Towards High Speed Galvanizing – Mastering Wiping Conditions Using Hydrodynamic Pads Strip Stabilization

Increasing the galvanizing line speed is challenging for reducing production costs while steel customers still demand high coating quality without any surface defects. A lot of galvanizing lines are presently reaching speed about 160 m/min depending on the strip format. However several issues arising at bath area are limiting the increase of line speed up to and above 200 m/min. Among those topics, corrosion and wear of bath immersed hardware, skimming volumes and wiping conditions are of major importance. In the frame of the European project “High Speed Galvanizing” (RFCS-2017-800769) involving a large consortium of companies across Europe, one objective was notably to develop a strip stabilization device able to act directly at wiping level.
During that project CRM Group and its partners have pushed the limits of strip stabilization under TRL-5 conditions at low industrial speed (Z150 at 80 m/min) on its Annealing and Hot-Dip Galvanizing Pilot Line. For that purpose hydrodynamic strip stabilizing pads (WO2017129391) acting on both sides of the strip have been placed very close to the wiping level. As well, the damping parameters of pads supports were optimized thanks to a dedicated Finite Element model of the line, which has been validated based on the measurements of a remote laser vibrometer.
As a result, a flat shape and stable running strip could be achieved right between air knives. Precisely, extremely low residual strip displacements were measured even under forced vibrations representative of harsh industrial working conditions (i.e. from 1.2 mm-RMS without stabilization down to 0.2 mm-RMS with stabilization). Finally, the coated product so-obtained was characterized with a similar reduction of final coating thickness variations (i.e. from 2.5 μm-StDev without stabilization down to 0.5 μm-StDev with stabilization).