US2081990A - Furnace - Google Patents

Description

Patented June l, 1937 UNITED STATES 2,081,990 FURNACE Josef Eberwein, Wilkinsburg, Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January s1, msaserial No.' 4,286

8 Claims.

vMy inventionrelates to furnaces and particularly to heat treating furnaces.

An object of my invention is to provide a heat treating furnace that shall embody means to insure uniform-heating of a charge placed therein.

Another object of my invention is to provide a heat treating furnace that shall embody means to insure a, minimum heat loss from a charge to its support.

Another object voit' my invention is to provide a heat treating furnace that shall embody means to reduce the time of heating up a charge placed therein. Y

Other objects of my invention will either be l5 pointed out specifically in the course of a description of several forms of furnaces embodying my invention or will'be apparent from such descrip- `tion. In practicing my invention, I provide, in combination with a furnace casing including a base and superposed walls thereover constituting' a casing, an extended heating means, either fuel or electric, and particularly one or more heat-insulating pads having high thermal reluctance spaced from a refractory supporting base by 'a skelton frame having a small heat conducting area.

In the single 'sheet of drawing, Figure 1 is a view in vertical section through 30 one form of device embodying myinvention;

Fig. 2 is a view in vertical section through a second form of furnace embodying my invention;

and

4 Fig. 3 is a view on an enlarged scale of a part of a. furnace particularly enbodying Ymy invention.

I Wish it to be understood that the showing of the furnace structures made herein is schematic or general only, insofar as it relates to details other than those comprehended within my invention, and that while specific embodiments of furnaces are shown'and described, my invention is not limited to these, but is applicable to any kind of furnace wherein material is to be heat treated while resting upon a supporting base. 'I 'hus the source of heat may be hot gases, a gas flame or an electric resistance heater, and the furnace structure may be of circular shape in cross-section or of rectangular shape, and the furnace in general may either be of thel vertical or of the horizontal type.

In the heat treating of material, be it of annular material, suchas coils of wires stacked one upon another, or of sheets of metal which may be laid 55 ilatwise one upon another or which may be stood on edge on a support, it has been found vdifficult to obtain a uniform temperature extending vertically of the mass of material to be heat treated. Particularly is this true in the case of the so-called bell type furnace, in which a substantially xed refractory base structure may be used and in which the bell-like cover carrying the electric heating elementsis movable, as by a crane, so that, as soon as one charge, which may becovered with a thin-sheet-metal hood, has been treated to the desired temperature, the furnace casing or cover may be removed therefrom and immediately placed over a cold charge located on another base. It is obvious lthat if the material to be heat treated rests directly on the base, a large amount of heat will flow downwardly into the base from the material as its temperature is raised, and I have found that is possible to overcome this excessive loss of heat downwardly by the use of aV skeleton frame resting upon the base and in turn supporting the material tobe heated.

Referring rst to Fig. 1 of the'drawing, I have there illustrated a furnace structure II shown as comprising a refractory base I3 resting upon a metal base plate I5, which in turn is supported as by structural metal members I1 of any 'desired kind. However, as. my invention is not limited to fixed bases, the base I3 may be provided with wheels or rollers to permit of its being moved from one place to another,l if desired. 'I'he base I3 is provided with a, raised central portion I9 and with a lower outer annular portion 2| for a purpose to be hereinafter set forth.

A bell-shaped cover 23 includes an outer metal casing 25, which may be of substantially circular. shape in contour in the case of a circular furnace,

lor which may be of rectangular or square shape f as may be desired.` The casing structure 25 has located therein a refractory lining which is here designated generally by the numeral 21, and which is to be understood as being built up either as a monolith or of suitable bricks or blocks of high temperature resisting and heat-insulating material iii a manner well known in the art. This lining 21 is adapted to be held in the shell 25 by metal structural members 29 suitably secured to the lower edge of casing 25. Means for lifting the entire casing may be constituted by one or more horizontally extending cross bars 3l and one or more lifting lugs 33. These details are shown for purposes of completely illustrating a furnace structure, but form no part of my invention.

Heating means for the purpose above described is provided in the form of a plurality lof resistor elements 35, 31, 39 and 4I, which may be of the kind disclosed and claimed in Patent y No. 1,490,732' to'T. F. Callaghan. It is to be noted particularly lthat any desired distribution of heat may be obtained within the furnace chamber 43 by suitable design of the resistor elements 354t0 4I, inclusive, which are to be considered as extending entirely around the inner periphery of the wall enclosing the furnace chamber in a manner well known in the prior art.

Upon the raised central portion I9 of the base, I locate a skeleton frame structure 45 which includes, in addition to' an upper and a lower thin metal y plate x41 and 49, vertically extending perforated webs 5I to provide a structure having suflcient strength to support relatively heavy loa-ds,'while at the same time having acminimum heat storage capacity and a relatively high thermal reluctance against flow of heat vertically therethrough. Immediately above the upper metal plate 4l, I provide a layer or pad 53 of substantially so-lid heat-insulating material having a relatively high thermal reluctance and having sufficient mechanical strength to support theload of material superposed thereon to be heat treated in the furnace. For this reason, I preferably make the pad 53 of substantially solid heatinsulating material.

While the use of one skeleton frame structure and one pad of heat-insulating material thereabove may be sufcient in some cases, I have found it desirable, under certain conditions, to provide two such sets of elements, and, as shown in Fig. 1 of the drawing, I may provide a. second skeleton frame 54 including a lower plate 55, an upper plate 51, and a plurality of perforated webs 59 therebetween of the same general designv as was hereinbeforevdescribed for the lower skeleton frame 45. A second pad 6I of heat insulating material having a high thermal reluctance is located above the upper plate 51, and'a metal plate 63 rests upon the pad 6I to directly support a mass of annular material 65 which may be, for instance, coils of wire to be heat treated in the furnace.

As it may happen that moisture may have condensed on the untreated material 65, which moisture may deleteriously aect the material of the pads 53 and, 6I, the plates of the skeleton frames may be provided with vertically extending flange portions 61 .integral therewith which may be secured together over substantially, but not entirely, the entire peripheral surface ,to substantially enclose the pads, a small opening being provided to permit the moisture to escape from the pads upon heating up thereof.

As it may be desirable to protect the material 65 against oxidation, as may be necessary for certain classes of material, I may provide a thin sheet metal hood 69 of substantially annular shape and of suflicient diameter to enclose the material 65 and to fit within the heating elements herein described. The hood 65 is further provided with a horizontally-extendingv flange II and a depending flange portion 'I3 thereon which lits into an oil or sand seal I5 provided at theA outer periphery of base plate I5. MeansV for introducing a neutral gas may comprise an inlet pipe 11 extending centrallyfupwardly through the base I3 and with its upper end located closely beneath the top of the domed hood 69, any gas entering the furnace chamber being caused to llow radially outwardly and then downwardly, .as indicated by the arrows `19, and through outlet pipes 8 I. It is to be understood that the furnace structure, either circular, square or rectangular in cross section, is such as to provide a substantially wardly into the base.

nace casing as resting upon the fiat annular por-4 tion 1I, I do not desire to be limited thereto, since the furnace casing may rest upon a support other than the base, but it is necessary that a substantially air-tight furnace chamber structure be provided.

In operation, a plurality of bases I3, either xed or movable, may be provided, and a lesser number'of bell-like furnace casings, so that as soon as a charge 65 locate'don a base has been heated to the desired temperature, the furnace casing with its associated heater may be removed and immediately located on a -coldcharge resting upon a second similar base.

When the hot furnace casing is placed uponor in operative relation to the base with its cold charge, a large amount of heat will be absorbed -by the cold base, as well'as by the cold charge,

and if no heating pad or pads and the associated skeleton frame or frames were provided, a relatively large amount of heat would flow ydown- The heating element is, of course, immediately energized as soon as the proper positioning of bell like furnace casing 23 on vthe base I3 has been effected, and if no heat insulating pads whatsoever are provided, a relatively large amount of heat from the charge While it is being heated would continue to ow downwardly into the refractory base particularly, for instance, if thecharge 65 `were to be located directly upon and in contact with plate 49, assuming this to have been provided to protect the refractory structure I3.

If, for instance, a thermo-couple is placed in theupper portion of charge 65 in order to determine when the charge has been heated to the desired temperature, it may happen that the temperature of the lower portion of the charge is much lower than that of the charge where the thermo-couple is located, if no heat insulating pad 0r pads and skeleton frame or frames are provided. 'Ihis loss of heat is deleterious for several reasons, one of which is, as has just been stated, that'the temperature of the material being heat treated is not. uniform from top to bottom of the mass, and secondly, that a much longer time is required' to insure that all of the material being heat treated has been raised to substantially the same desired temperature.

However, by the use of my invention including at least one skeleton frame structure having a high thermal reluctance to the ow of heat therethrough and at least one pad of heat insulating material, preferably solid, and also having high thermal reluctance, 1 have found it possible to heat a. mas's of material to a temperature on the order of 1500 F. with a maximum varia- `tion of temperature from top to bottom of the mass of approximately 5 F. This compares with a ligure of 100 F. or even more when no insulating pad or skeleton frame is used.

I attribute this result not only to the use of at least one pad and skeleton frame work, but also to the fact that a part of the heat means is located in substantially the same horizontal plane as are the skeleton frames which, as was hereinbefore stated, are of open construction and, as will be noted from Fig. 1 of the drawing, the lower one may be of greater vertical height than the upper one. Thus heating element 4I is located in substantially the same horizontal vplane as skeleton frame 45 .and will heat the same through the hood 69, or will heat not only the frame but also any air or gas located therein, to such an extent, that its temperature will be but slightly below that of the mass 65. The same comments hold good with regardto heating element 39, which is located in substantially horizontal alignment with the' upper skeleton frame, so that it and any air or gas located therein will be subjected to radiated heat to thereby cause the temperature thereof to almost equal that of the mass 65 being heat treated. I, therefore, provide at least one horizontally extending zone of high temperature located between the bottom of a mass of metal being heat treated `and a base, which is highly effective in preventtreated product.

Referring now to Fig. 2 of the drawing, I have there illustrated a modified form of furnace structure embodying my invention. A furnace 9| includes a refractory base 93 resting upon a base plate 95 which is supported by aplurality of structural beams 91 'Ihe base includes, in addition to the raised central portion 93, a lower outer peripheral portion 99, which latter may be provided with a sand or oil seal |0| in a manner well known in the structure art.

A skeleton frame .structure |03 rests upon the central annular portion 98, which latter may be covered b y a thin sheet metal member |05 to protect the same against the influence of moisture or other deleterious agents. The frame |03 is substantially the same, in general design, as the 'other skeleton frames herein described in connection with Fig. 1 of the drawing, in that it provides the necessary mechanical-strength with a minimum amount of heat-absorbing or heat-transmitting material;

A pad |01 of heat insulating material is located on the upper face of-frame |03 and may be cov- 'ered by a thin sheet metal casing |09 which is substantially entirely closed except for a small opening to permit the escape of moisture duringoperation of the furnace. Means for supporting a charge I0 on the metal encased pad |01 may be constituted by a plurality of segmental metal plates or by a single metal plate as may be desirable or necessary.

The charge ||0 may be covered by a thin sheet metal hood I3 which has, in addition to an outer wall ||5, an inner wall |1 adapted Ato surround a central axial heating element ||9.

A furnace casing |2| is of substantially the same design as was hereinbefore described for the casing 23, that is, it includes an outer metal shell |23, a refractory lining |25 therein, from which wall lining a plurality of annular heating elements |21, |29, |3| and |33 are adapted to be supported, these heating elements being the same as were hereinbefore described in connection with the furnace structure shown in Fig. 1 of the drawing.` The furnace casing |2| is provided with a plurality of horizontally extending beams.

|35 and cross beams |36 having one or more lifting-lugs |31 thereon, the central heater I9 being ing gas underthe hood ||3 may comprise an inlet pipe |39 which ends just below the central portion of the lhood I3 the gas flowing upwardly inside of the hood and between wall ||1 and the charge ||0 and then downwardly on the inside of outer wall |5 and outwardly through one or more outlet pipes |l||. The outer wall ||5 of the hood has a flat vannular flange |43 secured thereto which ends in a depending annular flange |45 adapted to fit into the seal structure |0|.

Since it is desired that the gas entering through the `pipe |39 flow upwardly into the upper end portion of the hood and then downwardly, I may provide a suitable thin metal closure member |41 secured to the inner periphery of the skeleton frame |03 to close olf any possible outlet of the gas, and itis noted that the vertical webs of frame |03 may be solid or perforated while the vertical webs 5| and 59 (Fig. 1) may be perforated, as has already been pointed out. 1

The operation of the furnace structure shown in Fig. 2 of the drawing is substantially the same as was herei'nbefore set forthin Fig. 1 of the drawing, and, therefore, need not be repeated.

In Fig. 3 of the drawing'fI have illustrated, on an enlarged scale, one yform of heat insulating pad |5| which comprises a bottom sheet metal wall |53'of dish-shape and an upper `sheet metal wall |55 also of dish-shape whose annularedges may meet to enclose the pad |51 of refractory heatinsulating material having not yonly a lowl thermal.

capacity but having also a high thermal reluctance. A charge to be heat treated and to be supported upon the p'ad structure |5| may rest directly upon a plurality of metal plates |59 having inner depending flanges |6| tting into a well |63 in the upper sheet metal member 55. An inlet pipe |65 comparable to inlet pipe 11 may extend upwardly through a central opening |61, and in order to hold the plurality of segmental plates A|59 in their proper operative and relativev positions, I may provide an annular member |69 centrally perforated to permit of pipe |65 extending therethrough.

The device embodying my invention is, as has already been hereinbefore set forth, applicable to any kind of furnace structure irrespective of whether the casing. of the furnace is vertically removable from the base or not, and while I have shown two furnace structures with asubstantially xed base and a removable cover thereover, my invention is not to be considered as being limited thereto,l since the furnace cover or casing may also be located in substantially'xed. position relatively to the base. It is obvious also that a plurality of spaced pads may be located in the same horizontal plane instead of only a single pad.

As has already been'hereinbefore set forth, I have found it possible, by the use of the heat insulating pads and the skeleton frame structures embodying my invention, to insure substantially uniformv heating of a relatively high stack of material so that the temperatures of the different parts thereof will be substantially the same.

I have found it possible also to operateafurnace sumption of gas, fuel or electric energy, but also to obtain quicker heating up and, therefore, a

greatereconomy in the use of the furnace, since it is possible to obtain a much greater output from a given furnace or from a given number of furnaces than would otherwise be possible.

Various further modifications may be made in the device-embodying 4my invention without departing from the spirit and scope thereof, and I 4of this kind more economically not only as to condesire, therefore, that only such limitations shall be placed thereon as are imposed. by the prior art or are set forth in the appended claims.

I claim as my invention:

l. A heat treating furnace comprising in combination, a fiat base, a furnace casing thereabove cooperating with the base to enclose a metallic charge supported on the base, a skeleton frame work having a relatively low rthermal conductivity on the base, a metal-bound layer of substantially solid heat-insulating material having high thermal reluctance on the skeleton frame work, directly operatively supporting Va charge to bev heat treated', and an extended electric heating means in the furnace casing for-heating thecharge and having a bottom section thereof lo; cated below the plane of said layer to vsupply heat to the skeleton frame and the bottom "of the layer of solid heat-insulating material.

2. An electric furnace comprisin-g in combination, a substantially solid flat base, av furnace casing thereabove and cooperating with the base vto provide a furnace chamber to contain a metallic charge, a metal-boundpad of heat-insulating material of high thermal reluctance directly operatively supporting a charge to b'e heat treated, a plural-section electric heating unit within the furnace casing to supply heat to a charge therein and means providing a high temperature zone between the pad and the base, comprising a lower section of the heating unit disposed below the plane `of said pad and a hollow frame supporting the pad on and spacing it from the base.

3. An electric heat treating furnace comprising in combination, a substantially flat base, a furnace casing, of bell-shape, above the base and cooperating therewith to enclose a furnace chamber, askeleton frame of low heat storage capacity and high thermal reluctance on` the base, a metal-bound pad of substantially solid wheat-insulating material on thev skeleton frame and adapted to directly operatively support a metallic charge to be heat treated, and an extended electric resistor heater supported by the casing adjacent its inner surface. and having a complete section located in substantially the same horizontal plane as the skeleton frame to Y heat it and any gas located between the base and the pad to provide a high .temperature zone below -the pad.

l 4. An electric heat treating furnace comprising in combination, a substantially flat base of solid refractory material, a `removable furnace sulating material of high thermal reluctance on*4 the skeleton frame and adapted to directly operatively support a metallic charge to be heat treated in the furnace chamber and an extended electric resistor heater supported by the furnace casing adjacent to' the charge to heat the same and having a segregated section specially located to heat asl a unit the skeleton frame and any gas located between the base and the pad to provide a high temperature zone below the pad and thereby reduce heat flow from a heatedl charge tothe base.

5. An electric furnace 'comprising in combination, a base. on which material to be heattreated is located, a casing enclosing the material, heating means Within the'casing, and a metal-bound pad o'f heat-insulating 4material having high thermal reluctance located between the base and the material, said pad having an opening therethrough for permitting the passage `of a gas for treating said material.

gas through said layer to the charge.

7. A heat treating furnace comprising in comi bination, a flat base, a furnace casing thereabove cooperating with the base to enclose a charge supported on 'the base, a skeleton frame work having a relatively low thermal conductivity on the base, a metal-bound layer of substantially solid heat-insulating material having high thermal reluctance on the skeleton frame Work directly operatively supporting a charge to be heat treated, an extended heating means in the furnace casing for heating the charge and having a bottom portion thereof located to supply heat to the skeleton frame and the bottom of the layer of solid heat-insulating material, and means for conducting a neutral gas through said layer tothe charge. y

8. An electric furnace comprising in combination, a substantially solid at base; a furnace casing thereabove and cooperating with the base to provide a furnace chamber to contain a lcharge, a metal-bound pad of heat-insulating material of high thermal reluctance directly operatively supporting a charge to be heat treated, a plural-section electric heating unit within the furnace casing to supply heat to a charge therein and means providing a high temperature zone between the pad and the base, comprising a lower section of the heating unit and a hollow frame supporting the pad on and spacing it from the base, said pad having an opening therethrough for permitting the passage of a gas for treating said material.

JOSEF EBERWEIN.

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