US2766941A - Dry grinding feed control - Google Patents

Dry grinding feed control Download PDF

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Publication number
US2766941A
US2766941A US426721A US42672154A US2766941A US 2766941 A US2766941 A US 2766941A US 426721 A US426721 A US 426721A US 42672154 A US42672154 A US 42672154A US 2766941 A US2766941 A US 2766941A
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mill
signal
point
curve
sound
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Weston David
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Priority to DENDAT1070478D priority Critical patent/DE1070478B/de
Priority to FR1118659D priority patent/FR1118659A/fr
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Priority to US426721A priority patent/US2766941A/en
Priority to SE911/55A priority patent/SE307057B/xx
Priority to GB4820/55A priority patent/GB782523A/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C25/00—Control arrangements specially adapted for crushing or disintegrating

Definitions

  • This invention relates to the automatic control of material reduction mills of the type adapted to reduce material in its dry state.
  • dry grinding mills are known such as dry ball mills, pebble mills, tube mills, and the like, as well as combined dry crushing and grinding mills of the general type described in my prior Patent No. 2,555,171.
  • FIG. 2 is a block diagram illustrating the control system of the invention
  • Figure 3 is a block diagram illustrating a control system according to the invention where the system is monitored
  • Figure 4 diagrammatically illustrates the components of the sound signal source
  • Figure 5 is a circuit diagram illustrating a suitable means for deriving the power signal
  • Figure 6 illustrates a suitable circuit arrangement for the application of a monitoring signal to the system.
  • curve A represents what is termed in the art the grinding curve.
  • This curve represents tons per hour versus charge volume, and, although its shape will vary from mill to mill its characteristics are generally the same for all mills, namely tons per hour commence at zero at the point of origin, increase to a maximum as the total charge volume increases and then decrease.
  • the product produced by the mill is substantially the same regardless of the point on the grinding curve at which the mill is operated, and, therefore, it is the usual practice to operate the mill insofar as it is possible at a point which corresponds to the peak of the grinding curve.
  • the second characteristic curve is that of power consumption versus charge volume, and is represented by curve B and referred to herein as the power curve.
  • the power curve is generally similar in shape to the grinding curve and has the same characteristic peak in it although, since what is being plotted against charge volume is power consumption, the peak of the power curve does not necessarily occur at the same charge volume as does the peak on the grinding curve. Generally speaking, however, in ball mills, the peak on the power curve will occur at a slightly greater charge volume than the peak on the grinding curve. Unlike the grinding curve, however, the power curve does not pass through the origin inasmuch as a certain amount of power is required to turn the mill over when it is empty.
  • the third characteristic curve is that of sound of vibration produced by the mill during operation versus charge volume. In Figure 1, this is represented by curve C, and
  • Curve C is generally of the same characteristic shape for all types of mill and may represent sound produced by the mill, vibration produced by the mill, or may represent sonic or non-sonic vibration produced by the mill within selected frequency ranges.
  • the steepest part of the power curve occurs in the region of low charge volumes, whereas the steepest part of the sound curve occurs in the region of high charge volumes.
  • a curve is most ideally suited as a control signal, and accordingly, in accordance with the present invention, if it is desired to operate a mill with a large charge volume, or near its point of maximum capacity, I use sound or vibration as the source of the control signal.
  • the mill is to be operated at a small charge volume, I prefer to use power consumption as the source of the control signal.
  • I determine either empirically or from available data the value of the control signal at the desired point of operation and use this as the value of a reference signal which is continually produced from an independent source. I then continually produce the control signal and compare it to the reference signal to produce a ditference signal, and I vary the rate of feed to the mill in accordance with the sense and magnitude of the difference signal, thus keeping the operation of the mill comparatively steady at a point which corresponds to the point which I originally selected on the grinding curve.
  • a monitoring signal which is functional to or varies with the condition of operation on the basis of which it is desired to monitor is applied to the system in such a manner that whenever the said condition is exceeded the rate of feed to the mill is diminished regardless of the sense and magnitude of the difference signal referred to above. 7
  • the procedure to be followed is substantially the same except that the point selected on the grinding curve representing the desired point of operation of the mill will be selected having regard to the degree of comminution of the product desired rather than upon the basis of therate of production desired. It will be normal in these circum stances to operate the mill at various points on the grinding curve for purposes of determining the point at which the mill produces a product having the desired characteristics. If the mill has previously been calibrated in respect of the particular ore which is being comminuted, the selection may be made on the basis of the available data, and it may not be necessary to determine the desired operational point experimentally. Once the operating point has been selected, the control signal is selected and control is applied in exactly the same manner as previously explained in connection with ball mills and other more conventional forms of mill. 1 I
  • control system of the invention is illustrated diagrammatically in Figure 2 where box 10 illustrates a source of a control signal (either power, sound or vibration) and box 11 represents the source of a reference signal.
  • the control signal and reference signal are cornpared in a comparator represented by box 12, and the difference signal thus produced is amplified in amplifier 13.
  • the amplified signal from amplifier 13 is applied to vary the rate at which the feeder 14 feeds the mill 15.
  • the controlsystern illustrated in Figure 3 is exactly the same as that illustrated in Figure 2 except for the presence of a source of a monitoring signal represented by'box 16 which takes over control of the system and reduces the feed to the mill whenever the monitoring
  • a source of a monitoring signal represented by'box 16 which takes over control of the system and reduces the feed to the mill whenever the monitoring
  • One common form of monitoring is the monitoring of the system to prevent an overload being placed on the mill motor when a control signal is used which is derived from sound produced in the mill. In such a case, the
  • ' monitoring signal simply causes reduction in the rate of feed to the mill whenever the horsepower drawn by the mill motor exceeds a predetermined value (usually its rated horsepower).
  • the circuit 7 a'iaoii 3 components repfesented by the box 10 in Figures 2 and 3 will consist essentially of a dynamic microphone, an amplifier and a rectifier (as indicated in Figure 4). If it is desired that the signal thus produced be proportional to the sound emitted within only a limited frequency band, the circuit can include a band pass filter, or the elements of the sound pickup system can be selected so that they are very sensitive to the sound frequencies which it is desired to utilize and relatively insensitive to sound frequencies outside the selected range.
  • audible frequencies emitted from a primary ball mill which are above 2,000 cycles per second vary in intensity in close relationship to the actual conditions within the mill
  • frequencies substantially below 2,000 cycles per second are not very satisfactory as a source of a control signal for purposes of the present invention because an appreciable proportion of the intensity of sound within these low frequencies can be attributed to extraneous causes such as the mechanical noise of the mill and power transfer system.
  • control signal is to be derived from vibrations other than sonic emitted by the mill during operation, apart from the type of pickup used, the circuit components required will be essentially the same as they will be when sound is used. In this case, however, the selection of a predetermined frequency band will more conveniently take place essentially within the circuit rather than as a result of selection of pickup components of selected characteristics.
  • control signal is to be derived from the power consumed by the mill motor
  • the circuit components necessary to produce the control signal will consist essentially of a watt-meter circuit applied across the power input lines to the mill motor and producing a voltage proportional to the motor input and a rectifier.
  • Figure 5 shows an electronic watt-meter connected in the power lines to the mill motor from which is produced as output a rectified voltage proportional to the power input to the mill motor.
  • the circuit components represented by the box 11 in Figure 2 consist essentially of a means for providing a regulated voltage which can be adjusted to a predetermined desired value and a rectifier.
  • a voltage regulator which receives as input the standard 115 volts line voltage and produces as output a regulated voltage of say 210 volts, a rectifier, and a potentiometer which may be set at a desired value to give as final output a desired rectified voltage which may be used as a reference signal.
  • the circuit components represented by the comparator box 12 may be of any conventional type.
  • the comparator may consist of a simple bridge circuit, or alternatively an electronic grid which may or may not, depending upon the circumstances, be connected so as to form an integral grid system with components of the amplifier.
  • the only important feature of the comparator circuit is that it must produce as output a signal which is proportional to the difierence between the reference signal and the control signal and which has a sense which is opposite for opposite values of the algebraic sum of the control signal and the reference signal.
  • Amplifier Any suitable amplifier may be used which will fulfil the functions required in the particular application, the function of the amplifier simply being to amplify the signal produced by the comparator to a suificient extent so that it may eifect control of the particular type of feeder being used.
  • the amplifier may, and in the preferred instance is, integrally associated with the comparator grid system.
  • Proportioning feeders There are various types of proportioning feeders which are available on the market, perhaps the commonest type being the electromagnet pulse type feeder of which a typical example is the type manufactured by the Syntron Company of Homer City, Pennsylvania, United States of America. This type of feeder feeds solids from the bottom of a bin along a plate which is vibrated by a magnetic pulse with an amplitude which varies as the amount of power fed to the feeder is varied. The amount of material fed is a function of the amplitude of the vibration of the feeder plate.
  • Another suitable type of proportioning feeder consists of a variable speed conveyor belt arranged beneath the feed bin in such a way that, as the belt moves, a relatively constant load of ore per foot of belt is fed from the bin. In this type of feeder, the rate of feed to the mill is approximately proportional to the speed of the belt.
  • the proportioning feeder illustrated diagrammatically in Figures 2 and 3 may be a single feeder where there is no separate storage of feed, or on the other hand, it may represent a battery of feeders feeding simultaneously from two or more separate storage bins. A typical example of the latter type of system is described in my copending application Serial No.
  • the monitoring signal may either be a power derived signal or a sound derived signal, depending upon the source of the control signal.
  • the monitoring signal is applied to the system in a manner which prevents the system from creating conditions wherein a particular condition of the mill operation is exceeded.
  • the commonest condition in connection with which it may be desired to affect monitoring is the rated power load of the mill motor.
  • certain other conditions such as the capacity of the follow-up metallurgical circuit or the ultimate capacity of the feed supply circuit may also impose limitations on the operation of the mill, and render monitoring desirable, and it may, when operating under certain conditions be desired to monitor a power derived control signal on the basis of a desired charge volume as represented by a signal derived from sound :emanating from the mill.
  • the normal controlling signal is received at terminal 60, is compared with the reference signal received at terminal 61 across a potentiometer 62, the centre tap 62A of which is connected to the grid 63 of the first half of tube 64.
  • the potential of this grid with respect to the cathode 65 determines the platecurrent of this half of the tube and hence the potential of point 66, since there is anIR drop across resistor 67 porportional to the plate current.
  • point 66 will be 50 volts negative with respect to terminal 68 and approximately 50 volts positive with respect to terminal 69. Since 50 volts can not be put on the grid 70A of tube 70, this voltage is dropped across resistor 71 and approximately 100 volts dropped across resistor 72 between point 73 and 74.
  • tube 70 passes suflicient current through terminal 75 to the vDJ C. winding of a saturable core reactor (not shown) connected between 75 and 68 so as to control the output of that reactor to the thyratron tubes.
  • a saturable core reactor (not shown) connected between 75 and 68 so as to control the output of that reactor to the thyratron tubes.
  • the monitoring signal from watt meter 76 (see Figure is received at terminal 77 and is compared in rheostat 78 with an arbitrary reference which is received at terminal 77A, the centre point 78A of rheostat 78 picks up the difference and is connected to the grid 79 of the second half of tube 64. Since the cathode 80 of the second half of tube 64 is connected to 69 under normal conditions, the grid 79 will be negative with respect to cathode 84) and no current will flow, but so soon as the monitoring signal voltage increases or becomes positive with respect to terminal 69 and hence to the cathode 80 of the second half of tube 64, current flows from the plate 81 through the second half of the tube.
  • Thisrincreased current'flow increases the voltage drop across resistor 67 in efiect making point 66 more negative, and hence making the grid 7 ilA of tube 70 more negative. This reduces the plate current to terminal 75 hence to the D. C. winding of the saturable core reactor so that the output of the reactor is reduced in proportion to the reduced current through tube 76.
  • Terminals 82 and 83 are connected across the normal 115 v. A. C. supply and provide heating current through transformer 86 to the elements 84 and 85 of the tubes 64 and 70 respectively.
  • Terminals 87 and 88 may be connected through capacitorsysterns to increase the stabilityof the system and reduce hunting if required.
  • I refer to the datum or reference signal as being similar to the electrical signal which is produced and which is functional to an operation condition within the mill.
  • I mean that the datum or reference signal and the electrical signal must be capable of being compared to produce a diiference signal; that is to say, they must be generally the same type of signal, and their values must be expressed electrically in an analogous manner.
  • the signals used are all D. C. pulses obtained by rectifying a 60 cycle A. C. voltage. V i
  • I refer to the total charge. By this phrase, I mean the total of all the material in the mill including such reduction media as may be present in addition to the material which is undergoing comminution.
  • a method of controlling the operation of dry material reduction mills of the rotating drum type whereby to maintain said operation substantially constant at a desired operating point corresponding to a particular point on a. pre-e-stablished grinding curve comprises; continuously producing an electrical signal which varies with an operating condition in the milling system which, at the desired operating point is subject to appre' ciable change for small changes in total charge volume in said mill; continuously producing a similar datum signal equal in value to an established value of said electrical signal at said desired operating point; continuously comparing said electrical signal with said datum signal to produce a difference signal and varying in a continuous manner-the rate at which feed material is supplied to said mill inaccordance with the sense and magnitude of said difference signal.
  • a method of controlling the operation of dry material reduction mills of the rotating drum type whereby to maintain said operation substantially constant with a relatively large total charge volume in said mill comprises; continuously producing an electrical signal which varies with sound emitted by said mill; continuously producing a similar datum signal equal in value to an established value of said electrical signal at the operational point of said mill which it is desired to maintain;
  • a method of controlling the operation of dry material reduction mills of the rotating drum type whereby to maintain said operation substantially constant with a relatively low total charge volume in said mill comprises; continuously producing an electrical signal which varies with the power drawn by the mill motor, continuously producing a similar datum signal equal in value to an established value of said electrical signal at the operating point of said mill which it is desired to maintain; continuously comparing said electrical signal with'said datum signal to produce a difference signal and varying in a continuous manner the rate at which feed material is supplied to said mill in accordance with the sense and magnitude of said difference signal.
  • a method of controlling the operation of dry material reduction mills of the rotating drum type whereby to maintain said operation substantially constant at a desired operating point corresponding to a particular point on a pre-established grinding curve comprises; continuously producing an electrical signal which varies with an operating condition in the milling system which, at the desired operating point is subject to appreciable change for small changes in total charge volume in said mill; continuously producing a similar datum signal equal in value to an established value of said electrical signal at said desired operating point; continuously comparing said electrical signal with said datum signal to produce a difference signal; varying in a continuous manner the rate at which feed material is supplied to said mill in accordance with the sense and magnitude of said difierence signal, and applying a similar monitoring signal to reduce the rate at which feed material is supplied to said mill, regardless of the sense and magnitude of said difierence signal whenever a predetermined operating condition of said milling system is exceeded.
  • a method of controlling the operation of dry material reduction mills of the rotating drum type whereby to maintain said operation substantially constant with a relatively large total charge volume in said mill comprises; continuously producing an electrical signal which varies with an operating condition of said mill selected from the group consisting of sound and vibration; continuously producing a similar datum signal equal in value to an established value of said electrical signal at the operating point of said mill which it is desired to maintain; continuously comparing said electrical signal with said datum signal to produce a difference signal; varying in a continuous manner the rate at which feed material is supplied to said mill in accordance with the sense and magnitude of said difierence signal; and applying a similar monitoring signal functional to power input to the mill motor to reduce the rate at which feed material is supplied to said mill regardless of the sense and magnitude of said difierence signal whenever the power input to the mill motor exceeds a predetermined value.
  • a method of controlling the operation of dry material reduction mills of the rotating drum type whereby to maintain said operation substantially constant with a relatively small total charge volume in said mill comprises; continuously producing an electrical signal which varies with power input to the mill motor; continuously producing a similar datum signal equal in value to an established value of said electrical signal at the operating point of said mill which it is desired to maintain; continuously comparing said electrical signal with said datum signal to produce a difierence signal; varying in a continuous manner the rate at which feed material is supplied to said mill in accordance with the sense and magnitude of said difierence signal; and applying a monitoring signal functional to sound emitted by said mill to reduce the rate at which feed material is supplied to said mill, regardless of the sense and magnitude of said difference signal whenever the sound emitted by said mill falls below a predetermined value.

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  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Crushing And Grinding (AREA)
  • Disintegrating Or Milling (AREA)
US426721A 1954-04-30 1954-04-30 Dry grinding feed control Expired - Lifetime US2766941A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
DENDAT1070478D DE1070478B (enrdf_load_stackoverflow) 1954-04-30
FR1118659D FR1118659A (enrdf_load_stackoverflow) 1954-04-30
US426721A US2766941A (en) 1954-04-30 1954-04-30 Dry grinding feed control
SE911/55A SE307057B (enrdf_load_stackoverflow) 1954-04-30 1955-01-31
GB4820/55A GB782523A (en) 1954-04-30 1955-02-17 Dry grinding control

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Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2824700A (en) * 1954-05-25 1958-02-25 Weston David Method of reducing materials
US2922587A (en) * 1954-04-05 1960-01-26 Federal Ind Ind Group Inc Monitoring system for automatic controls
US2952414A (en) * 1956-08-31 1960-09-13 Union Corp Ltd Electrically operated grinding mills
US3078050A (en) * 1960-01-08 1963-02-19 Hardinge Harlowe Autogenous grinding process and mill systems to perform the same
DE1145843B (de) * 1958-07-31 1963-03-21 Licentia Gmbh Anordnung zur Stoerschallkompensation bei schallabhaengigen Regelungen
DE1161111B (de) * 1957-07-26 1964-01-09 Bolidens Gruv Ab Verfahren zum Regeln von Trommelmuehlen zwecks Aufrechterhaltung eines von der Muehle erzeugten Feinheitsgrades des Mahlgutes
US3117734A (en) * 1961-03-17 1964-01-14 Duval Sulphur & Potash Company Method and system for treating ore
US3179140A (en) * 1963-06-19 1965-04-20 Satake Toshihiko Automatic load controlling apparatus for grain polishing machine
US3471094A (en) * 1966-12-01 1969-10-07 Terry R Kearney Hydraulic control system for mills
US3480212A (en) * 1967-02-23 1969-11-25 Reserve Mining Co Control apparatus
US4404640A (en) * 1981-01-09 1983-09-13 W. R. Grace & Co. Grinding mill monitoring instrumentation
US4586146A (en) * 1981-02-27 1986-04-29 W. R. Grace & Co. Grinding mill control system
FR2581898A1 (fr) * 1985-05-14 1986-11-21 Anglo Amer Corp South Africa Procede et dispositif de controle du niveau de charge d'un broyeur
US4635858A (en) * 1981-01-09 1987-01-13 W. R. Grace & Co. Methods of operating ball grinding mills

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1262410B (de) * 1961-06-13 1968-03-07 Rex Chainbelt Inc Regeleinrichtung fuer eine Verarbeitungsanordnung mit einem Vibrationsfoerderer
DE1216080B (de) * 1961-08-02 1966-05-05 Steinmueller Gmbh L & C Verfahren zur Regelung von Zerkleinerungsmaschinen
DE1194231B (de) * 1961-08-21 1965-06-03 Polysius Gmbh Verfahren zum Regeln von Sichtermahlanlagen
DE19756099A1 (de) 1997-12-17 1999-07-01 Waeschle Gmbh Verfahren zum Sichten von Schüttgut

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2001543A (en) * 1930-01-28 1935-05-14 Gen Electric Control system
US2136907A (en) * 1936-05-18 1938-11-15 Smidth & Co As F L Mill control
US2235928A (en) * 1939-01-04 1941-03-25 Hardinge Co Inc Apparatus for and method for controlling grinding devices
US2381351A (en) * 1942-04-23 1945-08-07 Hardinge Co Inc Method and means of feeding material to grinding mills
US2491466A (en) * 1943-10-12 1949-12-20 Mine And Smelter Supply Compan Apparatus for controlling the feed to a mill in a grinding circuit

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2001543A (en) * 1930-01-28 1935-05-14 Gen Electric Control system
US2136907A (en) * 1936-05-18 1938-11-15 Smidth & Co As F L Mill control
US2235928A (en) * 1939-01-04 1941-03-25 Hardinge Co Inc Apparatus for and method for controlling grinding devices
US2381351A (en) * 1942-04-23 1945-08-07 Hardinge Co Inc Method and means of feeding material to grinding mills
US2491466A (en) * 1943-10-12 1949-12-20 Mine And Smelter Supply Compan Apparatus for controlling the feed to a mill in a grinding circuit

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2922587A (en) * 1954-04-05 1960-01-26 Federal Ind Ind Group Inc Monitoring system for automatic controls
US2824700A (en) * 1954-05-25 1958-02-25 Weston David Method of reducing materials
US2952414A (en) * 1956-08-31 1960-09-13 Union Corp Ltd Electrically operated grinding mills
DE1161111B (de) * 1957-07-26 1964-01-09 Bolidens Gruv Ab Verfahren zum Regeln von Trommelmuehlen zwecks Aufrechterhaltung eines von der Muehle erzeugten Feinheitsgrades des Mahlgutes
DE1145843B (de) * 1958-07-31 1963-03-21 Licentia Gmbh Anordnung zur Stoerschallkompensation bei schallabhaengigen Regelungen
US3078050A (en) * 1960-01-08 1963-02-19 Hardinge Harlowe Autogenous grinding process and mill systems to perform the same
US3117734A (en) * 1961-03-17 1964-01-14 Duval Sulphur & Potash Company Method and system for treating ore
US3179140A (en) * 1963-06-19 1965-04-20 Satake Toshihiko Automatic load controlling apparatus for grain polishing machine
US3471094A (en) * 1966-12-01 1969-10-07 Terry R Kearney Hydraulic control system for mills
US3480212A (en) * 1967-02-23 1969-11-25 Reserve Mining Co Control apparatus
US4404640A (en) * 1981-01-09 1983-09-13 W. R. Grace & Co. Grinding mill monitoring instrumentation
US4635858A (en) * 1981-01-09 1987-01-13 W. R. Grace & Co. Methods of operating ball grinding mills
US4586146A (en) * 1981-02-27 1986-04-29 W. R. Grace & Co. Grinding mill control system
FR2581898A1 (fr) * 1985-05-14 1986-11-21 Anglo Amer Corp South Africa Procede et dispositif de controle du niveau de charge d'un broyeur

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DE1070478B (enrdf_load_stackoverflow) 1959-12-03
SE307057B (enrdf_load_stackoverflow) 1968-12-16

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