STUDY ON CASING PERFORMANCES IN CENTRIFUGAL SLURRY PUMPS

The pump casing is the most expensive wear component of a centrifugal slurry pump. It determines to a large extent the hydraulic performance of the pump and plays a major role in the overall wear life of the unit.

This paper suggests a new approach to compute the mixture velocity and solid particle dynamics in the casing, and on this basis the erosion wear distribution inside the pump casing. Numerical analysis was performed using the finite element method. The model was tested using Georgia Iron Works (GIW) pump casings, at flowrates between 2000 and 4000 US-GPM (US gallons ner minute). The experimental results were obtained in the Hydrualic Laboratory and in field applications in mining and dredging industries. The suggested techniques are useful for estimating casing wear rates and for the optimal design and selection of slurry pumps.     

PARTICULATE MOTION AND CONCENTRATION FIELDS IN CENTRIFUGAL SLURRY PUMPS

ABSTRACT

Erosion wear of centrifugal slurry pumps is primarily governed by the particulate motion and concentration as well as their physical properties. This paper presents a quasi-3D approach to predict particulate phase motion and concentration in an arbitrary radial section of a centrifugal slurry pump. A brief discussion of the fully developed turbulent flow solution of the carrier fluid is followed by a computation of the particulate phase velocity resulting from a force balance between the pressure, gravity, viscous and inertial effects. The concentration distribution is obtained by invoking the convection-diffusion equation. The governing partial differential equation is cast into a weak Galerkin finite element form. The system of algebraic equations is solved by a Newton-Raphson scheme via a frontal solver. An iterative solution scheme is employed to alternate between the fields of particle motion and concentration. Numerical solutions are examined in light of their applicability to the solution of the pump wear problem.     

Media Wear in Stirred Milling

ABSTRACT

A method for measuring media wear using a commercially available 0.751 stirred mill is described. Five material groups, namely steel, ceramics, natural materials, glass, and ore pebbles (autogenous grinding) were tested using water alone and a 60% by weight slurry of sulfide ore. Other variables were stirrer speed and media size. The relative wear rates of the different materials and their effects on grinding efficiency are reported. Relative costs of media were taken into account in the assessment. Ottawa sand was the most cost effective medium for wear, and steel shot for grinding efficiency.     

Synthesis and characterisation of free standing,one­dimensional,Al–SiC based functionally gradient material

Abstract

In the present study, an aluminium–silicon carbide based functionally gradient material was successfully synthesised using a new technique termed here as gradient slurry disintegration and deposition process. The gradient of SiC was successfully established using this technique for 21 wt-%SiC. The results were confirmed using microstructural characterisation techniques, microhardness measurements, and wear rate determination. The results further revealed that an increase in the weight percentage of silicon carbide particulates along the deposition direction lead to a concurrent increase in porosity, degree of clustering, and microhardness while the nature of silicon carbide/aluminium interfacial integrity remained the same. The results of wear rate determination indicated that a difference of ～9.53 vol.-%SiC on the opposite faces of the functionally gradient material led to the wear resistance increasing to ～31.5× that of the high aluminium end. An attempt is made to interrelate the processing methodology, microstructure, microhardness, and wear rate results obtained in the present study.     

Numerical simulation of a centrifugal slurry pump handling solid-liquid mixture: Effect of solids on flow field and performance

The effect of solids on a centrifugal slurry pump performance is a major concern to the design of slurry transportation system. In the present study, the multiphase modeling of centrifugal slurry pump is performed using two models, Mixture and Eulerian-Eulerian multiphase. Sliding mesh approach is employed for unsteady simulation of the pump. The accuracy of the simulations is ascertained by comparing the performance characteristics of the pump obtained numerically and experimentally. Experimental results are obtained by measurements in a pilot plant test rig with three different mean size sand particulate slurries. The Eulerian-Eulerian multiphase model predicted the effect of the solids on pump performance close to the experimental results as compared to Mixture model. The obtained accuracy with Eulerian-Eulerian model for predicting the effect of solids on head and efficiency is around ±2% and ±3%, respectively. The predicted results using Eulerian-Eulerian model confirm that the head and efficiency of the pump decrease with the increase in particle size and concentration. The particles of high specific gravity show less reduction in head and efficiency of the pump. Further, the effect of variation in particle size and concentration on the flow field in the impeller and casing has also been analyzed at best efficiency point operation. Non-homogeneous suspension of particles inside the blade channels and casing passages is examined. The particulate concentration is observed higher near the impeller back shroud, pressure side of the blades, and non-suction side of the casing as compared to other locations.     

Effect of particle size distribution on performance and particle kinetics in a centrifugal slurry pump handling multi-size particulate slurry

A significant variation in particle size distribution (PSD) is generally encountered in slurry transportation. The goal of this work is to establish the effect of variation in PSD on the centrifugal slurry pump (CSP) performance and particle kinetics. Computational fluid dynamics (CFD) modeling of a CSP with multi-size particulate slurry has been performed with a sliding mesh approach using the granular Eulerian-Eulerian model. The numerical model is validated with the experimental data of the pump performance for multi-size particulate fly ash slurry. The maximum deviations in the predicted head and efficiency compared to the measured values are of the order of ±2% and ±3.5%, respectively. Simulations with a single representative particle size for multi-size particulate slurry using median and weighted mean diameter approach are also carried out to understand the difference in performance prediction with equi-size and multi-size slurry. The predicted trend of pump performance variation with PSD is linear and non-linear with equi-size and multi-size slurries, respectively. The median and weighted mean approaches showed error in capturing the effect of variation in PSD on pump performance. The variation in PSD significantly affects the flow of particles inside the impeller and casing flow passages due to particle kinetics. Reduction in the intensity of granular pressure, maximum granular viscosity, and the head loss due to friction in impeller and casing flow passages are found with the increase in the fine size particles.     

Synthesis and wear of Al based,free standing functionally gradient materials: effects of different reinforcements

Abstract

In the present study, three aluminium based functionally gradient materials (FGMs), reinforced with different ceramic particulates (silicon carbide, aluminium oxide, and titanium carbide), were successfully synthesised using the innovative gradient slurry disintegration and deposition (GSDD) technique. The results for Al/SiC and Al/Al₂O₃ revealed, in common, an increase in the weight percentage of reinforcement along the direction of deposition, to result in an increase in porosity and microhardness. However, for Al/TiC, the reverse trend was observed, with porosity and microhardness decreasing with increasing distance from the base of the ingot. The porosity levels for Al/TiC were also found to be significantly lower than those ofthe other two FGMs. Thermomechanical analysis of the FGMs showed thatthe average coefficient of thermal expansion of the high reinforcement end was reduced, as compared to the high aluminium end. Sliding wear test results also revealed that the high reinforcement end was more wear resistant than the high aluminium end, except for the case of Al/Al₂O₃. An attempt is made to interrelate the effects of different types of particulates, with microstructural development, microhardness and wear rate results obtained in the present study.     

MORPHOLOGICAL ANALYSIS,TEN YEARS OF PROGRESS

ABSTRACT

The need for and the principles of morphological analysis as applied to particulate matter are briefly discussed. Applications of morphological analysis to a number of problems are cited. Topics include: relating morphology to the mechanisms of powder production; wear debris analysis by morphological analysis; and kinetic modeling of crystallization processes. Relationships between the behavior of particulate materials and the morphology of the particles are discussed in connection with: abrasive wear of metals; sedimentation In low flow regimes; measuring of bulk properties including internal angle of friction and flow times; dry separation technology; and scrap recovery techniques. The adaptation of the particle image analyzing system to analyze color as a morphic feature is presented. A number of examples of mixture analysis - classification studies are detailed and finally future work in packed and fluidized beds and slurry transportation is outlined.     

A Simplified Model to Estimate the Size Distribution Change of Polydispersed Aerosol for Cyclone Separator

ABSTRACT

Although the air-lift pump has been superseded by submersible pumps in raising water from wells and mines, it still provides an attractive means of lifting abrasive slurries because, unlike mechanical pumps, it has no moving parts to wear. However, current design of air-lift pumps must rely on empirical equations, or, at best, incremental computer solutions. Design is complicated by the fact that relative velocities of the phases change over the whole pump length. A new design equation is developed to predict the lift of an air-lift pump, given the flowrates of air, liquid and solid in the pump, and the dimensions of the air-lift tube. The new equation is baaed on well-established multiphase flow theory, and offers significant advantages over current design techniques. In combination with an equation for the overall pump efficiency, the new equation provides a method for optimizing the design parameters for the air-lift pump.     

Erosion-corrosion-abrasion characteristics in slurry of a zinc based alloy and its composite containing alumina particle dispersoid

Abstract

This study presents observations made pertaining to the slurry wear behaviour of a zinc based alloy and its composite containing dispersed alumina particles. The influence of varying the sand concentration in the medium and the traversal distance on the response of the specimens has also been investigated. Wear rate increased initially with traversal sliding distance, attained a peak, and then decreased thereafter at longer traversal distances. This trend was much more pronounced when tests were conducted in a liquid only medium than in liquid with sand. The presence of suspended sand particles in the test environment led to a considerably reduced wear rate of the specimens when compared with that of the liquid only medium. Furthermore, intermediate sand content caused the maximum wear rate within the slurries, although it was substantially less than that caused by the liquid only medium. A comparison of the wear response of the composite and the matrix alloy suggested a mixed trend in the liquid only medium and the slurry with 60 wt- sand. The composite exhibited a lower wear rate than the matrix alloy when tested in slurries with 20 and 40 wt- suspended sand particles. The observed wear response of the specimens has been discussed in terms of specific characteristics, such as susceptibility to corrosion and hardness of various phases, and the interfacial effects in the specimens. The changing nature of the medium, such as the corrosivity and impingingabrading efficiency, has also been discussed. Analysis of the affected surfaces and subsurface regions of typical specimens by SEM enabled the understanding of the operating wear mechanisms under specific test conditions and thereby it was possible to substantiate the observed wear characteristics of the specimens.     

Laser surface alloying of case hardening steel with tungsten carbide and carbon

Abstract

The laser surface alloying process was used to introduce two different alloying materials, tungsten carbide (WC/Co) and carbon, into the molten surface of a case hardening steel (16MnCrS5), to improve its hardness and wear resistance. The chemical composition and the resulting microstructure in the alloyed layers were of particular interest in this investigation, because the strengthening mechanism was strongly dependent upon the type and amount of the alloy material. For laser alloying with carbon the increase in hardness and wear resistance was based on the martensitic transformation in the composition range concerned. For alloying with tungsten carbide it was necessary to consider two different strengthening mechanisms, namely, martensitic transformation and precipitation of carbides. In both cases the grain refinement in the laser affected zone had an additional effect. Resistance to dry abrasive sliding wear was measured using a conventional pin-on-disc wear testing machine. For both alloy materials the wear rate was substantially lower than that of a substrate that had been laser remelted without alloying additions.

MST/1556     

Wear perfornance of 0·6%Cr alloyed cast and heat treated steels with carbon contents of 0·7, 1·0, and 1·3%

Abstract

The effect of carbon content and heat treatment on the abrasive wear performance of three 0·6%Cr alloyed cast steels with carbon contents near the eutectoid composition (0·7, 1·0 and, 1·3%) were investigated using a pin on drum abrasion tester. Specimens were austenitised at 870,970, or 1070°C for 1 h and quenched. Additionally, a 1·3%C specimen was spheroidised, then austenitised at 870°C and quenched. The microstructure, which was dependent on heat treatment and carbon content, significantly influenced the wear rate. The wear rate is related non-linearly to hardness. The lowest wear rate was obtained for the 1·3%C alloy austenitised at 1070°C producing a quenched microstructure of 40% retained austenite and 60% martensite. This specimen also exhibited the lowest quenched hardness. However, for a practical industrial heat treatment, the 1·0 %C alloy austenitised at 970°C provides the best wear performance.

MST/3130     

Microstructure and wear resistance of laser clad TiC particle reinforced coating

Abstract

A TiC–Ni alloy composite coating was clad to 1045 steel substrate using a 2 kW CO₂ laser. The microstructural constituents of the clad layer arefound to be γ-Ni and TiC_p in the dendrites, and afine eutectic of γ-Ni plus (Fe,Cr)₂₃C₆ in the interdendritic areas. Partial dissolution and aggregation of the original TiC particles during melting of the Ni alloy and their growth during resolidification on cooling are observed. The TiC particles offer significantly enhanced wear resistance, the degree of wear depending primarily on the debonding removal of the particles.

MST/3018     

Tribological investigation of Zamak alloys reinforced with alumina (Al2O3) and fly ash

ABSTRACT

In this study, zinc aluminum alloy (Zamak) (ZA-27) composites reinforced by different weight fractions of fly ash, alumina (Al₂O₃), or both particles were produced using compo-casting technique. The composites were subjected to hardness and wear tests. The hardness of the composites increases with increase of the weight fractions of reinforcements. In wear test, the composites were examined under dry sliding conditions using pin on disc apparatus. The wear results revealed that the wear resistance increases with increase of the weight fractions of reinforcements. However, the effect of fly ash particles on the wear resistance of the produced composites is more statistically significant than the effect of Al₂O₃ particles. The morphology of the composites was examined using scanning electron microscopy (SEM) after the test. The SEM images revealed the existence of adhesion and delamination wear mechanism.     

Effects of yttrium on sliding wear of 304 stainless steel in dilute sulphuric acid and air

Abstract

Effects of an oxygen active element, yttrium, on the resistance of 304 stainless steel to corrosive siding wear in 0·1M H₂ SO₄ solution and to dry sliding wear in air, respectively, were investigated using a pin-on-disc wear tester. The worn surfaces and debris were examined by scanning electron microscopy. The results demonstrated that alloying with yttrium greatly improved the wear resistance of 304 stainless steel in both the corrosive and air environments.     

Rotating cylinder manufacturing method and investment casting of SiCp/AZ91HP magnesium composites

Abstract

This paper describes the rotating cylinder method for manufacturing, and investment casting for forming, composite slurry. Microstructural features, such as SiC particle distribution and grain refinement of the as cast composites, were investigated. Also the effect of SiC particle fraction and size, and process parameters on the microstructure and the mechanical properties are discussed. Attempts were made to evaluate the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZrO₃, and silica bonded Al₂O₃ and zircon flour. Finally, the tensile properties, hardness, and wear resistance of the as cast composites were evaluated and the results are compared with those of the as cast alloy.     

Diffusion wear in milling titanium alloys

Abstract

In this paper, diffusion wear during milling of titanium alloys is reported. In high speed milling, tool wear is mainly caused by diffusion. The wear pattern is characterised by the combined extension of crater wear on the rake face and glacier wear on the flank. Evidence of diffusion of cobalt and carbon at the interface between the milling cutter and the workpiece has been obtained. It was demonstrated for the first time that, as diffusion wear occurred, a carbon rich layer was formed at the tool/workpiece interface while the tool material below the flank wearland was depleted in carbon. Wear occurred as a result of embrittlement and weakening of the tool surface resulting from the diffusion process.

MST/674     

Study of effect of aging on martensitic transformation and tribological properties of TiNi alloy using DSC,neutron diffraction,and micromechanical probing techniques

Abstract

Recent studies have demonstrated that TiNi shape memory alloy exhibits excellent wear resistance, benefiting from their pseudoelasticity (PE) due to a thermoelastic martensitic transformation. The maximum wear resistance of the alloys corresponds to an optimum balance between the PE and hardness, which is strongly influenced by heat treatment. In this work, the effect of aging treatment on martenstic transformation behaviour, mechanical properties, including the pseudoelasticity and hardness, and wear behaviour of a Ti–51 at.-%Ni alloy was investigated using differential scanning calorimetry, neutron diffraction, and micromechanical probing techniques. The main objective of the study was to understand the aging effect on wear behaviour of the TiNi alloy and explore the mechanisms involved for further improvement of this novel tribo-alloy.     

Wear resistance of laser processed 1·0%C tool steel

Abstract

The wear resistance of both laser melted and conventionally quenched 1·0%C tool steel has been investigated. From unlubricated wear tests, the abrasion resistance of laser treated material was found to be superior to that of conventionally treated material, both in the as treated condition and after a range of tempering treatments (room temperature at 300°C), as a result of the presence of retained austenite.

MST/1326     

Indentation phenomena and wear of surfaces and edges

Abstract

Indentation tests are well established methods of measuring the hardness and toughness of surfaces, and the results can often be related to wear behaviour. Response to indentation in simple tests has been used in models for sliding wear, abrasion, and impact erosion; more sophisticated procedures can provide additional information about wear by stress corrosion. Despite the increased refinement of indentation fracture models, the scope for assessing the accuracy of theoretical predictions is limited considerably by the approximations used in the theories and the poor reproducibility of wear test data. An aspect of wear usually neglected is the brittle failure of edges and corners of components and tools. Recently, many of the experimental problems associated with using indentation to measure the susceptibility to edge flaking have been overcome, and it may soon be possible to recommend a test procedure for measuring this property.

MST/452