Impact Load Cell Research Articles

Hard/stiff surface coatings for particle weakening, part I: Methodology

Size-reduction processes are essential for liberating valuable minerals yet energy-inefficient, which needs to be remedied by developing energy-efficient methods. This work is the first part of a wide study that (i) describes a surface coating method, namely, spray coating, and (ii) presents some preliminary results that hard or stiff surface coatings can be used to weaken softer ore particles. The hard surface coatings were achieved with a ceramic spray and two inorganic precipitates (CaCO3 and silica). The fracture energy and/or strength of spray-coated and uncoated particles was measured using the Short Impact Load Cell (SILC). Spray coating can only yield low surface coverage (up to 1–2% of the mass of particles), which is only apparent if particle surfaces are washed before coating. Nevertheless, the preliminary results suggest significant reductions in the fracture force and energy of soft ore particles after they are coated.

Analysis of force–deformation and force–time profiles of 3D-printed specimens of single and binary mineral composition tested with Short Impact Load Cell

In mineral processing, accurate characterisation of the mechanical properties of particles of various mineral composite, texture and scale is critical for the development of improved breakage modelling. Additionally, these models should emphasise the primary breakage properties of the particles on the models rather than breakage in test devices that introduce substantial secondary fragmentation events. This work explores the use of the Short Impact Load Cell (SILC) test to investigate the mechanical properties of fabricated 3D-printed (3DP) specimens of single and binary mineral composition, i.e., iron oxide, silica, and layered specimens with both minerals. The fabricated quasi-identical specimens are useful to explore the repeatability and contrast of controlled additively manufactured 3DP specimens and the SILC testing performance. The fracture characteristics of printed quasi-identical specimens were observed using an ultra-high-speed digital camera. The study showed that the specimen properties, such as tensile strength and fracture energy are strongly influenced by the number of beds, bed thickness, and mineral composition. The force–deformation as well as force–time profiles and specimen fragmentation are studied to understand better the variability of the results and the specimen’s physical response to a single impact. The contour of force–time profiles allows for interpretations of how the striker contacts the specimen and to infer the crack initiation and fracture propagation through beds of brittle or ductile material. The use of hierarchical clusters facilitates the analysis as they enhance contrasts and give more insight into breakage and fragmentation, which is worthwhile investigating for natural rocks in the future.

Characterising tensile strength and elastic moduli of altered igneous rocks at comminution scale using the Short Impact Load Cell

The primary breakage properties of rocks such a strength (σ) and elastic moduli (i.e. Young's modulus (E) and Poisson's ratio (ѵ)) are not usually characterised at comminution scale. Traditional comminution tests such as the Bond Work Index grinding test and the Drop Weight Test are used for describing the breakage behaviour of different ores. Nevertheless, these tests do not decouple the ore characteristics from the mode of breakage. The primary breakage properties control the initiation and propagation of fractures in rocks and exert control over the resultant progeny of breakage events when the rock is stressed. However, how these properties change as the particle size decreases in comminution is not clear yet. This work explores the change of primary breakage properties and the derived quantities estimated using the Short Impact Load Cell (SILC) (e.g. apparent stiffness and mass-specific fracture energy) within a particle size relevant to ball milling, using a suite of real ores.The results of this work show that the median values of strength in populations of cylindrical (minicore) particles do not vary with size within the range size studied (3–30 mm) for all the ore types studied. In contrast, the stiffness and the mass-specific fracture energy derived from the primary breakage properties data show a size dependency for all of the ore types in agreement with Weibull's weakest link theory. The degree of variation of the primary breakage properties has also been studied over a range of particle sizes. The results show that this degree of variation tends to increase for some of the rocks as the particle size decreases, but the variation is size-independent for other rock types. These results align with previous results in the literature that indicate the size independency of tensile strength in small samples but are contrary to earlier researchers' findings that suggest that the variance decreases with size. The ore dependent nature of the primary breakage properties found in this work requires further research. Understanding the behaviour of the primary breakage properties in a comminution context might help to characterise the comminution potential of ores better, as well as to develop characterisation and modelling techniques that are more responsive to the ore characteristics.

The Effect of Feed Characteristics on Particles Breakage and Weakening Behavior in High Pressure Grinding Rolls (HPGR)

ABSTRACT High Pressure Grinding Rolls (HPGR) is a high-energy efficiency device that has the ability to weaken the particle. This leads to lower energy consumption at subsequent grinding stages. Currently, no commonly used standard indices exist for predicting breakage, and weakening behavior of particles by HPGR. Accordingly, the current study mainly aimed at investigating the relationship between the common grindability/mechanical characteristics of rock (including work index, Brazilian tensile strength, elasticity module, and uniaxial compressive strength) and the breakage and weakening behaviors of HPGR products. For this purpose, six samples (pure calcite, pure magnetite, pure quartz, marmarite rock, travertine rock, and copper ore) with identical particle size distribution were comminuted by HPGR at three pressure force levels of 2.5, 4.5, and 7.5 MPa. Then, the breakage behavior of the samples was evaluated based on the size reduction ratio, followed by studying the weakening of particles by measuring changes in the fundamental breakage and deformation characteristics (mass-specific fracture energy and stiffness) by Impact Load Cell (ILC). The results revealed an excellent relationship between the breakage behavior of particles and their Brazilian tensile strength, as well as their weakening behavior and elasticity module. For particles with a higher module of elasticity (resistivity toward deformation), energy would be consumed for the formation of cracks and subsequently, particle weakening. In the case of particles with a lower module of elasticity, energy is probably dissipated as particle deformation, resulting in more cake formation and less weakening in particles.

Investigation of Particles Breakage and Weakening Behaviors in Multi-Component Feed Grinding by High Pressure Grinding Rolls (HPGR)

ABSTRACT One of the main merits of using High Pressure Grinding Rolls (HPGR) is particle weakening, which leads to less energy consumption at downstream grinding processes. Normally, HPGR feed contains various minerals with different weakening behaviors. Therefore, understanding the difference between particle weakening behavior in pure and multi-component feed grinding by HPGR is very important. In the current study, the difference of particle weakening behaviors in pure and mixture feed grinding by HPGR was investigated. To this purpose, the pure and different mixture ratios of magnetite (hard component) and calcite (soft component) minerals were comminuted by HPGR under three different pressures. After grinding, particles breakage behavior was investigated based on the relation of consumed energy and the particle size distribution of products. Particle weakening was studied through measuring changes in fundamental breakage and deformation parameters by Impact Load Cell (ILC). It was concluded that, at pressures resulting in breakage saturation state, the weakening of soft component in mixture feed grinding is more than grinding alone, but the changes in weakening of hard component in the mixture and pure feed grinding are insignificant. It was observed that the weakening of soft component particles in pure feed grinding are 15%, and by increasing hard component to 50 V%, their weakening increases by 19%. It resulted that the presence of hard components led to more energy consumption in soft component breakage and decreased energy dissipation toward particles deformation, leading to an increase of induced damage to soft component particles.

Back-calculation of particle fracture energies using data from rotary breakage testing devices

Breakage probabilities and fracture energy distributions have now found application in several mathematical models that simulate both degradation during handling and comminution devices. Unfortunately, measurement of these at the range of sizes of interest, in particular in the case of fine sizes, is not a straight-forward task. The paper proposes a procedure to estimate breakage probability distributions over a wide range of particle sizes by combining direct measurements of fracture energies at a selected size to back-calculated values estimated on the basis of progeny size distributions from breaking single particles over a wider range. Whereas direct measurements of fracture energies were carried out in a short impact load cell device, energy-dependent progeny size distributions were conducted by propelling particles against a target in rotary breakage testing devices. The work demonstrates how the parameters that characterize the variation of particle fracture energies with size can be fitted in a stage-by-stage process, with successful application to characterizing breakage of a copper ore contained in the range from 37.5 to 0.25 mm.

The impact load cell as a tool to link comminution properties to geomechanical properties of rocks

Current tests for characterising rock breakage in comminution do not allow decoupling of rock breakage properties from the machine environment. Furthermore, it is difficult to predict the comminution behaviour of different ores or how they might behave in another breakage device. Consequently, this decoupling process is essential for comminution modelling of variable ores and blends, which interact with different breakage equipment. Previous studies have shown that the Short Impact Load Cell (SILC) is a versatile tool for characterising the primary ore breakage properties such as strength, apparent stiffness and mass-specific fracture energy, regardless of breakage environment. However, its potential as an ore characterisation technique to relate these mechanical properties to the ore characteristics (e.g. mineralogy, texture) has not been investigated in detail. In this first paper, the results from breaking cylindrical and irregular particles from different ore types in the SILC and Slow Compression Testing demonstrate the SILC’s ability to accurately measure strength, stiffness and specific energy of different ore types at different particle sizes which is relevant either for comminution modelling or for rock mechanics testing. The results of breaking cylindrical particles of nine different rock types show that the SILC is capable of matching the results of the slow compression machine for Indirect Tensile Strength from the Brazilian Test and the apparent stiffness results from the Uniaxial Compression test, allowing the accurate calculation of the mass-specific fracture energy distribution for each rock at different sizes. In addition to the cylindrical samples, sets of irregular particles were produced for three rock types and were broken with the SILC. The results show that the median values of strength and stiffness do not change significantly with the shape of the particle, but the standard deviation does increase when irregular particles are tested. If these results are compared with the cylindrical particle results, it can be seen that the geological characteristics of the rock control the median values of the parameters. When the variation around median value is considered it is apparent that particle shape exerts the major control, but geological characteristics still contribute up to 30% of the variation in strength, 25% in stiffness and 25% in the mass-specific fracture energy. The results indicate that the SILC is a suitable device that allows measurement of the primary breakage properties relevant to comminution, which can be easily associated with the geomechanical properties of the rock mass and geological characteristics. The further development of the proposed testing methodology can provide a more comprehensive and less empirical comminution testing for future modelling, incorporating geological and geomechanical properties of the rock.

DIRECT MEASUREMENT OF REACTION FORCES DURING FAST DYNAMIC LOADING

The presented paper is focused on embedding of the serially manufactured piezo-electric impact loadcell into Open Hopkinson Pressure Bar (OHPB) and it’s modifications for a direct force measurement during dynamic loading. Conventionally, during the SHPB test dynamic force equilibrium is investigated by a comparison of the transmitted signal wave and the difference between the incident, reflected and transmitted signals measured by strain gauges [1]. However, in the experiments with specimens with low mechanical impedance, a major portion of the incident wave is reflected back on the interface between the bar and the specimen. Comparison between two-large amplitude incident and reflected pulse and a small-amplitude transmitted pulse can be influenced by large error and resulting force equilibrium can be inaccurate. Therefore, a piezo-electric quartz impact force transducer was used to directly measure the axial forces in the vicinity of the specimen end surfaces.

Testing Impact Load Cell Calculations of Material Fracture Toughness and Strength Using 3D-Printed Sandstone

Short impact load cell (SILC) tests provide insight on the dynamic breakage behaviour of rocks. The measured impact force to first fracture of a rock specimen is used to calculate properties such as fracture toughness, tensile strength, and stiffness. To explore the repeatability and performance of the SILC test and verify the underlying assumptions for interpreting the test measurements, a comprehensive SILC testing program was conducted using additively manufactured (3D-printed) sandstone. 3D-printed sandstone specimens with known mechanical properties were used to indirectly determine the mechanical properties of specimens from SILC test measurements with respect to different sizes (from 5 to 12 mm diameter), shapes (sphere, flattened sphere, ellipsoid, and cylinder) and fabric orientations (i.e. angle variation of microstructures relative to the impact or loading direction). Unconfined compressive strength tests were also conducted on twin sets of various sized cylinder-shaped specimens to verify the estimation of compressive strength from the SILC test. Confidence in interpretation of SILC testing results is obtained by excluding the intrinsic material variability. Ultrahigh-speed digital camera was used to observe the fracture mechanism and to verify the force–time profiles against specimen physical response. Well-defined shaped specimens instead of irregular single-particles showed clear peaks corresponding to the force to first fracture on the force–time profiles. The study found that the minimum energy required to fracture the specimen, therefore the specimen strength, was strongly influenced by the shape effect.

The use of short impact load cell to derive geomechanical properties of sub-bituminous coal and mudstone

This study estimates the geomechanical properties of coal of varied ply lithotypes and mudstone by using the experimental Short Impact Load Cell (SILC) test. SILC is an alternative laboratory test for measuring tensile strength, stiffness, and specific fracture energy (fracture toughness). Available coal data is rare for low rank sub-bituminous coals that are the target for coal seam gas stimulation and extraction in the Surat Basin, Australia. Tested specimens include mini-core and irregular particles. The results demonstrate geomechanical properties can be derived and used in the reservoir numerical modelling investigation.

Static and dynamic compressive loading of fired iron ore pellets

Slow compression tests are routinely used both in quality control of fired iron ore pellets during production and in negotiating commercial contracts. In spite of their widespread use, such tests represent stressing conditions consistent with those experienced by pellets during transportation in ships, wagons and conveyor belts, as well as when they are stored in silos and hoppers. However, operations that are most likely to damage pellets occur during transfers in chutes, screening, ship and wagon loading, stockpiling and reclaiming, where they are subjected to rapid loading. The present work compares the mechanical behavior of individual pellets subjected to slow compression and rapid loading, this later in an impact load cell device. Besides pellet strength, fracture energy and also stiffness of the pellets are analyzed, demonstrating that pellets present significantly higher stiffness when subjected to impact, with only marginally higher pellet strengths and no clear trend regarding fracture energy. These strain rates differences are then discussed and their potential effect on deformation behavior and wave propagation in the pellets are analyzed.

Comparison of impact energy absorbance by various combinations of hip protector and flooring material

Background: Understanding the nature of blunt force trauma and the energies involved is key to their effective attenuation. This study compares and analyzes the energy absorbance of various combinations of hip protectors and flooring materials to identify fracture prevention design variables. Methods: Testing was performed using a dynamic impact rig instrumented with linear encoders and a piezoelectric impact load cell, which allows for high rate of force and displacement measurements to be achieved during impact. Results show the effects of deceleration rate on peak load and measurably define the impact patterns for a range of protective materials, with compliant flooring and hip protectors reducing impact forces below the suggested fracture threshold (3742N). Results: The force reduction provided by a hip protector depends on the type of flooring and is greatest for falls onto carpet with a foam underlay. A combination of soft-shell protector with carpet and underlay showed the highest force attenuation (68%). Conclusions: The study showed that the effective selection and implementation of hip protectors in homes and care facilities must include the consideration of flooring type. The identification of peak deceleration rates also will inform the future development of multi-material protective aids.

Quantifying of impact breakage of cylindrical rock particles on an impact load cell

The detailed understanding of rock impact breakage represents a key challenge in the development of comminution models. Semi-empirical properties have been used to describe ore competencies, such as the JK breakage index t10 and Axb values, but are not able to estimate mechanical properties linked with particle fracture. The information derived from particle breakage testing on impact load cells devices, have the potential estimates such mechanical properties. However, the large intrinsic natural variability of rocks and ores composition and shape makes the results difficult to analyze and difficult to compare against each other for particles with similar properties. This study investigates the effect of rock shape on the variability of the impact breakage test conducted on impact load cells. The test methodology was modified to account for shape when testing regular shape samples such as drilled mini-cores, with objective of reducing the intrinsic variability caused by rock shape, using a controlled shaped sample. The promising results open new avenues for establishing relationships between rock composition, texture and mechanical properties.

A phenomenological model of single particle breakage as a multi-stage process

Understanding ore breakage is the key for the development of appropriate breakage characterisation experiments. Hence, there has been significant effort to understand a single breakage event, both from the experimental and the modelling standpoints. One particularly interesting approach is to consider breakage of a particle, for instance in a drop weight tester, as a sequence of primary and secondary breakage components. Secondary breakage is defined as subsequent breakage of progeny that takes place after the primary fracture of the parent particle due to surplus energy that is provided by the comminution or breakage testing device. This influences the spatial distribution of fragments as well as their selection. Due to the complex nature of secondary breakage, most of the researches in the past have either been dedicated to understanding primary fracture as a basic element of every comminution process or to describe the breakage process as a whole. However, the progression of breakage may be modelled properly by incorporating the sequential breakage of fragments into a breakage process model. In the paper, a novel approach is proposed to describe a single breakage event by modelling it as a process through several stages of primary fracture while appreciating the effect of sequential fragmentation. The model has three main components: the primary breakage, the selection, and the classification functions. The data that served as the basis for demonstrating this model were a number of impact experiments in an impact load cell on quartz and apatite particles. The results indicate a good correspondence between experiments and model fit. Additionally, a sensitivity analysis to changes in selection and classification functions was performed, which indicated a strong dependency of a breakage event on its sub-processes. It is envisaged that this approach will allow decoupling the contributions of the ore and of the stressing conditions on the outcome of the breakage event.

OS1705 発泡構造体用衝撃荷重測定装置の荷重振動現象の実験および解析的検討

OS1705 発泡構造体用衝撃荷重測定装置の荷重振動現象の実験および解析的検討

Contact parameter estimation for DEM simulation of iron ore pellet handling

The appropriate choice of contact parameters is of great importance, particularly when simulations using the discrete element method (DEM) are run with the aim of capturing quantitative information on collision events that occur among the individual particles, as what happens during handling of iron ore pellets. The paper analyzes the use of tests conducted with single pellets for estimating material and contact parameters that are required in DEM simulations using the no-slip Hertz–Mindlin model. Tests included impact load cell, tribometer, drop tests and a simple test in which the rolling angle of individual pellets is measured. It is concluded that, provided particle shapes are described appropriately, DEM simulations provide reasonably realistic predictions of pellet motion in assemblies from contact parameters measured on the basis of single-particle tests. In this case the physical significance of the contact parameters is maintained. However, if pellets are described in a simplistic way as spheres, then the DEM simulation of their flow no longer matches the experimental results, requiring fitting some of the contact parameters in order to match the observed global flow, so that much of the physical meaning of the parameters is lost.

607 微小検知部を有する衝撃荷重測定装置の最適設計

607 微小検知部を有する衝撃荷重測定装置の最適設計

Modeling ore degradation during handling using continuum damage mechanics

Degradation of steelmaking materials during handling causes a significant economic impact, given the higher prices achieved by lump ore in comparison to finer products. It is relevant to model the amenability of ores to degradation, since it may be used to simulate the response of ores to different sequences of handling and transportation events from mine to port. The paper presents a mechanistic model to describe degradation caused by transfers and drops of particulate materials. The model is based on damage mechanics and the distribution of fracture energies of the original particles, using data collected in impact load cell and tumbling tests. This model, which is capable of predicting the proportion of particles broken and the entire size distribution resulting from any sequence of drops, has been validated at a preliminary level using data from drop tests of a Brazilian iron ore.

2008 微小検知部を有する衝撃荷重測定装置の振動抑制(OS20-2.衝撃・崩壊問題(2),OS・一般セッション講演)

2008 微小検知部を有する衝撃荷重測定装置の振動抑制(OS20-2.衝撃・崩壊問題(2),OS・一般セッション講演)

Modeling ore degradation during handling using continuum damage mechanics

Degradation of steelmaking materials during handling causes a significant economic impact, given the higher prices achieved by lump ore in comparison to finer products. It is relevant to model the amenability of ores to degradation, since it may be used to simulate the response of ores to different sequences of handling and transportation events from mine to port. The paper presents a mechanistic model to describe degradation caused by transfers and drops of particulate materials. The model is based on damage mechanics and the distribution of fracture energies of the original particles, using data collected in impact load cell and tumbling tests. This model, which is capable of predicting the proportion of particles broken and the entire size distribution resulting from any sequence of drops, has been validated at a preliminary level using data from drop tests of a Brazilian iron ore.