US 3618919 A
Description (OCR text may contain errors)
United States Patent Inventor Appl. No.
Filed Patented Assignee Jacob Howard Beck Waban, Mass.
Nov. 3, 1969 Nov. 9, 1971 BTU Engineering Corporation Waltham, Mass.
ADJUSTABLE HEAT AND GAS BARRIER 7 Claims, 8 Drawing Figs.
11.8. CI 263/37, 263/50 Int. Cl. F27b 5/02 Field of Search 263/36, 37, 38, 39, 5O
References Cited UNITED STATES PATENTS Baehr et al Browning Beck Guirl et al Primary Examiner-John .l. Camby Anomey-Joseph Weingarten ABSTRACT: A heat and gas barrier for a muffle furnace having a gas gate adjustable to selected heights within the muffle and effective to controllably isolate the respective gas atmospheres of adjacent muffle zones.
EXHAUST AIR 3e 49 J i f FLAME E: ,M I AIR t 18-5 F" 6' l g FROM FROM I/\1\'I 'IN'H m EXHAUST EXHAUST JACOB HOWARD BECK TUBE 40 TUBE 42 PLg. 5. 74 46 ADJUSTABLE HEAT AND GAS BARRIER FIELD OF THE INVENTION BACKGROUND OF THE INVENTION Muffle furnaces are often employed for the precise and controlled heat processing of products such as semiconductor devices; microcircuits and powder metals. In general, such furnaces comprise an elongated muffle which may be divided into adjacent zones, and a conveyor disposed within and movable through the muffle for the transport of products therethrough. To suit particular heat processes, a different gas atmosphere can be maintained within each muffle zone and in such instances a gas barrier is employed between adjacent zones to isolate the respective gas atmospheres. In addition, a different operating temperature can be provided and maintained within each muffle zone to provide an intended temperature profile, in which case a heat and gas barrier can be provided for thermal as well as gas isolation between adjacent muffle zones.
Barriers of known construction are usually formed integrally with the furnace structure and are of fixed size and configuration conforming to the interior shape and dimensions of the muffle cross section. For certain heat processes where a finer degree of isolation control is required, it would be useful if the effective area of the barrier could be adjusted to permit such fine control; however, conventional barrier construction does not allow any such adjustment since the effective area is fixed by the opening dimensions of the barrier.
SUMMARY OF THE INVENTION In accordance with the invention, a novel adjustable barrier for a furnace muffle is provided which efficiently and controllably isolates the respective gas atmospheres of adjacent muffle zones and which is readily adjustable to achieve precise isolation control to selectively accommodate products of different heights being conveyed through the furnace. The barrier includes an adjustable gate which is operative to provide a controlled gas curtain between adjacent zones of the muffle and in the immediate vicinity of products passing therethrough. The gate is adjustable in height to permit passage of a product of particular height while maintainingthe most effective gas curtain for that product size. A sharp transition between the gas atmosphere of one muffle zone and the gas atmosphere of an adjacent muffle zone is provided, such that products being processed are conveyed through a consistent and controlled gas atmosphere throughout each zone.
In those instances where thermal isolation is desired between adjacent muffle zones, as well as gas isolation, the invention can be employed in conjunction with a heat and gas barrier. Where a heat barrier alone is employed, the novel adjustable gate provides additional radiation shielding to aid in maintaining selected different temperatures in adjacent muffle zones.
DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a partly broken away pictorial view of an adjustable gas barrier according to the invention;
FIG. 2 is a broken away elevation view of the embodiment of FIG. 1;
FIG. 3 is a partly broken away pictorial view of the gate assembly of FIG. 1 in its uppermost position;
FIG. 4 is a pictorial view of the gate assembly of FIG. 1 in its lowermost position;
FIG. 5 is a partly broken away elevation view of a gas exhaust system useful in the invention;
FIG. 6 is a broken away elevation view of an alternative embodiment of the invention;
FIG. 7 is a broken away elevation view of a further embodiment of the invention; and
FIG. 8 is a pictorial view of the gate assembly of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION The invention as embodied in a gas barrier employed between adjacent sections of a furnace muffle is illustrated in FIGS. 1 and 2. A gas barrier 10 is disposed between and joined to a first muffle section 12 and an adjacent muffle section 14. The muffle sections 12 and 14 and the gas barrier 10 are fabricated of a metal capable of withstanding the relatively high temperatures encountered during furnace operation. The muffle sections 12 and 14 are formed as an elongated tubular structure and in the illustrated embodiment are of generally rectangular cross section with barrier 10 being a transition section therebetween. The bottom wall of the mufi'le serves as a hearth for the support of a conveyor belt 16 which is trans ported through the muffle by a suitable conveyor mechanism (not shown). Conveyor belt 16 is typically formed of a flexible wire mesh or'chain link of suitable high temperature alloy or metal.
Each of the muffle sections 12 and 14 defines a zone and each is provided with means for maintaining a selected gas atmosphere within respective zones. In addition, each muffle section may include means for providing and maintaining a selected temperature within respective zones to provide a temperature profile suitable for the particular heat process being accomplished. Typically, the muffle is heated by electrical heaters disposed around the outside surface of the muffle, and an insulatingfire brick or other suitable material is built up around the muffle to provide thermal insulation. Depending upon the heat process desired, the temperature of muffle sections 12 and 14 may be at the same or different temperatures.
The gas barrier 10 separating muffle sections 12 and 14 includes first and second cylindrical plates 18 and 20 welded to respective muffle sections 12 and 14. An opening is provided centrally of plates 18 and 20 confonning to the interior configuration of muffle sections 12 and 14. A circular flange 22 is welded to the periphery of plates l8 and 20 to provide a closed annular structure. A second pair of circular plates 24 and 26 are welded to flange 22 in spaced-apart relation between outer plates 18 and 20. Openings are also provided centrally of plates 24 and 26 conforming to the interior configuration of mufile sections 12 and 14. Portions 28 and 30 of respective plates 24 and 26 extend downwardly by a selected amount into the interior of the mufile, and each portion 28 and 30 includes a respective outwardly turned flange 32 and 34.
Gas barrier 10 includes a first annular chamber 36 defined by plates 18, and 24, and a second annular chamber 38 defined by plates 20 and 26, each chamber being operatively associated with respective muffle sections 12 and 14. A pipe 40 is welded to flange 22 and communicates with chamber 36, while a pipe 42 also welded to flange 22 communicates with chamber 38. A gas gate assembly is provided within barrier 10 and includes a three sided tubular member 44 welded to the confronting surfaces of plates 24 and 26 and having a plurality of openings 46 lying substantially in the planes of the interior muffle walls. More particularly, the tubular member includes a bottom tube 48 and side tubes 50 and 52 connected to and upstanding from'respective opposite ends of tube 47. Tubes 48 and 50 are. sealed at their upper ends 49 and a pipe 54 is welded to tube 46 and is operative to supply gas to gate 44 to cause flow of gas from openings 52 into the muffle interior, as will be further explained hereinbelow. The gate assembly includes an adjustable damper gate member 56 attached to a pipe 58 slidably disposed within a journal section 60 welded to flange 22. Pipe 58 and gate 56 can be maintained at selected heights for example by screw 61 threaded in an opening in flange 60. Member 56 is operative to be adjustably maintained at any predetermined height within the muffle and to deliver a downwardly flowing curtain of gas supplied to the gate via pipe 58.
The adjustable gate structure itself is illustrated more clearly in FIGS. 3 and 4 which depict the gate in uppermost and lowermost positions, respectively. Member 56 is of generally wedge-shaped configuration and includes a top wall 62 attached to a pipe 58 and first and second sidewalls 64 and 66, which taper downwardly to a relatively narrow orifice defined by the thickness of spacers 68 disposed along the lower edges of sidewalls 64 and 66. The lowermost edges of walls 64 and 66 include outwardly extending flanges 70, and the walls 64 and 66 are secured in spaced-apart relation by rivets 72 or other suitable fasteners which pass through respective spacers 68. First and second generally triangular walls 74 complete the adjustable gate structure. The adjustable gate is of a width adapted to be vertically movable between tubes 50 and 52 of the tubular member 44.
In FIG. 3 member 56 is illustrated in its uppermost position to permit the transport of a relatively high product '76 through the furnace on conveyor belt 16. In FIG. 4 member 56 is depicted in its lowermost position which defines a relatively narrow space sufficient for passage of a relatively thin product 78 through the furnace. A curtain of gas is provided by the adjustable gate, and the cross-sectional extent of the gas curtain is easily adjustable according to the invention to permit a furnace to accommodate work products of different heights while maintaining precise and controllable gas isolation between adjacent zones of the furnace. Overall furnace operation is thus rendered more versatile by virtue of the invention since a relatively simple adjustment permits the accommodation of products of various sizes while maintaining the most effective gas isolation for a particular product size.
The adjustable gas gate is operative within the gas barrier to provide isolation between the atmospheres of adjacent muffle zones in the following manner. Gas contained within muffle section 12, for example hydrogen, is drawn by suction on exhaust tube 40 from muffle section 12 into chamber 36 and thence through tube 40. Gas, such as air, contained within muffle section 14 is, in similar manner, drawn by suction on exhaust tube 42 into chamber 38 and thence through exhaust tube 42. At the same time, a nonreacting gas, such as nitrogen, is introduced via tubes 54 and 58 to cause a curtain of nitrogen to flow in the opening defined by the gas gate. The nitrogen mixes with the gases in respective chambers 36 and 38 and is withdrawn via associated exhaust tubes 40 and 42. Any gases emitted by the work product are similarly withdrawn from the muffle. The distinct chambers 36 and 38 and their respective exhaust tubes 40 and 42 prevent possible combustion gases within the barrier which could generate back pressure in addition to causing explosive conditions within the furnace. Pressure within the barrier should be maintained negative with respect to the muffle pressure, with gases being removed by suction. There is usually a drop in available energy of the gas within the annular chambers 36 and 38 by reason of the enlarged barrier volume, and in this instance, an ejector can be employed to permit suitable gas removal.
Referring to FIG. 5, there is shown an exhaust system utilizing an ejector and useful to safely and effectively dispose of combustible gas, such as hydrogen. Tubes 41 and 43 are coupled, respectively, to barrier exhaust tubes 40 and 42. A flow valve 45 is provided in each tube 41 and 43, and tubes 41 and 43 merge into a single chamber 47 having a nozzle 49. An air ejector 51 is provided in chamber 47 for introduction of air at a controlled rate to cause intended exhaust of gases via tubes 41 and 43 from the barrier. In operation, a mixture of hydrogen and nitrogen from chamber 36 is drawn by action of ejector 51 via tubes 40 and 41 into chamber 47, while a mixture of air and nitrogen from chamber 38 is similarly drawn via tubes 42 and 43 into chamber 47. The gases emanate from nozzle 49 and the combustible gas is ignited for safe gas disposal. The gas curtain is provided at a rate of flow sufficient to maintain an intended transition between the gas atmospheres of adjacent muffle zones and, according to the invention, barrier efficiency is markedly improved by the novel adjustable gate which permits selective variation of the area of the gas curtain to provide extremely precise isolation control for particular gate positions.
The invention can also be embodied in a heat and gas barrier which is operative to provide isolation between the respec tive temperatures of adjacent muffle zones, as well as providing isolation of the respective gas atmospheres. Such a heat and gas barrier can be similar to the embodiment depicted in FIGS. 1 and 2, with the addition of a water jacket which encircles the barrier structure and which is operative to conduct heat away from the surfaces of the barrier. Referring to FIG. 6 there is shown a portion of the barrier, similar to the structure of FIG. 2, with the addition of a water jacket 91 which also serves as the encircling channel for attachment of outer plates 18 and 20 and inner plates 24 and 26. Inlet and outlet ports are provided for flow of water or other cooling fluid through jacket 91.
A further embodiment of the invention is illustrated in FIGS. 7 and 8 wherein an adjustable water cooled gate is employed in conjunction with a heat barrier to provide additional radiation shielding for maintenance of selected different temperatures in adjacent zones of the furnace. Referring to FIG. 7, there is shown a heat barrier disposed between adjacent muffle sections 82 and 84 and having a vertically adjustable gate 86 disposed therein and extending part way into the muffle interior. The adjustable gate 86, as seen more clearly in FIG. 8, includes a generally rectangular plate 88 of thermally conductive material such as metal welded or otherwise attached along the upper edge thereof to a channel-shaped pipe 90. The upstanding portions 92 of pipe serve to physically support gate member 88 at predetermined dispositions within the muffle interior, as well as providing a passage for the flow of a cooling fluid such as water therethrough to cool the as sociated gate member 88. The adjustable gate 86 is of a width slightly less than the interior width of the furnace muffle to permit vertical adjustment of the gate therein.
The heat barrier 80 itself can be of any well-known barrier construction, a particularly efficient heat barrier being described in detail in U.S. Pat. No. 3,138,372, assigned to the assignee of the present invention. The operation of the heat barrier need not be described in detail herein. In general, the heated atmosphere within each adjacent muffle zone is withdrawn through respective annular chambers of barrier 80 to maintain a predetermined temperature profile across the region of the barrier.
Gate 86 can be adjusted in height to permit passage of a work product 94 through the furnace on a conveyor belt 96, while providing, for work products of a given height, the most effective radiation shielding. To accommodate a work product of different height, it is merely necessary to alter the vertical disposition of gate 86 to pennit passage of the work product and still provide optimum radiation shielding for that product size.
VArious modifications and alternative implementations will now occur to those versed in the art and it is not intended to limit the invention by what has been particularly shown and described.
What is claimed is:
1. An adjustable gas barrier adapted for disposition between adjacent sections of a muffle and operative to isolate the gas atmospheres of adjacent muffle zones, said barrier comprismg:
first and second plates in parallel-spaced relation to each other;
third and fourth plates disposed between said first and second plates in parallel-spaced relation thereto and being substantially coextensive therewith;
a flange secured to the periphery of said plates and enclos ing the space between said plates;
a pair of exhaust tubes connected to said flange and each communicating with a respective space between said first and third plates and said second and fourth plates and each beingadapted for coupling to exhaust means;
an adjustable gate assembly disposed between said third and fourth plates and operative to controllably introduce gas into said muffle, said gate including:
a gas tube connected to confronting portions of said third and fourth plates adjacent said muffle and operative to introduce a curtain of gas therein; and
a member slidably disposed between said third and fourth plates and adjustable to selected positions within said muffle and operative to introduce a'curtain of gas into said muffle,
said adjustable gate assembly providing precisely controlled isolation of respective gas atmospheres in adjacent muffle zones and selective accommodation of products of different heights being processed in said muffle.
2. A barrier according to claim 1 wherein said member is of a width slightly less than the width of said muffle to permit slidable adjustment therein, said member having an orifice along substantially the width thereof, a pipe attached to said member and being disposed between said third and fourth plates and operative to support said member at selected positions within said muffle and to introduce gas therein.
6. A barrier according to claim 1 including exhaust means coupled to said pair of exhaust tubes for removing gases from said barrier.
7. An adjustable heat barrier adapted for disposition between adjacent sections of a muffle and operative to isolate the temperatures of adjacent muffle zones, said barrier comprising:
a plurality of plates in parallel-spaced relation to each other defining first and second annular chambers each communicative .with arespective one of said adjacent muffle zones;
exhaust means connected to each of said first and second annular chambers and operative to withdraw the heated atmosphere within each of said adjacent muffle zones to maintain a predetermined temperature profile therebetween; and
an adjustable gate disposed between said first and second annular chambers, said gate including:
a generally rectangular metal-plate substantially coextensive with the cross-sectional area of said muffle and and adapted to be positioned at predetermined heights within said muffle to provide for each height, efficient radiation shielding;
a tube attached to and coextensive with the upper edge of said plate and adapted to contain cooling fluid flowing therein to conduct heat from said plate, said tube being formed with first and second upstanding portions at each end thereof for supporting said plate at predetennined heights within said mufile and providing a passage for flow of cooling fluid through said tube.