US2402190A - Furnace hood construction - Google Patents

Description

June 18, 1946. E. VAN DER PYL ETAL 2,402,190

FURNACE HOOD CONSTRUCTION Filed Aug. 11, 1944 4 Sheets-Sheet 1 SEPARATOR.

a o T U B R T m D Edward Van. der' PyL June 1946; E. VAN DER PYL ET AL 2,402,190

FURNACE HOOD CONS TRUCTI ON Filed Aug. 11, 1944 4 Sheets-Sheet 2 94-9 3 5 na-97 e as grwe/wtom E'dwzz-rd Van der P 1 John A- Up er l 1945. E. VAN DER PYL ET AL 2,402,190

FURNACE HOOD CONSTRUCTION Filed Aug. 11, 1944 4 Sheets-Sheet 3 Edward .Van. der P 1.

John. A U er- M/MWWM June 18, 1946.

E. VAN DER PYL ET AL FURNACE HOOD CONSTRUCTION Filed Aug. 11, 1944 4 Sheets-Sheet 4 V NT Edward Van der- Pyt John. A- Upper Patented June 18, 1946 FURNACE HOQD CONSTRUCTION Edward Van der Pyl, Holden, Mass and John A, Upper, Chlppawa, Ontario, Canada, minors to Norton Company, Worcester, Mass" a. cornotation of Massachusetts Application August 11, 1944, Serial No. 541mm 30 Claims. (011.13-)

This invention relates to furnace construction, more particularly to a hood structure for a furnace, of a type adapted for the fusion of high fusing-point materials such as alumina.

One of the objects of this invention is to pro= vide a practical and dependable hood or top closure structure for a furnace for the fusion or heat treatment of various materials such as alumina, and to provide a hood structure that will be well adapted to meet the widely varying conditions and requirements met with in such furnaces, particularly in furnaces operating at relatively high temperatures such as a furnace for fusing alumina. Another object is to provide a hood structure that will furnish adequate closure for the furnace and yet permit facility and wide range of access to the interior of the furnace for various purposes. Another object is to provide a hood structure of the above-mentioned nature that will be well adapted to function in an electric furnace such as a furnace having controllable electrodes projecting into it; another object is to carry out this last-mentioned object in an electric furnace in which the furnace shell or structure is mounted for movement, as by tilting, relative to the electrodes as for example, for purposes of pouring or withdrawing molten material from the furnace.

Another object is to provide a hood structure for an electrode type of furnace so constructed and operating that tilting or like movements of the furnace relative to the fixed electrode or electrodes may be effected without detrimentally affecting the closure desired to be maintained by the hood structure. Other objects are to provide for the dependable prevention of emanation of dust or the like from a furnace of the abovementioned type, to maintain such prevention during relative tilting movements between theelectrodes and the furnace, to provide adequate heat insulation by and for a hood structure for a furnace of the above-mentioned type, and to provide a hood structure that will give access, as by a tool or probe, to the contents of the furnace without detrimentally interfering with the prevention of dust emanation.

Another object is to provide a hood construction that will be inexpensive and simple to build, light in weight so as to lessen interference with effecting tilting movements of the furnace where it is tiltable, and yet be strong and rigid. Another object is in general to provide an improved hood or closure structure for furnaces of the above-mentioned types. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts as will be exemplified in the structure to be hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings in which is shown one of the various possible embodiments of this invention,

Figure 1 is a side elevation, partly diagram= matic and partly schematic, of a furnace installation;

1 Figure 2 is a plan view of the furnace installation, certain parts being shown in horizontal section or omitted and other parts being shown diagrammatically;

Figure 3 is a fragmentary side elevation on a larger scale showing a portion of the furnace shell and all of the hood structure as seen along the line 3-3 of Figure 2, certain parts being omitted;

Figure 4 is a fragmentary front elevation on an enlarged scale showing a portion of the furnace shell and all of the hood structure as seen along the line 44 of Figure 1; 7

Figure 5 is a detailed'plan view, on an enlarged scale, of the hood structure as seen along the line 5-5 of Figure 1;

Figure 6 is a vertical transverse sectional view as seen along the line $-6 of Figure 5;

Figure 7 is a detached or fragmentary side elevation on an enlarged scale showing certain features of construction of the sides of the hood;

Figure 8 is a vertical sectional view as seen along the line 8-8 of Figure '7.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referring to Figures 1 and 2, the hood struc-= ture is generally indicated by the reference character Iii and in the form shown provides a closure for the top of a furnace generally indicated the reference character H, the furnace, illustratively, being of the type that is tiltable as for purposes of pour, and it has projecting downwardly into it electrodes which illustratively are three in number and shown at it, it, and i5 and which are thereby adapted for 3-phase operation. The electrodes are supported, as is later described, for certain adjustments vertically, as viewed in Figure l, but, in the type of furnace shown to illustrate better certain features of this invention, the electrodes do not partake of tilting move ment with the furnace ii and in such case it is preferred that each electrode be supported independently of the furnace assembly l'ii as lining generally indicated by the reference charreleasing or tightening the clampon the electrode so that each may be initially set or subsequently reset downwardly as it is consumed during operation in order thereby to achieve the same lengths of the three electrodes projecting downwardly into the furnace. I

The three masts l 3, 20, and 2! are suitably supported and controlled for up and down movement, and any suitable means may be employed for thi purpose. For example, the three masts may be polygonal in cross-section (Figure 2) and extend downwardly into suitable guideways 27 provided in a casing-like standard 28 which can contain any suitable form of mechanism or control for effecting movement and control in an up and down direction of the masts and hence of the electrodes and since such mechanism may take any known form, it is not shown in detail and it willsuiiice to indicate three hand wheels 29, 36, and 3| for actuating or controlling the mechanism contained in the standard 23.

Electrical energy from any suitable source is supplied to the electrodes by any suitable circuit and conductor arrangement and since various such arrangements are known they are not described or shown in detail.

The furnace II is of any suitable construction but preferably comprises a side shell 33 preferably frusto-conical and hence with downwardly and outwardly sloping walls, closed off by a bot tom shell 34 which is preferably a segment of a sphere made in one piece or of several sectorshaped pieces welded together, and in turn welded to the side shell 33, these parts being preferably made of sheet steel comparable to boiler plate.

Where the furnace is to be mounted so as to be tiltable, it-is preferred to provide it with a plurality ofrockers, illustratively two in number, as shown at 35 and 33, these being preferably built up to rest against and to reinforce the bottom shell 34 to which they are welded and they are preferably provided with spaced teeth 31 which meshwith suitable holes 38 in two correspondingy spaced and parallel truss- like supports 39 and 40 which are provided with upper curved plates 4| and 42, in which are formed the abovementioned holes 38, for supporting the rockers 35 and 36 in rolling contact during tilting movement of the furnace assembly. As indicated in Figure l the trackway provided by the plates il l2 of the supports 39-40 may be curved if desired and the truss supports are positioned to guide the furnace assembly for tilting in directions toward or away from the place or target which it is desired to have the pour stream from the furnace spout 43 strike. The spout 43 is only diagrammatically indicated in the drawings and may take any suitable form, preferably like that de-' scribed and shown in the copending application of Raymond R. Ridgway, Serial No. 534,653, filed May 8, 1944, or in the application of Edward Van der Pyl, Serial No. 549,007, filed August 1, 1944, may be provided with stoppers, as disclosed in the said applications, and is preferably posiacter 36, being of substantial or appropriate thickness and extending upwardly along the inner walls of the side shell 88 as indicated at w and 66 in Figure 1, the portion 65'' extending into coaction with the refractory material, illustratively graphite, which comprises the lining for the spout 33 which extends through a suitable hole in the side shell wall 33 and may be constructed and supported as described in the abovementioned applications. The lining 65 may be of any suitable refractory material, illustratively fused alumina, and may be constructed and maintained, particularly where the furnace is to function to fuse alumina, as described in the aforesaid Ridgway application. As described in the latter, the material to be treated in the furnace may be supplied to the furnace through the hooded top of the furnace and the supply may be continuous, the material being fed in powdered, granular or broken-up form, preferably at a rate which is interrelated with the rate of energy supplied to the electrodes and with the rate of withdrawal of molten material from the furnace; as therein disclosed and claimed, a melt may be built up within the furnace as in-feed of unfused material progresses and when built up to a certain amount the furnace structure may be tilted, in clockwise direction as seen in Figure 1, thus to lower the spout 63 relative to the head or level of the molten material in the furnace, thus to effect pour thereof through the spout, reverse tilt of the furnace being effected to return it to normal upright position and cut off the pour at such a. point that a substantial quantity of melt remains in the furnace to which in-feed of unfused material and to the electrodes of which the supply of electrical energy are continued even during tilt of the furnace and hence during the interval of pour.

With such an arrangement and illustrative mode of operation, according to the said Ridgway application, an entire series of molds or containers may be charged uninterruptedly, during the interval of pour, with the molte alumina or other material; thus, there may be provided rails d1-4i8 by which a succession of trucks or cars d3 (Figures 1 and 2), each carrying a suitable number, illustrativel three, of molds or containers 30 are guided and moved step by step so that the desired number of molds are successively charged with molten material during the interval of pour and without having to interrupt the p0urby water supplied through apertures in pipes suitably related to the surface and of which for illustrative purposes two pipes or conduits are indicated at 5| and 52, being ringed about the side shell 33 at suitably spaced intervals and supplying water to the shell surfaces at a. suitable rate,

' the downward and outward inclination of the side Any suitable means may be employed to actuate I or control the tilting of th furnace assembly out of or into its normal position and in Figure 1 such a means is only diagrammatically indicated by the reference character 53 and it may include a link 54 pivotally connected to the furnace i I as at 58.

The upper peripheral edge of the furnace shell 33 is strengthened and reinforced preferably by a structural steel element 51 which is preferably of angle section as isbetter shown in Figure 8, hav. ing a horizontal web 51* which is welded through= out and to the upper edge or periphery of the side shell 39, externally thereof so that its vertical web 51' peripherally overhangs the side shell 33, the two webs thus forming with the side shell 33 a strong, rigid, and unyielding ring-like frame or support and forming also a good barrier against water splashing over or entering into the furnace shell from the external surface of the furnace,

Upon this ring-like frame or support, the hood structure I is built or secured and, referring now to Figures 3, 4, and 5, the hood structure preferably comprises a built-up cantilever frame overhanging the furnace It so as to leave the front and two sides of the upper end of the side shell 33 and hence also the front and two side portions of the supporting and reinforcing frame 51 substantially unobstructed for purposes later described. Accordingly, it is preferred to support and anchor this cantilever frame preferably only from the rear portion of the supporting frame 51, that being the portion nearest the electrode masts and mast control mechanism 28, to the left of the furnace structure as seen in Figures 1 and 2, it being therefore assumed, for illustrative purposes, that, as is later described, ready access to the interior of the furnace It i desired to be gained from the two sides and the front. Accordingly, an arcuate portion of about 100 and extending from the point A in Figure to point B, of the reinforcing frame 5! has secured to it, as by welding, a suitable number of upright structural steel members, indicated at El, 62, B3, 64, 65, and 66; they may be'of any suitable section, illustratively angle section, and in such case they may be employed singly or in pairs, members 63 and 64 comprising two angle sections welded together.

As shown in Figures 2 and 3 the electrodes l3, M, and I5 are preferably positioned so that their vertical axes are at the apex of an equilateral triangle with the side joining the axes of electrodes l3 and 14 parallel to the flattened front wall portion 33 of the side shell 33, for reasons described in the aforesaid Ridgway application. In such case members 62, 6t, 64, and 65 are preferably spaced so as to lie in parallel vertical planes that are substantially equidistantly spaced from each other and from the vertical axes of the three electrodes, and with such a relationship the lower chord of the cantilever fram may be built up to form also suitable supports for certain parts that are to coact with the hood structure and the electrodes, particularly where the hood structure tilts with the furnace and hence relative to the elec trodes. Thus the lower chord may comprise two angle-sectioned ring-like members 58 and 69 (see Figure 8), formed to the peripheral outline or shape of the upper end of the furnace i i and hence to the shape of the supporting frame 5i of the latter, these two members 68 and 59 receivin: between their two horizontal webs a relatively heavy sheet metal 10, the three being secured together in an suitable wa as by welding and in effect forming a flat or plane roof-like structure which matches the outline of the otherwise open end of the furnace II and which is to be supported in horizontal position and spaced upwardly from the upper edge of the furnace II.

In the sheet metal member 10 are provided parallel slots H, 12, and 13, one for each of the three electrodes, each slot being materially wider than the diameter of the electrode and being of a length, in the direction of tilt of the furnace structure relative to the electrodes sufllciently great to permit the furnace and hood assembly to partake of its intended range of tilting movement without having the electrodes contact the ends of the slots. To reinforce the sheet metal member ID and permit the latter also t be built up in sections, there are provided transverse structural steel members, preferably of angle section, and positioned and related to-the abovementioned slots. Preferably at least some of them extend entirely across the roof structure.

For example, angle-sectioned members H and 15 extend parallel to each other and respectively alongside the adjacent parallel edges of the slots it and if, being welded at their rear ends to the vertical web of the chord member 69 at points in the latter which overlie the vertical membars 63 and 64 which are in turn welded at their upper ends to both webs of the angle-sectioned chord member 68, as indicated at 16 in Figure 3; at their front ends the transverse members 14 and I5 (Figure5) are welded to the vertical web of chord element 65. The lower webs of each member I4 and 15 fall in the same plane with the horizontal web of chord element 59 as is true also of the other angle-sectioned transverse structural members about to be described so that thereby their under faces and the under face of the horizontal web of the chord element 69 lie in the same plane and hence in the plane of the sheet metal member 70 which may thus be welded to these horizontal webs where it is made up in one piece or in several sections.

The angle of the transverse member 14 faces toward the slot H and another transverse anglesectioned member ll extends parallel to member 14 along the opposite side of slot 74 with its angle facing the latter, and with its rear end abutting against and welded to the chord element 59 at a point closely adjacent the point where vertical member 69 is welded to the companion chord element 68. The two angle members 14 and I? are thus made also to function as parallel guideways for a heavy sheet metal plate 18 that covers over the slot it and that has the electrode H! extending through a suitable aperture and suitably insulated therefrom as is later described. A transverse angle section member 8G is cylindrically positioned with respect to the just described member TE, extending along one longitudinal edge of the slot 13 with its angle facing toward the angle of member 15 and forming with the latter two parallel guideways for slidably supporting the heavy sheet metal cover plate 8i through which the electrode Hi extends and which remains stationary with the electrode during tilting of the furnace structure.

Members i? and Bil need not if so desired extend forwardly to the front portion of the chord element 69 and, in any case it is preferred that a suitable number of cross elements, illustratively of angle section, connect these two mem- 7 bers ii and as to the side portions of the chord element 89 and in Figure to such members 82 are shown connected" to each of these members Ti and 8d and also to the side portions of the chord element $8. The elements 82 thus also provide parts in addition to the members '77, id, 85, and st to the under faces of which the sheet metal sheathing or member it may be secured as by welding or with respect to which it may be made up in sections and welded thereto.

The slot 12 for electrode i 5 is also covered over with a slidable cover plate shown at 83, being also apertured to receive therethrough the electrode 85; guideways for the sliding movement of the hood structure relative to it are also provided as later described.

The upper chord of the cantilever frame comprises a structural steel member preferably of angle section generally indicated by the reference character 55, cut away, however, as later described; member 35 overlies the lower chord element 58t@, having a shape or outline similar thereto and throughout the peripheral portion from point A to point B in Figure 5 it lies in a plane parallel to the plane of the lower chord elements 68-59 and spaced upwardly therefrom, but from points A and B respectivey the upper chord element 85 lies in a plane that is inclined from the heights of points A and B above the lower chord, element 59 at its rear end to a zero height at the front portion of the lower chord element 59 and since that front portion is along a straight line, the two ends 35 and 85 of the upper chord element 85 (see Figure 4) terminate in spaced relation, both, however, merging into the lower chord element at to which these ends are secured as by welding.

The upper chord element 85 and the 'lower chord element 55 are joined together by suitably heavy sheet metal indicated generally by the reference character- 85 and welded to each, the sheet metal member 85 partaking of the curvatures of the chord elements, curvatures which are geometrically similar to those of the supporting frame 57. The three element 85-85-69, because of these curvatures and particularly the curvature of the sheet metal element 85, are thus given great rigidity and great resistance to distortion, particularly to distortionof the front portion from point A to point B (Figure 5) of the resultant cantilever frame relative to the rear portion from point B to point A thereof, and the frame, though light in weight and inexpensive in construction, is thus well suited for anchorage to and support from the furnace frame 51; such anchorage and support are effected by the abovementioned vertical members 6!, 52, 53, 66, 55, and 88 which are welded at their upper ends to the webs of the lower chord elements 58 and welded at their lower ends to the furnace frame 51, the arcuate disposition of these vertical members being appropriate for such anchorage in that the rearmost members such as members 63 and 64 can be placed in tension and forward vertical members such as members SI, 62, 65, and 66 can be placed in compression. The cantilever frame with its roof-like sheathing of sheet metal 70 may thus be supported dependably at a, substantial height above the upper edge of the furnace H (see Figures 3 and 4) thus leaving the two sides and front, from point A to point B, unobstructed by any vertical supporting members.

The rear portion from point A to point B of the upper end of the furnace ll, being nearest to the electrode masts and to the control structure 28 therefor may be permanently closed off and this may be done by suitably heavy sheet metal. indicated in Figure 3 at 58 which follows the curvature of the rear portion of the structure from point A to point B, rests against each of the vertical members iii to 56 inclusive, being welded to each and being welded also along its lower edge to the upper furnace frame 57 and along its upper edge to the lower chord element 68. The sheet metal member st thus aids in giving the lust-described cantilever anchorage and support greater rigidity and strength.

The rear portion of the upper chord element 85 and also of the sheet metal 8% (see Figure 4) are cut away as indicated at ti, 92, and es, in line with the vertical projections, as viewed in Figures 1 and 2, of the three arms or Jibg 22, 2E, and 28 respectively that support the three electrodes. the cut away portion ti, 92, and 93 being of adequate width and depth to accommodate the Jibs should it be necessa y, through the mechanism in the structure 28 to continue to lower the electrode masts and jibs to follow up consumption during operation, of the electrodes. To compensate for any possible weakening that results from such cutting away, and further to provide better support for the roof structure it and related parts, particularly where the latter are of substantial area or expanse, it is preferred to provide suitable individual cantilever elements which conveniently can be made of suitably heavy sheet metal. Thus a sheet metal member 94 (Figures 3, 4, and 5), in the shape of a right angle triangle, has a vertical leg of the same height as the rear portion of the sheet metal member 56 against which it abuts and to which it is welded, while its horizontal leg or base portion extends along the vertical web of the member (Figure 5) to which it is secured as by welding, being of suitable extent toward the front of the structure to give the desired reinforcing action. A similar member 95 is similarly secured to the member at the rear and to the vertical web of the angle section member Ti.

In similar manner triangular sheet metal elements and 91 extend with their base portions alongside and are welded to the vertical webs of the angle members 76 and 75 respectively, having their rear or vertical portions welded to the member 88 and upper chord 85. In so mounting these members 95, 96, 97, and 94, they are also made to give greater rigidity to the angle section members to which they are welded and thus aid in avoiding saggin of the sheet metal sheathing Also, as is better shown in Figure 4, the members 95 and 98 hold those portions of the member 85 and upper chord member 85 that-are adjacent the cut-outs 9i and 93 against distortion and members '96 and 91 hold the portions of these parts that intervene the cut-outs against similar distortion, giving the ultimate structure'as good if not better strength, rigidity and cantilever action as it would have without the cut-outs, while all four members 95, 98, 91, and 94 have such spacings and parallelism relative to the downward paths of movement of the electrode jibs 22, 24, and 23 as to adequately accommodate the latter therebetween, upon downward movement. If desired and preferably the lower chord element 69 and the upper chord element 85 may be rigidly interconnected as by suitably spaced vertical elements indicated at 98 -in Figures 3 and 5 and welded to each, and with the sheet member 86 also welded thereto; vertical members 98 are preferably peripherally spaced in the same manner as are the members BI, 82, II, 64, II,

and 88, are preferably of similar'cross-sections and aligned respectively therewith, so as in eflect to form vertical extensions thereof, the welding giving each member Ol, 82, 63, N, 65, and 66 with its upward extension 98 a substantial integral or unitary construction whereby the abovedescribed rigidity of mounting of the members ii to 86 inclusive becomes communicated to the extension members 98 themselves. With the chord element made up of two angle section members 88-49 (Figure 8), it is preferable to make up each of the vertical members in the manner above-described, namely, each with an extension portion 88 rather than initially to make each of one continuous piece and then have to virtually cut away to interfit it with the weldedtogether horizontal flanges of the angle members t8 and 69. Welded in place against the members 36 and 91 (Figure are two angle-sectioned members S9ill0 forming a guideway for cover plate 83 over slot '12.

In Figure 6 is shown in vertical sectional view how each of the slot-covering plates :18, 83, and at of Figure 5 is related to its electrode; each plate is provided with a round hole lill therein through which the electrode passes with ample clearance for electrical and mechanical reasons and how each electrode is insulated from its cover plate while at the same time making adequate provision for change in angularity between the cover plate and the electrode as the cover plate tilts during tilting of the furnace assembly. Thus about each round hole is secured a ring tilt which is conveniently formed out of angle sectioned structural steel and welded to the cover plate to form an inwardly exposed annular seat hi3 in which is received and seated a relatively large collar W4 made of any suitable non conductive and refractory or semi-refractory material capable of withstanding substantial heat. it. suitable material may be clay, ceramically bonded refractory grains, or asbestos composition such as asbestos lumber.

The collar 854 has an internal diameter ma terially larger than the diameter of the electrode; for example, a clearance on the order of one or two inches may sufice for an electrode diameter of about twelve inches. The inner face of the collar is preferably bevelled at top and bottom so as to avoid presenting for contact with the cylindrical electrode a surface of substantial axial dimension and instead to present to the electrode an approximation in a general way to a knife edge effect, thereby avoiding binding or jamming during change in relative angularity between the electrode and the cover ate and collar even though the collar is pressed,

ring tilting of the furnace, against the electrade to hold the cover plate against motion of translation in the direction of swing of the hood.

its the hood therefore moves in an arc toward the right or left, as viewed in Figure i, that is, into and out of pouring position, a relative sliding movement between the hood structure and the three cover plates i8, 83, and ti takes place along the guideways provided by the pairs of angle-sectioned structural members. ll-l4, ell-i011, and l5-8l1 for the cover plates l8, c3, and 8! respectively. Any suitable means such as a heat-resistant or refractory cement may be employed if desired to secure the collars 804 in their respective seats ills and thus guard against tendency of a vertical component of force, during iurnace l0 tilting, causing a collar to be lifted out of its seat.

As above noted, the vertical spaces between the vertical members 8! to 66 inclusive may be and preferably are permanently closed off by the sheet metal sheathing 88, since it is found that, in operation oiv the furnace, access to the interior thereof throughout that peripheral region, being more or less hampered or made. inconvenient by the electrode supporting and moving arrangement; the remaining peripheral space between the cantilever roof structure and the furnace shell 33 is, however, closed of! in a manner to permit the operator, usually standing on a platform (not shown) surrounding the sides and front of the furnace, to insert tools, probes or the like for purposes later described and to permit also, during a shut-down of the furnace, the entry of workmen into the furnace shell 33 for purposes of inspection or repair or replacement of various parts such as the lining, the spout structure, etc. A preferred arrangement for carrying out these objects comprises the provision of movable and preferably heat-insulating closure members I 06 (Figures 1, 3, 4, and 5) which are of individual curvatures (see Figure 5) and in suilicient numher to fill in the curved space between the lower cantilever chord 58-69 and the upper rim frame 5'!- ol the furnace shell 33, excepting for a substantially peripherally extending gap between the edges of the closures W5 and the upper rim frame 57, this gap being indicated at iii'i and in practice it may be oi a vertical dimension on the order of four or five inches.

The closure members tilt are preferably supported from the cantilever frame, conveniently from the composite lower chord member 6889, in any suitable manner to permit movement thereof out of closing ;ccsition, as for example when the furnace has to be entered for purposes of repair, inspection or the like, and a convenient arrangement for this purpose comprises any suitable detachable hingedilre construction for suepending each closure member liit from the canti= lever frame so that it may be swung about a horizontal axis outwardly and upwardly or so that it may be detached irom its pivotal support and removed it desired. Such an arrangement is in dicated in Figures 3, i, and 8.

The cantilever construction above described and the suspension therefrom of the closure members lull, with the latter spaced their lower ends from contact with the furnace rim ti by the gap ltl, take part in improving the elec= trlcal operating characteristics of the furnace; the cantilever structure will be seen, as above described, to make it possible to arrive at a strong and dependable construction, yet one which iacilitates the use oi metal elements of relatively very small cross-section, particularly in those portions of the structure that form a continuous conductive loop or loops linking the individual circuits oi which the principal portions now to consider are represented by the electrodes themselves.

For example, and hearing in mind that the current flowing through each electrode is oi very substantial magnitude, on the order of several thousand amperes, any two electrodes, with the conductive path or paths existing within th furnace, including the conductive path of the molten material itself, may he considered as a single turn transformer winding with which metal parts of the hood structure are linked, forming in effect inductively related secondary transformer winding in which current thus be induced,

With the arrangement as seen in Figure and with 3-phase operation, it is desirable that the effective reactances, represented by the pertinent or looping portions of the hood structure, be substantially equal so as to avoid material unbalance of the 3-phase power supply circuit and it is also desirable that they be not of a substantial order of magnitude, in value.

If the effective reactances for the respective phases are not equal, unbalance in the 3-phase power cir cpit can take place and external and sometimes complicated means would have to be resorted to to attempt to correct such unbalance, or, if correction ,of unbalance is attempted by relative adjustment vertically of the electrodes, thus to change impedance factors within the furnace itself, it might be possible that the desired symmetry of action of the three electrodes upon the material being treated might be departed from. If the effective reactances are of substantial order of magnitude, substantial reactance drops can exist in the three phases or in the electrode circuits, and theefiect upon power factor is detrimental or in' the wrong direction.

Referring to Figures 5 and 6, the metal sheathing can be made of very thin sheet metal and the structural steel members, such as the members 11, 14, 80 etc. and other members that make up the lower chord of the cantilever frame, can also be made of small cross-section material, thus increasing the resistance to induced currents and increasing the reluctance of such paths of magnetic material in which the flux or magnetic field created by the primary or electrode circuits is effective.

Moreover, these reluctances are made substantially equal for each primary circuit of the three phases; for example, in the primary circuit or loop represented by electrodes I4 and I5, the same effective cross-section of metal of the roof structure is looped thereby as is looped by the primary circuit represented by electrodes I5 and I3, the

structure in these respects being symmetrical; the

roof structure looped in the first circuit Just mentioned includes the cross section of metal that reaches, at the shortest distance therebetween, from slot 13 to slot 12 and that includes the structural angle member 15, while a similar crosssection of metal of the roof structure forms the inside part of a loop that is looped by the second mentioned circuit, being the cross-section of metal joining the slot H and slot I2 at the shortest distance therebetween, and that includes the angle-shaped structural member 14 which is of the same cross-section as the member 15. The cover plates 18, 83 and BI, although shiftable, do not materially affect these factors inasmuch as there is interposed between them and their supports substantial contact resistance and irregular air gaps, but even if they have some effect, the effects remain not materially changed because of the sliding relationship during tilt.

In the circuit of the loop represented by electrodes I3 and I4, the intervening metal of the roof structure includes the thin sheet metal of the sheathing 10 in the shortest distance between the slots 13 and 1|, and both structural members 14 and 15; since that cross-section is somewhat larger than the equal cross-sections looped by the other two circuits, substantial equality of effective cross-section is achieved by causing the sheet metal web elements 96 and 81 to function as compensating elements in that (see Figures 3 and 5) these elements taper ofi in height from the left to the right and thus a greater cross-section thereof is added for each of the roof portions looped by the circuits of electrodes I4II and I3-l5 and a smaller cross-section of the two, along the line Joining the centers of electrodes B and I4, is added to the metal roofportions looped by the circuit of the latter two electrodes. These web members 98 and 91 need not of themselves be of substantial cross-section, being reinforced by their attachmentto the members 94 and 16, respectively. and by other parts, and being aided in load carrying effect by other elements of the roof structure anyway.

Thus it is possible to achieve substantial equality' of "electric and magnetic characteristics amongst theportions of the roof structure looped by the electrode circuits, even though there is no mechanical symmetry.

The cantilver structure (see Figures 1 and 3) also has the advantage that it is possible to avoid having the metal shell 33-34 of the furnace, or material portions of it, form magnetic orelectric circuits paralleling the portions of the roof or hood structure that are actually looped by the electrode circuits, and it will also be seen that the closure members I06, suspended from the cantilever structure, can be made to avoid con-' tact with the furnace shell and thus also take part in the just described advantage. The gap I01 can be of substantial vertical height and interposes a substantial air gap to any magnetic flux tending to bridge it.

Thus, referring to these figures, each closure member may comprise a generally rectangular frame I08 preferably made up, as shown in Figure 8, of channel-sectioned structural steel elements so as to provide spaced inwardly directed flanges I 09 and III! by which construction any suitable means preferably of low heat conductivity may be supported or secured. A suitable means of this kind may comprise two sheets III and H2 of suitably heavy wire screen secured in any suitable way as by welding to'the peripheral flanges I09 and III) respectively, the flanges thus also holding the two sheet elements III-l I2 in spaced relation, for example, several inches apart.

and together with the air space therebetween, the screens sufficiently retard the flow of heat laterally from the hood to permit the operator or operators to work without discomfort in close proximity to the furnace.

To the upper horizontal region or portion of each closure frame I 08' are secured, as by welding,

' angle of the chord element 68. The upper portion of the strap member H4 is curved inwardly and downwardly as at II 5 to coact with the horizontal portion H6 of inverted U-shaped hinge-pin members 1 whose two arms or legs are secured as by Welding to one of the flanges of the chord element 69, preferably the horizontal flange as shown in Figure 8.

Where it is desired to detachably support the closure members I06, the curved portion H5 does not completely envelop the hinge pin H6 and hence is curved to form a hook so that the closure member may be unhooked from its two hinge pins I l 6 and removed or it may be simply swung outwardly and upwardly throughout what is t3 somewhat more than 180 to bring it to rest in an inwardly inclined position leaning against the upper chord element 85 (see Figure 4), or each closure member may be held in open or outwardly swung position by any suitable means (not shown).

The closing off, as by the sheathing 88, of the rear portion of the space between the cantilever roof and the rim of the furnace shell 33 and the provision of the gap I01 and of perforated or screened closure members I08 is made to coact also with a suction apparatus diagrammatically indicated in Figure 1 at H9 which may be in the form of any suitable suction fan or the like, being connected by a flexible conduit I20 '0! substantial diameter to a funnel-shaped flanged conduit coupling IZI which is secured as by welding to a heavy sheet metal elbow I22 which in turn I is secured to the sheet metal sheathing 88, and

tains a steady how, in sufficient volume, of air through the space above the melt in the furnace and hence also through the space underneath the hood structure, carrying with it and out through the elbow and conduit 5263 small or dust-like par ticles of material with which the above-described spaces become charged due to the agitation of in-fed and unmolten material that floats upon and is, as in the case of alumina, purposely maintained in a relatively thick layer on the top of the melt.

Such charging of this atmosphere is also contributed to by the means employed to feed uniused material to the furnace; such means preferably comprises a plurality of conduits that extend through the roof structure or sheathing it (Figure in suitable relation to the disposition of the electrodes. Thus where three electrodes 13, i l, and 55 are employed as in Figures 2 and 5, three in-feed conduits 52 t, i255, and 526, leading from a suitable distributing or equalizing means diagrammatically indicated at 132?, are employed and they have flexible portions which extend through suitable bushing and securing means (not shown) through the sheathing it at points making substantially an equilateral triangle with the apexes of the triangle formed by the three electrodes.

Underneath the roof structure it, the flexible portions or these conduits depend for a substantial distance, a distance which may be several feet as from the plane of the roof sheathing it to points somewhat below the plane of the rim edge of the furnace shell 33. This arrangement is preferred so that the operator can insert a suitable tool through the peripheral gap 307 and engage these flexible depending portions of the conduits, one by one and deflect or bend them so as to guide the material being discharged through them to such regions within or without the area of the triangle formed by the three electrodes as conditions may require, and in this manner a blanket or layer of unfused material, floating on top of the melt, may be maintained in substantially uniiorm thickness throughout and upon the Kill top surface of the melt. The extensive and uninterrupted extent oi. the gap or space 8| permits ease and facility of visual inspection, from the outside of the furnace, usually from the abovementioned platform, of conditions within the furnace, and the above-mentioned blanket, the material of which is progressively fused to increase the volume of the melt but is continuously replenished through the in-feed conduits I24, I25, and H6, functions also as a heat insulating medium, opposing heat losses in upward direction from the heat content of the melt and thus also protecting the entire hood structure that is above the furnace shell, as is set forth in the abovementioned Ridgway application. The latter also describes how, where the lining 45 is of a material like alumina, a probe is used to gage the thickness of the lining 45 to determine progression or recession of fusion of the lining, and by the hood construction of the present invention, the cantilever structure makes it possible to have a, gap, gap till, of very substantial peripheral extent and uninterrupted by verticalstuds or the like, so that the operator, by inserting the probe through this gap till, may carry on the probing quickly and eficiently and progress it from point to point peripherally of the furnace assembly, the operator simply following through along the platform which as above noted is of at least the same peripheral extent about the sides and front of the furnace as is the gap till itself.

The charging of the atmosphere Within the furnace with small or dust particles or" material, particularly when the unfused material, such as powdered alumina, is continuously supplied to the furnace through the in-feed tubes, may thus be greatly aggravated, also by the agitation caused by the arcs, also by the probing operations, and also by the shifting of the flexible discharge ends of the iii-feed conduits. Egress from the furnace and entry into the outside working atmosphere of such dust-laden air is dependably guarded against by the above-described construction, the roof sheathing it and the arcuate side sheathing 38 together with the closure members tut forming in eifect mechanical barriers against such movement of dust particles or the like but also form guiding bafiles for air drawn into the furnace atmosphere through the gap till, and to some extent also through the screening of the closure members tilt; such inwardly drawn air, due to the disposition of the bafiie parts in relation to the connection of the elbow 322, insure a substantially uniform intake of air throughout the large peripheral extent or the gap it? with sub stantially uniform rate of movement to the elbow E22. Likewise, any apertures or leaks such as the clearance provided between the electrodes and their insulating collars W4 are prevented from leaking dust particles out into the working atmosphere and instead they constitute points of ingress of air into the interior, and the inwardly moving air blocks egress of any solid particles.

Such particles as do not settle on to the blanket overlying the melt are carried'with the air out through the conduit ltd whence they may be separated from the air by any suitable separating device diagrammatically indicated at 830, whence the separated solid material may be carried by a conduit 33 to the conduit 532 which leads from a suitable source of supply of unfused material (not shown) the distributing head [121, being thu retrieved for fusion or treatment in the furnace.

thus be seen ther been prol vided in this invention a furnace hood structure in which the various objects above noted together with many thoroughly practical advantages are successfully achieved. The construction will be seen to be inexpensive and light in weight, being capable of ease of inexpensive prefabrication of its various parts which in turn will be seen to be capable of ease and inexpensiveness of assembly. The hood structure is well adapted for coaction that electrodes relative to which it and the furnace are movable or tiltable and unbalance or undue loading of the movable furnace structure by the hood structure itself are avoided. And it will be seen that the construction has many functional advantages, greatly facilitating operation and. manual control or manipulation of various parts of the entire assemblage.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings. is to be interpreted as illustrative and not in a limiting sense.

. We claim:

1. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means and having means mounting it to tilt about a'horizontal axis, spout means positioned in a side wall of the shell to discharge molten material upon tilt of the furnace shell, truss supporting means built up throughout only a portion of the upper periphcry of the shell and substantially to one-side of the vertical plane through the axis of tilt, said truss supporting means including sheet-like mean extending throughout said portion and upwardly beyond the top edge of the shell, a cantilever truss comprising a lower chord extending substantially parallel to and spaced upwardly from the shell periphery and an upper chord with web means connecting the two chords, said'cantilever truss being secured to said truss supporting means and providing an uninterrupted lateral space above the periphery of the shell excepting for said portion of the periphery, sheathing means secured to said cantilever truss and joining said sheet-like means and forming therewith a hood, conduit-connection means carried by said hood and connected thereto above the shell periphery within that portion occupied by .said truss supporting means for connecting thereto a conduit whereby said sheathing and said sheet-like means coact to function as a guiding baflie for material handled through said conduit-connection means.

21A furnace as claimed in claim 1 in which said sheathing means is mounted substantially in the plane of said lower chord and the connection of said conduit-connecting means is through said sheet-like means of said truss supporting means, said web means including web elements extending between the planes of said two chords and having means coacting to support said sheathing means.

3. A furnace as claimed in claim 1 in which said sheathing means is in a plane below the upper chord of said cantilever truss, electrode means projecting through said sheathing means and into the furnace, substantially horizontal jib means supporting said electrode means independently of said furnace shell and having means for raising or lowering the jib mean relative to the furnace shell, portions of the upper chord being cut away or shaped, in the path of relacal dimensions corresponding generally to the diminishing spacing between the upper and lower chords, said sheathing means extending in a plane below the plane of the upper chord, a vertically movable electrode supporting arm overlying said hood structure for supporting an electrade that projects through said sheathingmeans into the furnace shell, said upper chord being shaped in a portion thereof above said sheathing means to provide clearance for said horizontal arm.

5. A furnace comprising a furnace shell of substantially round section having truss supporting means extending upwardly from only a portion of the upper periphery of the shell, a cantilever truss overlying said shell and secured to said truss supporting means and comprising a lower chord having a shape substantially similar to said round section of the shell and extending substantially parallel to and spaced upwardly from the shell periphery and an upper substantially similarly shaped chord the plane of which is inclined downwardly from a point materially above said lower chord at said first-mentioned portion of the shell periphery and web means connecting said two chords, and. sheathing means forming a hood overlying the upper end of said furnace shell and carried by said cantilever truss.

6. A furnace as claimed in claim 5 in which said web means includes sheet metal means extending vertically between and secured to said chords and substantially along the lines of upward projection of the shell periphery and thereby partaking of substantially the same curvatures as do the side walls of said shell.

7. A furnace as claimed in claim 5 in which said truss supporting means includes sheet means extending throughout its peripheral extent and from said portion of the shell periphery to said sheathing means and coacting therewith to form said hood, and means forming a conduit connection to the space underlying said sheathing and connected to said space adjacent the junction of said sheathing means with said sheet metal means whereby said sheathing andsaid sheet. means coact to function as a guiding baflle for material handled through said conduit connection.

8. A furnace as claimed in claim 1 in which said sheathing means extends in substantially the plane of one of said chords and said web means includes at least one sheet metal member extending lengthwise of said cantilever truss and of diminishing height generally commensurate with the diminishing space between the planes of said two chords.

9. A furnace as claimed in claim 1 provided with electrode means projecting through said sheathing means and into said shell, said sheathing means having slot means elongated in the direction of tilt of said furnace shell with the electrode means projecting through said slot means, means supporting said electrode means independently f tilting movement of the furnace 17 shell, and closure means extending about the electrode means and slidably overlying said slot means to maintain closure of the latter during tilt of the furnace shell relative to the electrode means.

10, A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means and having spout means positioned in a side wall, means mounting the shell for tilting into or out of a position to discharge molten material through said spout supporting means, truss means extending throughout only a portion of the upper periphery of the shell, a cantilever truss comprising upper and lower chords interconnected by web means and supported from said truss supporting means in position to overlie the upper end of the furnace shell, sheathing means carried by said cantilever truss and forming substantially a roof over said shell, said cantilever truss and truss supporting means providing a substantially uninterrupted space above the periphery of the shell excepting for the portion of the periphery occupied by said truss means.

11. A furnace as claimed in claim provided with electrode means projecting through said sheathing means and into the furnace shell, said sheathing means having aperture means for the passage therethrough of the electrode means, and means including insulating material providing a flexible closure about the electrode means of said aperture means throughout change in angularity between said electrode means and said furnace shell upon tilt of the latter.

12. A furnace as claimed in claim 10 in which one of said chords includes spaced substantially parallel structural members extending in the direction of tilt of the furnace shell, said sheathing means being connected to said parallel members, slot means extending lengthwise between said members, electrode means projecting through said slot means, and closure means about the electrode means and slidably guided by said structural members during tilting movement of the furnace.

13. A furnace as claimed in claim 10 in which one of said chords includes spaced substantially 1 parallel structural members extending in the di rection of tilt of the furnace shell, said sheathing means being connected to said parallel members, slot means extending lengthwise between said members, electrode means projecting through said slot means, and closure means about the electrode means and slidably guided by said struc= tural members during tilting movement of the furnace, a collar of insulating material extending about said electrode means, and means securing said collar to said closure means to hold the latter against material movement relative to the electrode means during tilting of the furnace.

14. A furnace as claimed in claim 10 provided with sheet-like means closing off the space between the shell periphery and said sheathing means throughout the peripheral extent of said truss supporting means, and a plurality of closure means supported from said cantilever truss throughout the remainder of the periphery of the shell and substantially aligned with the side wall of the shell.

15. A furnace as claimed in claim 10 provided with sheet-like means closing off the space between the shell periphery and said sheathing means throughout the peripheral extent of said truss supporting means, and a plurality of closure means supported from said cantilever truss throughout the remainder of the periphery of the shell and substantially aligned with the side wall of the shell. said closure means terminating Short 1 the pper edge of the metal shell to provide a substantially uninterrupted slot-like lateral opening.

16. A furnace as claimed in claim 10 provided with sheet-like means closing oil the space between the shell periphery and said sheathing means throughout the peripheral extent of said truss supporting means and a plurality of closure means supported from said cantilever truss throughout the remainder of the periphery of the shell and substantially aligned with the side wall of the shell, said closure means having means forming hinged connections with said cantilever truss whereby they may be swung into or out of closure position.

17. A furnace as claimed in claim 10 provided with sheet-like means closing oil! the space between the shell periphery and said sheathing means throughout the peripheral extent of said truss supporting means, and a plurality of closure means supported from said cantilever truss throughout the remainder of the periphery of the shell and substantially aligned with the side wall of the shell, said closure means having connections with said cantilever truss pivotally supporting them for movement into or out of closure position about substantially horizontal axes.

18. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means, truss supporting means extending throughout only a portion of the upper periphery of the shell, a cantilever truss supported by said truss supporting means and carrying sheathing means to form substantially a roof structure above said furnace shell.

19. A; furnace as claimed in claim 18 in which said cantilever truss comprises upper and lower chords having arcuate substantially peripheral portions and web means connecting said two chords and including sheet metal means curved to conform to said arcuate portions and thereby contribute to the cantilever truss action the resistance of said curved sheet metal means to distortion.

20. A furnace as claimed in claim 18 in which said sheathing means has means supporting it in substantially the plane of one of said chords, and sheet metal means extending lengthwise of the cantilever truss with its plane substantially vertical and having means joining it to both the upper and lower chords.

21. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means and having a metal hood structure with aperture means therethrough, a plurality of electrodes projecting through said aperture means and having mean supporting them, and means for preventing said metal shell from taking a material part in forming a portion or portions of the conductive circuit of metal of said hood structure electromagnetically linked by the loop-like circuit or circuits of said electrodes, said means comprising a cantilever structure embodied in said hood structure and means forming a mechanical supporting connection between. the cantilever structure and the furnace shell and connected to the furnace shell throughout only a portion of the periphery of the latter that is remote from the metal linked by said circuit or circuits.

22. A furnace as claimed in claim 21 in which said electrodes are more than two in number and are substantially equidistantly and equiangularly spaced from a fixed point and in which said aperture means are correspondingly numbered and substantially similarly positioned thereby providing more than two portions of the metal of said hood structure that are linked by said circuits, said hood structure comprising sheathing of relatively small thickness and said cantilever structure comprising structural elementsthat are looped by said circuits and that are respectively cross-sectioned in relation to the cross-section of the looped sheathingto provide substantially equal cross-sections of metal for the respective metal portions looped by said circuits, whereby to substantially equalize and to lessen their reactance effects.

23. A furnace as claimed in claim 21 in which said electrodes are more than two in number and are substantially equidistantly and equiangularly spaced from a fixed point and in which said aperture means are correspondingly numbered and substantially similarly positioned thereby providing more than two portions of the metal of said hood structure that are linked by said circuits, said hood structure comprising sheet metal sheathing of relatively small thickness and said cantilever structure comprising metallic struc tural elements certain of which are looped electromagnetically by electrode circuits, and means for substantially equalizing the effective crosssection of looped metal parts, said means including metallic structural elements of said cantilever truss also looped by certain of said electrode circuits and proportioned in cross-section to substantially equalize the aggregate cross-sections of all of the looped portions, thereby to lessen and substantially equalize their reactance effects.

24. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means and having a metal hood structure with aperture means therethrough, a plurality of electrodes projecting through said aperture means and having means supporting them, said hood structure comprising sheet metal sheathing of relatively small thickness in those regions thereof that are electromagnetically looped by electrode circuits and metallic structural members supporting said sheathing with at least one or more thereof being looped by one or more of said electrode circuits, the cross-sections of the respective looped portions of said hood structure being substantially equal thereby to substantially equalize inductive effects therein and to substantially equalize their respective electrical reactions uponthe respective electrode cir,- cuits.

25. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means and having a metal hood structure with aperture means therethrough, a plurality of electrodes projecting through said aperture means and having means supporting them, and means for preventing said metal shell from taking a material part in forming a portion or portions of the conductive circuit of metal of said hood structure electro-magnetically linked by the loop-like circuit or circuits of said electrodes, said means comprising a trus structure embodied in said hood structure and means forming a mechanical supporting connection between the truss structure and the furnace shell and connected to the furnace shell throughout only a mote from the metal linked by said circuit or circuits, the hood structure terminating in spaced relation from the remaining portion of the periphery of the furnace shell to provide therebetween an air gap in the path of possible flow of magnetic flux.

26. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means and having a metal hood structure with aperture means therethrough, a plurality of electrodes projecting through said aperture means and having means supporting them, and means for preventing said metal shell from taking a material part in forming a portion or portions of the conductive circuit of metal of said hood structure electro-magnetically linked by the loop-like circuit or circuits of said electrodes, said means comprising a truss structure embodied in said hood structure and means forming a mechanical supporting connection between the truss structure and the furnace shell and connected to the furnace shell throughout only a portion of the periphery of the latter that is remote from the metal linked by said circuit or circuits, the hood structure comprising also movable closure means terminating in spaced relation from the periphery of the furnace shell to interpose therebetween a substantial air gap to magnetic flux tending to pass between the closure means and the metal furnace shell.

27. A furnace for fusing refractory material or the like comprising a metal furnace shell having refractory lining means, a cantilever truss overlying said furnace shell and carrying sheathing means to form substantially a roof structure above the furnace shell, and means for supporting said cantilever truss from said furnace shell, said supporting means having connection with the furnace shell throughout only a portion of the periphery of the latter,

28. A furnace for fusing refractory material or the like comprising a furnace shell having refractory lining means, means forming a hood structure over said furnace shell and comprising a cantilever truss having means connected to only a portion of the periphery of the furnace shell for supporting the cantilever truss in spaced relation from the periphery of the furnace shell, sheathing means carried by said cantilever truss, and means substantially closing oil the space between the periphery of the furnace shell and the cantilever truss and including movable closure means.

29. A furnace as claimed in claim 28 in which said last-mentioned closing-ofi means terminates short of that portion of the periphery of the furnace shell not occupied by said cantilever truss supporting means, thereby to form a substantial gap therebetween.

30. A furnace as claimed in claim 28 in which said movable closure means and said cantilever truss are provided with means movably supporting the former from the latter for movement into or out of closing position, said movable closure means being positioned within the region of that portion of the periphery of the furnace shell that is not occupied by said cantilever supporting means.

EDWARD VAN nss PYL. JOHN A. UPPER.

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