US1697373A - Furnace - Google Patents

Description

Jane 1 H. F. SMITH I FURNACE Filed April 22, 1925 4 Sheets-Sheet 1' Jan. 1, 1929.

H. F. SMITH FURNACE 4 Sheets-Sheet 2 Filed April 22. 1925 Elem nu; S

Jan. 1, 1929.

H. F. SMITH FURNACE Filed April 22, 1925 4 Sheets-Sheet Jan. 1, 1929. r 1,697,373

H. F. SMITH 7 FURNACE Filed April 22, 1925 4 Sheets-Sheet 4 after/hogs Patented Jan. 1, 1929.

. UNITED" STATES PATENT caries.

HARRY F. sMI'M oF DAYTON, OHIO, ASSIGNOR! no: THE ens nnsnanem commas. or

DAYTON, -1110, AGORPORATION or oirtroz.

FURNACE.

Application filediA' ril 22, 1925. Serial No; 2'5;1'54;

This invention relatesto heat tra'ns'ferring devices,and more particularlytofurnaces or ovens such. as are used for" heat treating, enameling, and the like.

One of the principal objects of the invention is to provide apparatus of this character, for utilizing a combustible fuel such as oil, gas, or the like, which is so constructed and arranged thatthe products of: combus} tion resulting from the burning of the fuel do notenter the work-receiving chamber, so that any desired atmosphere may; be maintainedwithin the. work-receiving chamber; while at the same time high thermal efiiciency isattained.

Another object of the invention is to pro vide apparatus of this character in which'the heat generated by the burningof the fuel is transferred to a refractory memberwhich turn transfers the received heat, primarily;

by radiation, to the Work within. the work-- receiving chamber.

Other'object's andadvantage's' ofthe' in- Fig. 2 is a verticalsectionalview'alon'g'the line 2-2 of Fig. 1 ,1

the line 33:of Fig.2;

Fig. 4 is a detail sectional view'through the recuperator manifold, and one of the recuperator tubes; I r

Fig. 5 is an enlarged detail View of the manifold construction; 7 7 Figs. 6, 7, 8, 9 and lO arecross' sectional views through somewhat modified forms of recuperator tubes a furnace provided with a' pl'l'lra'lity;- of refractory. elements, in lieu. of the large re fractory element housing'the work receiving chamber as shown particularly in Figs. 2 so and 3;

Fig. 12 is a planview, with parts broken away and shown'in section, of the construction shownin Fig. 11; v

Fig. 13 is a fragmentarysectional view of Fig. 3 is a vertical; sectional View along;

Fig. 11 is a vertical sectionalviewthrough a slightly modified form of. furnace conistructi'on; and v 1 p Fig. 14. is a plan View? of the door corrst'r'ucti'on and mounting;

Furnaces adapted tible fuel such as -oil, g'as, coal,,andtheil'ike,

as heretofore used have been objectionable to o-perate' -u on' combus for two general reasons ,-first, that where" the fuel burned, and the resultingjhqt products of combustion are brought through the work-receiving chamber adequate cfo'fitrol of' the atmosphere Within the, work-reg ceiving chamber cannot be secured; and second, where a mufiie type furnace is" pro; vided' in which the hot product's ofcombu's;

tion' do not pass through the work receiving chamber, either efii'ciency of the furnace,

operation; This invention avoids both. of

low 'or'thei furnace'has" failed to stand. iii

these broad grounds of objection, and.v pro.-

vides a furnace in which: the atmosphere .i... 7-. .4 .u 1.. within the wo-rk-recelvln chamber may be just" as readily controlled as may be dime" with an electric furnace, and yet a Very higihdegree of efiicien'cy may be, secured}. e

cienci'e's' quite as high as any" secured; with:

other known forms or furnaces, electriiof or otherwise;

As illustratihg a preferred embodiment of theinvention, and by; way of description, the invention is herein shown as, applied. the type of" furnace particularlyides'ignfed' fer use inbra'zing or solderinggcopper fins upon: an'i'ron or steelcylinderfor use in airjceoledi gas'engines, such for instances as, the Well known DeIcO Light engifie. for this particular braz-ing' or soldering operationxthe work within the? workereceiving cliamlder is" heated to atempe'ratur'e of about 1850 F'Z Inthe form of" fi'irna'ce' shown particu larly' in Figs. 1 the furnace comprises the usual" metallic" shell 20 provided with. brick Work within which is arrangeda suhistantially circular combustion space" 21,. a layer of suitable refractory material 22" forming the effective wall off this combus; tion space; A gas and fuel inlet orifice 23 is connected to thecombustion pace, more gas outlet passa e or orifice 24* is alsdcon nected thereto, t e inletjand outlet orifices,

as shown particularly in Fig; 3, beili'gjllb cated" adjacent each other" and separated means of a wall 25', so thatthe'incoming'fuel and products of *combustion ass completely? earth work, or some of the commercially known hlghly heat resistant nickel l1rO1Il1 receiving chamber.

um alloys. As is clearly shown in Fig. 2 this refractory cylinder or wall has its ends suitably mounted or imbedded in the lining, 'thework-receiving chamber 31 with in this element 30 being thus completely separated from the combustion space so that none of the products of combustion within the combustion space can pass into the work- As a consequence the atmosphere within the work-receiving chamber may' be'co ntrolled as desired, just as readily as is the case with an eiectrlc furnace. The refractory element 30 is prefer- 7 ablyflmade as thinas consistent with safety and long life. In a furnace used in the -manufacture of copper fin cylinders, as re ferred to above, the refractory metallic element30 was constructed to give a work-re ceiving chamber approximately 27 inches in diameter, the wall of this element being about one half to three quarters of an inch thick. h r i 'Asstated the airand fuel forming the l combustible mixture are introduced through the passage 23 and the hot products of combu'stion resulting from the burning of this mixture pass completely around the refractory wall 30. f As shown in the drawing,

particularly in Figs. 2 and 3, the wall 25 is so arranged that the combustion space 21 is oppositely tapered, its maximum width being at approximately the point of contact ofthe wall 25 with the surface of the refractory element 30. This combustion space 21 has a progressively increasing width from the fuelinlet reaching a maximum at substantially the point of contact of the wall 25 with the refractory element 30, andhaving a progressively decreasing width from then on around the refractory element to the outlet end] As a result substantially uniform velocity of flow of the burning gases, and the resulting products of combustion, through the combustion space is secured. As they thus pass around through the combustion space they heat the refractory wall 30, and the opposed surface of the layer of refractory material 22, by convection, as the hot products of combustion wipe over the respective surfaces of these members at considerable velocity. In addition,fesp ecially at high temperatures, there will b'ea very considerable transfer of heat from the surface of the heat resisting lining 22 to the refractory element 30by radiation, so that the refractory element 30 will be heated to a high temperature, well above the temperature ofincandescence in the embodt .ment of the invention shown.

ergy from the incandescent refractory member 30 to the work. And inasmuch as the tendency for a heated body to radiate heat energy varies as the fourth power of the.

temperature of that body, it is evident that a very efiicient transfer of the heat energy from the member 30 into the work will be secured.

As the heated products of combustion pass through the combustion space and around the refractory element there is, of course, a temperature drop-the incoming gases being hotter than the ofi'going gases. Consequently there is a tendency toward uneven heating of the refractory element, with resultinguneven distribution of heatenergy to the work within the work chamber. In order to overcome this tendency to'uneven heating a series of plates or screens 82 are arranged within the combustion space, in the path of the flowing heated products of combustion; these plates picking up the heat energy from the heated gases and in turn radiating such received heat energy to the refractory'element 30. And b progressively increasing the number of t ese plates so that as the temperature of the products of combustion falls the number of plates is increased, the heat input. into the member 30 may be maintained substantially uniform throughout. For a greater number of plates under a decreased temperature difierential will absorb as much heat as a smaller number of plates under a greater differential. As shown in Figs. 1 and 2 no plates are positioned within the inlet end .of the combus tion space where the temperature is highest. Some plates are positioned beginning about half way round, and an additional number adjacent the outlet opening.

In order to still further increase the efiiciencyof the furnace, the air, or the fuel, or both, are preheated. As shown in Figs. 1, 2 and '3 the furnace is arranged to operate upon gas, such as producer gas, as a fuel, and the construction is such that both the air and the gas are preheated. As a matter of fact the furnace referred to above for the manufacture of copper finned cylinders has been operated very satisfactorily with preheating of both the air and the gas, and also with the preheating of the air alone. Where both air and gas are preheated the efliciency is greater than where only the air alone is preheated.

For accomplishing this preheating of the air recuperator tubes are positioned within the passage 26, where they are subjected within the path of travel of the heated products of combustion passing from the outlet orifice 24 to the vent or stack 27. Where both air and gas are to be preheated a divided manifold 40 is provided, the construction of which is shown most clearly in Figs. 1 and 4. This divided manifold has a partition 41 dividing it into two passages 42 and 43. 'One of these passages 42 is connected to a supply ofair under suitable pressure, while the other 43 is connected to a supply of gas, or other suitable combustible fluid. A plurality of recuperator tubes 45 are provided, each of which has a down turned end 46, constructed for tight connection with the upper surface of the manifold, as shown particularly in Fig. 4. Any desired means for securing the tight connection may be used, but preferably the down turned end 1 of the recuperator tube and the surface of the manifold are both machined so that a tight metal to metal joint may be had. To

hold the various recuperator tubes tightly positioned with respect to the manifold each tube is provided with a tapered outstanding flange 47,. surrounding its down turned end.

The manifold is provided with a plurality of openings 48 each ofwhich is adapted to register with the passage within a cooperating recuperator tube; and adjacent each of these openings 48 the manifold is provided with two upstanding lugs 49 and 50. The lug 49 is provided with an overhanging portion 51, which is shaped to cooperate with the tapered flange 47. The lug 50, upon the opposite side of the manifold, carries a threaded bolt 52 therein, the construction being such that the end of this bolt may be brought against the cooperating tapered flange 47 upon the recuperator tube, forward movement of this bolt resulting in a wedging of the inclined faces of the flanges 47' between the overhanging portion 51 of the lug-49' and the bolt 52, whereby'tight contact of the machined surfaces of the overthe recupera'tor tubes are positioned in place, these'tubes will be .connected alternately to the air supply and the fuel supply. The discharge ends of the recuperator tubes,las will be seen in F 'ig. 3, are located withinthe dividing wall 25 so that the air and the fuel discharged from these tubes pass into the inlet passage 23 where they mix and burn, the hot products of combustion passing around through the combustion space 22. A suitable removable hollow plug 55 is positioned in the outer-end of the passage. 23, which plug has a swinging cover plate by' means of which access .to the passage 23 pia-y be had to ignite the mixture of air and uel.

Preferably the recuperator tubes have positioned within them means forucausing the transfer of heat energy from the tubes to the air and gass passing vtherethrough at a rate in excess of that which would normally be attendant upon the transfer of heat from these tubes by convection into the airor fuel passing through them. 7

In Figs. 6, 7 and 8 areshown three constructions whereby in a 'recuperator tube which is rectangular in cross section, as are the tubes shown in Figs. 1-4, this increased heat transfer may be secured. The tube has positioned therein as shown in Fig. 6, for example, a plurality of layers of wire screen, which should be of some suitable material, such for example, as nickel chromium alloy, or any other material of a nature adaptedato stand up under the temperatures attained by it. The hot products .of combustion passing through the passage 26 will heat the recuperator tubes to incandescence and the heat energy received by these tubes will be transferred by radiation :to the .screens '60 shown in Fig. 6. Because of the very rap-id increase in the rate of transfer of heat energy byradiation with increases in temperature, the rate of transfer where the temperature of the tube is above the temperature of incandescence will be extremely rapid so that the screens will-receive radiant energy in large quantities. Furthermore these screens because of their construction tend to break the flowing currents-of air or fuel into very finely divided streams so that an extremely intimate contact is secured as between the flowing fluid and the surfaces of heated screens. As a'result the transfer by means of convection from these screens to the flowing fluid is very much more rapid,

and much greater in amount, than is the transfer from the wall of the recuperator tube direct to the flowing fluid. Thusthe temperature of the screens is maintained compartively quite low even though large quantities of heat are radiated from the recuperator tube to these screens As a result of this large temperature drop the tube itself isenabled to receive considerably greater quantities of heat by convection from the hot products of combustion passing over the outside. And as a consequence a large proportion of the heat contained in the hot products of combustion when they escape from the combustion space 22 through the outlet orifice 2 1- is removed, so that the heat loss in the products of combustion passing through the vent or stack 27 is'compa-rative- 1y quite low; that is the thermal efficiency of the furnace is quite high.

The heat imparted to the fluid flowing through the recuperator tubes of course goes toward the setting up of higher combustion temperatures within the combustion space 22, and this in turn increases the rate of transfer of heat to the work within the work-receiving chamber.

In Fig. 7 is shown a somewhat different arrangement of the screens within the recuperator tubes. It might happen that the mesh inthe screens would tend to match so that the screens will pack and so adequate passages for the movement of the air or other fluid through the rccuperator tube will not be present. In such case the de sired intimate contact of the flowing fluid and the screens would not be secured. In the form shown in Fig. 7 the screens before they are inserted within the recuperaior tube are stamped or dimpled to provide projections G5, which tend to space the screens adequately and prevent this packing. In

. the form shown in Fig. 7, as well as in the form shown in Fig. 6 a partition 62 is provided. It has been found that the penetrating power of the energy radiations from the recuperator tube is limited because of the interference of the strands or wires of the screen, and where more than two or three layers of screen. are used the remaining layers not only do not tend to add to the efficiency of the device, but actually decrease its efficiency, since they merely permit a passage through which the gases may flow without being brought into contact with the heated metal. As a consequence the recuperator tubes are divided by partitions and the layers of screen are so arranged that not only will the energy radiations heat up the several screenson each side of the parion but they will also heat the partition itself so that the efficiency of the transfer within the tubes by means of convection is very greatly increased.

In Fig. 8 is shown a different form of recuperatortube in which the tube is filled with a plurality of smaller tubes to split the flowing fluid into streams of small diameter and to effect intimacy of contact between the heated metal and the flowing fluid.

In Figs; 9 and 10 the recuperator tube is shown as of cylindrical shape instead of rectangular shape as is true in the previous figures, In Fig. 9 the tube comprises the same as with the forms described above.

In Fig. 10 the tube is also formedby spaced walls 73 and 74, between which are positioned small tubes 75, which serve the same purpose as the small tubes shown in Fig. 8.

As descrioed above the furnace has the usual construction of brick, with the combustion space provided with alining of refractory material, such as fire clay, or fire brick. The rear end of the work-receiving chamber, within the cylindrical refrae tory member 22, is closed by means of suitable refractory material, and the front end is also so closed. The front end of the work-receiving chamber is provided with an opening adapted to receive a door 101,

the body of the door being composed of suitable refractory material, mounted upon a metal plate 102. ries a pair of lugs 103, which are arranged along substantially the vertical diameter of the door. Positioned within these lugs and pinned thereto is a vertical shaft 10 1, the arrangement being such that the shaft and the door move together. The-upper and lower ends of this shaft are rotatably mounted respectively in two aligned passages within the free ends of two links the other ends of which are rigidly mounted upon the shaft 100 which is in turn rotatably supported in standard 107 carried by the shell of the furnace. Rigidly carried upon the shell of the furnace, adjacent the upper standards 107 is an additional standard 108, which has pivotally attached thereto a link 109, the free end of which connected by means of a second link to the door through the medium of the shaft 104, the link 110 being fixed upon the upper end of the shaft 104. i

The links 109 and 105 are so arranged that as the door swings open the path oftravel of the free ends of the two links will intersect. As a result of this construction as the door swings open it will move through such path that its inner face, the face which is presented to the interior of the work-receiving chamber and is therefore at extremely high temperature during operation, will at all times face toward the furnace, so thatthe likelihood of injury to the operator n In as a result of coming in contact with the hot This metal plate 102 car-v erating'motor 118, the other end passing over a similar sheave or sprocket 120, and havin a counterbalance-weight 1 21 hung on the free end thereof. Any suitable con trol switch, illustrated diagrammatically at 122 may be included in the motor circuit 123. When it is desired to open the door the motor 118 is actuated to cause rotation of the wheel 115, which acting through the shaft 106 and the links 105 pinned thereto swings the door outwardly upon these links. But because of the inter-connection of the links the path of travel of the door is controlled as set out above.

When the door of a furnace as ordinarily constructed is open the furnace tends to cool down partly because of the possible ingress of cold air, partly because of the insertion of cold work to be heated up, and also because of the very high rate of heat loss from the heated material of the door and the inlet within which the door sets. lVhere copper fins are to be brazed to a cylinder, as referred to above, the walls of 1 the work chamber are at a temperature of approximately 1850 F. when the furnace is closed and operating at normal temperature. Naturally at this high temperature the heat losses, when the door is opened, from heated surfaces exposed to the outside would be extremely high. In order to cut down these l the inner wall of thework chamber.

heat losses the face of the door is covered with a comparatively thin layer of some heat insulating material 135 such as fibrous asbestos or the like, and over this is arranged a layer of wire screen, or the like, 136 preferably of some metal such as nickel chromium alloy whichis highly resistant to oxidation at high temperature. This screen serves primarily to hold the fibrous asbestos in position. The thickness of the layer of asbestos may be varied as desired but it should preferably be of small heat capacity so that even if cooled down only a comparatively small heat loss will result. And as a result of this construction the heat losses are very materially cut down. In actual operation when the interior of the material of the door is at white heat with the door open, the

screen and the layers of asbestos may be cooled to such a low temperature as to be not incandescent; the high resistance to transfer of heat from the body of the door through the asbestos preventing substantial. cooling of the main body of the door. Not only does the layer of heat insulating material thus out down heat losses; but in addition the door is so arranged and mounted that when in closed position in the inlet to the work chamber it substantially fills the inlet, with its inner face nearly flush with This tends to prevent heating of the side wall of the door and of the wall of the inlet passage so that these parts are of much lower temperature than the inside of the work I chamber, generally well below incandescence and consequently the heat lostwhenv the door is open both by radiation from the wall of the inlet and by direct contact with the air is much less than with the usual constructionv p Inaddition the door and the wall of the inlet passage to the work chamber are made of varying diameter, being given a stepped down construction as shown by the numeral 137 to provide aplurality of ledges or walls which interrupt the transfer of radiant-en: ergy from inside the work chamber through the space between the doorand the wallo the inlet opening. a I 3 By means of these several constructions the heat losses when the door is opened are very materially reduced, consequently. the

furnace comes up to temperature more quickly after 1t is charged, and greater efficiency is thus secured together with a greater work output. g 1

'In Figs. 11 and 12 is shown a somewhat modified form of furnace construction. ,In' the form of furnace described above the work is received within a refractory member 30, the hot products of combustion passing around the outside of this refractory member. This construction of course. is not essential, and the character of thework-re ceiving chamber, and the formand position of the refractory radiating elements may be varied as desired, and to accord with the character of the work to be handled.

lln Figs. 11 and 12, for example," the single refractory member 30 is dispensed with and in lieu thereof aplurality of small refractory members are provided, which extend through a work-receiving chamber 150,

formed in any conventional manner within a suitable furnace construction, this construction being illustrated generally as comprising a metallic shell151 and suitable refractory or heat resisting lining 152.- The hot products of combustionmay'be introduced in any desired way to the refractory elements 153. As shown each refractory I element or tube 153 is provided with a suitable burner 15ft, through which air and asuitable fuel are introduced for burning within the refractory tube itself. Eachzof the tubes is shown as provided with its own burner element, butof course this con struction is not necessary. A single burner.

element may be provided-for a manifold, or combustion space, the hot products of combustion passing from such combustion space into the refractory tubes. Also the form 'of the recuperator elements is not shown inv Figs. 11 and 12 but it is 'to be understood that preheating of the air, the fuel, or :both, may be accomplished in the manner' described above;

V The hot products of combustion passing:

through the refractory tubes heat those tubes, and the heat energy received by them is radiated to the work within the workreceiving chamber 150, and also to the walls of that chamber. As shown the upper wall of the chamber is so shaped that the heat received thereby is in turn radiated downwardly toward the work within the chamher. As a result high efficiency is secured.

'In order to'effect proper transfer of the heat energy from the product-s of combustion to the refractory tubes, means is prefer: ably provided within these tubes to give an increased transfer of heat over that which would normally result from convection as the products of combustion sweep over the inner walls of the tubes. These means consist of screens or perforated plates 160 such as are described above in connection with the recuperator tubes, these plates picking up the heat from the hot products of combustion as those .products pass over and through the screens, the heated screens then in turn radiating the received heat to the refractory tubes to heat those tubes; the transfer of the heat energy being thus just the reverse of the transfer in the recuperator tubes.

In order to maintain a uniform temperature throughout the work-receiving chamber 150, especially where that chamber is of considerable size, it is preferable to so locate the screens 160 that the refractory tubes will be uniformly heated throughout their length despite the fact that the products of combustion are of progressively decreasing temperature as they pass through the tubes, due to the giving up of heat to the tubes. The desired arrangement of these elements is shown in Fig. 12, wherein no screens or perforated plates are provided in the extreme end of the tube where the combustible mixture is burned orenters and the number of screens is progressively increased from that end of the tube to the outlet end. As a result as the temperature tends tofall the number of screens is increased so that even though the temperature differential between the increased number of screens and the products of combustion is less nevertheless the number of screens being greater the actual amount of heat energy received by the increased number of screens will be substantially the same as the amount received by a lesser number of screens but under a higher temperature differential. By means of this construction not only is the transfer of heat to the refractory elements made more efficient, but also a more uniform distribution of heat is secured.

In Fig. 13 is shown a slightly modified form of construction in which only the air is, preheated. A divided manifold is not I needed here so a single manifold 170 is provided to which are connected in the manner descr bed above recuperator tubes which deliver heated air into the inlet passage 23 of the combustion space. The gas, or other fuel, is introduced through a suitable burner element 171 into the inlet of the combustion space to mingle with the incoming air and burn therewith. It has been found that with this construction a somewhat more uni form temperature distribution may be at times secured, but at the expense of efii ciency, than where there is recuperation both as to air and fuel.

While the forms of apparatus herein dis closed constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in.

the appended claims.

What is claimed is:

1. A furnace for operating upon combustible fuels comprising a combustion space, a refractory wall within said combustion space defining and enclosing a work-receiving chamber the construction being such that products of the combustion within the combustion space will not enter the work-receiving chamber, and means positioned within the combustion space and out of substantial heat conducting contact with the said refractory wall for receiving heat energy from the burning of the fuel within the com bustion space and for transferring such heat energy primarily by radiation into the said refractory wall.

2. Heat transferring apparatus of the character described for operating upon combustible fuels,comprising a work-receiving chamber, a combustion space separate from said work-receiving chamber whereby pro 1 ducts of combustion of the fuel will not enter the work chamber, and means positioned out of substantial heat conducting contact for receiving heat energy from the burning of the fuel within the combustion space and for transferring such heat energy primarily by radiation into the work inside the work-receiving chamber.

3, Heat transferring apparatus of the character described adapted to operate upon combustible fuel comprising a combustion space, a refractory wall separating said combustion space from a work-receivingchamber, the construction being such that products of the combustion within the combustion space will not enter the work-receiving chamher, said refractory wall being positioned and constructed to receive heat energy on one side thereof from the products of combustion and transfer said heat energy from the other side thereof into the work chamber, primarily by radiation, and members associated with the refractory wall constructed for receiving heat energy by convection from the products of combustion and for transferring J eonora such received heat energy to the refractory Wall, said members being arranged in progressively increasing numbers as the temperature of the products of combustion decreases.

4. A furnace of the character described, adapted to operate upon combustible fuels, having a circular chamber therein, a refractory element positioned within said circular chamber and dividing said chamber into a Work-receiving chamber and a surrounding combustion space, the said refractory element so separating the work-receiving chamber and the combustion space as to prevent prod nets of combustion passing from the combustion space into the wort-receiving chamber, a fuel inlet'passage within the furnace wall opening into the combustion space and a fuel outlet passage Within the furnace wall connected to the combustion space, the said inlet and outlet passages beingarranged in juxtaposition, whereby the products of combustion within the combusion space are caused to travel completely around the refractory wall enclosing the work-receiving chamber.

5, A furnace of the character described, adapted to operate upon combustible fuels, having a circular chamber therein, a r fractory element positioned Within said circular chamber and dividing said chamber into a work-receiving chamber and a surrounding combustion space, the said refractory element so separating the work-receiving chamber and the combustionspace as to prevent products of combustion passing from the combustion space into the work-receiving chamher, a fuel inlet passage within the furnace wall opening into the combustion space and a fuel outlet passage within the furnacerwall connected to the combustion space, the said inlet and outlet passages being arranged in juxtaposition, whereby the products of combustion Within the combustion space are caused to travel completely around the refractory wall enclosing the work-receiving chamber, and recuperator tubes within the said outlet passage.

6. A furnace of the character described, adapted to operate upon combustible fuels, having a circular chamber therein, a refractory element positioned within said circular chamber and dividing said chamber into a work-receiving chamber and a surrounding combustion space, the said refractory element so separating the Work-receiving chamber and the combustion space as to prevent products of combustion passing from the combustion space into the worlereceiving chamber, a fuel inlet passage within the furnace wall opening into the combustion space and a fuel outlet passage within the furnace wall connected to the combustion space, the said inlet and outlet passages being arranged in juxtaposition, whereby the products of combustion within the combustion space are caused to travel completely around the refractory wall enclosing the Worlereceiving chamber, and a recuperator tube located Within said outlet passage, one end of said tube being connected to a source of supply of one of the constituents of the combustion, and the other end opening into the said fuel inlet passage.

7. A furnace of the character described, adapted to operate upon combustible fuels, having a circular chamber therein, a refractory element positioned Within said circular chamber and dividing said chamber into a Work-receiving chamber and a surrounding combustion space, the said refractory element so separating the work-receiving chamber and the combustion space as to prevent prod nets of combustion passing from the combustion space into the work-receiving cham her, a fuel inlet passage Within the furnace Wall opening into the combustion space and a fuel outlet passage Within the furnace Wall connected to the combustion space, the said inlet and outlet passages being arranged in juxtaposition, whereby the products of combustion Within the combustion space are caused to travel completely around the refractory Wall enclosing the work-receiving chamber, and a recuperator tube located within said outlet passage,'one end of said tube being connected to a source of supply of one of the constituents of the combustion, andthe other end opening into the said fuel inlet passage said recuperator tube having means therein for receiving heat by radiation from the tube and transferring such heat by convection to the fluid passing through the tube. p v

8. A furnace of the characterdescribed,

ada ited to o erate u on combustible fuels having a circular chamber therein, a refractory element positioned Within said circular chamber and dividing said chamber into a work-receiving chamber and a surrounding combustion space, the said refractory element so separating the workr ceiving Gllfillh her and the combustion space as to prevent products of combustion passing from the combustion space into the Work receiving chamber, a' fuel inlet passage within the furnace wall opening into the combustion space and a fuel outlet passage within the furnace wall connected to the combustion space, the said inlet and outlet passages being arranged in juxtaposition, whereby the products of combustion Within the combustion space are caused to travel completely around the refractory wall enclosing the WOllC-I'O- ceiving chamber, a plurality of recuperator tubes Within said outlet passage, a divided manifold associated with said tubes, the said tubes being alternately connected to opposite sides of said manifold, each of said tubes being connected to the said inlet pas- I bustible fuels "ing arranged in progressively increasingsage, and means for introducing air and a combustible fuel to opposite sides of said divided manifold.

9. Heat transferring apparatus of the character described adapted to operate upon combustible fuel, comprising a work-receiving chamber, means for burning a fuel, and heat transferring elements interposed within the path of travel of the resultin products of combustion, said elements being adapted to receive heat by convection and transfer such received heat primarily radiation, the number of said elements being progressively increased as the effective temperature of the products of combustion decreases.

10. A furnace for operating upon comcomprising a combustion space, a refractory wall within said combustion space defining and enclosing a workreceiving chamber, the construction being such that products of the combustion with in the combustion space will not the work-receiving chamber, said refractory wall being positioned and constructed to receive heat energy on one side thereof from, the products of combustion and transfer said received heat energy from theether side thereof into the work chamber largely by radiation, perforated members within the combustion space constructed and positioned for dividing the flowing products of combustion into fine streams and for effecting intimate contact between the flowing products of combustion and the surface of the perforated members to receive heat energy by direct transfer from the flowing products of combustion and to transfer said received heat energyprimarily-by radiation to the refractory Wall.

11. A furnace for operating upon combustible fuels comprising a combustion space,'a refractory wall within said combustion space defining and enclosing a workreceiving chamber, the construction being such that products of the combustion within the combustion space Will not enter the work-receiving chamber, said refractory wall being posltionedand constructed to rece ve heat energy on one s de thereof from the prodnets of combustion and transfer said received heat energy from the other side thereof into the work chamber largely by radiation, perforated members within the combustion space constructed and positioned for dividing the flowing products of combustion into fine streams andfor effecting intimate contact between the flowing products of combustion and the surface of the perforated members to receive heat energy by direct transfer from the flowing products of combustion and to transfer said received heat energy primarily by radiation to the refractory wall, said perforated members benumbers as the temperature of the products 'of combustion decreases to maintain the temperature of the refractory wall substantially uniform throughout its extent.

12. In a furnace of the character described a main cylindrical chamber, means for closing said chamber at both ends, a combustion space surrounding said chamber for the greater part of its length the opposite walls of the said chamber and said combustion space being substantially parallel, a tangential inlet for the heated prodnets of combustion into the combustion space, an outlet from the said combustion space for the escape of the products of combustion, and a. rec-uperator tube through which the fuel to be burned is passed on its way to the combustion space arranged with its outlet end opening into the said inlet, the construction being such that the combustible fuel introduced through said recuperator tube burns within the said inlet passage.

13. A furnace of the character described comprising a main cylindrical chamber, combustion space surrounding said chamber, means for preventing the products of the combustion within the combustion space from entering the cylindrical chamber, a fuel inlet passage opening into said combustion space, a preheating chamber above said combustion space, an outlet passage connecting the said combustion space and the preheating chamber, a plurality of recuperator tubes within said preheating chamber, and a divided manifold to which said recuperator tubes are connected.

14. A furnace of the character described comprising a work chamber, a combustion space surrounding said work chamber, means for preventing the products of the combustion within the combustion space from entering the Work chamber, a fuel inlet passage opening into said combustion 1 space, a preheating chamber above said combustion space, an outlet passage connecting the said combustion space and the preheating chamber, recuperator tubes positioned Within said preheating chamber, and openelement opening into the said inlet passage adjacent the ends of the recuperator tubes.

15. In a furnace of the character described a Work chamber, a combustion space surrounding said work chamber, means for pre venting the products of the combustion within the combustion space from entering the said work chamber, an inlet passage connected to the said combustion space, said passage intermedlate its length belng oppositely tapered, so that itseffective area is progressivelyincreased and then progressively decreased.

16. A furnace of the character described comprising a combustion space, a refractory wall'within said combustion space defining and enclosing a work chamber, said wall ing into the said inlet passage, and a burner V being so positioned as to also define. a combustion passage completely surrounding the said refractory Wall, said combustion passage being of progressively decreasing cross section throughout tne greater part of its length.

17. A furnace of the character described comprising a chamber, a refractory Wall positioned Within said chamber defining and enclosing a work space Within the said Wall and a combustion space surrounding the said wall, a fuel inlet passage and an outlet passage connected to said combustion space, the said combustion space being of enlarged cross section area intermediate the point of fuel inlet and the point of exit of the burned gases.

18. A furnace for operating upon combustible fuels comprising a combustion space, a refractory .Wall Within said combustion space defining and enclosing a Work receiving chamber, the construction being such that products of the combustion Within the combustion space Will not enter the Work-receiv- .ing chamber, said refractory Wall being positioned and constructed to receive heat energy on one si'de thereof from the products of combustion and transfer said received heat energy from the other side thereof into the Work chamber largely by radiation, and heat energy receiving means for maintaining the temperature of the refractory Wall sub stantially uniform throughout its extent.

19. A furnace of the character described comprising a main cylindrical chamber, a combustion space surrounding said chamber, means for preventing the' products of the combustion Within the combustion space from entering the cylindrical chamber, a

fuel inlet passage opening into said combusion space, a preheating chamber above said combustion space, an outlet passage connecting the said combustion space and the preheating chamber, a plurality of recuperator tubes Within said preheating chamber, and a divided manifold to which said recuperator tubes are connected the said divided manifold and recuperator tubes being arranged With alternate tubes connected to the same side of the manifold.

20. In a furnace of the character described, comprising a Work-receiving chant ber, and means for heating said chamber, a closure door for said Work-receiving chamber having a body of heat resisting material thereon, and means upon the surface of said body of heat resisting material for prevent ing the transfer of heat from said material when the door is in open position.

21. A furnace comprising a Work space, means for heating the Work space and the Work therein, a closure member for said Work space, and a layer of heat insulating material upon that portion of the closure member presented to the interior of the Work space for preventing loss of heat from the body of the closure'member when said closure member is opened.

22. A furnace comprising aworks aace, means for heating said 'Work space an the Work therein, a closure member for said work space,- the body of said closure member being'composed of a refractory material, and a layer of heat insulating material upon that portion of the closure member which is presented to the interior of'the Work space for preventing the loss of heat from the bodies of the closure member When the closure member is opened and means for retaining said insulating material in place upon the body portion of said closure.

A furnace of. the character described comprising a Work'space, means for. heating the Work space and thework therein, a closure member for said Work space, land a layer of insulating material consisting of asbestos fibre or the like upon that. portion of the closure member which is presented to the interior of the .Work space for preventing loss of heat from thebodyof'the clesure member when that closure member is opened.

24-. A furnace of thecharacter. describec comprising a workspace having an "opening thereinto, means for J heating .:-said Work space and the Work therein, a swinging closure member ferC-pesitioning Within "said opening,.and..-means for supporting theIclosure me'inbervadapted for actuation to swing the closure into or out 0f said .openingito open or close the Work space, said means being so constructed that the inner face of the closure is at all timespresented toward the Work. space as the closure is swungito open enclosed position.

v 25. A furnace of the. character idescribed comprising a Work space, a closure member for said Work space, a rotatable rod mounted on the outer portion of said closure, an ari'n attached to said rod a rotatable shaft carried by the furnace, a second shaft carried by the furnace, means on one of saidv shafts for causing rotation thereof, supporting means connecting such shaft and the said rod to support the closure, and controlling means connecting the other shaft and the arm on the said rod.

26. A furnace of the character described comprising a Work space, a closure member for said Work space, a rotatable rod mounted on the outer portion of said closure, an arm attached to said rod; a rotatable shaft carried by the furnace, a second shaft carried by the furnace, means on one of said shafts for causing rotation thereof, supporting means connecting such shaft and the said rod to support the closure, and controlling means connecting the other shaft and the arm on the said rod, and operating means tending to normally urge the closure toward closed position and means for positively opening the closure against the action of said operating means.

27. A furnace of the character described comprising a work space, a closure member for said work space, a rotatable rod mounted on the outer portion of said closure, an arm attached to said rod; a rotatable shaft carried by the furnace, a second shaft carried by the furnace, means on one of said shafts for causing rotation thereof, supporting means connecting such shaft and the said rod to support the closure, and controlling means connecting the other shaft and the arm. on the said rod, operating means for moving the closure toward open or closed position comprising a weight arranged to normally urge the closure toward closing position and a motor for positively opening the closure against the action of said weight.

28. A furnace of the character described comprising a work chamber adapted to contain work to be heated, a refractory element associated with said work chamber, a combustion space, means for supplying a fuel to be burned within said combustion space and means for transferring heat energy from said heated products of combustion to the said refractory element the heat energy received by the said refractory element being in turn transferred therefrom into the wor and means associated with said refractory elements for increasing the transfer of heat energy from the products of combustion into the said refractory elements said means being of progressively increasing number as the temperature of the products of combustion decrease, to maintain the refractory element at substantially uniform temperature throughout its extent.

29. A furnace of the character described comprising a work chamber adapted to contain work to be heated, a refractory element associated with said work chamber, a combustion space, means for supplying a fuel to be burned within said combustion space and means for transferring heat energy from said heated products of combustion to the said refractory element the heat energy received by the said refractory element being in turn transferred therefrom. into the work, a perforated body associated with said refractory element for receiving heat directly from the products of combustion flowing through the said refractory element and transferring said received heat energy by radiation to the refractory element.

30. In a furnace of the character described, comprising a work-receiving chamber having an inlet opening therein, and means for heating said chamber; a closure door for said work-receiving chamber hav ing means associated therewith for preventing the transfer of radiant energy through the space between the door and the wall of the inlet opening when the door is closed.

31. A furnace comprising a work space, means for heating the work space and the work therein, a closure member for said work space, and a layer of heat insulating material upon the closure member and constructed to be presented to the interior of the work space for preventing loss of heat from the body of the closure member when said closure member is opened, said layer being of small heat capacity.

In testimony whereof I hereto aflix my signature.

HARRY F. SMITH

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