Study Of Particle Sizing On Welding Fume Based On Laser Scattering

The ray disseminates along the straight line in homogeneous medium. However,when it passes heterogeneous medium,the ray will scatter, that is to say, it will offsetfrom its straight dissemenating direction. Laser scattering is a corporate process ofabsorption, diffraction, reflection,transmission and refraction. The laser scatteringmethod is an advanced method for particle sizing.This technique has manyadvantages,such as neither disturbing nor contacting the liquid field and the particlefield,having broad dimension range of measured particle, short response time ofoptoelectronic conversion and high resolving power.For the use of laser,which is astrong coherent light source,the scattering technique is developed prodigioussly.Andin the aspect of numerical calculation,the electronic computer is in commission.Therefore,the combination of laser and computer becomes the characteristic ofmodern optical testing method.The strict light scattering theory takes the light-wave as electromagnetic wave.Under the boundary condition decided by stated object figure and dimension,thistheory can resolve the Maxwell equation of both inner and outer particle area. Miescattering thoery is a strict analytical solution to homogeneous sphere irradiated bythe homochromous ray just under this condition.The laser scattering measuring experiments were based on Mie theory in thispaper.The theory is available for every particle whose dimension is under 10 μm. Inthe whole Mie theory formulas, the scattering characteristics of particles withdifferent dimensions and different refractive indexes are strictly given. Based on thistheory, a system of light road device, which is available for laser scattering happening,was built with He-Ne laser, photomultiplier tube,oscillograph and lens.Andconsidering the strong calculating function of Matlab numerical calculation software,the Mie theory formulas were translated into Matlab form,and some Matlab functionswhich can be used to perform Mie calculation were compiled.In order to study the dimension of the particle in welding arc space as well as itsdistributing characteristics, this paper started from simulated welding fume, used thebuilt laser scattering light road device and performed practical measurement on thelaser scattering of standard particle and the simulated welding fume particle.Then,thescattering signal voltage values of the standard particle and the simulated weldingfume particle got from experiment measurement were taken into the compiled Matlabfunctions,and the relative light intensity and relative voltage values were obtainedrespectively. At last,by way of several extrapolation conversion, the dimension ofsimulated welding fume was gained.A firm foundation has been laid in this paper for further laser scattering testing onthe different particles in welding fume. At the same time, actual welding fume can beextended to be known by way of measuring simulated welding fume particles, whichhelps to measure and analyze the deleterious granular particles in welding fume,especially to improve welding condition and to enhance welding quality.