Pickling lines remove any rust and scale from hot-rolled strips. The process is based on passing the strip through hydrochloric acid baths to dissolve the surface oxides. The pickling process largely depends on the chemical composition of the strip material, the temperature of the baths, bath agitation, acid concentration and the length of the tanks. Pickling line has three sections namely Entry section, Wet process section and Exit section (Recoiler) as shown in figure 1. The coil passed through pickling line has a typical weight of 25MT with thickness varying from 1.6mm to 3.2mm and width 700-1300mm. The coil moves at a speed between 80 metre per minute (mpm) to 90mpm.
Hot rolled coil from HRM is the input to the CRM. The quality of the pickled coil entering CRM is very important as it leads to good production rates as well as less down time.
There are various types of edge defects, some being the part of the incoming coil and rest developed during the pickling process. The defects need to be addressed at pickling line and appropriate decisions needs to be initiated by the quality inspectors. Defects unattended to might lead to stoppage or further damage to the coil in CRM. At present, inspector is posted at the exit (near re-coiler) 24X7, who observes the pickled HR Coil and takes decision for rework, reject or passing it to CRM as shown in figure 2. Since we are dependent only on manual visual inspection, there is chance that some defect can go unnoticed and create problems at CRM. Thus, an alternate to manual inspection is sought to inspect the complete coil for defects especially for the detection of edge-related defects such as edge crack, busted edge, chipped edge etc as shown in figure 3.
We are seeking for solutions to monitor the edges at the exit of pickling line. The edge inspection system installed, should record the condition of the edges. The new edge inspection system should not affect the productivity of the line and should actually inspect all the edge defects, which if not caught, would result in CRM strip breakage.