Method and an arrangement for determining a degree of fullness of a large grinding mill drum, and a large grinding mill drum

Abstract

The present invention relates to the field of mineral and metallurgical processes, to disintegrating in general and to disintegrating by tumbling mills, and more particularly to a method and arrangement for determining a degree of fullness of a large grinding mill drum, and to a large grinding mill drum. An arrangement for determining a degree of fullness of a grinding mill drum has a sensor arrangement attached to at least one lifting bar bolt of an at least one lifting bar of the grinding mill. The sensor arrangement includes at least one force transducer attached to the at least one lifting bar bolt. With the help of the measurement arrangement, more reliable measurement data can be provided for the determination of the degree of fullness of a grinding mill drum.

Claims

1. An arrangement for determining a degree of fullness of a grinding mill drum, comprising a sensor arrangement coupled to at least one lifting bar bolt of an at least one lifting bar of a grinding mill, said sensor arrangement having at least one force transducer coupled to the at least one lifting bar bolt.

2. The arrangement according to claim 1, wherein said sensor arrangement comprises at least one of an accelerometer and inclinometer coupled to said at least one lifting bar bolt.

3. The arrangement according to claim 1, wherein said sensor arrangement comprises at least one of an accelerometer and inclinometer disposed next to said at least one lifting bar bolt.

4. The arrangement according to claim 1, said arrangement further comprising: a data processing and transmitting unit disposed on the grinding mill drum casing surface, said data processing and transmitting unit being operatively coupled to said sensor arrangement; a data receiving unit disposed outside the mill drum on a fixed surrounding structure outside the mill drum; and a data processing device.

5. The arrangement according to claim 4, wherein said data processing and transmitting unit comprises a signal acquisition module for receiving the measurement signals from the sensor arrangement and a transmitter for transmitting the measurement data wirelessly to said data receiving unit.

6. The arrangement according to claim 4 wherein said data processing and transmitting unit comprises a relay wirelessly actuating the data processing and transmitting unit.

7. The arrangement according to claim 4, wherein said data processing and transmitting unit further comprises at least one of a power supply, a regulator, and an amplifier.

8. The arrangement according to claim 1, wherein said sensor arrangement is attached to at least one lifting bar bolt on the grinding mill drum casing surface.

9. The arrangement according to claim 1, wherein several sensor arrangements are attached to several lifting bar bolts in one row on the grinding mill drum casing surface.

10. The arrangement according to claim 1, wherein several sensor arrangements are attached to several lifting bar bolts in several rows on the grinding mill drum casing surface.

11. A grinding mill drum, wherein said grinding mill drum comprises an arrangement for determining a degree of fullness of the grinding mill drum according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross-sectional view of a large grinding mill drum according to the prior art;

(2) FIG. 2 shows a partial cross-sectional view of a one embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention;

(3) FIG. 3 shows a partial cross-sectional view of a another embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention;

(4) FIG. 4 shows a perspective view of a third embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention;

(5) FIG. 5 shows a schematic diagram of one embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention;

(6) FIG. 6 shows a perspective view of a fourth embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention;

(7) FIG. 7 shows a perspective view of a fifth embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention.

(8) The prior art drawing of FIG. 1 has been presented earlier. In the following, the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings of FIGS. 2 to 7.

DETAILED DESCRIPTION OF THE INVENTION

(9) The present invention relates to a method and an arrangement for registering the instant volume or the instant level of the charge in an ore-grinding drum of the kind that is provided with internal lifting means.

(10) FIG. 2 shows a partial cross-sectional view of a one embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention. In FIG. 2 the grinding mill has a drum casing 3, which drum casing 3 is provided with linings 4. The linings 4 of the drum casing 3 comprise lifting bars 5, 6, which lifting bars 5, 6 have been attached to the drum casing 3 of the grinding mill with lifting bar bolts 7, 8.

(11) In the presented embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention said determining arrangement has at least one lifting bar bolt 7, which has been provided with a force transducer 9. In the presented embodiment of a determining arrangement said force transducer 9 has been attached to the said at least one lifting bar bolt 7 with the help of a shim 10 and a nut 11. The force transducer 9 is used to measure reactions caused by the grinding material said reactions subjected to the lifting bar 5 and to the said at least one lifting bar bolt 7 of the grinding mill. The determining arrangement according to the presented embodiment of the present invention may also have an accelerometer and/or an inclinometer arranged next to the said at least one lifting bar bolt 7 of the grinding mill.

(12) FIG. 3 shows a partial cross-sectional view of another embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention. In FIG. 3 the grinding mill has a drum casing 3, which drum casing 3 is provided with linings 4. The linings 4 of the drum casing 3 comprise lifting bars 5, 6, which lifting bars 5, 6 have been attached to the drum casing 3 of the grinding mill with lifting bar bolts 7, 8.

(13) In the presented another embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention said determining arrangement has an at least one lifting bar bolt 7, which has been provided with a force transducer 9 and an accelerometer 12 and/or an inclinometer. In the presented another embodiment of a determining arrangement said force transducer 9 has been attached to the said at least one lifting bar bolt 7 with the help of a shim 10 and a nut 11. Furthermore in the presented another embodiment of a determining arrangement said accelerometer 12 and/or inclinometer has been attached to the said at least one lifting bar bolt 7.

(14) The force transducer 9 is used to measure reactions caused by the grinding material to the lifting bar 5 and to the said at least one lifting bar bolt 7 of the grinding mill. The accelerometer 12 and/or inclinometer is used to measure the position and the angle or rotation of the said at least one lifting bar bolt 7 of the grinding mill and of the force transducer 9 attached to the said at least one lifting bar bolt 7. The accelerometer 12 and/or inclinometer is used to synchronize the output of the force transducer 9 to the mill rotation and to define the phase angle of the lifting bar with respect to the earth gravity.

(15) FIG. 4 shows a perspective view of a third embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention. The third embodiment of a determining arrangement comprises a sensor arrangement 13 attached to one lifting bar bolt on the grinding mill drum casing surface 3 and a data processing and transmitting unit 14 arranged on the grinding mill drum casing surface 3, said data processing and transmitting unit 14 connected to said sensor arrangement 13. Said data processing and transmitting unit 14 may also be attached to the one or more lifting bar bolts on the grinding mill drum casing surface 3. Furthermore the third embodiment of a determining arrangement comprises a data receiving unit 15 and a data processing device 16, e.g. a personal computer (PC) 16, said data receiving unit 15 and said data processing device 16 being arranged outside the mill drum on any fixed surrounding structure outside the mill drum. The data processing and transmitting unit 14 is responsible for handling raw measurement signals obtained from the sensor arrangement 13, and transmitting those wirelessly to the data receiving unit 15 and further to the data processing device 16. With apparatus having a sensor arrangement 13 consisting of one force transducer and one accelerometer it is possible to measure the degree of fullness in one mill cross section.

(16) FIG. 5 shows a schematic diagram of one embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention. The one embodiment of a determining arrangement shown in FIG. 5 comprises a data processing and transmitting unit 17 arranged on the grinding mill drum surface and a sensor arrangement 18 attached to the said at least one lifting bar bolt on the grinding mill drum surface.

(17) The data processing and transmitting unit 17 of the determining arrangement according to an embodiment of the present invention comprises a signal acquisition module 19 for receiving the measurement signals from the a sensor arrangement 18; a transmitter 20 for transmitting the measurement data wirelessly to a data receiving unit 15 arranged outside the mill drum on any fixed surrounding structure outside the mill drum; and a relay 21 for switching the data processing and transmitting unit 17 on wirelessly.

(18) The data processing and transmitting unit 17 of the determining arrangement according to an embodiment of the present invention may also comprise a power supply 22 for providing electrical power to the determining arrangement; a regulator 23 for providing regulated voltage to the sensor arrangement 18; and an amplifier 24 for providing regulated power to a force transducer 25 of the sensor arrangement 18 and amplifying the signal from said force transducer 25 of the sensor arrangement 18 to a signal acquisition module.

(19) The sensor arrangement 18 of the determining arrangement according to an embodiment of the present invention comprises a force transducer 25 for measuring reactions caused by the grinding material to a lifting bar bolt of the grinding mill; and an accelerometer 26 and an inclinometer 27 for measuring the position and the angle or rotation of a lifting bar bolt of the grinding mill and of the force transducer 25 attached to the said lifting bar bolt. The accelerometer 26 and an inclinometer 27 is used to synchronize the output of the force transducer 25 to the mill rotation and to define the phase angle of the lifting bar with respect to the earth gravity. The force transducer 25 may be any kind of force transducer 25 suitable for measuring reactions on a lifting bar bolt such as e.g. a strain gage type transducer. The accelerometer 26 may be any kind of accelerometer 26 suitable for measuring the position and the angle or rotation of a lifting bar bolt such as e.g. a capacitive accelerometer. The force transducer 25 may also be based on a force sensor, on a pressure sensor, on a strain gauge or on a piezoelectric sensor.

(20) FIG. 6 shows a perspective view of a fourth embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention. The fourth embodiment of a determining arrangement comprises several sensor arrangements 28 attached to the several lifting bar bolts in one row on the grinding mill drum casing surface 3 and a data processing and transmitting unit 14 arranged on the grinding mill drum casing surface 3, said data processing and transmitting unit 14 connected to said several sensor arrangements 28. Said data processing and transmitting unit 14 may also be attached to the one or more lifting bar bolts on the grinding mill drum casing surface 3. Furthermore the fourth embodiment of a determining arrangement comprises a data receiving unit 15 and a data processing device 16, e.g. a personal computer (PC) 16, said data receiving unit 15 and said data processing device 16 being arranged outside the mill drum on any fixed surrounding structure outside the mill drum. The data processing and transmitting unit 14 is responsible for handling raw measurement signals obtained from the sensor arrangements 28, and transmitting those wirelessly to the data receiving unit 15 and further to the data processing device 16. With apparatus having several sensor arrangements 28 consisting of several force transducers and several accelerometers it is possible to measure the degree of fullness in several mill cross sections. In addition an apparatus with several force transducers and several accelerometers becomes more reliable.

(21) FIG. 7 shows a perspective view of a fifth embodiment of an arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention. The fifth embodiment of a determining arrangement comprises several sensor arrangements 29, 30 attached to the several lifting bar bolts in several rows on the grinding mill drum casing surface 3 and a data processing and transmitting unit 14 arranged on the grinding mill drum casing surface 3, said data processing and transmitting unit 14 connected to said several sensor arrangements 29, 30. Said data processing and transmitting unit 14 may also be attached to the one or more lifting bar bolts on the grinding mill drum casing surface 3. Furthermore the fifth embodiment of a determining arrangement comprises a data receiving unit 15 and a data processing device 16, e.g. a personal computer (PC) 16, said data receiving unit 15 and said data processing device 16 being arranged outside the mill drum on any fixed surrounding structure outside the mill drum. The data processing and transmitting unit 14 is responsible for handling raw measurement signals obtained from the sensor arrangements 29, 30, and transmitting those wirelessly to the data receiving unit 15 and further to the data processing device 16. With apparatus having several sensor arrangements 29, 30 consisting of several force transducers and several accelerometers it is possible to provide a three dimensional picture of the conditions and the state inside the grinding mill. In addition an apparatus with several force transducers and several accelerometers becomes more reliable.

(22) In the method and arrangement for determining a degree of fullness of a large grinding mill drum according to the present invention there is measured force measurement data on reactions caused by the grinding material to an at least one lifting bar bolt of the grinding mill as well as measurement data on the position and the angle or rotation of the at least one lifting bar bolt of the grinding mill. With the help of this force measurement data the degree of fullness of a large grinding mill is then calculated. In this calculation there can be the toe angle .sub.k and/or the shoulder angle .sub.s first calculated.

(23) In the method and arrangement according to the present invention the degree of fullness of a large grinding mill may be calculated e.g. as explained in the following and also disclosed in U.S. Pat. No. 7,699,249 B2. In the analysis of the measurement results the phase of the force or power oscillation caused by the lifter bars is calculated by using a sample data P(n) that is equidistant in relation to the angle of rotation and is obtained e.g. on the basis of the mill power draw of one rotation cycle, according to the following formula:

(24) $=\arg \left[\underset{n=0}{\overset{N-1}{.Math.}}P\left(n\right)\exp \left(\frac{-2{\mathrm{nN}}_n}{N}\right)\right]$

(25) where i={square root over (1)}=imaginary unit

(26) $\arg z=\arctan \frac{\mathrm{Im}z}{\mathrm{Re}z}=\mathrm{the}\mathrm{polar}\mathrm{angle},$

(27) i.e. argument, of a complex number z,

(28) N=number of samples in a sample data P(n),

(29) N.sub.n=number of lifter bars in the mill,

(30) n=number of sample, and

(31) =the phase of the oscillation caused by the lifter bars.

(32) The toe angle is calculated from the phase of the power oscillation caused by the lifter bars as follows, according to the following formula:

(33) ${}_k=\frac{2\left(k_n+1\right)-}{N_n}+{}_n$

(34) where k.sub.n=number of lifter bars, remaining in between the lifter bar located nearest to the axis x and the lifter bar located nearest to the toe position,

(35) .sub.k=toe angle, and

(36) .sub.n=angle from the axis x to the lifter bar located nearest to the axis x, so that it has a positive value in the rotation direction of the mill.

(37) The degree of fullness is calculated from the toe angle and the rotation speed of the mill by means of various mathematical models, such as the model defined in the Julius Kruttschitt Mineral Research Center (JKMRC). Said model is described in more detail for example in the book Napier-Munn, T., Morrell, S., Morrison, R., Kojovic, T.: Mineral Comminution Circuits, Their Operation and Optimisation (Julius Kruttschnitt Mineral Research Centre, University of Queensland, Indooroopilly, Australia, 1999). The calculation formula of the JKMRC model for the degree of fullness in a mill is given in the following formula:

(38) $\{\begin{array}{c}{n}_{c,i+1}=0,35\left(3,364-V_i\right)\\ V_{i+1}=1,2796-\frac{{}_{\mathrm{toe}}-\frac{}{2}}{2,5307\left(1-{}^{-19,42\left(n_{c,i+1}-n_p\right)}\right)}\end{array},$

(39) where the degree of fullness is defined by iterating the degree of fullness of the mill in relation to the interior volume of the mill. In the above formula, n.sub.c is an experimentally calculated portion of the critical speed of the mill, in which case centrifugation is complete, n.sub.p is the rotation speed of the mill in relation to the critical speed, V.sub.i is the previous degree of fullness of the mill, and V.sub.i+1 is the degree of fullness to be defined, in relation to the interior volume of the mill.

(40) The solution for determining a degree of fullness of a large grinding mill drum according to the present invention provides a direct measurement of the reactions caused by the grinding material. The degree of fullness of the grinding mill drum can therefore be determined irrespective of possible stops and interruptions. With the help of the arrangement according to the present invention consisting of several force transducers and several accelerometers it is possible to provide a three dimensional image of the conditions inside the grinding mill.

(41) As the measurement according to the present invention is a direct measurement of the phenomena and related measurement of the reactions caused by the grinding material, there is no need for calibration. As the position and the angle of the sensors are continuously known online there is no need for external trigger to determine the rotation. This is of particular importance in the analysis and calculation, as this simplifies calculations substantially and makes the result more reliable. As the measurement solution with sensor arrangements is quite simple and straightforward also installation and maintenance is easy.

(42) With the help of the solution according to the present invention the manufacturers of large grinding mill drums will be able to provide grinding mill with a measurement arrangement producing more reliable measurement data for the determination of the degree of fullness of a large grinding mill drum with said measurement arrangement having better measurement sensitivity. The solution according to the present invention may be utilised in any kind of large grinding mill having lifter bars inside the grinding mill drum.

(43) It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.