US 2100848 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Nov. 30, 1937. R. M. HARDGROVE FEEDER CONTROL MECHANI SM Filed April 5, 1954 INVENTOR Pa/ph M Hat cl grove W ATTORN EY -Patented Nov. 30, 1937 PATENT OFFICE 2,100,848 FEEDER CONTROL MECHANISM Ralph M. Hardgrove, Westfleld, N. 3., asslgnor to The Babcock 8a Wilcox Company, Newark N. J a corporation of New Jersey Application April 3, 1934, Serial No. 718,756
The present invention relates in general to feeder control mechanisms, and more particularly to mechanisms oi this type for controlling the supply of material to an endless bucket elevator. Such elevators are usually enclosed in a casing to confine the dusty atmosphere which usually exists about the moving buckets and belt or chain upon whichthey are mounted, and to return material spilled from the buckets to the bottom or boot of the elevator casing. The material to be elevated is supplied to the elevator casing boot where it is scooped up by the moving buckets as they pass about the lower chain sprocket wheel. As the bucketspass over the upper pulley of the elevatonthe material is discharged by centrifugal force and gravity into an adjacent discharge chute. operation requires the supplying of material at a rate' substantially corresponding to the bucket capacity. When that rate is exceeded the height of material in the boot tends to increase, causing an increase in loadv on the elevator driving means, increased wear, and overloading of the buckets with a resultant increase in the amount oiqnaterial spilled from the buckets. I have discovered that the air pressure conditions in, the
elevator casing tend to fluctuate with changes in the amount of material spilled from the moving buckets and I advantageouslyemploy such fluctuations in air pressure from a predetermined value to control the amount of material supplied to the elevator.
Elevators oi the above described type are used extensively in closed circuit pulverizer systems to receive the discharge from a pulverizer and transfer the same to an elevated separator, from which the separatedcoarse material is returned to the pulverizer and the fines delivered to a storage system or point of use. .The raw material is normally delivered to the-pulverizer by a regulable feeder mechanism, which, when a constant speed pulverizer driveis used, may be regulated to vary'the amount of material passing through the pulverizer. Grinding conditions in the pulverizer maychange during operation, and cause the quality of the pulverized product to vary and the pulverizer drive motor to be overloaded or the', eleva'tor capacity to be exceeded. For/a given material having a deflhite'grindability, there is an optimum rate of feed and recirculation of material for the desired fineness.
The general object of my invention is the provision of an elevator of the character described with an improved system of controlling the supply of material thereto. A further and more Economical elevatorspecific object is the provision of an elevator feed control system operable in response to fluctuations in air pressure in the elevator casing. A further specific objects the provision of a material pulverizing system having provisions for controlling the supply of material to the pulverizer in response to the load on the pulverizer drive mechanism and/or on an elevator of the type described receiving pulverized material from the pulverizer.
The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.
0f the drawing:
Fig. 1 is a partly diagrammatic elevation 01' a closed-circuit pulverizer system incorporating my invention; and
Fig. 2 is a schematic diagram of the feeder control provisions. p v
In the closed-circuit grinding system illus trated in Fig. 1, raw material is discharged from a feed bin ID to a suitable feeder ll driven by a direct current shunt wound electric motor 82 in a well known manner. The raw'material is discharged by the feeder at a 'rate dependent on the speed of the motor l2 into a pipe l3 leading to a pulverizer ll of the gravity-discharge type. The pulverizer is preferably driven by a three phase constant speed electric motor l5 and the pulverized material discharged through an inclinedconduit l6- into the boot of a vertical elevator casing H. The casing l1 contains upper andlower sprocket wheels l8 and-.ldrespectively for driving an endless belt or chain 20 having a series of buckets 2i buckets are arranged to pick up material in the casing boot during their passage therethrough and carry the same upwardly. As the buckets pass over theupper sprocket wheel, the material therein is discharged by gravity and centrifugal force into a chute 22,which discharges into the upper end of a conical 'air separator 23. The
' fine and coarse particles of material are separated therein, the fines passing through the pipe 24 to 'a pump or conveyor 25, having a vent pipe mounted thereon. The
26, and delivered to a storage system or point oi! use, while the coarse particles or tailings are returned. to the pulverizer through a spout 28. The
to the boot of the casing [1, then the amount of granular material spilled in transit will correspondingly increase.
The elevator being of substantial height and the material conveyed of a relatively high density, the spilled material in falling exerts a dragging effect on the air in the upper portion of the casing and causes the air pressure in the lower part of the casing to build up correspondingly. I have discovered that the fluctuations in air pressure in the elevator casing bear a definite relation to the amount of material accumulated in the casing boot such that these fluctuations can be used as a basis for controlling the pulverizer feeder motor l2.
It has been found desirable to employ'a constant speed motor l5 for driving the pulverizer it. 'Any increase in supply of material to the pulverizer beyond the pulverizer capacity tends to overload the motor l5 and adversely affect the fineness ratio, and a supplementary control may advantageously be employed in conjunction with the elevator casing air pressure responsive control, by which supplementary control the supply of material may besuitably decreased whenever the motor l5'tends to become overloaded.
One form of suitable control system is illustrated in Fig. 2. The air pressure control may comprise a suitable pressure responsive device 30 consisting of a liquid sealed floating bell- 3|, to the interior of which is connected an air pipe 32, opening through one side of the elevator casing, as shown in Fig.' 1, slightly above the axis of the lower sprocket wheel I3 Above the bell 3| is mounted a counterweighted lever 33 pivoted at 34 and carrying a suitable mercury contact switch 35, which is closed when the lever 33 is raised. A connecting member 36 is mounted on the bell 3! for connecting the latter to and actuating the lever 33 on a change in air pressure in the elevator casing. In operation, the closing of switch 35 is used to short circuit a sector 31 of a rheostat 38 in the field 39 of the feeder motor l2 to thereby effect a predetermined decrease in the motor speed and consequently in the amount of material delivered by the feeder H. The decrease in the amount of material delivered to the pulverizer causes a decrease in the amount of material supplied to the elevator casing. The air pressure in the lower part of the casing consequently falls, causing the bell 3| to drop and the switch 35 to open, restoring the previous operating conditions.
A corresponding controllingeifect on the feeder motor l2 may be effected on a predetermined increase in the load on the pulverizer drive motor V 15. For this purpose an overload relay 40 is inserted in the power line ll to the pulverizer motor I5. On a predetermined increase in the current through the relay, the contacts 42 and 43 I motor.
42 and 43 to open. A switch 44 is advantageously positioned in the control system to permit the controls being thrown out of operation.
While the two parts of the control system operate independently, and either may be used to the exclusion of the other, the simultaneous use of the two forms of control means has been found to be preferable, so that the feeder is controlled not only in response to the load on the pulverizer drive motor IE, but also in response to the amount of material delivered to the elevator.
While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that Cir changes maybe made in the form of the apparatus disclosed without departing from the spirit of the invention coveredby my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.
1. In combination, an elevator casing having a material inlet at its lower end and a material outlet at its upper end, a feeder for supplying material to be delivered to said casing inlet, a motor for drivingsaid feeder, an endless elevator having-substantially vertical runs insaid casing and having a series of buckets thereon arranged to pick up material in the lower end of said casing and discharge it at the upper end of said casing, and means responsive to fluctuations in the air pressure in said casing due to changes in the amount of falling material therein for controlling the operation of said feeder 2. In combination, an' elevator casing having a material inlet at its lower end and a material outlet at its upper end, a feeder for supplying material to be delivered to said casing inlet, a motor for driving said feeder, an endless elevator having substantially vertical runs in said casing and having a series of buckets thereon arranged to pick up material in the lower end of said casing and discharge it at the upper end of said casing, an air conduit opening to said casing and responsive to fluctuations in air pressure insaid casing due to changes in the amountof falling material, an air pressure responsive deviceconnected to the lower portion of said casing, and means actuated by said pressure responsive device forcontrolling the operation of said feeder motor.
3. A grinding system including a pulverizer, a feeder for supplying material to said pulverizer, an elevator casing arranged to receive the discharge of material by gravity from said pulverizer, endless bucket elevator means, in said casing, arranged to mechanically raise material in said casing and means responsive to pressure changes in said casing for controlling the. operation of'said feeder.
4. A grinding system including a pulverizer, a feeder for supplying material to said pulverizer, a substantially vertical elevator casing arranged to receive the discharge from said pulverizer, an endless bucket elevator in said casing, and a device responsive to pressure changes in said casing for controlling the speed of said feeder.
5. In a grinding system comprising a pulverizer, a drive motor therefor, a feeder for supplying material to said pulverizer, a drive motor for said feeder, an elevator casing arranged to receive the material discharged by'said pulverizer, and an endless elevator having oppositely moving verti-"" cal ms in said casing and having a series of buckets thereon arranged to pick up material in the lower end of said casing and discharge said material at the upper end of said casing, means for controlling the operation of said feeder motor, and means responsive to changes in the air pressure in Said casing for actuating said feeder motor control means.
6. In a grinding system comprising a pulverizer, a drive motor therefor, a feeder for supplying material to said pulverizer, a drive motor for said feeder, an elevator casing arranged to receive the material discharged by said pulverizer, and an endless elevator having oppositely moving vertical runs in said casing and having a series of buckets thereon arranged to pick up material in the lower end of said casing and discharge said material in the upper end of said casing, means for controlling the operation of said feeder motor, means responsive to changes in load on said pulverizer motor for actuating said feeder motor control means, and means responsive to changes in the air pressure in said casing for actuating said feeder motor control means.
7. In combination, a casing, an endless bucket elevator in said casing, means for supplying material to said casing to be raised therein by said elevator, and means responsive to variations in the air pressure in said casing efiected by changes in the amount of material falling from said elevator during operation for controlling the operation of said material supplying means.
8. In combination, a substantially vertical casing, means for supplying material to said casing, means for passing material through said casing and causing a variable supply of material to have a gravity drop in said casing, and means responsive to variations in the air pressure in the lower part of said casing effected by changes in the amount of descending material passing through said lower part of said casing for controlling the amount 0! material supplied to said casing. I
RALPH M. HARDGROVE.