Joseph I. Achebo

Development of a New Flux for Aluminium Gas Welding

A new flux based on NaCl – CaCl2 – CaF2 – Na3AlF6 was developed for the gas welding of aluminium and its alloys. The flux was generated by the application of the Hadamard multivariate chemical composition model. The model uses a 8 x 8 matrix and a full factorial analysis to generate several compositions within given ranges of the constituent flux elements. Mechanical and field tests were carried out on weldments made with the flux. The tensile strength, Izod impact strength and hardness of the all – weld metal were 310MPa, 5.35J and 100BHN. The weld deposition efficiency was 90.3%.The new flux and two popular commercial fluxes were given to five expert aluminium welders to use for three months, and were requested to rate the performances. The results showed that there was an agreement between the responses of the welders that the new flux performed better than the commercial versions available in Nigeria.

Toxicokinetic Analysis of Asymptomatic Hazard Profile of Welding Fumes and Gases

In this research paper, 15 welders with about 1–20 years working experience in a welding firm, and who had also been diagnosed with fume related illnesses, were investigated. The fumes generated from E6010 electrodes using the shielded metal arc welding (SMAW) process, were collected and analyzed. A fume formation rate of 0.195 g/min was obtained under normal operating conditions and the average size of the agglomerated particles was found to be 2.14 ?m. Such fine particles would easily settle within the welders’ lungs; and the minute morphology of these fume particles, makes them deleterious to health. It was discovered that the critical time frame of 8.1–13.3 years, was the expected time range within which the welders were likely to begin to have symptoms. Crucially, it was determined that hazard rate is proportional to the expected time within which a welder actually becomes ill. Hence it is recommended that the evolution of toxic gases should be controlled at source. This study has comprehensively considered the hazard profile of welding fumes and gases which have evolved during the SMAW process.

A Multi-Parametric Analysis of Drift Flux Models to Pipeline Applications

Several interactions occur between the constituents of effluents within a pipeline (fluid, particles, and the pipeline interface). These interactions are birthed from their constant motion in one point in a pipeline relative to another point within the same pipeline. These constant motions expressed through various Drift Flux models are amenable to multi-parametric analysis. This particular exercise successfully elucidates the working parameters used in obtaining the drift flux equations. It utilizes a step by step self explanatory method for calculating the terminal velocity of effluents, being the volumetric flux or relative velocity of fluid/fluid or fluid/particle or fluid-particle/wall interfacial flow contact. Thus, forces encountered as a result of these relative motions are then specifically examined within the parameters of drift flux models. This study, in further applying a multi-parametric analysis of these drift flux models therefore acts as a template which could be used for solving pipeline problems involving these relative motions, once the necessary data has been collated and subsequently computed.

Development of a predictive model for determining mechanical properties of AA 6061 using regression analysis

Aluminum alloys (AA) such as AA 6061 are difficult to weld, and their application to high-strength demands tends to be limited because of their inherently low-strength threshold levels when compared to other alloys. To effectively use this alloy to its full potential, its tensile strength, is investigated. In actual manufacturing settings, it has proven beneficial to attempt a prediction of the tensile properties of potential weld joints. To achieve this, a model was developed using the multiple linear regression analysis to predict these tensile properties such as the ultimate tensile strength, the yield strength (YS), and percentage elongation (% Elong). It was found from the scattered diagrams that the measured and predicted values were almost a perfect fit with a coefficient of determination of between 0.99 and 1.0. The analysis of variance further validated the adequacy of the model. The analysis showed that the claims observed in the study match with those of other investigators. The predictive model obtained is expected to help the welding community to pre-determine the tensile properties of AA 6061 weldment using selected values for each of the process parameters applied in this study.

Numerical Computation of Melting Efficiency of Aluminum Alloy 5083 During CO 2 Laser Welding Process

This chapter is aimed at determining the melting efficiency of aluminum alloy 5083 during CO2 laser welding process. Theoretical models were used for the melting efficiency determination as proposed by other investigators which also included an examination of the fluid flow pattern of the alloy. The results obtained indicate that the acceptable melting efficiency calculated was 38%. This value compares well with and falls within the range of other values reported in other literature. The theory of metal melting as it relates to laser welding depends on the thermal state of the material under investigation. Applying high laser power under a controlled environment would achieve deeper penetration with fewer heat affected zones; therefore a deep understanding of the chemo-physical properties of a metal is required to determine its melting efficiency and these properties have been adequately treated in this study.

Comparative Analysis of Vaporization Rates of 5456 Aluminum Alloying Elements during CO2 Laser Welding

In this paper, the vaporization rates of Mg2+ and Al+ alloying elements of a 5456 aluminum plate were investigated using the CO2 laser welding process. The models proposed and used by Block-Bolten and Eagar in 1984 and Zhao and DebRoy in 2003 were applied with experimental results generated from this study. The vaporization rate of Mg2+ ions and Al+ ions using the equations proposed by Block-Bolten and Eagar gave 8.76 μgs-1cm-2 and 0.0465 μgs-1cm-2 respectively, whereas the equation proposed by Zhao and DebRoy gave 6.7 μgs-1cm-2 and 0.016 μgs-1cm-2 respectively. These values are within the reported values obtained by Block-Bolten and Eagar (1984). The heat transfer coefficient for Mg2+ and Al+ ions were also obtained. The vapor bubble radius including the surface tension and buoyancy forces were examined. The evaporative power and energy losses as a result of these bubbles’ collapse were calculated. The paper clearly shows the comparative analysis of alloying elements’ vaporization process in the aluminum metal heating process.

Rheological Flow Study of Molten Weld Metal Using the Modified Casson Prediction Model

This paper principally examines the flow pattern that occurs when molten weld metal droplets are detached from globule formations at the tip of an electrode and are thereafter transported to the weldpool. This viscoplastic flow study was done using the modified Casson prediction model which is based on the Newtonian Homogenous Flow equations. Both chemical and mechanical tests were done. The inclusions (Slag) were found to possess an upward flow of 3 ms-1. The mechanical test results show that the shear stress of 483.2 MPa, which exceeded a yield stress of 230 MPa, was responsible for the continuous slipping movement of the molten metal towards the center of the weld pool at a velocity of 1.2ms-1. The results obtained by the application of this model were validated by both computational and experimental results obtained by other researchers.

Computational Analysis of Condensed Vaporized Alloying Elements of 5456 Aluminum Alloy

A lot of research has been done regarding the vaporization rates of alloying elements in general. However, not as much has been done on vaporized alloying element condensates. This paper investigates the drop wise pattern under a controlled thermal environment using some existing models with a few modifications to suit experimental results. From the analysis it was found that the condensation factors for Mg2+ and Al+ ions were 0.7 and 0.98 respectively. These results show that Mg2+ ions are more volatile than Al+ , and that any ions left which are usually unaccounted for would usually have been lost to spatter, or alternatively absorbed by the plasma ions within the laser welding environment. The conduction mode of heat transfer was found to be a dominant factor especially in the vicinity of the cooler regions of the metal. A vapor temperature of 2537oC was also calculated. This amounted to about 2% more than the expected boiling temperature. This paper has effectively and quantitatively analyzed the condensation process of 5456 aluminum alloy. It explicitly elucidated the approximate values of vaporized alloying elements and clearly shows how their molecular weights were affected by temperature.

Quantitative Determination of Fluid Flow Induced Corrosion Rate of an Oil Pipeline

This paper is aimed at discussing the effect ofcorrosion propagation caused by the presence ofoxygen in fluid flow induced corrosion in a pipeline.The yield and wall shear stresses of the carbon steelpipeline and the fluid flow pattern were studiedrespectively using the Newtonian flow model. It wasobserved that mass momentum and mass transfer ofthe fluid velocity properties induced the shear stressthat surpasses the yield stress of the internal surfaceof the pipeline. The shear properties which could beresponsible for wear could further expose theinternal geometry of the pipe which would alter themicrostructural arrangement of the pipe. This ineffect influenced the oxygen penetration that allowedthe electrochemical reaction between the metal andthe water to occur. Numerical method was used tocompute the expected corrosion rate of 35.6 mm/yearand compared with the measured corrosion rate of35.95 mm/year which nearly matched. This resultshows that the generated numerical method waspotent.

Computational Analysis of Flow Properties That Could Cause Pipeline Failure

This paper examines a fluid-particle flow systemwith constant pipe burst problems. Particles fromthe reservoir were found to be a major threat to theservice life of conveying pipelines. This isresponsible for about 65% of pipeline leakages inNigeria. This study was done to find computationalmethods to solve the problem. Equations derivedcould be used to determine fluid flow propertiesresponsible for pipe failure. Pipeline material yieldstress was integrated as a substantial factor; theshear stress that would ordinarily develop throughhard particle inclusions in the turbulent mass flowoccurring in the transmission pipelines, couldincrease the pressure and at the same timepropagate wear, in turn leading to pipe burst.Model equations were developed that could help tocontrol such failure. The study also expresses themass transfer behavioral pattern of any such fluidand the interaction with the internal surface ofpipelines. The expected pressure drop is alsointegrated to obtain realistic results of the flowproperties. Adaptation of this equation couldreduce pipeline leakages.