A monitoring system for measuring physical variables inside a mill

Abstract

The present invention relates to a monitoring system for measuring physical variables inside a mill in order to determine the level of wear of the linings. The system comprises at least one sensorised lining formed by: a base block (D); a sensor block (A); load cells (B); an angular position sensor; instrumentation; sealing elements (C); elements for attaching the load cells (E, G); bolts (F, H); communication elements; power elements; and a data processing and display unit.

Description

[0001] A MONITORING SYSTEM TO MEASURE PHYSICAL VARIABLES INSIDE A MILL.

[0002] Technical Sector

[0003] The present invention relates to the mining industry, more particularly to a monitoring system for measuring physical variables inside a mill.

[0004] Previous Technique

[0005] Chile is the world's leading copper producer, with the mining industry being the most important sector of the economy, accounting for 10% of GDP and 60% of exports. Therefore, any development that helps improve the productivity, efficiency, and availability of equipment and processes in mining activity represents a significant benefit to the country's economy.

[0006] Within the copper extraction process, concentrators are associated with the highest resource consumption. A significant part of the concentration process is carried out by large rotary mills, which reduce the size of the ore particles for subsequent copper extraction. These mills consist primarily of a horizontally oriented hollow cylinder called a drum, which rotates around its axial axis and into which the grinding charge is placed. This grinding charge comprises the ore whose size is to be reduced, water, and a charge of grinding media, generally steel balls, which help accelerate the comminution of the ore particles. The drum is closed at both ends, through which the ore enters and exits. The inner surface of the drum is lined with liners and lifters.The liners protect the drum from wear, while the lifters transmit the energy associated with the mill's rotation to the grinding media, thus generating its movement. Comminution occurs through abrasion and impact, resulting from contact between the mineral particles themselves and between the particles and the grinding media.

[0007] The main costs associated with the comminution process carried out in mills are related to energy consumption, lining replacement, and the cost of grinding media. Furthermore, the main factors affecting the normal operation of mills are detailed below: a. Movement of the load inside the mills.

[0008] The grinding charge is lifted onto one side of the mill (see Figure 1) due to the rotation of the drum (1.1) and the action of the liners (1.2), acquiring a kidney-like shape (1.3). Its movement is characterized by three main points, which are defined by their angular positions with respect to the mill's axis of rotation. The charge is raised to an equilibrium position called the shoulder (1.4), defined by the angle or s , which corresponds to the upper limit of the kidney where the particles begin to become independent of the movement of the drum and the coatings, subsequently falling and describing free fall movements (1.5). The point of impact (1.6), defined by the angular position <j> E , corresponds to the highest position at which the particles from the shoulder fall onto the inner surface of the mill. The heel of the charge (1.7), defined by the angular position or T , is the position where lifters and liners begin to lift the load after it falls from the shoulder and corresponds to the limit of the kidney at the opposite end from the shoulder.

[0009] Among the variables that determine the behavior of the load inside the mill are: the operating speed, which is defined in terms of the critical speed of the mill, which corresponds to the speed at which the load begins to centrifuge; the filling level, which corresponds to the fraction of the internal volume of the mill that is occupied by both the grinding media and the ore load; and the internal geometry of the mill, which is determined by the geometry of the liners and lifters.

[0010] The operating speed is controlled by the mill drive control system. The fill level changes due to variations in the inflow and outflow of ore and the replacement of grinding media. The geometry of the liners and lifters changes over time due to wear from contact with the particles inside the mill. Since the lifters transmit the energy associated with the mill's rotation to the load, their wear affects the mill's lifting capacity, thus reducing its productivity. To compensate for this, in practice, the operating speed is increased as the lifters wear down.This continuous change in speed, filling, and internal geometry of the mill opens the possibility that it may operate under detrimental conditions, both in terms of mill productivity and the maintenance operations it requires, along with their corresponding economic consequences. b. Measurement of the degree of wear of the linings.

[0011] The linings (liners and lifters) wear down progressively as the mill operates due to contact with the ore particles and grinding media, decreasing in volume over time. This wear alters the geometry of the linings, compromising their ability to protect the mill drum from wear and affecting their lifting capacity, thus negatively impacting mill productivity.

[0012] In the industry, maintenance operations are organized into production campaigns, which begin when new linings have been installed and end when these linings are worn and need to be replaced. Replacement operations can take between four and five days and are performed several times a year. Furthermore, due to the critical nature of these machines, the degree of lining wear is monitored through periodic inspections carried out throughout the production campaigns. During these inspections, the mill is shut down so that maintenance crews can enter and measure the thickness of the liners and lifters. This results in production losses due to mill shutdowns and safety concerns due to personnel entering the mill.Systems that allow for non-invasive wear estimation would reduce production losses associated with inspection operations and the associated safety risks. c. Accelerated wear of linings and grinding media.

[0013] Mill linings can wear down through corrosion, abrasion, or impact. While wear from corrosion or abrasion is inevitable, it is possible to increase their lifespan by preventing impact wear.

[0014] One of the main problems associated with mill operation is the phenomenon of critical impacts on the linings, illustrated in Figure 2. This occurs when operating conditions are incorrectly set, causing part of the load to fall directly onto the linings; that is, when the impact point (2.1) is located above the heel position (2.2). This results in accelerated wear of the linings and grinding media, shortening their lifespan and increasing the frequency of replacement, leading to production losses and an increased risk of accidents. A system that allows for real-time prevention of lining impacts would help reduce wear from impacts, maximizing the lifespan of the linings and grinding media, and thus reducing the frequency of replacement. d. Maximizing mill productivity.

[0015] In general, particle grinding occurs through abrasion and impact, with the latter being the most important mechanism. Impact comminution is produced by particles falling from the shoulder onto the kidney, with impacts associated with the grinding media being particularly significant. The energy of these impacts increases with operating speed, as the particles fall at higher velocities, reaching its maximum when the point of impact coincides with the heel. Increasing the speed beyond this point generates critical impacts on the linings and does not improve comminution, since the particles fall onto the linings instead of the kidney, and their energy is used to wear down the linings instead of grinding the ore particles. This adjustment of operating conditions is shown in Figure 3.Therefore, to maximize mill productivity, it is desirable to increase its speed from a condition where the impact point is below the heel position (3.A) to a point where these positions coincide (3.B), preventing the load from falling directly onto the liners (3.C). Similarly, when adjusting operating conditions to correct critical impacts on the liners, these conditions should be set so that the heel position coincides with the impact point. Because liner geometry and fill level are constantly changing, finding this point of maximum productivity without compromising liner life is difficult.This is why implementing systems that help locate it in real time and non-invasively generates value by increasing mill productivity without harming the life of the linings and grinding media. e. Monitoring the loads received by the mill as a result of the grinding load.

[0016] Mills are critical machines in the mining process, making their structural integrity vital to ensuring the proper development of production activities. Changes in the grinding charge or operating conditions can produce loads or stresses that can endanger mill components, such as impacts on the linings that can lead to fatigue failures or fracture of the bolts that attach them to the drum. Therefore, monitoring the loads exerted by the particles on the linings can extend the equipment's lifespan and prevent catastrophic failures that jeopardize the mine's production capacity and the safety of personnel. f. Lack of knowledge of the actual filling level.

[0017] The fill level is a crucial process variable that affects mill productivity, energy consumption, and the internal flow of the material. In practice, determining the actual fill level is complex, requiring periodic shutdowns for checks, which entails production losses and risks to personnel performing these tasks. Lack of knowledge regarding this variable can lead to problems such as overfilling or underfilling the mill, which negatively impact productivity and increase operational costs. Estimating the mill fill level without needing to shut it down would improve control of the grinding process, thereby increasing mill productivity and availability.

[0018] Today, the following solutions have been proposed to mitigate these conditions that affect the normal grinding process:

[0019] • Impactometer / Electronic Ear (1) This system consists of a set of microphones positioned outside the mill around the drum. These microphones capture the noise produced by the various contacts occurring inside the mill, which is then processed by a fuzzy logic system. This system identifies the presence of impacts on the linings. Finally, if impacts are detected, the system allows the mill's operating conditions to be adjusted to correct the problem. Several mill monitoring systems have been developed following this principle, such as FLSmidth's SAGwise system or Metso's Smart Ear system.

[0020] • Wear Sensor Bolt (SSD)®: This technology, developed by HighService, consists of an instrumented fastening bolt with electronic devices at one end. It is mounted in the holes of the liner fastening bolts. As liners and lifters wear, the SSD bolt wears along with them and emits a signal proportional to the liner wear. This signal is transmitted wirelessly, and processing allows for highly accurate prediction of the tonnage at which liners should be changed and identification of changes in the wear rate, all without stopping equipment.

[0021] • LoadlQ (3) and M¡IISense (4) These systems, belonging to FLSmith and Metso respectively, use accelerometers located in the mill shell to measure vibrations and detect those generated by the impact of the grinding media on the liners. They then use this information to adjust the mill speed so that these impacts cease.

[0022] Solutions based on noise and vibration measurements of the mill shell depend on the vibration response of the mill structure and rely on identifying the physical phenomenon causing the vibrations. The amplitude and frequency of these vibrations depend on many factors that are difficult to control and that evolve during equipment operation. This makes it difficult to distinguish whether the vibrations originate from particle impacts on the linings or from some other physical phenomenon. This also compromises the accuracy with which impacts on the linings can be detected and the severity of those impacts estimated. Furthermore, the wear sensor bolt only provides a snapshot estimate of wear.

[0023] Some patents related to this technology are detailed below:

[0024] • Patent CL52.286 disclosing a system for real-time monitoring of the wear of the rib thickness of a SAG mill grate, comprising a sensor located on the outer surface, a wireless transmitter, a wireless receiver and a signal acquirer; in addition to the system calibration method.

[0025] • US Patent 6,874,366 protecting a system and method for direct online measurement of variables to estimate and analyze the dynamic internal load of rotary mills in mineral grinding processes comprising wireless acoustic sensors to sense sound inside the mill and attached to the outer mantle or cover of the mill; timing sensors and processing and control means.

[0026] • Application W02020 / 132741, which covers a device and system for monitoring the wear of a consumable component mounted on mining equipment, comprising: an elongated bolt adapted to retain the consumable component in place on a face of the mining equipment, wherein this bolt comprises: a threaded section and a shank terminating at a distal end of the elongated bolt opposite the proximal end; and an electromagnetic acoustic transducer (EMAT) coupled to the proximal end of the elongated bolt. References:

[0027] 1. Conicyt, Chile invents "impactometer" that is now used in giant mineral mills around the world. <https: / / www.conicyt.cl / fondef / 2010 / 07 / 12 / inventan-en-chile- impactometro-que-hoy-se-usa-en-gigantescos-molinos-de-minerales-de- todo-el-mundo / >

[0028] 2. SSD - Wear Sensor System for Mill Liners and Wear Plates https: / / www.hiqhservice.com / es / hiqhservice-technoloqy / ssd-sistema-sensor-de-desqaste /

[0029] 3. Optimal mill loading with smart sensor technology https: / / www.flsmidth.com / en-qb / products / knowledqescape-loadiq.

[0030] 4. MillSense™ Enabling optimization through sense https: / / www.metso.com / portfolio / millsense / .

[0031] Brief description of figures

[0032] Figure 1: Schematic of the movement of the load inside a mill where the following are indicated: (1.1) the direction of rotation of the mill, (1.2) the linings, (1.3) the mass of the load that takes on a kidney shape on one side of the mill, (1.4) the position of the shoulder, (1.5) the particles that fall from the shoulder in free fall, (1.6) the position of the point of impact and (1.7) the position of the heel.

[0033] Figure 2: Schematic of the movement of the load inside a mill where there are critical impacts on the coatings, where (2.1) corresponds to the point of impact and (2.2) to the position of the heel.

[0034] Figure 3: Schematic of the adjustment of operating conditions for their maximization in the mill, where (3.A) corresponds to the mill operating in a sub-optimal condition, where the position of the impact point is below the position of the heel; (3.B) to the mill operating with operating conditions that maximize its productivity, where the position of the heel coincides with that of the impact point and (3.C) to the incorrect adjustment of operating conditions, where the impact point is located above the position of the heel.

[0035] Figure 4: Exploded view of a sensorized coating with its main components: (A) sensor block; (B) load cells; (C) sealing elements; (D) base block; (E) and (G) load cell fixing elements; and (F) and (H) fixing bolts to the mill mantle.

[0036] Figure 5: Cutaway view of a sensorized coating, showing some of its main components: (A) sensor block, (B) load cells, (C) sealing elements, (E) and (G) load cell fixing elements, (F) fixing bolts to the mill mantle.

[0037] Figure 6: Mounting of a pair of sensorized coatings on the mantle of a mill.

[0038] Figure 7: Schematic of forces to which a sensorized coating is subjected when: (7.1) it is in the angular range where the coatings are in contact with the particles and (7.2) when it is in the angular range where the coatings are not in contact with the particles.

[0039] Figure 8: Front cross-section view of a sensorized coating, under different degrees of wear: (8.1) new coating; (8.2) semi-worn coating; and (8.3) worn coating.

[0040] Figure 9: Representation of the forces acting on the different coatings of a mill based on their angular opposition in the radial and tangential directions.

[0041] Figure 10: Laboratory scale mill where the monitoring system is tested, where (10.1) corresponds to the sensorized coating installed inside the scale mill; (10.2) to the transparent end for observing the movement of the load inside the mill; and (10.3) data acquisition and transmission system from the sensorized coating.

[0042] Figure 11: Laboratory scale mill in operation, where (11.1) corresponds to the sensorized coating located inside the mill, which is about to meet (11.3) the grinding load; (11.2) indicates the direction of rotation of the mill; and (11.4) corresponds to the phototachometer used to record the angular position of the sensorized coating.

[0043] Figure 12: Measurement graph made by the sensorized coating (12.1 ), where (12.2) indicates the times when it passes through the reference position given by the phototachometer (12.2).

[0044] Figure 13: Pulse obtained by a sensorized coating during a mill rotation, where (13.A) corresponds to the pulse obtained directly from the coating and (13.B) to the pulse from which the force resulting from contact with the particles has been separated (F P fí ) of the weight force of the sensor block in the radial direction (mg p ), and from which the effect of the centrifugal force U= has been removed c ).

[0045] Figure 14: Determination of the arrangement of particles inside the mill from the force exerted by the particles on the sensor block (F p ñ ) where (14.1) corresponds to the initial contact position; (14.2) to the heel position; (14.3) to the shoulder position; (14.4) to the angular interval in which critical impacts occur and with which the impact coefficient is calculated; and (14.5) to the position of maximum force value.

[0046] Figure 15: Comparison of the results obtained with an image of the mill operating at 85% of its critical speed, where (15.1) corresponds to the contact start position; (15.2) to the heel position; (15.3) to the shoulder position; and (15.4) to the angular interval with which the impact coefficient is calculated.

[0047] Figure 16: Comparison of the results obtained with an image of the mill operating at 70% of its critical speed, where (16.1) corresponds to the contact start position; (16.2) to the heel position; (16.3) to the shoulder position; and (16.4) to the angular interval with which the impact coefficient is calculated.

[0048] Figure 17: Comparison of the results obtained with an image of the mill operating at 75% of its critical speed, where (17.1) corresponds to the contact start position; (17.2) to the heel position; (17.3) to the shoulder position; and (17.4) to the angular interval with which the impact coefficient is calculated.

[0049] Figure 18: Comparison of the results obtained with an image of the mill operating at 80% of its critical speed, where (17.1) corresponds to the contact start position; (17.2) to the heel position; (17.3) to the shoulder position; and (17.4) to the angular interval with which the impact coefficient is calculated.

[0050] Figure 19: Variation of the impact coefficient (IC) as a function of the operating speed, where (19.1) corresponds to the range of speeds where there are no critical impacts on the coatings; (19.2) to the optimum speed; and (19.3) to the range of speeds where critical impacts occur on the coatings.

[0051] Figure 20: Representation of the forces to which the coatings (20.1 ) to (20.22) are subjected, calculated from the measurement made by the sensorized coating.

[0052] Disclosure of the Invention

[0053] This technology is a monitoring system for measuring physical variables inside a mill. More specifically, this system comprises one or more sensor-equipped linings for measuring physical variables resulting from the interaction between the grinding media and the linings inside the mill. These measurements can include deformation, vibration, force, orientation, or other variables arising from the interaction between the sensor-equipped linings and the particles inside the mill, as well as the effect of weight.

[0054] For a better understanding of the technology, Figures 4 and 5 are used as a reference, where the components of the sensorized coatings for force measurement are shown, which are detailed below: a. a base block (D): corresponding to a section of the coating that is fixed to the inner surface of the mill by means of bolts (F and H) and on which the rest of the elements necessary for the measurement are mounted; b. a sensor block (A): corresponding to the section of the coating that is in direct contact with the particles and from where the measurements are extracted; for which, the instrumentation implemented is oriented to measure the interaction between this part of the coating, the acceleration of gravity and the interactions with the grinding load; c.Load cells (B): Composed of at least two load cells used to connect the base block (D) and the sensor block (A), and instrumented to measure the forces to which the sensor block (A) is subjected; and where the load cells (B) receive the net load exerted by the particles and the acceleration due to gravity on the sensor block (A); d. Angular position sensor: This can be an inclinometer located inside the sensorized lining or on the mill shell, or a tachometer located outside the mill. This allows the angular position of the sensorized lining to be determined as it rotates along with the rest of the mill; e. Instrumentation: Composed of signal acquisition and conditioning devices necessary for the correct measurement of the sensor elements (B). These are located inside the sensorized lining or on the outside of the mill shell.The electronics communicate with the outside of the mill via radio signals; f. sealing elements (C): composed of a rubber seal (or similarly flexible material) and adhesives. Their function is to prevent the entry of moisture or particulate matter that could affect the correct operation of the sensors and electronics located inside the sensing lining. Their rigidity is such that it does not interfere with the measurement of the forces exerted by the load cells (B); g. load cell fixing elements (E and G): comprising a set of elements that allow the load cell (B) to be fixed to both the base block (D) and the sensor block (A), safely supporting the loads transmitted by the load cell (B); h. bolts (F and H): allowing the sensing lining to be fixed to the mill shell.Unlike standard coatings, the bolts are located inside the sensing coating and secure the base block (D) to the mill. This allows the load received by the sensor block (A) to be transmitted to the base block (D) only through the load cells (B), ensuring accurate measurement of the forces it receives. Specifically, bolt (H) is perforated and serves as a fixing bolt with a hole along its longitudinal axis. Through this hole pass the cables that enable communication and power to the electronics. i. Communication elements: These components receive signals from the instrumentation and transmit them from inside the sensing coating to the outside for further processing.This function can be performed by a repeater or access point located on the exterior of the mill shell, which consists of three main elements: a receiving antenna, the repeater body, and a transmitting antenna. The receiving antenna receives the radio signals, the repeater body or access point "repeats" them, and they are transmitted again via the transmitting antenna. In this case, the receiving antenna is located inside the sensor-equipped casing. This allows the radio signals emitted by the instrumentation to be received by the repeater's receiving antenna and transmitted to the repeater body via a cable. The repeater body and the transmitting antenna are located on the mill shell, receiving data from the instrumentation and transmitting it via radio signals to the surrounding area of ​​the mill.Another alternative for extracting instrumentation data from inside the sensing lining to the outside of the mill involves connecting the instrumentation by cable directly to a controller located on the mill shell, which then transmits the signals via radio to the surrounding area. In both cases, the cables pass from inside the sensing lining to the mill shell on the outside through the perforated bolt (H). The signals from the mill shell are then received by access points located around the mill and connected to a processing unit; j. Power supply elements: these consist of a set of batteries that power the instrumentation and communication elements located both inside the sensing lining and on the mill shell.The cables that power the elements located inside the sensorized lining pass through the perforated bolt (H); and k. a data processing and visualization unit: this corresponds to a computer mounted outside the mill, which receives the signals for processing, storage, and visualization of the results. This includes a set of algorithms that process the signals, as well as a data visualization system that allows the processing results to be transmitted to the mill operator.

[0055] These sensor-equipped liners are mounted inside the mill in a manner similar to a standard liner (Figure 6), allowing for direct, real-time measurement of the contact effect between the load and the liner. Their design is compatible with the existing mill liners, simplifying implementation. Advantageously, this technology does not require any additional mill modifications for the installation of the sensor-equipped liners.

[0056] Because the sensorized coatings adapt to the geometry of the coatings already present in the mill, the geometry of its components may vary.

[0057] Finally, the system, through its algorithms that process the signals, allows: i. estimating the amount of mass that the coatings have lost due to wear compared to their original state (new condition), that is, the degree of wear that they have suffered during a certain interval of time;

[0058] i. Measure the heel position of the load; iii. Measure the shoulder position of the load; iv. Measure the magnitude of the forces exerted by the particles on the linings around the heel position, allowing us to distinguish whether or not there is a load directly impacting the mill linings above the heel position (critical impacts); v. Estimate in real time the optimal mill operating speed; vi. Estimate in real time the mill filling level; vii. Estimate the magnitude of the forces exerted by the particles on the linings and on the mill structure; and viii. Estimate the grinding torque, calculated from the forces exerted by the particles on the linings.

[0059] The process for determining the mill's condition from one or more sensorized liners is based on analyzing parameters related to how these sensorized liners interact with the grinding media. In the mill, these liners rotate around their axis of rotation along with the drum and the other liners, and under normal operating conditions, they come into contact with the particles within a defined angular range, from the heel position (or point of impact in the case of critical impacts on the liners) to the shoulder of the load (Figure 7, range 7.1). During this angular range, the liner is subjected to the weight force (mg) and the centrifugal force (F). c ) and the forces resulting from the interaction with the grinding load in the radial directions (F P fí ) and tangential (F P T Outside this angular range, between the shoulder and the heel position (or point of impact), the sensing coating is subjected only to weight and centrifugal force (Figure 7, interval 7.2). Since the sensing block of the sensing coating is connected to the base block via load cells, the latter are able to measure the magnitude of these forces in the radial and tangential directions. During mill rotation, the centrifugal force, being a constant in the force measurements, can be eliminated by balancing the load cell measurements.

[0060] To estimate the amount of mass lost by the sensing liner due to wear, the forces to which it is subjected must be measured in the angular range where it is not in contact with the particles (Figure 7, range 7.2). During this angular range, the sensing liner is subjected to weight and centrifugal force. Weight manifests in the load cell measurements in the radial and tangential directions as a sinusoidal signal whose frequency corresponds to the mill's rotational frequency and whose amplitude is directly proportional to the mass of the sensor block. This occurs because the orientation of the cells with respect to the direction of gravitational acceleration changes as the sensing liner rotates around the mill's axis of rotation. When the sensor block is in its new state (see Figure 8, state 8).1), the amplitude of this sinusoidal signal is at its maximum and decreases as wear occurs. In this way, the amplitude of the sinusoidal wave can be obtained for each mill rotation, so its variation over time provides a continuous indicator of the evolution of the overall wear of the linings. Since this determination is made from measurements taken from the load cell, the mass lost by the linings can be determined online, without needing to stop the mill, unlike the currently used method which requires periodic shutdowns and personnel to enter the mill to take specific measurements.Additionally, by determining the amplitude of the sinusoidal wave produced by the weight force in the angular range where the sensorized coatings are not in contact with the particles, it is possible to extract the effect of the weight force from the measurements taken in the angular range where the sensing coating is in contact with the particles. This eliminates the effect of centrifugal force on the signal due to the balancing of the load cells and separates the effect of the weight force from the forces resulting from contact with the particles. When the sensing coating reaches the heel position and begins to make contact with the load particles to lift them along the kidney, the force it is subjected to increases rapidly and consistently. Therefore, it is possible to estimate the heel position from the instant when this force begins to increase with a steep gradient.In this way, since the position of the sensing coating is known thanks to the angular position sensor, it is possible to locate the angular position of the heel by identifying the moment when this high increase in forces occurs. Subsequently, when the coating is no longer in contact with the particles and passes through the shoulder position, the force it is subjected to again becomes the weight and centrifugal force, and the moment when this begins can be detected in a similar way to how the heel position is detected.

[0061] When critical impacts occur, the forces measured directly above the heel position in the angular range between points (2.1) and (2.2) in Figure 2 exhibit irregular magnitudes that increase and decrease rapidly. Since the heel position is known, it is possible to estimate the intensity of the impacts from the load cell measurements. Therefore, if the magnitude of the force measured from the sensing coating above the heel position is low and does not exhibit significant fluctuations, it implies that no critical impacts exist. If the magnitude of the forces fluctuates significantly over a large angular range above the heel position, it implies that the forces originate from critical impacts on the coatings.These characteristics can be summarized in an indicator called the impact coefficient, which is calculated by integrating the force signal exerted by the particles on the sensored coating, measured by the load cell, from a point where the sensored coating is not in contact with the particles until it reaches the heel position. The impact coefficient links the magnitude of the forces resulting from impacts with the angular range in which they occur. When there are no critical impacts, the magnitude of the impact coefficient is low and remains approximately constant regardless of operating conditions, since the load falling from the shoulder is dampened by falling on itself. When critical impacts occur, the magnitude of this coefficient increases rapidly, allowing the identification of this problem and the quantification of its severity.

[0062] Additionally, the impact coefficient can be used to set operating conditions such that the heel and impact point positions coincide. This is achieved through an iterative process, in which the mill operator makes small speed increments, starting from a state where no critical impacts occur, until the point at which the impact coefficient begins to increase is reached. At this point, the impact point position is known to coincide with the heel position.

[0063] The fill level significantly influences the forces measured by the load cells and defines the angular range in which the coatings are in contact with the particles. When the fill level increases—that is, when the volume of charge inside the mill increases—the heel position rises, widening the angular range in which the particles are in contact with the coatings, and the amplitude of the forces measured by the sensing coating increases significantly. From this, variations in the fill level are estimated in real time.

[0064] The movement of the load inside the mill has a random component due to the nature of particle motion, but it also has a stationary component. This means that the forces exerted on the coatings are approximately the same when they are in the same angular position and while operating conditions remain the same. Therefore, it is possible to estimate the load exerted by the particles on all the coatings based on a measurement taken with a single sensing coating, since the angular position of the other coatings is fixed relative to the position of the sensing coating.When the sensorized coating is in a specific angular position around the mill's axis of rotation, it is subjected to a force of a certain amplitude. When the other coatings are in that same angular position, they are subjected to a force approximately equal to that experienced by the sensorized coating when it was in that position. This is represented in Figure 9, which shows the coatings of a typical mill, numbered from one to thirty. Arrows are drawn on these coatings to represent the forces resulting from contact with the particles acting on each coating, in the tangential and radial directions, at a given instant. Coatings 9.7 to 9.24 are subjected to forces because they are in contact with the particles, while the others are not.Now, considering that at the represented time point the sensorized coating is in position 9.13, the coatings in positions 9.11 and 9.12 are subjected to the same force as the sensorized coating was when it was in those positions, which is valid for all coatings. Since their position relative to that of the sensorized coating is known, it is possible to estimate the forces to which each coating is subjected based on its position at each time point and the measurement taken by a single sensorized coating.Therefore, given that the load cells measure in two perpendicular directions and that the position of the sensing lining is known, the system allows the calculation of the total force exerted by the grinding load on the mill drum by summing the estimated forces to which each lining is subjected, as well as how this force is distributed in space. The torque associated with the drum linings, which must be delivered by the mill drive, is also obtained thanks to the measurements of the forces in the tangential direction. Since it is calculated from measurements taken inside the mill, this measurement of the mechanical grinding torque is the most direct that can be obtained.Advantageously, this technology allows for estimating the degree of wear on the linings online, without needing to stop the mill and enter its interior; increasing the life of the linings by preventing the load from directly impacting them, thus avoiding accelerated wear and possible fracture; reducing the costs associated with the renewal of the grinding media by preventing them from impacting the linings; increasing mill productivity without compromising the life of the linings; knowing important dynamic operating variables such as the filling level, the position of the heel and shoulder; and safeguarding the structural integrity of the mills by recognizing the existence of excessive loads during their operation.

[0065] Application examples

[0066] Example 1: Evaluation of the monitoring system in a laboratory-scale mill.

[0067] The monitoring system was tested on a test bench corresponding to a laboratory-scale replica of a real copper mine mill with an internal diameter of 1.2 m and a length of 0.55 m (see Figure 10). Its interior was fitted with 48 linings, including the sensor linings (10.1). This mill was also fitted with a transparent end (10.2), which allowed observation of the load's movement inside and its recording in photographs. The instrumentation, communication equipment, and power supply elements required were installed on the mill's mantle (10.3). Figure 11 shows the mill in operation, where the sensor lining (11.1) rotated counterclockwise with the mill (11.2) and interacted with the grinding load (11.3). Additionally, a phototachometer (1 1 .4) was installed which in this case was used to provide a reference angular position.Several tests were carried out, which are detailed below:.

[0068] 1.1. Measurement tests with the sensed coatings

[0069] Various measurement tests were performed on the sensor-equipped coatings. These tests involved varying the operating speed and fill level to validate the system's capabilities under the different conditions encountered in a mill in practice. The operating speed was varied from 55% to 90% of its critical speed in 5% increments. Between 75% and 80% of the critical speed, variations were made in 1.25% increments to obtain more precise results in this range. The fill level used was 25% of the mill's internal volume.

[0070] 1.1.1. Measurement taken by the sensor coating.

[0071] Figure 12 shows a force measurement performed by the sensor-guided coating in the radial direction (12.1), where the phototachometer allowed for the determination of the coating's position over time. To facilitate signal processing, a reference position located 135° from the horizontal was selected, and each time the sensor-guided coating passed through this position, the corresponding time was recorded (12.2). This allowed the signal to be divided into "pulses," which begin when the coating passes through the reference position and end when it passes through it again, completing a full rotation around the mill's axis of rotation. In this same figure, five pulses (R1, P2, P3, P4, P5) can be observed. This resulted in a series of consecutive pulses that traverse 360° around the mill's axis of rotation, starting from the reference position.

[0072] 1.1.2. Extraction of weight and particle contact forces. Figure 13 shows a pulse measured by the sensored coating in the radial direction; specifically, (13.A) shows the pulse obtained directly from the sensored coating, which contains the effects of the particle contact force in the radial direction F P P , the weight force of the sensor block mg R and the centrifugal force F c Subsequently, this pulse was subjected to processing that allowed the effect of centrifugal force to be eliminated and the force of the particles to be separated from the weight force of the sensor, where the result can be seen in Figure 13.B.

[0073] Regarding the weight force of the sensor block, it was observed that:

[0074] • The force mg showed a sinusoidal shape in the radial direction, which matched expectations;

[0075] • Its maximum value was found at point (13.1), at the 270° position; while its minimum value was found at point (13.2), at the 90° position. This is because at 90° and 270°, the sensor block was oriented vertically. Its magnitude is 0 at the 180° and 0° positions. o where the sensor block was located in a horizontal direction; and

[0076] • The maximum amplitude of the weight force was 34.6 N, which indicates that the mass of the sensor block of the sensing coating was approximately 3.5 kg, this value being very close to the actual value of 3.6 kg.

[0077] 1.1.3. Calculation of heel position, start of contact, shoulder and impact coefficient.

[0078] With respect to the force resulting from contact with the particles in the radial direction F P fí It was observed that in the angular range between 135° and 215°, the value was approximately 0, since in this range the sensor block was not in contact with particles. For the range between 215° and 30°, the magnitude of F P fí was different from 0, since the sensor block came into contact with the particles; and in the angular range between 30° and 135°, F P fí It became 0 again, as the sensing coating was once again out of contact with the particles.

[0079] The position at which the sensorized coating began to make contact with the particles inside the mill is called the "contact start position" and may correspond to the heel position or the impact point position, depending on whether or not critical impacts occur. In this test, as can be seen in Figure 14, the magnitude of the force F is shown at 215° P fí The force increased irregularly up to 240°, the latter being the heel position. That is, between the initial contact position (14.1) and the heel position (14.2), there was a 25° segment (14.4) where critical impacts occurred. From the heel position, the force magnitude increased steadily until reaching its maximum at 292° (14.5). From this point, it decreased steadily until returning to 0 at 35°, the position corresponding to the shoulder of the load (14.3). This general behavior is present in the mills regardless of operating conditions. Algorithms were implemented to process the signals, and the initial contact, heel, and shoulder positions, the angular segment of critical impacts, and the impact coefficient were obtained.

[0080] The exact results of applying these algorithms were:

[0081] • Position (14.1) corresponds to the contact start position at 213.4°;

[0082] • Position (14.2) corresponds to the heel position at 241°;

[0083] • Position (14.3) corresponds to the shoulder position, at 35.7°;

[0084] • (14.4) corresponds to the angular range of critical impacts;

[0085] • (14.5) corresponds to the point where the force F P P reaches its maximum value; and

[0086] • starting from the magnitude F P R In the interval (14.4) the impact coefficient was calculated, whose value was 17.7 for this test.

[0087] 1.2. Experimental validation.

[0088] To validate the results of the previous tests, the images of the load's movement inside the mill were superimposed, as shown in Figure 15. It can be seen that the initial contact, heel, and shoulder positions obtained from the sensorized coating correctly identified the load's behavior inside the mill. In this case, the mill was operating at 85% of its critical speed. Figures 16 to 18 show the mill under other operating conditions, with speeds equivalent to 70%, 75%, and 80% of the critical speed, respectively. It can be observed that, despite the speed changes, the system allowed for accurate determination of the heel, impact point, and shoulder positions.

[0089] Additionally, Figures 16 and 17 show no critical impacts, with these appearing in Figure 18. This indicates that the optimal operating speed was between 75% and 80% of the critical speed. Figure 19 shows the variation of the impact coefficient for tests performed at operating speeds ranging from 55% to 90% of the mill's critical speed. It can be seen that when the mill operated at 75% of the critical speed, the impact coefficient was 2.08, remaining approximately constant up to 78.75% of the critical speed. This indicates that for speeds below this value (19.1), there were no impacts on the linings, and that 78.75% of the critical speed (19.2) corresponded to its optimal speed.Then, at 80% of the critical speed, the impact coefficient increased to 6.16 and subsequently increased steadily as the speed increased, indicating that critical impacts on the coatings occurred at speeds above 78.75% of the critical speed (19.3). Therefore, the impact coefficient can be used as an indicator to adjust the mill speed to its optimum speed without jeopardizing the coating life due to accelerated wear caused by critical impacts.

[0090] 1.3. Calculation of the loads exerted by the particles on the mill from the measurement of the sensorized coating.

[0091] Since the sensor-equipped coating records the force at different angular positions of the mill, and considering that all the lifters have the same geometry (or a similar one, if worn), it was possible to estimate the force to which each lifter is subjected at any given instant. Figure 20 shows, in particular, where the coating was in position 15. e And since the position of the rest of the coatings with respect to the latter is also known, the force to which each of the coatings was subjected was estimated.

[0092] The sensorized coating, corresponding to coating (20.22), was subjected to a force of 9.8 N and, when at 315°, was subjected to a force of 196.9 N. Therefore, coating (20.9) was subjected to this same force while the sensorized coating was at 15°. This is valid for all coatings, at any instant in time, and the magnitudes of the forces for each of them are shown in Table 1.

[0093] Table 1. Detail of the force at different positions of the sensed coating.

[0094] The other 26 coatings were not subjected to forces resulting from contact with the particles, as they were not in contact with them. This made it possible to obtain the distribution of forces exerted by the particles on the mill coatings, both in the radial and tangential directions.< / j>

Claims

Claims 1. Monitoring system for measuring physical variables inside a mill to determine the level of wear of the coatings CHARACTERIZED in that it comprises at least one sensing coating composed of: a. a base block (D): corresponding to a section of the coating that is fixed to the inner surface of the mill and on which the rest of the elements are mounted to perform the measurement on the sensing coating; b. a sensor block (A): corresponding to the section of the coating from which the measurements are extracted; for which purpose, the instrumentation implemented is oriented to measure the interaction between this part of the coating, the acceleration of gravity and the interactions with the grinding load; c. load cells (B): composed of at least two load cells that are used to connect the base block (D) and the sensor block (A), and which are instrumented to measure the forces to which the sensor block (A) is subjected; d.an angular position sensor; e. instrumentation: composed of signal acquisition and conditioning devices for measuring the sensor elements (B) and are located inside the sensing coating or on the mill mantle, on its exterior and where the electronics communicate with the outside of the mill by means of radio signals; f. sealing elements (C): composed of a rubber seal and adhesives, which prevent the entry of moisture and particulate matter into the interior of the sensing coating; g. elements for fixing the load cells (E, G): comprises a set of elements that allow fixing the load cell (B), both to the base block (D) and to the sensor block (A), supporting the loads transmitted by the load cell (B) safely; h.Bolts (F, H): These allow the sensor-coated lining to be fixed to the mill mantle; they are located inside the mill and fix the base block (D) to the mill, allowing the load received by the sensor block (A) to be transmitted to the base block (D) only through the load cells (B); i. Communication elements: These comprise a transmitter component that receives the signals from the instrumentation and sends them to the outside of the mill via radio signals; j. Power supply elements: These correspond to a set of batteries that energizes the instrumentation and the communication elements located both inside the sensor-coated lining and in the mill mantle; and k.A data processing and visualization unit: This corresponds to a computer mounted outside the mill, which receives the signals for processing, storage and visualization of the results, including algorithms that process the signals, and a data visualization system to transmit the processing results to the mill. mill operator.

2. Monitoring system for measuring physical variables inside a mill according to claim 1, CHARACTERIZED in that the angular position sensor is an inclinometer located inside the sensorized lining or in the mill mantle.

3. Monitoring system for measuring physical variables inside a mill according to claim 1, CHARACTERIZED in that the angular position sensor is a tachometer located outside the mill and allows knowing the angular position of the sensed coating while it rotates along with the rest of the mill.

4. Monitoring system for measuring physical variables inside a mill according to claim 1, CHARACTERIZED in that the bolt (H) is perforated and corresponds to a fixing bolt that has a hole in its transverse axis, through which the cables pass that allow communication and power supply to the electronics.

5. Monitoring system for measuring physical variables inside a mill according to claim 1, CHARACTERIZED in that communication and power elements are located inside the sensorized lining and in the mill mantle.

6. Monitoring system for measuring physical variables inside a mill according to claim 1, CHARACTERIZED in that the cables that communicate and power the electronics and sensors pass from the inside of the mill to the outside through the perforated bolt (H).

7. Monitoring system for measuring physical variables inside a mill according to claim 1, CHARACTERIZED in that the communication element is an access point located in the mill mantle, which is composed of a receiving antenna that receives radio signals and is located inside the sensed coating; the repeater body that repeats them and a transmitting antenna that are located in the mantle.

Images