US1308624A - Henby coates - Google Patents

Description

H. COATES.

ELECTRIC ARC FURNACE APPLICATION FILED NOV.27, IQIB. v

Patented July 1, 1919. 2 SHEETSSHET I H. COATES.

ELECTRIC ARC FURNACE.

APPLICATION F| LE D Nov 27. 1918.

Patented July 1, 1919.

Z SHEETS-SHEET 2 J usti ng HENRY COATES, OF WAT'FORD, ENGLAND.

ELECTRIC-ARG FURNACE.

Specification of Letters Patent.

Patented July 1, 191a.

.Applicationfiled November 27, 1918. Serial No. 264,392.

To all whom it may concern:

Be it known that 1, Honor CoATns, a subjeet of the King of England, residing in ld 'atford, l-lertfordshire, England, have in vented certain new and useful Improvements in Electric-Arc Furnaces, of which the following is a specification.

This invention relates to electric arc furnaces and the means whereby they are regulated. -lt is customary at thepresent time to provide such furnaces both with handopcrated means for raising and lowering the electrodes and with automatic means for adjusting them. The hand-operated means arebonnnonly employed when the furnace is started and when approximately stable conditions have been reached the duty of adthe electrodes is transferred to the automatic gear. Such automatic gear or anton'iatic regulators are both well-known, and are of more than one kind. The type I of such regulator to which the present invention in part relates, is that which has its action determined. by the strength of the current flowing through the arc, and it is hereinafter referred to as an automatic regulator controlled by the current-strength of the are. 1

Automatic regulators of the kind defined, controlled by the current-strength of the are, are sometimes arranged to move the electrode or electrodes in the direction determined by the automatic control, not with a continuous movement, but by a succession of short movements separated from one another by short periods of rest; the object of this arrangement is to prevent hunting and a regulator arranged in this manner is hereinafter described as a stepby-step regulator. I

All automatic regulators of the step-bystep type controlled entirely by the current-strength of the are are open to the objection that on certain classes of work, such for example as the melting of turnings and boring s, they do not respond at all times in such a way as to prevent tripping the circuit-breaker for the furnace. Each time a circuit-breaker is tripped, and the furnace has to be re-startcd, a loss of time occurs which, in. the case of a reasonably large plant. may be so long as a quarter of an hour, and this loss of time is very objcc tionable. The pizcsent invention has for its prime object the obviating of risk of tripping the circuit-breaker in the said manner but has other objects which will hereinafter appear.

According to the present invention there is combined with an arc-furnace an automatic regulator controlled by the current-strength ofthe arc, a voltage-controlled automaticv switch having two or more positions controlled bythe voltage at the arc, and means so connecting the switch with the said regulator that in one position the switch permits the said automatic regulator to operate in its normal manner but in the other position-coiiperates with other parts of the apparatus so that the are is lengthened at a more rapid rate than by the norn'ial operation of the said regulator.

Preferably the voltage-sensitive portion of the said switch is constructed to move a live contactor between two yieldingly supported contact pieces whereof one affords an idle circuit and the other formspart of the operating circuit for the switch and the parts are so constructed that the contactor docs-not, when moving in either direction, break circuit with one said contact piece until after it has made circuit with the till other. By this means the voltage-sensitive closed electro-magnctically on to its contacts in each of its said two positions. Other features of novelty will hereinafter appear and are pointed out in the claims.

The accompanying drawings illustrate one embodiment of this invention intended to be employed as an accessory to an automatic step-bystep regulator- F :igure 1 being a front view of the automatic switch portion, and

Fig. 2 a similar view of the voltagesensit-ive'device controlling the switch of Fig. 1.

The parts are shown in such positions that the switch of Fig. 1. is at the con'lmencemcnt of the movement called for by the position of the parts of Fig. 2. The switch of Fig. 1 is operated by a solenoid A whose plunger A carries a yokeA each end of which is linked by a link A to one of two pivoted switch arms B pivoted at B. Each switch arm B cooperates with two contacts C and I), and the arm carries a tail piece B on which is mounted a roller B to cooperate with a cam-track E carried by an arm E pivoted at E Beneath each arm E, which constitutes a switch arm, is a yieldingly mounted carbon block F suitable stops and return springs are provided for the arms E.

Below the yoke A the plunger carries an armature (1 for an electro-magnetG mounted on the panel below the switch. The yoke A and the armature G are resiliently connected in any convenient manner to the plunger, as for example through the medium of the coiled spring A*.

To the right-hand side of the panel is a voltage-sensitive device comprising a coil H mounted on the center limb of a blocl; of U-shaped stampin gs H between whose polar embrace is a pivoted armature H of stampings carrying short-circuited coils H Fast upon the spindle of the armature H is a tongue J constituting a contactor, to play between two carbon contact pieces J slidingly and resiliently mounted in boxes in such a way that as the contactor moves away from one in the direction of the other, the former .follows it until the other has been reached, but so that continued movement of the contactor causes it ultimately to leave the first said block and break circuit therewith. Suitable controls are provided for the armaturel l and some such are indicated by the dashpot K and counterweight K The coil H is connected by the wires it across the are which it is desired to control by the means illustrated. Above the voltage-sensitive device H H is a small electrically operated switch comprising a magnet L, its pivoted armature L and a pivoted switch arm L weighted or spring controlled to tend constantly to assume the position in which it is shown in the drawing. The free end of the arm L plays between two contacts L L whereof L is a dummy,

The electrical circuits of the apparatus are indicated in full lines, chain lines, and dotted lines, indicating respectively, a heavy current supply of direct current, a light current control circuit fed with direct current and a light control circuit fed with aiternating current.

The contacts C are connected by wires 0 to the Thury regulator or hand control feed supply and serve to bring supply current controlled by it through the switch arms B anud the wires 2) t0 the armature of the electrode-operating motor. The wires 6' are also tapped into connection with the arms E, 'and the carbon blocks F are connected through their housings to the two ends of a braking resistance f. The motor has its shunt field constantly excited independently of the circuits-indicated in the drawing.

A supply of direct current power at the full voltage at which the electrode motor carbon J .allel with the wire 7'.

may be operated, is brought by the wires (Z to the contacts D.

From the right-hand contact D two control circuits are taken, the upper one by the wire I through the contact L and the wire a to the solenoid A, from which a wire a continues the circuit to the left-hand contact D.

The other control circuit passes by way of a limiting resistance R to the contactor J which is thus always alive, and thence by way either of the upper or of the l wer In the drawing the path is by way of the lower contact and the wire j direct to the left-hand main at D. A ta-p pin is taken from the wire j to the coil of the magnet Gr this circuit being completed by way of the wire 9, and the winding of the magnet L to the upper carbon J When the parts are in the position shown in the drawing the voltage across the arc has fallen to a value below that which it is desired to maintain and the contactor J has therefore fallen on to the lower carbon block. In this position there is no circuit through the magnets L and G, and the armature of the former therefore drops and its switch arm L closes upon the contact L moreover the magnet G being new uneXcited its armature G is free. The plunger A is thereupon pulled upward and the circuit at the contacts C interrupted thereby disconnecting the motor from the ordinary automatic control. As the plunger moves up: ward the rollers B press the arms E on to the contacts F thus momentarily connecting the motor armature to the braking resistance f and finallythe circuit to the motor armature is established from the contacts D through the arms B, the brake resistance be ing in this posit-ion disconnected. The mutor armature is now supplied with an uninterrupted supply at full voltage from the contacts D through the arms B and wires 7). It therefore revolves in the direction to raise the electrode and does so at the maximum speed obtainable. Meanwhile the current is flowing idly from the right-hand contact D through the resistance R and the contactor J to the left-hand block D. As the electrode rises and the voltage across the arc increases the contactor J slowly rises until it meets the upper block J which causes the circuit composed of the magnets L and G in series with one another to be put in par- They are thus, it' energized at all, energized too feeblv to effect any movement of their armatures. Further rise in the voltage at the .arc causes the contactor to rise still further until eventually it breaks circuit with the lower block J. This causes the magnets L and G to be fully energized, and the former throws the switch arm L so interrupting the circuit through the solenoid A. The plunger A thereupon thus preventing overrunning.

the electrode can In the normal operation of n r-phase furnace lieret .)fore practised without the aid of this invention, and when employed. for the melting down of iron and steel turnings and borings, it is started by throwing the autonmtic regulator out of operation and by putting nninuu-i labor on to each of the three electrodes, switching on the higlrtension side of the usual transformer feeding; the furnace and carefully and gradually lowering each electrode by the seid n'uinuul labor. In result the charge on the hearth becomes gradually heated and when this has proceeded sulhciently :ler for the production of. a substratum of liquid metal, the duty of controlling the electrodes is train red from the operatives to the mitomutic regulators It, however, frequently happens tlnit, it cuvity having been formed in the uniss of the charge, the material forming the side of such cevity suddenly falls in siiert-cii- .:uiting the are in. the cavity and cventuelly tripping the c-ircuit-l'n'enlier. it such tiines tlie tripping of the breaker may be avoided if "e rnised with sullicicnt rapidity,

It will he observed thut the apparatus provided by this invention may form it simple addition to existing phmt. switch on the regulutor for raising the electrodc be on elcctro-nnig 'neticully operated switch, then the particular construction of ports shown in 1 may be dispensed. with it desireih and. the ports of li ig. Zbe so counccte l to the said switch us to operate it in the inunncr provided. by this invention. This invention enublcs manual control of electrodes to be dispensed with, The

' furnace n'niy thus be started up cold and switched in and out and otherwise handled the ordinary "21y but without the need for menuul udjustment oi the lectrodes zit sl'urting nor subsequently.

If for any reason the supply of power to the timisii'orincr or tinnsl oru'icrs supplying the lurnz'ice cut oil", the furnace electrodes will "not. with the nrrnugemeut provided by this invaution. rcmuin close to or in contact with lhe church nor will thcyg (as with the ordinary Thury regulator under current- C(Hlll'i'll alone teed continuously down into the furnace -hurgc uniil solid opposition iii-ct witln either Ul which conditions liable to result in sci'crc short circuits. unless grout cure is exercised by the semi-skilled opera,- tors when reclosiug the switch.

llhe present invention meets these condi- Shoul d the tions by the automatic raising of the clec trode quite cleur from the charge im1nedizitcly the voltage is cut oil', until. at the upwnrd limit of travel of the electrode, at limit switch (either existing or which. could be readily installed) stops this movement automatically; thereafter the mniu switch can be closed and. the electrodes moved down to the charge without dung-er of serious short circuits.

A further advantage results from the fact that the loud variation on automatic furnace regulators oi the kind in which the control is dependent onv the currcnt-streugth of the arc, is sometii'ncs obtained. by on urrungg'cmcnt in. which the combined current in. the rcgulutor coil and a loud adjusting circuit is kept in u predetermined ratio to the muin furnace current.

.lt sometimes occurs in practice that these iul iustments having been set for it certain loud current in ouch clcctrmle conditions of the charge in the furnace ell'erd at content sullicieut for smull currents but of lliSullicicnt area for the large current for which the rcgulutor hes been set. The regulator then supplies energy to the electrodemotor to drive the electrode downwurd to obtain :in increusc of current up to the predetermined; value. and. this frequently results in broken GlOOid'OllPs. "il'ith. the attachment provided by this iuvcntion ucontuctof this nature would result in the electrode being first ruised and then lowered until the nrciv oi" coutuct had been improved by the nornuil switch permits the said uuton'uitic regulator to o icrute in its normal i'nzinner but in the other position cooperates with other parts of the uppninl'us so that the arc is lengthened :it u more rapid rate then by the nornnil opcl'ution of the said regulzitoiz 2. Appurutus according to clziin'iing-cluuse No. 1 wherein the voltage-sensitive portion of the said switch is constructed to move it live contuctor between two yieldingly supported contact pieces whereof one lllil)l(.l8 an idle circuit and the other forms part of the operating circuit for the switch and the ports are so constructed that the eontzictor does not, when moving in either direction,

break circuit with one said contact piece until after it has made circuit with the other, for the purpose described.

3. Apparatus according to claimin -ciause operated by the switch to put a brake for N0. 1 wherein the said switch cont-r0 s a secthe arcmd usting motor on and off tutoond switch closed. eiectro-m'agneticaliy in matically as the switch passes from one po- 10 each of its said twc positions for the purpose sition to the other.

5 described. in testimony whereof I affix my signature.

4:. The combination with the switch of claiming-clauses No. l and N0. 3 of means HENRY COATEE}.

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