M.S Bingley

A model to predict the solid particle erosion rate of metals and its assessment using heat-treated steels

Abstract A new predictive model for the wear rate of metals during solid particle impact erosion is presented. The model proposes that erosion rate is related to the product of toughness ( U T ) and uniform strain ( e U ). Predictions for the variation of erosion rate with impact angle are also made. The validity of the model was assessed using an extensive set of new experimental data generated for heat-treated steels. Two steels were heat treated to form a total of 12 different microstructures, each having distinctly different mechanical behaviour. Erosion tests were carried out at a combination of three impact velocities and three angles of particle impingement in a rotating disc accelerator erosion tester. Fine olivine sand was used as the abrasive at one feed rate. Tensile tests were carried out on all the heat-treated steels over a range of temperatures from room temperature to 400°C. The model predictions were not satisfied by mechanical property measurements made at room temperature. However, for each given erosion test condition, a good linear relationship was found between room temperature erosion rate and 1/ U T e U when mechanical properties were measured at elevated temperatures. The elevated temperature chosen to give the best-fit was between 200 and 300°C depending on the impact velocity. It is believed that the significance of the elevated temperature property measurements is that they account for localised heating occurring at the impacting particle during the high strain/strain-rate deformation typical of erosion. Certain heat-treatments gave a poorer fit to the relationship and explanations for this are proffered. The model was also able to account for changes in erosion rate with impact angle. Suggestions are made for improving the model and to refine its predictive capability.

The influence of particle rotation on the solid particle erosion rate of metals

Abstract It has long been recognised that particle spin may have a significant effect on the impact erosion rate, particularly of ductile metals. However, no work has previously been carried out to quantify this effect, partly due to the practical difficulty of measuring the magnitude of the rotational speed. Particle spin is a feature of the centrifugal accelerator erosion tester. In this tester it has proved possible to examine the effect on erosion of particle spin direction by varying the target orientation. The results indicated a strong effect of the spin direction on erosion rate at low impact angles when the targets were impacted by angular particles. A quantitative model was developed to explain the effect of particle spin direction on the observed differences. The model is a modification of the Finnie–Bitter model [Wear 3 (1960) 87; Wear 6 (1963) 5; Wear 6 (1963) 160], and is the first to explicitly incorporate the effect of rotating particles on the subsequent erosion rate when the particles impact a metal target. The model supposes that the effective impact velocity, the contact velocity between the particle and the target, is altered due to spin of the particles. The predictions of the model were validated through actual measurement of particle rotational speed by high-speed photographic techniques; the first such measurements. Experimental erosion results conformed to the predictions of the model. An effect of particle spin on the peak erosion rate is also predicted by the model and confirmed by the experimental results.

An investigation of particle dynamics within a centrifugal accelerator type erosion tester

Abstract Particle impact erosion is usually tested experimentally using one of two major types of erosion testing device; the gas-blast tester and the centrifugal accelerator type tester. The influence of the choice of the tester on the erosion results obtained has been recognised, together with the need for a better understanding of particle dynamics within the testers to allow correct interpretation of the erosion test results. To date, relatively little work has been carried out on understanding particle dynamics in the centrifugal tester, and this paper attempts to redress this. The paper considers the dynamics of particles travelling down the acceleration tube in the tester. A comprehensive physical model is described taking account of airflow in the acceleration tubes, particle rotation and friction effects. This led to the development of a computational model to predict the particle velocity vector (particle velocity and exit angle). The predictive model indicates the important influence of particle shape on particle dynamics and suggests that particle size has little effect. This implies a sensitivity of particle velocity and exit angle to the coefficient of friction of the particle in the acceleration tubes. Experimental measurements were carried out and the results verified the predictions of the model.

Anomalies in the results obtained from rotating disc accelerator erosion testers: a discussion of possible causes

During recent erosion research at the University of Greenwich using a rotating disc accelerator erosion tester no peak has been observed in the curve of erosion damage vs. angle of impingement. This lack of peak has been observed for tests on a range of steels at a variety of particle impact velocities and fluxes and is contrary to previously reported results. Results of erosion tests on targets at various orientations are given in this paper. The targets used in this work were all made from 0.8% carbon steel (SAE1074). It is shown that changing the orientation of the target in such a tester can lead to different mechanisms of impact erosion occurring owing to changes in the particle dynamics at impact. Several reasons for this behaviour are suggested by the authors including: (a) the variation of particle flux across the target surface as the angle of orientation of the target to the flow of particles is changed, (b) the variation in the occurrence of inter-particulate collisions with the angle of target orientation, and (c) the effects of particle sliding on the walls of the acceleration mechanism inducing particle spin such that the mechanism of cutting is increased at low angles of particle impingement.

Influence of particle dynamics on erosion test conditions within the centrifugal accelerator type erosion tester

Abstract It is well known that particle dynamics behaviour in an erosion tester has a significant influence on test parameters and conditions and, consequently, the erosion test result. This paper examines aspects of particle dynamics in the centrifugal accelerator type erosion tester and their influence on the erosion test conditions, particularly the particle concentration in the particle jet stream and the mass flux on the surface of the eroded target. The effect of particle and particle jet characteristics on particle jet dispersion, particle positional distribution within the jet and particle velocity distribution, and how these in turn effect the mass flux on the target, are examined both theoretically and experimentally. Experimental results showed that a narrow velocity distribution was generally obtained for this type of erosion tester. The velocity distribution was, however, seen to be sensitive to particle characteristics. Experimental measurement of jet dispersion was necessary to allow the mass flux to be estimated. The jet dispersion was determined using a novel technique in which an optical photo-densitometer was utilised to define and measure the diameter of the wear scar on a target. The particle positional distribution was also indicated by this technique. Mass flux was found to vary with position on the target surface and additionally at any given position varied with impact angle. The effect of inter-particulate collisions on mass flux was also considered.

Abrasive wear of steels in handling of bulk particulates : an appraisal of wall friction measurement as an indicator of wear rate

The advantages of using wall friction instead of hardness to indicate likely relative wear rates are given consideration and discussed. The results of sliding abrasive wear tests on a variety of commercially available steels using two particulate solids are presented, together with the results of wall friction tests between the same steels and one of the particulate solids. Correlations found between the wear rates and wall friction data are presented, and are shown to hold for both particulate solids.