Advanced Materials and Processes Research Institute
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Wear Behaviour of Zinc-Based Alloys as Influenced by Alloy Composition, Nature of the Slurry and Traversal distance
No full textIn this study, the influence of microstructural alterations brought about by adding silicon on the slurry wear behaviour of a zinc-based alloy has been investigated. Wear tests were conducted using sample rotation method at a speed of 4.71 m/s over a range of traversal distance and sand concentration in the test environment. The electrolyte (i.e. liquid part of the slurry) contained chloride and sulphate ions which are essential constituents of mine water. The study suggests maximum wear loss and rate of the samples in the liquid-only medium. The presence of suspended sand particles in the liquid led to substantially decrease the wear rate/loss. A comparison of the wear response of the samples in the liquid plus sand environments showed\ud
that intermediate concentration, i.e. 40%, of the suspended sand particles in the test environment caused maximum wear rate/loss. However, this was substantially less than the liquid-only medium. The wear loss increased with traversal distance. The slope of the wear loss versus traversal\ud
distance plots was high initially followed by a reduced slope at longer traversal distances. This trend was very clearly visible in the liquid-only environment. Increasing traversal distance initially led to higher wear rate. This was followed by the attainment of a wear rate peak, a reduction in wear rate and finally a steady state wear rate at longer traversal distances. The average (cumulative) wear rate versus average (cumulative) wear loss plots showed acceleration, steady state and deceleration zones depending on the test conditions. Silicon particles, generated as a result of silicon addition in the alloy system, led to improved wear behaviour. Observed wear characteristics of the samples have been explained on the basis of operating wear mechanisms such as corrosion, erosion and abrasion. Predominance of one mechanism of material removal over the other(s) and the nature of various reaction products formed on the affected surfaces were thought to be responsible for specific wear behaviour of the samples under a given set of conditions. Examination of affected surfaces and subsurface regions further supported the wear characteristics of the specimens
STATIC AND DYNAMIC ANALYSIS OF TWO–LOBE FLOATING BUSH BEARING IN TURBULENT REGIME WITH NON–NEWTONIAN LUBRICANTS\ud
No full textModern large capacity turbo generators usually produce power in a range of 500–1200 MW running at 3000/3600 rpm. These turbo generators use rotor bearings which have diameter of 0.50m or more, leading to high journal surface speeds. The flow behaviour of the lubricant used in these bearings is in the super laminar regimes. In the published literature, Reynolds number as high as 7500 have already been reported. Still higher trends for Reynolds number are expected for larger turbo generators likely to be used in future. Further, to improve the characteristics of lubricants, the additives are added for specific engineering requirements. The viscosity of these lubricants having additives is not constant and usually some nonlinear relation between the shear stress and shear strain rate is found. In the field of hydrodynamic lubrication no significant progress has been made to find the performance characteristics of bearings using non-Newtonian lubricant due to difficulties involved in analytical treatment.\ud
In high speed applications, where stiffness and stability are major considerations, non-circular bearings (two-lobe, three-lobe etc.) are used. The non-circular bearing configuration, in general, gives better dynamic stability, reduced power loss and also provides larger oil flow as compared to plain journal bearing.\ud
The floating-bush bearings have definite advantage compared to the conventional journal bearings. The purpose of the ring is to reduce the shear losses by decreasing the relative speed between the matting surfaces.\ud
In the present work, static and dynamic performance characteristics of two-lobe floating bush bearing operating in turbulent regime using non-Newtonian lubricants have been studied.\ud
The modified Navier-Stokes equations along with the continuity equation in cylindrical co-ordinates, representing the flow-field in the clearance space of hydrodynamic journal bearing, are solved by Finite Element Method applying the Galerkin’s technique to obtain the bearing characteristics. A three-dimensional isoparametric element using 20 nodes for velocity and 8 nodes for pressure are used. The quadratic shape function for velocity distribution and linear for pressure distribution is employed to solve the Navier-Stokes and continuity equations. Mixed type of formulation for the interpolation function has been adopted for generating the element matrix as well as global fluidity matrix.\ud
To obtain a solution for non-Newtonian lubricant, firstly the three dimensional momentum and continuity equations for Newtonian lubricant are solved and then the solution is upgraded iteratively. The non-Newtonian effect is incorporated in each iteration by modifying the viscosity term using the cubic shear stress law and power law model. The nodal pressure and velocity components obtained for the Newtonian case is taken as initial trial solution for the non-Newtonian models. The shear strain rate for the respective non-Newtonian model is computed at each gaussian integration point for every element of the positive pressure fluid film region. The Newton-Raphson method has been used to compute the value of shear stress. The non-linear theory proposed by Elrod and Ng has been used to compute the turbulent viscosity coefficient. A direct iteration scheme with nested iteration is used first to upgrade the viscosity term and then to upgrade the local shear stress. The iterations are continued till the convergence criteria is achieved or the number of iteration exceeds a prescribed limit.\ud
As both the turbulence lubrication theory as well as the non-Newtonian lubricant models are non-linear, successive iterative scheme is used for computing the bearing characteristics. The static and dynamic characteristics are computed at various eccentricities over a range of Reynolds number up to 12000. The results for laminar condition are also obtained.\ud
A computer software in FORTRAN has been developed for computing the various static and dynamic characteristics of the bearing.\ud
Static characteristics of two-lobe floating bush bearing in terms of load carrying capacity, attitude angle, axial oil flow, friction coefficient and temperature rise parameter are computed for various Reynolds numbers in turbulent regime using both non-Newtonian models.\ud
Dynamic characteristics of the bearing in terms of four stiffness coefficients and four damping coefficients are calculated for various Reynolds numbers. The dynamic stability characteristics in terms of critical journal mass is also computed using routh's criteria.\ud
The results obtained revealed better performance in turbulent regime as compared to laminar condition for both non-Newtonian models. Two-lobe floating bush bearing has better dynamic stability in comparison to circular floating bush bearing.\u
Development and electrical conductivity behavior of copper-powder-filled-epoxy graded composites.
No full textAn analytical model for explosive compaction of powder to cylindrical billets through axial detonation.
No full textAn analytical model, describing an explosive compaction process performed axially on a powder assembly of cylindrical geometry, is discussed. The powder is encapsulated in a cylindrical metal container surrounded by an explosive pad, which is detonated parallel to the major axis of the compact. The pressure generated in the powder is a function of the nature and the thickness of the explosive material as well as the powder characteristics. The model is based on the principle of shock propagation in powder aggregate and, the detonation as well as the refraction wave characteristics of the explosives. For the purpose of validation and illustration, this investigation considers the explosive compaction of aluminium powder particles for different explosive pad thicknesses. The model brings-out a closed-form solution for densification of powders. The density of the final powder compact depends on the pad thickness. Inadequate pad thickness leads to under compacted core, while higher pad thickness leads to melting at the core leading to over all low density. The optimum pad thickness of the explosive to produce the highest densification is thus determined using the model. The densification depends on the size of the powder particles also, since; the heat generated by the high pressure shock wave melts the surface of the powder particles depending on the specific heat, thermal conductivity and the latent heat of the powder material. The study essentially covers the effect of the explosive pad thickness and the particle size of the powder on densification. The analytical results are compared with a few experimental data and the comparison is found to be satisfactory
High Sress Abrasive Wear Behaviour of Shot Peened AA2014 Al-Alloy
No full textAA2014 Al alloy specimens (in the form of plates) have been shot peened to varying intensity levels (0.14 to 0.48 mm ALMEN ‘N’) and the effect of shot peening intensity on the subsurface plastic deformation, surface and subsurface residual stress field, depth of peening and microstructure evolution has been investigated. The influence of shot peening intensity on the high stress abrasive wear behaviour has also been investigated. The wear rate reduced significantly due to mild shot peening. Intensive shot peening did not lead to any significant improvement in wear resistance, rather beyond a critical peening intensity, the wear resistance of material starts deteriorating.\u
`Multi-component sorption of Pb(II), Cu(II) and Zn(II) onto low-cost mineral adsorbent'.
No full textMulti-component sorption studies were carried out for attenuation of divalent heavy metal cations (Pb2+, Cu2+ and Zn2+) by a low-cost mineral adsorbent from the aqueous solution. Kinetic and equilibrium batch-type sorption experiments were conducted under variable conditions for multi-component using low-grade (<12%P2O5) phosphate rock. Percentage of multiple heavy metal species removal increases with decreasing initial metals concentration and particle size. The equilibrium data were well described to a lesser extent by Freundlich model but Langmuir model seemed to be more appropriate with the fixation capacity obtained at room temperature for Pb2+, Cu2+ and Zn2+ was 227.2, 769.2 and 666.6 micromol g(-1), respectively. Two simple kinetic models were tested to investigate the adsorption mechanism. Rate constants have been found nearly constant at all metal concentrations for first order. The comparison of adsorption capacity of low-grade phosphate rock decreases in multi-component system as compared to single component due to ionic interactions. X-ray powder diffraction (XRPD) technique was used to ascertain the formation of new metal phases followed by surface complexation. Used adsorbents have been converted into a value added product by utilizing innovative Zero-waste concept to solve the used adsorbents disposal problem and thus protecting the environment
Development and sliding wear behavior of milled carbon fiber reinforced epoxy gradient composites.
No full textMilled carbon fibre reinforced epoxy gradient composites were developed at different centrifugation speeds having 3 wt% of milled carbon fibre. Composites were also prepared at different RPMs. There is a gradient formation at all the speeds, which has been confirmed by variation in density of different zones. Highest rpm centrifuged sample gave best wear resistance as compared to others up to transition zone, i.e. 7.0 mm from outer most side. After transition zone, wear resistance suddenly decreased. This is because maximum compaction of milled carbon fibres occurred at outer most surface at 1100 rpm, which has been confirmed by observing the worn microstructure of composite. Sample prepared at 900 rpm after the transition zone shows maximum wear resistance due to the presence of more number of carbon fibres. In the worn microstructure flower formation as occurred at few places, after sliding where a few milled carbon fibres segregated in the composite due to minimum energy consideration
High stress abrasive behavior of shot peened AA2014A1-alloy.
No full textAA2014 Al alloy specimens (in the form of plates) have been shot peened to varying intensity levels (0.14 to 0.48 mm ALMEN ‘N’) and the effect of shot peening intensity on the subsurface plastic deformation, surface and subsurface residual stress field, depth of peening and microstructure evolution has been investigated. The influence of shot peening intensity on the high stress abrasive wear behaviour has also been investigated. The wear rate reduced significantly due to mild shot peening. Intensive shot peening did not lead to any significant improvement in wear resistance, rather beyond a critical peening intensity, the wear resistance of material starts deteriorating
Failure Analysis of Boiler Tubes
No full textLeakages were observedfrom the roof tubes on the secondpass of boilers # 6, 7 and 8 of\ud
Jeddah Phase-3 plant. Saturated steam flowed through the roof panel tubes made of\ud
carbon steel, the temperature outside the tube was around 1280°C and inside\ud
temperature was about 450°C. The tubes were having surficial cracks and pits on the\ud
fire-side of the tube wall. Methods of ultrasonic testing, optical and scanning electron\ud
microscopy, X-ray diffraction analysis and energy dispersive X-ray analysis were\ud
applied during investigations. The causes of the failure have been determined and the\ud
mechanism of corrosion has been discussed
Development of UHMWPE Modified PP/PET Blends and Their Mechanical and Abrasive Wear Behaviou
No full textIn this study, polypropylene and polyethylene terephthalate blend were modified by incorporating different percentages of ultrahigh molecular weight polyethylene (UHMWPE) ranging from 1 to 5 phr. Modified blends were prepared by melt mixing the PP/PET blend and UHMWPE. Ultimate tensile strength of UHMWPE filled blend was determined at 10, 20, 50, and 100 mm/min cross head speeds of testing. It was found that increase of cross head speed from 10 to 100 mm/min increases the tensile strength of PP/PET/UHMWPE blends. Maximum ultimate tensile strength is exhibited by the blend containing 2 phr UHMWPE. Breaking strain of the UHMWPE modified and unmodified PP/PET blend increased with the increase of cross head speed due to the highly entangled chain structure of UHMWPE. Shore A hardness of the filled blends also increased from 341 to 356, which is highest for 2 phr UHMWPE. High stress abrasive wear of UHMWPE modified blend was determined by using Suga abrasion tester, model NUS-1 Japan. Wear rate of the PP/PET(90/10) blends having 1, 2, and 5 phr of UHMWPE was determined at different loads such as 1, 3, 5, and 7 N and sliding distances from 6.4 m to 25.6 m. Wear rate values show that UHMWPE has prominent effect on abrasive wear of PP/PET blends. Addition of 2 and 5 phr UHMWPE improved the wear resistance of PP/PET blends at different loads, which has been explained on the basis of improved bonding as compared with pure PP/PET blend and increased hardness. Maximum abrasive wear rate reduction was achieved by adding 2 phr UHMWPE in PP/PET(90/10) blend. POLYM