Fabrication And Influencing Factors Of Mono-sized Spherical Micro Particles By Pulsated Orifice Ejection Method (POEM)

Mono-sized micro droplets and particles can be widely used in the fields of basic scientific research, electronic packaging, new energy, chemical industry, etc. Among the existing preparation methods, drop-on-demand (DOD) method shows practical potential because of its low cost, simplicity, stability and wide applications. Pulsated Orifice Ejection Method (POEM) is one of the DOD methods, in which, reciprocating action of a rod or a diaphragm, which is driven by a piezoelectric actuator, intermittently pushes the molten metal droplets with a constant volume out of a small orifice which is equipped at the bottom of a crucible. Droplets become spherical due to its surface tension and solidify during the falling process. The obtained mono-sized particles are collected by collecting system. POEM meets the requirements of multiple material particles, and the particles produced by POEM showed the characteristics of identical and controllable size, high sphericity, good surface quality and same thermal history.In this paper,63Sn-37Pb mono-sized micro sphere particles were successfully prepared by self-developed POEM system. Physical property conditions which meet the needs for preparing droplets were discussed by simulation method. The effects of device parameters and experimental parameters on particle diameter were discussed. Based on the model proposed for ejecting part of the equipment, a formula of particle diameter was derived. According to the results and discussion, main conclusions can be drawn in the following. POEM system could be used to prepare particles with the characteristics of identical size, high sphericity and good surface quality, while POEM showed good practical potential. Contact angle between molten metal and material of orifice had obvious effect on droplet formation, and a contact angle larger than90°is required for droplet ejection. Surface tension of the molten metal showed great effect on droplet formation. Droplet could not be stably ejected when surface tension is too large or too small. Necking time extended as the viscosity increased, but viscosity had little effect on droplet formation and droplet size. Within the range of experiment, the particle diameter was positively correlated with orifice diameter, applied pressure difference, rod diameter, applied voltage and the rise edge of the waveform of the piezoelectric actuator. Among which, orifice diameter, applied pressure difference, rod diameter and rise edge of the waveform of the piezoelectric actuator showed significant effect on droplet diameter, while droplet diameter increased slowly as applied voltage of the piezoelectric actuator increased. The hold edge of the waveform of the piezoelectric actuator, frequency and melting temperature showed no obvious effect on particle diameter. Based on Hagen-Poiseuille’s law and the law of steady flow in concentric annular channel. formula of particle diameter had been derived and the results were in agreement with experimental results.