US2412990A - Drying oven control - Google Patents

Description

Dec. 24, 1946. 0, us 2,412,990

. DRYING OVEN CONTROL Filed July 6, 1942 3 Sheets-Sheet l INVENTOR.

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flTTOE/YEYS Dec. 24, 1946. Q KRUSE 2,412,990

DRYING OVEN CONTROL Filed July 6, 1942 3 Sheets-Sheet 2 Dec. 24, 1946. o. o. KRUSE DRYING OVEN CONTROL 3 Sheets-Sheet 3 Filed July 6, 1942 INVENTOR.

'XYM ATTOE/VEYS Patented Dec. 24; 1946 DRYING OVEN CONTROL Orlln 0. Kruse, Oak Park, 111., assignor to American Can Company, New York, N. Y., a corporation of New Jersey Application July6,.1942, Serial No. 449,939 5 Claims. (Cl. 158-28),

The present invention relates to drying ovens and the like which are heated by gas burners and has particular reference to devices for controlling the lighting of the burners and for purging the oven of unburned gases and other vapors prior to lighting the burners to safeguard the oven against explosions.

In drying ovens used for baking coated and lithographed metal sheets, such as tin plate and the like from which container or can parts are produced, the drying of the sheets usually is effected by circulating heated air through the ovens. ers. In starting up such an oven and when relighting a burner, which for some reason has gone out, unburned gas sometimes collects in the oven and results in a terrific explosion if proper' precautions are not taken.

The instant invention contemplates the prevention of such explosions by the provision of control devices which insure purging of the oven prior to the lighting of the burners.

An object therefore of the invention is the pro- I vision in a drying oven which is heated by gas burners, of control devices which operate to purge the'oven of unburned gases prior to the lighting 4 predetermined time cycle after the beginning of the purging operation so that the burners are not lighted until the oven is cleared of explosive gases. 7 Another object is the provision of control de- The air is heated by way of gas burn- Fi 2 is a transverse sectional view taken substantially along the broken line 2-2 in Fig. 1; Fig. 31s a view similar to Fig. 1 with parts omitted and with other parts shown in section; and

Fig. 4 is a. wiring diagram of the electric apparatus used with the devices.

As a preferred embodiment of the invention the drawi'ngsillustrate a portion of a sheet dryin oven of the general character disclosed in United States'Patent 1,691,683, issued July 6, 1926, to

- C. G. Preis. In such an oven freshly coated or Q through the chamber is heated to a predetermined I lithographed sheets of tin plate or the like material are conveyed through a. drying chamber in an upright or "on-edge position while heated air is circulated through the chamber to dry'the coating on the sheets.

In the instant oven the air to be circulated temperature by a ring shaped main gas burner H (Fig. 1) which is located in a sheet metal duct l2 formed on top of the oven. The duot communicates, by way of suitable entrance and retum openings, with the drying chamber in the even. The burner is supplied with gas by a pipe 13 which leads from any suitable supply of gas outside the oven.

with a locking electric solenoid I! which when vices of this character wherein electric instrumentalities and suitable electric circuits are interconnected insuch manner as to interlock the control devices so thatthey are dependent for operation upon the flow of air through the oven with-the result thatthe latter 'will be purged fully of unburned gases before" the burneris made ready for lighting.

Numerous other objects and' advantages of the Figure 1 is a sectional view taken-through the 7 burner and air circulating portion of a drying oven embodying the instant invention,'with parts.

broken away;

a preferred embodiment gearstl, 32 and a worm wheel 33. The wormenergized permits of opening the valve by manipulation of the lever I8 and holds it open regardless of any further manipulation of the lever.

Closing of the valve is effected by the solenoid. Theregulatorvalve I6 is' partially opened or closed, as the case may require, tocontrol the 'heat, output of the burner and to maintain the j aircirculated through the oven at a predetermined constant temperature. Actuation of the valve is efiected preferably by a valve arm 2| which is connected by a link'22 to an actuating arm 23 mounted on a gear shaft 24 carried in suitable bearings formed in a bracket assembly 25 bolted ,or otherwise secured to the burner.

end of the duct l2.

The gear shaft 24 is part of a, speed reduction" transmission which includes a pair of meshing wheel is rotatable in either direction by a worm 34 which is mounted on a rotor shaft 35 of a reversible electric motor 36 bolted to the bracket elongated slots 51.

assembly 25. The motor is operated by suitable circuits which will be explained hereinarter in connection with the wiring diagram in Fig. '4.

Air heated by the burner II is circulated through the drying chamber of the oven by a rapidly rotating fan'll which is located within the duct I2 and which is disposed in axial alignment with the burner. The fan is mounted on a horizontal shaft 42 iournaled in bearing brackets 83 secured in place within the duct I2. The fan shaft is rotated in any suitable manner by an electric motor 44, which is indicated in the wiring diagram in Fig. 4. A pair of spaced and aligned sheet metal i'rusto-conical deflector elements 8 located around and adjacent the burner II direct the heated air toward the circulating fan ll. These deflector elements are secured to transverse support beams 41 secured in place within the duct I 2.

Provision is made to safeguard the oven against explosion when first lighting the burner II or when relighting the burner if for any reason it goes out during operation of the oven. This is brought about by purging the duct I2 and the drying chamber for a predetermined time cycle oi. any unburned gases, fumes, or vapors which may have collected in the oven and around the burner. It has been found that a time cycle of approximately three minutes is sufllcient to clear the average oven ofunburned gases.

When the burner II goes out, the main gas service valve I5 closes and cuts oil the supply of gas to the burner. Before the .burner' can be again ignited the circulating fan 4| must be in operation or must be set in operation. The setting of the fan in operation at the starting of the purging time cycle is accompanied by the opening of a rotary damper 5| (Figs. 1, 2 and 3) which admits large quantities of fresh air into the duct. This unheated air is circulated through the drying chamber and is discharged by way or a vent pipe.

The rotary damper 5| includes a stationary hollow cylinder 52 which surrounds the burner supply pipe I3 and which is or may be bolted to the burner end of the duct I2. The inner end of the cylinder is open and communicates with the interior of the duct by way or an opening 58 formed in the end wall of the duct. Th cylindrical wall or the cylinder is formed with a plurality of elongated periperally spaced slots 55.

The stationary cylinder 52 carries a surrounding sleeve 56 which is formed with a plurality of Normally these slots are held out of register with the slots 55 in the cylinder so that no air passes through them. The sleeve is held in this position by a weight 58 which is connected to the sleeve by an arm 58. The weight is fixed to a plurality of vertical rods 5| which are connected to a vertically movable member of what may be termed an oil gear'thrustor unit which includes an electric solenoid 82. The thruster unit usually is actuated by a motor through a solenoid. In order to make the explanationbriei it is sufllcient at this time to show in the wiring diagram the solenoid directly connected to the damper.

when the solenoid 82 is energized the weight 58 and'its arm 58 are raised and this rotates the sleeve 58 onthe cylinder and-thus brings theslots;

clamped on the rotary damper and is provided to permit air to enter the duct for combustion purposes. The holes communicate with cooperating circumierentially spaced holes or apertures 88 in the outer end oi. the cylinder for this p p se.

At the end of the purging cycle, the rotary damper 5'] is closed and a pilot 68 located adjacent the burner II, is lighted. The pilot is formed on the inner end of a gas supply tube 80 connected into the main gas pipe I 3 adjacent the inlet side of the service valve I5. A normally closed valve 12 connected into the pilot supply tube is opened at the end of the purging cycle by a connecting solenoid I3. This permits gas to flow to the pilot.

Lighting 01 the pilot 68 is effected by a spark from a spark plug 15 which is located adjacent the pilot. The operation or this spark plug and the solenoid I8 of the pilot valve I2 will be more fully explained hereinafter in connection with the wiring diagram.

After lighting the pilot 68, the burner II is ignited therefrom by the opening of the main service valve I5. This is brought about by energizing the-valve solenoid I9 by suitable circuits hereinafter to be explained. These circuits are established by ionized gas given ofl by the lighted pilot 88.

Reference should now be had to the wiring diagram shown in Fig. 4. In this diagram the circulating fan motor 44 is directly connected by three main lead lines 8|, 82, 83, to a suitable source of power such as an electric generator 85. This constitutes a fan or main circuit A. A service switch 86 is interposed in the line to start and stop the Ian motor. Closing of this switch sets the fan in motion and starts the oven purging cycle through a control circuit B and a time delay circuit C which'will now be explained.

The control circuit B includes a conventional flame operated protecting relay unit 88 of the character disclosed in United States Reissue Patent 20,210, issued December 22, 1936, to Dewey D. Knowles, on Safety system. Such a unit picks up low voltage current set in motion by ionized gas from the burner I I and from the pilot 88 and this current is amplified to operate certain switches in the unit. This unit is supplied with electric energy from the generator by way oi a pair of wires 9 I, 92 which connect with the main lead wires 8|, 82.

Hence when the main line service switch 86 is closed the unit 88 is immediately actuated and sets a normally closed switch having contacts 84, 95 which are included in-the time delay circuit C. Contact 94 is connected by a wir 96 to the main lead wire 82. Contact 95 is connected by a wire 91 to one side of a solenoid relay 98 having a movable core 98. The other side of the solenoid coil is connected by a wire IOI to the main lead wire 8|. Electric energy passing along this circuit energizes the solenoid relay 98 and closes a switch I05 which is actuated by the core of the solenoid. Closing of the switch I05 establishes a motor circuit D and a damper circuit E. The motor circuit D is part of the time delay circuit C and includes a motor I08 and a timing cam I08 that is rotated by the motor in any suitable manner. Electric energy for the motor flows from the main lead wire 8I along aconnectlng wire I I I, through the closed switch I05, a wire II2, motor I08, a wir 8, a normally closed cam actuated switch I, and a connecting wire II5 backto the main lead wire 82.

Electric energy passing along this motor circuit drives the motor I08 which rotates the cam I99 through one revolution. It is this cam that holds the threeminute purging cyclehereinbefore mentioned.,- At the completion of said revolution of the cam, the cam switch I I4 is opened and this breaks the circuit D. The cam switch motor thereupon ceases operation.

The damper circuit E includes the solenoid52 that opens the rotary damper 5|. This solenoid is connected by a wire I ii to one side oi the switch I85 and by a wire II8 to one side of the switch I I4, as shown in the wiring diagram. Thus when the switch I85 closes, electric energy passes from the lead wire 8i, along wire III, closed switch I85, wire IILsOlenoid 52, wire II8, closed switch II4,

andwire I I5 back to the lead wire 82. This flow of energy energizes the solenoid 52 and thus opens the damper.

Opening of the cam switch II4 by the cam I89 the spark circuit H and electric energy passes through the-transformer I43 and is induced into the spark plug I5 to create a spark adjacent the pilot 58. It is this spark that ignites the pilot.. When the pilot 58 is lighted, ionized gas from V thepilot impinges against a detector element or electrode I53 which is located adjacent thereto. .This electrode is connected by a wire I54 to the ground I48 and by a wire I55 to the flame operated relay unit 88 hereinbefore mentioned. This unit is also connected by a wire I55 to the ground.

The -.flow of ionized gas between the electrode I53 and the ground I 48 sets up a flow of low voltage electric energy in the flame operated relay unit 88 and this is amplified sufficiently to open the normally closed switch bridging the contacts 94, 95. It also closes a normally open switch ineluding a pair of contacts I5I, I52 located within the unit. Contact I5I .is connected by a short jump wire-to the 'contact 94. Contact I52 is connected by a wire I53 to a pivotally mounted norbrings the movable element of the switch into closing engagement with two'normally open con- .tacts I2I, I22 of a holding circuit F which cuts out the cam motor I88. Contact I2! is connected by a wire I24 to th switch I85 of the motor circuit D. Contact I22 is connected to one side of a solenoid relay I25 which surrounds a movable core I25 connecting with the switch element I I4. The

other side of the solenoid is connected by a wire I2! to the main lead wire 82. Electric energy passing along this holding circuit energizes the This mally open conventionalmercury switch I54 I which is rocked or. its pivotinto closed position by. a vane I55 secured to theswitch. Vane I55 is located adjacent the fan 4| and is disposed in .the path of travel of the air set in motion thereby.

The mercury, switch I55 is connected by a wire I51 to one side of a solenoid I58 of a relay switch I59 which forms a part of a burner circuit J. The opposite side of the solenoid coil is connectedby a wire ill 'to the main lead wire 8i.

Hence with the circulating fan M in operation and the vane switch I54 closed, electric energy from the main lead wire 82 flows along the wire 95, contacts 94, I5I, I52, wire I53, closed vane switch I54, wire I51, solenoid-I58, and wire I'IIv back to the main lead wire 8I. This electric energy energizes the solenoid I58 and thus closes the relay switch. I59 for the burner circuit J.

' The burner circuit J includes the main gas valve solenoid I9. One side of the solenoid coil is v I connected by a wireJI'I5 to the main lead wire 82 switch element I I4 also establishes a pilot circuit U G which includes the pilotgas valve solenoid 1-3 and an auxiliary solenoid relay I3I. Contact I22.

i connected by a wire I32 to one side of the auxiliary solenoid relay I3I and to a wire I33 which connects with one side of the pi ot valve solenoid 13. The opposite sides of these solenoids are conthe contacts I2 i, I22 electric energy from thewire I II passes along the holding circuit F and the pilot circuit G and thus energizes the two solenoids I3, I3I. Energizing 0f the pilot gas valve solenoid I3 opens the pilot gas valve 1-2 and permits gas to flow to the pilot 58. Energizing-of the auxiliarysolenoidrelay I3I establishes a spark circuit H which is associated with the spark plug I15.

while the opposite side is connected by a wire I18 to-the relay switch I59. This switch is connected bya wire I" to the main lead wire 8|.

Hence closing of the relay switch I69 establishes the burner circuit J and permits electric energy toenergize the main gas valve solenoid I9.

As hereinbefore mentioned the energizing of this v of the switch contacts 94, 95 breaks the time de- The spark circuit H includes a normally open switch I38 which constitutes a part of' thesolenoid relay I3 I.

One side of the switch is con- JIBOIZEd by a wir Hi to the lead wire 82. The opposite side of the switchvis connected by a wire.

I42 to the primary side of a step-uptransformer I43. The primary side of the transformer also The other wire of the plug is connected to the ground I48.

Hence closing of the'relay switch I38 completes lay circuit C and thus deenergizes the solenoid 98 of this circuit. The de-energizing of solenoid 98 opens the switch I and thus breaks the motor circuit D, the holding circuit F, the pilot circuit G and the spark circuit H. This restores all of thesecircuits to original open condition inreadinessfor subsequent establishment by the same procedure as just explained, in case the burner I I is, extinguished for any reason after it is once lighted.

-In order to permit of suflicienttime for the lighting'of the burner II after-the burner circuit J is established, a time delay dash pot I8I may be secured to the movable core of the control circuit-solenoid 98.' This dash pot preve s too rapid an opening of the switch I85 following the opening of the switch that bridges the flame operated relay unit contacts 88 and 88. This allows suflicient time for the burner valve I! to open and for the burner to be lighted, before the circuits controlling the pilot 88, act to extinguish the pilot.

If the .fan II is not in operation when an attempt is made to light the burner or if for any reason the. fan should stop operating, the gravity controlled vane switch I84 would be opened and the circuit leading to the solenoid I88 of the relay' switch I69 would be broken. The solenoid I68 would be deenergized and thus the relay switch is open. The burner circuit J being broken under such circumstances, the valve solenoid l9 would be deenergized. A deenergizing of the solenoid I9 immediately closes the burner valve I and locks it against'opening until the valve solenoid is again energized.

Opening of the main switch 88 as by manual actuation disconnects the generator 85 from all of the circuits. All solenoids are deenergized when their respective circuits are open and the entire apparatus remains inoperative since all motors are idle.

After the burner II is lighted its heat output is controlled by a thermo-couple I82 which is located within the duct I2 and which is disposed adjacent the circulating fan II on its discharge side. The thermo-couple is connected by wires I83, I88 to a conventional temperature control electric relay panel I85 which in turn is connected by wires I88. I 81. I88, I89 to the reversible electric motor 36. v This motor it will be recalled opens and closes the regulator valve I6 as it operates in forward or reverse. The motor is connected by wires I9I, I92 to the main lead wires 82., 83.

Thus the thermo-couple I82 detects a temperature higher than a predetermined desired amount and then acts through the control panel, to set the motor 38 in operation in one direction to close the gas regulator valve I8 an amount in accordance with the actual temperature. This reduces the flow of gas and thus reduces the heat output of the burner.

When the temperature falls below the predetermined set value, the thermo-couple acts through the control panel to rotate the motor in the opposite direction to open the valve and thus increase the heat output ofthe burner as required. In this manner the thermo-couple maintains the temperature of the air heated by the burner at a constant predetermined value.

It is thought that the invention and many ofits attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advan- 8 I determined period or time to admit fresh air into the oven for purging it of unburned gases prior to the lighting of the burner to safeguard the oven against explosion, said time delay means after apredetermined period being operative to close said damper and light said pilot burner. to ignite said main gas burner, and means energized by a flow of ionized gas issuing from the lighted pilot burner for controlling the actuation or said burner control valve.

2. In an oven for drying coated metallic sheets and the like, the combination of a gas burner designed for issuing ionized gas for heating the oven, a normally closed and locked shut-oil. burner valve controlling the flow of gas to said burner, a gas pilot for lighting said burner, a normally closed pilot valve controlling the flow of gas to said pilot, electric means for lighting said pilot, a fan for circulating air heated by said burner through said oven, time delay means connecting with said pilot valve and with said electric means for delaying the opening or said pilot valve for .a predetermined interval of time to insure purging of the oven of unburned gases by said Ian before the lighting of said pilot, said time delay means being further operative to commence and to terminate the purging operation for said pre- I determined time interval, and electric instrumentalities disposed adjacent said pilot and connecting with said burner valve and operable by ionized gas issuing from the lighted pilot for unlocking said burner valve to permit the burner valve to be opened to light said burner by said pilot after the purging of the oven, thereby safeguarding the oven against explosion.

3. In an oven for drying coated metallic sheets and the like, the combination of a gas burner dea fan for circulating air heated by said burner through said oven, time delay means connecting with said pilot valve and with said electric means for delaying the opening of said pilot valve for v be opened to light said burner by said pilot tages, the form hereinbefore described being merely a preferred embodiment thereof.

I claim: I

1. In an oven for drying coated metallic sheets and the like, the combination of a main gas burner for heating'the oven, a valve for controlling the admission of gas to said burner, electric devices including a pilot burner for lighting said gas burner, a fan for circulating air heated by devices for first opening said damper for a preafter the purging of the oven, whereby to safeguard the oven against explosion, and means operable by air circulated by said fan for closing said burner valve when the air fan stops operating, thereby extinguishing said burner.

4. In an oven for drying coated metallic sheets and the like, the combination of a gas burner for heating the oven, a valve-for controlling the admission of gas to said burner, means for lighting said burner, purging means for exhausting unburned gases from the oven, time delay means interconnected with said burner lighting means and with ,said purging'means for delaying the ing operation to safeguard the oven against explosion, said time delay means being further operative to commence and to terminate the purg ing operation for said predetermined time interval, a regulator valve disposed between said burner and said burner control valve for regulating the flow of gas to said burner, and means for. actuating said valve in accordance with the heat output of said burner, thereby maintaining said oven at a predetermined constant temperature.

5. In an oven for drying coated metallic sheets and the like, the combination of a gas burner for heating the oven, a valve for controlling the admission of gas to said burner, means for lighting said burner, purging means for exhausting unburned gases from the oven, time delay means interconnected with said burner lighting means 10 and with said purging means for delaying the lighting of the burner for a predetermined time interval after the beginning of the oven purging operation to safeguard the oven against explosion, said time delay means being further operative to commence and to terminate the purging operation for said predetermined time interval, a reguw lator valve disposed between said burner and said burner control valve for regulating the flow of gas to said burner, a reversible electric motor for actuating said valve, and means disposed in said oven for controllingthe operation of said motor in accordance with the heat output of said burner, thereby maintaining said oven at a predetermined constant temperature.

ORLIN o. aUsEQ

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