During the plastic deformation of steel strip, excessive localized pressure can inflict varying degrees of damage upon the material; an abnormal incident resulting in the perforation or rupture of the strip is termed a “roll-through.” A roll-through not only severely compromises production stability but, once it occurs, also leads to the adhesion of steel to the rolling rolls, thereby adversely affecting the quality of the finished steel strip.
“Roll piercing” refers to the occurrence of non-uniform deformation within the roll gap zone; in practical terms, it represents a mismatch between the strip’s crown profile and the geometry of the load-bearing roll gap. The primary factors influencing the variations in these two elements are generally as follows:
Thermal Expansion of Rolling Rolls
During typical rolling operations, the plastic deformation of the steel strip—combined with friction against the work rolls during high-speed rolling—generates a significant amount of heat. Consequently, due to variations in continuous rolling speeds and the uneven temperature distribution across the working surface of the rolls, the thermal crown of the rolls is in a constant state of flux, thereby altering the geometry of the roll gap. If one assumes, for the sake of argument, that the initial crown of the steel strip remains constant, then these fluctuations in the roll gap geometry will directly impact and alter the shape of the steel strip.
Steel Strip Misalignment
Due to the influence of raw material crown, wedge, and camber, if sudden variations or significant deviations occur—leaving insufficient time for correction—the steel strip’s centerline will deviate from the rolling centerline. Furthermore, as the degree of deformation increases and the rolling force rises, the severity of this strip wandering will intensify.
Steel Strip Thickness and Tension Variations
Variations in either factor result in changes to the rolling force; however, while the former alters the actual deflection of the work rolls, the latter additionally affects the lateral distribution pattern of the strip steel, thereby inducing non-uniform deformation.
Adjustment Measures
Adjust the relative reduction ratio.
The reduction ratio parameter set in the Level 2 model is lowered to mitigate fluctuations in rolling force. By reducing the relative reduction ratio, the load on the F1 stand is alleviated; this keeps the rolling force coefficient per unit of strip width within a lower range, thereby ensuring uniform deformation of the steel strip’s cross-section within the roll gap and consequently reducing the occurrence of strip-piercing accidents.
Adjusted Tension Parameters
Piercing accidents are positively correlated with tension parameters; specifically, the greater the tension deviation, the more likely a piercing accident is to occur. Adjustments are therefore made to the entry unit tension to minimize this deviation. Increasing the entry unit tension serves not only to reduce the rolling force but also to mitigate strip wandering caused by tension fluctuations and deviations. Furthermore, as the rolling force decreases and the exit tension increases, the forward slip value at the F1 stand can be maintained within a narrow range. The implementation of this measure has resulted in a substantial reduction in the incidence of piercing accidents at the F1 stand.
