US2825547A - Muffle type furnace with movable support struts - Google Patents

Description

March 4, 1958 A. H. VAUGHAN MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT STRUTS 6 Sheets-Sheet 1 Filed May 24, 1955 v INVENTOR. 1i Vaughan 9W4? Arthur BY ATTORNEYS Filed May 24, 1955 March 4, 1958 A. H. VAUGHAN 2,825, 7

MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT s'rRUTs 6 Sheets-Sheet 2 WWII? M n b INVENTOR.

yr'z'hurHI a han game/2% ATTORNEYS March 4, 1958 A. H. VAUGHAN 2,825,547 MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT'STRUTS Filed May 24, 1955 6 Sheebs-Sheet 3 IN V EN TOR. A H h'zughan flrihur ATTORZWZYS .March 4, 19583 A. H. VAUGHAN MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT STRUTS 6 Sheets-Sheet 4 Filed May 24, 1955 IN V EN TOR. H Vazyhan flri'hur v &

ATTORNEYS March 4, 1958 A. H. VAUGHAN ,8

' MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT STRUTS Filed 5 /24, 1955 e Sheets-Sheet 5 I INVENTOR.

. ArthurH Vizuyhan ATTORNEYS March 4, 195

A. H. VAUGHAN MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT STRUTS Filed May 24, 1955 IWII' 6 Sheets-Sheet 6 INVENTOR.

Arthur H Viuz han ATTORNEYS United States Patent MUFFLE TYPE FURNACE WITH MOVABLE SUPPORT STRUTS Arthur H. Vaughan, Salem, Ohio, assignor to The Elecgilc Furnace Company, Salem, Ohio, a corporation of Application May 24, 1955, Serial No. 510,711

23 Claims. (1. 26342) The invention relates to mufile type furnaces such as are used for continuous bright annealing of stainless steel strip and the like. Furnaces for this purpose ordinarily include an elongated refractory lined furnace chamber, a heat resisting alloy mufile extending longitudinally through the furnace chamber, a water-jacketed cooling chamber, and entrance and exit vestibules with suitable air-excluding means such as curtains.

The muffie, cooling chamber and vestibules are connected by gas-tight joints. The interior of the mufile and cooling chamber is filled, when in operation, with a protective atmosphere, preferably hydrogen or dissociated ammonia, maintained at a dew point of minus 40 C. or lower by careful exclusion of oxygen.

In a representative furnace of this type, the mufile, cooling chamber and entrance and exit passages may have an inside width of about 24 inches, the furnace heating chamber may have a length of about 25 feet and the cooling chamber may have a length of about 75 to 100 feet.

Under present practice, a common muflle construction involves a centrifugally cast, circular cylinder of suitable length to extend through the end walls of the furnace heating chamber. This mufile is anchored at or near the point of connection to the cooling chamber so as to expand, under heat, toward the entrance end of the furnace.

At temperatures approaching 2000 F., the metal of the mufiie has extremely low strength, and, with ordinary methods of support, flattening caused by the action of gravity is a serious problem. Experiment indicates that for a circular cylinder of alloy containing 30% Cr and 20% Ni, operated at 2000 F. and supported between points 30 degrees each side of the vertical, longitudinal, central plane, the thickness of the mufile wall must be at least 3 /2%, and preferably approaching 5%, of the mean diameter of the cylinder, in order to obtain a rate of flattening low enough to be tolerable.

For a cylinder of 25 inches mean diameter, this corresponds to between 78 and 1% inches wall thickness. Such a mufl'le is obviously very heavy and therefore expensive, and in addition, the support loads are high enough to cause great resistance to the longitudinal movement of the muffie required by expansion of the same under high temperatures.

One common method of support is to provide a series of transverse refractory piers in the bottom of the furnace chamber. These piers may be shaped to fit the contour of the bottom of the muffle and may be provided with metal caps.

A continuous support for the muffie is objectionable, because of the large amount of surface area to be rendered inactive, and because of the thermal stresses which would result. Even spaced piers which carry the entire load of the mufile produce these effects to an appreciable degree. The space around the mufile, both above and below the same, should be largely open for satisfactory results.

. Ifsuch piers are fitted around the underside of the 'ice muffie for a sufiicient distance to resist flattening, the mufile first settles into a snug fit upon the piers when heated, and the metal of the muflle then further subsides adjacent to the piers, producing appreciable indentations.

When the muflle shrinks upon cooling, the piers are often destroyed because the intended sliding of the muflle upon the piers, due to contraction, has thus become impossible.

It is therefore an object of the present invention to provide a. mufile support which overcomes the above described difficulties and disadvantages.

Another object is to provide improved mufile support means having certain distinct advantages over common practice.

A further object is to provide mufile support means, whereby gravity produces a spreading effect in the upper portion, and a narrowing efiect in the lower portion of the muflle, these effects largely neutralizing each other.

A still further object is to provide a muffle support producing minimum interference with heat absorption by the muflle, and therefore good heating capacity and small temperature stresses.

Another object of the invention is to provide resilient mufile supports which do not become inactive in the event of muflle warpage.

A further object is to provide for low unit pressure at the supports.

A still further object is to provide mufile support means including support struts tiltably engaging the muffle adjacent each marginal edge thereof.

Another object of the invention is to provide spaced, fixed piers shaped to substantially conform to the contour of the under portion of the muffle, and spaced pairs of movable struts carrying the larger portion of the load, but less than the full load, of the muflle.

A further object is to provide muffle support means including a spaced pair of struts tiltably engaging the mufile adjacent each marginal edge thereof, the line of action of said struts intersecting the plane of greatest mufiie width at points near the marginal edges of the mufiie.

A still further object is to provide such a muflle support means including means for applying a predetermined lifting force to the lower end of each strut.

It is also an object of the invention to provide lifting means of the character referred to in which the total of lifting forces applied to the struts is less than the weight of the muffle.

And finally, it is an object of the invention to provide a muffle of such cross-sectional shape that the lower half of the mufile is in the form of a catenary curve and the upper half thereof in the form of an inverted catenary curve with upright supports at the junction points between the two portions.

These and other objects, apparent from the drawings and following description, may be attained, the above described difficulties overcome and the advantages and results obtained, by the apparatus, construction, arrangement and combinations, subcombinations and parts which comprise the present invention, a preferred embodiment of which, illustrative of the best mode in which applicant has contemplated applying the principle, being set forth in detail in the following description and illustrated in the accompanying drawings.

Briefly stated, the invention may be described as comprising a mufile type furnace including an elongated refractory lined furnace chamber, a heat resisting alloy mufile extending longitudinally through the chamber, spaced fixed piers supporting the muflle at intervals, spaced pairs of movable struts tiltably engaging the mufile adjacent each marginal edge thereof, means for applying a predetermined lifting force to each strut, and means anchoring' thepmlfie against longitudinal movement at a -Z:Fzvi-Ffieifie'aiitpoii1t,'for example near the exit end of the furnace.

-- The mulfie mayextend through one or b th end walls of the heatingchamber, 213(13: cooling-chamber of 'considerab le length may beat-tached tothedischarge end of the muflle by means of an air-tightjoint.

7 Entrance and exit "vestibules may be provided-having suitable-air excludingrneans such-as-curtains the vestibul'esbeing connected" by gas-tight joints,- -so"-that'the--interior of the muffle and cooling chamber may be filled with a protective atmosphere. M

--In' the application of the invention-to a batch4ype-furnace, at least one end ofthemuffle mayterminate-withinthe heating chamber of the furnace, the cooling chamber aria exit vestibule being omittedin the-batchtypefurnace. -Having thus described the invention in general terms, reference is now made to the accompanyingdrawings, in

w v, t

v Fig. 1' is a diagrammatic'viewpfaround or-Lcylindrical amine supported upon a fiat SllljfaCefiShOWipg successive de'forrned' or flattened shapes which the mufile assumes 'when submitted to high temperatures; V

Fig; 2 a similar diagrammatic view of a round-or cylindrical miifiie supported by a curved surface showing-successive distorted or flattened shapes which-themuflle-as- "shines under high temperatures;

Fig. 3 a diagrammatic view ilIustrating-the-use-ofcatenary curves as applied to muffle construction;

Fig." 4a is a side elevation of a complete furnace showing an embodiment of the invention; v n "Fig. '45 is a side elevation of water-jacketed cooling chamber; a H a Fig. 5 -an enlarged, longitudinal, sectional view of -the i j b v Fig 6 atransv'er se, sectional -view through the-furnace, taken"as "on the-line 66,-Fig.- 5, and showing the movable struts'upp'o'rt means forming -an*-important; part of the invention; l a I I "Fig, 7a transverse, sectional view; taken onthe line 7 -'-7,'- Fig-. 5; showing one of the fixed support piers;

Fig. 8 an' enlarged view of one of the movable-support-struts, viewed at right angles to -the-fur;nace length;

Fig. 9' an' enlarged fragmentary sectional view ofthe upper spring disc and the lower end of the tubular center pg'niea'brbne of the-struts;

Figi 'lda'long i'tudinal sectional view through-a batch furnace-of the vacuum type-with' removable -muflle-' or retort, embodying the invention;

' Fig. ll la' transverse; sectional-view through the furnace shown inFig. 10f taken partially as on' theline11---11 and partially -on the line Ila-1112,, Fig. 10; "Fig. 12' a longitudinal sectional view through another t pe 'of been furnace; and, a k I Fig. 13 a tra'n'sy'erse sectional'view thrqugh-thePfurhaceshown in Fig. l2 talcen partially on the line--13-13 and" partiall on" the line'1'3a- -13a, Fig. '12. Referring now more particularly to the embodiment "of the invention --illu strated in the -drawings,- in which stmnafauniralsrefei to similarparts thrgughout referef rice'isf fir'st made to'the diagrams shown-inFigs; 1146-3.

"-In 'Fig." 1 l is a diagrammatic showing of -'a-- circular, cylindiical muffle, indicated at 15,'supported along a single line contact, indicated at 16, upon afiat-supporting merm b'er '17. At a the cylindrical Hume--15-is-shOWn= in-the original form before it has been subjected 1 to high temperature.

When this nufiie is subj ected-to considerable tenifira- =ture-a-ndtime it-wilhflatten to-substantially'elliptical-shape *as -shown at bpand the 'lower 'sideof 'the inufile}? contact'withthe support 17, will"be flattened as indicated at lil. V 1 -with additional time at-high teniperatureg it will becqme increasinglya-flattened 'as shown at :cg? thet-top iside ofthe mufiie beceming slightly cohcaved as at 19 and-12hr assel-e47 bottom side of themufie becoming increasingly flattened The diagram in Fig. 2 shows a cylindrical muflle 21supported upon a curved or concaved support member--22.

If this support member fits the cylinder through an angle of about degrees, the original circular cross-sectional shape d distorts successively to the shapes indicatedat e arid'f. 7

Assuming that rhe-enrvdeuppiirt 22 is in the form of spacedpiers, the mufliefirst moves into a snug fit upon' the piers under'the effect-of temperature andtimeg and the metal of the miiflle then further subsides adjacent' the piers, producing appreciable indentations, so that when the mufile shrinkson cbbling'the piers areotten dcstroyed as it has become-impossible for the muflle to slide thereon.

In Fig. 3 is diagrammatically shown the use of catenary curves in the formation of amuflle. At g. is shown aview with'tl'1e"'shapeof'afcatenary curve, and .at' h is asiniilar ziwrepresentieg an'invrtd catenary curve of thesame shape 'andsiie. 'With such sections if supported by ver- 'tica1 'and"hofi2oiital'forces,there is no bendingstress. Since the horizontalforces are equal and oppositea completdiband as sh'ownfat 'kITOrmd' of like uppenand lewerca't'enaryshap'edi ortioiis,'wi ll"have no tendency. to flatten, if vertical SIIPPUfts areTPrOVidd' at thef-junetion points between the two portions. 'A' eatenar rofile'er' c'res sectio such as this'eoilld be adopted for a' tubular 'niiiiffle; and in theiase con- "s'truction by welding 'of"forined' plates; erase bfstillca'st metal, it woulclbe'entirely practical.

However, much of the advantage "isfstill'fetained'if a 'circular"or even anelliptical"cylindfical'muflie, is. snp p'or't'ed 'infthenei hberhood of"the"ifitersetion of 'its mammal-diameter andthe op 'ositewans.

"It'is not practical to provide continuous "support throughoilt' the 'le'ngth'of"the mufflefbilt, if local supports are spaced at-reasonably frequent intervals, the stresses duetobe'am aetienwiunot be. great.

furnace structure, prcferably outside 'of-theiurnacerch'amber as by a fla'nge-29,-to prevent longitudinahmovement at the muffle atthis point, so that-upon-heati-ng: the end of the muflle -towhich -the entrance vestibule 25 is at. tached, expands to the left -as viewed in Fig: 4.

As shown in Figs. 5, 6a'nd 7-, theturnacev proper includes the steel shell upperand-lower halves30-and 61 respecti ely,- a' refractory lining 32' enclosing a" cylindrical heating chamber--33; and refractory-end walls 34 and-'35. :The furnace chambermay be heated in any conventional-manner-by fuel or electric heating elements.

- Anchor-members '36 are integrally attached- tofihe steel shells 30 and 31, for the purpose of attaching=the=flange 29 of the mufile at the working exitendof tllefurnace} or the right hand end, as viewed in the drawings.

L A-.spaced plurality of refractory'piers '37 a're locatedin the bottom-of the furnace chamber; and the-'aup'per su'r ate band 39, curved to conform to the lower half of the mufiie 26, and a pair of struts indicated generally at 40, tiltably engaged with said band.

The bands 39 are preferably so attached to the mufiie 26 as to permit them to wrap into conformity with the muttle. One method of obtaining this result is to weld or otherwise attach the bands to the mufile near the bottom center point, leaving the ends of the band free, thus permitting the desired wrapping action, while preventing displacement of the bands lengthwise or circumferentially of themufile.

Slots 50 are formed in the refractory lining 32, of such size as to permit the necessary rocking motion of the struts. For a heated length of feet, the distance from the anchoring point to the most remote pair of struts is about 23 feet.

The expansion of the mufile at the rate of .30 inch per foot, allowing for only partial heating of the portion of the mufiie located through the end wall 35, is about 7 inches, assuming that the mufiie is formed of an alloy of Ni and 15% Cr, heated to 2000 F. It is practical to allow for this much movement. The movement is preferably divided so that the fixed parts, such as the sockets 42, are about midway in the range of movement of the corresponding bands 39.

The struts are shown in the drawings tilted inward toward the muflle at a slight angle to the vertical. The desirable angle of the struts will generally be between vertical and about 30 degrees inward tilt. in practice, this inward tilt is found to exert some sidewise flattening action to counteract the vertical flattening tendency produced at the piers. If there are no piers, as in a short furnace, the struts may be vertical or nearly so.

The lower end of each center portion 41 of each strut is mounted within a spring socket 42, attached to the lower half of shell 31 and extending downwardly and below the shell. A spring seat 43 is adjustably mounted in the lower end portion of each socket 42, as by the adjusting screw 44, and fits the lower end of a coil spring 45, upon the upper end of which is mounted the upper spring disc 46, having a socket 47 in its upper surface within which is mounted the axial pin 48 fixed upon the lower end of the tubular center portion 41 of the strut.

This tubular center portion is filled with insulation 49, to prevent the flow of excessive amounts of heat outward from the heated chamber 33 of the furnace. Thus the spring 45 is not subjected to a high enough temperature to destroy its elasticity.

Recesses 51 are formed in the bands 39, near opposite ends thereof, and the upper portion 52 of each strut is of rocker shape, as best shown in Fig. 8, so as to permit tilting of the strut caused by longitudinal expansion or contraction of the muffle.

The springs are adjusted by the screws 44, so as to support at least a substantial part of the weight of the muffie, the exact proportion being subject to wide choice. Excellent results were obtained in a furnace in which two pairs of struts were located between each pair of.

piers, and the load of the muffie was supported about-% by the struts and 50% by the piers.

A desirable upper limit for strut loading might be of the order of 75% of the total weight of the muflie, in which case the permissible error in spring adjustment is still fairly large without danger of lifting the mufile completely off of the piers.

In the case of a short mufile, such as one with a heated length 5 times its diameter, all piers in the furnace chamber proper may be omitted, the mufile receiving fixed support only by the surrounding brickwork in the end Walls of the furnace chamber or by external support members.

In. such a case, the struts are preferably adjusted to carry a major portion, say 75 to 100%, of the average load per unit length. Thus, for a 3 foot strut spacing,

with a muffle weight of pounds per foot, each pair of struts may be adjusted to carry from 225 to 300 pounds.

In the drawings the struts are shown tilted inward at a slight angle to the vertical. Applicant has used this arrangement in actual practice, in order to exert some sidewise flattening action to counteract the vertical flattening tendency produced at the piers.

However, in any event, the force exerted is predominately upward. The desirable angle of tilt of the struts will generally be between vertical and about 30 inward tilt, a preferred angle being about 10 degrees to the vertical, as best shown in Fig. 6. If there are no supporting piers, as in a short furnace, the struts may be vertical or nearly so.

The strut seats 51, in the support bands 39, are located below the horizontal center line of the mufile 26, so that the line of action of the strut passes through or near, preferably inside, the mufiie wall at the widest point. Thus, the lines of action of the struts intersect the plane of greatest mufile width at points near the marginal edges of the mufile, as best shown in Fig. 6.

It will be seen that the marginal edges of the mufile referred to are located in a horizontal plane passing through the axis of the muffle, this horizontal plane being the plane of greatest muflie width.

While the strut seats 51 are shown in the support plate 39, it should be understood that correspondingly located strut seats may be formed integral with the mutfle. However, the use of separate support bands 39, with strut seats therein, is convenient, effective and practical.

Although the mufiie 26 is shown as circular in cross section, it should be understood that this cross section may be varied. As previously pointed out, a mufile cross section as shown in Fig. 3 is very desirable, in which the shape is that of a catenary curve for the lower half combined with a like inverted catenary curve for the upper half. Such a shape has the least possible bending stresses tending to produce flattening, and this would be a very desirable shape for a muffle made of rolled sheet or plate.

Another cross sectional shape which is very useful is that of an ellipse with its major axis horizontal, substantially as shown at b in Fig. 1 with the omission of the flattened lower portion 18. This cross-sectional shape of muffle is economical for handling wide strip, and while very unsatisfactory when supported only in the bottom region, as shown in Fig. 1, since it resembles a round muflie which already is flattened by heat, and bending stresses are excessive, such stresses may be reduced to a safe value by the support means above described and illustrated.

It should be understood that with this elliptical form of mufiie, there will be some tendency for the upper, center portion to buckle inward, and for the upper portion near the axis to be forced upward and outward, while corresponding areas in the lower portion tend to be distorted in opposite directions relative to the major axis of the ellipse.

Although the above description has mentioned only muffles of circular, elliptical and catenary profile, it should be understood that other curves or combinations of curves may be used to develop a suitable profile by the use of the supporting means herein described.

It is not absolutely necessary that the profile be exactly symmetrical about a horizontal diameter, although symmetry is preferred in the absence of some reason for a special shape. The struts, as above described, are positioned so that their lines of action are directed through regions near the mufiie wall at the level of greatest width, whereby gravity acts on the upper part of the muffle wall to produce a widening efiect, and on the lower part thereof to produce a narrowing effect, these opposing efiects counteracting each other at least to a considerable degree.

141b, pivotally mounted in the car frame 84, as indicated at 131, The piston rod 102 of each cylinder is pivotally connected to one arm 103 of a bell crank, fulcrumed as at 1% upon the frame of the car. A roller 105 is journailed upon the free end of the other arm 106 of each bell crank, and is movably mounted within a yoke 107. depending from the T-bar 97.

The fluid pressure in the cylinders 190 will urge the pistons inwardly therein, and through the bell cranks NBS-1%, the T-bar 97 will be raised, increasing the lifting force of the struts. Thus the desired fluid pressure may be maintained in the cylinders 100 to produce any desired or necessary lifting force for the movable struts.

The furnace chamber 99 may be heated to desired temperature by any conventional means such as gas or oil burners located through the burner openings 108, or by electric heating elements, or other conventional means.

In this embodiment of the invention, the muflie being anchored at its forward end as at 89, the elongation thereof under high temperatures will be toward the rear end thereof. It will be seen that as the muffle expands and contracts the movable struts 92 will tilt rearwardly and forwardly, carrying the entire weight of the muffle within the furnace chamber. An insulation plug 109, of any suitable material, is removably mounted in the forward end of the muffle and may be removed for loading and unloading the muffle.

Although springs are illustrated in the drawings and above described in detail, for providing the lifting force, it should be understood that an equivalent means, such as air cylinders, counter-weights or the like, may be provided for producing the lifting force, the only requirement being that a predetermined lifting force Within reasonable limits be exerted, regardless of movement of the muffle.

The muffie support means is illustrated and described as applied to a horizontal mufile, but it should be understood that it is also useful for a muffle located in a somewhat inclined position, since the flattening tendency still exists in such a mufile.

Throughout the description and claims, the terms cylindrical and tubular apply to muffies of generally cylindrical form, not necessarily circular, where both the portions above and below the plane of greatest width are curved so as to be outwardly convex at substantially all points, and further, that the profile or cross section is such that the action of gravity on the upper portion results in outward forces, and the action of gravity on the lower portion results in inward forces, these opposing forces being of at least the same order of magnitude.

in other words, the improved support means to which the invention pertains is applicable to muffies of any cylindrical form, whether the profile or cross section thereof be circular or otherwise curved.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for descriptive purposes herein and are intended to be broadly construed.

Moreover, the embodiments of the improved construction illustrated and described herein are by way of example, and the scope of the present invention is not limited to the exact details of construction.

Having now described the invention or discovery, the construction, the operation, and use of preferred embodi ments thereof, and the advantageous new and useful results obtained thereby; the new and useful construction, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.

I claim:

1. In a furnace, walls defining a heating chamber, a cylindrical murlie located through one end wall of the furnace chamber and terminating within the chamber at a point spaced from the opposite end wall thereof, means anchoring the muflie adjacent said one end wall, and support means for the muflie within said chamber in cluding a pair of pivoted upwardly acting struts tiltably engaging opposite sides of the mufiie near a horizontal plane located through the axis of the muffle.

2. In a furnace, walls defining a heating chamber, a cylindrical muffle extending longitudinally within said chamber, a support band conforming to the underside of said mufiie, means connecting said support band to the mufile at only one point an upwardly acting support strut adjacent each side of the muffle, seat means associated with said support band and tiltably engaging the upper end of each of the struts, and means for applying a predetermined lifting force to the lower end of each strut, the lines of action of said struts intersecting points near the marginal edges of the mufile in a horizontal plane located through the axis of the cylindrical mufHe.

3. In a furnace, walls defining a heating chamber, a cylindrical mufile extending longitudinally within said chamber, spaced fixed support piers Within the chamber, said piers having concave supporting surfaces substantially conforming to the shape of the mufiie bottom, spaced pairs of upwardly acting support struts between said piers, the struts of each pair having lines of action intersecting the horizontal plane of greatest muffie width near the intersection of the opposite muffle walls with said horizontal plane, seat means associated with the muflie and tiltably engaging the upper ends of the struts, and means for applying a predetermined lifting force to the lower end of each strut.

4. In a furnace, walls defining a heating chamber, a cylindrical muflle extending longitudinally within said chamber, spaced fixed support piers within the chamber, said piers having concave supporting surfaces substantially conforming to the shape of the muffle bottom, spaced pairs of upwardly acting support struts between said piers, the struts of each pair having lines of action intersecting the horizontal plane of greatest mufl'le width near the intersection of the opposite muffie walls with said horizontal plane, seat means associated with the muffle and tiltably engaging the upper ends of the struts, and means for applying a predetermined lifting force to the lower end of each strut, the total of said lifting forces being such as to leave an appreciable load upon said piers thus tending to prevent lateral warpage of the muffle.

5. In a furnace, walls defining a heating chamber, a cylindrical muffle extending longitudinally within said chamber, spaced fixed support piers within the chamber, said piers having concave supporting surfaces substantially conforming to the shape of the muffie bottom, spaced pairs of upwardly acting support struts between said piers, the struts of each pair having lines of action intersecting the horizontal plane of greatest muffle width near the intersection of the opposite muflie walls with said horizontal plane, seat means associated with the muffle and tiltably engaging the upper ends of the struts, and means for applying a predetermined lifting force to the lower end of each strut, the total of said lifting forces being more than half the total load of the muffle.

6. In a furnace, walls defining a heating chamber, a cylindrical muffie extending longitudinally within said chamber, spaced fixed support piers within the chamber, said piers having concave supporting surfaces substan tially conforming to the shape of the mufiie bottom, spaced pairs of upwardly acting support struts between said piers, the struts of each pair having lines of action intersecting the horizontal plane of greatest muffle width near the intersection of the opposite muffie walls with said horizontal plane, seat means associated with the mufiie and tiltably engaging the upper ends of the struts, and means for applying a predetermined lifting force to the lower end of each strut, the struts carrying a major portion of the load of the muffle but less than the f load thereof. 7

- 1 1 *7."-;I nea-=furnace, walls defining-=a;heating-chamber, a *cylindricab muflle extending longitudinally -within said ehamben-"thecross section of said muflle-comprising-a catenarycurve forming the lowerha'lf of the mufile-and -an inverted' catenary curve forming the upper-ha-lfizt-hereof, said lower and upper halves-being joined ata-hori- -zontali planerf greatestmuffle =width support means for fthemi'ifile, and'-'means associated with the-muffle for eng aging'fthesupport means, =the line of action of-said-support-means intersectingsaidplane of greatest mu'file width tat-points near the intersection of said-curves with said plane.

Ina furnace; sidewalls; a rearend wall and aatop Wall; and a 'car movable-relative to'the-fur-nace and having a horizontal-platform forming amova'ble bottomwall "and together'with said furnace walls-defining aheating *ehar'nber; a; cylindrical, mi1flie =carried-by said -car and terminating-within said chamber; at a point spacedfrom f;'said"*rear end"wall; means-anchoring *themufiie adjacent "to'fthe front end of the car,- and support means within -said ichamber including spaced pairs of upwardlyacting jsnutstiltably;engaging opposite sides :of' "the innfile ad- :iacent the point 'of' maximum muffie width-, the 'lowerends 'bf said struts being supported-uponsaid car.

*9: In;-a*furnace,- walls defining a'-'heating; chamber,-- a j-ho'rizontal cylindriclal'mufile "extendinglongitudinally within the chamber; apair of support seats associated with s'aid'mtifile'adjacent its opposite sidewalls and near its *horizontal plant: Off greatest -width; there being tension- "resistingconnecting-means -betweensaid: seats circumferentially of the v lower portion of the--rni1flle,- a pair ofnpwardly-acting support struts engaging said seats, and means forapplying a-predetermined force tothelower ends-of'said' struts; whereby a-tension component ofstress is'applied to' said tension-resisting connecting means.

1-05 In a--furnace, walls defining a heating Jchamber, a horizontal cylindrical mufile extending longitudinally with- '-in-" the-chamber-,-a* pair ofv support seats associated with -saidm'uftle adjacentits opposite sidewalls andnear-its horizontal plane of' greatest width, there being tensionresisting connecting -means" between said seats circum- "=-ferenti'a'lly of the -lower portion of the mufiie a pair of ppwardly ac'ting support struts engaging said seats; and

spring meanskfor applying a predetermined forcel'to the 'lower ends ofsaid struts,--whereby a tension component of stress is appliedto -s aid 'tension-resisting connecting :means.

lli ln a furnacey'wallsdefining a heating chamber,; a

' horizontal cylindrical mufile extending longitudina'lly :-.-resisting conneeting--- means 1 between said seats circum 'l*,=ferential ly'of the lower-portion of the-muffle, a pair of ,"upwa'r dly-acting" tiltable support struts engaging said --seats;* and--means ton-applying a predetermined force tof th'e lowereends Ofsaid-Struts, whereby a tension com- ;r'vponent- 'of stress isappliedto I said tension-resisting conectingemeans.

1 13 Iii-a furnacerwalls glefining er -heating chamber, a o'r-izontaP-eylindrical mu'file extending longitudinally #Withllf the clrair'iben a pair or support seats formed-upon said mufiie adjacent its opposite side wallsandnear its horizontal plane of greatesflwidth, the lower portion of 'the mufile forming tension-resisting connecting means between saidseatisg apair-of upwardly-acting support struts engaging -said seats, and means 'for applyinga predetermined forceto the lower ends of said struts, whereby a tension component of stress-is applied to said tensionresisting connecting means.

1 14.i In afur-nzieepwalls defining a heating chamber, a horizontal cylindrical mufile extending longitudinally within the chamber,- a pair of support seats formed upon saidadjacentitsopposite side walls and nearits horizontal-plane of greatest width,-the lower portion of the muifie forming tension-resisting connecting means 'between-said=seats, a pair'of upwardly-acting support struts engaging saidseats,;and' spring means for applying a-predeter'minedforce to the lower ends'of said struts,

whereby-a-tension'component of-stressis applied to said -.-tension-resisting connecting means.

15. -Ina'1fu'r-nace, :Walls' defining a heating chamber, a horizontal cy lindr-ical muffle extending longitudinally withinthe' chamber, a pair of support seats formed upon said -mufiie adjacent its opposite side walls and near its horizontal; plane of greatest width, the lower portion of the muffie forming tension-resisting connecting means -between said seats,a:pair'of upwardly-acting support struts engaging said-seats, and-fiuidcylinder means for applying a predetermined force to the lower ends ofsaid struts; wherebya tension component of stress -is applied to I said =ten sion resis'ting' connecting means.

-16.-- ln a-furnace,ewallsdefining a heating chamber,-a horizontal cylindrical mufile extending longitudinally within thechamber,a pair of support seats forrriedupon said mufileadjace'nt it's opposite side walls and nearits horizontal-plane of greatest width, the lower portion of the mufile forming tension-resisting connectingmeans between said seats a pair of upwardly-acting tiltable support-struts engaging said seats, and means for applying a predetermined force to'the lower ends of said struts, whereby a tension component of stress isapplied to said tension-resisting connecting means.

17. In a furnace walls defining a heating chamber, a horizontal cylindrical .mufile extending longitudinally withinthe chamber, a support band conforming to the -underside of the muffle, a pair of support seats formed upon said support band at points adjacent opposite side walls of'the-mufiie near- -the horizontal plane of greatest 'width'or' the-mufile, said support band forming tensionresisting.connectingrneans between said seats, a pair of .upwardly-actingsupport su'uts engaging said seats, and means'L-for applying a predetermined force to the lower ends of the--struts', -whereby a tension component of stress 'is-applied-to saidtension-resisting connecting means.

'18. Ina furnace, walls defining a heating chamber, a horizontal cylindrical muflle extending longitudinally 7 withinthe 'chamber, a support band conforming to the underside of-thernufl'le, a pair of support seats formed uponsaid supportband-at points adjacentopposite side walls of the muffle near-the horizontal planeof greatest Width of-the'mufi1e,--saidsupport band forming tensionresisting connecting means between said seats, a pair of upwardly-acting support struts-engaging said seats, and spring means for applying a predetermined force to--the I lower ends of-the struts, whereby atension component of stress is applied-to said tension-resisting connecting-means.

' 19. In a furnace, walls defining a heating chamber, a horizontal cylindrical mufiie extending longitudinally within thechamber, asupport band conforming 'to the 'mderside-of' the"muffie, a pairof support seats formed upon said support bandat points adjacent opposite side --walls:of the muflie near the horizontal plane of greatest width of the muflle, said support band forming tensionresisting connecting means between said seats, a-pair of "upwardly'acting support struts I engaging} said seats, and

fluidcylinder' means foriapplyin'g a predetermined force --to'*the*lower -ends of the struts pwhereby a tension cornponent of stress is applied to said tension-resisting connecting means.

20. In a furnace, walls defining a heating chamber, a horizontal cylindrical mufile extending longitudinally within the chamber, a support band conforming to the underside of the mufiie, a pair of support seats formed upon said support band at points adjacent opposite side walls of the mufiie near the horizontal plane of greatest width of the mufile, said support band forming tensionresisting connecting means between said seats, a pair of upwardly-acting tiltable support struts engaging said seats, and means for applying a predetermined force to the lower ends of the struts, whereby a tension component of stress is applied to said tension-resisting connecting means.

21. In a furnace, walls defining a heating chamber, a cylindrical mufile extending longitudinally within said chamber, seat means adjacent opposite sides of the muffie, upwardly-acting support struts engaging said seat means, each of said struts having a line of action substantially tangential to each side of the mufile near a horizontal plane located through the axis of the mufiie, and means for applying a predetermined lifting force to the lower end of each strut.

22. In a furnace, walls defining a heating chamber, a cylindrical muffie extending longitudinally within said chamber, seat means adjacent opposite sides of the muffle, upwardly-acting support struts engaging said seat means, each of said struts having a line of action sub- 14 stantially tangential to each side of the mufile near a horizontal plane located through the axis of the mufile, and spring means for applying a predetermined lifting force to the lower end of each strut.

23. In a furnace, walls defining a heating chamber, a cylindrical mufile extending longitudinally within said chamber seat means adjacent opposite sides of the muffle, upwardly acting support struts engaging said seat means, each of said struts having a line of action substantially tangential to each side of the muffle near a horizontal plane located through the axis of the muflle, and fluid cylinder means for applying a predetermined lifting force to the lower end of each strut.

References Cited in the file of this patent UNITED STATES PATENTS 916,518 Wurts Mar. 30, 1909 980,640 Hughes Jan. 3, 1911 1,489,626 Buttenbender et a1. Apr. 8, 1924 1,695,950 Carpenter Dec. 18, 1928 2,113,083 Height Apr. 5, 1938 2,307,915 Boardman Jan. 12, 1943 2,373,845 Norton Apr. 17, 1945 2,671,655 Osterman et al Mar. 9, 1954 FOREIGN PATENTS 482,659 Great Britain Apr. 1, 1938

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