US2365521A - Electric arc furnace - Google Patents

Description

Dec. 19, 1944. w BROOKE 2,365,521

ELECTRI C ARC FURNACE Filed Feb. 16, 1943 4 Sheets-SheetZ Dec. 19, 1944. F. w. BROOKE ELECTRIC ARC FURNACE Filed Feb. 16, 1943 4.Sheets-Sheet 3 INVENTOR Fnw/v/r n4 5:?60/(5 [91/ ATTORNEY Dec. 19, 1944. E w BROOKE 2,365,521

ELECTRIC ARC FURNACE Filed Feb. 16, 1343 4 Sheets-Sheet 4 INVENTOR fiMN/r 1 55100415 BY Q/MMQ ATTORNEY Patented Dec. 19, 1944 2,365,521 ELECTRIC ARC FURNACE Frank W. Brooke, Pittsburgh, Pa., asslgnor to Swindell-Dressler Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application February 16, 1943, Serial No. 476,078

2 Claims.

The general object of the present invention is to provide an electric arc furnace of the well known type comprising mechanism for raising (and lowering the heavy vertically disposed graphite or amorphous carbon electrodes extending into the furnace, with simple and effective emergency stop mechanisms operative to lock each of the electrodes and the apparatus moving with it, against down movement as a result of a breakage or failure of the electrode adjusting mechanism, which otherwise would permit the electrode to plun e down. t tact with the furnace hearth.

The present invention was primarily devised for usewith the most useful type of electrode adjusting mechanism, namely, the type in which .the electrode is suspended from a crosshead which is movable longitudinally of a vertical mast and which is suspended from the top of the mast by a loop or bight portion of a cable which has its dead end connected to the top of the mast and which has its other end connected to a winch rotated by an electric motor to raise and lower the crosshead and suspended electrode. In modern are furnaces, each electrode and its supporting crosshead and connections may weigh thousands of pounds and much damage may result from any failure of the electrode adjusting mechanism which will permit the electrode tomove down into the furnace until its movement is arrested by the furnace hearth. In addition to the electrode and furnace injury which may result from such electrode movement, the material undergoing treatment in the furnace may be damaged by carbon pick-up.

A specific object of the present invention is to provide a furnace having each of its electrodes suspended from a crosshead which is itself suspended and moved up and down along-a vertical mast by a cable, with means for mechanically locking the corresponding electrode supporting crosshead against down movement along its mast, on and as a result of the reduction in the suspension cable tension which occurs when the cable breaks, or which might occur as a result of some breakdown of the cable guiding or actuating mechanism. My improved emergency stop mechanism in its preferred form, also'operates to positively lock each electrode against down movement on a failure in the energizing current for the corresponding winch motor.

Heretofore, safety arrangements of various kinds have been devised to eliminate or minimize risk of damage on a failure, or on an interruption in the normal operation, of the electrode adjusting mechanism of arc furnaces. One such arrangement heretofore developed operates on a breakage in an electrode suspension cable to interrupt the energization of the corresponding winch motor. So far as I am aware, however, no electric arc furnace has been provided with means effective to prevent an electrode from falling down into the furnace when the electrode suspension cable breaks.

The various features of novelty which characterize my invention are pointed out with particularity in the claims anneired to and forming a part of this specification. For a better understanding of the invention, however, its advantages, and specific objects attained with its 'use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred embodiments of the invention.

Of the drawings:

Fig. 1 is an elevation, with parts broken away. of a portion of an electric furnace;

Fig. 2 is a plan view, with parts broken away and in section, of the furnace structure shown in Fig. 1;

Fig. 3 is a partial section on the plane indicated by the line 33 of Fig. 1 and of Fig. 4;

Fig. 4 is an elevation, on a larger scale and in more detail, of a portion of the apparatus shown in Figs. 1 and 2;

Fig. 5 is a rear elevation of an electrode supporting a mast shown in Figs. 1-4;

Fig. 6 is a section on the line 6-6 of Fig. 5;

Fig. 7..is a plan-of electrode adjusting apparatus mounted at the top of the electrode supporting mast;

Fig. 8 is a sectional elevation on the broken line 8-8 ofFlg. 7; Fig. 9 is a diagrammatic representation of ap paratus illustrated in Figs. 1-8;

Fig. 10 is a diagrammatic elevation; and

Fig. 11 is a plan illustrating a modified form of my invention.

In Figs. 1-9 of the drawings I have illustrated the use of apreferred form of the present invention in an electric arc furnace A of conventional type. In the furnace illustrated, the cylindrical metallic furnace shell is pivotally connected at one side by hinge'pintles B to a metallic supporting framework C for tilting movements incidental to the discharge of molten furnace contents through the furnace pouring spout A. At the opposite side of the furnace from the spout A, the furnace is provided with 8 t ca ly movable door A, and the top of the furnace chamber is normally closed by a vertically movable roof A supported by the furnace shell. The furnace roof A is formed with three electrode openings and surrounding glands A through which three suitably spaced vertically disposed electrodes D respectively extend downward into the furnace chamber. the type shown customarily includes liquid wall cooling provisions and power mechanism for tilting the furnace, but no further reference to the construction, form and disposition of the furnace features already mentioned is necessary, as those parts are well known and their particular form and disposition constitute no part of the present invention.

The furnace structure illustrated includes separate means for supporting and adjusting each of the different electrodes D, and said means may be, and as shown are of well known form, except in respect to safety features provided in accordance with the present invention to lock each electrode against down movement under certain abnormal conditions. As shown, each electrode D has a portion above the furnace roof A which extends through, and is secured by wedges e in a supporting collar E carried at one end of a horizontal arm or boom E The latter has its other end attached to and supported by a crosshead or carriage E mounted on and longitudinally movable along a corresponding vertical mast F which has its lower end attached to and supported by the shell of the furnace A. Each mast F with the crosshead E mounted thereon, and associated mechanism hereinafter described for adjusting and supporting the crosshead, constitute an adjusting and supporting mechanism for the corresponding electrode D, which is separate from, though shown as identical in construction and operation with, the mechanism for supporting and adjustmg each of the other electrodes D.

Each crosshead E shown is a hollow open ended box-lik structure surrounding the corresponding mast F. As shown, each crosshead E comprises upper and lower horizontal roller shafts G journalled at their ends in the crosshead and each supporting a pair of rollers G engaging the side of the corresponding mast adjacent the electrode D supported by the crosshead. At the opposite side of said mast, upper and lower horizontal roller shafts g are journalled in the crosshead and support rollers g engaging the adjacent side of the mast. As shown, the rollers G and g are formed at their outer ends with outwardly extending flanges G and 9 re spectively, which engage the edges of the mast sides engaged by the rollers, and thereby prevent lateral displacement of the crosshead. Each crosshead comprises supports E at its opposite sides for conductor elements H which connect the corresponding electrode D to the source (not shown) of electrode current.

As shown best in Figs. 3 and 4. the side of each mast F engaged by the corresponding rollers G. is formed by an elongated metal plate or bar F which is riveted or otherwise secured to one flanged edge of each of a pair of channel bars F The opposite flanged edges of the channel bars F are riveted or otherwise secured to a metallic plate or bar like member F, comprising end portions which may be similar in cross-section to the bar F and comprising an intermediate portion having a longitudinally extending central portion formed with a row of slots F separating bar like looking teeth portions F of the mem- A furnace of ber F provided for the purposes of the present invention. The side edge portions of the member F form track surfaces for the rollers g.

In the furnace shown each crosshead E, and thereb the corresponding electrode D, is supported by means of a cable I in the manner indicated diagrammatically in Fig. 9. The cable I has a dead end connected to the top of the corresponding mast F through a resilient dead end connection J supported by the top plate F secured to the upper end of the corresponding mast F. From its dead connection to the top of the mast, the cable I extends downward to and under a pulley or sheave E and thence upward and over guide pulleys or sheaves K mounted on the top plate of said mast. Th sheave E is connected to and supports the crosshead E through a horizontal shaft E From the sheaves K the cable I extends into operative connection with a winch or winding drum L rotated by a corresponding motor M. 'l 'he latter is customarily subject to automatic control by and in accordance with variations in the current through the corresponding electrode, so that the electrode will be raised and lowered as required to maintain said current at an approximately constant value. Customarily, the motor M is also subject to manual control. However, the particular character of the control provisions for the motor M forms no part of the present invention and need not be illustrated or described in detail.

In the form illustrated, the dead end connection device J serves as an emergency trip device and comprises a base plate J which rests on the corresponding mast top plate F, and is provided with uprising posts Jlextending through openings in the plate like top portion of a vertically movable spring abutment member J. -A helical spring J acting between the abutment member J and base plate J, is under tension sufficient to hold the abutment member J in engagement with nuts J on the upper end of the post J as shown in Fig. 8, when the cable I is not under tension. Under normal conditions, however, in which the cable loop or bight extending under the sheave E supports the weight of the corresponding crosshead E and the electrode supported by the latter, the spring J 5 compressed so that the depending tubular skirtportion of the abutment member J is in engagement with, and is directly supported by the base plate J. A tubular guide part J fitting snugly about the cable I, has its upper end attached to the abutment member J and has its lower end extending through the registering openings in the base plate J and mast stop plate F. The tube J eliminates risk of injurious contact of the cable I with the plates J and F, and also serves as an elongated guide for the vertical movements of the abutment member I.

The dead end portion of the cable I extends axially through the spring J and through registering openings in the top plate F, base plate J and abutment member J into an axial passage I, formed in a cylindrical member P which engages the upper side of the abutment member J at the.margin of the opening through which the cable I passes. In the customary construction illustrated, the passage I increases in crosssection from its bottom to its top, and the portions of the cable strands within the passage are spread apart and rigidly connected by zinc or the like, poured into place while in a molten condition.

.In modern furnaces, the gear connection between the motor M and winch L is ordinarily not of a character to arrest down movement oi. the electrode when the energizing current normally supplied by conductors I and 2 to the motor M is interrupted and the motor M is thereby deenergized. With the arrangement shown in Fig. 9, however, an interruption in the current supply which deenergizes the motor M, will also eifeet the actuation of emergency stop mechanism to lock the crosshead a ainst down movement.

In accordance with the present invention, the vertical movements of each abutment member J control the operation of the corresponding emergency stop mechanism through a switch N mounted on the corresponding base plate J and including a switch arm N pivoted on a supporting'pin N". The switch arm N is held in its circuit closing position by a projection J from the corresponding abutment member J when the latter occupies its normal depressed position shown in Fig. 9. A bridging contact N carried by the switch arm N, engages and connects stationary switch contacts n when the switch arm is in the circuit closing position. However, if the cable I breaks, or has its tension otherwise relieved so that the abutment J is free to move into its position shown in Fig. 8, the switch arm N turns clockwise, as seen in Fig. 9, under the action of a bias spring N and thus moves the bridging contact N out of engagement with the contacts n.

In the form shown in the drawings, each of my novel emergency stop mechanisms include an oscillating locking element mounted on the corresponding crosshead E, and controlled by the corresponding switch N as hereinafter described. The locking element 0 comprises the locking pawl 0', an actuating arm 0 and horizontally aligned trunnions which are journalled in bracket extension E of the sides of the corresponding crosshead E, so that the pawl 0' may turn about the common axis of the trunnions from its normal inoperative position shown in Fig. 4, into its operative position shown in Fig. 6. In the operative position of the pawl 0' its bevelled end engages the horizontal upper side of the lower one, and the inclined front face of the upper one, of the two adjacent locking teeth F of the adjacent section F of the mast.

The pawl 0' is biased for movement into looking engagement with the mast teeth F by a bias spring 0 having its upper end attached to the arm 0 and having its lower end anchored to a lower portion of the carriage E. In the normal condition of the apparatus, the pawl O is held in the inoperative position shown in Fig. 4 against the action of the bias spring 0 by electro-magnetic means comprising a solenoid coil Q, then energized, an armature Q, and a link Q connecting the armature Q to the arm 0 As shown in Figs. 3 and 4, the solenoid coil is covered by a shield Q and is mechanically connected by bolts R. to a bracket R, and'the latter is connected by bolts l t to the bearing housings for the upper shaft g of the corresponding crosshead.

y In the arrangement shown diagrammatically by way of example in Fig. 9, the solenoid Q is energized when the switch arm N occupies its circuit closing position, by an energizing circuit which includes supply conductors l and 2, a con ductor 3 running from a supply conductor l to one terminal of the solenoid Q, a conductor 4 connecting the second terminal of the solenoid to one of the switch contacts n, the bridging contact N and a conductor 8 which connects one of the switch contacts 1': to the supply conductor 2. Desirably in some cases a manually operable switch 6 is included in the conductor 3 or, as shown, in the conductor 4.

As above stated, the particular form of the control provisions for the motor M forms no part of the present invention. Advantageously, however, the switch N is used in a known manner to prevent undesirable operation of the winch motor M when the corresponding cable breaks. This previously known safety action is attained with the arrangement shown in Fig. 9, by means including a conductor 1 extending from the third contact n to a motor starting and control apparatus S which may be of known type and through which the energization of the motor M by current supplied by conductors l and 2 and branch conductors 8 and 9 is controlled.

Preferably, the conductors l and 2 direct current and the motor M includes dynamic brake provisions which need not be described as they may be of customary type and form no part of the present invention. The apparatus S will ordinarily include control mechanism which may be of well known type and which operates on and in accordance with variations in the current fiow through the associated electrode, to raise and lower the latter as required to maintain said current at approximately the desired value. The apparatus S may also include means through which the energization of the motor M may be manually controlled.

In the contemplated mode of use of the apparatus illustrated in Figs. 1-9, the motor M operates under ,normal conditions to raise and lower the corresponding electrode D as required to maintain the proper current flow through the electrodeyand the weight of the carriage E and associated parts including the suspended electrode D then put sufilcient tension on the cable I to hold thedevice J in its depressed or collapsed position shown in Fig. 9. When in that position, the device J holds the bridgim contact N of the switch N in engagement with the contacts n. In consequence, the solenoid Q is then energized by current flowing between the supply conductors l and 2 through circuit connections 3, 4, N and 5. With the solenoid Q energized, its armature Q is retracted and the locking pawl 0 is held out of engagement with the locking teeth F When the cable I breaks or has its normal tension otherwise relieved, the device J elongates and the projection J actuates the switch mechanism N to move the bridging switch contact N out of engagement with the contacts n. This disconnects thecircuit conductors 4 and 5 and Y deenergizes the solenoid Q, whereupon the bias spring 0 turns the member 0 into the position in which its pawl O engages the adjacent locking tooth F as shown in Fig. 6. With suitably designed apparatus, the emergency stop pawl 0' is brought into locking engagement with the mast so quickly following the release of the cable tension, that the falling movement of the crosshead and electrode is arrested before it can have harmful results.

A similar safety action is effected when the supply of current through the conductors l and 2 is interrupted. Such a power failure deenergizes the solenoid Q and the bias spring 0 then turns the pawl 0' into engagement with the looking teeth F just as it does when the solenoid Q is deenergized through the switch N when the cable tension is abnormally reduced...

As will be readily apparent to those skilled in the art, my invention may take widely different forms, and, in particular, it is possible to employ mechanical safetymeans, in lieu of the electrical illustrated in Figs. 1-9, to positively lock an electrode supporting crosshead against objectionable down movement on a rupture in the electrode suspending cable or development of some other abnormal condition relieving the cable tension and rendering the cable inoperative to hold the electrode against objectionable down movement. One form which such mechanical safety means may take, is illustrated in Figs. 10 and 11.

The apparatus shown in Figs. 10 and 11 comprises electrode supporting means including a crosshead EA, a cable I, a dead end connection device JA, guide pulleys K, and a cable winch L, generally like the elements E, I, J, K and L of the construction first described. In Figs. 10 and 11, however, the vertical movements of the dead end connection device JA are employed to give oscillatory movements to a vertically disposed splined shaft T which is suspendedslfrom and has its upper end journalled in the corresponding mast head E As shown, the device JA oscillates the shaft T through an arm T secured to the upper end of the shaft I, a link N pivotall connected at one end to the free end of the arm T and pivotally connected at its other end to the uprising arm of a bell crank lever NA which has a horizontal arm extending between and thereby operatively connected to upper and lower projections J from the cylindrical spring enclosing member element of the device JA. The bell crank lever NA is journalled on a pivot pin N mounted in uprising brackets on the base J of the memberJA.

The splined shaft T extends through and is longitudinally and rotatably movable in bearing openings formed in upper and lower projections E from the associated crosshead E. A cam member U is splined on the shaft T so as to rotate with the latter and is received between the upper and lower projections E so as to share the up and down movements of the crosshead EA. In the normal operative condition of the apparatus illustrated in Figs. 10 and 11, a portion U of the cam U extends beneath and is horizontally engaged by the hook portion of a detent 0 having its lower end connected by a pivot O to an arm 0 of a locking element 0A mounted on the crosshead E. The locking element 0A may be identical in construction and the detent 0 is prevented from turning in the clockwise direction about its pivot O" away from the position shown in Fig. 10 by a stop lug or portion 0" of the arm 0 The intended operation of the mechanism shown in Figs. 10 and 11 will be apparent without further explanation. With the apparatus in the condition shown in Figs. 9 and 10, the pawl O' is locked out of engagement with the locking teeth F by the interengagement of the detent 0 and cam U. On any abnormal reduction in the tension of the cable I resulting in the expansion of the spring J and up movement of the abutment member J of the device JA, the shaft is given a clockwise adjustment as seen in Fig. 11. That adjustment of the shaft 'I' turns the cam U out of operative engagement with the detent O and the spring W then angularly adjusts the locking element 0A, and to bring the pawl 0' into operative engagement with a pair of locking teeth J just as such locking engagement is effected in the construction first described on the deenergization of the solenoid coil Q. When thereafter the operative condition of the supporting mechanism for the crosshead EA is reestablished so that the weight of the crosshead and electrode is transferred from the locking teeth J engaged by the pawl O to the cable I, the detent 0 and cam U may be reengaged, thus restoring the apparatus to the condition shown in Figs. 10 and 11.

While in accordance with the provisions of the statutes, I have illustrated and described the best forms of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the forms of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of general mode of operation with the previously described locking element 0, except that the arm 0 of the device 0A, which replaces the arm 0 of the device 0, is connected to the locking detent 0 instead of the armature of an electromagnet. As shown, the arm 0 is provided with a handle 0 to facilitate manual angular adjustment of the element CA as may be desirable in some cases, and particularly in reestablishing engagement of the detent 0 with the cam U following a disengagement of those parts. A tension spring W connected at its lowerend to the crosshead EA, has its upper end connected to the detent 0 at one side of its pivot 0 so that the spring W biases the detent for counterclockwise rotation about its pivot 0 and also biases the locking element 0A for angular movement-in the clockwise direction about its trunnion axis, so as to bring the pawl 0' into locking engagement with the mast teeth F when the cam U is turned out of its position of operative engagement with the detent 0 As shown,

other features.

Having now described my invention what I claim as new and desire to secure by Letters Patent, is:

1. In an electric arc furnace, the combination of a vertical mast, an electrode supporting crosshead mounted on said mast for movement longitudinally thereof, a cable connection between the upper end of said mast and said crosshead through which the latter is supported, said cable connection comprising a resilient deadend connection device and a guide pulley, each mounted on said mast at its upper end, a winch, a cable extending over said pulley and connected at one end to said winch and having its other end connected to said device and having a portion between said pulley and device forming a depending loop engaging and supporting said crosshead, a switch mounted on the top of the mast and actuated by said device on an interruption in the normal cable tension, a locking device mounted on said crosshead and biased for movement into locking engagement with the mast, an electro magnet for holding said locking device in an idle position, an electric motor for operating said winch and means including said switch for connecting said electromagnet and motor to an energizing source of current whereby said electromagnet is deenergized by a failure of the source to supply current and by an abnormal reduction in the tension of the cable.

2. In an electric arc furnace, the combination of a vertical mast, an electrode supporting crosshead mounted on said mast for movement 1ongitudinaliy thereof, a cable connection between the upper end or said mast and said crosshead through which the latter is supported, said cable connection comprising a cable, a resilient deadend connection device and a guide each mounted on said mast at its upper end, a winch, a cable connected at one end to said winch and having its other end connected to the top of the mast through said device and having an intermediate portion between said pulley and device forming 9. depending loop engaging and supporting said crosshead, a switch mounted on the top of the mast and actuated by said device means on an abnormal decrease in the oabie tension,

Images