US2638889A - Heat-treating element for heattreating furnaces - Google Patents

Description

May 19., 1953 J. A. Dow 2,638,889

HEAT-TREATING ELEMENT FOR HEAT-TREATING FURNAcEs Filed May 8, 194? 2 sheets-sheet 1 INVENToR. JOHN A. Dow

n Tram/ev May 19, 1953 J'. A. Dcw

HEAT-TREATING AELEMENT FOR HEAT-TREATING FURNACES Filed May 8, 1947 2 Sheets-Sheet 2 mm-nrnrr-ez se.

L23 JOHN A. Dow

A T TORNEY Patented May 19, l1:953

A UNITED .l STAT-Es PATENT OFFICE.

* "f f n* 2,638,839 e' f Henares-Arise' ELEMENT roey HEAT- f 1 TREATING FURNAcEs y John Antw, `Husein'gian weeds. Mich.; Doris B.

Dow, administratrix of saidJbhn -Ai Dow, de ceased, assignorto Doris B. Dow, fRoyal. Oak,

f Mich., as trustee [Appleman May, 8.31947, serai 10.146.124

This application is a continuation in Apart of the subject matter contained in my copending applications for United States Letters Patent, Serial No.'664,1948 forLiquid Salt or Fusible 4lVleta-l Bath, led April 25, 1945,v vnow abandoned, and Serial No. 670,436 for Heat'lreating Furnace, sied May 17, 1946. Y Y y The invention relates to improvements-in radi'- ant heating elements 'or tubesto be' employed in heat treating furnaces andfhas'particularrelation toheating elements rof thisl type in'whieh a combustible mixture is employed internally thereof for the purpose of heating the *elements* o1' tubes to radiant temperatures.

In heating elementsy of this type as these have been constructed heretofore* lit has been a problem to construct the tubes so that the exterior surface thereof would be of unliffirm.y temperature from one end thereof tothe other'. In such heating elements there has''arisen the difficultyv that some parts lofthe `surface wereconsiderably hotter than the average temperature 'of the entire 3 Claims. (Cl. 126-91) crease in the amount of floor space necessary for the installation of any number of furnaces due to the fact that 4a considerable 'amount -of space "is vrequired at one side beside a furnace for operating and servicing the heating tubes. If'

this work has to be done from both sides -of a furnace,V then 'more space must beutilized than Wouldotherwise be required.

It has been proposed 'heretofore Ato attempt to improve the performance of such tubes by employingv devices therein to increase the velocity andthe turbulence and 4sinffafce*scrubbing action surface and consequently these hot spots would burn out and hence makenecessarythe replacement of an element, when perhaps 'the' vlarger portion of the heating element was in condi-tion to render service for a considerably longer-period of time. Also these 'hotspots-land Asuch 'irre-'guiar h eatingmadeit'necessaryto'usea 'greater ameunt of heating f surface `in `any @givenfurnace v '-th'a'n would be required `Were 'it' possible to i'ernplw heating' elements "of" uriiforniA temperature rom one extremity thereof to another.Suoh'lael of.

uniformity of temperature in a 'furnaceemploy#l ing these heatingvelements also caused ,nenunis formv heatingl of the work in radiation furnaces and-sometimes caused nonuniform heatingl o'f-the ycirculzfiting mediuml in conve'ctici'n' furnaces. I

Not only have heating element-'slof this type been subject v'to nonuniforr-A temperatures throughout the 'length thereof I toapconsiderableextent but it 'has beencharacteristi-c thereof l'that the' tern-v perature of the surface-tended progressively' to decrease toward-the 'outlet ends thereof. -Under such circumstances litjliasgenerally been considered not the best praeticeeto placejallf'of- 'the tubes" in the 'furnace-trom -oneside Wall thereof. instead of suehL desirable practieef'it' has been necessary -hereto'f-oreto insert one rowl *of tubes Ain the furnace llrcm "one side wall thereof "and another 'from thelop'pos'ite side ofthe lfurnace. This practice of 'inserting the tubes inthis Inan- -ner vfrom'opposite side wallshastended t vide more lu'niiorn'ilnaating throughout "the entire -furnace, but it has required''a censiderable 'inof the heating fluid Within the tubes in particular regions therein Where it was considered desirable to -inerease'fthe surface temperature ofthe elements. These expedients have been'objectionable from the standpoint that theycreated other -hot spots the heating elements which likewise reduced the 'life thereof. Also 'these expedients tended to greatly reduce 'and render vnomir'iif'orrn the space provided -forthe combustible fluid With inthe heatingelements and'lconsequently made it necessary either to make the heating elements largeror to tolerate V'in'eflicie'nt combustion of the combustible fluid employed.

such heat by radiation through the combustible uid to the heat radiating surface of the heating elements. Itis furthermore proposed` to. employ relatively uniform heat kabsorbing and radiating i means' Yofthis character which will not create excessive Yturbulence or scrubbing action and. will not excessively increase anddecrease the velocity of the combustible nuid within `the heating .ele-

ment. y y.

Such means may be arranged Within the heating -elerne.rits in such manner as t0 progressively increase. the radi'atn of vheat to the exterior surface of the heating elements toward the outlet thereof so that the heating .effect of the elements will remain relatively constant notwithstanding the reduction' in 'temperature in such region of the Ico'mbustible uid contained therein. y Alsosuch means 'may be employed merely for the purpose of increasing the capacity of the heating tubes employed in any furnace. ASuch increase in capacity will result from the improved elliciency in absorbing and radiating heat resulting from the combustion of fuelA supplied to the Vfuel inthe `tubes employing such means.

One of the objects of the invention is to provide a heating element having a temperature throughout the extent of the heat radiating surface thereof in which the variation from the average temperature of the surface of the heating element is reduced .-to a minimum. v f

Another object of the invention is yto increase the life of heating elements employed in heat treating furnaces by eliminating hot spots from the elements which tend to burn o ut and to cause replacement of the elements sooner than VWould otherwise be necessary. y

Another object of the invention isvto provide for more uniform heating of radiant heating ele l ments from one end of such'felements to another so that all of the elements can be placed in a furnace from one side of the furnace, and as `4 within the heating elements employed there- 1n;

Figs. 8, 10 and 12 are longitudinal sectional views through heating tubes or elements employing other forms of heat absorbing and radiating means therein;` and v f Figs.\'9,f11 and 13 are cross sectional views through the structures disclosed by Figs. 8, l and l2 taken respectively in the planes of lines 9--9,

a consequence thereof the floor space required for heat treating Work will be reduced.

the capacity of radiant heating tubes employed in such furnace by increasing the heat transfer rate from the products of combustion to the heat radiating surfaces of the tubes, and consequently the rate at which heat may be transferred from said surfaces to the work being processed.

A still further object of the invention is to increase the combustion efficiency within radiant heating tubes of such type by increasing the amount of heat absorbing and radiating surfaces Within the tubes and with which surface the burning gases are brought into intimate contact during the combustion process.

Other and further objects of the invention will be apparent by reference to the accompanying drawings of which there are two sheets, which by wayof illustrationshow preferred embodiments and the principles thereof and what I now consider to be the best mode in which' I have contemplated applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art Without departing from the present invention and thepurview of the appended claims. I also contemplate that of the several different features of my invention, certain ones thereof may be advantageously employed in some applications separate and apart from the remainder of the features.

In the drawings:

Fig. 1 is a cross sectional view of a heat treating furnace employing heating elements -or tubes embracing the principles of the invention;

Fig. 2 is a longitudinal sectional view through a heating element such as those employed in the structure disclosed by Fig. 1; l Fig. 3 is a longitudinal sectional view of a modied form of heating element such as might be employed in the structure disclosed by Fig, l; Figs. 4 and 'I are longitudinal sectional views through the outlet sections of heating tubes such as those disclosed by Figs. 2 and 3 and illustrating other forms of heat radiating and absorbing means that may be employed therein;

Fig. 5 is a cross sectional View of the heating tube disclosed by Fig. 4 taken substantially in the plane of line 5 5 thereon;

Fig. 6 is a cross sectional view of a lower portion of the furnace illustrated by Fig. 1 disclosing the transversely disposed passages formed in the lower Wall in which the heating elements are disposed and disclosing another form of heat radiating and absorbing means which may be employed II-II and I3-I3 thereof. n Referring particularly to Fig. l, the numeral Hl indicates a heat treating furnace of conventional design comprising side walls Il, a lower wall I2,

and an uppervwall I3. An opening in the front wall, not shown, provides means for inserting work baskets or containers I 4 within the heat treating compartment I 6 provided by the walls of the container, these work baskets being supported on ai supporting rack I'I having wheels or rollers I8 mounted thereon, on which the Work baskets are adapted to roll easily into and out of the furnace. l

The heating chamber I6 of the furnace I8 is adapted to be heated by a plurality of heating elements indicated at 20, the heating elements being dividedfinto an upper row indicated at I9 and a lower row indicated at 2I. These heating elements may be positioned in the furnace in any desired angular position, although in the structure shown by Fig. 1 they are positioned horizontally in spaced relation to one another from front to rear of the furnace and are provided with removable heads indicated at 22 adapted to be inserted in openings 23 formed in one of the furnacenside walls I I It` Will be noted that the openings 23 are all formed in the same side wall I I of the furnace ID thereby permitting the changing of all of the tubes or the servicing or adjustment thereof from the same side of the furnace. Since this work requires considerable space, vthere will be a considerable saving in the over all space required for a number of furnaces due to the fact that two furnaces can be placed very close together when all of the heating elements are available from the adjacent sides thereof.

In the form of heating element disclosed by Fig. 2 the heating elements 20 comprise U-shaped tubes 24 similar to the tubes disclosed by copending application Serial No. 670,436 previously referred to. In such structure the tubes 24 each comprise a straight tubular inlet section 26, a straight tubular outlet section 21, the two sections being connected at one end by a curved tubular section 28. The inlet section 26 has an inlet end 29 projecting through the head 22 and into which is introduced by a conduit 3| the combustible gas employed in heatingfthe tubes. Inside the inlet 29 and disposed in spaced and concentric relation thereto is a short section of tubing indicated at 32, the interior of which is connected to a conduit 33 employed in introducing air required to form the combustible charge within the interior of the tube 24. The air emerges from the inner end of the tube 32` and there mixes with the combustible gas supplied by the conduit 3| to the interior of the inlet 29 of the tube 24. Within the interior of the tube 32 there is concentrcally disposed a smaller and longer heat absorbing and radiating means, member or tube 34 which is adapted to extend from one end to another of the straight section 26, the opposite end thereof being secured in an opening formed at 36 in the curved section 28. The tube 32 projects putwardly beyond the end of the straight deteste tubular -se'etioh zit-,good 'thespdeebetweeh the' tubes et the endofrtheseeti'oh {z ffls closed byftih annular cop 31. The -tubesaz and terminate in' the seme region lun-d the I'erids thereof are liliew'sje 'closedb'y'd'dlso738.L ,l l -f y 1 f While such is essentiel, lthe space with-ih the tube 34 may be employed"lrlf-fdrodueingia controlled gas 'ettiV pher'e to be'oirohldtediihthe heating eliamber tu; 'fassuoh spade is employedih the structure disdlosed by my opehdihg appli-otttin "Serltl No.6'70;436. Hgwver; 'the 'til-bef :ea't' be util-ized shtml?l f'for 'radietingfahd dbs'obl heetehd for transferring this heezt by rfa lotion to the 'section 26 orthetube 'n' for the fi'oiirposes hereinstated. 'l

Beyond the 'inlet 29' the sldethe tube 24 -eonipri'ses a ooihbtlstlo e amber ihditedjajt '39, the outlet to 'whifeh isiindieete'dfbythe'humoral u. This outlet fori-ris lilffp'ortion ofthe straight section `l1 which lprojeots youi-wetreilly of the iur: heee through titel-lead i212. Thee'oihbustib'le funx; ture to be burnedihtheioorrlbstio heim er afs is supplied to the 'oohduitsfal lon-d 3:5. endjlgriited in the combl'lstlollhdnbrbyy suitable me'grls for 'this purpose. not shown. The mixture the tubes is generally igh-ited lmerely "by 'throwlhgje lighted metoh lrlt'o theoutl'et'eridof e tubeiwheri the misrtu're'is turned on. Also 'the products of eombustion'diseharged from 'the' outlet t] irioybe cre'd away a-Ild ictlltlgd `'tol the v`"elf/ifiio'sfpll'e by esuitable exheust'ihdnifoldjhot showt.; y 'AS is indicated.bytheidrawlnegjthe oo Abustin of the eofhbustlblejhlixture ihtrod'eed into he tbe 2i Obousplihpa11yil1`tht jghtjsec n motion or thefoo'lbustible huid within the'ntbe 28.' Also when the products'of combustion pass beyond the ends ofthe tubes 43, 44, 46 and-",V the temperaturelthereof;can be maintained at the-lowest possible value-thatthe temperature of such uid can be and still maintain the temperature of -the section21 at a substantially uni-` form value. Y

It will be noted that the combustible fluid, practically from one lend to another of the tube 24, encounters only relatively smooth surfaces and passages of somewhat different but relatively uniform cross section. This tends to cause the combustible fluidto flow in relatively straight lines, thereby producing a relatively uniform rate of combustion in the fluid-during-the period of combustion of the fluid within vthe combustion chamber 39. Thereafter thev heat absorbing and radiating surface is increased within the cornbustion chamber so as to absorb and radiate heat at an increasing rate during the period just prior to the dischargerof the products of combustion fromthe tube 24. During such period the combustible fluid is not luminous to as great. an extent as before and consequently more surface is required to absorb the heat from the products of combustion and more surface is required to radiate such heat to the section 21 to maintain a'relatively constant rate of radiation from such section from one end to the other thereof.

In the structure disclosed by Fig. 3, where corresponding reference numerals are employed to indicate elements similar to `those disclosed by Fig. 2, the straight section 26 is employed as a combustion chamber throughout the entire extent of the cross sectional area thereof, andas the luminous products of combustion pass therethrough such products radiate heat to the interior surface of the section at -asubstantially uniform rate. The heat radiating means or member 42d employed in the section 21 comprises open end tubes 48, 49 and 5| similar to the heat radiating and absorbing tubes employed in Fig. 2 except that there is a less number ofA said tubes and the centrally disposed tube is somewhat larger and shorter. Such variation in the heating elements may be made when it is not desired to employ means such astube 34 in the inlet end of the combustion chamber 39 and when Va Alesser amount of heat absorbing and radiating surface is desirable in the outlet end of such combustion chamber. In this structure any suitable means such as -that employed in the structure disclosed by Fig. 2 may be employed for supplying combustible fluid to the inlet end 29 of the heating element 26.

Figs. 4 and 5 disclose a section of a heating element or tube 24 having a heat absorbing and radiating member or means 42 disposed therein consisting of a pair of strips of sheet metal 54 and 56. The strips 54 and 56 each are bent along a middle longitudinal element thereof to provide portions 51 and 58 disposed at right angles to one another. The strips may be welded together at 59 along the longitudinal bent portions thereof so as to secure the strips together to provide a single unit, the strips being secured together in such manner that the portions 51 and 58 of the two strips extend radially outwardly from the axis of the section of the tube 24 at right angles to one another. The portions 51 and 58 are cut away as is indicated at 6l to provide longitudinally extending portions of decreasing width, the presence of which in the element 42"` provides a progressive increase in the amount of metal and surfacecomprising the element 42' from the inlet toward the outlet endsthereof. e Ifheportions 6l vterminate a short distance from the outlet end of theelement 42 to provide supporting flat portions 63 at one end thereof so as to support the member 42 Within the interior of the section of the vtube v24. Itwill be apparent that as the hot gases or products of combustion'within the tube 24 pass along the smooth exposed surfaces of the element 42', the element surfaces will absorb from the gases a progressively increasing amount of heat and will thereafter radiate such heat to the interior surface of the tube 24 from whence it will be picked up'by convection or radiated to the circulating medium or work being. processed within a furnace in which the tube isemployed.

In the structure disclosed by Fig. 6 there is employed in the tubes 24 a heat absorbing and radiating member 42 consisting of a plurality of tubes 64, 66 and 61, disposed one within another and being respectively of decreasing diameters toy provide parallel crescent shaped spaces between the tubes to providefor the flow of heated gases or products of combustion within the tubes. It .will be noted that the tubes 64, 66 and 61 are not concentrically disposed within the heating tube or element 24 but extend along the bottom of the tube 24 in such manner that the surface of one tube rests upon and is tangent to the surface of another along a longitudinal portion of the length ofthe tube 24. When located in such position the tubes 64, 66 and 61 can merely be placed within one or more sections of atube 24 without requiring anyv supporting means or spacers for properly positioning the tubes within the vheating element 24.

In Fig. 6 the heatingtubes 24 are positioned in transversely disposed wells 65 formed in the heat insulating fire brick or other suitable material of which thebottom or lower wall l2 with whichk a furnace -such as that disclosed by Fig. l is provided. Due to the nonconcentric position of the tubes 64, 66l and 61 in the section of the tube 24, as disclosed by Fig. y6, it will be apparent that the closer proximity of thesurfaces of the tubes 64, 66 and 61 adjacent the bottom portion of the tube 24 will tend to decrease the amount of heat-which can be absorbed and radiated by such surfaces Vin such region.A In other Words, the top longitudinal portions of the tubes 64, 66 and 61 will absorb and radiate a maximum amount of heat due to the greater separation of the surfaces of the tubesand the greater amount offgases which may affect such surfaces.

From the tops of the tubes the amount of heat which it is possi-ble for the tubes to absorb and radiateprogressively decreases toward the bottom of thetubes due to the progressively closer spacing of the surfaces thereof and the progressively decreasing amount of the products of combustion which may affect such surfaces. The tubes.64, 66 and 61 therefore providea directional heating effect in the heating element 24 in which they are employed to such an extent that a minimum amount of heat will be radiated bythe heating element 24 to the portion of the bottom wall l2 directly beneath the heating element, a progressively increasing amount of heat laterally to the side walls of the Well 65 and a maximum amount upwardly in the direction of the work containers I4.

Fig. '7 discloses a section of a heating element or tube 24 provided with a heat absorbing and radiating element 42a consisting of a plurality of concentric tubes 68,' 69 and 1| disposed therein in such manner that all the tubes terminate di- "surface temperature along theoutlet portion of said heating tiibe relatively uniform and at a value which approximates the average tempera.- ture of said'tube along the inlet portion thereof, said radiant heat absorbing and radiating means comprising an elongated thin-walled structure dividing the interior of said heating tube into a plurality o-f substantially parallel paths of flow for the products of combustion withoutmaterial- 1y obstructing or deflecting the flow of said products of combustion and affording an extended radiating Asurface -presentf'ed toward but spaced from the heating 'tube wall.v

2. A heating element for-heat treating furnaces comprising a heating tube adapted to be disposed within a furnace for heating Work to be disposed therein, the interior of said heating tube providing a combustion chamber for the combustion of a gaseous combustible mixture to be supplied thereto, the exterior of said heating tube providing a heating surface for yheating said work in response to the combustion of said mixture therein, said heating tube being provided with inlet and outlet means for supplying thereto 'and discharging therefrom said mixture and the products of said combustion respectively, and radiant heat absorbing and radiating means disposed within the outlet portion of said combustion chamber for increasing the heating effect of said heating element at said portion, said radiant heat absorbing and radiating means comprising" an elongated thin-walled structure dividing the interior of said heating tube into al plurality of substantially parallel paths of ilow for the products of combustion without materially obstructing or defiecting the flow of said products of combustion and affording an extended radiating surface presented toward but spaced from the heating tube wall, said means being formed of a plurality of sheet material members having opposite surfaces parallel to oneV another and with longitudinal portions thereofl parallel to the interior surface of saidheating tube, said members being of different lengths and arranged to provide increasing heat absorbing and radiating areas from the inlet end to thev outlet ends thereof so as to tend to maintain the' exterior surface ltemperature along the tube at the-outlet portieri thereof relaa =tively uniform and' at a value-which approximates the average temperature -of the tube at the inlet portion-thereof.

3. A heating element for heat treating furnaces comprising a heating -tubeadapted to be disposed within a furnace for vheating Work to be disposed therein, the interiorof said heating tube providing a combustion chamber for the combustion of a gaseous combustible mixture to be supplied thereto, the exterior of said heating tube providing a heating surface for heating said Work in response to the combustion of said mixture therein, said heating tubebeingi'provided with inlet and outlet means for'supplying thereto and discharging therefrom said mixture and the products of said combustion respectively, and radiant heat absorbing' and f radiating Ameans disposed within the outlet portion of said combustion chamber for'increasing the heating effect of said heating element at the outlet portion thereof so as to tend to maintain the exterior surface temperature along the tube at the outlet portion thereof relatively uniform and at a value which approximates the average temperature of the tube at the inlet portion thereof, said means comprising a plurality of sheets of material having parallel opposite-surfaces, said sheets being of diiferent lengths, said lengths decreasing from. said inlet towardsa'id outlet.

" JOHN A. DOW.

References Cited in the file'of this patent y UNITEDSTATES PATENTS Number'

Images