Body Breakage Research Articles

Effects of different breakage mechanisms on the physical, water sorption, and mechanical characteristics of infant milk formula

Two main breakage mechanisms, surface breakage and body breakage, were both found during laboratory dilute-phase pneumatic conveying and high-speed mixing of infant milk formula, respectively. Body breakage had a greater influence on powder physical properties, particle shapes, and surface compositions than surface breakage. In particular, the particle size of samples decreased by only 10% after surface breakage but by 60% after body breakage. For samples where body breakage predominated, significant changes to both water sorption and mechanical properties of the powder were seen while surface breakage had very little effect on them. Body breakage significantly increased the water sorption rate of samples, at around 10%–126% higher than the other samples for the first 3 h, which accelerated the time-dependent crystallization. Moreover, at a W 0.11 to 0.33, the final water contents of body breakage samples were 3.5%–22% higher than control samples. This decreased the crystallization temperature, by between 2 °C and 10 °C, and the overall molecular mobility of samples. These changes were due to the increase in the number of adsorbed monolayers, sorption surface area, and monolayer value of samples after body breakage. • Surface breakage affected physical properties but not water sorption behavior. • Body breakage greatly deteriorated physical and surface properties. • Body breakage increased water sorption rates, monolayer values and water contents. • Body breakage decreased the instant crystallization and overall molecular mobility. • Body breakage slightly decreased glass transition and α-relaxation temperatures.

Theoretical consideration of fatigue strengthening of conical picks for rock cutting

Rock mining is a key process associated with the drilling of tunnels and underground mine roadways and the extraction of useful minerals in mines. Under suitable conditions (rock workability), it is performed through cutting using conical picks. This technique is used not only in tunneling or mining but also in civil engineering—for example, in the construction of underground architectural objects using trenchless, approaches, or in road construction—for example, to renovate asphalt and concrete road surfaces, squares, or runways at airports. Picks experience wear and tear during the cutting process, or even destruction, which can decrease mining efficiency. Thus, it is necessary to replace picks on the working units of mining machines. Body breakage is one of the most severe forms of pick damage. This effect can be ad hoc, or more often fatigue. Fatigue cracking occurs suddenly in the pick bodies, without any clear preceding signs to allow corrective actions to be taken. Such loss of picks significantly affects the mining process, resulting in dynamic overloads of the mining machine, increased vibrations accompanying its operation, high energy consumption during the mining process, and increased exposure to dust. Damage resulting from the loss of picks due to various causes, such as breakage, is usually costly to repair, as it necessitates the replacement of important elements of the cutting system (e.g. cutting heads), which leads to unplanned downtime and expenditure. This article addresses the issue of eliminating such undesirable defects of cutting picks. The mechanism underlying fatigue destruction of conical pick bodies during their operation is described. The paper also defines pick fatigue life and highlights the factors influencing this parameter. Furthermore, this work aimed to propose a new design and technological solution for the conical picks equipped with a compressed reinforcing sleeve. The design requirements for this type of picks were determined with the goal of ensuring efficient strengthening action of the reinforcing sleeve, which in turn can significantly increase the fatigue life of conical picks.

Modeling breakage by impact of fragments of fired iron ore pellets

As soon as fired iron ore pellets suffer their first breakage event, fragments are created. During handling from the pelletizing plant to the steelmaker furnace, several stages of handling occur, so that if a well-formed and nearly spherical pellet breaks early in the handling chain, its fragments may also end up undergoing breakage. This is particularly important if one wishes to predict breakage during all handling stages. Unfortunately, no study in the past analyzed breakage of fragments of fired iron ore pellets, which will likely differ in comparison to the nearly spherical pellets owing to the irregular shapes of fragments. This work investigates breakage of fragments of iron ore pellets by impact using a pneumatic gun device, investigating the effect of fragment history and impact velocity on the breakage probability, the generation of fines by surface breakage as well as the fragment size distribution from body breakage. Results show that fragments are more amenable to surface breakage than well-formed pellets and also that their strength increases as fragment sizes reduce.

Study on attrition of spherical-shaped Mo/HZSM-5 catalyst for methane dehydro-aromatization in a gas–solid fluidized bed

As a potential methane efficient conversion process, non-oxidative aromatization of methane in fluidized bed requires a catalyst with good attrition resistance, especially in the states of high temperature, long-time rapid movement and chemical reaction. Existing evaluation methods for attrition resistance, such as ASTM D5757 and Jet Cup test, are targeted for fresh catalysts at ambient temperature, which cannot well reflect the real process. In this study, spherical-shaped Mo/HZSM-5 catalyst prepared by dipping and spray drying was placed in a self-made apparatus for attrition testing, in which the catalyst attrition under different system temperatures, running time and process factors was investigated with percent mass loss (PML), particle size-mass distribution (PSMD) and scanning electron microscope (SEM). Carbon deposition on the catalyst before and after activation, aromatization and regeneration was analyzed by thermogravimetry (TG), and the attrited catalysts were evaluated for methane dehydro-aromatization (MDA). The results show that the surface abrasion and body breakage of catalyst particles occur continuously, with the increase of system temperature and running time, and make the PML rise gradually. The process factors of activation, aromatization and regeneration can cause the catalyst attrition and carbon deposits, which broaden the PSMD in varying degrees, and the carbon-substances on catalysts greatly improve their attrition resistance at high temperature. Catalyst attrition has a certain influence on its catalytic performance, and the main reasons point to particle breakage and fine powder escape.

Modeling of degradation by impact of individual iron ore pellets

Mechanical degradation of iron ore pellets can have important economic and environmental implications. The work initially describes a pneumatic gun device that has been developed for characterizing breakage of pellets, by impacting them one-by-one against a target at controlled velocities, angles and against different types of surfaces. It shows that body breakage probability was only a function of the normal component of the impact and that pellets presented higher resistance and lower variability when subjected to impact than to slow compression. Mass loss due to surface breakage was well described using a model that accounts for the energy dissipated in the impact, including both normal and shear components. Parameters capturing their amenability to break either catastrophically or only undergoing surface breakage were estimated from data and the model has been validated on the basis of data from different sequences of impacts, also being used to predict the phenomenon of stabilization.

Adapting a breakage model to discrete elements using polyhedral particles

Several approaches have been proposed in the past to describe particle breakage inside the DEM environment. The large number of particles dealt with in most operations of interest and the associated computing power demanded, however, requires computationally-efficient approaches to describe breakage that do not sacrifice accuracy in describing the details of the physical phenomenon. The present work describes a detailed empirical-phenomenological model that characterizes all relevant aspects of body breakage that has been implemented in a commercial DEM package (Rocky DEM) using a particle replacement scheme. It describes the size-dependent breakage probability distribution, the weakening by repeated stressing events and the energy-dependent fragment size distribution. The model has been initially verified from a comparison of the analytical model, previously fitted to data, to simulations of single-particle breakage. The simulation model is then validated by comparing its results to drop ball test experiments on unconfined particle beds, demonstrating very good agreement.

Effect of particle shape on structure of the charge and nature of energy utilisation in a SAG mill

Particle shape affects the resistance to shear of a granular material and its flow characteristics. Rocks in a Semi-Autogenous Grinding (SAG) mill range in shape from quite rounded to quite angular depending on how long they have been in the mill and whether they have undergone body breakage recently due to collisions within the mill. However, almost all Discrete Element Method (DEM) modelling of SAG mills, particularly at industrial scale, has used spherical representations for the rocks. Here we explore the consequences for including a realistic range of particle shapes for the rock particles on the charge structure, power draw and energy utilization over a representative range of operating conditions.

Incremental damage and particle size reduction in a pilot SAG mill: DEM breakage method extension and validation

Applying DEM to prediction of tumbling mill performance is challenging because several different modes of breakage are active in the process. Here we use measured data from a well characterised ore in a well instrumented, 1.2 m diameter pilot scale mill to validate direct DEM prediction of particle size reduction. The key comminution mechanisms involved for a SAG mill are: (1) incremental breakage where parent particles break into progeny based on the cumulative energy absorption above the elastic damage threshold, (2) abrasion, and (3) chipping/rounding due to preferential contact and breakage of corners and edges of non-round particles. In this paper, a method for including incremental damage breakage in DEM is presented. The inclusion of all the size reduction mechanisms in the same DEM framework allows direct prediction of the evolution of the resident rock particle size and shape distributions and the product throughput rate. The surface mass loss mechanisms are shown to be critical for reducing the particle size to the point where the accumulation of incremental damage becomes significant leading to body breakage of these damaged particles. The energy split between ball and rock is also important for exceeding the elastic threshold and creating damage. Comparison of the predicted particle sizes at the completion of ten minutes of grinding operation with the measured experimental values from the pilot mill provides quantitative validation of the breakage predictions of this DEM breakage model.

Comminution mechanisms, particle shape evolution and collision energy partitioning in tumbling mills

A computational model for use with DEM (Discrete Element Method) is proposed for the five mechanisms applying to particle comminution in AG, SAG and coarse feed ball mills. Chipping and rounding are mechanisms that lead to preferential mass loss from corners and edges of particles and which produce shape change for the particles as well as size reduction. These are controlled by the energy dissipation at a contact and the location of the contact on the surfaces of the particles. These mechanisms lead to rounding or conditioning of angular feed particles. Single impact body breakage is a very weak contributor to overall size reduction with most body breakage occurring via damage accumulation over many contacts. This incremental damage mechanism is inherently less inefficient but leads to size reduction from the many weak collisions experienced by particles within the mill. Finally, size reduction from abrasion is well represented by the shear energy absorption of the particles. Particle size and shape evolution due to chipping, rounding and attrition is demonstrated using a well characterised pilot mill for which detailed particle mass data is available. The relative contributions of the five mechanisms and a quantification of the wasted energy for both AG and SAG charges and for new and substantially comminuted material are reported. Changes in the energy spectra with the decreasing particle sizes over time are described with increases in the fraction of collisions above the elastic energy threshold leading to faster damage accumulation and reduced energy wastage. Finally, it is shown that the attribution of dissipated energy between particles in a collision is material dependent with significantly more energy absorbed by rock particles than balls. This needs to be accounted for in DEM models, particularly when attempting to explicitly predict particle size reduction.

Ore particle breakage behaviour in a pilot scale high voltage pulse machine

SELFRAG AG has developed a flexible pilot scale Pre-Weakening Testing Station (PWTS) using high voltage pulses (HVP). This provides a unique opportunity to investigate the machine setting conditions on ore breakage behaviour. A joint campaign was undertaken by the Julius Kruttschnitt Mineral Research Centre and SELFRAG AG to investigate the breakage behaviour of two copper–gold ores and one iron ore in the PWTS. The effects of specific energy, pulse voltage, cumulative discharges, feed particle size and ore particle breakage pattern (body breakage or surface breakage) were investigated. The investigation revealed that the mass-specific energy of HVP was the most significant factor affecting the breakage behaviour in the PWTS. This effect was compounded with the effects of ore properties and particle size. Comparison between the PWTS and a laboratory HVP machine indicates that there is considerable scope for optimisation of HVP performance based on processing zone design.

Modelling of high voltage pulse breakage of ores

A high voltage pulse (HVP) breakage model was developed as a general modelling structure to represent the three HVP breakage indices: body breakage probability (the D1-model), body breakage product fineness (the D2-model), and body breakage product pre-weakening degree (the D3-model). Relations between the HVP breakage indices and HVP pre-concentration characterisation curves were established. The preliminary result indicated that the HVP breakage model has the potential to predict the recovery of valuable metals from the calibrated model parameters. A tn-family of curves (tn is defined as cumulative percentage of product passing 1/n of the initial size) was used to describe the HVP breakage product size distribution. The tn-family of curves can be employed to estimate the product size distribution from the predicted t10 values by the D2-model.

Pre-concentration of copper ores by high voltage pulses. Part 1: Principle and major findings

A novel ore pre-concentration technique using high voltage pulses is proposed in this study. The technique utilises metalliferous grain-induced selective breakage, under a controlled pulse energy loading, and size-based screening to separate the feed ore into body breakage and surface breakage products for splitting of ores by grade. Four copper ore samples were tested to demonstrate the viability of this technique. This study consists of two parts: Part 1 presents the principle, the validation and the major findings; Part 2 discusses the new opportunities and challenges for the mining and mineral industry to take up this technique.

Pre-concentration of copper ores by high voltage pulses. Part 2: Opportunities and challenges

The JKMRC has recently reported a novel ore pre-concentration method using high voltage electrical pulses (Part 1 of this paper). The technique utilises metalliferous grain-induced selective breakage under a controlled pulse energy input, and size-based screening to separate the feed ore into body breakage and surface breakage components, leading to ore grade splitting. This technique offers new opportunities for barren pebbles rejection from the AG/SAG mill pebble stream, coarse waste rejection at mine site to reduce the RoM haulage, pre-treatment of AG/SAG mill feed taking the combined advantages of pre-weakening and pre-concentration, and multi-grade comminution and recovery circuits. The challenges for industrial uptake of this technique include ore variation and machine scale up. A diagram describing the pulse energy input in relation to the mass yield, grade, and recovery for various feed particle sizes is proposed for the ore pre-concentration characterisation. The research gaps are discussed and the technical approach is suggested.