US2277595A - Furnace - Google Patents

Description

Mai-ch 24, 1942. N EVY HAL 2,217,595

FURNACE Filed May 15, 1941 3 Sheets-Sheet 1 S. N. LEVY EI'AL FURNACE March 24-, 1942.

5 Sheets-Sheet. 2

7 Filed May 15, 1941 I I! 3 5 Leo H Bite 6 flfirneys 2 March 24, 1942. VY EI'AL FURNACE Filed May 15, 1941 3 Sheets-Sheet a l the combustion chamber,

uniformly Patented Mar. 24, 1942 [UNITED TATES PATENT .OFFICE Sylvan N. Levy and Bchevy, Arden, Del. Application May 15, 1941,:8erlalNo. 393,624

(cum-1o acclaim.

This invention relates to metal-heating furnaces, and especially to those of the muflle type employed principally for heat-treating trial specimens, tools, machine parts or other articles composed of various grades ferent base metals, or metal alloys adapted to be heated or treated in such a furnace.

of steel, or of dif-,

One object of the present invention is to provide a heat-treating brought up to a high a minimum amount of time.

Another object of the invention is to construct the furnace and themuflie in such a maner that the muflle will heat uniformly in all parts thereof, simultaneously, and hold such uniformity throughout the operation of the furnace, thereby eliminating localized hot spots and increasing the operating efliciency of the furnace.

Another object of the invention is to construct and mount the muiile in such amanner that it and contract during the thereof'without producing may readily expand heating and cooling age is reduced to a minimum.

Another object of the invention the furnace and the muflie in such a manner that replacement or substitution of one muflle for another may be readily accomplished without dismantling major parts of the furnace.

Another object of the invention is to support the muflle solely at its oppos'te ends, respectively, with the major intermediate portion of the mufile suspended in the clear, within the combustion chamber of thefurnace, whereby substantially the full length of the muflle will be available for use to treat work specimens uniformly, at all points throughout substantially the whole length of the muffle.

Another object of the invention is to so form the furnace and to so deliver the heat to the interior of the combustion chamber thereof that the front open end of the muflle may be subjected to a suction action from the interior of terior of the muflie may be completely isolated from communication with the interior of the combustion chamber, whereby, in either case, a predetermined atmosphere may be maintained in the mufile at all times during the operation of the furnace.

Another object of the invention atmosphere within the muflle is composed,

is to construct furnace which can be operating temperature in and maintained or varied at will. to'a predeter- I mined extent while'thefurnace is in operation, and whereby any desired percentages of CO2, 02,

or C O-may be established and maintained in the I muflie without resorting to any time-consuming trial and test method for any desiredatmosmay be readily cleaned out, if necessary, while the furnace is in operation.

Another object of the invention resides in the provision of a mixing chamber forthe atmosdestructive strains therein, whereby mume breake pheric gases, exterior of the furnace, and to provide the chamber with a removable plug or cap providing access to the outer end of the inlet tube, for readily replacing the tube if and when such replacement becomes necessary.

Another object of the invention is to provide the furnace with a readily removable casing for enclosing the thermocouple within the muiile, whereby the aligned openings in the rear walls of the furnace andmuille, respectively, through which the thermo-couple casing projects, may' be employed to support one end of a guide bar inserted from the open front end of the furnace to align -the rear end of the mufile with a seat therefor in the rear wall of the furnace, in replacing a or, if desired, the inis to provide independent calibrated controls and individual indicators for the component gases of which the muflle in the furnace.

Another object of a work support or hearth tile in the bottom of the muflle, with. the ends only of said tile supported at and by the supported ends solely of the muflle, whereby the intermediate portionvof the floor of the muflie will be relieved of the weight of the work contained within the mufile,

thereby prolonging the life of the muffle.

Another object of the invention is to provide a vent for escape of the atmospheric gases from within the muffle to a point outside the furnace when the interior of the muflie is completely isolated from the combustion chamber; and to position the external outlet of the vent in juxtaposition to an exhaust port for the hot combustion gases coming from the combustion chamber, whereby the escaping atmospheric gases will be lighted by the flaming exhaust from the combustion chamber and constantly consumed, to eliminate accumulation of said atmospheric gases in the vicinity of the furnace. v Another object of the invention resides in providing readily interchangeable closure tiles with varioussized openings respectively, for use, singly, in the front opening of the furnace, between the open end of the muflle and the door of the the invention is to providefurnace, to reduce the furnace and mufile opening to a size just large enough for the passage of single piecesof work into and out of the muffle, whereby the area of exposure of the door to the interior of the mufile is reduced to a minimum, thereby effecting a considerable saving in heat losses through and around the door of the furnace; and whereby the temperature of the atmosphere at the open end of the muflie is not materially affected during loading and unloading of the muflle.

Another object of the invention is to provide a removable plate for covering the small work opening in the closure tiles while the work is being treated, to close the muflle completely; to eliminate all possibility of outside air entering the muffle; to keep the front end of the muflie from chilling; and to protect the refractory lining of the furnace door from the muffle heat.

Another object of the invention is to make the muffle of a rectangular cross-section to provide greater work-supporting area within the muille.

Another object of the invention is to provide a circular combustion chamber around the muflle and to'project heating flames into the interior of the combustion chamber substantially tangential to the circular wall thereof, whereby the flame will hug said circular wall and will not impinge upon any local portion of the muffle to create a hot spot therein.

Another object of the invention is to provide a plurality of said tangential flames in laterally overlapping relation, longitudinally of the combustion chamber, whereby uniform heating of the muflle from end to end thereof is accomplished. I

In the accompanying drawings:

Fig. 1 is a side elevation of a furnace constructed and adapted to operate in accordance with the principles of the present invention;

Fig. 2 is a longitudinal vertical sectional elevation of the furnace shown in Fig. 1;

Fig. 3 is a transverse sectional elevation taken on the line 3-3, Fig. 2;

Fig. 4 is a transverse sectional elevation taken on the line 4-4, Fig. 2;

Fig. 5 is a fragmentary front elevation of the furnace and muflie, with the door of the furnace removed;

Fig. 6 is a perspective view of the removable closure plate for the muffle closure tiles; and

Fig. '7 is a fragmentary face view of the front wall of the combustion chamber and the front end of the muiile.

As shown in the drawings, the furnace comprises an outer metallic shell I, of usual conone type of heat-insulating material, such forexample, as an asbestos plaster, etc., and an inill 7 formed of premolded units of high test refractory material, such as silicon carbide, sillimanite, or suitable equivalents. l

The combustion chamber I0 is of circular crosssection and is preferably formed of a plurality of segmental wall tiles II, II and segmental burner or flame tiles l2, l2 fltted and cemented together to form the cylindrical barrel of the combustion chamber III, with theflame tiles l2, lz staggered circumferentially and longitudinally of said chamber, as shown in Figs. 2 and 3.

The flame tiles l2, l2 are of the type disclosed in the prior U. S. patent to Sylvan N. Levy (one of the joint inventors inthe present case) No. 2,230,960, dated February 4, 1941.

Each flame tile I2 is provided with a flame outlet 13 which is contracted in the direction of ner insulating shell 8 composed of a different type of heat-insulating material, such as fi e clay. However, the insulating envelopes 5 and 6 may, if desired, be composed of a single body of insulating material of any of the well-known kinds employed for preventing transmission of high temperatures to the outer metal shell of the furnace.

Enclosed within the insulating shell, composed of the combined bodies 5 and 6, is the combustion chamber II), which in the present instance is the circumference of the combustion chamber l0 and elongated in the direction of the axis of the combustion chamber III, to discharge a flat or ribbon type flame against and tangent to the circular inner surface of 'the combustion chamber Ill. The series of flame ports l3," l3, four in number in the present case, are staggered as shown in Fig. 3, whereby the lateral edges of the several flat ribbon-like flames are in laterally abutting or overlapping relation to each other and form a substantially solid cylindrical sheet of flame which is caused to swirl about the axis of the chamber II), from end to end of said chamber, in contact with and adjacent the inner circular wall of said chamber.

The axially elongated flame ports l3, l3, within the respective flame tiles l2, l2, communicate cation with the flame inlet H of the flame tile l2. At the opposite end of each flame tube It is a circular opening which terminates in an annular shoulder l9 formed by an annular flange 20, in which is a restricted flame passage 2| in axial alignment with the flame port I1. A metal fuel tube 22 fits snugly in the circular opening l8 llflsith its inner end in contact with the shoulder The flame ignites and burns at, and outwardly from, the base of the tapered port I! and the overhanging flange 20 protects the inner end of the fuel tube 22' from the heat of the flame, thus considerably prolonging the life of the fuel tube. The outer end of the fuel tube 22 is fixed in a manifold 23, in spaced relation, axially of the furnace, to another of the fuel tubes located at the same side of the furnace.

The manifolds 23, 23 at the opposite sides respectively of the furnace, are connected by a fuel pipe 24, which, in turn is connected by a pipe 25 to a mixing fitting 26.

The products of combustion are permitted to exhaust from the interior of the combustion chamber I0 through a pair of refractory sleeves 3|, 3| located and spaced apart in the top of the furnace. The sleeves 3| pass through the outer shell I and the insulating shell 5-6, and rest .on the tops of the uppermost segmental wall tiles I la, each of which is provided with an opening llb affording communication between the is formed in a lip or flange 32 around the exterior of the sleeve 3|, between said sleeve and the opening in the outer shell I through which said sleeve projects, for-the purpose of reducing or eliminating transmission of heat from the exhaust sleeve 3| to the metal shell I. As shown in Fig. 2, there are two exhaust sleevesll disposed in staggered relation to the flame ports l3, I3

so that neither of the exhaust sleeves is in direct line with any of the flame ports. I

In addition to the segmental wall tiles l i, Na and 12, the "combustion chamber includes a front wall 33 and a back wall 34 composed of refractory material, such'as silicon carbide, sillimanite, etc. The front and rear walls 33 and 34'are provided with axially aligned rectangular openlug 35 and 38, respectively, for the reception of the muffle 40, which, as shown in Fig. 2. extends the full length of chamber I3, with its open front end 4|, substantially flush with theouter face of the front wall 33, and the outer surface of its closed rear end 42 substantially flushwith the outer surface of the rear wall 34 of the combustion chamber l0.

. The said rear end of the muflie a plate 43 composed 'of refractory material and .inserted in the body 6 of insulating material,

with the marginal edges of the refractory plate 63 in overlapping relation to the edges of the muii'le opening 36 in the rear wall 34 of the combvstion chamber.

As shown in Figs. 2, 3 and 4, all of the corners of the rectangular muflie 40 are internally filleted and externally rounded where the adjacent walls of the muiiie join, in order to reduce breakage of the mulile as a result-of expansion and contraction thereof, as shown at 44 in Fig. 3.

The muiile 40 is'supported solely by those portions of the floor 45 thereof which are adjacent the opposite ends 4! and 42 thereof and which rest on the front and rear walls 33 and 34, respectively, of the combustion chamber l3, whereby all obstruction to free rotary swirling motion of the sheet of flame projected into the combustion chamber by the flame ports l3, I3 is eliminated.

40 abuts againstthe combustion chamber. For the purpose of preventing thepassage of combustion gases from the interior of the combustion chamber It to the interior of the mume 43 the area of the exterior cross-sectional contour of the muiiie is slightly less, but of the same shape as the muffle-supporting opening formed in the front wall of the combustion chamber l3, with suflicient clearance provided to'enable the muilie to be readily inserted in or removed from the combustion chamber. When it is desired to isolate the interior of the mume from the interior of the combustion chamber, to insure sealing of the muffle, the small clearance between the exterior of the muflie and the interior of the opening 35 is closed by fire clay or .other refractory material 33, Fig. 2.

Asshown in Figs. 2 and 3, the mixed component gases which constitute the atmosphere within the muflie 43 are admitted to the muiile through the rear wall thereof, into the space 41 between the hearth tile 43 and the floor 45 of the mume, intermediate the rear feet 49, 43 of the hearth tile 43, through an atmosphere tube 53 which projects through an opening formed in the outer rear wall-4 of the furnace, through the insulation shell 5-8, through the closure plate 43 forming part of the rear wall 34 of the combustion chamber, and through the rear wall 42 of the muffle. Preferably the atmosphere tube II is composed be readily removable from and. replaced. in the furnace. For this purpose a block SI of suitable metal is welded or otherwise secured to the rear wall 4 of the furnace. The block II is provided As shown in Fig. 2, the interior of the muflle 40 tween. Adjacent the front and rear ends 4| and 42 of the muffle 40,, the hearth tile is provided with laterally spaced feet 48, 48 and 49, 49, re-

spectively, which rest on the floor of the muf-' he immediately in line with or immediately adjacent those portions of sad floor '45 which bear on the front and rear walls 33 and 34 of the com brstion chamber l0, whereby the weight of work specimens W resting on and supported by the hearth tile 46 is carried substantially directly by the end walls of the combustion chamber, thus eliminating strains on the floor 45 0f the muffle which would normally result from supporting the weight of the loadwithin the mufii. In this manner, the life of the muille is considerably prolonged. I

In the treatment of steel, it is particularly desirable to maintain either a neutral, a reducing,

or an oxidizing atmosphere within the muflie,

with a counterbored opening 52, for reception of the body of the tube 50. The counterbore 52 provides an annular shoulder against which an annular flange 53 on the outer endof said tube rests. The counterbore 52 communicates with an enlarged cavity 58 formed in the block 5|. A ring of sealing compound 55 is provided in the open end of the counterbore 52 between the outer vend of the tube 53 and-the enlarged cavity 54.

The block 5! is drilled and tapped for the reception of a removable plug 56 in axial alignment with the counterbore 52, to provide access to the interior of the cavity 54 and providing for removal of the tube, which may be driven out through the block Si by inserting a rod through the front of the muiiie and furnace.

The cavity 54 acts as a chamber for thoroughly 'and completely mixing. the component gases constituting the atmosphere entering the muflle 40 through the tube 33. The primarily mixed component atmospheric gases enter the chamber 54 through a pipe 51 which is connected to a primary mixer fitting 53.

The mixer fittings 53 and 26 for the muffle 40 and combustion chamber II, respectively, are

supplied with gaseous fuel from a supply pipe 53,'

through an automatic fuel pressure regulator 60, when the fumaceis gas fired.

In some instances the furnace may be fired with fuel oil, in which case the fitting 26 would 'be'connected to a, suitable source of fuel oil through a suitable pressure pump or gravity feed, while the fitting 53 would be connected to a suitable source of air under pressure through a suitable automatic pressure regulator.

In the" present instance, the automatic pressure regulator 60 supplies gaseous fuel, i. e. either natural or manufactured gas, to a pipe 6| at a constant uniform and predetermined pressure.

The pipe ii is connected to the combustion chamber fuel mixer 26 by a pipe 32, under control of a hand valve 53, and to the muiiie mixer 58 through an auxiliary pressure regulator" by a pipe 65.

The auxiliary automatic pressure regulator 64 maintains a constant uniform supply of fuel to the muflle mixer 50 regardless of the manipulations of the valve 63, by which the flow of'fuel to the combustion chamber mixer 26 is governed to increase or decrease the oper'ating tempera-- ture of the furnace, and the regulator 60 maintains a constant uniform flow of fuel to the furnace as a whole.

Air is supplied to the mixers 26 and 58 from a suitable source under pressure through a pipe 06.

The pipe 66 is connected directly to the com-.

The gas and air pipes 65 and 69 for the muffle mixer 58 are provided with hand valves and I I respectively, by which the flow of the air and of the gas to the mixer 58 may be separately and accurately adjusted to admit predetermined proportions of gas and air to the mixer 58 for providing a predetermined neutral, reducing, or-oxidizing atmosphere in the muille 40, and for that purpose each valve body is provided with a dial l2 and the valve stem is provided with a pointer I3 operating over the dial to indicate the extent of flow, or of valve opening.

With the air and gas under definitely known pressures; respectively, and with the flows through the valves 10 and 'II, respectively, being definitely known for each degree of rotation of the valve stems, by setting the arrows 13, I3 to definitely calibrated markings on the dials 12, I2, respectively, the relative volumes of gas and air passing into the mixer 50, and consequently the atmosphere passing from the mixer 08 into the muffle 40, are definitely known and controlled,

whereby any desired reducing atmosphere or,

oxidizing atmosphere may be created and maintained in the muiiie 40, or a neutral atmosphere may be produced and held inthe muiiiedn lieu of either of the others, by merely setting the pointers to spots on the dials which are known to indicate the proper mixture of gas and air for the atmosphere which is desired.

As a matter of check against variation in the gas or air entering the mufile, from the amounts required according to the dial setting of thevalves 10 and II, as by failure ofv one or the other of the pressure regulators 64 and 60, or for other reasons beyond the control of the operator, a manometer I00 of any ordinary commercial type is connected by pipes IM and I02 to the gas and air lines 65 and 69, respectively. This manometer is provided with juxtapositioned sight tubes I03 and I04 adjacent a scale I05 and includes a colored liquid which rises and falls in each tube in accordance with the pressure and/or volume of the gas or air entering the muffle, by which the relationship of the two entering the mixer 58- is at all times clearly visible to the operator of the furnace.

The atmospheric mixture formed in the mixer 58 passes therefrom into the pipe 51 and from the pipe 51 into the chamber 54 where a second or complete mixing of the air and gas is effected, by reason of the pipe 51 entering the chamber from one side thereof, at 90 to the axis of the tube 50 which conducts the mixture from the chamber 54 into the rear end of the muiiie 40. below the hearth tile 46.

From the inner end of the tube 00 the atmosphere flows along under the hearth tile 46 and around the marginal edges thereof, through slots 15, I5 formed between said marginal edges of the hearth tile and the vertical walls of the muflie, into the interior of the muflie above the hearth tile and around the work specimens W supported thereby.

As shown in Fig. 2, the front end 4| of the muffle 40 terminates at the outer wall of the front plate 33 of the combustion chamber I0, in inwardly spaced relation to the outer surface of the front plate 3 of the outer casting I, thereby providing a space 16 between the front end of the mufile and the front of the furnace, which has a shape and area correspondingto the crosssectional shape of the muiiie, which normally is closed only by the door 11 of the furnace. The atmospheric gases normally flow from the open end H of the muflle into this space 16.

In furnaces of the prior art, the doors fit the furnace openings rather loosely and the atmospheric gases escape from the furnace between the rear face of the door and the front face of the furnace, around the marginal edges of the door. If a reducing atmosphere is being used, the escaping gas, upon coming into contact with the air outside the furnace, bursts into flame around the edges of the door.

In the present case, when the interior of the muflie is completely isolated from the'interior of the combustion chamber, the atmospheric gases are conducted from the space 16, between the door 11 and the front end H of the mufiie, to a point outside the furnace and remote to said door through and by a vent pipe I8, which,'as shown in Fig. 2, passes upwardly from said space through the insulating shell 5-0 and outer shell I to a point above the top of the furnace and rearwardly. located with respect to the front of the furnace. In the present instance, the outer end- I0 of the vent I0 terminates over one of the exhausts 3| for the gases coming from the combustion chamber I0, which are usually flaming or of such heat as to cause the atmospheric gases escaping from the end of the vent to ignite and burn. This structure and arrangement of parts eliminates the undesirable escape, burning, etc., of the atmospheric gases around the door of the furnace.

In some instances the sealing material 39, between theinner surfaceof the muilie opening 35 in the front wall 33 of the combustion chamber I0 and the exterior surface of the front end H of the muffle 40 is eliminated, leaving a space 30, Fig. 7, therebetween, through which the swirling products of combustion in the chamber I0 sets up a suction action and draws the atmosj pheric gases into the combustion chamber from the frontend of the muflle 40. In such cases, the vent pipe 18 may be plugged with fire clay, or eliminated.

In order to eliminate further the escape of the atmospheric gases around the door of the furnace, the opening I6 is framed in premolded units 80 of silicon carbide, sillimanite or the like, and which project to some extent beyond the front face of the front plate 3 of the furnace. The outer faces of the framing units 80, 00 are set in one common plane represented by the surface 0I, against which the rear planar face 82 of the door I1 bears and substantially seals the opening 16 against the escape of gas from the muiile. The sealing or frame tiles 80, 00 may be readily replaced when necessary without dismantling the furnace, whereby a practical seal may also be maintained around the furnace opening.

The top or roof 83 of the muflle 40 is disposed a sufficient distance above the top surface of the hearth 46 to accommodate relatively large articles and to providea suflicient volumetric capacity in the muiile to contain a sufflcient quantity of atmosphere for properly treating any and all work placed on the hearth tile 48 which can be inserted through the furnace entrance opening I8.

However, it frequently happens that the furnace is used for heat-treating tools or specimens of small size. The operator of the furnace will frequently raise the door to a greater elevation than is necessary for inserting such small work into the mufile for treatment or in removing the treated specimens from the mui'lle. This results 'in excessive losses of heat and atmosphere from the muflie.

In the present case, to avoid such losses, and to avoid heat losses by radiation through the door, an interchangeable bailie wall 85, of high refractory material, is removably placed inthe normally open space 16 between the front edge tl of the m'ufiie and the rear face 82 of the door, and an opening 85 of an area commensurate with the size of the individual pieces of work being treated is formed in the baffle wall 85 for passage of the work pieces therethrough. This reduces the losses of atmosphere when the door is open and reduces the heat losses when the door is closed.

In order to keep the heat of the muflle from impinging against the inside surface of the door 11, while the work W isundergoing treatment, and in order to maintain uniform heat throughout the full length of the muilie clear up to the open end 4i thereof, an auxiliary closure plate I85 (Figs. 2 and 6) is provided to close the work opening 86 in the baffle wall 85. A substantial lug i350. is formed onthe closure plate I85 to be gripped by work tongs in setting the closure plate in place and when removing it from the opening A passage 81 is formed in the rear and top surfaces of the baffle wall 85 to afford communication between the front of the muffle and the inlet end of the vent l8, when-the mullle 4B is com- I pletely isolated from the interior of the combustion chamber, as noted above.

A slot 88 is also formed between the front edge 8% of the hearth tile 46 and the rear face of the baffle wall 85, which permits the atmospheric gases to flow from the space 41 beneath the hearth tile 46 upwardly across the work opening- 86 in the baiile wall 85 in the form of a curtain to shield the muffle against entrance of exterior atmosphere when the door 11 is raised.

The baiile wall 85 is provided with a peep hole 89 in axial alignment with the atmosphere inlet tube 50, whereby the condition of the tube or fiame, if a neutral or reducing atmosphere is he'- ing used, may be readily observed, or through which a cleaning rod may be inserted into the tube from the front ofthe furnace while the furnace is in operation.

Preferably, as shown in Fig. 5, the baflle wall is made in two pieces, i. e. a bottom or base piece or -section 85a which rests on the bottom wall of the furnace opening 16, extends from side wall 'to side wall across said opening, and terminates,

vertically, in a horizontal plane substantially coincident with the top surface of the hearth tile .46; and a second or upper section 85b which rests on the upper edge of the base section 85a and substantially fills the remaining area of the furnace opening 18, with the exception of the work opening 88 formed in the upper section 85b and which may vary in area in different sections 85b,

respectively, in accordance with the sizes of the work pieces to be passed through the work openper section 851; may also be secured in'place by fire-proof cement. However, in any case, the baffie wall may be readily removed in whole or in part without serious interruption in the operation of the furnace.

As shown in Fig. 2, a casing 90, in the form of a tube closed at one end and open at its opposite end, is inserted through an opening 9! formed in the rear wall of the furnace, including the back plate I, insulating shell 5-6, and rear wall plate 13 of the combustion chamber ill. and an opening 92 formed in the rear'wall 42 of the mufile 40, for the accommodation of a thermo-couple for indicating the interior temperature of the mufile.

The casing 90 is fixed in a boss at, welded or otherwise secured to the rear plate 4', with a bore 93 axially aligned with the tube opening 9!. A counterbore 85 is formed in the boss 94 at the outer side thereof and is filled with a ring of suitable sealing compound 96. A set screw 81, tapped into the boss 94, bears against the tube 90 and holds the same rigidly in place.

If for any reason it should become necessary to replace the muflle 40, it is only necessary to remove the casing 90 and atmosphere tube 50, through the rear of the furnace; and the baffle 85, if such has been .used, through the front opening 18 of the furnace. If the front end ll of the muffle has been sealed in the opening 35 in the front wall 33 of thecombustion chamber It, the seal 39 between the marginal edges of the open end M of the muflie and the adjacent surfaces of the opening 35 in the front wall 33 of the combustion chamber I0 is then broken, whereupon the old mufflemay be moved out of the furnace through the front opening 18.

'In order to place a new muflie in the furnace, a long rod of metal, or other suitable material, of a diameter substantially equal to the outside diameter of the thermo-couple casing 90 may be inserted, fromthe rear of the furnace, through the opening 93 therein and through the aligned opening 9! in the rear wall of the furnace. The

' length of the rod should be sufficient to extend completely through the combustion chamber l0 and out through the front furnace opening 16, with the end ofthe rod extending outwardly beyond the front wall of the furnace. This exposed .end of the rod is then inserted through the opening 92 in the rear wall of the new muffle, whereupon the new muiiie is inserted through the front opening 16 of the furnace into the combustion chamber. The rod will function as a, means to guide the rear end of the muflie into the opening 38 in the rear wall 34 of the combustion chamber Ill. A similar rod can, if desired, be passed through the opening 91 in the rear wall of the furnace through which the atmos here tube 50 normally passes.

in following the above procedure, the openings 82 and 98 in the rear wall 42 of the muflie will be assured of axial alignment with the openings 9i and 91 in the rear wall. of the furnace through which the thermo-couple casing tube 90 and the atmosphere tube 50, respectively, project. This tube may then be reinserted and secured in place and the seal provided between the marginal edges of the open frontend ll of the muflle and the respectively adjacent walls of the front opening 16 of the furnace and/or the opening 35 in the front wall 33 of the combustion chamber I 0.

chamber consisting of a fabrication of premolded side and end wall-units composed of high refractory material, a body of heat-insulating material including at least one premolded flame tube, and

The foregoing description and the drawings referred to therein includes a number of details of construction which contribute largely to the successful, efllcient, economical, and convenient operation and maintenance of the furnace of the present invention as a whole.

We claim:

1. A muilie furnace comprising a, combustion chamber consisting of a fabrication of premolded side and end wall units composed of high refractory material, a body of heat-insulating material molded en masse about the combustion chamber, said end walls being respectively provided .with axially aligned openings formed therein, and said body of insulating material having a similarly aligned opening extending from the exterior of the furnace to one of said end walls, and a muiiie extending from one end wall to the other end wall of said combustion chamber and having its opposite ends respectively seated in said end wall openings, said end walls functioning as the sole means of support for the'muflie with the muflle spaced from said side walls completely around the muille along the length thereof intermediate said end walls.

2. A muille furnace comprising a combustion chamber consisting of a fabrication of premolded side and end wall units composed of high refractory material, a body of heat-insulatingmaterial about the combustion chamber, said end walls being respectively provided with axially aligned openings formed therein, and said body of insulating material having a similarly aligned opening extending from the exterior of the furnace to one of said end walls, and a muflle extending from one end wall to the other end wall of said combustion chamber and having its opposite ends respectively seated in said end wall openings, said end walls functioning as the sole means of support-for the muffle with the mume spaced from said side walls completely around the muiile along the length thereof intermediate said end walls, and a plate of refractory material located in said insulating material adjacent the second of the end walls of the combustion chamber, with the marginal. edgesof the plate in overlapping relation to the marginal edges of the opening in said second end wall and functioning as a closure therefor.

3. A mulile furnace according to claim 2', and

- including an end wall of the muilie disposed adat least one exhaust conduit, each composed of refractory material, extending through said body of insulating material from the exterior of the furnace to the side wall of the combustion chamber, with a flame passage in said flame tube communicating with a flame-distributing port formed in one of the refractory units of said side wall, and an exhaust passage in said conduit communicating with an exhaust port in another of said side wall units.

6. A muflie furnace comprising an outer shell, including side and end walls, a combustion chamber within said shell and composed of a fabrication of premolded side and end wall units of high refractory material, an intermediate body of heat-insulating material molded en masse around the sides and ends of the combustion chamber within said outer shell, one end wall of the outer shell, the adjacent end wall of the combustion I chamber, and the insulating material intermediate these two end walls being provided with aligned openings forming an entrance into the interior of the combustion chamber from the exterior of the furnace, and a frame around said entrance opening composed of premolded high refractory'material embedded in the insulating material and projecting outwardly therefrom through the entrance opening in the outer shell.

7. A muilie furnace according to claim 6, wherein the frame'units are shouldered to overlap the marginal edges of the entrance opening in the outer'shell.

8. A muflle furnace comprising an outer shell,

including side and end walls, a combustion chamber within said shell and composed of a fabrication of'premolded side and end wall units of high refractory material, an intermediate body of heat-insulating material around the sides and ends of the combustion chamber within said outer shell, one end wall of the outer shell, the adjacent end wall of the combustion chamber and the insulating material intermediate these two end walls being provided with aligned openings jacent the plate, and an atmosphere tube removably projecting through said muiiie end well, said plate, and the insulating material from the exterior of the furnace to the interior of the muffle.

4. A muilie furnace according to claim 2, and

including a thermo-couple casing removably projecting from the exterior of the furnace through axially-aligned openings in the insulating material, the plate and an end wall of the muffle adjacent the pla e, with said aligned openings being adjacent the top of the muiile.

5. A muille furnace comprising a combustion forming an entrance into the interior of the combustion chamber from the exterior of the furnace, a muilie within said combustion chamber arranged with an open end thereof disposed in said enrance openingintermediate the end wall of the outer shell and the adjacent end wall of the combustion chamber, and a readily removable baiile of hi h refractory material located in and substantially closing said entrance opening intermediate said open end of the baffle and the plane of the end wall of the outer shell.

9. A muilie furnace according to claim 8, wherein the removable bailie is provided with a through opening of relatively smaller area than the entrance opening of the furnace for passage of ,work specimens into the mume.

10. A muiile furnace according to claim 8, I

' tangential relation temporarily closing said work passage 2,277,565 openingin the bailie while the furnace is in operation.

11. A muiiie furnace comprising a horizontal cylindrical combustion chamber including vertical end walls, a mu e coaxially arranged in said chamber with its opposite ends respectively seated in corresponding '-1openings in said end walls which constitutes the sole means of support for the muiile, a

said chamber and directed in substantially to said cylindrical wall to produce a substantially continuous sheet from one end wall to the second end wall of said chamber in rotating contact with said cylindrical wall around and out of direct muilie, and a plurality of exhaust ports contact with said in longitudinally spaced relation in the top of said combustion chamber, flame ports. to convey in staggered relation to said products of combustion beyond the exterior of the furnace directlyfrom said chamber. v

12. A mufie furnace cylindrical combustion comprising a horizontal chamber including vertical walls at the opposite ends respectively thereof, a muflie of rectangular cross-section located in said chamber with resting in openings formed in said end speciively of said combustion chamber,

the opposite ends of the muille walls re-' said end walls affording the sole means of support for the muffle, and a work plate within the muille and provided with relatively spaced legsresting on plurality of flame ports inthe the bottom of the muille at the places where the ends of the muiile bottom rest on the end walls of the combustion chamber, said legs constituting the sole means of support for the work plate in the muffle.

13. A muille wherein the I the area of the bottom clearance between the marginal edges of furnace according to claim 12, area of the work plate is less than of the muffle and provides the work plate and the respectively adjacent walls of the muille, and means for injecting gaseous fluid into one end of the mufile intermediate and parallel to the bottom of the muiile andthe under side of the work plate to'flow longitudinally of the muille and upwardly around the marginal edges of the work plate around the work on said work plate.

14. A mufiie furnace comprising an outer shell, including side and'end walls, a combustion chamber within said shell and composed of a fabrication of premolded side and refractory material, an intermediate end wall units of high body of heat-insulating material around the sides and ends of the combustion chamber within said outer shell, one end wall of the outer shell, the

adjacent end wall of the combustion chamber and the insulating material intermediate these two end walls being provided wi h aligned openings forming an entrance into the interior of the combustion chamber from the exterior of the furnace. a

muflle within said combustion chamber with an open end thereof disposed in arranged said entrance opening intermediate the end wall of the I outer shell and the adjacent end wall of bustion chamber, means for closing said the com-,

entrance opening outwardly beyond the open end oi the muflie, means atmosphere within said mulile.

for maintaining a predetermined independent means for supplying a mixture of flaming com- .bustible fluids to the interior of the combustion chamber around said muille, means for exhaustchamber. Y

-'able closure element for the furnace, and a ing resultant hot gases from the interior of the combustion chamber, means affording escape of excess atmosphere fromlthe interior of the muflle through'said open end thereof in said entrance opening ofthe furnace, and means for conducting the atmosphere escaping from the muflie into contact with the flaming gases of the combustion 15. A muilie furnace according to claim 8, wherein the means conducting the atmosphere escaping from the muffle into contact with the flaming gases from the combustion chamber at a point exterior of the furnace comprises a pipe having one end communicating with the entrance opening of the furnace adjacent the open end of themuille and its opposite end disposed adjacent the exhaust from the combustion chamber.

16. A muille furnace comprising an including end and side walls, an inner combustion chamber including endand side walls respectiyely spaced from those of the outer shell, a body of heat-insulating material intermediate the walls of the shell and the walls of the combustion chamber, a muilie within the combustion chamber, means for injecting gaseous fluid into the interior of the muille from the exterior of the furnace comprising a fixture secured to one end wall of the shell of the furnace and having an internal gas chamber, a tube afiording communication between the interior of said gas chamber and the interior of the mufile, said tube being removably mounted in aligned openings'formed in the adjacent end walls'of chamber intermediate insulating material and the mufile and a corresponding aligned opening in one side of said fixture, and a readily removside of 'said fixture opposite to that through which said tube projects.

17. A muflle furnace comprising an outer shell including and and side walls, a combustion chamber within said shell and including end and side walls respectively spaced from those of said shell a body of insulating material intermediate said spaced walls, a horizontal opening 'of predetermined contour formed in the end wall of the shell, the end wall of the combustion chamber, and the intermediate body of. insulating material at one end of the furnace and in the second end wall of the combustion chamber at the second end of the furnace, a mufile of corresponding cross-sectional contour insertable through said passage into said combustion chamber with the opposite ends of the muille resting respectively on the opposite end walls of .the combustion chamber, the end of the muille adjacent said second end of the furnace being closed by an end wall integrally formed with the. side walls ofthe muffle, the opposite end of the muille be ing open and in communication with the mufflereceiving opening ,in the said one end of the furnace, said closed end wall of the muille and the' adjacent end walls of the shell, the combustion chamber, and the intermediate insulating material having aligned openings near the top of the muille for the purpose of facilitating the seating of the closed end of the muflle in the muille opening formed in the end wall of the combustion chamber at said second end of the thermo-couple casing normally projecting into the interiorof the muille from the exterior of the furnace through said aligned openings in said second end of the furnace.

18. A muille furnace comprising an outer shell including end and side walls, a combustion chamouter shell the shell combustion opposite ends of the muiiie resting respectively on the opposite end walls of the combustion chamber, the end of the mume adjacent said second end of the furnace being closed by an end wall integrally formed with the side walls of-the muille, the opposite end of the muflle being openand in communication with the muiiie-receiving opening in the said one end of the furnace, a door normally closing the muflle-receiving opening at the one end of the furnace, and a baiile wall removably mounted in said mimic-receiving opening between the open end of the muiiie and said door.

19. A muifle furnace comprising an outer shell including end and side walls, a combustion chamber within said shell and including end and side walls respectively spaced from those of said shell, a body of insulating material intermediate said spaced walls, a horizontal opening of predetermined contour formed in the end wall of the shell, the end wall of the combustion chamber,. Y and the intermediate body of insulating material at one end of the furnace and in the second end wall of the combustion chamber at the second end of the furnace, a muille of corresponding cross-sectional contour insertable through said passage into said combustion chamber with the opposite ends of the muflle resting respectively on the opposite end' walls of the combustion chamber, the end of the muilie adjacent saidsecond end of the furnace being closed by an end wall integrally formed with the side walls of the muifle, 'tlie opposite end of the muffle being open and in communication with the muiilereceiving opening in the said one end of the furnace, a door normally closing the mumereceiving opening at the one end of the furnace, a baille wall removably mounted insaid muil'iereceiving opening between theopen' end of the 'muflie and said door, means for' injecting atmospheric gases into the interior of the muiile remotely with respect to the open end of the muiile, and a vent for excess atmosphere passing upward through the insulating material at the one end of the furnace from the top of the muiliereceiving opening to the exterior of the furnace between the wall of the shell and the wall of the combustion chamber at said one end of the furnace.

-20. A muflle furnace comprising an outer shell including end and side walls, a combustion chamber within said shell and including end and side walls respectively spaced from those of said shell, a body of insulaing material intermediate said spaced walls, a horizontal opening of predetermined contour formed in the end wall of the shell. the end wall of the combustion chamber. and the intermediate body of insulating material at one end of the furnace and in the second end wall of the combustion chamber at the second end of the furnace, a muilie of corresponding crosssectional contour insertable through said passage into said combustion chamber with the opposite ends of the muiiie resting respectively on the opposite end walls of the combustion chamber, the end of the muflle adjacent said second end of the furnace being closed .by an end wall integrally formed with the side walls of the muiiie,

. the opposite end of the'muifle being open and in communication with the muiiie-receiving openingrin the said one end of the furnace, a door normally closing the muffle-receiving opening at the one end of the furnace, a bailie wall removably mounted in said muille-receiving openingbetween the open end of the muiiie and said door, means for injecting atmospheric gases into the inerior of the muiiie remotely with respect to the open end of the mume, and a vent for excess atmosphere passing upward through the insulatingthe mume to afford passage of work specimens to and from the interior of the muffle.

21. A heat-treating furnace having a cylindrical combustion chamber arranged with its axis horizontally disposed, said furnace comprising a front wall of predetermined thickness with an opening extending therethrough from the inner to the-outer face thereof, a muille of rectangular cross-section disposed in said furnace chamber with its longitudinal axis substantiallycoinciding with that of said chamber and having an open end located in said opening near said outer face and remote to said inner face of said front wall. the outer cross-sectional contour of said end of the muflie being similar to but of slightly lesser area than said opening to provide a clearance therebetween, a series of relatively staggered flame and exhaust ports spaced axially of said chamber and-mume with said flame ports elon gated in the direction of said axes to provide laterally abutting ribbons of flame forming a whirling sheet-like current of gaseous ,fluid around and substantially in contact with the inner circular wall of said fumacechamber along the full length of said muiiie and creating'a draft current through said clearance for drawing gaseous fluid into the furnace from beyond the open end of the muiile, and means for producing a predetermined atmosphere in said muiller Y 22. A heat-treating fumace comprising a front wall of predetermined thickness with an opening extending therethrough from the inner to the outer face thereof, a muiiie of rectangular cross- ,current through said clearance for drawing gaseous fluid into the furnace from beyond the open end of the muiiie, a hearth tile in said muille in vertically spaced relation to the bottom wall of said mufl'ie with the marginal edges of the hearth tile spaced inwardly from the side and back walls of the muilie, the opposite end and the walls intermediate said ends of said muflie being closed against entrance. of said external fluid him said mume, means for introducing a gaseous fluid into said muiile below-said hearth tile comprising a. I pipe extending through the rear wall of the mume below-and parallel to said hearth tile with an hearth tile and through said rnuflle to said open 10 Y end thereof to all said muflle with an atmosphere of predetermined character and whereby escapin excess atmosphere. from the mume will be caught in said draft current and carriedinto said furnace, and means for closing said opening beyond and in spaced relation to said open end of said muflle and the marginal edge of the hearth tile adjacent thereto.

SYLVAN" N. v B. LEVY.

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