Abstract: In the four-high mill used for rolling plate, an offset is generally set to keep the rolls parallel and prevent the cross between the rolls, and which becomes the parallel positioning mechanism of roll system in four-high mill entered into the textbook of rolling mills. In all contemporary four-high mills, there is an offset between the rolls. But the offset cannot ensure the certainty of its mechanism, and the dynamic cross between the rolls happens frequently, which induces ultra-large axial force to damage the thrust rolling bearing or generate support reaction deviation in rolling to break the stability of plate shape control. Online inspection test of the axial force of a high-speed four-high mill for rolling aluminum foil and with a 3 mm offset distance is carried out, which reveals the occurrence of regular dynamic cross between work roll and backup roll during the rolling process. The dynamic cross behavior between the rolls is corresponding to the size of small clearance between bearing seat and housing window column, limited only in the range of β0.05° cross angle of rolling mill, and far lower than β=1°～1.5° cross angle of PC mill. But the derivative axial force of the dynamic cross exceeds three times of the rated value The static acyclic test of the offset distance of four-high mill roll system proves that with constant original installation position between the rolls there is no horizontal displacement of rolls. The dynamic cross phenomenon and zero static horizontal displacement reveal the indeterminacy of the mechanism of setting offset distance, so it cannot be used for parallel positioning and stability design of four-high mill.

Key words: Asymmetric cross, Dynamic cross, Four-high mill, Offset, Parallel positioning of roll system, Running stability, Blade tip winglet Compressor cascade Tip clearance flow Experimental study Vortex structure