Towards a virtual comminution machine

Towards the end of the 1990s readily available personal computers became sufficiently powerful - when combined with an efficient numerical code - to use discrete element modelling (DEM) in two dimensions for models involving a few hundred to a few thousand particles in commercially available packages. Some proprietary codes reported up to 200,000 particles [Herbst, J.A., Nordell, L., 2001. Optimization of the design of sag mill internals using high fidelity simulation. In: Vancouver, B.C., Barratt, D.J., Allan, M.J., Mular, A.L. (Eds.), Proceedings of the SAG Conference, University of British Columbia, IV, 150-164; Cleary, P.W., 2001a. Charge behaviour and power consumption in ball mills: Sensitivity to mill operating conditions, liner geometry and charge composition. Int. J. Min. Process. 63, 79-114 and Cleary, P.W., 2001b. Recent advances in DEM modelling of tumbling mills. Minerals Eng. 14, 1295-1319]. In early 2000, JKMRC and CSIRO-MIS agreed to an informal collaboration with the objective of testing various DEM approaches against detailed process measurements. The initial collaboration demonstrated that 3D-DEM using spheres was sufficiently realistic for flow patterns and power estimation within tumbling mills. The results were reported in papers which were presented at SAG 2001 and in the technical literature [Morrison, R.D., Cleary, P.W., Valery, W., 2001. Comparing power and performance trends from DEM and JK modelling. SAG 2001, Department of Mining and Minerals Process Engineering. University of British Columbia, Vancouver, 284-300; Cleary, P.W., Morrison, R., Morrell, S., 2003. Comparison of DEM and experiment for a scale model SAG mill. Int. J. Min. Process. 68, 129-165]. The commencement of the CRC for Sustainable Resource Processing in 2003 provided an opportunity to formalize the collaboration and bring increased resources to bear. The objective of this collaboration is to develop a virtual comminution machine (VCM). The VCM will allow a comminution machine design which exists as a suitably detailed design in a 3D Computer aided design file (CAD) to simulate processing an ore (which has been characterised by suitable test work) to predict progeny, power consumption, wear and even machine component loadings. This paper reports on the substantial progress made to date towards a practical Virtual Comminution Machine

DESIGN AND OPERATIONS CHALLENGES OF A SINGLE TOGGLE JAW CRUSHER: A REVIEW

A review on the design and operations challenges of a single toggle jaw crusher is presented. Strength and fracture toughness of the material to be crushed are intrinsic properties that determine the time and energy required to crush the material. Economy of the crushing process is partly dependent on the angle of nip. Productivity of the crusher can be improved upon by increasing the eccentricity of the eccentric shaft, use of reversible jaws, bush bearing and easily adjustable toggle plate. Vibrations and fatigue cracks in the crusher frame will be nipped in the bud through structural analysis at design stage. Determination of the optimal angle of inclination of the toggle plate, development of jaws with varying wear rate along the crushing chamber, and development of comminution energy models that take into cognizance relevant crushing parameters for simulation and optimization of the crushing process are some areas that require close attention.  http://dx.doi.org/10.4314/njt.v36i3.2

Particle motion and energy dissipation spectra in a planetary ball mill

The charge motion and energy dissipation in a planetary ball mill are investigated using the Discrete Element Method (DEM). In addition to simulations of the grinding media (balls) only, different fill levels of the ground material (fine particles) are considered to examine its effect on the mill charge dynamics. The energy dissipation spectra determined from the DEM simulations provide insights into the comminution processes that occur in the planetary mill, and how they are influenced by the fill level and size distribution of the fine particles

Optimization Capabilities for Crushing Plants

Responsible production and minimal consumption of resources are becoming competitive factors in the industry. The aggregates and minerals processing industries consist of multiple heavy mechanized industrial processes handling large volumes of materials and are energy-intensive. One such process is a crushing plant operation consisting of rock size reduction (comminution) and particle size separation (classification) processes. The objective of the crushing plant operation for the aggregates industry is to supply specific size fractions of rock material for infrastructure development, while the objective in minerals processing is to maximize material ore throughput below a target size fraction for the subsequent process. The operation of a crushing plant is complex and suffers variabilities during the process operation, resulting in a drive for optimization functionality development. Process knowledge and understanding are needed to make proactive decisions to enable operations to maintain and elevate performance levels. To examine the complex relationships and interdependencies of the physical processes of crushing plants, a simulation platform can be used at the design stage. Process simulation for crushing plants can be classified as either steady-state simulation or dynamic simulation. The steady-state simulation models are based on instantaneous mass balancing while the dynamic simulation models can capture the process change over time due to non-ideal operating conditions. Both simulation types can replicate the process performance at different fidelities for industrial applications but are limited in application for everyday operation. Most companies operating crushing plants are equipped with digital data-collection systems capturing continuous production data such as mass flow and power draw. The use of the production data for the daily decision-making process is still not utilized to its full potential. There are opportunities to integrate optimization functions with the simulation platform and digital data platforms to create decision-making functionality for everyday operation in a crushing plant. This thesis presents a multi-layered modular framework for the development of the optimization capabilities in a crushing plant aimed at achieving process optimization and process improvements. The optimization capabilities for crushing plants comprise a system solution with the two-fold application of 1) Utilizing the simulation platform for identification and exploration of operational settings based on the stakeholder’s need to generate knowledge about the process operation, 2) Assuring the reliability of the equipment model and production data to create validated process simulations that can be utilized for process optimization and performance improvements.During the iterative development work, multiple optimization methods such as multi-objective optimization (MOO) and multi-disciplinary optimization (MDO) are applied for process optimization. An adaptation of the ISO 22400 standard for the aggregates production process is performed and applied in dynamic simulations of crushing plants. A detailed optimization method for calibration and validation of process simulation and production data, especially for mass flow data, is presented. Standard optimization problem formulations for each of the applications are demonstrated, which is essential for the replicability of the application. The proposed framework poses a challenge in the future development of a large-scale integrated digital solution for realizing the potential of production data, simulation, and optimization. In conclusion, optimization capabilities are essential for the modernization of the decision-making process in crushing plant operations

Modeling of Vertical Shaft Impact Crushers

One of the largest products in most civilized societies is concrete used to build various types of constructions. To create this product, a mixture of cement, chemical binders, and rock aggregates are combined and then poured into molds where it hardens. The sand part of the rock aggregates is either from natural sources or manufactured. Vertical shaft impact crushers can be used to create this machine sand but existing models make it hard to plan new sites and achieve a viable replacement to the natural sand.In this thesis, the use of vertical shaft impact crushers to crush aggregate rock to rounder particles is investigated. The main aim of this is to develop and further the understanding of the relationship between the machine and material properties with respect to the resulting crushed product in an effort to achieve an improved product. In order to gain a better understanding of the underlying mechanics of particle breakage, Discrete Element Method has been used to obtain particle collision energies. Several different product size distribution models have also been used to better predict the behavior of different crushers and feed sizes. To facilitate this, a framework to improve sites has been developed.The resulting framework simulates existing VSI machines and optimizes the machine parameters with respect to the specified feed material and PSD to create sought products. The framework can also be used to optimize existing sites which increases the effectiveness in terms of minimizing energy usage and waste products

Double wheel crusher prototype

Abstract. This thesis presents a proof of concept for a new testing device. The prototype device was commissioned as a part of a project to develop a fast, low-cost, and reliable breakage characterization test for geo-metallurgical modelling. One of the key processes involved in minerals extraction is comminution: mineral ores are broken down with crushing and grinding machinery. Comminution testing can be used for the purposes of optimizing these processes. Various testing methods used in the industry subject rock particles to varying levels of crushing impact to measure the amount of fine materials liberated relative to the input energy. The role of mechatronic engineering in this context is to design and develop intelligent machines that ease the work of the researchers and technicians performing these tests. The structure of the new device was proposed as a variation of an instrumented roll crusher with an adjustable gap. The trial operation of the prototype was done using rocks from different mine sites around Finland. The test set resulted in data with a clearly identifiable correspondence of energy to the amount of breakage, proving the plausibility of the device. Some issues were found with the accuracy of energy measurements. The programming error behind the fault was corrected and the improved device was found to produce a standard deviation of measurement of 1.07 Joules. Means to further improve the accuracy of the energy and force measurements are discussed, with recommendations and suggestions for other improvements to the device in the future.Kaksoispyörämurskaimen prototyyppi. Tiivistelmä. Tässä työssä koetetaan uuden mittauslaiteen konseptia. Prototyyppilaite tilattiin osana projektia, jonka tarkoituksena on kehittää uusi nopea, varma, ja edullinen menetelmä mineraalien hienontumisen testaamiseen geometallurgisen mallinnuksen tarpeisiin. Eräs mineraalien louhinnan ja jalostamisen keskeisistä prosesseista on malmin hienontaminen murskaus- ja jauhatuskoneilla. Hienonnustestausta voidaan hyödyntää näiden prosessien optimointiin. Kaivosteollisuudessa käytetyissä testausmenetelmissä kivipartikkeleihin kohdistetaan erisuuruisia iskuvoimia, joiden hienonnusvaikutusta mitataan suhteessa syötetyn energian määrään. Mekatronisen suunnittelun tehtävä tässä yhteydessä on kehittää älykkäitä laitteita helpottamaan näitä kokeita suorittavien tutkijoiden ja teknikkojen työtä. Uuden laitteen rakenne mukailee telamurskaimen toimintaperiaatetta. Prototyyppiä testattiin murskaamalla eri puolelta Suomea tuotuja kivinäytteitä. Testin tuloksista on selvästi tunnistettavissa käytetyn energian vaikutus murtumismäärään. Testien aikana havaittiin ongelmia energiamittauksen tarkkuudessa. Vian aiheuttanut ohjelmointivirhe korjattiin ja parannellun laitteiston mittaustuloksen hajonnaksi todettiin 1,07 Joulea. Työn lopussa esitetään ehdotuksia energian ja voiman mittaustarkkuuden parantamiseksi, sekä muita mahdollisia parannuksia laitteen jatkokehitystä varten

A study of impact breakage of single rock specimen using discrete element method

Comminution is a critical stage of mineral processing which aims to reduce the size of ore particles through breakage, consequently increasing the likelihood of the liberation of valuable minerals. However, comminution is highly energy-intensive and an understanding of the key breakage mechanisms has been identified as an important factor in improving the efficiency of the process. Several factors, such as pre-existing cracks, mineralogical composition, ore shape and size are known to affect ore breakage behaviour during breakage. To investigate breakage mechanisms, it is important to be able to determine how individual factor influences the breakage behaviour of rock specimens. However, isolating and investigating individual factors under experimental conditions is challenging and typically impractical. Numerical techniques such as the Bonded Particle Model-Discrete Element Method (BPMDEM) have been developed as a means of investigating in isolation, the effects of different factors on ore breakage behaviour under closely controlled breakage conditions using synthetic rock specimens. This study investigates how individual factors influence rock specimen breakage using BPM-DEM numerical methods. Numerical simulations were conducted using ESyS-particle 2.3.5, an open-source discrete element method (DEM) software package which uses Python-based libraries to generate geometries and simulations and a C++ engine for mathematical computations. Empirical calibration relationships were developed to relate microstructural model parameters to the macroscopic mechanical properties that are typically obtained from standard geotechnical breakage experiments. The robustness of the model was evaluated by considering the sensitivity of fracture measures to the variation of model resolution, size-dependency and macroscopic mechanical properties (Young's modulus and uniaxial compressive strength) of the numerical specimens. A comparative study of single rock specimen breakage using the current BPM-DEM and laboratory SILC experiments carried out by Barbosa et al. (2019) was conducted. The measured fracture force and fracture patterns at different sizes for both cylindrical and spherical synthetic rock specimens were examined. Furthermore, the model was used to study, in isolation, the influence of pre-existing cracks in rock specimens and differing mineralogical compositions upon measurable breakage properties. Numerical rock specimens with pre-existing cracks were constructed using a microcrack approach, while a unique approach with the insertion of "seed points" was developed and demonstrated to construct numerical rock specimens with varying mineralogical compositions. Results from the numerical simulations showed that a high model resolution with a sufficiently large number of DEM-spheres exhibited results with the least deviation and error with respect to fracture measures, and, was therefore considered numerically stable. The dependency of fracture measurements on specimen size showed an expected increase in the measured fracture force as the specimen size increases. The variation of the macroscopic Young's modulus and uniaxial compressive strength against the fracture measures emphasised that the locus of these mechanical properties against the fracture measure can be used to specify a calibration relationship. Results of the comparative study showed that for both cylindrical and spherical rock specimens, the DEM consistently predicted the fragment patterns as well as the increase in the measured fracture force as the specimen size increased. The investigation on the effect of pre-existing cracks revealed that an increasing number of pre-existing cracks in rock specimens necessitated lower fracture force and consequently produced a low amount of new fracture surface area. For the binary phase mineralogical composition in the study, it was found that the fracture force decreased with an increase in the concentration of the softer component due to the increased percentage of weakness in the specimen. It was concluded that, with an appropriate calibration exercise and a realistic specification of material properties from the evaluation study, the DEM as a tool was sufficient to act as a "virtual laboratory" to isolate and study the individual effects of factors that influence ore breakage. The understanding of these results highlighted two important points. Firstly, this study was able to unravel some of the possible causes of the inefficiency in comminution practices, whereby significant amounts of energy can be expended to achieve minimal gains in respect of enhancing liberation due to pre-weakening and mineralogical composition. Secondly, it emphasised some of the causes of the variation observed during ore characterisation on a laboratory breakage device, attributable to pre-weakening and mineralogical composition

Comminution in the Minerals Industry

Size reduction processes represent a significant part of the capital as well as the operating cost in ore processing. Advancing the understanding of and improving such processes is worthwhile since any measurable enhancement may lead to benefits, which may materialize as reductions in energy consumption or wear or improved performance in downstream processes. This book contains contributions dealing with various aspects of comminution, including those intended to improve our current level of understanding and quantification of particle breakage and ore characterization techniques that are relevant to size reduction, as well as studies involving modeling and simulation techniques. The affiliations of the authors of the articles published in this book span 14 countries around the globe, which attests to the highly international nature of research in this field. The themes of the manuscripts also vary widely, from several that are more focused on experimental studies to those that deal, in greater detail, with the development and application of modeling and simulation techniques in comminution. Size reduction technologies more directly addressed in the manuscripts include jaw crushing, vertical shaft impact crushing, SAG milling, stirred milling, planetary milling, and vertical roller milling. Ores involved directly in the investigations include those of copper, lead–zinc, gold, and iron as well as coal, talc, and quartz