US2402852A - Induction furnace load control - Google Patents

Description

n 25, 1946- .H. A. STRICKL AND, JR

INDUCTION FURNACE LOAD CONTROL Filed March 2, 3 Sheets-Sheet l w.) ME

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ATTORNEY June 25, 1946. N H. A. STRICKLAND, JR 2,402,852

INDUCTION FURNACE LOAD-CONTROL ATTORNEY Patenterl- June 25, 1946 INDUCTION FURNAQELOAD CONTROL Harold A. Strickland, In, Detroit, Mich., as

slgnor, by mesnc assignments, to Budd Wheel Company, a corporation of Pennsylvania Application March 2, 1943, Serial No. 477,749

furnaces, and more specifically to induction furnaces adapted to heat billet or bar stock for forging purposes. In such furnaces it may readily occur that due to various causes such as power failure to the control circuits, or operation of limit switches within the induction furnace control or by direct or accidental stoppage of the heating cycle circuits, the timers controlling the heating cycle of the furnace are reset. Consequently, if a new heating cycle is instituted without removal of a partly heated billet, the furnace may be damaged by melting of the billet.

It is, therefore, an outstanding object of the present invention to provide an induction furnace control requiring complete removal of a workpiece from the furnace in which the normal heating cycle has been interrupted. Another object is to prevent reheating of a workpiece after a normal heating cycle without first completely removing the workpiece from the furnace. An additional object is to provide furnace control means for preventing overheating or melting of a workpiece. An object also is to prevent oper ation of an induction heater unless the workpiece is completely inserted in the furnace.

The above and other objects are 'efiectuated by the mechanism and procedures hereinafter de scribed and illustrated in the accompanying drawings, in which Fig. 1 is a side view of a furnace embodying the invention;

Fig. 2 is a rear elevational view showing details of the switch operating mechanism;

Figs. 3, 4, and 5 are diagrammatic views showing the workpiece entering, partly entered, and fully entered into the furnace chamber;

Fig. 6 is a wiring diagram of the electrical circuits; and

Fig. '7 is a section ofthe apparatus shown in Fig. 2.

The general physical arrangement of the furnace follows that of my co pending application Serial No. 384,503, filed March 21, 1941, on which this invention is an improvement. r isdisclosed in said application and as shown in Fig. l, the furnace includes an upright rear section 80 formingan L-shape with a front lower section it, the section if) containing control apparatus and, section ii, capacitors l2.

Placed closely in the angle of the L-shape is the furnace unit l3 having a casing i a ventilating screen 85. hood switch box is and hood or door H. In dotted outline within-the'casing 9 Claims. (01. 219-13) ll are shown the heating coil l8, heating chamber l8. mouthpiece 20, c-bracket furnace supports 22, and bus bars 23 having depending connections to the bus framework 25 and power inlet connection 26 in section II. Furnace section [0 includes the ejector rod 30 extending into the furnace chamber as shown in Fig. 3, ejector collar 3|, bell crank arms 32 and 33 on pivot 34, bell crank spring 35, bell crank cam 36, limit switch 31, bell crank arms '38,'bell crank rod 39 and full load limit switch 40, these elements being mounted on the partition plate 9, separating the furnace section III and 13.

At the right hand base of furnace section H is illustrated a footlever 4|, pivoted at 42, which on actuation against tension of spring 43, compresses fluid in a servo-motor M thereby transmitting pressure through pipe line 35 to the floating fluid pressure piston-cylinder unit 86 shown in Figs. 2 and 7. The cylinder has pivotal connection to the bracket 8! to which the depending hell crank spring 35 is also attached. The piston of unit to is pivotally connected to the hell crank arm so that on extension of the piston on pressure of foot pedal ii the bell crank 32-33 is rotated to move the ejector rod into the fur ace chamber iii, thus forcing outwardly the con tained workpiece. Simultaneously the limit switch hell crank arms will follow collar 36 due to spring loading as will now be more fully described.

Reference is made to Fig. 2 for further structural details relative to the load switch operating mechanism. in this figure it appears that the pivot pin lid for the pedal operated ejector hell crank 322-33 also supports hell crank cam it with its associated arm Elli and arm 3%. While bell crank lit-3t is an integral unit, the position of cam 36 in the -35 hell crank unit is adjust= able to control the point of operation of switch 3?, this switch having a normally open switch contact element Bio and a normally closed switch contact element ilh.

As shown more clearly in Figs. 3-5, the earn element 325 has a circular periphery 5i ternil mating in a recess 52? on the far side from the furnace chamber. Adapted to move over the cam periphery is the switch arm 53 terminating in the arm roller lid. When the roller rests in recess 52 the limit switch li'l is in its open position. Rearward movement of the cam away from the furnace will lift the arm roller out of recess 52 thus closing switch contact element 31a and opening till). This movement is opposed by coil 3 spring I, attached to arm The bell crank arm II of the bell crank unit H! is fixed relative to arm 50, and at its end has pivotal connection to the rod 39 extending upwardly to a point adjacent load limit switch III. This switch has an arm Iii carrying at its end a fitting 5!, vertically apertured to receive the end of the upstanding bell crank rod 39. The arm BI is pivotally mounted on the fitting 58 so that movement or the fitting on the rod operates the switch 40. A collar 51 is adjustably fixed to rod II at a predetermined distance from the lower rod pivot such that when the bell crank I048 is moved to its extreme rearwardposition the collar 51 will have engaged the fitting BI and moved the arm of switch 40 to closed position. At the other positions of hell crank movement the switch II is open, as appears from Figs. 4 and 5.

Figs. 3, 4, and 5 show diagrammatically the relative position of furnace and load limit switch mechanism. The switches and controls are mounted on the rear of back plate 9 in operative relationship with the elector rod 30 and the attached rod collar II. On the front of back plate 9 the ejector rod 3! extends into furnace chamber ll, substantially axially thereof, and is thus adapted to contact with the bar 60 or other workpiece inserted through the furnace mouth 20. Adjacent and below the mouth is the single pole double throw load limit switch Ii having switch contact elements "a and 8ib and also having a sprkig controlled operating arm 62 and roller arm terminal 63, this terminal being adapted to engage yieldingly the work-piece while it is being inserted removed from the furnace chamber. This engagement is such as to cause opening of the normally closed switch element B In closure of the normally open switch contact element Bib only when the switch arm I! is forced downwardly by the workpiece the spring moving the switch arm to position to close Bio and open Bib as soon as the load moves out of contact with roller ll.

Having in mind the physical arrangement of furnace and switch elements, as shown in Figures 3 to 5 particularly, the operation is as follows. Prior tointroduction of the workpiece all load switch contact elements except 31b and Uia are in open position. Upon engagement of the workpiece with the arm of load switch 6i, as shown in Fig, 3, contact element Bib is closed and lid is opened. Further movementof the bar to the position of Fig. 4 brings about engage-' ment of bar and ejector rod, thus moving out collar 3| to rotate cam 38 and close switch contact element 31a and open 31b. In the final position of mg. 5, with the bar fully within the furnace chamber, cam rod 39 is at its uppermost po. sition thus closing the switch 40. At the same time the mouth switch II is freed of workpiece zagement and lb switch element is opened and in closed. It may be here observed that if the workpiece element lib closed when the workpiece is at the rear chamber fere with the successful operation of the furnace.

Having described the physical features of the invention it remains to describe the electrical circuits, through the functioning of which the switches are controlled so as to require complete removal of a workpiece in case of accidental power stoppage due to causes within or wit o the furnace circuits.

is over-long so as to keep switch 4 The wiring diagram is shown'in Fig. 6, the power source supplying alternating current being I indicated at ill, and the mainline-s at H and l2.

The circuits may be roughly classified in five sections designated as supply, starting, load safety, timer and high frequency and identified in the drawings as A, B, C, D, and K, respectively. The supply section A includes fuses I3, overload disconnecting heaters and main switches".

Included also are the main 60 cycle pilot lamp 16, water pressure switches 11, water pressure pilot lamp [8, water heater l9, and water thermostat 80.

Main lines H and 12 extend from the supply circuit A into the starting and load protective circuits B and C, these two sections being mutually dependent for operation. Starting circuit B is based on a pilot contactor relay li which on energization is adapted to close its switches 82 and 83. In addition to the basic elements mentioned the starting circuit includes the hood switches 84 and 85, pilot lamp 86 and main contactor relay switch 81, the circuit passing from main line 72 through tap line 5, pilot lamp 86 and relay 8| in parallel, main relay switch ll, pilot lamp relay contact 83 and hood switch 84 in parallel, and hood switch 85 to the load safety section C. Also from hoodand pilot relay switches 83 and 84 a branch line leads through pilot relay switch 82 to a sequence or distributor switch II, which selects the particular furnace of a bank of furnaces for energization, and thence to the timer circuit section D.

limit, such closure will not inte'r- The basic elements of the'lOBd-Sitffity section V C are the anti-reset relay 8! and switch contact elements 37a, 31b, and am, no. Anti-reset relay 89 is adapted on energization to open the normally closed anti-reset relay switches II and 92.

In addition to the enumerated basic elements there is included in the C section the anti-reset pilot lamp 96, and water temperature and flow switches I00 and iii. The circuit leads from main line ll through water temperature and fiow coil 89 and pilot lamp 88 in parallel to a common Junction I02,- thence by anti-reset relay switch 9| to a common junction "II. From point )3 the circuit leads through switch contact elements Bib and 31b to point M2.

The timer current section D is formed principally of two timers of any appropriate commercial make together with related elements. The function of the timer is to effect a time limit, sublect to adjustment, on the amount of heat received by the workpiece and two timers are used to insure completion of a heating cycle in case one timer should fail to perform properly. Timer I it includes the timer solenoid ill, motor H2 and magnetic timer lock switch iii. Associated with this timer are the timer on-relay ill and timer on-relay switch I II. A switch for the motor ill and the relay ill includes a contact arm H6 which is movable to an on contact element H1 and to an 03" contact element III. 8lmi larly in timer III) is included the solenoid III. motor I22, and magnetic lock switch ill. Asso- 'ciated with this timer I20 are timer on-rela I, timer on-relay switch I25, and contact arm m movable to on contact element I21 and "oi!" contact element ill. The timer section D also includes the hood solenoid I28 for operating the hood latch, and hood pilot lamp I80 for indicating completion of the heating cycle.

The timer circuit is traced from the sequence selector switch 88 through parallel lines III and I82, including timer solenoids III and I2I respectively, to the main line I2. power after opening of sequence switch 88, tap lines are connected at points I88 and I84 on lines III and I82 respectively at points between the sequence switch 88 and solenoid coils III and I2I respectively, these tap lines leading through the timer switches II8 and I28 respectively and a common return line I88 to point I04 between B and C sections. Line I88 also supplies power to the timer switch arms I I8 and I28. The timer onrelay coils H4 and I24 are connected to the main line I2 from points intermediate the on timer contact elements I I1 and I21 and the corresponding motor. The hood solenoid connects the main line I2 to the ofl" timer contact elements H8 and I28. Associated with timer section D is the main contactor relay I H with the heat-on pilot lamp I42 connected in parallel therewith. Circuit connections with the timer section are made by extension of timer circuit I85 from tap point I31 through load switch 40, furnace panel door switches I88 associated with various side or rear panel doors, on-relay timer switches I25 and H5 to tap point I40 at the relay I4I. Also the main line I2 is extended from tap point I48 through tap point I88 and hood switch I44 (in the switch box I8) to the main contactor relay I4I. A pilot iamp'I48, indicating complete insertion of the workpiece, connects the power side of the panel door switches I88 with the main line I2.

There remains to be described the high-frequency section E. This section includes the main contactors relay contacts and a rectifying circuit for supplying direct current for operation of the high frequency contactor operating coil. There are two main contactor relay switches I50, I SI and the previously mentioned switch 81 in the starter section B, also operated by the contactor relay.

The rectifying means is embodied as a conventional bridge I52 comprising four branches I58, I84, I85 and I58 with copper oxide or equivalent elements inserted, one in each branch, with such polarity as to produce a direct current potential at tap points I51 and I58, as indicated. Alternating current is led to tap points I58 and I80 on the rectifier from main line I2 at tap point I38 and from the C-Dline I85 at a tap point I8I, the resultant tap line'including in series a resistance cut-in combination of a resistance I82 and normally closed by-pass switch I88 on the resistance, and the main contactor relay switch I5I; The rectified circuit connects in series the main contactor relay switch I80 and the high frequency contactor operating coil I84. Energization oi' magnet coil I84 closes the switch I88 of the high frequency high voltage circuit I88 including the power source, I81, capacitor I88 (corresponding to I2 previously mentioned) and heating coil I8. Usually the power source provides current at about 800 volts and 3000 cycles in the heating circuit.

Having in mind the complete organization with associated electrical and mechanical features, the operation of the furnace control follows. The side and rear panel doors are closed closing panel door switches I88. The water cooling system is turned on, this resulting in closureof pressure To maintain switch 11 and flow switch Ill. The main switches II are then closed, current flow being indicated by the various current flow indicating lamps I8, 18 and 88. Illumination of lamp 88 indicates a closed circuit through anti-reset relay 88, by way of normally closed load switch contact elements 8Ib and 81b. Simultaneously, anti-reset relay switches 8I and 82 are closed thus locking the anti-reset relay closed and conditioning the circuits for application of voltage on the starter section B and timer section D on introduction of the workpiece.

The workpiece is now inserted in the furnace chamber causing the closure of load switch contact element 8Ib and thereby applying voltage to point I04 and starter section B and timer section D.

Before the workpiece has passed completely over load switch arm roller 83, it engages the ejector rod 80, thus actuating the arm of load switch 81. This switch has two contact elements 81a and 31b which are simultaneously actuated, switch contact element 31a serving on closure, to maintain a voltage on the starting and timing circuits irrespective of the action of load switch 8|. Opening of either or both 81b or 8Ia shifts the anti-reset relay circuit entirely through antireset relay switch 8| so thatshould the power be withdrawn from this relay permitting opening of the switch 8|, it cannot again be closed unless both load switch contacts 81b and 8Ia are closed, this requiring complete unloading of the furnace.

The workpiece is now moved to the rear end of the furnace chamber closing load switch 40 in the timer D section. The furnace hood is then closed bringing about closure of hood switches 85 and I44, and a momentary closure of hood switch 84. On the closure of hood switches 85 and 84, a closed circuit is at once established through normally closed main contactor relay switch 81 and the pilot contactor relay 8| with its associated lamp 88. 'Ihereupon the two pilot contactor relay switches 82 and 83 are closed, switch 88 locking the pilot relay 8| closed since hood switch 84 is closed only momentarily during the hood closing movement. Also power is applied by way of switch 82 to the sequence switch 88.

The system of circuits is now conditioned for initiation of a heating cycle. This will develop when the sequence switch 88 which controls the sequence of power application in the furnace bank are already closed, power is at once supplied from circuit point I04 between sections B and C through line I 85. and from main line I2 to the main contactor relay HI and its associated signal lamp I42.

The energization of relay I4I closes main contactor control relay switches I58 and I5I, and opens switch 81 in the starting section circuit. The effect of opening switch 81 is to deenergize pilot contactor coil 8i and cause the opening of I pilot contactor relay switches 82 and 88, thus breaking the circuit through the sequence switch. Additionally, closure of main contactor relay switch I5I closes a circuit from point IN on power line I35 through the resistance cut-in switch I83 to point I89 on the rectifier bridge I", thus, applying a voltage at point I68 from main line 12, creating a direct current voltage at points I81 and III which is effective through closed switch I88 to energize the high-frequency contactor coil I84. Thereupon, the switch I85 in the main induction heating coil circuit are closed and power from the source I8! is applied to heating coil II.

On completion of the heating cycle either timer contact arm breaks contact at I" or. I21 and opens relay switches H or I25, thus disconnecting relay I II and opening the main circuit and stopping the application of power. In addition, timer contact arms 8 and I28 engage contact elements I I8 and I28 causing functioning of hood solenoid I29 to open the furnace door and hood switches 88 and I. The workpiece may now be removed from the furnace by actuation of foot pedal ll and application of tongs.

An outstanding feature of the described system has already been referred to, namely, the impossibility of reinstituting the heating cycle, on interruption of the cycle due to limit switch operation because of drop in cooling water pressure or temperature or control power failure. Should any one of these conditions develop, and the workpiece remain in the furnace, the anti-reset relay coil 89 would be de-energized thus holding switch 82 open and preventing the re-application of voltage on the timer section. In order, therefore, to continue furnace operation it is necessary to remove the billet, bar or other work-: piece completely from the furnace in order to reset the anti-reset relay. It is then obvious to the operator that the workpiece has already been fully or partially heated and thus the likelihood of reheating of partially heated bars to the fusion point with resulting damage to the furnace and loss of time and material is avoided.

On normal operation it is impossible to recycle the equipment without completely removing the workpiece from the furnace because it is necessary to remove control voltage from the timers to reset them and this can only be done by opening both load switch contact elements 31a and 8 I b which due to their mechanical arrangement require the complete removal of the workpiece- It is observed further that in the described control it is necessary to move the bar or other workpiece completely within the furnace to the rear end thereof before the heating cycle can commence. This is due to the necessity of closing load switch Additionally it is pointed out that the hood switch I, movable to closed position only on lowering of the hood I1, prevents the main contactor relay from functioning when the hood is open and also automatically break the main contactor relay circuit when the hood is opened.

In operation the described system and apparatus work effectively and positively accomplishing diversified results with a relatively simplified arrangement. Obviously, some modification may be made in the details of the system and structure, and hence the scope of the invention should be read from the appended claims.

What is claimed is:

1. In electrical heating apparatus, a heating coil adapted to receive and heat a workpiece, switch means for inducing a heating cycle in said coil on insertion of said workpiece, and means for in :venting a renewed heating cycle in said coil after failure and re-establishment of power and prior to complete removal of said workpiece from 80 before heating power can flow.-

8 the coil, said means including a workpiece operated switch mechanism in operative relation with said coil at each end thereof.

2. In electrical heating apparatus, a heating coil adapted to receive and heat a workpiece. switch means for inducing a heating cycle in said coil on insertion of said workpiece, and means for preventing a renewed heating cycle in said coil after failure and re-establishment of power and prior to complete removal of said workpiece from the coil, said means including at least two switches, and plural means actuated by the workpiece for operating said switches, one of said switch actuating means being adjacent the coil end.

3. An induction heating coil having a hollow heating chamber substantially closed at one end, and adapted to receive a load, plural switches. load .pperated switch means adjacent the open end of said chamber adapted to operate one of said switches, and load operated switch means intermediate the chamber ends adapted to operate another of said switches, a control circuit connected to said switches for energizing said heating coil, and relay means connected in parallel with said switches effective to prevent reenergizing of said heating coil after an initial heating period and prior to complete removal of the load from said switch means.

4. In electrical heating apparatus, a heating coil adapted to receive and heat a load, power mains, switch means connected to said mains for opening and closing the circuit of said coil, timer means connected to said switch means for timing the heating cycle, a starting control means connected to the timer means and load safety means connected to the starting control means for preventing re-heating of said load. without complete removal of the load from said coil, said load safety means'including a switch operated by the movement of the'load into and out of said coil.

5. In electrical heating-apparatus, a heating coil adapted to receive and heat a load, power mains, switch means connected to said power mains for opening and closing the circuit of said coil, timer means connected to said switch means for timing the heating cycle, a starting control means connected to said timer means, and load safety means connected to said starting control means for. preventing re-heating of said load. without complete removal of the load from said coil, said load safety means including plural switches connected across said means and switch operating means positioned at each end of said coil and adapted for separate operation at entry and full insertion of the load within said coil to prevent re-heating of the load prior to complete removal thereof.

6. In electrical heating apparatus, a heating coil adapted to receive and heat a load, switch means for opening and closing the circuit of said coil, power mains, timer means for timing the heating cycle, a starting control means, and load safety means for preventing re-heating of said load, without complete removal of the load from the said coil, said load safety means comprising a relay coil and a relay contact normally open when the relay coil is deenergized connected in series across said mains, load switches connected in parallel with said relay contact and normally closed on removal of load from said heating coil, and additional load switches normally open on removal of load from said heating coil operatively connected to said closed switches and electrically connected to one of said power mains,

for closure or opening of said closed switches, said relay contact being adapted for closure on the energization of the relay coil, and said closed switches to open and open switches to close on the insertion of load within said heating coil, the closing of said open switches by the load, conditioning the timer means for closure of the heating coil circuit.

7. In electrical heating apparatus a heating coil for heating a workpiece, and load safetycontrol means for requiring complete removal of the v for operating one each of said closed and open,

switches.

8. In electrical heating apparatus, a heating coil for heating a workpiece, and load safety control means for requiring complete removal of the workpiece after a partial or complete heat treatment thereof prior to additional heating, said means comprising power mains, two switches is free of load connected in parallel around said contact whereby on application of power, the relay coil is energized to close and lock said contact, and load operated means effective at one end, and at a point intermediate the ends of the heating coil to close one of said open switches and open one of said closed switches, whereby on opening of the contacts power cannot be .reestablished in said relay coil prior to complete removal of said load.

9. In electrical heating apparatus, a heating coil adapted to receive a workpiece, switchmechanism for establishing current flow in said coil on insertion of a workpiece therein, and means for preventing a renewal of current flow in said coil after cessation of current flow therein and prior to removal of said workpiece from the coil, said means including a workpiece operable switch in operative relation to said coil at the point adjacent that of full workpiece insertion.

HAROLD A; STRICIUJAND, JR.

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