Enhancement on Al–Mg–Si alloys against failure due to lightning arc occurred in energy transmission lines

This article has been prepared to share some experience and technical investigation related to lightning and short circuit strength of the OPGW type conductor used in transmission lines. It is well known that overhead ground wires are vulnerable to strand breakage due to lightning strikes. Recently applications of composite fiber optic ground wire have become more important to protect them from such damage. In this paper, we present test results before and after application of modification to the main conductive part of the conductor, which is composed of AA-6101 alloy, galvanized steel and SS-steel tube with fibers. Modification of AA-6101 aluminum alloy was performed by adding 3% AlB₂ into molten metal. After having completed manufacturing of the improved feedstock at CCL, we performed the drawing and stranding of wires.     

Modification of AA-6201 alloy for manufacturing of high conductivity and extra high conductivity wires with property of high tensile stress after artificial aging heat treatment for all-aluminium alloy conductors

In this paper, a modification method to manufacture high conductivity (HC) and extra high conductivity (EHC) wires with high strength properties from AA-6201 redraw rod has been presented. In the experiments, redraw rod has been produced using an extrusion press. In conventional heat treatment processing of HC and EHC wires produced from unmodified AA-6201 alloy, the wires should be exposed to artificial aging at 175 °C with soaking time higher than 6 h or at 195 °C/4 h to have conductivity above nominal value 52.5–53%IACS. Thus, wires gain high conductivity but decrease their tensile stress due to incoherence precipitation. However, this negative effect on the tensile stress can be prevented by the method explained in this study. This is inoculation of molten AA-6201 alloy in tundish with 3% AlB₂ compound in 9.5-mm rod form to decrease detrimental effect of Ti, Cr, Zr and V on the conductivity. Thus the wires produced from modified alloy do not need treatment time higher than 6 h at 175 °C to reach high and extra high conductivity. So, the alloy wires have got rid of exposing excessive aging and keep their tensile stresses at maximum level due to treatment at low temperature. Inoculation principles of the molten metal and homogenisation parameters that affect properties of HC and EHC wires were explained in details. Using modified AA-6201 wires AAAC conductor with extreme conductivity and also tensile stress was manufactured. Results from measurements of tensile and conductivity of HC and EHC wires taken from conductor samples have been tabulated to show effects of AlB₂.     

Influence of Tool Geometry in Friction Stir Welding

In this article we highlight the results of a recent study undertaken to understand the influence of tool geometry on friction stir welding (FSW) of an aluminum alloy with specific reference to microstructural development, defect formation, and mechanical response. The welding trials were made on 4.4 mm thick sheets using tools made of die steel and having different diameters of the shoulder and the pin, and the profile of the pin. Throughout the welding operation, the rotational speed, traverse speed, and tool axial tilt were held constant at 1400 rpm, 80 mm/minute, and 0 degrees, respectively. For a shoulder diameter of 20 mm and a pin diameter of 6 mm, the severity of defects in the weld was found to be the least and the resultant tensile strength of the weld was high. For the welds that were made using a tool having a shoulder diameter of 10 mm and a pin diameter of 3 mm the tensile strength of the weld was the least since the degree of defects observed were higher.     

Preceramic polymer derived cellular ceramics

Ceramic foams were prepared by a self-blowing process of a poly(silsesquioxane) melt at 270 °C. The cell size, the interconnectivity density and the shape of the foam cells were adjusted by a thermal pre-curing procedure of the polymer at 200 °C. Inorganic fillers were used to modify processing behaviour and properties of the pyrolysed ceramic foam. After pyrolysis in inert atmosphere at 1200 °C ceramic composite foams with a total porosity up to 87% were obtained. The open cell ceramic foams had a mean cell diameter of 1.2 mm and a mean strut thickness of 0.2 mm. Interpenetrating phase composites (IPCs) were fabricated by infiltrating the open cellular ceramic preform with Mg alloy melt at 680 °C and a pressure of 86 MPa. The mechanical properties were found to depend on the reactions between the metal and the ceramic forming MgO, Mg₂Si and Al₁₂Mg₁₇ as the major reaction products. The IPCs showed a significantly higher creep resistance at 135 °C, compression strength and elastic modulus compared to the unreinforced magnesium alloys.     

DISTRIBUTIONS OF THE TANGENTIAL VELOCITIES ON THE DUST LADEN GAS FLOW IN THE CYLINDRICAL CYCLONE DUST COLLECTOR

The authors measured the distributions of the tangential velocities of the feed dust concentration C_o = 0. 6 ~15. 0 g/ m³ by the hot wire anemometers. The test dust was fly-ash which had the mean diameter Xpn = 2.03 μm. The used cylindrical cyclone had the diameter D1 = 140 mm, the diameter of the exit pipe D2 = 50 mn and the total length HT = 382 mm. In order to measure the fluctuating velocities and the time mean velocity on the dust Iaden gas flow and on the pure air flow, we had applied two kinds of the hot-wires. The flow Reynolds number Rec was Rec = Qo/HiV = 797~5582. The expert mental results sho-ed that there were no distinct differences of the time mean and fl uctuating velocities between the pure air flow and the dust laden gas flow. Then the authors have tried to explain those expert mental results by the response time of the fine solid particles and that of the scale of the nixing length in the turbulent rotational air flow.     

PIPELINE TRANSPORT OF COARSE PARTICLES BY WATER AND BY FLUIDS WITH YIELD STRESSES

Experiments have been conducted using 1.7 mm and 4 mm particles transported in a pipe 52 mm in diameter. The carrier fluids were water and clay slurries with yield stresses. In several experiments the yield stresses were high enough to support the particles in non-flow situations.

A two layer model was found to be appropriate for interpreting the pressure gradients, with both Coulombic and kinematic friction playing important roles. Kinematic friction appeared to confirm recent experimental results obtained with relatively coarse particles in vertical flows.     

Compression Testing of Ti-6Al-4V in the Temperature Range of 303-873K

Compression testing of Ti-6Al-4V alloy has been carried out at temperatures between 303 K to 873 K. To prevent embrittlement due to atmospheric oxygen and nitrogen, the samples were given a glass coating, which also acts as a lubricant simultaneously. Dynamic Strain Aging was observed to occur in the temperature range of 600 K to 800 K. Below 600 K stresses were high. Warm working has to be done above 800 K but below 1163 K (0.6 T_m where T_m = 1940 K) which is the recrystallization temperature. Based on these conclusions, warm extrusion has been successfully carried out in the Materials Forming Laboratory of I.I.T., Madras, Chennai, India.     

Optical Probe for the In-Line Determination of Particle Shape, Size, and Velocity

A laboratory optical probe was developed to simultaneously determine the following particle characteristics: circularity, particle projection area, equivalent diameter of a circle, length of the particle outline or perimeter, maximum chord length, aspect ratio, and particle velocity. Using the projection area and the perimeter, the particle shape factor circularity can be determined. The aspect ratio was approximated by the ratio of the equivalent diameter to the maximum chord length. The basic measuring principle is multi-point scanning of the particle shadow image by a line of optical fibers. In addition, the particle velocity can be measured by a differential spatial filter of optical fibers. These fibers are step index fibers with a core diameter of 64 µm and cladding of 70 µm. The shadow image of a single particle was generated by a parallel laser beam. The uncertainty of the measured circularity and aspect ratio was investigated by using metal wires with diameters of 0.12 to 0.5 mm as test particles with known circularity and aspect ratio. The standard deviations were 1.9% for the circularity and 15.5% for the approximated aspect ratio. In addition, the optical probe system was investigated by measurements of solid particles with different shapes. As an example, the results of sand, marjoram seed, and metallic oxide particles are shown. Using 1000 sand particles, the correlation between equivalent diameter and particle velocity could be demonstrated. The presented configuration of the optical probe is applicable in the size range of 0.1 to 0.9 mm and up to a particle velocity of 5 m/s.     

GAS HOLDUP IN BAFFLED BUBBLE COLUMNS OF DILUTE SLURRIES OF FINE POWDERS AND VISCOUS LIQUIDS

Experimental gas phase holdup data reported by the authors as taken on two baffled bubble columns and involving slurries of fine powders (average particle diameter ≤90 μm) and dilute suspensions (mass fraction ≤ 20 percent) in viscous fluids are re-examined after correction for a small calculation error in superficial gas velocity. The two bubble columns are: a Plexiglas bubble column, 0.108 m in diameter and 2.25 m tall, equipped with seven 19 mm tubes arranged in equilateral triangular configuration with a pitch of 36.5 mm and a Pyrex glass column, 0.305 m in diameter and 3.24 m tall, equipped with thirty-seven 19 mm tubes arranged in the same configuration. Air and nitrogen are used as gas phase, water and Therminol as liquid phase, and iron oxide powders, glass beads and sand as solid phase. The small column data are at ambient temperature while those belonging to the large column extend from ambient to 473K. These data are examined to assess the influence of column diameter (scale-up), temperature, slurry concentration and viscosity, and superficial gas velocity on gas holdup for baffled columns.

It is found that in the 0.108 m diameter column the holdup is about the same for axial probes of different diameters, 19 mm, 31.8 mm and 50.8 mm, for two-phase systems involving liquids of small (water) and large (Therminol) viscosities. However, when a seven-tube bundle is installed, the holdup increases. This is consistent with the bubble dynamics and observed bubble sizes. This qualitative trend is also upheld by three-phase systems involving dilute slurries of fine powders. In the larger column when fully packed with a thirty-seven tube bundle, the holdup is found to be the same as for the small column. A loosely packed bundle gives smaller holdup at temperatures greater than the ambient due to the larger size of bubbles. The gas holdup is greater for a less viscous system and this is again due to the larger size of bubbles in a more viscous system. The influence of temperature is pronounced and is very characteristic of the nature of liquid involved. For example for water and Therminol the variations are in opposite directions with change in temperature. Bubble splitting and foaming control the nature of these dependencies. With the addition of solids the holdup is almost insignificantly altered at all temperatures.     

Metal foams as compact high performance heat exchangers

Open-cell metal foams with an average cell diameter of 2.3 mm were manufactured from 6101-T6 aluminum alloy and were compressed and fashioned into compact heat exchangers measuring 40.0 mm × 40.0 mm × 2.0 mm high, possessing a surface area to volume ratio on the order of 10,000 m²/m³. They were placed into a forced convection arrangement using water as the coolant. Heat fluxes measured from the heater-foam interface ranged up to 688 kW m⁻², which corresponded to Nusselt numbers up to 134 when calculated based on the heater-foam interface area of 1600 mm² and a Darcian coolant flow velocity of approximately 1.4 m/s. These experiments performed with water were scaled to estimate the heat exchangers’ performance when used with a 50% water–ethylene glycol solution, and were then compared to the performance of commercially available heat exchangers which were designed for the same heat transfer application. The heat exchangers were compared on the basis of required pumping power versus thermal resistance. The compressed open-cell aluminum foam heat exchangers generated thermal resistances that were two to three times lower than the best commercially available heat exchanger tested, while requiring the same pumping power.     

COARSE PARTICLE WALL FRICTION IN VERTICAL SLURRY FLOWS

Experiments have been conducted using spherical glass particles transported in a recirculating flow loop with internal pipe diameter of 40.9 mm by water and by ethylene glycol solutions. Particle diameters were 1.8 and 4.6 mm and the solids concentrations ranged from 9% to 38% by volume.

Pressure gradients have been interpreted in terms of a particle friction factor which depends upon factors first identified by R.A. Bagnold in experiments conducted by shearing neutrally buoyant suspensions in a concentric cylinder viscometer.     

Age Hardening Behavior of Wrought Al-Mg-Sc Alloy

Ageing of Al-6Mg alloy doped with varying concentration of scandium ranging from 0.2 wt% to 0.6 wt% has been carried out. Cold-rolled alloy samples are isochronally aged for 60 minutes at different temperatures. The cast and hot-rolled samples are also aged isochronally for 90 minutes at different temperatures up to 450°C. Isothermal ageing of cold-rolled samples is conducted at various temperatures for different periods of time ranging from 30 to 480 minutes. Hardness values of the differently processed alloys have been measured to understand the ageing behavior of Al-6Mg alloy with scandium addition. The hot-rolled alloys after ageing do not show any hardening response due to ageing. Ageing of cold-rolled alloys envisaged precipitation of Al₃Sc which is not noted to be dislocation induced. The kinetics of precipitation of Al₃Sc in Al-6Mg-Sc alloys are found to be controlled by the diffusion of scandium in aluminum.     

CHARACTERISTICS OF A HORIZONTAL SWIRLING FLOW PNEUMATIC CONVEYING WITH A CURVED PIPE

In order to prevent flow blockage phenomenon and to reduce the impact of particles on the wall of the bend, an experimental study of the swirling flow pneumatic conveying system with a horizontal curved pipe was carried out in this work. The experiment was performed in a 90-deg pipe bend with pipe diameter 75 mm and centerline curvature ratio 12. The straight pipes with 75 mm inside diameter at the upstream and downstream of the bend were 1.3 m and 4.0 m in lengths, respectively. The initial swirl number was varied from 0.22 to 0.60, the mean air velocity from 10 to 20 m/s, and the solid mass flow rate from 0.07 to 0.68 kg/s. It is found that in the lower air velocity range, the overall pressure drop of the swirling flow pneumatic conveying shows a lower tendency than that of axial flow pneumatic conveying. The minimum air velocities can be decreased by using the swirling flow pneumatic conveying. From the visualization of particle flow patterns, the impact of particles on the wall of the bend can be reduced using the swirling flow.     

Controlling the Structural Integrity of Injection Molded Parts in Debinding and Sintering by Experimental Design

The preservation of the structural integrity of injection molded Fe-8% Ni in debinding and sintering was studied using four spherical ball specimens having diameters of 10 mm, 20 mm, 30 mm and 40 mm. Different degrees of defects existed in the as-molded specimens due to jetting during molding, which subsequently transformed into cracks when the debinding conditions were not properly controlled. The manifestation of molding defects during debinding was most severe for specimens having a green diameter of 40 mm, but could be avoided by optimizing the extraction temperature in solvent debinding and the heating rate in thermal debinding. For the processing conditions selected in the experimental trials which were designed using the Taguchi method, distortion as a result of slumping could be reduced to a magnitude close to the ±0.3% tolerance commonly quoted for metal injection molded parts.     

Fixed Abrasive Diamond Wire Saw Slicing of Single-Crystal Silicon Carbide Wafers

This article investigates the slicing of single-crystal silicon carbide (SiC) with a fixed abrasive diamond wire. A spool-to-spool rocking motion diamond wire saw machine using a 0.22 mm nominal diameter diamond wire with 20 µm average size diamond grit was used. The effect of wire downfeed speed on wafer surface roughness and subsurface damage was first investigated. The surface marks generated by loose diamond grit and stagnation of the wire during the change of the wire-cutting direction were studied. The use of scanning acoustic microscopy (SAcM) as a nondestructive evaluation method to identify the subsurface damage was explored. Effects of using a new diamond wire on cutting forces and surface roughness were also investigated. Scanning electron microscopy has been used to examine the machined surfaces and wire wear. This study demonstrated the feasibility of fixed abrasive diamond wire cutting of SiC wafers and the usage of a SAcM to examine the subsurface damage.     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

Extrusion Processing of High-Strength Al Alloy 7055

The effects of a combination of extrusion processing parameters and aging schedules on the microstructure and mechanical properties of the 7055 Al alloy were investigated. A safe extrusion processing zone is determined through a limit diagram constructed over the experimental initial billet temperature ranging from 380° to 420°C, extrusion ratio from 10:1 to 40:1, and the ram speed ranging from 1 to 15 mm s^-1. Microstructural characterization of as-extruded, solution-treated, and artificially-aged materials was carried out using polarized light microscopy (for grain structure) and transmission electron microscopy (for precipitate morphology). A combination of hardness and tensile tests was used to evaluate mechanical properties. It is shown that in 7055 Al alloy, the optimization of alloy composition, extrusion processing parameters, and peak aging treatment results in reproducible tensile properties of 0.2% P.S. = 725 MPa, UTS = 750 MPa, and % elongation = 12.9. In order to improve the stress-corrosion resistance of peak aged material, retrogression and reaging (RRA) temper was established. A strength-electrical conductivity relationship has been established for the RRA temper between 36% and 37% International Annealed Copper Standard (IACS) electrical conductivity to enable selection of suitable combination of properties.     

PARTICLE SIZE ANALYSIS FOR OFLOXACIN, PREDNISOLONE ACETATE, AND AN OPHTHALMIC SUSPENSION CONTAINING THE OFLOXACIN/STEROID DRUG COMBINATION

Image analysis (LA), Photon Correlation Spectroscopy (PCS), and Single Particle Optical Sizing (SPOS) have been applied to the analysis of particle size for ofloxacin, prednisolone acetate and an ofloxacin/prednisolone acetate ophthalmic suspension. LA shows that ofloxacin particles suspended in mineral oil are on the order of 10 µor less. LA of prednisolone acetate in H₂O shows that the steroid particles are agglomerated and range in size from 20 to 50 µ. SPOS is used to verify LA results for prednisolone acetate. LA of the ofloxacin/steroid balled milled suspension yields a particle size of ∼ 1 µ with a few particles on the order of 5 µ, PCS analysis of three batches of ball-milled ofloxacin/steroid suspension shows that increased ball-milling time increases the reproducibility of the mean diameter value as determined by PCS. It is also observed by PCS that the mean diameter of the steroid achieves a constant value with ball-milling from 11 to 14 days (1386.4 to 1383.4 nm). Extended ball-milling past the 14 day time point (18 days) appears to reduce sample inhomogeneity, thereby eliminating larger particulates with a subsequent reduction in the mean diameter to 1097.4 nm, Results for PCS analysis of the ball-milled ofloxacin/steroid suspension are verified by SPOS.     

Motion of Large Particles in a Horizontal Pneumatic Pipe

The horizontal pneumatic transport of large particles with particle to pipe diameter ratio of 0.6 and particle densities of 928 kg/m³ and 2193 kg/m³ was examined experimentally and numerically. The pipe diameter and length were 10 mm and 8.8 m, respectively. The mean air velocity was between 14.2 m/s and 23.0 m/s and the number feed rate of particle was almost constant at seven per second. In this study, the method of characteristics was used for the simulation of gas flow, which considered not only the particle-particle collisions but also the particle-wall collisions. It is found that particle transport is possible even when the mean air velocity is smaller than the terminal settling velocity of particle's and that the arrival time intervals at the downstream section are not always uniform although the particles are fed uniformly. Furthermore, the velocity difference between different density particles becomes small as the mean air velocity decreases, because the particle velocities become uniform due to particle-particle collisions, and the ratio of particle velocity to the mean air velocity is almost independent of air velocity. In addition, it is shown that the particle-wall collision at the pipe joint due to pipeline misalignment can be one of the sources of bouncing motion of particles as shown by simulation results.     

SIZE AND HYDRATION CHARACTERISTICS OF LABORATORY SIMULATED JET ENGINE COMBUSTION AEROSOLS

Size and hydration characteristics for laboratory simulated jet engine combustion aerosols are reported and the validity of these simulated data is discussed. The jet fuels JP4, JP5, JP8 and JET A were burned in laboratory burners designed to simulate the lean pre-mixed, pre-vaporized advanced combustor concept. Significant quantities of aerosols were detected and in most cases their size and hydration properties were similar. Dry particle size distributions were single mode extending over the diameter range 0.014 to 0.200 microns, with peak diameters in the range 0.020 to 0.050 microns. The distributions were observed to vary with combustion stoichiometry, increasing the peak particle diameter as the combustion stoichiometry shifted from leaner to richer conditions. Critical supersaturation spectra for each fuel are presented. A mean ratio of cloud condensation nuclei to condensation nuclei (CCN/CH) has been calculate for each fuel: JP4 = 32%, JP5 = 42%, JET A = 39%, and JP8 = 35% indicating that in general 30 - 40% of the combustion aerosols generated with these laboratory burners can be considered cloud condensation nuclei.