Extrusion of axi-symmetric tubes from hollow and solid circular billets: : a generalised slab method of analysis and some experiments

To analyse the mechanics of extrusion of an axi-symmetric tube starting from either a hollow or a solid circular billet, a generalised analytical approach based on the slab method of analysis is developed for a somewhat general case of tube extrusion through a general profile-shaped die and over a general profile-shaped mandrel. The results of mean extrusion pressures obtained from the theoretical analysis for the various die–mandrel combinations are compared with the experimental investigation carried out on a model material and with the work of other authors. These show reasonably good agreements.     

Laser nitriding of tool steel: thermal stress analysis

In this paper, bees algorithm (BA) has been used for determine the optimal number of material handling equipment (MHE) used on the production centers. The unmet demands become zero at the end of the planning horizon, i.e., the part demands are totally satisfied through the horizon. The newly developed model provides network information, such as unmet demands and number of loaded and empty of MHE at any given time and centers. Consequently, the model provides a tool for helping managers with planning and decision-making in manufacturing systems. Computational tests showed that small-sized instances can be solved by the exact approach in a fair amount of central processing unit time, but it is not feasible for medium and large-sized instances. To tackle this problem, a bees algorithm is proposed to solve the model. The algorithm is a search procedure inspired by the way honeybees forage for food. The results obtained show the robust performance of the bees algorithm.     

Evaluation of corrosion behavior of Al-Mg-Li alloys in seawater

Weldalite 050, a high-strength Al-Mg-Li alloy, was evaluated for its corrosion resistance in deaerated and air saturated Arabian Gulf water to determine its suitability for marine applications. Weight loss and electrochemical studies showed that the alloy had minimum corrosion rates of 1.82 and 4.82 mpy (mils per year), respectively, in deaerated and air saturated Arabian Gulf water with very high total dissolved solids (TDS) content. Weldalite 050 exhibited good resistance to corrosion at velocities up to 3.9 m/s. The formation of Al₂MgLi, Al-Li, Al₁₂Mg₁₇, and Al-Li precipitates has a pronounced effect on its corrosion resistance. The corrosion resistance of Weldalite 050 compares favorably with that of alloys 5052 and 5054, wrought alloys 6061 and 6013, and silicon carbide (SiC) reinforced alloys 6061 and 6013.     

A new asymmetric dual source multilevel inverter topology with reduced power switches

Multilevel inverters can synthesize a high-voltage staircase waveform with low- and medium-voltage components. A new multilevel inverter topology called Asymmetric Dual Source Multilevel Inverter (ADS-MLI) is proposed. When compared to the topologies found in the literature, it can produce multiple levels in the output voltage with fewer power switches. Most of the topologies found in the literature require cascading features to achieve asymmetric operation; but the ADS-MLI can operate without the need for cascading. A simulation prototype capable of synthesizing 13 levels is developed in MATLAB Simulink environment. Its performance is evaluated in the aspects of; number of switching components, efficiency, THD, switching voltage stress and common mode voltage. The simulated efficiency and power quality of the DS-MLI is validated using a 1 kW prototype fabricated using FGA25N120-ANTD controlled by FPGA-SPARTAN 6 processor. Further, the DS-MLI is field tested with a 1 kW solar PV unit and the results are presented.     

Effect of suspended solids on the flow-induced corrosion of a modified Al-2.5Mg alloy in arabian gulf water

Suspended solids increase the rate of corrosion and decrease the resistance of a modified Al-2.5Mg alloy to pitting in Arabian Gulf water. It has been shown by electrochemical studies that the pitting potential of the alloy shifts to more negative values in the presence of suspended solids. The rate of mass transfer and the limiting current is significantly increased by suspended particles.     

The clearing of dyed polyester. Part 1. A comparison of traditional reduction clearing with treatments using organic reducing agents

Reduction clearing using aqueous sodium dithionite under alkaline conditions at elevated temperatures is commonly carried out as an aftertreatment to remove deposits of disperse dye and other impurity residues from the surface of dyed polyester. In this paper, the effect of conventional reduction clearing on the colour and fastness properties of polyester dyed with a series of selected commercial disperse dyes at a range of depths of shade is established, and an understanding of the scientific principles is developed. The results correlate closely with an assessment of surface dye removal by cold acetone extraction of the dyed samples. Because of certain environmental, technological, and economic disadvantages associated with traditional reduction clearing using sodium dithionite, there is industrial interest in alternatives. Thus, this paper also describes a study of the use of two organic reducing agents, thiourea dioxide and hydroxyacetone, and the relative merits of the three processes are discussed. The outcome of clearing varies with the particular dye. Mechanistic explanations are proposed, based on individual characteristics of the molecular structures of the dyes. Scanning electron microscopic investigations of the surface of dyed samples before and after reduction clearing were qualitatively consistent with the assessments of the technical performance. This paper is the first in a series in which we will subsequently report further comparative studies, based on similar methodology, exploring alternative clearing processes.     

MICROBIALLY FORMED CATALYSTS FOR ENHANCEMENT OF DIRECT COAL LIQUEFACTION

The present study examines the potential to biologically precipitate active catalytic compounds on the surface of coal particles in a water slurry. These compounds could be active forms of iron, an element abundant in coal, or active forms of molybdenum added as a soluble salt. The acidophilic microorganisms Thiobacillus ferrooxida/ns and Acidianus brierlyi were added to a 5% coal slurry at a pH of 3·0 or less. Experiments were carried out for 21 days in shake flasks/automated fermentor at constant temperature and pH. Deposition of iron and molybdenum compounds on the particle surface was confirmed by several spectroscopic methods. After bio-treatment, the coal was removed by filtration and dried. A sample was then liquified in a bomb at 385°C in tetralin and hydrogen for 15 minutes. In some runs the sulfiding agent dimethyl disulfide (DMDS) was added to the mixture. Separation of the products was by soxhlet extraction. Total conversion, gas + oil + asphaltenes + preasphaltenes, of the pretreated coal was compared with the conversion of raw, untreated coal. Statistically significant increases in conversion were achieved for various pre-treatment methods. The maximum conversion achieved was with coal pre-treatment in the presence of Acidianus brierleyi, and with the addition of 200 mg/1 of ammonium molybdate to the slurry. Under these conditions, liquefaction of 2 separate runs, in the presence of DMDS, produced conversion of 78 and 81%. This compared with 48% conversion for the raw coal under the same liquefaction conditions.     

Effect of nano Al (Scx−1Zrx) precipitates on the mechanical and corrosion behavior of Al‐2.5 Mg alloys

Microanalytical, mechanical, and corrosion studies were undertaken to investigate the effect of nano‐precipitates of Al(Sc_x−1Zr_x) on the mechanical and corrosion characteristics of Al 2.5 alloy containing 0, 0.15, 0.3, 0.6, and 0.9 wt% of Sc with 0.15 wt% Zr. Addition of 0.3% Sc significantly increased the yield strength due to small precipitates sizes (5–19 nm) and the high coherency of the nano‐particles. Largest contributor to the strength was grain boundary strengthening caused by pinning of grain boundary precipitates. The alloys showed a good resistance to corrosion in 3.5 wt% neutral chloride solution. The alloy offered a high passivation tendency because of homogeneous coherent nano Al(Sc_x−1Zr_x) precipitates. The nano precipitates interfaces and homogeneously distributed Al₃Sc precipitates offer a high degree of corrosion resistance to Al 2.5 Mg Sc alloys compared to conventional aluminum alloys, such as Al 6061 and Al6013.