US2232545A - Stoker driving arrangement - Google Patents

Description

Feb. 18, 1941. w. o. LUM

STOKER DRIVING ARRANGEMENT Filed Nov. 16, 1959 3 Sheets-Sheet l Inventor: Walter O. Lurn,

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His

Feb. 18, 1941. w. o. LUM 2,232,545

STOKE]! DRIVING ARRANGEMENT Filed Nov. 16, 1939 3 Sheets-Sheet Fig. 12.

Inventor: Walter O. Lum,

His Attofneg.

Feb. 18,1941. UM 2,232,545

STOKER DRIVING ARRANGEMENT Filed Nov. 16, 1939 3 Sheets-Sheet 5 Ihventof: Walter O. Lum,

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Patented Feb. 18, i941 UNITED STATES STOKER DRIVING ARRANGEMENT Walter 0. Lum, West Orange, N. J., assignor to General Electric Company, a corporation of New York Application November 16, 1939, Serial No. 304,754

15 Claims.

This invention relates generally to operating mechanisms for material conveying systems and more particularly for screw type coal conveyors of a furnace-stoker arrangement.

6 Material conveying systems such as mechanical fuel stokers are liable'to become clogged for various reasons such as by congestion of the material, or by large pieces of coal, pieces of metal or other foreign material becoming caught between the screw and the edges of the hopper opening, resulting in the stalling of the driving motor. Means are usually provided in the driving connection between the motor and the conveyor screw to automatically sever the connection or to deenergize the motor upon the occurrence, of a .predetermined overload condition. Each time the motor becomes stalled and disconnected by reason of the conveyor becoming jammed, it is necessary for a person to investigate the cause of the difficulty and to clear away the obstruction before the motor may be reset for the continuation of operation. This procedure involves more or less manual labor, is expensive and generally unsatisfactory. In the majority of instances, the jammed condition of the conveyor may be rectified by temporarily reversing the direction of operation of the motor and subsequently operating it forward again. If necessary, the reversal of the motor may be repeated several times until the passage becomes clear and free of the obstruction. It is therefore the principal object of this invention to providea driving mechanism for a material conveying system which is automatically controlled upon the occurrence of a clogged condition of the conveyor system for temporarily reversing the direction of operation of the driving motor, which operation is repeated until the conveyor is free of the ob struction causing its clogging. Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with greater particularity in the claims annexed hereto and forming a part of this specification. v

For a better understanding of my invention,

reference may be had to the accompanying drawings in which Fig. 1 represents a furnace equipped with a stoker mechanism and driving means therefor; Figs. 2 and 3 are enlarged views partly in section of a torque responsive coupling arranged between the motor and stoker shown in Fig. 1; Figs. 4 and 5 are views similar to Figs. 2

and 3, respectively, showing the coupling ina sec- 0nd operative position; Fig. 6 is a schematic cir cuit diagram illustrating a control scheme for the motor of Fig. 1; Fig. 7 illustrates a second embodiment of the invention in which a different and particular type of motor is substituted for 5 that shown in Fig. 1; Figs. 8, 9 and 10 illustrate various positions of the mechanical control means for the motor illustrated in Fig. 7; Fig. llis a schematic circuit diagram for the control of the motor shown in Fig. 7; and Fig. 12 is a schematic l0 diagram illustrating an automatic timing mechanism for use in connection with either modification.

Referring now to Fig. l of the drawings, I0 is a furnace having a firepot II arranged in the 15 lower portion thereof to which fuel is fed by means of a suitable stoker or conveyor screw I2 from a storage bin or hopper l3. A suitable motor I4 having a speed reduction gearing I5 is coupled through a torque responsive device It to 20 the shaft ll of the conveyor screw. The motor I4 is of a reversible type, as will be more fully described hereinafter, and is adapted for driving the conveyor screw in the forward direction to advance fuel from the bin I3 to the firepot II 25 Upon the conveyor screw I2 becoming clogged or stalled for any reason, such as by a large lump of coal getting caught at the' inlet thereto, the torque responsive device I6 will effect the reversal of the connection to the motor I 4 to reverse the 30 rotation of the screw for a predetermined period of time. The period of reverse operation of the motor is limited to merely one or two revolutions of the conveyor screw I2 so as not to feed live coals from the firepot II into the storage bin I3, 35 Subsequent to the period of reverse operation, the motor I4 will be automatically reconnected for operation in the forward directionagain and after a number of such reversals the congestion causing the stalling will be cleared away, or the 4 large lump of coal willbe broken up and the advancement of fuel will continue in the regular manner.

Referring now to Figs. 2 and 3, the details of the torque responsive device I6 will be described. 5 This device comprises a pair of similar disks 30 and 3|, disk 30 being keyed to the motor drivin shaft while disk 3| is keyed to the driven or conveyor shaft I1. A portion of disk 3| is broken away for the purpose of more clearly illustrating 50 the structure of the facing surfaces of the cooperating disks. A number of suitably spaced apart lugs 32 are integral with the peripheral" portion'of the disk 39. A similar number of similarly spaced apart lugs 33 are provided integral with the adjacent face of the disk 3i. Springs 33 are arranged between the lugs 33 and 33 to maintain the backs of the pairs of adjacent lugs of the two disks in an abutting relationship as shown. Assuming now that the coupling is being driven'in the fuel advancing direction, or counterclockwise, and that the conveyor screw l2 operating in the forward direction becomes clogged creating" a predetermined abnormal increased resistance to rotation of the driven disk 3|, due to an increase in torque applied to the driving disk 33 by the motor, the springs 34 will be compressed and the normally abutting lugs 33 and 33 will be separated, as indicated more clearly in Fig. 4. This relative angular displacement of the disks 33 and 3| from their normal relationship will cause the cams 33, which are integral with disk 33, to engage with the plungers 33, which are slidably mounted in bushings 31 secured to disk 3|, to force the plungers to the right against the collar 33. The collar 33 is normally biased to the left by means of a spring 33 arranged between the collar 33 and a stop 43 fixed to the shaft II. The collar 33 being axially movable upon the shaft II, when engaged by-the end of the plunger 33, will be forced to the right to pivot the engaging circuit controller lever ll in the counterclockwise direction against the force of the biasing spring 42 as shown in Fig. 5. The upper end of the controller lever ll is loosely connected to the overcenter snap acting switch arm 44 and upon actuation of the lever 4|, the switch 34 is thrown over to its second operativeposition, disengaging the fixed contact 43 and engaging fixed contact 43. Connected to the lever ll is a suitable time delay device I which retains the lever ll in the operated position, illustrated in Fig. 5, for a predetermined length of time after which the lever 4| is returned to its normal position, as indicated in Fig. 2, by the biasing spring 42. It is understood that immediately following the initial operation of the lever 4|, the motor connections are reversed whereupon the conveyor screw I2 is driven in the reversed or clockwise direction. During reverse operation of the motor the lugs 32 of the driving disk 33 engage directly with the abutting faces of the lugs 33 of the driven disk 3| and positively rotate the conveyor screw I! in the reversing direction. It is obvious, therefore, that the collar 38 will be restored to its normal position immediately following the reversal of the motor connections, while the time delay device maintains the reversing connection for the stoker motor II for a predetermined length of time, sufficient for the screw I! to make one or two complete revolutions in the backward direction.

Referring now 'to Fig. 6, the electrical control system for the stoker driving motor M will be described. Current may besupplied to the system from a suitable alternating-current source indicated by the supply lines SI and 52. To initially energize the system the control switch 53 may be closed, which connects the primary winding of the transformer 53 directly across the supply lines. The operation of the stoker is normally primarily controlled by means of a thrmostat 33 which may be suitably arranged within the enclosure to be heated by the furnace ID. The thermostat 55 comprises a temperature responsive bimetallic element 53 which upon a predetermined low temperature condition engages with the fixed contact BI to connect the winding of relay I3 across the secondary winding of the transformer SI. Upon the pick-up of the relay 33 a holding circuit is completed therefor through the conductors I3 and x33 and contact arm 3| paralleling the thermostat element 33 and fixed contact II. Upon a predetermined high temperature condition occurring within the enclosure the thermostat element 33 will bend to the left engaging with the fixed contact 33, thereby short circuiting the relay winding 33 causing it to drop v to the deenergized position.

Assume first that the furnace is in normal operation and that the enclosure thermostat calls for heat. The contact arm II of the relay II establishes a control circuit for connecting the stoker motor II for operation in the forward direction. This circuit extends from the left-hand terminal of the secondary winding of transformer 34 through the contact arm II, line 12, torque switch arm 44, fixed contact 48, winding of relay 13, to theright-hand terminal of the secondary winding of transformer 54. As the relay I3 picks up, its contact arms 14 and I! establish circuits for energizing the motor I for operation in the forward running direction. The motor will be maintained in operation until the demand for heat by the enclosure is satisfied, when the thermostat element 33 will engage with the fixed contact 32 to cause the relay 53 to drop out, thereby deenergizing the control relay 13. If, however, the conveyor screw I 2 becomes stalled, the torque switch 43 will be operated to engage the fixed contact 43, thereby energizing the relay I3 which picks up contact arms II and 13 to establish circuits for operating the motor ll in the reverse direction. As previously explained, after a predetermined time the torque switch 44 will be restored to the normal position engaging with fixed contact 43, thereby deenergizing relay I3 and energizing relay 13 to again connect the motor H for operation in the forward direction.

The forward running circuit for the motor established by the pick-up of relay I3 extends from the supply line 3| through line 30, contact arm 15 of the relay 13 in the energized position, line 3|, the running winding 32 of the motor l3, contact arm I3 of the relay 13 in the deenergized position, lines 33, 34, contact arm II of relay 13, line 35, to the other supply line 32. Another circuit is established for energizing the starting winding of the, motor I 4 extending from the supply line 5| through line 33, contactor 31 of the motor speed responsive device 33, line 33, motor starting winding 9i, capacitor 32, lines 33, 33, 33, contact arm 14 of the relay I3, line 33, to the other supply line 32. As soon as the motor reaches approximately normal speed, the centrifugal device 33 will open the contacts 31 to effect the deenergization of .the starting winding 3!. The reversing circuit for the motor established by the pick-up of relay 13 extends from the supply line 5| through line 33, contact arm 13 of the relay 13 in its upper position, running winding 32 of the motor H, .the contactor arm II of the relay I3 in its lower position, connection 34, line 34, contact arm II of the relay 13 in its upper position, line 35, to the other supply line 32. The starting winding connection is of coursenot reversed but is completed through contact arm II of relay I3.

In a second and preferred embodiment of my invention, I utilize a self-reversing motor in lieu of the motor ll described above. Such a motor is described in the Patent No. 2,105,514, Alfred S. Welch, issued January 18, 1938, and assigned to the General Electric Company, the assignee of the present invention. This motor has such a characteristic that it will drive any load less than that corresponding to its pullout torque but when it encounters a load which it,cannot carry at synchronous speed, it immediately stops because its synchronous torque is greater than any torque .below synchronous speed and if the motor remains energized when thus stopped by an overload in one direction, it will immediately start up in the opposite direction. tinue to run in this direction until it is again stalled, when it will commence to rotate in the forward direction again. Referring to Fig. '2, such a motor I is shown provided with suitable speed reducing gearing in casing Ill and is adapted to be fast coupled to the-fuel advancing screw shaft I1. When initially energized, the motor may start in either direction and will drive the fuel conveyor screw in either direction until it is stalled for any reason, when the motor will automatically reverse its direction of rotation. A ratchet means is provided for limiting the rotation of the motor in the reverse direction which is more clearly shown in the end views 0, I and I0. A ratchet disk I02 is secured to the shaft I1 andis provided with a shoulder or stop I03 facing away from the direction of normal or forward rotation of the motor. A cooperating pawl I04 is pivoted as at I05 to the gear housing IN and is provided with a toe I06 and a heel I01. The pawl I04 is biased to either of two positions by means of an overcenter spring I08 arranged between a stud I03 and one end IIO of the pawl I04. During forward rotation of the motor, when the disk I02 is rotated in the counterclockwise direction, the pawl I04 will be merely rocked about its pivot as the tip of the stop I03 alternately strikes the heel I01 and the toe I06. Now assume that the torque of themotor in the forward direction has been overpowered by the resistance of the fuel advancing screw by reason of its having become clogged. The motor will immediately start up in the opposite or clockwise direction of rotation. Assume that'at the moment of reversal the ratchet disk and pawl are inthe relative positions in Fig. 9. The disk I02 rotating clockwise will first strike the heel I01, which is riding on the edge of the disk, rocking the pawl about its pivot so that the toe I06 is moved into engagement with the disk edge by means of the overcenter spring I08. As the stop I03 comes around a second time, it will engage with the toe I06 of the pawl I04. The motor thereupon will be stalled and it will immediately start up in the opposite or forward direction of rotation. The motor will continue to operate in the forward direction until the fuel advancing screw jams again or until the motor is deenergized by the operation of the control to the open circuit position. By the ratchet arrangement shown, the rotation of the motor in v the reversing direction will continue, for more than one revolution and is positively limited to a maximum of two complete revolutions of the fuel conveyor screw.

The electrical control system for the motor just described is relatively simple in that no opparatus is required for reversing the motor connections. As illustrated in Fig. 11, power is adapted to be supplied to the stoker motor from a suitable alternating-current source of supply through the leads I20, I2I, a suitable switch I22 being provided in the line I20 for controlling the energization of the system. Upon the closure of switch I22, the primary winding of the transformer I23 is connected across the supply lines,

It will conthereby energizing the enclosure thermostat I24. The enclosure thermostat I24 is similar to the thermostat 55 and comprises a bimetallic temperature responsive element I23 adapted to engage with either of two oppositely arranged fixed contacts I21 and I28. Upon the temperature within the enclosure dropping below a predetermined value, the element I26 will bend to the right engaging with fixed contact I28, thereby connecting the winding of relay I26 across the secondary winding of the transformer I23. Upon the pick-up of relay I 23, a holding circuit will be established therefor by its contactor HI and the lines I32 and I33 paralleling the thermal responsive element I26 and fixed contact I28. Upon the pick-up of relay I28, its contactor I34 will complete an energizing circuit for the motor I00. The operation of the motor I00 will be continued until the demand for heat by the enclosure is satisfied, as indicated by the bending of the thermal responsive element I26 to the left engaging with the fixed contact I21 which shortmatically in Fig. 12. A collar I40 may be secured to the conveyor shaft IT by means of a set screw I, the collar being provided with a cam projection I42. The cam is adapted to engage with an end I43 of a lever I44 which is pivoted as at I45 and biasedin a counterclockwise direction by means of a relatively light spring I46. The lever I44 is arranged for operating a pawl I41 into engagement with a ratchet wheel I48 to rotate it by steps in a clockwise direction. The pawl I41 is biased against a stop I49 by means of a spring I50 and is provided with a slot I5I for receiving a pin I52 secured to the arm I44. The end of the arm I44 is provided with a hinged tip I55 which is adapted to engage with the end of the pivoted lever I56 to carry it upwardly but not downwardly. Secured to the lever I56 is a spring pawl I51, the end of which is adapted to engage with the teeth of the ratchet disk I40 to retain it in the actuated position as it is moved by the pawl I41. The lever I56 and spring I51 are normally biased to the inoperative position by means of a spring I50. The return of the lever I56 to the inoperative position after actuation by the lever I44 is delayed by a suitable time delay device 159 which is connected to the end of the lever I56 by link I60. Operatively secured for rotation with the ratchet wheel I48 is a switch operating arm I6I which, when rotated through the requisite angle, will engage with the switch lever I62. The switch lever I62 is stationarily pivoted as at I63 and is biased to either one of two operative positions by an overcenter spring I64.

'The other end of the lever I62 is provided with completing an energizing circuit for a suitable alarm device indicated at I".

The ratchet wheel Ill isbiased to the reset position by means of a suitable spring I, this position being determined as by the engagement of lever I" with the stop I.

Whm the conveyor shaft is rotated in the fuel advancing or counterclockwise direction the cam I" will strike the end of the operating lever I to rotate the lever I in the clockwise direction. The pin II! will merely slide downwardly in the slot Iii causing no operation of the pawl M1,. The lever I will be returned to the normal III of the arm I to rotate the latter lever in the counterclockwise direction and actuate the pawl Il'l upwardly into engagement with the teeth of the ratchet wheel I. The hinged end I" of the lever I will simultaneously engage with the end of the lever I to carry the spring IS'I into engagement with the teeth of the ratchet wheel I". Under the impulse of the pawl I 41 the ratchet wheel will be turned through a predetermined angle as measured by the spacing of the teeth. The wheel will be retained in the actuated position for a predetermined time by the spring II'I against the biasing force of the restoring spring I88. The spring I58 will tend to move the lever I58 and spring I51 to the inoperative position but due to the action of the time delay device I59, the return movement will be somewhat delayed.

The time delay device I" is so adjusted that it will retain the lever I in the actuated position for a period, for example, twice as great as the period of each reverse operation of the stoker driving motor. motor continues to alternate in the direction of rotation, the reversals following each other in relatively rapid succession, the ratchet wheel I48 will be progressively advanced until after a predetermined number of reverse operations the switch operating arm ItI engages with the lever I62 to deenergize the motor circuit and close the alarm circuit. After the motor is stopped, the time delay device I59 will drop out, permitting spring I58 to withdraw pawl I51 from the ratchet wheel. Under force of spring I68 the ratchet wheel will be reset, arm IBI moving free of the tripped switch operating lever I62 and into engagement with stop I69. However, if the stoker driving motor should succeed in breaking through the obstruction after a fewer number of reversals, and the conveyor shaft be operated in the forward direction for a period of time greater than-the time for which the time delay device I" is set, the spring I51 will be withdrawn from'the ratchet wheel I48 and permit the spring I68 to return the ratchet wheel and the lever iii to the normal or reset position.

when the alarm circuit is closed indicating that the stoker motor has been shut down by virtue of its inability to break through the obstruction, an attendant may correct the difficulty and reset the switch arm It! to the operative position indicated.

Having described the principle of operation of my invention together with the apparatus which apparatus shown is merely illustrative and that the invention may be carried out by other means.

As long as the stoker drivingv aasaus whatlclaimasnewanddesirstosecureby Letters Patent of the United States. is;

i. Ina furnace stoker apparatus, the combination comprising a fuel conveyor, motor means connected to said conveyor for normally driving said conveyor in the forward direction, said motor being automatically reversible in response to a predetermined torque exerted thereby to said conveyor, means for limiting the reverse operation of said conveyor, means for counting the consecutive number of reverse'op'erations of said conveyor, means for dg said motor upon a predetermined consecutive number of reverse operations of said conveyor being counted by said counting means, and means for auto matically resetting said counting means upon the consecutive number of reverse operations of said conveyor being less than said predetermined number.

2. In a furnace stoker apparatus, the combina- 20 tion comprising fuel advancing means, motor means connected for normally driving said fuel advancing means in the forward direction, means including said motor for causing the direction of operation of said fuel advancing means to be automatically reversed in response to a predetermined torque exerted thereto by said motor means. means for limiting the reverse operation of said fuel advancing means, means responsive to a predetermined consecutive number of reverse operations of said fuel advancing means for causing the deenergization of said motor, and signal means adapted to be energized upon the deenergization of said motor.

3. In a bulk material handling apparatus, the combination comprising a material conveyor, a motor connected for driving said conveyor normally in the forward direction, means including said motor for automatically reversing the direction of operation of said conveyor in response to said conveyor encountering a predetermined resistance to operation in the forward direction, means for limiting the reverse operation of said conveyor and for causing said conveyor to be operated again in the forward direction, means responsive to a predetermined consecutive number of reverse operations of said conveyor for deenergizing said motor.

4. In a bulk material handling apparatus, material conveying means, a motor connected for normally driving said conveying means in the forward direction, torque responsive means for causing said motor to operate in the reverse direction upon said conveying means encountering a predetermined resistance to operation in the forward direction, means for limiting the reverse operation of said motor, and means responsive to a predetermined consecutive number of reverse operations of said motor for causing the deener- Bization thereof.

5. In a stoker, the combination with fuel advancing means, a motor for normally driving said fuel advancing means in the forward direction, said motor having the characteristic that it automatically reverses its direction of rotation upon encountering a predetermined resistance to operation in either direction, and ratchet means for limiting the operation of said motor in the reverse direction as regards said fuel advancing matically reversible upon a predetermined torque being exerted thereby to said conveyor, means for stalling said conveyor after a predetermined period of reverse operation thereof so that said motor may operate in the forward direction again.

7. In combination, a stoker apparatus comprising a spiral screw fuel conveyor, a motor fast coupled to said conveyor screw, said motor being automatically reversible upon said conveyor screw encountering a predetermined resistance to operation in the one direction, and means for automatically limiting the operation of said conveyor screw in the reverse direction to a predetermined maximum number of revolutions.

8. In a stoker apparatus, the combination including fuel advancing means, a motor for driving said fuel advancing means, said motor being arranged for normally driving said fuel advancing means in the forward direction, a torqueresponsive device between said motor and said fuel advancing means, a switch responsive to a predetermined actuation of said torque responsive device for altering the electrical connections for said motor for causing the reverse rotation thereof, and means for restoring said switch to the normal condition a predetermined time following the actuation thereof by said torque responsive device.

9. In a furnace stoker apparatus, the combination comprising a rotatable screw type fuel conveyor, 'an electric motor coupled to said conveyor for normally rotating same in the forward direction, means responsive to a predetermined abnormal resistance to rotation of said conveyor in the forward direction, switch means actuable by said means for changing the connections of said motor to cause a reverse operation thereof, and means for restoring said switch to the previous condition a predetermined time following actuation thereof by said first means.

10. In a furnace stoker apparatus, the combination comprising fuel advancing meansflnotor means for normally driving said fuel advancing transmitted by said motor to said conveyor, means actuable by said last mentioned means for changing the connections of said motor to reverse the direction of operation thereof and said' material conveyor means, and means for 5 limiting the reverse operation of said motor and reconnecting said motor for operation in the forward direction.

12. In a bulk material handling apparatus, the combination comprising a material conveyor, means for driving said conveyor normally-in the forward direction, means for automatically causing said driving means to reverse the direction of operation of said conveyor means upon said conveyor means encountering a predetermined abnormal resistance to operation in the forward direction, and means for automatically causing said driving means to operate said conveyor means in the forward direction again following a predetermined reverse operation thereof.

13. In a furnace stoker, the combination comprising fuel advancing means, motor means connected for normally driving said fuel advancing means in the forward direction, means including said motor means for causing the direction of 25 operation of said fuel advancing means to be automatically reversed upon said fuel advancing means encountering a predetermined abnormal resistance to operation in the forward direction, and means for limiting the reverse operation of said fuel advancing means and causing said motor means to again drive said fuel advancing means in the forward direction.

14. In a stoker, the combination with fuel advancing means, a motor for driving said fuel advancing means, said motor being arranged for normally driving said fuel advancing means in the forward direction, means including said motor responsive to a predetermined abnormal resistance to forward operation of said fuel advancing means for reversing the direction of operation of said motor, and means for reconditioning said motor for operation in the forward direction after a predetermined period of operation in the reverse direction.

15. In a bulk material handling apparatus, the combination comprising a material conveyor, motor means connected to said conveyor for normally driving said conveyor in the forward direction, means including said motor for causing the .direction of operation of said motor to be automatically reversed upon said conveyor encountering a predetermined resistance to operation in the forward direction, and means for limiting the reverse operation of said motor and said conveyor. 55

WALTER O. LUM.

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