Modular Heater Furnace

Abstract

A heat treating furnace having distinct easily replaceable modular heating elements disposed in an effectively continuous array along the furnace for efficient high temperature operation. Each heating element is in the form of a sinuous ribbon of high temperature metal and is supported within the furnace in a manner to permit easy removability without furnace disassembly.

Description

FIELD OF THE INVENTION

This invention relates to heat treating furnaces and more particularly to a furnace having an array of easily removable modular heating elements disposed along the active length of the furnace.

BACKGROUND OF THE INVENTION

In precision furnaces employed in the heat processing of materials and products, it is often necessary to replace the heating elements therein which can periodically fail by reason of the extremely high temperatures at which such furnaces operate. In many furnaces of conventional construction, the design of the heating elements and their disposition within the furnace is such to require dismantling of the furnace structure in order to gain access to the heating elements for repair or replacement. Such disassembly requires considerable time and labor and results in a decrease in the time the furnace is operative. In addition, in certain operating environments disassembly of the furnace to gain access to the heating elements is completely impractical. For example, where a furnace contains a contaminating environment, disassembly of the furnace structure can cause release of contaminants into the surrounding environment, and decontaminating procedures must be undertaken before any such disassembly is possible. Various furnaces have been proposed in which heating elements are removably disposed within the furnace. However, such furnaces have generally been of rather simple construction unsuitable for many modern heat processes and have usually been operative at only relatively low temperatures.

SUMMARY OF THE INVENTION

In accordance with the present invention, a furnace is provided in which an array of easily replaceable modular heating elements is disposed therein to provide efficient high temperature operation and which can be removed without material affect on the strength and integrity of the furnace. Each heating element includes a ribbon of high temperature metal such as molybdenum formed in a folded or sinuous configuration and supported by a collar of electrically and thermally insulative material. The heating elements are each disposed within a furnace chamber by means of the mounting collar cooperative with a receptacle portion provided in the roof of the furnace, and are readily removable from the furnace without requiring furnace disassembly and without affecting the structural strength of the furnace. The roof of the furnace chamber can be supported along its length by a plurality of piers each constructed to provide intended structural support without detracting from the thermal transmission between respective heating elements. Electrical connection to the array of elements is provided externally of the furnace by means of bus bars or other suitable connecting means. Preferably, each heating element is disposed within the chamber with the metal ribbon angularly disposed such that a major portion of the heating surface thereof confronts the chamber for efficient heating radiation therein.

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 cutaway pictorial view of a furnace constructed according to the invention;

FIG. 2 is a pictorial view of a modular heating element embodying the present invention;

FIG. 3 is a cutaway elevation view of the modular heating element of FIG. 2; and

FIG. 4 is a top view of the modular heating element of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

A heat treating furnace for providing efficient high temperature operation and having modular and easily removable and replaceable heating elements according to the invention is illustrated in FIG. 1. An elongated furnace chamber 10 is defined by thermal insulation usually in the form of refractory brick 12. The brick work is contained within a sheet metal housing 14 and includes a roof portion 16 supported along the length thereof by a plurality of piers 18 also formed of refractory material and disposed in spaced relationship along each side of the furnace chamber 10. A channel shaped hearth plate 20, also of refractory material, is supported on the floor 22 of the furnace chamber by members 24 and extends along the active length of the chamber 10. A work product 26 is supported on hearth 20 and is conveyed through the furnace by a suitable conveyor mechanism, such as a push rod assembly operative to incrementally advance the work product through the furnace. The conveyor mechanism could alternatively be embodied within the furnace structure itself and can be for example of the movable hearth type wherein the hearth is disposed within the floor of the furnace chamber and is supported by a cooperative beam structure to provide cyclic movement of the hearth to convey a work product therealong.

An array of modular and easily removable heaters 28 is provided along each side of furnace chamber 10. Each heater is supported by a collar 30 disposed within an opening provided in roof portion 16, with the active element 32 disposed within the chamber 10 between an adjacent pair of piers 18. The electrical leads 34 of each heater 28 extend from the roof of the furnace and, in operation, are connected to bus bars or other suitable means to which electrical energy is applied for activation.

The piers 18 supporting roof portion 16 of the furnace are each of tapered configuration having a wider upper end confronting the furnace roof and a narrower lower end confronting the floor 22 of the furnace chamber, the taper being dimensioned and configured to permit adjacent ribbon elements 32 to be in thermal radiating relationship with each other. The physically distinct heating elements within an array along a side of the furnace chamber, as well as each array of elements are thermally communicative to achieve an effectively continuous source of heat within the chamber and having a uniform heating capacity along the furnace. Heating efficiency is further enhanced by the angular disposition of ribbon elements 32 within furnace chamber 10, as will be further described hereinbelow, to permit radiation into the chamber from a plurality of heating surfaces of element 32.

It is a particular feature of the invention that the heaters 28 are each easily removable from the furnace without affect on the furnace strength and without furnace disassembly. The roof portion 16 is supported along its length by piers 18, and removal of one or more heaters 28 does not materially detract from the strength of the roof structure. To remove a heater 28, it is only necessary to disconnect the leads 34 from the associated electrical bus bar and to lift the heater out of its mounting opening in roof 16. A new heater is replaced just as readily by insertion through the mounting opening and connection of the leads thereof to an electrical energy source. It should be noted that since physically distinct heaters are employed in the novel furnace, failure of a single heating element will not cause degradation of the overall heating capacity of the heater array, as can occur in a furnace having a physically continuous heat source.

The heater 28 is illustrated in greater detail in FIGS. 2 through 4. Referring to these figures, a ribbon 40 of high temperature metal such as molybdenum is formed in a sinuous shape as illustrated and is supported at the upper end thereof by a collar 30 of electrically and thermally insulative material such as a high temperature ceramic. The collar 30 is of generally cylindrical configuration and has a portion of the ribbon 40 affixed thereto by means of a plurality of fasteners 42. The portions of ribbon 40 attached to collar 30 are sandwiched between first and second metal straps 44 and 46 which extend from below the lower end of collar 30 to he upper extremities of ribbon 40. The inner straps 44 each have a lower end 45 bent inward on the bottom end of collar 30 for support. The upper ends 48 of straps 44 and 46 and the interposed portion of ribbon 40 can be welded to provide a unitary electrical lead structure. Fasteners 49 can also be provided to further secure the electrical leads. Typically, an opening 50 is provided through each lead for electrical connection to associated bus bars or other electrical connection means.

The interior loop 52 of ribbon 40 is supported by a metal strap 54 which extends beneath this loop and along respective opposite sides of collar 30 in a position approximately orthogonal to the position of the respective straps 44, the upper ends 56 of strap 54 being bent inward on the top of collar 30 within a channel 58 provided thereacross to mechanically secure strap 54 in position. It is seen that the straps 44 and strap 54 extend outwardly by a small amount from the surface of collar 30. Upon installation of the heater within the mounting opening in roof portion 16, the metal straps are in contact with the surrounding refractory material of the furnace roof, rather than the refractory material of collar 30, and serve to prevent fusion of the mounting collar 30 to the furnace roof, which can occur at extremely high operating temperatures.

In the illustrated embodiment, each heater 28 is supported within an associated opening of the furnace roof 16 by flanges 60 provided at the upper end of the heater and extending substantially orthogonally outward from the axis of the electrical leads 34. The flanges 60 are supported on the upper surface 62 of the furnace structure for suspension of the respective heaters within furnace chamber 10. It will be appreciated that the heaters can be suspended within the furnace by a variety of mounting means which may include a keying element for predetermined angular disposition thereof within the furnace chamber.

It is a particular feature of the invention that each heater 28 is disposed within the furnace chamber with the heating element 32 angularly disposed, as depicted in FIG. 1, such that a major portion of the heated surfaces of element 32 confront the furnace chamber for efficient heat radiation. If the heaters were arranged such that the elements 32 were disposed with their edges facing across the furnace chamber 10, radiation would occur primarily from these edge surfaces. The heat being radiated from the broader surfaces of the ribbon elements would not be efficiently employed, as the adjacent heating elements would be radiating toward one another. Similarly, if the heaters were disposed with the broad surfaces of elements 32 facing orthogonally across the furnace chamber, radiation from the broader surfaces of the sinuous ribbon elements would be inefficient as the confronting heated surfaces of each ribbon element would be radiating toward one another. By angular disposition of the heating elements within the furnace chamber, the broad surfaces of the ribbon elements confront the furnace chamber to a greater extent than other dispositions, with the result of achieving a more optimum heat efficiency.

It will be evident that the invention can be embodied in a variety of furnace structures to suit particular heat processing requirements and that various modifications and alternative implementations of the invention will occur to those versed in the art. Accordingly, it is not intended to limit the invention by what has been particularly shown and described except as indicated in the appended claims.

Claims

What is claimed is:

1. A heat treating furnace comprising:

an elongated furnace of insulative material defining a furnace chamber and having a hearth in said chamber along which a work product is conveyed, a roof, and a plurality of piers spaced along the length of said chamber on respective opposite sides thereof for support of said roof;

an array of modular easily replaceable heating elements disposed in said furnace chamber along the active length thereof, each heating element being disposed between adjacent ones of said piers;

each of said heating elements including:

a sinuous ribbon of high temperature metal adapted to be electrically heated to an operating temperature and for disposition in said furnace chamber;

a mounting collar of electrically and thermally insulative material supporting said ribbon and cooperative with a receptacle portion of said roof for maintaining said ribbon in said furnace chamber for radiation into said chamber; and

first and second leads integrally formed with said sinuous ribbon and disposed outside of said chamber and adapted for connection to a source of electrical energy;

each of said piers being tapered from said roof to said hearth to permit radiation by said heating elements to adjacent ones to provide an effectively continuous array.

2. A heat treating furnace according to claim 1 wherein said sinuous ribbon is supported on said mounting collar by metal straps extending along the length of said collar, said straps being in contact with the receptacle portion of said furnace roof to maintain said receptacle portion and the confronting surface of said mounting collar in spaced relationship.

3. A heat treating furnace according to claim 1 wherein each of said heating elements is disposed with said sinuous ribbon angularly disposed within said furnace chamber to permit efficient radiation from the broad surfaces thereof into said chamber.

4. A heat treating furnace according to claim 1 wherein each of said heating elements further includes:

at least one elongated metal strap secured along the portions of said sinuous ribbon supported by said mounting collar and along said integrally formed leads and rigidly attached to said ribbon and to said mounting collar to provide a unitary structure.

5. A heat treating furnace according to claim 4 wherein said sinuous ribbon is of recurvate configuration having two outer loops disposed away from said mounting collar and an inner loop confronting said mounting collar; and

a metal strap supporting said inner loop and secured to said mounting collar.

6. A heat treating furnace according to claim 1 wherein each of said heating elements includes:

at least one metal strap in contact with and rigidly attached to the portions of said sinuous ribbon supported by said mounting collar and to said integrally formed leads, said metal straps being operative to provide structural support for said heating element and efficient electrical leads.

7. A heat treating furnace comprising an elongated furnace of insulative material defining a furnace chamber and having a hearth in said chamber along which a work product is conveyed, and a roof;

an array of modular easily replaceable heating elements disposed in said furnace chamber along the active length thereof;

each of said heating elements including:

an elongated mounting collar of electrically and thermally insulative material;

a sinuous ribbon of high temperature metal adapted to be electrically heated to an operating temperature and axially extending from and supported by said mounting collar; and

first and second leads integrally formed with said sinuous ribbon and extending from said collar in a position opposite to that of said sinuous ribbon;

said mounting collar being cooperative with a receptacle portion of said roof for maintaining said ribbon in said furnace chamber for radiation therein, said first and second leads being in a position, with said sinuous ribbon in said furnace chamber, outside of said chamber and adapted for connection to a source of electrical energy;

a plurality of piers spaced along the length of said chamber on respective opposite sides thereof for support of said roof, each adjacent pair of piers being disposed on respective sides of a heating element;

each of said piers being tapered from a broader portion at said roof to a narrower portion at said hearth, with said taper being such to permit thermal radiation between adjacent ones of said heating elements and provide an effectively continuous array.

8. A heat treating furnace according to claim 7 wherein said sinuous ribbon includes first and second portions longitudinally confronting said elongated mounting collar;

and wherein each of said heating elements further includes:

at least one elongated metal strap confronting each portion of said sinuous ribbon confronting said mounting collar and also confronting said first and second leads; and

means for rigidly securing each of said elongated straps to the associated portion of said ribbon and leads and to said mounting collar to provide a unitary structure.

9. A heat treating furnace comprising an elongated furnace of insulative material defining a furnace chamber and having a hearth in said chamber along which a work product is conveyed, and a roof;

an array of modular easily replaceable heating elements disposed in said furnace chamber along the active length thereof;

each of said heating elements including:

an elongated mounting collar of electrically and thermally insulative material;

a sinuous ribbon of high temperature metal adapted to be electrically heated to an operating temperature and axially extending from and supported by said mounting collar;

said sinuous ribbon having a plurality of substantially parallel flat surfaces angularly disposed within and confronting said furnace chamber to permit efficient radiation from said flat surfaces into said chamber; and

first and second leads integrally formed with said sinuous ribbon and extending from said collar in a position opposite to that of said sinuous ribbon; said mounting collar being cooperative with a receptacle portion of said roof for maintaining said ribbon in said furnace chamber for radiation therein, said first and second leads being in a position, with said sinuous ribbon in said furnace chamber, outside of said chamber and adapted for connection to a source of electrical energy;

a plurality of supports spaced along the length of said chamber on respective opposite sides thereof for support of said roof, said supports being configured to permit thermal radiation between adjacent ones of said heating elements and provide an effectively continuous heater array.