US2468456A

US2468456A - Furnace muffle and supporting means therefor

Info

Publication number: US2468456A
Application number: US531209A
Authority: US
Inventors: Harold J Ness
Original assignee: Metallurgical Processes Co
Current assignee: Metallurgical Processes Co
Priority date: 1944-04-15
Filing date: 1944-04-15
Publication date: 1949-04-26
Anticipated expiration: 1966-04-26

Description

A ril 26, 1949. H J, NESS' 2,468,456

FURNACE MUFFLE AND SUPPORTING MEANS THEREFOR Filed April 15, 1944 I 3 Sheets-Sheet 1 INVENTOR. .JZVss BY N n7 Mad A TORNEY April 26, 1949. H. J. NESS 2,468,456

FURNACE MUFFLE AND SUPPORTING MEANS THEREFOR Filed April 15. 1944 s Sheets-Sheet 2 IN VEN TOR.

IJZVESS Q17 1 LU A TORNEY April 26,1949. H. ,J. NESS 2,468,456

FURNACE MUFFLE AND SUPPORTING MEANS THEREFOR Filed April 15, 1944 a Shets-Sheet a INVENTOR. H IA/V655 ATTORNEY Patented Apr. 26, 1949 FURNACE MUFFLE AND SUPPORTING MEANS THEREFOR Harold J. Ness, Montclair, N. J assignor to Metallurgical Processes 00., Newark, N. J a partnership Application April 15, 1944, Serial No. 531,209

12 Claims.

This invention relates to industrial furnaces and more particularly to muflles for such furnaces and to the manner of supporting the same within the combustion chamber.

In furnaces of the controlled atmosphere type in which the parts to be treated are surrounded by a protective atmosphere such as, for instance, that disclosed in my copending application Serial No. 455,720, now Patent No. 2,394,002, filed August 20, 1942, and entitled Metallurgical furnace, of which the present application is a continuation in part, it is essential that the heating chamber be completely isolated from both the combustion gases employed to heat the work and the external atmosphere. For this purpose a work enclosing chamber or muffle, usually composed of a heat resisting alloy, is employed. The mufile may be of either the vertical or horizontal type, the present invention being concerned only with the latter type. Small horizontal muflles do not present any great dimculty but in larger sizes, adapted for heavy loads, two main problems are encountered, first, the supporting of the mufiieand its load over a large span, at elevated temperatures at which the strength of the metal of which the mufile is composed is greatly reduced, and the accommodating of the supporting means to the longitudinal and vertical expansion of the muflle as i temperature is raised and lowered, and secondly, the supporting of the roof of the muflle, so as to prevent collapse thereof under similar conditions of high temperature and expansion.

The principal object of the present invention to overcome the above enumerated difficulties.

Another object is to provide a muffle supporting means which will not impose frictional stresses on the mufile during the movement thereof in expanding and contracting.

Another object is to effect an economy of materia in the muflle and its supporting structure.

Other objects and advantages will hereinafter a, pear.

In accordance with the present invention, I provide both longitudinal and transverse reinforcement for the muffle body whereby the latter be composed of a relatively light stock construct the body thereof of rolled sheet bent to shape and welded into a composite structure. I have found that such structures have increased strength, greater uniformity in thickness of wall, and greater density and freedom from porcsity than cast material. The base of the muffle is supported on rollers at a number of longitudinally and transversely spaced. points in such manner as to distribute the weight over a large area of the muflle base, and the arch or roof of the muflle is supported from above by mechanism which compensates both for the rise and longitudinal movement thereof. The roof support also includes a, truss arrangement whereby great rigidity is imparted to the roof and its distributed load concentrated at a relativelyfew points of support outside of the heated area of the furnace.

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

Fig. 1 is a vertical sectional view of a furnace embodying the present invention;

Fig. 2 is a sectional view on the line 2--2 of Fig.

Fig. 3 is a bottom view of a section of the reinforcement and roller supporting structure for the underside of the floor of the muflle, along the line 3-3'of Fig. 1;

Fig. 4 is a front elevation of one of the mufile roof supporting units;

Fig. 5 is a, side elevation of the structure shown in Fig. 4; and

Fig. 6 is a fragmentary sectional view of a muffle fabricated'from clad metal plate.

Referring first to Fig. 1, the furnace there shown comprises a horizontally disposed muflie :l 0 of substantially rectangular cross section and having an arched roof Ii. It is composed preferably of a heat resisting metal, such as nickel or nickel-chromium alloy. However, since the interior of the muflle is continuously provided with a protective or non-oxidizing atmosphere, it may be provided with an iron or steel lining, preferably welded at one end to a nickel or nickel-chromium alloy jacket, or for low temperature usage,it may be composed entirely of copper plated iron. or steel.

The muffle [0 extends, at its forward end, through a rectangular opening l2 in the refractory combustion chamber l3, terminating in .a door 14, operated in any suitable manner, as by an air cylinder l5 connected thereto by a flexible cable I 6 passing over a pulley It. The rear of the muffie is shown terminating within an opening H in the rear wall of the combustion chamber l3 and is rigidly anchored to the rear of the furnace by removable pins I8 passing through angle brackets 19 and rearwardly extending plates 2| secured to the rear wall of the-mufiie. Therefore, as the muffle is heated, it expands forwardly. This has two advantages. First, it retains the mufile stationary at the point of entrance of the atmosphere inlet pipe 22 and it enables the forward movement of the muflle at any point to be accurately calculated and compensated for by the mufiie supporting structure, as will hereinafter appear.

The mufiie I is heated by two series of burners 23 extendin into the combustion chamber l3 at opposite sides thereof below the muflie l0 and two oppositely disposed series of burners 24 above the muflie. The

burners

23 and 24 are provided with a combustible mixture of air and gas in any desired manner, as shown for instance in my copending application Serial No. 495,113, filed July 1'7, 1943, and entitled Work handling and quenching mechanism for furnaces. The combustion chamber I3 is vented by a plurality of pipes 25 extending through the arched roof 26 of the combustion chamber.

The atmosphere admitted into the muflie through the inlet conduit 22 is of the nature disclosed in my aforesaid application Serial No. 455,720, and briefly comprises the products of combustion of a gaseous fuel and air which have been partially dried by condensation and further dried and rendered innocuous to the work to be treated by the addition of the vapor of lithium or of a compound or compounds thereof. The lithium or lithium compound generating means 21 is shown, in Fig. 1, mounted on the roof of the furnace on channel beams 28 supported on angle reinforcing brackets 29 extending about the top inner wall of the furnace shell 3|. This generator comprises a heat resisting alloy pot 32 suspended within a combustion chamber 33 formed in a mass of refractory insulation and provided with suitable burners 34 and a vent 35. The pot 32 is provided with a removable cover 36 through which a lithium compound containing cup 3'! may be inserted in or removed from the pot. The pot 32 and its contained cup are heated to a sufficient temperature to produce a vapor pressure of lithium or a compound of lithium above the cup, and this vapor is entrained by a suitable carrier gas admitted into the pot 32 through a conduit 38 extending from suitable gas generating and drying apparatus not shown. This gas is deflected by a plate 39-appended to the cover 36 so as to pass over the cup 31 and thence into the conduit 22 by which it is conveyed into the muiile Hi. It is distributed in the muiile through a group of three dispersion pipes 4| secured along the roof of the muflle and having a series of spaced slots 42 therein. The atmosphere is exhausted from the mufile through a vent 43 at the forward end thereof.

The mufile H), as stated, is preferably composed of rolled stock suitably bent and Welded into a composite structure. While the composite parts may be diiferently arranged, in the embodiment illustrated I have shown a mufiie composed of a bottom sheet 44, two

side sheets

45 and 46 of a somewhat lighter stock welded to the bottom sheet, and two

top sheets

41 and 48 of still thinner stock having upwardly turned flanges 49 welded together and to an upturned flange of each of the side sheets. The side and top sections of the muiiie, therefore, approximate a tapered arch, giving the required strength with maximum economy of metal. This economy of metal is not possible with cast muffles since it is necessary to employ relatively heavy walls in order to properly cast the metal. The thin walls of the composite welded mufile, moreover, permit faster heat transfer from the outer combustion gases to the inner atmosphere and to the work parts contained therein, thereby shortening the heat cycle and effecting increased production by the furnace. Cast metal structures, moreover, from the nature of their production have uneven wall thickness, which results in local hot spots during operation and this in turn sets up expansion strains which cause warpage and premature failures of the muflie. Blowholes, dross areas, and porosity, which are unavoidable in cast mufiies, are entirely absent in muflies composed of welded plate, as also are casting strains which in cast muflles are often of sufficient magnitude to cause rupture of the mass if it is subjected to unequal or sudden temperature changes. The rolled plate is much more homogeneous, denser and of much greater strength per unit of thickness than cast muffles and, therefore, may be used in lighter sections without sacrificing strength. This is of considerable importance not only in economy of material but in the dead load it imposes on the muffle supports. Moreover, due to the smooth, fiat surface of the rolled plate, it makes uniform contact with the various reinforcing members which must be welded thereto without the necessity of grinding or machinin flat or even surfaces thereon, as is required of cast muflles. After the casting of a muflie, it is necessary to examine it carefully and methodically by X-ray to detect any cracks or other defects therein and to grind away the major defective areas and repair the same by welding. The magnitude of this operation is often greater than the entire operation of welding together the individual plates of a fabricated muffle. In practice, it has been found that cast muflles are not reliable, often failing unexpectedly after very short periods of service, Whereas Welded plate mufiles are dependable for a long useful life under severe conditions of temperature variations in the furnace. They have the additional advantage that they may be quickly fabricated in any size or shape from stock plate. The flanges 49 form a rigid backbone structure for the arched roof H of the muiile which reinforces it against longitudinal sagging. Angle members 5| extend longitudinally of the muflle along each of the lower corners thereof and serve to strengthen the welds at these points. The base of the muffle is further reinforced by a series of channels 52 and interspersed T-sections 53 welded to the underside thereof.

The arch of the muffle is braced transversely by a series of T-section gusset plates 54 disposed at the base of the arch and spaced at suitable intervals along the length of the muffle. A series of angles 55 bent to the contour of the sides and top of the muffle are also welded thereto at suitable intervals to stiffen the arch transversely.

The flanges of the channel members 52 are provided at intervals therealong with open slots or bearings for a series of supporting rollers 56 by which the muffle is supported for forward expansion, upon a series of pedestals 51 projecting from the floor of the combustion chamber I 3. Between each pair of rollers 56 the flanges of the channels 52 are cross-braced by cast webs 58. The pedestals 51 consist of a hard burned refractory block 59, preferably composed of mullite, embedded in the refractory floor of the combustion chamber and having heat resisting alloy bearing caps resting on top thereof. The caps 60 have depending side flanges 6| fitting over the blocks 59 and upwardly extending side roller guides 62. The pedestals are so disposed along the floor of the combustion chamber that they will be centrally aligned with the rollers 56 when the mufile is at operating temperature. Since the forward movement of the muflle under expansion is accumulative, it is necessary to progressively increase the spacing of the pedestals from back to front. In Fig. 1 the muffle is shown inits cold position and it will be noted that the roller-s56 are spaced progressively greater distances from the centers of the pedestals from the front .to-

wards the rear of the furnace.

Mullite is employed for the pedestals 51 because of its extremely high crushing strength and its negligible coefficient of expansion. By virtue of this latter quality, the level of the pedestals replates 63- disposed at spaced intervals between the channel members 52 and the T-ribs 53.

The roof or arch of the muffle imposes a considerable load on the side walls of the mufile tending to cause buckling thereof at elevated temperaturc. collapse of the arch, I prefer to support the same independently of the underneath supports, as by hangers 64 secured to the muffie arch and suspended from above the furnace arch 26. As shown, each hanger comprises twospaced pairs 65 and 66 of plates, each'pair of plates having their lower ends spaced to straddle the upturned flanges 49 of the muffie arch, to which they are secured as by welding or bolting. The pairs of plates are united by cross-plates 69 welded thereto at opposite sides thereof. A truss structure, comprised of struts H secured to the'ha-ngers 64 and to the flanges 49, distribute the support to sections of the arch intermediate the hangers and add to the longitudinal strength and rigidity of the roof.

The hangers 64 pass upwardly through collars 12 contained in slots 13 in the roof 26 of the combustion chamber. A plate 14 loosely surrounds each of the hangers 64 and rests on the collar 12 so as to move forward and backward-with the hangers and thereby to close the opening in the collar to prevent leakage of the combustion gases upwardly therearound. Above the furnace roof the hangers are provided with rollers 15 by which the weight of the muffie arch is transferred to track supports 16.

The track supports 16 comprise angle members ll supported on the inturned lower flanges of pairs of channel beams 18 extending transversely racross the furnace, and resting in turn on the peripheral angles 29. The track angles 11 each have a wedge member 19 thereon with which the rollers l engage in the upward and forward expansion of the mufile. It will be appreciated that the vertical expansion of the muille and the heated portion of its supporting hanger 64 will be the same for all zones of the furnace and hence the rise of all of the wedges 19 is the same. However,

the forward expansion is cumulative so that the slope of the forward wedges decreases relative to the more rearwardly ones.

t should be noted that the slope of each wedge corresponds to the direction of movement of the base or point of contact of the roller therewith so that the lifting of the roller up the wedge is efiected entirely by the upward expansion of the heated parts rather than by forward movement of the roller in contact with the wedge. The purpose of the wedge is therefore not to apply To relieve this load and to prevent any upward tension to the arch butxto prevent the slow sagging or creeping thereof under long periods of operation at elevated temperatures.

In order to avoid any wedging action on the roll- "ers 15 during the forward movement thereof,

they are made adjustable relative to the track H, as more clearly shown in Figs. 4 and 5. Referring-to these figures, it will be seen that the hanger plates 64 terminate in a T-shaped head 8| secured thereto as by bolts 82. The shafts 83, on which the rollers 15 are mounted through antifriction bearings 84, pass loosely through a vertical slot in the stem of the member 8|. Pressure pads 86 engaging the shaft 83 are adjustable .up and down by adjusting screws 81 soas to regulate the pressure of the rollers 75 on the tracks 11.

In Fig. 6 I have shown a composite muffle composed of an inner layer 88 of steel and an outer layer 89 of a heat resisting metal or alloy, such as nickel, nickel-chromium alley, or a stainless steel, such as nickel-chromium steel. Nickel and nickel-chromium alloy unite with steel by rolling at temperatures of about 2200 F. forming a permanent-bond which'is not affected during operation of the composite metal in the furnace. The modulus of elasticity of nickel and nickelchromium alloys, particularly an alloy of from 78-80% nickel, from 1214% chromium, and 5 -23% iron is essentially the same assteel and its hot working range is the same. Consequently there'is an equal distribution of stresses across the section of the mufile with no sudden change at the interface of the two metals. The coefficient-of expansion of both nickel and nickelchromium alloys is so close to that of steel that they may be considered identical, and the meltprotective lithiated atmosphere within the muffle. For economy and strength I prefer to employ a relatively thick inner steel layer and an outer layer of from 5 to 10% of the thickness of the steel portion.

The composite muflle is fabricated in the same manner as the mu'flle of Figs. 1 and 2, namely, by welding suitably shaped plates of the'clad metal into a gas tight tubular body. In this operation the steel inner weld 9| is first made using a covered steel welding rod. The outer face of the joint is then groovedas at'92 and welded with a covered nickel or nickel-chromium alloy rod.

It will be understood that many variations may be made in the exact construction of the muffle and its supporting structure, and therefore I do not desire to be limited to the specific embodiment shown but contemplate all changes and modifications thereof coming within the terms of the appended claims.

Whart is claimed is:

1. A mufiie adapted to be disposed in a hori zontal position for the heating of metal atelevated temperatures by externally applied heat comprisingan elongated tubular body portion composed of a plurality of sheets of heat resisting metal or alloy having a relatively thin wall, said sheets having predetermined abutting edges and said abutting edges being upturnedand.

welded together to form a plurality of stiffening web members disposed substantially normal to said wall and extending longitudinally of said mufile.

2. A muiile adapted to be disposedin a horizontal position for the heating of metal at elevated temperatures by externally applied heat comprising an elongated tubular body portion, composed of welded sections of heat resisting metal or alloy plates having bottom, side and top walls of progressively reduced thickness in the order named, and a plurality of longitudinally extending stiffening flanges bent up from adjacent edges of said sections substantially normal thereto, and welded along their abutting surfaces.

3. A muffle adapted to be disposed in a horizontal position for the heating of metal at elevated temperatures by externally applied heat comprising an elongated tubular body portion composed of a heat resisting metal or alloy having bot-tom, side and arched roof walls, said side and roof walls being of reduced thickness relative to said bottom wall and a plurality of longitudinally extending stiffening ribs, each having a width several times its thickness, integral with said bottom and roof walls and disposed normal thereto.

4. A muffle adapted to be disposed in a horizontal position for the heating of metal at elevated temperatures by externally applied heat comprising an elongated tubular body portion composed of a heat resisting metal or alloy having bottom, side and arched roof walls composed respectively of separate plates of rolled stock having the adjoining edges thereof secured together by gas-tight welds, certain of the abutting longitudinal edges of said plates being upturned substantially normally of said plates to form a longitudinally extending stiffening rib.

5. A muffle adapted to be disposed in a horizontal position for the heating of metal at elevated temperatures by externally applied heat comprising an elongated tubular body portion composed of a heat resisting metal or alloy having bottom, side and arched roof walls composed respectively of separate plates of rolled stock having the adjoining edges thereof secured together by gas-tight welds, the adjoining edges of said roof and side plates being bent substantially normal to the body of the plates to provide Stifi'ening flanges extending longitudinally of said muflle.

6. A muflie adapted to be disposed in a horizontal position for the heating of metal at elevated temperatures by externally applied heat comprising an elongated tubular body portion composed of a heat resisting metal or alloy having a relatively thin wall, reinforcing structural members secured to the underside of said tubular body and having depending flanges, and a plurality of muflie supporting rollers carried by said flanges.

7. In a furnace structure, the combination of a supporting framework, refractory walls therein defining a heating chamber, a muffle horizontally disposed in said chamber and having one end thereof anchored to said framework, whereby the opposite end of said muffie expands longitudinally away from said anchored end, a plurality of supporting pedestals within said chamber beneath said muffle. trackways carried by said pedestals and rollers d sposed between said muffie and said trackways.

8. In a furnace structure, the combination of in defining a heating chamber, a muffle horizontally disposed in said chamber and having one end thereof anchored to said framework, whereby the opposite end of said muffle expands longitudinally away from said anchored end, reinforcing structural members disposed beneath said muffle and having depending flanges, a plurality of muffle supporting rollers carried by said flanges and pedestal means within said combustion chamber engaged by said rollers for supporting said muffle at a plurality of points between said ends.

9. In a furnace structure, the combination of a supporting framework, refractory side, top and bottom walls therein defining a combustion chamber, a horizontally disposed mufile in said chamber having bottom, side and arched roof walls, means for anchoring oneb end of said muflle to said framework whereby the opposite end thereof expands away from said anchored end, a support disposed above said refractory top wall and means carried thereby and extending through said latter wall into said combustion chamber for supporting said arched roof wall, said means maintaining substantially equal support for said arched roof irrespective of the extent of expansion of said muflie.

10. In a furnace structure, the combination of a supporting framework, refractory side, top and bottom walls therein defining a combustion chamber, a horizontally disposed muffle in said chamber having bottom, side and arched roof walls, means for anchoring one end of said muffle to said framework whereby the opposite end thereof expands away from said anchored end, a support disposed above said refractory top wall and means carried thereby and extending through said latter wall into said combustion chamber for supporting said arched roof wall, said means being movable with said mufiie during expansion and contraction thereof and anti-friction rollers between said support and said means.

11. In a furnace structure, the combination of a supporting framework, refractory side, top and bottom walls therein defining a combustion chamber, a horizontally disposed muffle in said chamber having bottom, side and arched roof walls, means for anchoring one end of said muffle to said framework whereby the opposite end thereof expands away from said anchored end, a support disposed above said refractory top wall and means carried thereby and extending through said latter wall into said combustion chamber for supporting said arched roof wall, said means being movable both upwardly and longitudinally during expansion and contraction of said muffle, and said support being maintained in supporting engagement with said means during said movement.

12. In a furnace structure, the combination of a supporting framework, refractory side, top and bottom walls therein defining a combustion chamber, a horizontally disposed muffle in said chamber having bottom, side and arched roof walls, means for anchoring one end of said mufile to said framework whereby the opposite end thereof expands away from said anchored end, a support disposed above said refractory top wall and means carried thereby and extending through said latter wall into said combustion chamber for supporting said arched roof wall, said means being movable both u wardly and longitudinally during ex ansion and contraction of said muffle, said support having an inclined track and said means having one or more anti-friction rollers engaging said track whereby said support and means are maintained in supporting engagement during said movement.

HAROLD J. NESS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 837,883 Quineau Dec. 4, 1906 1,076,346 Case Oct. 21, 1913 Number Number