In the process of rolling the most significant aspect is the generation of heat through friction and deformation in the roll bite. The most important aspects are:
Maintaining uniform, stable roll temperatures circumferentially around the roll and transversely across the roll width
Creating optimum thermal crowns and minimum differential in temperature in the upper and lower work rolls with optimum heat extraction
Because of the current demands on mills to process much lighter exit gages from increased incoming hot strip thickness, much larger reductions are necessary on individual mill stands, such high reductions at a nominal width result in a larger area of contact with corresponding higher rolling force, friction and heat generation.
These high reduction schedules combined with the requirement to produce widening range of material cross-sections with a more diverse range of softer and harder materials also result in increasingly greater challenges in the control of roll temperature and the effective transfer / extraction of heat.
Establishing a uniform homogenous cooling across the rolling width with a uniform and acceptable thermal distribution (no gradients) is the ultimate goal as regards cooling and assures that the universal problem of post cooled shape after recoil is minimized.
A well designed, cooling system in good operating condition will achieve several important objectives:
Maximum heat extraction at minimal coolant consumption
Symmetrical thermal profiles on the work rolls (minimum gradient in temperature)
Controlled thermal crowns
“Normal” steady state roll temperatures
No differentials in the thermal conditions between the top and bottom work roll
Ensure that the roll bending system is kept within range by maintaining the appropriate thermal crown height and symmetry
Symmetrical top and bottom roll cooling arrangements
Roll and coil transverse temperature gradients
Top and bottom spray header in line (parallel) to center lines of work rolls