant heaters 40 .may vbaaipartial,mixtureJ andasome of the air to accomplish completeburning of the combustible gaslmay-a be drawn into the spaces or vicinitiesl 4| .byethesuction pressure produced at the gaps v35. The admission of air into the ring zone I- may be due to leakage or maybe positivelycontrolled, as will presently be pointed out. Any-air passing:into the ringzone is heated therein and,

due to'suchpreheating, is capable of producing I highercombustion Atemperatures at .the radiant heaters Jiii rwhen drawn into the -spaces 4| thereof.

AInward movement of the heated airinto Vthe spacesor vicinities .4l of the radiant heaters 40 ispromoted dueto the pressure conditionsprevailing in the combustion spaces. There isa low .pressure regionat the centralparts of the spaces Jil, adjacent tothe enlarged ends .of the .distributor vtips. ii2, into which gases tend tobe drawn, as indicated diagrammatically by .the arrowsD in Eig. 13. Since the suction effect vproduced at the gaps-85 is strongest at the peripher-ieswof the spacesfil and weakest at the central regions'thereof, anadequate-flowof heated l gases containingI air may .bel induced atrthecentrai regionsvof--the spaces, as indicated diagrammatically by the arrows Ein Fig. 13, which supply partrofthe. combustion supporting gas toeiect combustion vvof the combustiblegas supplied ina partial .mixture to the spaces-ll I The kiln; l 4 is especial-ly yuseful in treating'work .to ,produce glazed surfaces thereon, as inthe .glost `iiring Y of ceramic ware `'and in vitreous enamelling, for example. Such -work vcan be red-,in'theiiring zone ltohigh temperatures by vradiant lheat projected vfrom the radiant heaters-Mi,-Witliout'the necessity of.` shielding the lwork by .a heat transfer wall ot'an'finternally 4ireid muiiie' ortube,.so that radiant heat transfer can 'zbeaeected at high temperaturesfrom the .combustion spaces or 'vicinities -fil whose wall surfaces are-heated tothe 4highest possible temperature.

ItV no provision were-made for divertingand .withdrawing through the gaps 85 the heated gases generated Yin *the combustion spaces 41, such heated gases cou-1d pass into lthe firing zone I6 rlandthe objectionable constituents in such gases, `such as-sulphur dioxide and sulphu-ric acid f 1'" fumes, forexarnple, would adversely affect the glazed'or glass-like surfaces produceden .the Work-beingrtreated. However, in firingwwork in the high '.temperaturezcne i5, the character of heatmosphere .enveloping the workcan'be conf trolled by 'producing the requisite suction. effect at,thef,gaps.85, whereby heated gases canv'pass :byidifusionronly from ythe spaces *M `.into the flringzone I6. f Since the ratel at which the. heatedgases canpassbydiffusioninto the atmos- 1*-2 phererof .the ring zonet-#Slisrelatively lowpthe extent to which objectionableconstituents.or impurities are carriedinto thering zone atmosphere is extremely 'small vandinsufficient to adversely affect the smooth and'lustrous glazed surfaces produced on work.

:During operation-of Vthe kiln I-4,-the sliding doors. 2'! andA 3l, atfthe entrance v.and exit-vestibules lZSfandfB, respectively, are normally. kept closed and opened only rfor the purpose of: admitti-ngearsv` I8 into the entrancevestibule andremoving such carsfrom the exitvestibule. .The Vpilaster or wal-l section 58 between V`the Apreheating.` zone A-I fand the ring zone M5` forms. a constriction in the kiln cham-ber whereby Vobjectionable' drift ormovement'of `.thegaseslbe- `tween thesekilnesections isminimiZed. :A similar pilaster or 'wa1l.:section -94f-may be provided at the Yjuncture of fthe-firing zone IE andthe cooling zone l1, -asfs'hown'in=Figs.-1A-and 2A. v:The 'gapsvZ-S between the `cars I8 and sides of the slot at the bottomof` thef'kiln. I s 'are' sealed at- 24 by the --train of carsyI8movingthrough1the=fkiln chamber in abutting relation, as `previouslyvexpla-ined. By' providing the` normally closed doors `at7 the 4entrance '-andfexit vestibules, the pilasters i58-and194 at each-end ofthe firing zone- |6,-and the sealing provisions 24 atthel sides of `thecars YI-8, the circulation of gases inthe atmosphere enveloping vvthewvork being treated in thering zone yI 6 is minimized rwhich contributes to the productioncf .'high quality glazed surfaces-on work. -Uncler these conditions the ring zone I6 :islled with gases-Which are impoverished in sulphur impurities.

By-providing afkiln likefthe `kiln Mwhichis relatively gas-tight, that is, akilnlstructureinto which the-:leakagevoffair linto the Vkilnchamber is at aY minimum, `thefpressure in the firing zone i6 may be maintained slightly below atmospheric pressure due tothe suction leiect produced at'the gaps s85. f Such operation ofthe kiln I4 differs from: they usual furnace or kiln operation in which the gaseous 'atmosphere is at a positivepressure a-nd slightlyl above that off-atmospheric, The fact that the'ringzone :it may bemaintained at a pressure slightly-below atmospheric can be vadvantageously utilizedzto promote purging of gases inl the'nring zone it, :aswill be vpointed outfpresently.

Itis to be understoodl that in a continuous tunnel kiln like that disclosedrherein, it is not possible to seal 1the-'firing-zone l'completely and thexnecessary care Vmust be taken to keepair leakage'into the -kiln chamber to a minimum. When the extent to which air leaks into thekiln chamber-.increases,A the suction eiect produced -at the gaps maybe increasedto overcome the adverseV affect such air inay'have in tending to reduce the high incandescent temperaturesto which the radiant heaters Mi areV heated.

.-When'work is being treatedin thehigh temperaturering zonei it, the atmosphere therein is desirablyoxidizing. In such case air admitted into the'ring zone vlf'purges the gasesin `the atmosphere enveloping the -work being treated and-.also contributes-to the production of high quality glazed'surfaces on the work. Such air, which may bereferred to as essential air, may pass-into lthering zone or section l-6 by leakage. in the normal operation of the kiln. However, such-leakage of vair into the ring zone -I6 should not be excessive because any-air-over and above that necessary fte effect the desired vend resultfmay be referred 'to'as unessential-air,

because such air causes an undesirable drop in temperature in the firing zone I and does not serve any useful purpose.

In the kiln I4 of the invention the admission therein of essential air, when an oxidizing atmosphere is desired, may be effectively controlled. Such an arrangement is diagrammatically shown in Fig. l2 wherein an air admission conduit 95 is provided in vestibule 30, for example. A suitable damper 96, which may be manually controlled, if desired, may be provided in the conduit 95 for controlling the rate at Which air is admitted into the cooling zone I'I of the kiln chamber. By providing a kiln structure which is reasonably air-tight, the pressure in the ring zone I6 may be maintained slightly below atmospheric pressure so as to cause movement of air through the conduit 95 into the cooling zone I1 and through the latter into the ring Zone I6 to purge the gases therein.

Such controlled movement of air through the cooling zone I'I to the ring zone I5 serves several useful purposes. First, the air in passing through the cooling zone eiects cooling of the treated goods or Wares therein and, in so doing, gradually becomes heated. Second, such heated air in entering the ring zone I6 effects purging of the gases and does not exercise any undesirable cooling effect in the firing Zone. Third, when a partial combustible gas mixture is supplied to the radiant heaters 4i), and gases from the atmosphere in the firing zone I6 are drawn into the spaces 4I to supply any deficiency in the combustion supporting gas to promote complete combustion in the spaces QI, the oxidizing gases of the firing zone atmosphere drawn into the spaces 4I will be at an elevated temperature, thereby promoting higher combustion temperatures at the radiant heaters 4i).

The admission of air through the conduit 95 into the kiln chamber may be automatically controlled, if desired, responsive to the temperature of the firing zone I6. Moreover, such control of the rate at which air is admitted into the kiln I4 may be associated with suitable control provisions for regulating the supply of the cornbustible gas mixture to the radiant heaters MI and the suction pressure produced at the gaps 85. As shown in Fig. l2, this may be accomplished by providing a control system including a thermocouple 91 arranged Within the ring Zone I6 so as to be subjected to the high temperatures produced therein. The thermo-couple is connected by conductors 98 to a suitable potentiometer control 99 of any Well known and conventional type which is connected by conductors itil to a source of electrical energy. The potentiometer control 99 may be connected by conductors IIJI and H32 to suitable control devices |03 and |04, such as servo-motors, for example, operatively associated with the dampers 93 and 95, respectively. The potentiometer control 99 may also be connected by conductors m5 to control devices IUE each ot which is operatively associated with a valve l0? provided in a conduit |03 through which the combustible gas mixture is supplied to the radiant heaters lili at one of the side Walls 36 of the ring zone.

In the firing of articles in the high temperatures zone Il; to produce glazed surfaces thereon, the control system just described is so adjustedthat the rate of now of the gas mixture through the main supply conduits |08 to the radiant heaters d is controlled by the valves I0? responsive to the temperature in the firing zone I6, such control being eiected by the thermocouple 9?, potentiometer control 99 and control devices IUE operatively associated with the valves. In this manner the desired high temperature may be maintained in the ring zone I6, the flow of the gas mixture supplied to the radiant heaters increasing and decreasing When the temperature decreases and increases, respectively, from the desired high temperature.

The damper il?. in conduit Eil is similarly controlled through the potentiometer control 99 and control device IIii operatively associated therewith and increases and decreases the suction pressure at the gaps With increase and decrease, respectively, in pressure at which the gas mixture is supplied to the radiant heaters 40.

The damper in conduit 95 for controlling the admission of air into the cooling Zone I 'I may be also regulated through the potentiometer 9S and control device Ii operatively associated therewith, whereby the desired admission of air into the ring zone I may be regulated to maintain a suitable oxidizing atmosphere in the latter. When the suction effect produced at the gaps 85 increases and decreases, the valve 95 moves toward and from its closed position, respectively, so that essential air only is supplied to the ring zone I5 to purge the gases therein, as previously explained. It is to be understood, however, that the damper QS may be manually controlled so that it will not be influenced by the temperature in the firing zone IS.

The vertical iiues 55 associated with the radiant heaters t are preferably of such size that the paths of fiow for the diverted heated gases will be adequate to withdraw practically all of such heated gases generated and developed in the combustion spaces 4i when the heaters are being operated at maximum capacity. Further, the vertical fines 55 are considerably larger in cross-section than the gaps B5, so that heated gases will pass at a lower velocity through the vertical i'lues and give up heat to the side walls 3@ in which they are incorporated and also to the Work through the ilue Walls formed by the plates 9|. In the event any unburned gases are withdrawn and diverted from the spaces AI through the gaps ii into the flues 55, combustion of such gases may be completed in the vertical iiues because the cover plates QI become heated to an incandescent temperature which is above the ignition temperature of the combustible gas. Under such conditions, the fines 55 serve as heat radiating muiiles and contribute to the heating of Work in the ring zone l.

When a combustible gas mixture of ordinary city gas and air is supplied to the radiant heaters dil, such gas having a rating of about 550 B. t. u. per cubic foot, the heat radiating regions or wall surfaces 54 may be heated to a temperature of 2806 F. and higher and are at a high thermal head for treating work passing through the firing zone I. The cover plates 83 for the radiant heaters are also heated to a high incandescent temperature which may be in the neighborhood of about 2500 F. and at a thermal head slightly below the wall surfaces 5d of the combustion spaces di. rThe plates @l for the vertical ues 55 are also heated to incandescence and are at a lower thermal head which may be from about 50 to 109 F. higher than the temperature of the atmosphere in the firing zone I5.

In view of the high temperatures produced at the cover plates 33, such cover plates and the `from 'the heated gases .-tie'rods Slfof-ther refractory blocks l2 vare prefer- 'vably fformed of a refractory material, such as :silicon-.carbide,'-for example, which is capable of 'holding'up under 'extremely high temperatures without ldeveloping cracks and also possesses high-tensile#strength and resistance to thermal `Yshock. The'refractory plates Si for the vertical luesfif also maybe formed of refractory niaterial consisting entirely or preponderantly oi' silicon carbide. Since heat transfer is effected passing through the vertical hues 55 through the cover plates 9i to ithe interior of the iiring zone l5, it is desirable to provide cover plates Si formed of refractory materialV possessing vgood thermal conductive properties.

'The refractory bodiesYiZ lof the radiant heaters 'fll'may be Yformed of mullite or any other suit- 'able refractory material having poor thermal conductive properties, so that the wall surfaces "54 of the combustion spaces All at the front faces Vofthe blocks i2 can be effectively heated to the highest possible temperatures. rThe tie rods Si effectively Vhold the refractory block d2 together when the inner faces thereof are heated to a highly radiant condition and stresses are induced in theblocks due to the rear parts revinaining lrelatively cool while the regions advgrowth of cracks after they have once occurred.

Further, when the refractory bodies i2 are subjected to repeated thermal shock over a long interval of time, the tie rods effectively hold such blocks together and prevent any part being dislodged.

In order to .promote uniform heating of the goods or wares when the cars i8 pass through the kiln chamber from the preheating zone l into the high temperature firing zone le, only a single radiant heater Il@ is'provided at the refractory side walls 3S, adjacent to the bottom 38 at the extreme inlet end of the'ring zone it, as shown inligs. 2 and 5. Adjacent to such `single radiant heater it in each refractory sidewall t5 are provided two radiant'heaters it one above the other. All of the remaining vertical rows of radiant heaters di! in the side walls 36, throughoutl the entire length of the firing zone, include three radiant heaters il@ disposed one above the other. With this arrangement of the radiant heaters si! in the side Walls of the firing zone the temperature of the work is increased more uniformly to the requisite'high temperature at which it is desired to fire the work in the firing zone I3. It is to be understood however, that the radiant heaters may be distributed along the refractory side walls 36 in any desired manner to produce the requisite heating curve during movement of the work through the firing zone.

It has previously been explained that the heated gases passing upwardly in the vertical iiues 59 at the inlet end of the firing zone i@ are subdivided by the passages 60 through which the heated gases pass into the horizontal heat transfer ues t! in the preheating zone t5. Due to the natural draft or iiue effect in the vertical :ues59, there is a tendency for the heated gases rin'g Vsection I6.

to be distributed unequally between rthe horizontal .flues @l in each =kilnfside wall, so :that each bottom horizontal uei lreceives less than itsproportionate share ofthe vheated gases.

ln order to compensatefor this unequal division of 'thc'heated-jgasesflowing through the horizontals'ues'fl, a row of gas-red radiantheaters m9 are-incorporated in the bottom part ofv'each lside wall of the preheating zone- I5, ata portion thereofV adjacent to the ring zone iii, as shown in Figs. l, 2 and 9. The radiant heaters 09 ycornpriseburner blocks, Isimilar to the-burner blocks -4-2 in the ring'zone It, which are mounted -in 'the kiln yside walls directly at the rear fof :the

refractory shapes or ltiles 62 forming the bottom horizontal fluesft l The .combustible gasniixture supplied tothe radiant heaters I-ElB is subdivided distributor tips HB `to produce `a plurality of-anies tolheat the `inner surfaces of theY radiant heaters to a high incandescent temperature.

Therefractory shapes `52 .at'thefbottom horicontalfluestl areheated vby the 'heaters I09'by both *radiant -and convection heating `components andthe heated gases generated and developed'by. such heaters mixes with the heated gases entering the bottomhorizontal flues from the Hence, the heaters |09 increase the heating accomplishedby the'bottom horizontalues |09 over and above -thatfeffected .by the heatedgases passing `therethroughfrom the vertical ilues. .Inthis way'mor-.ee effective heat transfer is accomplished through the inner walls ofthe bottom horizontal flueslfl, thereby compensating-for the unequal division of the` gas f Ypassing therethrough from the firing zone .i6

and 'promoting incre uniform heating of -Work the preheating zone 15in which thereis also a tendencyforfthe heatedgasesto riseinto the upper part thereof.

While the `exhaust blower' has been .provided to,v produce a suction effect at thegaps 35 ofthe radiant heaters .49 inv theiiring `section f I6, it will be understood that Vsuch suctioneifect may be producedin any other well known manner, such as, for-example, bya steamer air ejector.

En the embodiment of the-:invention shown and described, the'size of the openingoraperture in 'the'platef of each-radiant heater is suitably .related-to the-.opening inltheV cavity 4l at the rim so'thatrthe heated gases will be effectively Withdrawn from the cavity when. a suction eiect is produced at the gap Y85. This-is accomplished in the radiant heaters vbyproviding apertures .in the plates-33 whichare-slightly less in diameter than the extreme open ends-'of theburner cavities dL-as seen in Fig.-6.

Attention is called to my copending Vapplication Serial No. 663,157, iiledconcurrentlyherewith which is directed tothe construction `of the burner which is used in the kiln-wall hereof and attention is also called to my copending application Serial No. 663,159,which was l'lled concurrently herewith and which ris directed toa methodV of firing a kilnand which has become Patent 2,474,301.

Although I have shown and described a single crnbodirnent cf the invention, it will be obvious to those skilled in the art that modicationsy and changes may be made without departing from'the spirit and scope of the invention. Thus, other lforms of radiant heaters than the radiant heaters Lltdisclosed herein may be employedin which lthe heat radiating regions are heated to incandescence by a-gaseous heat producing medium. Also, the principles -of Vthe invention may zbe "applied equally well to other forms of heating --apparatus, such as furnaces or ovens, for example.

Itherefore aim in the. following claims to cover V:all modifications and changes which fall within the true spirit and scope of the invention.

through, a'plurality of refractory lined radiant heaters distributed along the ring section; means to supply a high temperature gaseous fuel adjacent to said radiant heaters at vieinities inv opencommunication with the kiln chamber at ,'the firing section Vto heat said heaters to incanidescence for radiating heat therefrom intothe chamber; i disposed passages in the side walls of the firing section which communicate with the vicinities passage means providing vertically adjacent toV said radiant heaters, horizontally 4disposed passages in the walls of the firing section Vwhich communicate with the vertical passages,

and horizontal passages in the preheating section communicating with the horizontal passages in the firing section; and means including an exlhaust blower connected to the horizontal passages vin the preheating section to produce a suction effect in the passages for diverting from the vicinities into the passages and withdrawing therethrough the burned gaseous fuel tending to pass from the vicinities into the kiln chamber at the firing section before such medium becomes an active component of the atmosphere in the firing section; at least the walls of the vertical passages in the firing sectionand the walls of the horizontal passages in the preheating section forming inner wall surfaces of the ring and preheating sections, respectively.

2. In a continuous tunnel kiln including a preheating section, an intermediate firing section and a cooling section having an elongated kiln chamber extending therethrough, heat radiating means for the firing section of the kiln chamber, means for heating said radiating means to ,incandescence by combustion of a gaseous fuel exposed to the kiln chamber atmosphere at the firing section, conduit means for supplying the gaseous fuel to effect heating of said radiating means, exhaust means including structure providing passages for withdrawing exteriorly of the kiln a substantial fraction of the heated gases developed by said combustion before such gases become a component of the chamber atmosphere at the firing section, said structure being formed to provide at least a portion of said passages in said preheating section, said cooling section hav- ,-1 ing an inlet for air at a, region removed from the ring section, temperature` responsive regulating `means for controlling the supply of the gaseous fuel through said conduit means, means associated with said regulating means for controlf ling the rate of withdrawal of the heated gases by said exhaust means, and means for controlling the flow of air through the inlet into said cooling section.

3. In a continuous tunnel kiln including a prej heating section, an intermediate firing section and a cooling section having an elongated kiln l chamber extending therethrough, heat radiating providing ilue passages for withdrawing exteriorly of the kiln a substantial fraction of the heated gases developed by said combustion before such gases become a component of the chamber atmosphere at the firing section, said structure being formed to provide a vertical flue passage in each side wall of the kiln at regions adjacent to the juncture of the preheating and firing sections through which upward flow of the heated gases is effected, and a plurality of horizontal flue passages extending longitudinally of the preheating section at the side walls thereof, said horizontal flue passages in each side wall of the preheating section being disposed one above the other and connected to receive heated gases from one of the vertical fines, said horizontal flues being effective to promote heating in said preheating section of the kiln chamber, and means for increasing the heating accomplished by the bottom horizontal fiue passages over and above that effected by the heating gases passing therethrough from the vertical nue passages.

4. The combination set forth in claim 3 in which said means for increasing the heating accomplished by the bottom flue passages comprises burners disposed within the flue passages.

5. The combination set forth in claim 3 in. which said means for 1ncreasing the heating accomplished by the bottom horizontal nue passages comprises gas-fired burners of a radiant type disposed within the flue passages.

6. The combination set forth in claim 3, in which the horizontal flue passages in the preheating section have refractory walls forming the inner wall surfaces of the preheating section of the kiln chamber, and said means for increasing the heating accomplished by the bottom flue passages comprising gas-iired radiant heat elements disposed therein from which radiant heat is adapted to be projected against the refractory walls forming said inner wall surfaces.

7. In a kiln having a, chamber, means forming a heat producing wall for said chamber including a series of members provided with surfaces adapted to radiate heat directly to said chamber, supply means for a fuel adapted to be burned adjacent said surfaces and thereby heat said surfaces to incandescence, additional members forining passages in said wall, said first-mentioned members including means forming paths between said passages .and surfaces whereby products of combustion may be removed from said surfaces through said paths to said passages, and means to apply a suction effect to said passages so products of combustion may be removed from said surfaces prior to the time they reach said furnace chamber.

8. In a kiln having a chamber, means forming a heat producing wall for said chamber including a plurality of members, each member having a cavity formed therein facing said chamber, mechanism to supply a fuel to be burned adjacent the surfaces of said cavities to heat them to incandescence and thereby direct radiant heat into said chamber, meansforming a plurality of passageways in said wall adjacent said cavities, means forming restricted paths of ilow between the edges of said cavities and said passageways,

epos-,ese

9. In--a `lrilnhaving a chamber, a heat-producing- -vvall forv said-chamber -includingfa 4plurality ofe'refractory blocks each having a cavity formed therein, means to Amount -said blocks in rows with the 'cavities facing said chamber, a plurality -of Vfurnace Wall members, means lto mount said members in--rows between 4said blocks, said members and the meansto mountvthem cooperating Jto -formpassagevva-ys between each row 'of blocks,

the edges of leach of `said cavities and saidy passageways, and means to applya pressure to said `passageway-s that is lessthan the pressure .in the furnacehchamben v10;v a-ki1n having a chamber, refractory -m'embers-forming the-walls ofsaid chamber, re- Vvfra'ctor-y burner blocks located in rows ine-said Vwalls, said block-s eachrbeing formed with :acavity open intosaidchamber, means to supply a `fuel-to-be burned V-irrsaid cavitiesto heat thesame andfthereby'produceradiant heat `tor-be projected directly into said'vchamber, refractory parts at- I tached -tosaid. wall.. betweenisaid .bleclrsand-con `operating with saidfwallito form passageyvayswith saidiparts facing said. chamber, said passageways i being formed. with openings extending tothe edges :of saideavities,` .and means to. draw the productsof combustionifrom.saidcavities through said openings .intorsaid passageways before said productsof. combustion. can `enter `said chamber, said parts beingheatedby..saidproducts of combustion ,so that Atheyialso,supply radiant heat to Asaid chamber.

Y11. Ina kiln having a chamber, a Wall for said chamber .including .refractoryistructure form ing-rows of radiant heat, emitting surfaces said structure including passageways extending .in said Wall between said rows of surfaces and an additional passage.. connecting said passagewaxs,

said. ipassageways. beingv ,provided` with an open ing adjacent vthe. edge .of each radiant .heat .emit- `tingsurface thatthey pass, means to Vsupply a fuel.- to` be burned closely adjacent said surfaces tdheat the same, ,and means to withdraw the products of ,combustion through said openings .saidchamberincluding .structure providing alternate-rows of radiant heat emitting burners open to said furnace chamber .andpassageways said passageways being provided with openings extending adjacent the edges and slightly infront of the burners which lie alongside them, means to supply fuel tobe burned in said burners to heat the same. and means to Withdraw the products of combustion from said burners thrmigh said openings and passageways before said products of combustion can enter said kiln chamber.

13. In a kiln having a chamber in which ware is fired, a wall for said chamber including-alternate rows of radiant burners each provided with a radiant heating cavity vopening directly into said chamber and rows of passagevvays extending in a verticaldirection between said burners, said passageways being provided with portions there-Y of extending to-theedges of said cavities, means to supply a fuel to said burners 'to be burnt in said cavities to heat the surfaces of the same and thereby radiate heat directly to said charnber, and means to Withdraw the hot'products 20 of combustion :from .said cavities. through. said passageways before; saidihot :products ofcombustion can enterr said' kiln chamber, -saidghdt products of combustion heating .the walls fnf; said passageways Yso 'that the .latter willY supply .additional radiant heat to said kilnchamber;

14. The combination vof claim 13 including means responsive to the temperaturefof said` kiln chamber, means to 'adjust said supply means vand thereby regulate the amount -of` fuel. supplied :to said burners, and mechanism operative Yin ac.- cordance With the responses .of :said responsive means to operate saidimeans toadjust.

15. In a kiln having a firingzzone,:means forming a heat producingk Wall forv s'aidfzone: including a plurality of radiant heaters each provided with a cavity opening vdirectly into Asaid zone, means-to supply fuel to be-burned closely adjacent thesurfaces of said cavities tothereby heat the same to incandescence. -refractorymembers forming passagevva-ys extending 'between said burners and valong saidwall, means cooperating with said members and said burners to form restricted paths of flow between the edges of said cavities and said passageways through which products of combustion mayow from said cavities to said passageways, and means to withdraw the products of Ycombustion from said cavities through said passageways before said products of combustion can enter Vinto said ring zone.

16. The combination of claim 15 including means responsive to the temperature of said'flr. ing zone, and mechanism operative in accordance with the responses of said means to regulate said means to supply fuel.

17. The combination of claim 15 including means to supply a desired gas to said firing zone, said gas being Withdrawn therefrom through said passageways by said means to withdraw along with said products of combustion.

'18. The combination of claim 15 including means responsive to the temperature of saidY firing zone, means to control the supply of fuel to said heaters, means to control the ow of products of combustion to saidmeans to Withdraw, and mechanism operative ,in accordance with the responses of said temperature responsive means to coordinate the operation of said two control means.

EMIL BLAI-IA.

REFERENCES ci'rnn The followingireferences .are of record inthe le of this patent.:

UNITED STAT-ES PATENTS Number Name Date 1,916,363 Dressler -July 4, '19.33 2,008,007 Dreffein Jul y v16, 1935 2,088,554 Robson July 273, 1937 2,127,742 Ladd Aug. 23, Y1938 l2,180,041 Durieux Nov. 14,' 1939 2,215,079 Hess -Sept. 17, 1940 2,220,928 Kienle et al. Nov.`12,V 1940 2,256,275 Boland Sept 16, 1941 .2,268,987 `I-Iess et al. dan. 6, 1942 2,268,988 ,Hess et al. Jan. Vv6, 1942 2,287,246 Hess `June `23, 1942 2,339,477 Hess et al ;Jan. 18,1944 2,371,420 Blaha Mar. 13,1945

OTHER REFERENCES Rice: Use of F'uels lin Tunnel Kilns, The Clar/worker, Jul-y 1929, pages 126-31, inclusive. V(Cepyin 'Z5-'1423 Y Y

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