WO2016107988A1

WO2016107988A1 - A method and an arrangement for determining a degree of fullness of a large grinding mill, and a large grinding mill

Info

Publication number: WO2016107988A1
Application number: PCT/FI2015/050954
Authority: WO
Inventors: Jukka PIRTTINIEMI; Esa PORKKA; Nikolai Vatanski
Original assignee: Outotec (Finland) Oy
Priority date: 2014-12-30
Filing date: 2015-12-29
Publication date: 2016-07-07
Also published as: FI20146166A; FI126803B

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, and to a large grinding mill. An arrangement for determining a degree of fullness of a large grinding mill according to the present invention has a vibration sensor arrangement (12), (13), (14) arranged to measure the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means (4), (5) of the drum casing (3), and determining the degree of fullness of the said large grinding mill based on the said measured vibration measurement data. With the help of the measurement arrangement according to the present invention more reliable measurement data can be provided for the determination of the degree of fullness of a large grinding mill.

Description

A METHOD AND AN ARRANGEMENT FOR DETERMINING A DEGREE OF FULLNESS OF A LARGE GRINDING MILL, AND A LARGE GRINDING MILL

FIELD OF THE INVENTION

The present invention relates to the field of mineral and metallurgi- cal 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, and to a large grinding mill.

BACKGROUND OF THE INVENTION

One of the most common processes in mining and metallurgy is the comminution processing or disintegrating of ore. When processing material for the selective or collective recovery of valuable material components, the processes concerned are preceded by comminution processing i.e. mechanical crushing or disintegration of the material in a manner to free the valuable components, one from the other. Comminution is particle size reduction of materi- als. Comminution is achieved by blasting, crushing and grinding. After comminution the components are then mutually isolated with the aid of known separation methods, this isolation being contingent on differences in color, shape, density or in differences in their respective surface active and magnetic properties, or other properties.

In comminution processing first ore or rock is excavated, broken down or removed by blasting. Blasting is the controlled use of explosives and other methods in mining, quarrying and civil engineering. Typically blasting produces particles in the size having a diameter of 500 mm or more.

Crushing is particle size reduction of ore or rock materials by using crushing devices i.e. crushers. Crushers e.g. jaw crushers, gyratory crushers or cone crushers are used to reduce the size, or change the form, of materials so that pieces of different composition can be differentiated. In the crushing process the crushing devices hold material being crushed between two parallel or tangent solid surfaces of a stronger material and apply sufficient force to bring said surfaces together. Typically in a crushing process particles having a diameter up to 1000 mm are crushed to particles having a diameter of 5 mm or more.

Grinding is particle size reduction of ore or rock materials in grinding mills. In hard rock mining and industrial mineral operations the demands for rotating mineral and metallurgical processing equipment such as grinding mills are very high both in terms of grinding efficiency and energy consumption. Typically in a grinding process particles having a diameter up to 1000 mm are grinded to particles having a diameter of 0,010 mm or more. This conventional grinding of materials results in considerable wear on the grinding bodies pre- sent in the mill, due to the hardness of the rock concerned, therewith also resulting in considerable costs for the provision of such grinding bodies.

The rotating mineral and metallurgical processing equipment such as grinding mills are typically very large, having a diameter of several meters. The grinding mills may be trunnion-supported or shell-supported. Trunnion support is the most common way of supporting a mill in a mineral processing application, especially in very large grinding mills. In a bearing arrangement of a trunnion-supported grinding mill the support bearings have a relatively small bearing diameter and the trunnion journals have a high consistent stiff journal surfaces, this facilitating the formation of a good bearing lubricant film distribu- tion. The shell-supported grinding mills are more compact, occupy less floor space and require simpler foundations than comparable trunnion-supported grinding mills. Because the end plates of the shell-supported grinding mill do not support the structure, the feed and discharge openings may be sized to meet process conditions without being constrained by trunnion bearing limita- tions.

A ball mill is a typical type of fine grinder. However, the rotating mineral and metallurgical grinding mills are today very often autogenous grinding mills or semi-autogenous grinding mills designed for grinding or primary crushed ore. Autogenous grinding mills are so-called due to the self-grinding of the ore. In an autogenous grinding mill a rotating drum throws larger rocks of ore in a cascading motion which causes impact breakage of larger rocks and compressive grinding of finer particles. In autogenous grinding the actual material itself, i.e. the material to be ground, forms the grinding bodies.

Semi-autogenous grinding mills are similar to autogenous mills, but utilize grinding balls e.g. steel grinding balls to aid in grinding like in a ball mill. Attrition between grinding balls and ore particles causes grinding of finer particles. Semi-autogenous grinding mills typically use a grinding ball charge of 8 to 21 %, sometimes a grinding ball charge of 5 to 60%. A semi-autogenous grinding mill is generally used as a primary or first stage grinding solution. Semi- autogenous grinding mills are primarily used at gold, copper and platinum mines with applications also in the lead, zinc, silver, alumina and nickel industries.

Autogenous and semi-autogenous grinding mills are characterized by their large diameter and short length as compared to ball mills. The rotating mineral and metallurgical processing equipment such as autogenous and semi-autogenous grinding mills are typically driven by ring gears, with a 360° fully enclosing guard.

The inside of an autogenous or semi-autogenous grinding mill is lined with mill linings. The mill lining materials typically include cast steel, cast iron, solid rubber, rubber-steel composites or ceramics. The mill linings include lifters, e.g. lifter bars to lift the material inside the mill, where it then falls off the lifters onto the rest of the ore charge.

Rotating mineral and metallurgical processing equipment that is provided with internal lifters is typically difficult to control. For example, in au- togenous grinding mills or semi-autogenous grinding mills the feed to the mill also acts as a grinding media, and changes in the feed have a strong effect on the grinding efficiency. The change in the feed properties is a normal phenomenon that needs to be considered in in controlling the rotating mineral and metallurgical processing equipment.

In autogenous or semi-autogenous grinding mills, the existing mineral deposits seldom have a homogenous structure and a homogenous mechanical strength. Material properties such as hardness, particle size, density and ore type also change constantly and consequently a varying energy input is required.

Conventionally grinding has been controlled on the basis of the mill power draw, but particularly in autogenous and semi-autogenous grinding, the power draw is extremely sensitive to changes in feed parameters. It has been discovered that the degree of fullness in the mill as percentages of the mill volume is a quantity that is remarkably more stable and much more descriptive as regards the state of the mill. But because the degree of fullness is difficult to infer in an on-line-measurement, the measurement of the load mass is often considered sufficient. However, the mass measurement has its own problems both in installation and in measurement drift. Moreover, there may be intensive variations in the load density, in which case changes in the mass do not nec- essarily result from changes in the degree of fullness. As a summary, the degree of fullness is an important parameter that describes the state of the grinding mill. The main challenge with the degree of the fullness is that the parameter is difficult to measure online. One prior art method for determining the degree of fullness of a large grinding mill has been to measure the weight of a large grinding mill and use the measured weight to calculate the degree of fullness of a large grinding mill. In this prior art method the weight of the grinding charge has been used as the deciding parameter for controlling the mill. This method is cost demanding, however, because of the weighing equipment needed to register continuously the changes in the weight of the grinding charge that occur during operation of the mill, which enables the steps necessary in order to improve prevailing operating conditions to be carried out as quickly as possible. Also the water content of the mill changes constantly, the density, hardness and particle size of the grinding charge changes constantly. Furthermore the mill linings typically constitute up to 30-50 % of total weight of the mill. As these linings wear off in time this has a considerable effect on the weight of the mill. Therefore the weight of the grinding mill is not a good indication the degree of fullness in the grinding mill. All in all it has been discovered that the weight of the grinding charge does not correlate good enough with the degree of fullness in the grinding mill as percentages of mill volume.

Another prior art method for determining the degree of fullness of a large grinding mill has been to measure and analyze the power consumption or the power intake signal of a large grinding mill and use the measured power consumption to calculate the degree of fullness of a large grinding mill. In pa- tent document US 5,325,027 there is presented a method for defining the degree of fullness in a mill is calculated on the basis of the monitored variation in power consumption. However, particularly in autogenous and semi- autogenous grinding mills, the power consumption is extremely sensitive to changing parameters. The energy or power requirement of a large grinding mill depends on several factors, such as the density of the grinding charge, a mill constant, the extent of mill charge replenishment, or the instant volume of charge in the grinding mill, relative mill speed, length and diameter of the grinding mill. Furthermore, it has been discovered that the grinding mill power consumption or the power intake signal does not correlate enough with the degree of fullness in the grinding mill as percentages of mill volume. In the following, the prior art will be described with reference to the accompanying figures, of which:

Figure 1 shows a cross-sectional view of a large grinding mill according to the prior art;

Figure 2 shows a perspective and partially cut open view of a large grinding mill arrangement according to the prior art.

Figure 1 shows a cross-sectional view of a large grinding mill according to the prior art. In Figure 1 the grinding mill has a drum casing 1 , which drum casing 1 is provided with linings. The linings of the drum casing 1 com- prise internal lifting means i.e. lifting bars 2, which lifting bars 2 lift the grinding charge material inside the mill, where it then falls off the lifting bars 2 onto the rest of the grinding charge. The angle in which the grinding charge material inside the mill first hits a lifting bar 2 is called "toe angle" <t>k. Respectively the angle in which the grinding charge material inside the mill first falls off a lifting bar 2 is called "shoulder angle" Φ₅.

Figure 2 shows a perspective and partially cut open view of a large grinding mill arrangement according to the prior art. In Figure 2 the grinding mill arrangement has a drum casing 3, which drum casing 3 is provided with linings. As can be seen from the partially cut open view of Figure 2 the linings of the drum casing 3 comprise internal lifting means i.e. lifting bars 4, 5 inside the mill for lifting of the grinding charge material.

The large grinding mill arrangement according to the prior art has a trunnion support with trunnion bearings 6, 7 on both sides of the drum casing 3 of the grinding mill. The large grinding mill arrangement according to the prior art also has a ring gear 8, with a 360° fully enclosing guard. The large grinding mill arrangement according to the prior art also has a pinion gear 9 and pinion bearings 10, 1 1 on both sides of the pinion gear 9.

In patent document US 6,874,364 a system for monitoring mechanical waves from a moving machine has been presented in which system a sen- sor arrangement is located on an exterior surface of the grinding mill. The presented sensor arrangement has an acoustic wave sensor for measuring acoustic wave properties and an accelerometer for measuring mechanical waves, i.e. vibrational events and low frequency events, event spatial localization, and events occurring on the ends of the mill. The presented mechanical wave monitoring method may also include a step of monitoring volumetric load in the machine based on the measured mechanical waves. However, even the presented on-mill-shell type device measured grinding mill acoustic wave properties do not correlate adequately enough with the degree of fullness in the grinding mill as percentages of mill volume.

There are also other prior art methods for determining the degree of fullness of a large grinding mill by measuring acoustic wave properties of a large grinding mill and using the measured acoustic wave properties, i.e. sound pressure and/or sound intensity to estimate the degree of fullness of a large grinding mill. In these other methods the acoustic wave property measurement sensors may be a single microphone or a series of microphones or microphone mats that are measuring acoustic wave properties coming from the large grinding mill. Also here, it has been discovered that the measured grinding mill acoustic wave properties provide only a rough estimate on the degree of fullness.

In patent document US 7,699,249 there is presented a method for defining the degree of fullness in a mill is calculated on the basis of the measured toe angle, the rotation speed of the mill and the geometrical dimensions of the mill. However, the presented sensor arrangement does not consistently enough provide straightforward and adequate measurement sensitivity required for a precise monitoring of the degree of fullness in the grinding mill as percentages of mill volume.

In general, there are some problems with the prior art solutions for measuring the degree of fullness of a large grinding mill. So far, the measuring solutions are relatively complex and difficult in order to provide reliable information. Also the measurement accuracy and reliability with the prior art meas- uring solutions has not been adequate enough.

The problem therefore is to find a solution for measuring the degree of fullness of a large grinding mill which can provide reliable measurement data for the determination of the degree of fullness of a large grinding mill with better measurement accuracy and reliability.

There is a demand in the market for a method for determining a degree of fullness of a large grinding mill which method would be more reliable and have a better measurement sensitivity when compared to the prior art solutions. Likewise, there is a demand in the market for an arrangement for determining a degree of fullness of a large grinding mill which arrangement would be more reliable and have a better measurement sensitivity when compared to the prior art solutions; and also a demand for a large grinding mill having such characteristics.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is thus to provide a method and an apparatus for implementing the method so as to overcome the above problems and to alleviate the above disadvantages.

The objects of the invention are achieved by a method for determining a degree of fullness of a large grinding mill, said grinding mill having a drum casing with internal lifting means arranged inside the said drum casing, which method comprises the steps of:

- measuring the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means of the drum casing; and

- calculating the degree of fullness of the said grinding mill based on the said measured vibration measurement data.

Preferably, after the step of measuring the method comprises the step of:

- analysing harmonic vibrations from the vibration measurement data.

Preferably, in the step of analysing the harmonic vibration analysis comprises analysis of the harmonic vibration caused by main internal lifting means of the drum casing: Further preferably, that in the step of analysing the harmonic vibration analysis comprises an analysis of the harmonic vibration caused by auxiliary side bars of the drum casing.

Preferably, in the step of calculating a toe angle <t>k of the grinding mill drum is first calculated.

Preferably, in the step of calculating the calculation procedure comprises one or more or all of the following phases:

- processing the measured vibration measurement data, - establishing the period of full rounds,

- determining harmonic vibrations,

- observing for the position of the mill drum angle, and

- calculating the toe angle <t>k.

Preferably, in the step of calculating the calculation procedure com- prises spectral analysis, e.g. Fourier-analysis. Preferably, in the step of measuring also rotational position of the mill drum is measured using at least one accelerometer e.g. synchronization sensor accelerometer attached on the rotating mill drum; and that in the step of calculating also the measured rotational position data is utilized. Further pref- erably, in the step of measuring also at least one inclinometer attached on the rotating mill drum is used.

Preferably, in the step of measuring also a phase locked loop arrangement is used.

Furthermore, the objects of the invention are achieved by an ar- rangement for determining a degree of fullness of a large grinding mill, said grinding mill having a drum casing with internal lifting means arranged inside the said drum casing, which arrangement has a vibration sensor arrangement arranged to measure the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means of the drum casing, and determining the degree of fullness of the said large grinding mill based on the said measured vibration measurement data.

Preferably, said vibration sensor arrangement is attached to the pinion gear arrangement of the large grinding mill arrangement. Alternatively, said vibration sensor arrangement is attached to the housing arrangement of the trunnion bearings of the large grinding mill arrangement. Further alternatively, said vibration sensor arrangement is attached to the pinion gear arrangement and to the housing arrangement of the trunnion bearings of the large grinding mill arrangement.

Preferably, said vibration sensor arrangement comprises one or more acceleration sensors. Preferably, said vibration sensor arrangement comprises one or more motion sensors and/or one or more force sensors and/or one or more pressure sensors. Further preferably, said one or more pressure sensors of the said vibration sensor arrangement are used to detect vibration by measuring the pressure in the surrounding structures of a large grinding mill drum and/or the pressure in the lubrication arrangement of the pinion bearing/bearings.

Preferably, the arrangement comprises a data processing device, said data processing device being physically or wirelessly connected to the said vibration sensor arrangement. Further preferably, said vibration sensor arrangement comprises a data processing and transmitting unit for handling raw measurement signals and transmitting the vibration measurement data wirelessly to the said data processing device; and that said data processing device comprises a data receiving unit for receiving the vibration measurement data wirelessly from the said vibration sensor arrangement.

Preferably, said vibration sensor arrangement is arranged as a movable unit suitable for placing into multiple measurement positions.

Furthermore, the objects of the invention are achieved by a large grinding mill, which comprises a drum casing with internal lifting means arranged inside the said drum casing and an arrangement for determining a degree of fullness of a large grinding mill, said arrangement having a vibration sensor arrangement arranged to measure the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means of the drum casing, and determining the degree of fullness of the said large grinding mill based on the said measured vibration measurement data. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 2 shows a perspective and partially cut open view of a large grinding mill arrangement according to the prior art;

Figure 3 shows a perspective and partially cut open view of a one embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention;

Figure 4 shows a perspective and partially cut open view of another embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention;

Figure 5 shows a perspective and partially cut open view of a third embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention;

Figure 6 shows a perspective and partially cut open view of a third embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention.

The prior art drawing of Figure 1 to 2 have 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 Fig- ures 3 to 6. DETAILED DESCRIPTION OF THE INVENTION

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.

The idea of the present invention is to measure the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means of the drum casing, and calculating and determining the degree of fullness of the said large grinding mill based on the said vibration.

Figure 3 shows a perspective and partially cut open view of a one embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention. In Figure 3 the grinding mill arrangement has a drum casing 3, which drum casing 3 is provided with linings. As can be seen from the partially cut open view of Figure 3 the linings of the drum casing 3 comprise internal lifting means i.e. lifting bars 4, 5 inside the mill for lifting of the grinding charge material. The large grinding mill arrangement according to the the present invention has a trunnion support with trunnion bearings 6, 7 on both sides of the drum casing 3 of the grinding mill, a ring gear 8, with a 360° fully enclosing guard, and a pinion gear arrangement com- prising a pinion gear 9 and pinion bearings 10, 1 1 arranged on both sides of the pinion gear 9.

The presented embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention also comprises a vibration sensor arrangement 12 attached to the pinion gear arrangement 9 of the large grinding mill arrangement. The said vibration sensor arrangement 12 measures the vibration in the surrounding structures of a large grinding mill drum and provides vibration measurement data.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention an important part in the calcula- tions of fullness using this apparatus and method is the knowledge of the rotation of the mill. In the said arrangement this information together with the vibration measurement data measured by the said vibration sensor arrangement 12 is used to calculate the toe angle <t>k of the internal lifting means hitting the grinding charge material and/or the shoulder angle Φ_δ and thereafter to calcu- late the degree of fullness of a large grinding mill. In said calculation a vibration magnitude signal of the said measured vibration measurement data may be synchronized in order to calculate the toe angle <t>k of the internal lifting means hitting the grinding charge material. Also a trigger e.g. inductive trigger or laser based trigger can be used in said synchronization.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the vibration sensor arrangement 12 may comprise one or more acceleration sensors for detecting and measuring the vibration in the surrounding structures of a large grinding mill drum. The vibration sensor arrangement 12 may also comprise one or more motion sensors and/or one or more force sensors and/or one or more pressure sensors. In said arrangement said one or more pressure sensors may be used for detecting vibration by measuring the pressure in the surrounding structures of a large grinding mill drum and/or the pressure in the lubrication arrangement of the pinion bearing/bearings 10, 1 1 .

Figure 4 shows a perspective and partially cut open view of another embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention. In Figure 4 the grinding mill arrangement has a drum casing 3, which drum casing 3 is provided with linings. The linings of the drum casing 3 comprise internal lifting means i.e. lifting bars 4, 5 inside the mill for lifting of the grinding charge material. The large grinding mill arrangement according to the the present invention has a trunnion support with trunnion bearings 6, 7 on both sides of the drum casing 3 of the grinding mill, a ring gear 8, with a 360° fully enclosing guard, and a pinion gear arrangement comprising a pinion gear 9 and pinion bearings 10, 1 1 arranged on both sides of the pinion gear 9.

The presented another embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention also comprises a vibration sensor arrangement 13 attached to the housing arrangement of the trunnion bearings 6, 7 of the large grinding mill arrangement. The said vibration sensor arrangement 13 measures the vibra- tion in the surrounding structures of a large grinding mill drum and provides vibration measurement data.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the knowledge of the rotation of the mill together with the vibration measurement data measured by the said vibration sensor arrangement 13 is used to calculate the toe angle <t>k of the internal lifting means hitting the grinding charge material and/or the shoulder angle Φ_δ and thereafter to calculate the degree of fullness of a large grinding mill.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the vibration sensor arrange- ment 13 may comprise one or more acceleration sensors for detecting and measuring the vibration in the surrounding structures of a large grinding mill drum. The vibration sensor arrangement 13 may also comprise one or more motion sensors and/or one or more force sensors and/or one or more pressure sensors. In said arrangement said one or more pressure sensors may be used for detecting vibration by measuring the pressure in the surrounding structures of a large grinding mill drum and/or the pressure in the trunnion bearing lubrication arrangement.

Figure 5 shows a perspective and partially cut open view of a third embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention. In Figure 5 the grinding mill arrangement has a drum casing 3, which drum casing 3 is provided with linings. The linings of the drum casing 3 comprise internal lifting means i.e. lifting bars 4, 5 inside the mill for lifting of the grinding charge material. The large grinding mill arrangement according to the the present invention has a trunnion support with trunnion bearings 6, 7 on both sides of the drum casing 3 of the grinding mill, a ring gear 8, with a 360° fully enclosing guard, and a pinion gear arrangement comprising a pinion gear 9 and pinion bearings 10, 1 1 arranged on both sides of the pinion gear 9.

The presented third embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention also comprises a vibration sensor arrangement 14 attached to the pinion gear arrangement 9 and to the housing arrangement of the trunnion bearings 6, 7 of the large grinding mill arrangement. The said vibration sensor arrangement 14 measures the vibration in the surrounding structures of a large grinding mill drum and provides vibration measurement data.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the knowledge of the rotation of the mill together with the vibration measurement data measured by the said vibration sensor arrangement 14 is used to calculate the toe angle <t>k of the internal lifting means hitting the grinding charge material and/or the shoulder angle Φ_δ and thereafter to calculate the degree of fullness of a large grinding mill.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the vibration sensor arrange- ment 14 may comprise one or more acceleration sensors for detecting and measuring the vibration in the surrounding structures of a large grinding mill drum. The vibration sensor arrangement 14 may also comprise one or more motion sensors and/or one or more force sensors and/or one or more pressure sensors. In said arrangement said one or more pressure sensors may be used for detecting vibration by measuring the pressure in the surrounding structures of a large grinding mill drum and/or the pressure in in the pinion bearing lubrication arrangement and/or the trunnion bearing lubrication arrangement.

Figure 6 shows a perspective and partially cut open view of a fourth embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention. In Figure 6 the grinding mill arrangement has a drum casing 3, which drum casing 3 is provided with linings. The linings of the drum casing 3 comprise internal lifting means i.e. lifting bars 4, 5 inside the mill for lifting of the grinding charge material. The large grinding mill arrangement according to the the present invention has a trunnion support with trunnion bearings 6, 7 on both sides of the drum casing 3 of the grinding mill, a ring gear 8, with a 360° fully enclosing guard, and a pinion gear arrangement comprising a pinion gear 9 and pinion bearings 10, 1 1 arranged on both sides of the pinion gear 9.

The presented fourth embodiment of an arrangement for determin- ing a degree of fullness of a large grinding mill according to the present invention also comprises a vibration sensor arrangement 14 attached to the pinion gear arrangement and to the trunnion bearings housing arrangement of the large grinding mill arrangement. The said vibration sensor arrangement 14 measures the vibration in the surrounding structures of a large grinding mill drum and provides vibration measurement data.

The presented fourth embodiment of an arrangement for determining a degree of fullness of a large grinding mill according to the present invention further comprises a data processing device 15, e.g. a personal computer (PC) 15, said data processing device 15 being physically or wirelessly con- nected to the said vibration sensor arrangement 14. The said vibration sensor arrangement 14 of the arrangement according to the present invention may comprise a data processing and transmitting unit for handling raw measurement signals and transmitting the vibration measurement data wirelessly to the said data processing device 15. Respec- tively, the data processing device 15 of the arrangement according to the present invention may comprise a data receiving unit for receiving the vibration measurement data wirelessly from the said vibration sensor arrangement 14.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the vibration sensor arrange- ment may be arranged as a movable unit which is suitable for placing into multiple measurement positions.

In the arrangement for determining a degree of fullness of a large grinding mill according to the present invention the data processing device 15 calculates the toe angle <t>k of the internal lifting means hitting the grinding charge material and/or the shoulder angle Φ_δ by using the knowledge of the rotation of the mill together with the vibration measurement data measured by the said vibration sensor arrangement 14 and thereafter calculates the degree of fullness of a large grinding mill.

In the method and arrangement for determining a degree of fullness of a large grinding mill according to the present invention there is measured the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means of the drum casing. From the vibration measurement data harmonic vibrations can be detected and analysed. In this method and arrangement the harmonic vibration analysis procedure comprises analysis of the harmonic vibration caused by main internal lifting means of the drum casing. Alternatively, the harmonic vibration analysis procedure comprises analysis of the harmonic vibration caused by auxiliary side bars of the drum casing.

With the help of the vibration measurement data the degree of full- ness of a large grinding mill is then calculated. In this method and arrangement the calculation procedure of the degree of fullness of a large grinding mill may comprise one or more or all of the following phases:

- processing the measured vibration measurement data,

- establishing the period of full rounds,

- determining harmonic vibrations, - observing and/or adjusting for the initial position of the mill drum angle, and

- calculating the toe angle <t>k and/or the shoulder angle Φ_δ. Furthermore, the calculation procedure of the degree of fullness of a large grinding mill may comprise spectral analysis, e.g. Fourier-analysis.

Furthermore, the arrangement for determining a degree of fullness of a large grinding mill according to the present invention may comprise at least one accelerometer and/or inclinometer attached on the rotating mill drum and arranged to detect and measure the rotational position of the mill drum and arranged to transmit the measured rotational position data wirelessly to the said data processing device 15. The data processing device 15 of the arrangement according to the present invention may then utilize the said measured rotational position data in the calculation of degree of fullness of a large grinding mill. Furthermore, the arrangement for determining a degree of full- ness of a large grinding mill according to the present invention may comprise a phase locked loop arrangement (PLL, Phase Locked Loop).

In the method and arrangement for determining a degree of fullness of a large grinding mill according to the present invention the vibration measurement may be carried out during the start-up of the large grinding mill. Fur- thermore, the vibration measurement may also be carried out during a routine check-up of the large grinding mill. The vibration measurement according to the present invention may also be carried out as an online measurement process. The said online vibration measurement according to the present invention may be carried as a maintenance procedure and/or as a control procedure and/or as an optimization procedure. The vibration measurement according to the present invention may be carried out as a remotely controlled procedure.

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. In the analysis of the measurement results the phase Θ 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:

where i = Λ . = imaginary unit arg z = arctan -^ = the polar angle, i.e. argument, of a complex number z,

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

N_n = number of lifter bars in the mill,

n = number of sample, and

Θ = the phase of the oscillation caused by the lifter bars.

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

^ 2n(k_n + 1) - Θ

Φ* = N ^{+ Φ}" where k_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,

Φ/c = toe angle, and

Φ_η = 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.

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: n_Cii+1 = 0,35(3,364 - Vf )

Φ -—

V_i+1 = 1,2796 ¾ 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_c is an experimentally calculated portion of the critical speed of the mill, in which case centrifugation is complete, n_p is the rotation speed of the mill in relation to the critical speed, V, is the previous degree of fullness of the mill, and V_i+1 is the degree of fullness to be defined, in relation to the interior volume of the mill.

The vibration sensor arrangement according to the present inven- tion provides a very sensitive measurement of the vibration in the surrounding structures of a large grinding mill drum. The said measurement is a direct measurement of the reactions caused by the grinding material which direct measurement that is not disturbed by any piece of equipment.

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. Direct measurement 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 straight- forward also installation and maintenance is easy.

With the help of the solution according to the present invention the manufacturers of large grinding mills 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 with said meas- urement 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.

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 in- vention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method for determining a degree of fullness of a large grinding mill, said grinding mill having a drum casing (3) with internal lifting means (4), (5) arranged inside the said drum casing (3), characterized by that the method comprising the steps of:

- measuring the vibration in the surrounding structures of a large grinding mill drum, said vibration caused by the internal lifting means (4), (5) of the drum casing (3); and

2. A method according to claim 1, characterized in that after the step of measuring the method comprises the step of

- analysing harmonic vibrations from the vibration measurement data.

3. A method according to claim 2, characterized in that in the step of analysing the harmonic vibration analysis comprises analysis of the harmonic vibration caused by main internal lifting means of the drum casing.

4. A method according to claim 3, characterized in that in the step of analysing the harmonic vibration analysis comprises an analysis of the harmonic vibration caused by auxiliary side bars of the drum casing.

5. A method according to any one of claims 1 to 4, characterize d in that in the step of calculating a toe angle <t>k of the grinding mill drum is first calculated.

6. A method according to any one of claims 1 to 5, character- i z e d in that in the step of calculating the calculation procedure comprises one or more or all of the following phases:

- processing the measured vibration measurement data,

- establishing the period of full rounds,

- determining harmonic vibrations,

- observing for the position of the mill drum angle, and

- calculating the toe angle <t>k.

7. A method according to any one of claims 1 to 6, characterize d in that in the step of calculating the calculation procedure comprises spectral analysis, e.g. Fourier-analysis.

8. A method according to any one of claims 1 to 7, characterize d in that in the step of measuring also rotational position of the mill drum is measured using at least one accelerometer e.g. synchronization sensor ac- celerometer attached on the rotating mill drum; and that in the step of calculating also the measured rotational position data is utilized.

9. A method according to claim 8, characterized in that in the step of measuring also at least one inclinometer attached on the rotating mill drum is used.

10. A method according to any one of claims 1 to 9, characterized in that in the step of measuring also a phase locked loop arrangement is used.

11. An arrangement for determining a degree of fullness of a large grinding mill, said grinding mill having a drum casing (3) with internal lifting means (4), (5) arranged inside the said drum casing (3), characterized by a vibration sensor arrangement (12), (13), (14) arranged to measure the vibration in the surrounding structures of a large grinding mill drum, said vibra- tion caused by the internal lifting means (4), (5) of the drum casing (3), and determining the degree of fullness of the said large grinding mill based on the said measured vibration measurement data.

12. An arrangement according to claim 11, characterized in that said vibration sensor arrangement (12) is attached to the pinion gear ar- rangement (9) of the large grinding mill arrangement.

13. An arrangement according to claim 11, characterized in that said vibration sensor arrangement (13) is attached to the housing arrangement of the trunnion bearings (6), (7) of the large grinding mill arrangement.

14. An arrangement according to claim 11, characterized in that said vibration sensor arrangement (14) is attached to the pinion gear arrangement (9) and to the housing arrangement of the trunnion bearings (6), (7) of the large grinding mill arrangement.

15. An arrangement according to any one of claims 11 to 14, characterized in that said vibration sensor arrangement (12), (13), (14) comprises one or more acceleration sensors.

16. An arrangement according to any one of claims 11 to 15, characterized in that said vibration sensor arrangement (12), (13), (14) comprises one or more motion sensors and/or one or more force sensors and/or one or more pressure sensors.

17. An arrangement according to claim 16, characterized in that said one or more pressure sensors of the said vibration sensor arrangement (12), (13), (14) are used to detect vibration by measuring the pressure in the surrounding structures of a large grinding mill drum and/or the pressure in the lubrication arrangement of the pinion bearing/bearings (10), (11 ).

18. An arrangement according to any one of claims 11 to 17, characterized in that the arrangement comprises a data processing device (15), said data processing device (15) being physically or wirelessly connected to the said vibration sensor arrangement (12), (13), (14).

19. An arrangement according to claim 18, c h a r a c t e r i z e d in that said vibration sensor arrangement (12), (13), (14) comprises a data processing and transmitting unit for handling raw measurement signals and transmitting the vibration measurement data wirelessly to the said data processing device (15); and that said data processing device (15) comprises a data receiving unit for receiving the vibration measurement data wirelessly from the said vibration sensor arrangement (12), (13), (14).

20. An arrangement according to any one of claims 11 to 19, characterized in that the said vibration sensor arrangement (12), (13), (14) is arranged as a movable unit suitable for placing into multiple measure- ment positions.

21. A large grinding mill, characterized in that said large grinding mill comprises a drum casing (3) with internal lifting means (4), (5) arranged inside the said drum casing (3) and an arrangement for determining a degree of fullness of a large grinding mill according to claim 6.