Cold rolled steel strips with deep drawing quality are manufactured economically by the CAPL (Continuous Annealing and Processing Line) after cold rolling. CAPL combines 5 conventional processes of electrolytic cleaning, annealing, cooling, temper rolling and recoiling with inspection into one line. Materials most suited for the purpose are low manganese steels (Mn≤0.25%) with K values of 0-0.15, which are coiled at 670°C or above after hot rolling. The K value is defined as follows:
(for capped and rimmed steels) K=Mn (%) -55/32. S (%) -55/16. O (%)
(for killed steels) K=Mn (%) -55/32. S (%)
These steels are cold rolled to the final thickness and then passed through the CAPL. The heat cycle of the CAPL furnace section consists of one-minute annealing, cooling to over-aging temperature at the rate of 5° to 30°C per second and over-aging at 350° to 450°C for a few minutes. The radius of the overaging chamber hearth roll has to satisfy the following relation;
d/R=2.02×10-3-1.05×10-3-log (t+1)
where d: strip thickness (mm), R: radius of hearth roll (mm), t: time during which bending stress occurs (min). The built-in temper mill of CAPL has a new type of work roll changing device which enables the replacement of work rolls in 2 min without the strip having to be cut. With other new devices such as direct strip temperature detector, or strip steering device, it has become possible to combine the above 5 processes organically into one single line to reduce man-power, investment cost, energy consumption and yield loss drastically.
