US3615082A

US3615082A - Furnace muffle

Info

Publication number: US3615082A
Application number: US854648A
Authority: US
Inventors: Jacob Howard Beck
Original assignee: BTU Engineering Corp
Current assignee: BTU Engineering Corp
Priority date: 1969-09-02
Filing date: 1969-09-02
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26
Also published as: FR2060770A5; NL7012976A; DE2042772B2; DE2042772C3; DE2042772A1; GB1249770A

Abstract

A FURNACE MUFFLE OF UNIQUE WELDED CONSTRUCTION AND ESPECIALLY ADAPTED FOR OPERATION AT EXTREME OPERATING TEMPERATURES. THE MUFFLE IS FORMED AS AN ELONGATED TUBULAR MEMBER HAVING ONE OR MORE GAS PIPES INTEGRALLY FORMED THEREIN TO INTRODUCE A GASEOUS ATMOSPHERE WITHIN THE MUFFLE. THE ENTIRE MUFFLE STRUCTURE INCLUDING THE GAS PIPES IS FORMED OF A METAL WHICH HAS EXPERIENCED THE SAME WORK HISTORY DURING FABRICATION, AND INDIVIDUAL ELEMENTS OF THE MUFFLE STRUCTURE ARE WELDED IN A UNIQUE MANNER TO PROVIDE A UNITARY STRUCTURE ARE WELDED IN A UNIQUE MANNER TO PROVIDE TION AT ELEVATED TEMPERATURES.

Description

Oct. 26, 1971 J. H. BECK 3,615,082

' FURNACE MUFFLE Filed Sept. 2, 1969 Fig. 4.

JACOB HOWARD BECK INVIN'l'( )R United States Patent Olhce 3,6I5,082 Patented Oct. 26, 1971 3,615,082 FURNACE MUFFLE Jacob Howard Beck, Waban, Mass., assignor to BTU Engineering Corporation, Waltham, Mass. Filed Sept. 2, 1969, Ser. No. 854,648 Int. Cl. F27b 5 04 U.S. Cl. 263-41 5 Claims ABSTRACT OF THE DISCLOSURE A furnace muiiie of unique welded construction and especially adapted for operation at extreme operating temperatures. The muflie is formed as an elongated tubular member having one or more gas pipes integrally formed therein to introduce a gaseous atmosphere within the muffle. The entire mui'lie structure including the gas pipes is formed of a metal which has experienced the same work history during fabrication, and individual elements of the mutiie structure are welded in a unique manner to provide a unitary muiile construction capable of superior operation at elevated temperatures.

FIELD OF THE INVENTION This invention relates to furnace muiiies and more particularly to a welded muflie construction capable of providing superior operation at extreme elevated temperatures.

BACKGROUND OF THE INVENTION Moving conveyor mufiie furnaces are widely employed in the heat processing of components and devices such as thick lilm circuits. The furnace muffle is formed as an elongated tubular member having a bottom wall which serves as a hearth for support of a moving conveyor thereon for transport of the work load through the furnace. The muflie may be divided into zones, each of which can be individually controlled to maintain separate temperatures and each of which may contain a different gaseous environment according to the particular heat processing being performed. In order to maintain uniform temperature within the muie and in order to provide a sealed gaseous atmosphere, the mufe is formed as a closed tu'bular member and it is important that the integrity of the mufiie structure be maintained over a wide range of operating temperatures without distortion in order not to detract from proper furnace operation.

The gaseous environment within the mufe is often provided by one or more gas pipes disposed along the length of the mutile and welded to the interior mui-lle wall. Such gas pipes, however, usually have different metallurgical characteristics and work history than the metal forming the muie. As a result, the gas pipe has different thermal expansion characteristics than that of the mul'lie, as a consequence of which the pipe can physically distort during furnace operation. In an attempt to avoid such distortion, conventional furnace mutiles have been constructed in which the gas pipe is supported within the muffle by means of brackets attached to the mufe wall. This latter approach, while lessening the problem of distortion to some extent, suffers the disadvantage of additional support structures within the mutlie, which add to the cost of muffle fabrication, as well as giving rise to possible sources of contamination with the mufie at elevated temperatures.

SUMMARY OF THE INVENTION In accordance with the present invention a furnace muffle of improved construction is provided which is especially adapted for superior operation at elevated temperatures. All elements of the muie structure are formed of metal having identical metallurgical characteristics and having the same cold and hot metal working history, such that a mulfle so constructed exhibits uniform thermal expansion and stress relieving over the operating temperature range. Typically, the muie is formed of first and second elongated metal members of generally U-shaped cross section, arranged to -be welded along their confronting edges to provide a closed tubular muiiie structure. The confronting edges of the mufe sections are of predetermined beveled configuration and a gas pipe formed from a metal having the same work history as the sections of the mufe is disposed between the beveled confronting edges of the mufiie sections. A portion of the gas pipes serves as a source of welding material and permits a mechanically strong unitary mutiie to be provided capable of operation at extreme elevated temperatures without distortion.

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. l is a cutaway pictorial View of a furnace mufie constructed according to the invention;

FIG. 2 is an elevation view, partly in section, of the unique mutlie construction prior to welding;

FIG, 3 is an elevation view, partly in section, of the muflle structure after welding; and

FIG. 4 is a cutaway pictorial view of an alternative ernbodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION A furnace muliie of unique unitary construction and adapted for superior operation at elevated temperatures is illustrated in FIG. l. The muflie 10 is of elongated tubular configuration and includes a first muflie section 12 of generally channel-shaped cross section intimately joined to a second mutlie section 14 of generally U-shaped configuration. First and second gas pipes 16 and 18 are respectively joined to

muflie sections

12 and 14 at their respective junctures. Gas pipes 16 and 18 each extend along the length of a respective side wall of muflie 10 and include a plurality of openings 20 therein spaced along the length of the gas pipes to transmit gas introduced within pipes 16 and 18 into the interior of the muliie 10. A predetermined gaseous environment can thus be maintained within the interior of the muie.

Muffle section 12 includes a bottom wall 22 which serves as a hearth for the support of a movable conveyor belt 24 thereon. Conveyor belt 24 is typically formed of woven wire or chain link construction and is transported through the interior of muflie 10 by a suitable transport mechanism (not shown). A work load is thereby transportable through the muiie by means of moving conveyor 24. Muflie section 12 also includes

side walls

13 and 15 formed at right angles to bottom wall 22 and joined to section 14 and respective gas pipes 16 and 18 by the unique continuous welds 17. The muflie section 14 is of a smoothly curved configuration and provides the arched roof of muflie 10.

The muie elements described hereinabove are continuously and uniquely welded to provide the unitary mufiie structure illustrated in FIG. 1 having a continuous weld 17 along each side wall thereof. The weld 17 is of large area and has substantially the same characteristics as the material forming the muie elements. As a result, a muie formed according to the invention, in a manner to be described, is operative over a wide temperature range and exhibits uniform stress relief and thermal expansion characteristics and maintains structural integrity even at extreme operating temperatures. It is a particular feature of the invention that all elements of the muiie are formed of metal which has experienced the same cold and hot Work history su'ch that the entire unitary mutiie structure exhibits the same thermal expansion characteristics and experiences substantially uniform stress relief over an operating temperature range. The muiie is formed of a high temperature alloy such as Inconel, the metal preferably being cross rolled to provide impro-ved stress-relieved characteristics. Gas pipes 16 and 18 are formed in a configuration operative to assist in the achievement of a mechanically strong weld between the

muie sections

12 and 14 and gas pipe contained therebetween.

The confronting edges of

muliie sections

12 and 14 and the portion of respective gas pipes 16 and 18 disposed therebetween and intimately bonded thereto are adapted according to the invention to provide a superior weld as a result of which a unique unitary mufiie structure is provided which is capable of operation and which maintains its structural integrity over a Wide range of operating temperatures.

Construction of the unitary muliie structure is accomplished by a unique welding technique which provides an extremely strong large area weld between the elements of the muiie being fabricated. Referring to FIG. 2, there is shown the confronting edges of

mutlie sections

12 and 14 with gas pipe 16 disposed therebetween, prior to welding of these elements into a unitary structure. Gas pipe 18 is identically fabricated on the other side wall of mufie 10. A bevel 40 is formed on the upper edge of se'ction 12 and a similar bevel 42 is formed on the edge of muflie section 14. The bevels extend across approximately half the Iwall thickness of

respective muiiie sections

12 and 14 and are formed on the side of the muflie sections opposite to the location of gas pipe 16.

The confronting edges of

muie sections

12 and 14 also include non-beveled

portions

41 and 43 which extend across the other half of the wall thickness of the muiiie sections and are formed substantially orthogonal to the plane of the mule side walls on which they are disposed. A V-shaped region is defined by the confronting beveled edges along the length of

muflie sections

12 and 14 and this region is effective to permit the formation of a deep large area weld, which, in accordance with the invention, provides the improved unitary muffle structure.

As discussed hereinabove, the gas pipes 16 and 18 are formed into the desired shape from a metal having the same work history as the metal employed to fabricate sections 12 and '14 of the furnace muiiie. As illustrated in FIG. 2, gas pipe 16 includes a tubular portion 44, and a ange portion 46 which is disposed between the confronting

non-beveled edges

41 and 43 of

respectice muiiie sections

12 and 14. The ange portion 46 extends into the V-shaped region defined by the beveled edges `40 and 42 and may extend beyond the plane of the substantially coplanar walls of

muiiie sections

12 and 14.

As a particular feature of the invention, the flange portion 46 of the gas pipes serves as a source of material for forming the unitary welded muiiie structure. This ange portion is of the same metal and has the same Work history as

muie sections

12 and 14, and the weld formed according to the invention has essentially the same metallurgical characteristics as the elements forming the muiiie. A mule thus constructed is capable of operation at extreme elevated temperatures without degradation or distortion of the weldments.

The confronting surfaces of

muflie sections

12 and 14 and the associated gas pipe are continuously Welded along the length of the muie typilly by Heliarc welding to form the welded structure depicted in FIG. 3. As discussed hereinabove, the metal of flange portion 46 serves as a source of welding material which flows into the V- shaped region dened by the

bevel edges

40 and 42 of

mu'lie sections

12 and 14, such that a relatively deep and large area weld of high physical strength is provided. The

surfaces

41 and 43 are also welded to the confronting portions of flange portion 56. The boundary of the weld is depicted in FIG. `3 by the dotted generally hemispherical line 48. The metal employed in muiiie sections 12 and A14 and the associated gas pipe is identical and has the same work history, and exhibits substantially uniform stress relieving as temperature varies. The gas pipes and associated muflie sections expand and contract by the same amount with temperature variation and the welds have less tendency to deteriorate under temperature cycling which may be experienced in operation and at high elevated temperatures at which the furnace employing the muffle operates. The muie constructed according to the invention therefor maintains its structural integrity even at extreme operating temperatures, with the result that reliable and controllable furnace operation is maintained.

An alternative embodiment of a muffle constructed according to the invention is illustrated in FIG. 4 and includes an elongated tubular structure 50 having an arched roof 52 and a substantially flat coplanar bottom. wall 54 which serves as the muiiie hearth for support of a movable conveyer belt 56 thereon. A generally V-shaped slot 5S is formed in bottom wall 54 of the muflie and extends longitudinally along the length thereof. A gas pipe 60, formed of a metal having the same metallurgical characteristics and work history as the metal forming the muiiie itself is disposed within the V-shaped slot 58 and is welded, in accordance with the invention, to the lowermost confronting edges of the slot tol provide the superior unitary muflie structure. The uppermost surface of gas pipe 60 lies substantially within or below the plane of the mufe hearth and does not interfere with movement of conveyer belt 56 through the muffle. With the gas pipe 60 disposed below conveyer 56, the mufe is free of protuberances, and gas pipe `60 is protected vagainst damage and undue wear. The gas provides, via

openings 62 provided along the length thereof, a fresh supply of gaseous atmosphere which is directed up through the conveyer belt and which iiows past the work product carried by the conveyer. As the gas is heated, it rises to the roof of the muflie away from the work product and can exit at the ends of the furnace.

lIn the embodiment of PEG. 4, the unitary muffle structure is formed with a single weld between the confronting edges of the mufe wall in V-shaped slot 58 and the associated gas pipe 60. As described hereinabove, continuous welding is employed to form a large area extremely strong weld. It will be appreciated that, prior to Welding, the confronting edges of the

inclined walls

64 and 66, deiine a V-shaped region in which is disposed the ange portion of gas pipe 60. A bevel need not be formed on the confronting edges of the muiiie wall in this instance since such a bevel is eifectively provided by the inclined disposition of the confronting muffle walls. As described hereinabove, the gas pipe 60 and the muiiie 50 are of a metal having the same metallurgical characteristics and work history, and the large area deep weld formed according to the invention provides a unitary muffle structure capable of operation at extreme elevated temperatures without degradation or distortion.

What is claimed is:

1. A furnace muflie comprising:

a first elongated member of generally U-shaped crosssection having first and second elongated parallel edges of predetermined beveled configuration adapted to provide a mechanically strong large area Weld;

a second elongated member of generally U-shaped cross-section having iirst and second elongated parallel edges of the same predetermined beveled configuration, the first and second edges of said second member confronting the first and second edges of said iirst member to form la tubular muffle structure, the beveled edges of said confronting members defining a groove in each outer side wall of said confronting members;

first and second gas pipes, each having a tubular portion and an outwardly extending flange portion, and each disposed on respective opposite sides of said muie structure with said tubular portion within said confronting members and with said flange portion between and in intimate contact with said confronting edges and disposed in said groove;

said flange portion and confronting edges being continuously welded along the length thereof, said flange portion serving as a source of welding metal to provide -a mechanically strong large area weld in the region of said predetermined beveled configuration and along the length of said mnie structure; and said irst and second elongated members and first and second gas pipes each being formed of an identical i metal having the same metallurgical characteristics and Work history such that said members and gas pipes exhibit substantially uniform thermal expansion and stress relieving.

2. A furnace muiiie according to claim 1 wherein said first and second members each include a bevel found on the outer elongated parallel edges thereof, the bevels of the confronting members defining a V-shaped groove in the outer side Wall of said confronting members, and said ange portion being disposed in said V-shaped groove.

3. A furnace muie according to claim 1 wherein said predetermined beveled configuration includes a beveled portion formed across approximately half the wall thickness of its elongated member, and a non-beveled portion formed across the other half of the wall thickness of said member in a direction orthogonal to the plane of the muffle wall, the bevels of said confronting members defining a V-shaped groove in the outer side wall of said confronting members, and said ange portion being disposed in said V-shaped groove.

4. A furnace muiiie comprising:

an elongated member of closed cross-sectional configuration having first and second confronting elongated parallel edges of predetermined beveled configuration defining a V-shaped groove in the outer wall of said member and adapted to provide a mechani- 40 cally strong large area weld; a gas pipe having a tubular portion and an outwardly extending ange portion disposed with said tubular portion within said closed conguration and with said ange portion within said V-shaped groove between and in intimate contact with said confronting edges;

said elongated member and gas pipe each being formed of an identical metal having the same metallurgical characteristics and work history such that said member and gas pipe exhibit substantially uniform ther- -mal expansion and stress relieving; and

said flange portion and confronting edges being continuously welded along the length thereof, said flange portion serving as a source of Welding metal to provide a mechanically strong large area weld in the region of said predetermined beveled configuration and along the length of said muie structure.

5. A method of fabricating a unitary elongated furnace muifle comprising the steps of:

forming a iirst and a second elongated section of generally U-shaped cross-section from a metal having predetermined metallurgical characteristics and Work history;

forming first and second rectangular sheets of a metal having the same characteristics and work history as said elongated sections into respective pipes each having a tubular portion and a flange portion;

forming a bevel on the outer elongated edges of said 'first yand second sections;

placing the flange portion of each of said pipes between and in contact with said beveled elongated edges ,with said flange portion disposed in the V-shaped groove defined by said beveled edges; and

heating said flange portions and adjacent portions of said confronting sections to cause formation of a large area mechanically strong weld using the metal of said flange portion as a source of Welding metal.

References Cited UNITED STATES PATENTS 3,410,544 l1/1968 Beck 263-41 JOHiN I. CAMBY, Primary Examiner U .S. Cl. X.R. 29-483 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,615, O82 Dated October 26+ 1971 Invencor(s) Jacob Howard Beck It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 49, "tice" should be tive Column 4, line 35, after "gas" insert pipe.

Column 5, line 20 (claim 2), "found" should be -formed Signed and sealed this 29th day of February 1972.

(SEAL) Attest:

ROBERT GOTTSGHALR EDNAHD I-LFLETCIIEII, JH.

Commissioner' of' Patents Atbestnn; Officer* RM P04050 (1059) uscoMM-Dc soave-p59 fr U S GOVENMENY PRINTING OFFICE |969 U-365-33l