Physicochemical wear of abrasive grains during grinding processes

One of the modes of the wear of abrasive grains that occur during grinding is physicochemical wear, which is caused by the intensive interaction between an abrasive material and a material being ground. Despite the short duration of contact between a grain and a blank at high surface temperatures with the friction of the material being ground against the wear site of the abrasive grain, as well as juvenile and subsequently oxidized surfaces, predetermine the physicochemical interaction between the abrasive material and the material being ground. The problem of developing a quantitative characteristic of these processes has not yet been solved. A system of coefficients of the chemical affinity of the abrasive material and the material being ground that characterize the intensity of the physicochemical processes that occur in the zone of contact is proposed.     

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.     

Predicting the physicochemical wear of an abrasive grain in grinding

Physicochemical wear in grinding is due to the intense interaction of the abrasive and the blank. A system of chemical-affinity coefficients is proposed for abrasive and machined materials, characterizing the intensity of the physicochemical processes in the contact zone.     

Simulation of grinding with wear of the abrasive grains

A geometric model of grinding is developed. For the first time, this model takes account of wear of the abrasive grain. That permits prediction of the surface roughness at any time of tool operation. The wear is taken into account in terms of the physicochemical and mechanical interaction of the abrasive and the workpiece. This is of great importance for multiproduct manufacturing.     

Feature extraction method of abrasive belt wear state for rail grinding

Abstract

Abrasive belt has the advantages of high removal efficiency and high waste collection; furthermore, it does not easily damage the rail when applied in rail grinding. However, the poor wear consistency and short service life restrict its development in this field. It is important to explore the theory and technology of monitoring the abrasive belt wear condition to evaluate the means of improving the grinding performance of the belt. This article discusses the contact stress state between the belt and the rail surface. In addition, the study establishes the belt rail grinding force model during operation using the abrasive grain distribution function. The analysis of the force model proposes that the belt abrasion condition be monitored by using the force ratio parameter of the abrasive belt in the grinding process. The extraction method of the force ratio information is proposed in accordance with the grinding environment. The results of experiments successfully verified the validity of the method.     

Corrosive wear in crosshead diesel engines

Existing theories describe corrosive wear in crosshead diesel engines in terms of acid condensation, when the temperature in the combustion space drops below the dew point. Here a theory is proposed which stresses the role of alkaline cylinder lubricants in protecting the metal surface. Calculated liner wear rates as a function of fuel sulphur content, feed rate and alkalinity of the oil, and axial position are in satisfactory agreement with experimental data.     

Principles of abrasive wear

The mechanisms of abrasive wear are reviewed and laboratory test methods assessed. The results of abrasive wear tests on technically pure metals, heat treated steels, cold work hardened materials, hard wear resistant materials and minerals against fixed abrasive grains are discussed. The correlation between abrasive wear resistance and the physical properties of materials is established; the effect of the relative hardness of the abrasive and impact loading is considered. The basic principles of abrasive wear derived are outlined.     

Corrosive wear of steel in gasoline-ethanol-water mixtures

Corrosion and wear tests of a steel in the gasoline-ethanol-water system, generally known as gasohol, were performed in order to examine the relationship between the corrosion and wear of the steel. The corrosion potential of the steel was also measured in ethanol, water and gasohol to estimate the effect of loading for a short period on the corrosion of steel in gasohol containing hygroscopic water.It was found from these tests that the wear rate of the steel in gasohol is closely related to the corrosion rate of the steel in gasohol, reaching a maximum at about a 20 vol.% ethanol content.     

Temperature fields in grinding by abrasive wheels

A method is proposed for calculating the temperatures at the surface of the workpiece and within its interior on grinding by abrasive wheels of different design (discontinuous, composite, or hybrid wheels). On that basis, the temperature fields in the cutting zone are calculated.

     

The abrasive wear of metals

A quite general relationship exists between abrasive wear and the ploughing contribution to friction. Tensile stresses are developed in the material displaced by the ploughing indenter and these give rise to wear particles.     

Microstructure and abrasive wear in silicon nitride ceramics

It is well known that abrasive wear resistance is not strictly a materials property, but also depends upon the specific conditions of the wear environment. Nonetheless, characteristics of the ceramic microstructure do influence its hardness and fracture toughness and must, therefore, play an active role in determining how a ceramic will respond to the specific stress states imposed upon it by the wear environment. In this study, the ways in which composition and microstructure influence the abrasive wear behavior of six commercially-produced silicon nitride based ceramics are examined. Results indicate that microstructural parameters, such as matrix grain size and orientation, porosity, and grain boundary microstructure, and thermal expansion mismatch stresses created as the result of second phase formation, influence the wear rate through their effect on wear sheet formation and subsurface fracture. It is also noted that the potential impact of these variables on the wear rate may not be reflected in conventional fracture toughness measurements.     

A study on wear mechanism and wear reduction strategies in grinding wheels used for ELID grinding

Metal-bonded superabrasive diamond grinding wheels have superior qualities such as high bond strength, high stability and high grindability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the grinding wheel. Electrolytic in-process dressing (ELID) is an effective method to dress the grinding wheel during grinding. The wear mechanism of metal-bonded grinding wheels dressed using ELID is different form the conventional grinding methods because the bond strength of the wheel-working surface is reduced by electrolysis. The reduction of bond strength reduces the grit-depth-of-cut and hence the surface finish is improved. The oxide layer formed on the surface of the grinding wheel experiences macrofracture at the end of wheel life while machining hard and brittle workpieces. When the wheel wear is dominated by macrofracture, the wheel-working surface is free from loaded chips and worn diamond grits. When the oxide layer is removed from the wheel surface, the electrical conductivity of the grinding wheel increases, and that stimulates electrolytic dressing. The conditions applied to the pulse current influence the amount of layer oxidizing from the grinding wheel surface. Longer pulse ‘on’ time increases the wheel wear. Shorter pulse ‘on’ time can be selected for a courser grit size wheel since that type of wheel needs high grinding efficiency. Equal pulse ‘on’ and ‘off’ time is desired for finer grit size wheels to obtain stable and ultraprecision surface finish.     

Investigation of abrasive wear resistance and wear mechanism of composite alloys

The abrasive wear resistance of composite alloys comprising hard tungsten carbide and soft CuNiMn matrix under different wear conditions has been investigated and compared with CrMo cast iron. It was found that Yz-composite alloy with hard cast angular tungsten carbide has greater wear resistance than CrMo cast iron under two-body wear conditions, but lower resistance than Cr-Mo cast iron under three-body wear conditions. It was found that under three-body wear conditions selective wear of the matrix and digging or fragmentation of tungsten carbide particles dominate in Yz-composite alloy, and microcutting and deformed ploughing is dominant under two-body wear conditions. The abrasive wear resistance of composite alloys under two-body wear condition is independent of bulk hardness, but is closely related to the microhardness of tungsten carbide.     

Metal transfer and wear in fine grinding

The transfer and wear characteristics of two widely used abrasive materials (A1₂O₃ and SiC) are studied when grinding two difficult materials (AISI T15 tool steel and Ti-6Al-4V titanium alloy). A newly developed accelerated wear technique (cluster overcut flygrinding) is employed together with Auger electron spectroscopy, X-ray diffraction and scanning transmission electron microscopy. Experimental results suggest that when grinding steel the wear of SiC is primarily due to oxidation, while the wear of Al₂O₃ is primarily due to metal build-up, resulting in microchipping. When a titanium alloy is being ground, both types of abrasive result in a microchipping type of wear, the rate of which decreases when the wheel speed is reduced.     

Corrosive wear of diesel engine cylinder bore

Deleterious wear of the cylinder bore in diesel engines can be aggravated by alteration of combustion conditions, such as that brought about by use of Exhaust Gas Recirculation (EGR) equipment and consequent high mileage. This paper describes the influence of combustion products — i.e. sulphuric acid and carbon soot, which can be primarily concerned in corrosive wear — on lubrication under reciprocating sliding of a piston ring and on the bore wear.     

Relating contact conditions to abrasive wear

Damage caused by particles within rolling/sliding contacts can severely reduce the operational life of machinery such as roller bearings, gears and pumps.Abrasive wear of spherical roller thrust bearings has been studied using a stylus apparatus and scanning electron microscopy (SEM). Both a standard bearing and a bearing with rollers coated with metal mixed amorphous carbon (Me-C:H) were studied. The SEM measurements were performed systematically across the contact surfaces so that surfaces with gradually different contact situations could be examined. These measurements were compared to the measured wear depth of the components of the roller bearing. Also, the calculated contact conditions in terms of creep, contact size and surface separation have been related to the observed wear pattern at various locations.To attempt to understand the wear behaviour of the bearing with coated rollers, the coating as well as the material content of the surfaces were examined using both SEM and energy dispersive X-ray spectrometry (EDS). This revealed that the coating did not flake off but rather was scratched off.It is possible to link the abrasive wear behaviour to the contact conditions. It is crucial to understand this relationship when building a simulation model of abrasive wear.     

The correlation of abrasive wear tests

Previous attempts to correlate theoretically the results obtained from some simple abrasive wear tests are reviewed briefly. While these theories all predict the behaviour of pure metals quite well, they fail with heat-treated alloys. It has been suggested that elastic deflections in these alloys may change significantly the shapes and depths of the scratches formed when they are abraded, but surprisingly no attempt has yet been made to include them in a model of abrasion. In this paper a simple plastic model of abrasion is modified to allow for elastic effects. An expression is deduced relating the abrasion resistance of a metal to its hardness and Young's modulus, and the values it predicts are found to agree well with a wide range of published experimental results.     

Two-body dry abrasive wear of cermets

The present paper concerns the two-body dry abrasive wear phenomenon of a series of cermets on the base of titanium and chromium carbides with different composition, using a “block on abrasive grinding wheel” test machine. WC–Co hardmetals were used as reference material. Abrasive wear resistance of WC-base hardmetals is superior to that of TiC- and Cr₃C₂-base cermets. The wear coefficient of the cermets reduces with the increase of carbide content in the composites. The volume wear decreases with the increase in bulk hardness. At the first period volume wear of cermets increases linearly with the sliding distance up to the first 100 m; after that the alumina grits become blunt. Scanning electron microscopy examination of the wear tracks in the worn blocks suggests that abrasive wear mechanisms of different cermets are similar and occur through surface elastic-plastic and plastic deformation (grooving). The fracturing of bigger carbide grains and carbide framework the formation of sub-surface cracks by a fatigue process under repeated abrasion is followed by loss of small volumes of the material.     

Some observations on two-body abrasive wear

Pin-on-disc-type two-body abrasion tests were carried out on five metals with seven particle sizes over a range of loads, lengths of travel and sliding speeds. The familiar results that two-body abrasive wear is proportional to load and to distance travelled were confirmed. The “size effect”, in which particles below about 100 μm produce progressively less wear, was shown to be independent of load, sliding speed and prior cold working. Increasing the sliding speed from 1 to about 100 mm s^?1 produced an increase in wear resistance of about 50% for AISI 1020 steel. An increase in velocity above 100 mm s^?1 had little effect on the wear resistance. Plots of the wear resistance against the hardness of the annealed metal showed significant deviations from the linear relationship reported in the literature. The result is influenced by both sliding velocity and particle size.