Work roll balance force setting method and rolling mill running method, rolling mill running switching method, and rolling mill

A work roll balance force setting method of a rolling mill that includes a pair of upper and lower work rolls, and one or more pairs of upper and lower rolls that are provided on sides of the work rolls that are opposite to a rolled material, the rolling mill driving the work rolls by supplying a rolling torque from the rolls to the work rolls, the work roll balance force setting method comprising:

• obtaining a mill longitudinal rigidity coefficient K of the rolling mill;
• determining a kiss roll load Pk of the work rolls in relation to a work roll angle θx of a tip position of the rolled material between a start of biting of the rolled material and completion of the biting, the kiss roll load Pk being determined by using the obtained mill longitudinal rigidity coefficient K and a rolling condition;
• determining a rolling load Pr and the rolling torque Tr in relation to the work roll angle θx of the tip position of the rolled material between a start of biting of the rolled material and completion of the biting;
• determining a traction coefficient μrt between the work rolls and the rolls, and a maximum value μrtmax of the traction coefficient in relation to the work roll angle θx of the tip position in a state in which a hypothetical work roll balance force Pb is applied, the traction coefficient μrt between the work rolls and the rolls and the maximum value μrtmax of the traction coefficient being determined from a sum P of the kiss roll load Pk, the rolling load Pr, and the hypothetical work roll balance force Pb, and the rolling torque Tr between a start of biting of the rolled material and completion of the biting;
• obtaining a tolerated value μrter of the traction coefficient μrt of the rolling mill;
• comparing the maximum value μrtmax determined at the step of determining the traction coefficient μrt with the tolerated value μrter;
• and
• resetting a work roll balance force at a start of biting of the rolled material to a value which is equal to or larger than the work roll balance force that is required when the traction coefficient μrt assumes the maximum value μrtmax, and equal to or smaller than the work roll balance force that is a limit based on a constraint in terms of strength of the rolling mill, when the tolerated value μrter is equal to or larger than the maximum value μrtmax.

A rolling mill comprising:

• a pair of upper and lower work rolls;
• one or more pairs of upper and lower rolls that are provided on sides of the work rolls that are opposite to a rolled material;
• and
• a controller configured to perform driving control of the rolls such that the work rolls are driven by supplying rolling torque Tr from the rolls to the work rolls, wherein the controller has:
• a first acquiring section configured to obtain a mill longitudinal rigidity coefficient K of the rolling mill;
• a first calculating section configured to determine a kiss roll load Pk of the work rolls in relation to a work roll angle θx of a tip position of the rolled material between a start of biting of the rolled material and completion of the biting, the first calculating section determining the kiss roll load Pk by using the acquired mill longitudinal rigidity coefficient K and a rolling condition;
• a second calculating section configured to determine a rolling load Pr and the rolling torque Tr in relation to the work roll angle θx of the tip position of the rolled material between a start of biting of the rolled material and completion of the biting;
• a traction coefficient calculating section configured to determine a traction coefficient μrt between the work rolls and the rolls, and a maximum value μrtmax of the traction coefficient in relation to the work roll angle θx of the tip position in a state in which a hypothetical work roll balance force Pb is applied, the traction coefficient calculating section determining the traction coefficient μrt between the work rolls and the rolls, and the maximum value μrtmax of the traction coefficient from a sum P of the kiss roll load Pk, the rolling load Pr and the hypothetical work roll balance force Pb, and the rolling torque Tr between a start of biting of the rolled material and completion of the biting;
• a second acquiring section configured to obtain a tolerated value μrter of the traction coefficient μrt of the rolling mill;
• a step comparing section configured to compare the maximum value μrtmax determined by the traction coefficient calculating section with the tolerated value μrter;
• and
• a setting section configured to reset a work roll balance force at a start of biting of the rolled material to a value which is equal to or larger than the work roll balance force that is required when the traction coefficient μrt assumes the maximum value μrtmax, and equal to or smaller than the work roll balance force that is a limit based on a constraint in terms of strength of the rolling mill, when the tolerated value μrter is equal to or larger than the maximum value μrtmax.