The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform

M. L. Quintino - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of the amount of nanoparticles emitted in welding fume from stainless steel using different shielding gases.
    Inhalation toxicology, 2017
    Co-Authors: Rafael Palhotas Pacheco, João Gomes, Rosa Maria Mendes Miranda, M. L. Quintino
    Abstract:

    The primary objective of this study was to correlate the emission of macro and nanoparticles released during the process of metal inert gas/metal active gas (MIG/MAG) of stainless steel with different gas mixtures. Using different gas mixtures with different heat inputs, it was possible to determine fume formation rates and surface areas of nanoparticles with alveolar lung deposition capacity. It was found, how the various Transfer Modes and the type of gas protection, in particular, the percentage of active elements in the chemical composition of the gas, affect the amount of fumes generated and also the generation of nanoparticles with a high capacity of deposition. The Spray Transfer Mode always shows higher values of nanoparticles surface area, unlike the fume formation rates. Among the tested mixtures 82%Ar + 18%CO2 generates higher emissions of nanoparticles as well as fume formation rates.

J Haidar - One of the best experts on this subject based on the ideXlab platform.

  • An analysis of the formation of metal droplets in arc welding
    Journal of Physics D: Applied Physics, 1998
    Co-Authors: J Haidar
    Abstract:

    A dynamic two-dimensional arc Model has been used to investigate the effects of the various forces acting on the droplet in gas metal arc welding (GMAW). The Model is based on the equations of conservation of mass, energy, momentum and current, Ohm's law and a Maxwell equation. The Model treats the welding wire, the plasma and the workpiece. For molten metal droplets at the tip of the welding wire, we account for effects of inertia, gravity, surface tension, magnetic force, viscous drag force and arc pressure. Calculations are presented for a 1.6 mm diameter wire of mild steel for arcs in argon to determine the separate effects of these forces on droplet formation. It is found that, for arcs in pure argon at currents around the transition from the globular Transfer Mode to the Spray Transfer Mode, viscous drag and arc pressure effects are approximately self-cancelling. It is also found that forces have a much larger effect than do forces on the transition from globular to Spray Modes of metal Transfer.

  • Predictions of metal droplet formation in arc welding
    Journal of Physics D: Applied Physics, 1996
    Co-Authors: J Haidar, John J. Lowke
    Abstract:

    A two-dimensional time-dependent Model has been developed for the prediction of droplet formation in gas metal arc welding. The Model is a unified treatment of the arc, the welding wire, taken as the anode, and the workpiece, taken as a plane cathode. Predictions are made of the formation and shape of the welding droplets as a function of time, accounting for effects of surface tension, gravity, inertia and magnetic pinch forces. The wire feed rate and gas flow rates are also incorporated into the Model. Calculations are made of current densities, electric potentials, temperatures, pressures and velocities in two dimensions both in the arc and also within the molten drop and solid electrodes. For an arc in argon with a mild steel wire of 1.6 mm diameter and a current of 325 A or more, we predict the formation of small drops of diameter 1.2 mm or less and large drop frequencies consistent with the Spray Transfer Mode observed in welding. At currents of less than 275 A, we predict large drop sizes of about 3.8 mm in diameter or more, consistent with the globular Transfer Mode in welding. At a current of 300 A, in a transition zone between the two Modes, we predict the presence of both small and large drops.

Francis Briand - One of the best experts on this subject based on the ideXlab platform.

  • Study of the Spray to globular transition in gas metal arc welding: a spectroscopic investigation
    Journal of Physics D: Applied Physics, 2013
    Co-Authors: Flavien Valensi, Stéphane Pellerin, Quentin Castillon, Amar Boutaghane, Krzysztof Dzierzega, Sylwia Zielinska, Nadia Pellerin, Francis Briand
    Abstract:

    The gas metal arc welding (GMAW) process is strongly influenced by the composition of the shielding gas. In particular, addition of CO2 increases the threshold current for the transition from unstable globular to more stable Spray Transfer Mode. We report on the diagnostics—using optical emission spectroscopy—of a GMAW plasma in pure argon and in mixtures of argon, CO2 and N2 while operated in Spray and globular Transfer Modes. The spatially resolved plasma parameters are obtained by applying the Abel transformation to laterally integrated emission data. The Stark widths of some iron lines are used to determine both electron density and temperature, and line intensities yield relative contents of neutral and ionized iron to argon.Our experimental results indicate a temperature drop on the arc axis in the case of Spray arc Transfer. This drop reduces with addition of N2 and disappears in globular Transfer Mode when CO2 is added. Despite the temperature increase, the electron density decreases with CO2 concentration. The highest concentration of iron is observed in the plasma column upper part (close to the anode) and for GMAW with CO2.Our results are compared with recently published works where the effect of non-homogeneous metal vapour concentration has been taken into account.

Rafael Palhotas Pacheco - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of the amount of nanoparticles emitted in welding fume from stainless steel using different shielding gases.
    Inhalation toxicology, 2017
    Co-Authors: Rafael Palhotas Pacheco, João Gomes, Rosa Maria Mendes Miranda, M. L. Quintino
    Abstract:

    The primary objective of this study was to correlate the emission of macro and nanoparticles released during the process of metal inert gas/metal active gas (MIG/MAG) of stainless steel with different gas mixtures. Using different gas mixtures with different heat inputs, it was possible to determine fume formation rates and surface areas of nanoparticles with alveolar lung deposition capacity. It was found, how the various Transfer Modes and the type of gas protection, in particular, the percentage of active elements in the chemical composition of the gas, affect the amount of fumes generated and also the generation of nanoparticles with a high capacity of deposition. The Spray Transfer Mode always shows higher values of nanoparticles surface area, unlike the fume formation rates. Among the tested mixtures 82%Ar + 18%CO2 generates higher emissions of nanoparticles as well as fume formation rates.

S W Simpson - One of the best experts on this subject based on the ideXlab platform.

  • Metal Transfer instability in gas metal arc welding
    Science and Technology of Welding and Joining, 2009
    Co-Authors: S W Simpson
    Abstract:

    AbstractThis work presents a simplified Model of metal Transfer in gas metal arc welding. The Model incorporates key features of metal Transfer including the change in droplet diameters as welding moves from the globular into the Spray metal Transfer region, and the increase in welding voltage that is observed to occur as the pendant droplet grows. The Model predicts that an instability arises in the globular metal Transfer region, which leads to deterministic chaos and complex limit cycles with many droplet sizes. The instability also causes deterministic chaos with a characteristic gap in droplet diameters at the transition to Spray Mode metal Transfer. The Model explains observed features of metal Transfer in some detail, including the existence and location of preferred bands of droplet sizes. Whether the instability is present or not defines the boundary between chaotic globular metal Transfer and the stable drop Spray Transfer Mode. The identification of deterministic chaos in gas metal arc welding ...

  • A theoretical study of a gas metal arc welding system
    Plasma Sources Science and Technology, 1995
    Co-Authors: P. Zhu, M Rados, S W Simpson
    Abstract:

    A theoretical Model of a gas metal arc welding system has been developed to make predictions of the anode temperature profile, welding arc length and arc current. The Model incorporates a one-dimensional thermal Model of the moving consumable anode and a two-dimensional Model for the arc plasma. The Model makes possible the calculation of the relationship between the welding arc current, wire feed rate and the supply voltages, for various wire diameters and shielding gases. The predicted welding current for a given wire feed rate shows good agreement with our experimental observation for operation in the Spray Transfer Mode, for steel wire of two different diameters, assuming a workpiece sheath voltage of 15 V.