Abrasivity and grindability study of mineral ores

The results of the milling experiments of different mineral ores and laboratory wear testing with different abrasives have shown that the abrasivity of treated materials does not depend only on their hardness, but, to a great extent, on the particle shape of the materials. The grindability of materials milled by collision depends on the properties of materials as well on the treatment parameters (specific treatment energy). The aims of this investigation were (1) to study the abrasivity and the grindability of different minerals (granite, quartzite, etc.) and (2) to predict the relative wear resistance of the materials prospective for the grinding media of milling equipment, using a centrifugal type impact wear tester. Experiments conducted with abrasives of different hardness and with particles of different shape have shown that the wear rate of materials used as wear resistant materials in grinding devices depend more on the angularity of abrasive particles than on their hardness. It was shown that the grindability depends more on the composition and properties (fracture toughness, homogeneity of the structure) than on the hardness of the mineral ores. The main size reduction occurs at first collision, later in the multiple milling of mineral materials particle rounding takes place. The angularity parameter has good correlation with the wear rate in the case of the studied commercial steels as well as with metal matrix composites. Experiments with cermets showed that erosion does not practically depend on abrasive particle shape.     

Computational investigation of testing parameter effects on abrasive wear behaviour of AL2O3 particle-reinforced MMCS using statistical analysis

The wear rate model of 7.3?vol.% Al₂O₃ particle-reinforced aluminium alloy composites with 16 and 66???m particle sizes fabricated by molten metal mixing method was developed in terms of applied load, particle size of reinforcement, abrasive grain size and sliding distance based on the Taguchi method. The two-body abrasive wear behaviour of the specimens was investigated using a pin-on-disc abrasion test apparatus where the sample slid against different SiC abrasives under the loads of 2 and 5?N at the room conditions. The orthogonal array, signal-to-noise ratio and analysis of variance were employed to find out the optimal testing parameters. The test results showed that particle size of reinforcement was found to be the most effective factor among the other control parameters on abrasive wear, followed by abrasive grain size. Moreover, the optimal combination of the testing parameters was determined and predicted. The predicted wear rate results were compared with experimental results and found to be quite reliable.     

Micro-abrasion mechanisms of cast CoCrMo in simulated body fluids

The abrasion seen on some of the retrieved CoCrMo hip joints has been reported to be caused by entrained hard particles in vivo. However, little work has been reported on the abrasion mechanisms of CoCrMo alloy in simulated body environments. Therefore, this study covers the mapping of micro-abrasion wear mechanisms of cast CoCrMo induced by third body hard particles under a wide range of abrasive test conditions. This study has a specific focus on covering the possible in vivo wear modes seen on metal-on-metal (MoM) surfaces. Nano-indentation and nano-scratch tests were also employed to further investigate the secondary wear mechanisms—nano-scale material deformation that involved in micro-abrasion processes. This work addresses the potential detrimental effects of third body hard particles in vivo such as increased wear rates (debris generation) and corrosion (metal-ion release). The abrasive wear mechanisms of cast CoCrMo have been investigated under various wear-corrosion conditions employing two abrasives, SiC (4 μm) and Al₂O₃ (1 μm), in two test solutions, 0.9% NaCl and 25% bovine serum. The specific wear rates, wear mechanisms and transitions between mechanisms are discussed in terms of the abrasive size, volume fraction and the test solutions deployed. The work shows that at high abrasive volume fractions, the presence of protein enhanced the wear loss due to the enhanced particle entrainment, whereas at much lower abrasive volume fractions, protein reduced the wear loss by acting as a boundary lubricant or rolling elements which reduced the abrasivity (load per particle) of the abrasive particles. The abrasive wear rate and wear mechanisms of the CoCrMo are dependent on the nature of the third body abrasives, their entrainment into the contact and the presence of the proteins.     

Two-body abrasion of some polymers against 6–50 μm SiC abrasives

Single- and multiple-pass two-body abrasion tests were run on Nylon $\text{6}\text{6}\text{+ 20\%}$ polytetrafluoroethylene (PTFE) and polycarbonate + 10% PTFE sliding dry against 6–50 μm SiC abrasives. A functional relationship was developed between the single-pass wear rate and the abrasive particle size for abrasive particle sizes less than or equal to 10.4 μm. The single-pass abrasive wear rate was 20–40 times greater than the multiple-pass wear rate for each material when it was slid against abrasive grains with a mean size not exceeding 10.4 μm. This was due to the formation of loose polymer fibril wear debris in single-pass sliding and of transferred plateaux of polymer in multiple-pass sliding. The rate of increase in wear with particle size was about 20 times greater for single-pass sliding than for multiple-pass sliding. Above a mean abrasive particle size of 10.4 μm the type of mechanism in both single-pass and multiple-pass sliding was that of ploughing.     

Some microscopical investigations of grinding and abrasive wear*

This work forms part of a broader investigation which explores the relationship between grinding and abrasive wear. Wear experiments were performed over a wide range of loads and speeds in which solid abrasives (typical of those in grinding wheels) were rubbed against metals (usually steels). Under certain conditions the rate of wear decreased with time; at the same time the worn debris changed from metallic particles to finely divided oxides and the surface of the abrasive became glazed. Optical and scanning electron microscopy have been used to study this transition in the wear mechanism and its relationship to the structure of abrasives and the nature of abraded surfaces. The investigation illustrates the role of microscopy in the examination of a complex engineering process.     

Influence of CrC addition in Ni-Cr-Si-B flame sprayed coatings on microstructure, microhardness and wear behaviour

In the present paper the influence of the addition of chromium carbide (CrC) particles on the microstructure, microhardness and abrasive wear behaviour of flame sprayed Ni-Cr-Si-B coatings deposited on low carbon steel substrate has been reported. Wear behaviour of the coatings was evaluated with a pin-on-block wear system against SiC abrasive medium (120 & 600 grades) over a range of normal load (5–20 N). It was observed that the wear behaviour is governed by the material related parameters (microstructure, microhardness of coating) and test parameters (abrasive grit size and normal load). The addition of CrC reduces the wear rate three to eightfold. Wear resistance was greater against coarse abrasives at high loads than against fine abrasives. Heat treatment of both unmodified (1004) and modified powder (1004-10%CrC, 1004-20%CrC) coatings deteriorated the abrasive wear resistance. SEM study of wear surfaces showed that wear of the coatings largely takes place by groove formation, plowing and scoring. Electron probe micro analysis (EPMA) of the coating was carried out for composition and phase analysis.     

Abrasive wear of steel against gravel with different rock–steel combinations

Wear testing equipment and tests used in research laboratories are often miniature or simplified versions of real applications. For example standardized ASTM dry sand rubber wheel abrasion test G 65 and pin abrasion test G 132 are widely used to study materials’ abrasion wear resistance. The test results, however, do not always correlate too well with the results obtained from real wear conditions. One reason for this is, for example, that in the crushing applications of mining industry the abrasive size is usually much larger than that used in the laboratory wear tests. To study the abrasive wear caused by larger size gravel, new three-body abrasion test equipment was therefore constructed. The equipment uses the pin-on-disk principle with free abrasive particles of sizes up to 10 mm. During the test the pin is repeatedly pressed against a fixed amount of abrasive that is rotating with the disk having confining walls. As the pin is prevented from touching the counterbody, only the abrasive acts as the wearing agent.Three steels of different hardnesses were cross-tested as pin–disk pairs and as pins against a rubber disk using three igneous rock gravels with different crushability properties as abrasives. The wear was measured as mass loss from both the pin and the disk, and the rock comminution was measured by sieving. The results indicate that the mechanism of wear is greatly affected by the hardness of the counterbody. When using large size abrasives, the rate of comminution is also a very important factor that can significantly affect the wear test results.     

Abrasive wear in ultrasonic drilling

Material removal in ultrasonic drilling is caused by the abrasives in the slurry. As a given charge of abrasive circulates, the mean particle size decreases and the initially sharp cutting edges become dull, reducing the machining rate. This paper discusses the mechanism of wear of the abrasive in ultrasonic drilling; the size of abrasives in the working zone governs machining rate, tool wear and production accuracy of the holes drilled     

A study on the formation of wear debris during abrasion

A set of five material specimens have been tested on five abrasives, some of which are harder, some softer than the materials, using the dynamic abrasive wear tester. Characteristics of selected wear debris have been observed by sem and wear debris of 9Cr2Mo steel analysed by Mossbauer spectroscopy. The test results show three wear mechanisms operating during abrasion: microcutting, plougging deformation and brittle fragmentation. Different abrasives formed different constituents of wear debris due to dissimilar wear conditions. Softer abrasive tended to form more ploughing debris, although some typical microcutting chips were produced. Crushing strength of abrasive may be an important factor in addition to hardness of abrasive. The microstructure of 9Cr2Mo steel wear debris has been changed by abrasion heat; this temperature could be estimated by Mossbauer spectroscopy.     

Three-body abrasive wear with small size diamond abrasives

Three-body abrasive wear rate was measured as a function of abrasive size and applied load using molybdenum alloy spheres of diameter 25.4 mm as test specimens. Diamond abrasives in the size range 1–60 μm normally used for metal lapping were tested. Tests were conducted at lap loads ranging from 9.8 to 107.9 N. For a given load it was found that there is a maximum abrasive size beyond which the wear rate will not increase and may even decrease. Several explanations of this critical size effect reported in the literature were evaluated on the basis of physical evidence.Wear rate generally increases linearly with increasing load. However, this did not occur with small abrasives. This deviation from linearity was found to be the result of an unusually effective abrasive wear condition. An explanation of this effect is given.     

Abrasive wear of high speed steels: Influence of abrasive particles and primary carbides on wear resistance

A ball cratering test has been used to investigate the abrasive wear of high speed steels with different volume fraction and size of primary carbides. Three different abrasives, SiC, Al₂O₃ and ZrO₂ were used. Wear mechanisms were investigated by scanning electron microscopy (SEM). A good correlation between the hardness of the abrasives and the abrasive wear coefficient was found. Higher abrasive wear resistance was determined for steels containing coarser primary carbides compared to those without or with smaller carbides. The most pronounced difference in abrasive wear resistance was found for Al₂O₃ abrasives. This indicates that in ball cratering the abrasive medium has to be chosen properly, i.e. with a hardness adjusted to those of both primary carbides and martensitic matrix, to obtain results suitable to rank high speed steels with respect to abrasion resistance.     

Using parallel scratches to simulate abrasive wear

Abrasive wear is currently classified according to different particle dynamics: (a) the sliding of active particles on the sample surface and (b) the rolling of abrasive particles between the surfaces. In this paper, instrumented laboratory tests are used to present a new methodology for the simulation of abrasive wear. The rolling of the abrasives is represented by a sequence of indentations, and the sliding of the active particle by a sequence of scratches. A new piece of equipment was especially developed to reproduce the action of an abrasive particle. Two high resolution sliders drive the sample horizontally while the indenter is moved vertically by another slider. Besides this, a high resolution piezoelectric translator is used to control the indenter movement while a 3D load cell controls the intensity of the process. A worn surface produced in a rubber wheel abrasive wear test was used as the reference for the simulation. Its topography was assessed by using laser interferometry and scanning electron microscopy and showed that the prevailing wear mechanism was parallel scratches. The results showed that the superimposition of scratches is the basis which makes it possible to correlate topographical parameters of the reference to the controlling variables used in the simulation. A special method to describe the average depth of the scratches in function of the distance between them (superimposition) was developed. Wear occurs when superimposition is greater than 80%. The average depth of the scratches increased according to an elevation in the degree of superimposition and to the augmentation of normal load. This simulation methodology produced a surface topographically and morphologically similar to that of the reference.     

Improved ball crater micro-abrasion test based on a ball on three disk configuration

An improved ball crater micro-abrasion test method has been developed that differs from the conventional ball crater method. A ball-on-three-disk (BOTD) configuration provides mechanical stability and three simultaneous measurements of abrasion. An inclined BOTD geometry allows the specimens to be totally immersed in abrasive, which allows the use of dry abrasives as well as slurries and pastes. Use of a rubber ball gives effective three-body abrasion and provides results that are highly correlated with the ASTM G65 method. Use of dry abrasive with a rubber surface, rather than use of slurries and a metal ball, provides cutting action that is closer to actual field conditions, and allows high temperature test. Flooding the substrate with abrasive also avoids the problems encountered in conventional ball crater tests in that it provides spherical scars even for large particle abrasives, and spherical geometry allows direct computation of the volume of wear. Modeling of the BOTD scar geometry indicates that the BOTD contact pressure is similar to the contact pressures used in the ASTM G65 test. The BOTD microabrasion method provided excellent ranking of the abrasion rates of bare steel and two thicknesses of a TiAlN coating.     

Morphology and Toughness of Abrasive Particles and Their Effects on the Friction and Wear of Friction Materials: A Case Study with Zircon and Quartz

This study examined the friction and wear of brake friction materials containing two different abrasives: zircon and quartz. Commercial grade abrasives with two different sizes (fine and coarse) were compared in terms of the effects of the size, shape, and toughness of the abrasive particles on the friction and wear of the friction material and counter discs. The results showed that the morphology of the abrasives has a considerable effect on the friction effectiveness and wear of the friction couple. The level of friction was higher in the case of using quartz than zircon, and smaller particles were more effective in increasing the coefficient of friction. The toughness of the abrasives also played important roles in determining the friction effectiveness. Improved heat resistance at elevated temperatures was achieved when coarse zircon was used. The wear of the friction material was also dependent on the morphology and toughness of the abrasives and the large abrasive particles produced more wear on the gray iron disc.     

Influence of abrasive hardness on the wear resistance of high chromium irons

The resistance to abrasive wear was determined for a series of alloyed white cast irons in a high stress abrasion test which utilizes a specimen in sliding contact with bonded abrasives. These were conducted on silicon carbide, alumina and two sizes of garnet abrasive.The results indicate that the hardness, or type, of abrasive used in the test significantly influenced the wear rate of white irons, i.e. the rate of wear increased with increasing hardness of the abrasive. Also, the results indicate that the type of abrasive used in the test was a significant factor in ranking white irons for resistance to high stress abrasion. When tested on silicon carbide or alumina abrasive, as-cast austenitic irons exhibited lower rates of wear than heat treated martensitic irons; when tested on garnet, an abrasive of lower hardness, those irons with martensitic matrix microstructures exhibited the same or less wear than irons with austenitic matrix microstructures. It was also evident that heat treated irons with martensitic matrix microstructures exhibited varying degrees of resistance to abrasive wear depending on cooling rates and alloy content.     

Mechanism of material removal during three-body abrasion of FRP composite

The low-stress abrasive wear behaviour of chopped-glass-fibre-reinforced polyester composites has been studied by using a rubber wheel abrasion test (RWAT) apparatus. Silica sand particles of two different size ranges were used in the current study as dry and loose abrasives. Weight loss of the composites during three-body abrasion has been examined as a function of the sliding distance. Abrasive wear of the composites shows dependence both on abrasive particle sizes and applied load, as well as the weight fraction of glass fibre reinforcement. It has also been observed that the wear rate becomes constant with the increasing sliding distance. Scanning electron microscopy was used to observe the worn surfaces and to understand the mechanism involved in material removal. This revised version was published online in June 2006 with corrections to the Cover Date.     

Abrasive wear and its application to digger teeth

Abrasive wear is receiving increased attention particularly as its economic importance is appreciated. Low alloy carbon steels are widely used in the heat treated condition to resist abrasion and, in particular, are used for digger teeth. Little information is available in the literature on field or service wear studies and it was necessary, therefore, to carry out field studies in parallel with a laboratory wear investigation.A particular feature of the field study is the realization that significant wear occurs by rubbing to produce smooth surfaces and surface transformation, as well as wear by cutting and micro-chipping.A laboratory investigation based upon two-body pin-on-disc testing has been used to investigate the wear of a wide range of experimental steels, a manganese steel and a commercial digger tooth steel for comparison. Wear is directly proportional to the load and inversely related to hardness, but not to sliding distance because of the degradation of the abrasive paper. Abrasion increases with harder abrasives and increased abrasive particle size.The analysis of these results, although important from a wear mechanism point of view, shows that there is currently a lack of direct correlation between the field and laboratory studies because of the different surface features developed. Further investigations are proceeding to improve this correlation.