Patent ID: 7799199
Filing Date: 2010-09-21
Classification: B21B,C23G,C25F

Abstract:
1. A process for descaling, pickling and finishing/passivating stainless steel strips, wherein the strip to be processed is subjected to the following sequence of steps: an electrochemical and/or chemical descaling treatment, differentiated into two hydraulically distinct units using aqueous solutions, wherein: said descaling, in case of electrolytic treatment, uses aqueous solutions containing in the first unit: with induction onto the strip of at least one anode-cathode or anode-cathode-anode polarity sequence applied by pairs of electrodes having the same polarity, between which the strip runs, with anodic treatment times (t a ) and anodic current density (I) selected so as to satisfy the relation where: t k is an experimental constant, its values ranging from 2 to 15 s; c is an experimental constant, its values ranging from 40 to 120 C/dm I is the anodic current density, its values ranging from 1 to 100 A/dm and with times during which the strip is not subjected to the electric field that range from the 5% to the 60% of the total electrolytic descaling time; said descaling, in case of chemical treatment, uses aqueous solutions containing in both units from 25 to 280 g/l H said strip being subjected to said descaling treatment for an overall time comprised in the range 10-250 s, at temperatures comprised in the range 20-105° C.; a chemical pickling, optional, and/or finishing/passivating treatment, differentiated into two hydraulically distinct units, wherein: said chemical pickling treatment uses aqueous solutions containing: from 20 to 180 g/l H from 5 to 50 g/l free HF; ≧15 g/l Fe Fe with <80 g/l total dissolved Fe; said chemical finishing/passivating treatment uses aqueous solutions containing: from 10 to 100 g/l H from 0 to 15 g/l Free HF; <20 g/l Fe >0.03 mol/l H said strip being subjected to said chemical pickling and/or finishing/passivating treatment for an overall time ranging from 2 to 250 s, at temperatures ranging from 20 to 80° C.; and there being provided, for each pickling and/or finishing/passivating treatment unit, a solution recirculation with a flow rate equal to at least 10 dm there being provided, at least at the end of each descaling, pickling and/or finishing/passivating treatment unit, a mechanical and/or hydromechanical and/or water-employing cleaning treatment, optionally by water jets having a >100 bar pressure.