US2816334A - Automatic ladling control for metal melting furnace - Google Patents

Description

Dec. 17, 1957 E. w. EDSTRAND 2,816,334

AUTOMATIC L ADLING CONTROL FOR METAL MEL-TING FURNACE ed Sept. 24, 1956 42 I19: 1.

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United States Patent AUTOMATIC LADLING CONTROL FOR METAL MELTING FURNACE Elmer W. Edstrand, Berkeley, lll., assignor to Lindberg Engineering Company, Chicago, 111., a corporation of ois Application September 24, 1956, Serial No. 611,419

12 Claims. (Cl. 22-79) This invention relates generally to metal melting furnaces and more particularly to an automatic ladling control for metal melting. furnaces.

Metal melting furnaces are known in the prior art wherein a charge of cold metal is heated to a molten state or is held in a molten state by electric induction, fuel combustion and the like and the molten metal re-' sulting from the heating is removed from the furnace by means of a pump associated with the furnace. Advantageously, the pump may be of the type which is seated over the open upper part of the furnace and which causes the molten metal to be discharged through a suitable. discharge channel connected to the pump byapplying gas pressure to the surface of the molten metal. Inasmuch as the discharge channel generally extends a substantial amount into the molten metal within the furnace it has been found that the amount of molten metal discharged by the operation of the pump for a set time varies in accordance with the level of the molten metal within the furnace. Manifestly this condition is a wholly unsatisfactory one as it is desirable in a large number of applications that a uniform amount of molten metal be discharged for every operation of the pump.

Accordingly, it is a general object of this invention to provide improved meansfor controlling the discharge of molten metal from a furnace.

More specifically it is an object of this invention to provide an improved control circuit which compensates for variations in the level of molten metal within a furnace to discharge a predetermined amount therefrom.-

It is another object of this invention to provide an improved ladling control for a metal melting furnace which automatically enables the discharge ofa uniform amount of metal therefrom regardless of the level of the metal within the furnace.

It is a further object of this invention to provide elec' tronic means responsive to the quantity of molten metalin a metal melting furnace for controlling the amount of molten metal discharged therefrom.

It is a still further object of this invention to provide an improved control circuit for automatically determining the period of operation of a discharge pump associated with the furnace.

It is a still further object of this invention to provide such an improved automatic ladling control for metal.

ing the discharge of molten metal therefrom. The period. of time during which the pump operating valve is en-' ergized is controlled by a novel electronic circuit having a discharge device which is maintained nonconductive;

for the desired length of time after the discharge opera-1:

tion is initiated.

2,816,334 Patented Dec. 17, 1957 The dischargedevice is held in normally nonconducting condition by a bias potential applied thereto. The control further comprises a float adapted to be placed in the molten metal within the furnace crucible such that its level varies in accordance with the level of the molten metal. The float is connected to a potentiometer wiper which provides an output voltage that varies in accordance with the position of the float. The potentiometer output voltage controls the magnitude of the bias potential applied to the discharge device, which potential is removed when the pump operation is imtiated. Thus, the position of the float, i. e., the level of the molten metal in the furnace crucible, determines the period of time after removal of the bias voltage, before the discharge device becomes conductive and stops the pump.

Therefore, it will be understood that for relatively high levels of molten metal within the furnace crucible the bias potential on the discharge device will be such as to cause it to become conductive a relatively short period of time after the pump is started and conversely for low levels of molten metal within the furnace crucible the biaspotential on the discharge device will be such as to cause it to become conductive a relatively long period of time after the pump is started. Since the energization of the pump operating valve for discharging the to' insure that an equal amount of molten metal is disspecification. For a better understanding of this invention, however, its advantages and specific objects attained by its use reference is had to the accompanying drawing and descriptive material in which is shown and described an illustrative embodiment of the invention. 7

In the drawing:

Figure 1 shows a metal melting furnace of a type embodying the present invention; and

Figure 2 is a schematic diagram of the electronic control circuitry embodying the invention.

Referring now to the drawing and more particularly to Figure 1 there is shown a dual chamber type induction furnace with which the invention advantageously may be used. The furnace as shown comprises a main body 10 which may be formed of ceramic or refractory material to withstand the heat of the molten metal without damage. In the dual chamber induction furnace shown the body is formed with a melting chamber 12 which may be relatively large and with a pouring or ladling chamber 14 spaced horizontally from chamber 12 and preferably smaller than the latter. Both chambers are adapted to-contain molten metal 16 and may be connected by spaced channels 18 formed in the body 10 and lying below the normal level of molten metal in the chambers through which the metal can flow from the melting chamber to the ladling chamber. 2

Metal in the chambers in heated by means of a transformer primary loop, indicated generally at 20, which is positioned between the melting and ladling chambers and is magnetically linked with channels 18. As is wellknown in the art the primary loop 20 is energized to produce a flow of secondary heating current for melting the metal in the furnace.

A pump assembly indicated generally as 22 is positionedin operative relation with the molten metal 16 in ladling crucible 14. Pump 22 comprises a pump chamber 24. which advantageously is formed of refractory material.

Pump-.chamber- 24. isl-hollowdand has an elongated body xtending .substantially. below. the... level.v of. moltenme al...

16. An opening 26 is provided at the bottom of pump chamber 24 for enabling the-.molten metal in chamber 14 torseekiitselevelnwithin rpumntchamberz 24:}. Aadiseh'arg manner-281th connectedate:vpumncchamber: 24mand;sis. adapted to communicate-withtthe.moltenimetahwithin the pump chamber by =ma X3i:Of. tan :openingmrovided there:

chamber: ,24 is forced. up, throughathedischarge channel 28,-andvout-of, the furnace. The inlet.opening;26 is made: small to dim-it backflow; of metal. to; thechamber :14, during this operation.

It: readily will be appreciated thatflwhenrtherpump chamberispressurizedfor set periods of timethe amount.

of molten metal discharged from, the furnacevaries. in accordance. withthe level of .themoltenmetal in thefur:

nace. amounts ,of molten metal from the. furnace; for each operationof thepump, an electroniecontrol circuitris provided with .the furnace to, automatically compensate for-changes in; level to thereby equalizetheamount of molten. metal discharged from the :furnace,

In accordance with an aspectof'this invention afloat 32, whichadvantageously maybe formedof .a ceramic. material, is-placed in supported position .within pump chamber 24 so as tofloaton-themolten-metal 16 therein. A- shaft :34 is connected to the float 32 andis adapted to follow the float in accordance, withchanges; in the level of moltemmetal in thefurnacen A'portionof the control circuit isprovided within ahousing .36-positioned above thefioat and is adaptedto cooperate with a suitable. electronic; timing circuit, as, described below, to. vary the operatingtimeofi the pump in accordancewith the level of-moltenmetal 16- asindicated by changesin the position of. shaft 34; As shown in Figure 2;.and as described belowvinzconnectiontherewith, shaft .34 is connected to the wiper 90 of a potentiometer 86 positioned within housing36- to the end that-variations in the level of the molten metal within the furnace are communicated by the.follQwer-,action of the float 32 and;shaft 34 to wiper 90 to thereby causecorrespondingchanges in the positionlof thewiper.

A preferred-embodirnent of the control circuit isshown imFigureiZ ofnthe drawing. The control circuit comprises aytransformer 40 :having .a primary winding 41 which is conuectedithroughfuse 39 across a pair of line conductors. 2 .-an d; 43, which,, in turn, are connected to -a source A.- C. supply voltagetnot shown). Onesecondary winding 4410f transformer: 40 is connected to filaments 45 4 and 46j';of a pair-of discharge..-devices 47 and 48, respectiyel-y,;tosupply heater voltage thereto. Another secondar-y winding 49, of transformer 40 is connected at one end-thereof to the anode 50 of rectifier tube 47 .3.11d at the other end-thereof through a capacitor 51 to cathode 510i rectifier tube 47.

Cathode 52 of. rectifier tube 47 is connected to a range and calibration. network comprising a calibration potentiometer 53 connected in series with a pair of fixed resistors: 5.4 and 55 and a calibration potentiometer- 56. The

contacts of a-range switch 57 are connected across potentiometerv 53 and resistor 54.

Discharge device 48 has its anode 60 'connectedthrough the; windings of relay 61 to line conductor 43; Control grid 62 of discharge device 48 is connected'through a resistor 63 to potentiometer: 56. Screen grid 64 and cathode 65 ofdischarge device 48 are connected through fuse 39-40 line conductor 42. Cathode'65 also is connected Asitnormally is.desirable to discharge; equalto one terminal of condenser 66, the other terminal of whichisconnected to control grid 62.

Condenser 67 is connected between potentiometer 56 and winding 49 of transformer 40. Resistor 68 is connected in series with contacts 69 and 70 of relay 71 across condenser 67. Contacts 72 and 73 of relay 71 are connected between cathode 65'of discharge device 48 and one terminal of a bleeder potentiometer. 74.

Potentiometer 74 is connected across the output of a rectifier which comprises a transformer 75 having a primary winding 7 6 connected across line conductors 42 and 43,, and a secondary winding 77 connected to a rectifier bridge network comprising rectifiers 78, 79, 80-and 81. The. output of the rectifier bridge network comprises a filter including condensers 82 and 83 and a resistance 84 connected therebetween. Bleeder potentiometer 74 is connected across condenser 83. Wiper 85 of potentiometer 74 is connected to a terminal of potentiometer 86, the other. terminal of which is connected to relay contact 73., One terminal of potentiometer 87 is connected to secondary winding 49 of transformer 40 and the other termnialis connected through resistance 88 to cathode 52 of rectifier 47. Wiper 90 of potentiometer 86-and wiper 91- of, potentiometer 87. are connectedelectrically and the former is mechanically coupled by shaft 34 to fioat32. Thus. wiper 90 is adapted to be. adjusted inaccordance with the position of the float as determined bythe ,level of the; molten metal 16 within ladling chamber 14..

Contacts-92 and 93 of initiating switch 94 are con nected between line conductor 43 and relay 71. Contact 92 of switch 94 also is connectedto armature contact 103 of switch; 102 .of relay 71. Contact 104 of switch 102 is connected to armature contact 95 of relay 61 and to a terminalof relay 101. The other terminal of relay 101 is; connected to line conductor 42. Contact 96 of relay 61 is connected to a terminal of ladling relay 97. The otherterminal of ladling relay 97 is connected to line conductor 42; Pump operating valve 98 is connected at its terminals to line conductor 42 and at its other terminal to armature contact99 of ladling relay 97. Contact 100 of ,ladlingrelay 97 is connected to line conductor 43.

In the operation of the control circuit, discharge device 48 normally is biased to its nonconducting condition"- by bias potentials applied betweenits control grid 62 and its cathode=65 from two separate voltage sources.

One bias potential is ,derived'from rectifier tube 47 and is applied through the circuit comprising potentiometer 53, resistances 54-and 55, potentiometer 56 and resistance 63 to the controlgrid. 62' of. discharge device 48." A

second bias potential is derived from the rectifier bridge network comprising the rectifiers 78, 79, 80 and 81, itsfilter network and potentiometer 74 and is applied through potentiometer 86uand its wiper 90 to wiper 91 of-postentiometer 87;

Wiper, 90 .of; potentiometer 861is mechanically coupled: to ceramic float 32 in the pump chamber 24. Thus, as the level ,of molten metal 16 in chamber 24 varies, the voltage at; wiper 90 of potentiometer 86 varies accordingly and is I added to the voltage at potentiometer 87.. The resultant bias voltage on discharge device 48 is the. sum of these two bias potentials and chargescapacitances 66and 59 to apply this voltage at cathode 65 of dischargedevice-48 the openingof its normally closed contacts 69 and 70 and;

the closing of itsnormally open contacts 103. and 104- The energization of relay 71 and the subsequent opening of its normally closed contacts 69 and 70 initiatesthe. timing cycleof the circuit. Atthistime, however, ladling; relay 97 also is energized th-rough'a circuit including line conductor 43, initiating switch contacts92 and 93, closed contacts 103 and 104 of relay 71, normally closed contacts 95 and 96 of relay 61, relay 97 and line conductor 42. The energization of relay 97 closes its normally open contacts 99 and 100 to energize the pump operating valve 98 and thereby initiate the pumping of molten metal from the furnace. Advantageously, pump valve 98 may be of the air or gas solenoid type whereby energization of the valve opens a line to pump chamber 24 to pressurize the latter and force molten metal 16 through discharge channel 28.

The opening of contacts 72 and 73 as a result of the energization of relay 101 and the opening of contacts 69 and 70 as a result of the energization of relay 71 removes the bias potential supplied from the rectifier bridge from the storage capacitors 66 and 59. Capacitors 66 and 59, which previously had been charged to a voltage representing the sum of the two bias potentials maintains the bias potential on cathode 65 of discharge device 48 and holds the latter in a nonconductive state. With contacts 69 and 70 of relay 71 open, capacitor 6! begins to charge to the value determined by storage capacitor 59. When capacitor 67 has charged to the 'predetermined bias voltage of capacitors 59 and 66, discharge device 48 starts to conduct and relay 61 in its anode circuit is energized. The energization of relay 61 causes its normally closed contacts 95 and 96 to open and thereby open the power circuit to ladling relay 97. The resultant de-energization of relay 97 reopens its contacts 99 and 100 and consequently de-energizes the pump valve 98 to terminate the pumping action in the crucible.

It will be understood by those skilled in the art that the period of time defined by the addition of the second bias potential to discharge device 48 and the additional subsequent conduction of the latter is determined by the amplitude of the second bias potential. Thus, for a relatively large second bias potential, the timing cycle will be considerably lengthened, for a relatively small second bias potential, the timing cycle will be correspondingly shorter. The reference time is set by suitable adjustment of potentiometer 87 in the control circuit and this time is varied in accordance with the metal level by potentiometer 86 coupled to float 32. Thus the amplitude of this second bias potential is determined by the position of float 32 in pump chamber 24 and the length of the timing cycle is varied directly by the level of the molten metal in the furnace. When this level is a relatively high one the second bias potential added to the first bias potential is small and the increase in the timing cycle is relatively short. When the level of the molten metal is low the second bias potential is correspondingly greater and the increase in the timing cycle is long. In this manner variations in the level of the molten metal 16 in the furnace are compensated for and a uniform amount of molten metal is discharged from the furnace for every ladling operation regardless of the level of molten metal Within the furnace.

It will be appreciated that the range of the automatic ladling circuit may be changed to conform with the size of the furnace used by changing the position of switch 57 in the output of rectifier tube 47 and by suitable adjustment of potentiometer 87. Potentiometers 53 and 56 are calibration potentiometers and once set are never changed in position. Additionally, the circuit may be adjusted and balanced by properly positioning wipers 85 and 91 of potentiometers 74 and 87 respectively.

It will be understood by those skilled in the art that modifications may be made in the construction and arrangement of the parts of the above described automatic ladling control means without departing from the real purpose and spirit of the invention and that it is intended to cover by the appended claims any modified forms of structures, circuits or use of equivalents which reasonably be included within their scope.

What is claimed is:

1.' A metal melting furnace having means for automa-tically ladling a predetermined amount of molten metal comprising a chamber to hold molten metal, a discharge channel disposed in said chamber, pump means for cansing the molten metal to be discharged through said discharge channel, a float positioned in said chamber such that its position is varied in accordance with the level of the molten metal therein and actuating means operatively connected to said float and responsive to the level of the molten metal as indicated by the position of said float for causing said pump means to be operated a period of time suflicient to discharge a predetermined amount of molten metal from the chamber regardless of the level of the molten metal therein.

2. A metal melting furnace comprising a chamber to hold molten metal, a discharge channel disposed in said chamber, pump means for causing the molten metal to be discharged through said discharge channel, switch means for initiating operation of said pump means, and a circuit including a timer responsive to the level of the molten metal in the chamber for automatically terminating the operation of said pump means after a period of time determined by the setting of the timer and the level of the molten metal.

3. A metal melting furnace in accordance with claim 2 wherein said circuit includes storage means for storing a bias potential having an amplitude varying with the level of the molten metal in said chamber.

4. A metal melting furnace in accordance with claim 3 further comprising a float adapted to be placed in said molten metal whereby its position is varied in accordance with the level of the molten metal, a source of potential. having an output controlled by the position of said float, and means for applying said output to said storage means.

5. A metal melting furnace having means for automatically ladling a predetermined amount of molten metal comprising a chamber to hold molten metal, a discharge channel disposed in said chamber, pump means including a solenoid valve adapted to render said pump means operative upon operation of said solenoid valve for causing the molten metal to be discharged through said discharge channel, actuating means controlled by the level of the molten metal for operating said solenoid valve for a period of time sufficient to discharge a predetermined amount of molten metal from the chamber regardless of.

the level of the molten metal therein.

6. An automatic ladling control circuit for a metal melting furnace of the type having pump means associated with a chamber for causing the discharge of molten metal therefrom comprising a first source of bias voltage, a second source of bias voltage, a discharge device including an anode, a cathode and a control grid, means for applying bias voltages from the first and second sources to the cathode and control grid of said discharge device to maintain the latter in a nonconducting condition, said means including storage capacitance means capable of being charged to said bias voltages and maintaining said bias voltages upon removal from said bias voltage sources, switch means operative to start the pump means and to remove the sources of bias voltage from said cathode and control grid whereby said storage capacitance means maintain predetermined cathode and grid bias voltages and allow said discharge device to remain nonconductive until a desired time cycle has been completed, switch means responsive to the conduction of said discharge device to stop the operation of said pump means and com trol means operative to vary the bias voltage from said second source in accordance with the level of the molten metal in said chamber whereby the period of operation of said pump means is varied by the level of the molten metal in the chamber.

7. An automatic ladling control in accordance with claim 6 wherein said control means comprises a float adapted to be supported by said moltenmetal attsubstantially, theilevelv of. the .latter,;,withinv the chamber.

8.1Anl automatic lladling control in. accordance with claim "7 Twhereinsaid second source ofibias potential com: prises a rectifier circuit having a D.v C.' voltage output, and further comprising a resistance connected to. said rectifier circuit, a wiper adjustably associated with said resistance, and shaft means mechanically coupling said float to said wiper whereby the voltage at said ,wiper is, varied in accordance with the position of said float.

9. Melting furnace apparatus comprising a chamber to hold molten metal, pump means, operatively associated with said chamber for causing molten-metal to bedis-r charged therefrom and circuit means for controlling the amount of molten material discharged,'said circuit means comprising a dischargedevice, means for maintaining said discharge device in a nonconducting condition including a source of bias potential, storage-capacitance means con-. nected to said discharge device and-adaptedto be charged to said bias potential, means operative to initiate operation of said pump means and-to remove said bias potential source .from said discharge device whereby said storage capacitance means maintains a bias potential on the discharge device until the latter is triggered into conduction, and means responsive to the conduction of said discharge device when said bias applied thereto attains a value more positive thanthe cutfoff potential of they discharge device for terminating the operation-of said pump means.

10.,Meltingfurnace apparatus a in accordance with claim,9.further comprising means responsive to the level of -the.molten.material-.in said chamber for varying said bias .potentialr whereby the-period of operation of said pump ;means, is varied by the level of said molten material.

1 1.. Melting furnace apparatus in accordance with claim 10 further .cornprisingmeans, for terminating the c0nductionlof saiddischarge device upon termination of the operation of said pump means whereby said circuit means is placed incondition for a further discharge of the molten metal from the crucible.

12. Melting furnace apparatus in accordance with claim 11 wherein. circuit means further comprises adjustable means for. selectively varying the range of operation of said circuit means.

References Cited in the file of this patent UNITED STATES PATENTS 465,212 Schilling Dec. 15, 1891 2,244,490 Doyen June 3, 1941 2,397,512 Schwartz et al Apr. 2, 1946 2,741,006 Kux Apr. 10, 1956 2,757,326 Boundy July 31, 1956

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