US2290028A - Electric furnace structure - Google Patents

Description

July 14, 1942.

F. w. BROOKE ELECTRIC FURNACE STRUCTURE Filed July 2, 1940 3 Sheets-Sheet l 7 INVENTOR FranKW BrooKe F. w. BROOKE 2,290,028

ELECTRIC FURNACE STRUCTURE July 14, 1942.

Fil ed July 2, 1940 5 sheets-Sheet 2 I INVENTOR Frank W Brooke Patented July 14, 1942 ELECTRIC FURNACE STRUCTURE Frank W. Brooke, Pittsburgh, Pa., assignor to Swindell-Dressler' Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application July 2, 1940, Serial No. 343,574

'4 Claims.

'This invention relates to electric fui nace structures and particularly to electric furnace structures of the type having a roof adapt-ed to be swung generally horizontally relatively to the body of the furnace.

Electric furnace structures of the type mentioned have heretofore had certain disadvantages which have not been satisfactorily obviated.

Such furnaces have beenequipped with one or more electrodes carried by the'furnace roof and mounted for generally vertical movement relatively thereto. Such movement of the electrodes have been controlledby a winch and cable, the winch being mounted on the floor of the furnace roomor in an adjacent room and the cable extending from the electrode support over a mast and thence through a complicated system of sheaves to the winch drum. It is important to the satisfactory operation of an electric furnace of this type thatthere shall be no substantial motion of the electrodes relative to the furnace roof caused by the movements of raising the roof, swinging it horizontally toone side and tilting: the furnace for the purpose of dischargingits contents. .In furnaces built heretofore it has been possible to approach this condition by reeving the electrode-operating cable over a complicated system-of sheaves located at the various axes, of movement of the furnace roof and of the furnace body. It has not, however, been possible to fully attain the desired condition, with the result that rangement above mentioned is that an undesirably long time lag intervenes between the com mencement of rotation of the cable drum on the winch and the commencement of movement of the electrode. Such time lag is due mainly to stretching or taking up slack in the cable. This time lag has ranged up to about one second,

which presents .a very serious disadvantage from the standpoint of practical operation of the furnace.

For example, inmelting down a charge of scrap the surface of the charge, which forms one pole of the arc, shifts, this shifting ordinarily being during any movement of the furnace orits roof there has becnsome substantial and unavoidable movement of the electrodes relative to the furnace roof.

g A further disadvantage in structures of the type mentioned has been in the inability to properly control the electrodes. Such control is ordinarily effected by means of automatic electric contactors responsive to changes? in current drawn by the arcing electrode, which, in turn, control the rotation of the electrode winches. In order to effect propercontrol of the electrodes it is necessary that the-time interval elapsing between a change in the arc current, and the corresponding correction movement of the electrode be reduced to a minimum. In the furnace strucgradual but sometimes being relatively rapid. If, for example, shifting of the charge during melting results in increase of the gap between the end of the electrode and the charge to a distance greater than that which the arc will span the arc is extinguishedand has to bedrawn anew. Inorder for the electrode to properly follow the surface of the charge as that surface changes during melting, and particularly when portions of the surface of the charge shift relatively rapidly,

it'is necessary that the electrode respond very.

quickly to current variations due to the change in the length of the gap between the end of the electrode and the charge.v oftentimes a very quick response of the control mechanism and almost immediate movement of the electrode will enable the electrode to follow' the change in the surface of the charge quickly enough to avoid extin'guishing the arc. Thetime lag which occurs in taking up slack and stretching the cable in furnaces of the type mentionedmay often be suflicient to prevent the electrode from following the change of the surface of the, charge quickly enough to avoid extinguishment of the arc. Consequently the time lagdue to taking up slack and stretching of the cable is 'quite material from the 40 practical standpoint.

Electric furnaces are equipped with a timea delay overload relay which opens the main circuit breaker and so cuts off the power when currentfluctuations occur which are 'not promptly compensated for by the electrode control mechanism.

tures heretofore in use, however, it has been necessary to use quite long cables in order. to exply line and, of courseAahe attendant extinguishtend from the electrode carrying arm over the top of the mast and thence about the various Sometimes the time lag above mentioned due to cable stretching and taking up of slack in furnaces of the type under discussion results in opening of the main circuit breaker in the suping of the are. When this occurs it is necessary to throw in the circuit breaker by hand and draw a new arc: Because of the time-delay'feature of the overload relay this undesirable opening of tion of such long cables and of the sheave arthe circuit. breaker can be avoided by prompt response of the electrode to changes in the arc current.

Consequently tilting and swinging roof furnaces having their electrodes controlled by cables extending to winches at points remote therefrom have not been fully satisfactory from the practical standpoint. In addition to the disadvantages above pointed out dimculty has been encountered because of undue heating from the heatof the furnace of the means for moving the roof to and from open position, as well as rapid destruction of the refractory lining of the furnace at the point of attachment of this means. 'Heretofore the furnace roof has been moved vertically and horizontally by means of an hydraulic cylinder attached to the steel shell of the furnace body in close proximity thereto. This construction has resulted in overheating of the hydraulic cylinder and has prevented the free escape of heat from the surface of the furnace shell atthis point, resulting in overheating and rapid destruction of the furnace lining. I

the furnace roof. Such cooling means provide for'removing heat so that the furnace lining adjacent thereto does not become unduly overheated and the means for moving the furnace. roof is maintained at such a temperature that it will operate properly. I prefer to employ a fluid cooling medium. Such medium may be gaseous or liquid. In one preferred'embodiment I provide one or more cooling chambers through which I circulate cooling water. In another embodiment I provide a passageway for the circulation of air. The cooling means is preferably employed in connection with the mounting means for the roof operating mechanism and I prefer to use as such mounting means a hollow casting through which or. through a portion of which the cooling fluid may be passed.

This subject matter is disclosed and claimed in my copending application Serial No. 423,811

I have devised an electric furnace structurefurnace body, an electrode support carried by the roof, an electrode carried by the support and generally vertically movablerelatively thereto and means also carried by the roof of the furnace separately from the electrode support for generally vertically moving the electrode. I preferably mount on the furnace roof itself the cable drum about which the electrode controlling cable is wound. In a preferred form of structure I provide a support connected with the edge of the furnace roof, a winch carried by such support and having a cable drum about which the electrode operating cable is adapted to be wound and means such as an electric motor for operating the winch drum. I have found that the electric motor for operating the cable drum on the winch can be mounted on the furnace roof without being damaged by the heat of the rub.

nace by the provision of guard means for guarding the motor from the heat of'the furnace when the roof is open and when the roof is closed.

Mounting of the cable drum on the furnace roof reduces the necessary length of the cable sufficiently that the small amount of slack taken up or stretching of the cable upon rotation of 1 the winch drum does not result in. atime-lag great enough to adversely affect the operation of the furnace. slack and stretching of the cable in my improved I furnace is but a small fraction of a second and the result is a close control of the electrodes The time lag due to taking up' and elimination of interruptions in operation due to excessive time lag between initiation of rotation of the cable drum and movementof the electrode. Also the elimination of the complicated system of sheaves at the axes of movement of furnace and roof' eliminates the unavoidable changes in cable length heretofore encountered as above mentioned. Moreover, I find it possibleby reason of the simplified cable and sheave arrangement to effect a substantial saving in cost of the furnace. v

for moving the furnace roof and of' the overheating of the furnace lining adjacent thereto by providing cooling means intermediate the body of the furnace and the means for moving filed December 20, 1941.

Other details, objects and advantages of the invention will become apparent as the following description of certain present preferred embodiments thereof proceeds.

In the accompanying-drawings I have shown certain presentpreferred embodiments of the invention, in which Figure 1 is a central vertical cross-sectional view through a tilting swinging roof electric furnace, the furnace being shown in its normal or untilted' position and with its roof in operative position thereon;

Figure 2 is a top plan view of the furnace shown in Figure 1 and showing in dot anddash lines the outline of the roof swung horizontally relatively to the furnace body so that the furnace body is substantially entirely upwardly open;

Figure 3 is a horizontal cross-sectional view taken on the line III-III of Figure 1;

Figure 4 is a horizontal cross-sectional view taken on-the line IV-IV of Figure 1;

Figure 5 is a fragmentary elevational view partly in vertical cross section showing a modified structure; V Figure 6 is a face view of a portion of the structure shown in Figure 5 showing the means for holding the roof operating mechanism in place on the furnace, the roof operating mechanism itself being removed to enable a clear showing of the holding means; and

' Figure '7 is an enlarged fragmentary horizontal cross-sectional view taken on the line Vfl--VII mounted upon a framework '4 and having a hearth 5, a pouring lip 6 and doors I. The furnace is of the tilting type, being mountedfor tilting movement about trunnions 8 for tapping. The furnace is tilted by any suitable tilting mechanism such, for example. as a hydraulic ram 9. whose piston I0 is connected through a link II with the frame 4 supporting-the furnace.

When the furnace is tilted for tapping the entire body and top of the furnace tilt together and gith them, of course, everything carried there- The furnace top or roof 3 is of the swinging type, being adapted to be first lifted out of the 'fumace and the roof.

makes it possible to move either the furnace as a whole or the roof alone without producing any contact with the top of the body of the furnace and then swung in a generally horizontal plane to a position substantially clear of the body of thefurnace to permit charging or cleaning of the interior of the furnace. The furnace is equipped with three electrodes |2 whose relative positions may be as shown in Figure 2.. These electrodes are all similarly supported and operated, so that description of the supporting and operating mechanism of any one thereof applies to all three. Each of the electrodes is carried by the member l2 through a mast I3 rigidly connected with the member I2 which also carmeans for controlling the movement of the elec-' trodes and the means for cooling the operating mechanism and the furnace wall.

A cable I! has one end fastened 'to a plate I8 at the top of each of the masts l3 and passes thence downwardly about a sheave I9 journaled in the electrode carrier I4, thence upwardly to the top of the mast and over sheaves 20 and 2| and thence downwardly to a cable drum 22 forming part of. a winch designated generally by referencenumeral 23. The winch 23 is mounted upon a support 24 carried by the edge of the member I2. Fastened to the bottom of the support 24 underneath the winch 23 is an electric motor 25. The shaft 23 of the motor 25 carries apinion 21 meshing with a spur ear 28 on a shaft 29 forming a portion of a worm ear speed reducer through which the cable drum 22 is rotated. When the motor 25 is rotated in one direction the cable drum winds up the cable I! and raises the electrode I2. When the motor 25 operates in the opposite direction the cable drum 22 pays out the cable *II and the electrode l2 moves downwardly by gravity, such movement being controlled by the cable drum. The cable passes directly from the electrode supportover the top of the mast and about the cable drum and is so short that slack take-upand stretching of the cable is not a factor of importance in operation of the furnace. All sheaves except those specifically described above and shown in the drawings are preferably eliminated. By mount-- ing the winches in the manner described above they will at all times follow the movements of This construction substantial movement of the electrodes relative to the roof, this being accomplished without resorting to any complicated system of sheaves or method of reeving the cable.

The means for initiating operation of the motor 25 may be such as are well known in the art. There is standard automatic electric furnace operating mechanism controlled through changes in currentvbrought about by changes in r the distance betwen the end of the electrode and the bath or charge. The particular furnace shown in the drawings is designed for operation by three-phase current, although the invention may equally be applied to furnaces of other types.

The end of the arm l5 Mounted on the side of the furnace body 2 ,in the form of structure shown in Figures .1 to 4, inclusive, is a hollow casting 30 which carries a vertical cylinder 3|. Within the cylinder -3| 'is a piston 32 which carries the member l2. A

portion of the piston is provided with teeth 33* with which-cooperates a fluid actuated rack 34 mounted in a cylinder 35 carried by the cylinder 3|. When the top of the furnace is to be opened fluid is admitted to the bottom of the cylinder 3|, which fluid raises the piston 32 to raise the furnace roof so that itclears the furnace body.

During this raising movement the teeth 33 of the piston 32 which are sufliciently elongated in the direction of the axis of the'piston 32 simply slide in the teeth of the rack 34. After the furnace roof has been raised a predetermined A amount itis swung laterally about the axis of the piston 32 as a pivot by actuating the rack 34 by admitting fluid to the right-hand end of the cylinder 35 viewing Figure 4. This piston, cylinder and rack mechanismfor opening the furnace roof is of standard construction and is not per se claimed as novel herein. However, the openings in the hollow casting 30 provide passageways for the circulation of fluid therethrough to counteract the tendency of the heat of the furnace to excessively heat the cylinders 3| and 35, and to counteract the tendency toward overheating of the furnace lining adjacent the casting 30. While the natural draft may be relied upon, it is desirable to position a fan or-blower 36 on the frame 4 which blows air up through the hollow casting 30. This provision is found to effectively counteract the tendency of the heat of the furnace. to excessively heat the cylinders I 3| and35 and the mechanism cooperating therewith. At the same time the furnace wall is sufficiently cooled toprevent overheatingof the refractory furnace lining in this area, thus materially prolonging its useful life.

The motors 25 are shielded from the heat of the furnace by-a plate 31 connected at its, top with the support 24 and whichis interposed between the motors and the body of the furnace when the furnace roof is in closed position.

There is also a plate 38, also-connected with the support 24, and which is interposed between the body of the furnace and the motors 25 when theroof is in open position. I have found that by provision of the plates 31 and 33 to shield the motors from the direct heat of the furnace the winches. and motors can be mounted on the edge of the furnace roof without being deleteriously aflected in operation of the furnace.

Figures 5, 6 and 7 show a modified structure for maintaining the roof operating mechanism in place on the furnace. There is shown a furnace body I02 mounted on the side of which is a hollow casting I30 which carries a verticalcylinder -|3|. The mechanism within and cooperating-with the cylinder |3| maybe identical with that within and cooperating with the cylinder 3| in the form of structure shown in Figures 1 to 4, inclusive, so will not be further described.' The casting I30 has portions I32 and I33 lying against the furnace body 2 and has generally vertically extending outwardly projecting spaced flanges I 34. The casting I30 is also suitably ribbed and provided with cut away portions for strength and lightness, as shown in Figure 6. Welded directly to the furnace body I02 intermediate the flanges |34 is a cooling receptacle I35 in the form of a five-sided metal box. A

portion of the furnace body furnishes the sixth side to close the box. Cooling water is adapted to be circulated within the box I35, the water entering through an inlet conduit I36 and Raw ing through an outlet conduit I31. A. clean out and draining conduit I38 opening into the bottom of the box I35 is also provided. Normally the conduit I38 is closed.

Welded to the outer extremity of each of the flanges I34 at I39 and to each of the portions I32 and I33 at I4!) is a plate I. The top and bottom edges of each plate MI are also welded Iclaimr 1. An electric furnace comprising a furnace body, a roof normaly disposed over the body and swingable laterally in opening and closing movements, an electrode carried by the roof and means including a motive unit carried by the roof and swingable therewith and at all times laterally offset from the body-for imparting operative movements to the electrode.

to generally horizontally projecting ribs or shelves formed in the casting I30 so that two cooling chambers "land I43 are thus formed.

Cooling water is circulated through each of these chambers, being admitted to each thereof through an inlet I44 and discharged through an outlet I45. Each of the chambers I42 and I43 2. An electric furnace comprising a furnace body, a roof normally disposed over the body and swingable laterally in opening and closin movements, a plurality .of electrodes carried by the roof and means including a plurality of motive units, one for each electrode, carried by the roof and swingable therewith and all at all times laterally ofiset from the body for imparthas a normally closed clean out and draining conduit I46.

Thus in the structure shown in Figures 5, 6

- and '7 there are provided three cooling chambers each having separate means for circulating cooling water or other cooling fluid therethrough. One of the cooling chambers is welded directly to the furnace body and the other two are formed in the casting I30 by welding plates Ill thereto. The structure of Figures 5, 6 and 7 has been found highly satisfactory in use and is'at present the preferred structure for supporting the roof operating mechanism 'and -providing cooling 'means adjacent the connection of the support- .ing means with the furnace body.

Certain of the details of the structure indicated in the drawings, as for example, the means for conducting the arc current to the electrodes, are not specificaly described as these details may be in accordance with standard practice. It is to be understood that the word cable as used in the claims contemplates any suitable flexible elongated member which can be used for the purpose herein described.

While I have shown and described certain ing operative movements to the electrodes.

3. An electric furnace comprising a furnace body, a roof, a plurality of electrodes carried by theroof, means including a plurality of motive units, one for each electrode, carried by theroof for imparting operative movements to the electrodes and a generally upright pivot at the side of the body upon which the roof is mounted for laterally swinging movement, the pivot being so constructed and arranged relatively tothe motive units so that-upon swinging of the roof to open position all of the motive units move to positions offset from the body.

4. An electric furnace comprising a furnace body, a roof, three electrodes carried by the roof,

three winches also carried by the roof, cable expresent preferred embodiments of the invention,

it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied within the scope of the following claims.

FRANK w, BROOKE

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