Mill Loading Research Articles

Role of reduced diameter disks in the performance of an IsaMill™

IsaMill™ is utilized mainly for ultrafine grinding of low-grade ores. Although highly efficient, it has certain operational challenges, such as frequent replacement of liners of disks and inner shells. To circumvent this challenge, a design modification of the disks, by introducing a reduced diameter disk (RDD), is commonly implemented. A discrete element method (DEM) based model is developed to investigate the effects of RDD and mill loading on media dynamics, force distribution, power draw, and collision energy. It is demonstrated that implementation of RDD results in a reduction of normal and shear stress on mill parts indicating a reduction in wear. Analysis of media dynamics shows that media mobility decreases hence decreasing total collision energy when RDDs are applied. This reduced mobility can potentially affect the grinding performance of the mill. A single-objective optimization approach based on collision energy data is employed to determine an optimal design configuration of the mill.

Керування газо-масопотоками в струминному обладнанні

Based on a numerical simulation of gas flows in an ejector unit and an analysis of grinding chamber acoustic signals, this paper shows ways to increase the efficiency of jet grinding. To prevent ejector speed-up tube wear and to obtain a ground product without impurities, the effect of feeding an additional energy carrier flow on the flow pattern in the speed-up tube of a jet mill was studied. A comparative analysis of the ejector flow pattern as a function of the presence of an additional feed and the speed-up tube shape was carried out. It was shown that the use of a conical nozzle offers a more uniform flow at the ejector outlet. The additional energy carrier feed provides a uniform increase in flow speed and reduces speed-up tube wall wear. The acoustic signals of the mill working zones were related to the jet grinding process parameters, around which a ground product quality control method was developed. The paper presents a technique for determining the material particle size in the energy carrier flow from the results of acoustic monitoring of the process. The technique uses the established relationship between the dispersion of the acoustic signal characteristic frequency and the mass of the corresponding fracture of the mixture in in-flow material transportation. The technique speeds up material particle size determination and improves the finished product quality. An automatic system was developed to control the grinding process by controlling the loading process according to the characteristics of the grinding zone acoustic signals. An operating model of a controlled hopper of a gas jet mill was made. The operability of the control system was verified on a simulation model, which includes a control objet (mill) model and a control system model. It was shown that the system of mill loading automatic control by the characteristics of the grinding zone acoustic signals offers an up to 10 percent increase in mill capacity, which was verified in industrial conditions at Vilnohorsk Mining and Metallurgical Plant.

Use of enameling wastewater in the wet milling process for ‘monoporosa’ tile composition

Water is becoming scarce for ceramic processing, even in certain regions of Brazil. In the wet milling process, the ceramic slips are formed by 30 wt% water to achieve the adequate density and viscosity for an efficient milling. Wastewater from other ceramic processes, as enameling, could be used for milling. The aim of this work was the study of the milling process of a ceramic tile composition using wastewater without treatment in place of clean water. The raw materials forming the ‘monoporosa’ composition and the wastewater were characterized (XRF, particle size) as well as the monoporosa composition (STD) (XRD, residue at #325 ASTM sieve, flow time viscosity, density). The milling parameters were mill rotation (15 or 19 rpm), mill loading capacity (70 or 100%) and type of water (wastewater or clean water) used as the factors (and levels) in a full factorial design, totaling 8 experiments (level factor = 2³). The tests were carried out in a mill of 148 L capacity, with a load of 87 kg of raw materials and addition of 34 L of wastewater (1.05 g/L) or clean water (1.0 g/L density). The density, viscosity, and residue at the 4, 6, 8 and 10th hour of milling were determined. As a result, the use of wastewater increases the density of the liquid medium and thus increases the milling residue, as evidenced in the 10th milling hour. At the end of the work, it was possible to reduce the total milling time in a 12,000 L industrial mill by 2 h (25%), without changing the characteristics of the slip, even using wastewater as liquid medium. • Wastewater from enameling was used in industrial milling process of ‘monoporosa’. • Mill rotation, loading capacity and wastewater were the main factors of the design. • The milling residue and slip viscosity were determined along milling time. • At the end of milling, the rotation was the most significant factor for milling. • A reduction of 25% of milling time (2 h) was possible even using wastewater.

Managing Risks in the Improved Model of Rolling Mill Loading: A Case Study

This article reflects the main sources of risks for metallurgical enterprises in Russia, presenting the implementation of an innovative approach to increasing the competitiveness of an industrial enterprise, which is a typical representative of large enterprises of the metallurgical industry, based on the development of risk-oriented thinking when loading rolling mills with orders of intersecting assortment according to a new model. To reduce the emerging risks of a new model of the loading process of rolling mills of a metallurgical enterprise, it is proposed to take into account the risks in a complex way, taking into account their interactions with the use of integrated risk management (IRM). Practical development of the implemented approach was carried out by identifying the risks of the new improved loading process and their causes at each stage of the process. Risks were identified by analysis, qualitative and quantitative assessment of the likelihood of risks and the severity of consequences from their implementation with the establishment of events with a high potential hazard. Possible causes of hazardous events have been identified. To reduce the likelihood of unfavorable events, measures have been developed to influence significant risks and their effectiveness has been determined. The development of an innovative approach using risk-based thinking in a previously unexplored field of the application provides competitive advantages for enterprises of the metallurgical industry, increases income by reducing the cost of manufacturing products and production volumes by reducing time costs, achieving an economic efficiency of up to 10 million rubles per year. The practical significance of the dissemination of development results in similar industries is obvious and relevant for metallurgy as a whole.

Simulation of the ball mill loading movement and study of its operation modes depending on geometrical parameters of the lining

The article analyzes virtual experiments of the lining of a ball-type drum mill depending on a number of factors: the diameter of a mill, the diameter of grinding bodies, the number and height of liner lifters. The numerical experiment was performed using the EDEM software; a parametric model of the mill housing with variable liner lifters was created and imported, studies were performed using the virtual simulation method. A virtual experiment made it possible to study the grinding process without interacting the equipment which eliminates the risk of injury during and allows for more accurate research data. As a result of simulation of virtual experiments, values of the average kinetic energy of grinding bodies and the number of their collisions were determined.

An аutomatic mode control of the jet mill loading

A thin jet grinding is quite an energy-consuming process. Its production depends on the fullness of the mill chamber with material. Therefore, it is extremely important to control the loading of the jets with material and to reload the necessary portion of material in time.Previous studies have shown the effectiveness of control the jet grinding process based on acoustic monitoring. The interrelation of technological, regime and acoustic parameters of the process has been established, an automated mill control system is being developed. For each required size of the ready product, its own grinding mode and classification and, accordingly, its range of acoustic signal characteristics are set to achieve maximum grinding productivity. This is the basis for controlling the jet mill operation according to the results of acoustic monitoring.The aim of the paper is to develop an automated control system for the loading bunker of the jet mill based on the analysis of the acoustic signals of the grinding zone.The study was conducted for different recording modes of acoustic monitoring signals and the grinding process of various bulk materials. To amplify the signal, an operational amplifier with a gain of 10 was used. To eliminate the measurement error, a sample of 100 values is taken. The used equipment has a limit time for the ADC polling for each program cycle. To estimate the error, an experimental study of signals was carried out. After processing all the data, the control signal is fed to the control unit of the solenoid, which is assembled on the basis of a field-effect transistor with an operating voltage of 60 V and a maximum current is up to 100 A. Then the control signal is transmitted to the opening or closing of the loading bunker gate.The numerical experiment improved the analyzing method of the acoustic signal of the grinding zone, reduced the error. A hardware base of the control system was created and a model of a controlled loading bunker was implemented. A mill loading control system has been developed through a controlled bunker based on the results of continuous acoustic monitoring of the grinding process.

Study of lifter wear and breakage rates for different lifter geometries in tumbling mill: Experimental and simulation analysis using population balance model

The lifter profile, mill speed and the amount of mill loading are the key elements influencing the load behavior, consequently the milling performance. In this paper, the effect of lifter face angle and height were studied for a lab scale ball mill. The effect of mill geometry on breakage rate and lifter wear rate was analyzed experimentally. A series of batch grinding tests were carried out using four different lifter (lifter I to IV) geometries and the rate of breakage was determined for each condition. Natural feed size of a top size 9.5 mm was ground in a Ø = 0.32 m test mill (Jb:40%, w/w: 68%, Nc: 55, 65, 75 and 85%). The torque was recorded against the wear measurement of each lifter. The results confirmed the phenomena that all the measured torque/power values decreased after a certain value of Nc, that is 75% in this study. Lifter IV produced the highest rate of breakage at Nc of 65–75% and the lowest wear. Based on the experiments, a simulation of an industrial mill (3.5-degree lifter face angle) was done using the estimated values. The results showed that, similar to the batch tests, Lifter IV (12 mm height, 22.5-degree face angle) may increase the breakage rate and fine particle generation. The overall value of SSE was calculated to observe the variability in milling experiments. The value obtained was 26.18, with an error 3.73%.

Amorphization of itraconazole by inorganic pharmaceutical excipients: comparison of excipients and processing methods

The aim of this study was to investigate the effects of solid carriers and processing routes on the properties of amorphous solid dispersions of itraconazole. Three solid carriers with a range of surface properties were studied, (1) a mesoporous silicate, magnesium aluminum silicate (Neusilin US2), (2) a nonporous silicate of corresponding composition (Veegum) and (3) a non-silicate, inorganic excipient, calcium phosphate dibasic anhydrous (A-TAB). The drug was incorporated via either solvent-deposition or ball milling. Both the maximum drug deposited by solvent-based method that produced an amorphous composite and the time for complete amorphization by co-milling was determined by X-ray powder diffraction (XRPD). Changes in the drug and excipients were monitored by nitrogen adsorption and wettability of the powder. The ability of the excipients to amorphize the drug and enhance its dissolution was related to the powder characteristics. Neusilin provided the fastest amorphization time in the mill and highest drug loading by solvent-deposition, compared with the other two excipients. Solvent-deposition provided greater dissolution enhancement than milling, due to the reduction in Neusilin porosity during high energy milling.This study confirms that substrates as well as the processing routes have notable influence on the drug deposition, amorphization, physical stability and drug in vitro release.

The Experimental Research on the Variable Loading System of LM18.20 Coal Mill

The paper research the loading methods of medium-speed coal mill and the variable loading system of LM18.20 coal mill. The experiment result has shown that using variable hydraulic loading system can make the coal mill running steadily with stable output under varies output conditions; and the mill's loading range is extended; the mill power consumption and wear rate of grinding parts are reduced.

The Experimental Research on the Variable Loading System of LM18.20 Coal Mill

The paper research the loading methods of medium-speed coal mill and the variable loading system of LM18.20 coal mill. The experiment result has shown that using variable hydraulic loading system can make the coal mill running steadily with stable output under varies output conditions; and the mill's loading range is extended; the mill power consumption and wear rate of grinding parts are reduced.

Research on the Improvement of MPS Coal Mill Loading Hydraulic System

Research on the Improvement of MPS Coal Mill Loading Hydraulic System

Research on the Improvement of MPS Coal Mill Loading Hydraulic System

This article introduces the design features of original loading mode of MPS coal mill and proposes that using technology of electro-hydraulic proportional to improve the loading mode. The original loading mode exists many defects. The improvement combines the hydraulic loading system with electronic technology so that the deficiencies of original system are solved and the automatic degree of coal mill loading mode is improved.

The Application of Electrohydraulic Proportional Technology in Mill Loading System

The paper designs electrohydraulic proportional loading system which meets the adaptive requirements of variable loading for the system by analyzing the structure and the theory of mill loading system. After being reformed, the adaptive control ability to the changes of coal’s quality and quantity is improved which guarantees the fineness of coal, strengthens remote control ability, increases the degree of automation, the efficiency and the production of the system and saves energy.

Effects of disc rotation speed and media loading on particle flow and grinding performance in a horizontal stirred mill

IsaMill™ is a high-speed stirred mill used in the mineral industry for a range of milling duties from ultra-fine to coarse grinding. In this work, numerical simulations based on the discrete element method (DEM) were performed to investigate the particle flow in a dry stirred mill with a similar configuration to that of an IsaMill™. The effects of operational variables such as mill loading and rotation speed on flow properties such as flow velocity, power draw, collision frequency, collision energy and total impact energy were analysed. The results showed that increasing mill loading or mill speed increases impact energy between particles. Moreover, physical experiments were conducted to quantify grinding performance under similar conditions. The experimental results showed that the grinding in the mill follows the first order kinetics, and the rate constant can be correlated to impact energy. The findings are useful to understand and optimise the particle flow and grinding behaviour of IsaMills™. The proposed methodology may also apply to other stirred mills.

Steady state inferential modeling of temperature and pressure in an air-swept coal pulverizing ball mill

Mill discharge temperature and differential pressure have a strong effect on efficiency and safety of a coal fired power plant. Therefore, it is imperative that they are closely monitored and controlled during mill operation to keep their levels within a predetermined safe and efficient operating range regardless of the rate at which the raw coal is fed to the mill. One way to achieve this is through a control schedule that compares the value obtained from the process to the stored set-point value to determine if there is any deviation that requires correction. This paper describes a steady state model that could be used alongside conventional controllers as an on-line shadow that provides inferential estimates of desired temperatures and pressure drops in the mill circuit which can be continuously compared with the actual values for adjustment. This would not only help to avoid the difficulties associated with direct measurement but also provide a means for early detection of drifts and failing sensors and serve as a temporal back-up for the out-of-order sensors. The model was tested using industrial data collected from four ball mills at a coal fired power plant in South Africa and the results show a reasonable agreement between the measured data and model predictions both qualitatively and quantitatively within a 5% error margin. The model outputs were found to be highly sensitive to the variation in mill loading, the primary air (PA) flow and the mill channel dimensions. Therefore, for validity of this model, accurate determination of all significant parameters is essential. For now, the model is only valid for the ball mills involved in the current study, but with availability of data it can be reproduced elsewhere.

Developments in the understanding of South African style SAG mills

The South African style SAG (RoM) mills operate in a window that is almost exclusive from the operation of the Australian and North American mills that have been used for the development of SAG mill models. Combining good quality test data from the RoM mills is extending and improving these models, and assisting in a practical manner in improving our understanding of SAG/AG milling.Data from high mill loads, both in absolute filling and ball loading, have been used to extend and improve the JK SAG mill model. This improved understanding has been successfully applied to increasing the throughput of a mill by 8%. Data is presented on relationships between power and load for high mill loading. Slurry pooling is common in closed-circuit RoM mills, and the detrimental effect of this has been dramatically demonstrated at ALCOA with a mill throughput increase of over 20%. Techniques for calculating the effects of slurry pooling have been developed and a new pulp lifter system designed to give optimal slurry discharge. The influence of mill speed in shifting the product size distribution has also been measured.

New ways of optimising grinding using simulation software and new measuring techniques

Today there is a strong interest in obtaining an accurate and direct measure¬ment of mill loading. The use of direct measurement methods removes much of the uncertainty associated with the heuristic inferential methods that are now commonly employed. The Continuous Charge Monitoring System (CCM) determines the toe and shoulder of the load in the mill, and indicates its volume and the angle of repose. For a long time there has been a desire to be able to compute the behavior of the ball charge movement in a tumbling mill. With the advent of computer codes like Milisoft® and similar DEM codes that are able to compute mass movements of large amounts (i.e. many thousands) of balls or rocks, the simulation of charge dynamics has started to emerge as a real possibility of achieving a better understanding of what is actually going on inside a tumbling mill.

New Automated System for Optimisation of Ore Grinding Process

As a result of the recent scientific and experimental studies new microprocessor devices have been developed of the ore grinding process control system. The brief description of the new method and a sensor for ball mill loading, the microprocessor control module the floating densimeter and the regulable ore and water feeders is given. The modem variant of the automated ore grinding control system build up with herewith described technical devices is shown in the paper. Besides the good economic results the system improves the overall labour organization.

Effect of mill operating parameters on mineral liberation

The primary objective of most comminution operations is liberation; however, mill performance is generally quantified in terms of particle size. Only recently has the use of image analysis equipment made it possible to quantify mill performance on the basis of liberation. In this investigation, a series of tests were carried out to study the effect of mill operating parameters on the liberation of sphalerite from a sphalerite/dolomite ore. The parameters studied included mill rotational speed, mill loading and ball size. The results of this work appear to indicate that sphalerite liberation is improved under conditions that promote impact breakage, while dolomite breakage is enhanced under attrition conditions.

On-Line Estimation of Maximum Power Draught in Semiautogenous Mills

In the operation of semiautogenous grinding mills a certain mill loading which produces maximum mill power draught, must not be exceeded because in such case a progressive degradation of the mill performance sets on. With the purpose of avoiding such event, in this paper a method is developed for estimating the maximum power draught of a semiautogenous grinding mill with respect to the volumetric contents of ore and water, in spite that these variables are not measured. The maximum power estimate is found by fitting linear dynamic models to input-output data measurements, first to estimate the derivative of power draught with respect to the feed flows, and then to estimate the maximum power draught. These models are periodically updated so that updated estimates are provided. The mill should then be operated in such a way that a safe margin is kept between mill power and the maximum power estimate. To this end the derivative estimate provides a useful additional reference. An important feature of the method is that it matches well with control strategies which aim at obtaining maximum mill power draught, although it may also be used in combination with stabilizing control systems. Tests of the method, provided by simulation, point to the possibility of good results if an industrial mill is tested.