Experiments to continuously separate Fe-Al-Zn dross phase from hot dip galvanising zinc melt were conducted on a laboratory scale apparatus by using high frequency alternating magnetic field. Effects of processing time (t) on separation efficiency were investigated. The experimental results show that using the electromagnetic repulsive force resulting from the electrical conductivity difference between zinc melt and Fe-Al-Zn dross phase, the deleterious zinc dross particles causing surface defects of galvanising steel sheets can be continuously separated from the zinc bath under alternating magnetic field, and the separation efficiency increases with the increase in processing time. When the magnetic frequency is 17?5 kHz, the effective magnetic flux intensity is 0?1 T, the cross-section of the ceramic square pipe is 10610 mm, and the processing time is 0?6-2?5 s, the separation efficiency of zinc dross varies from 43?76 to 85?71%, and the experimental results are in reasonable agreement with the theoretical results.

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Dross in zinc pots is the most important factor that impairs the surface quality of hot dip galvanising automobile steel sheet. Separation behaviour of zinc dross from galvanising melts of different Al concentrations (0?12, 4?5 and 55?0 wt-% by an alternating magnetic field has been investigated in order to reduce the dross defects on steel sheets. The properties of different zinc drosses were investigated by means of EDAX and the quantitative metallographic method and the conductivities were measured by physics property measurements system. The experimental results show that the zinc dross in different hot dip galvanising melts has different morphologies, compositions and structures, and the average particle size of the dross increases with the Al concentration. In the case of extra iron (above the solubility limit) in the zinc melt, zinc dross quantity also increases with the Al concentration. All of the three types of zinc dross particles .5 mm can be successfully separated when the magnetic frequency is 17?5 kHz, effective magnetic flux intensity is 0?05 T, imposed time is 15 s and the cross-section of the ceramic square pipe is 565 mm.

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