Controlling a strip tension during the flexible rolling of metal strip

A method for controlling a strip tension during flexible rolling of metal strip in a rolling mill with a dancer roll that is adjusted with a hydraulic drive, and further having a controllable valve arrangement disposed between a hydraulic pump and the hydraulic drive, and at least one hydraulic pressure accumulator arranged between the hydraulic pump and the valve arrangement, comprising the following steps:

• measuring a hydraulic pressure at the hydraulic drive,
• determining the strip tension of the metal strip based on the measured hydraulic pressure at the hydraulic drive,
• controlling the valve arrangement depending on the strip tension of the metal strip,
• storing hydraulic fluid in the at least one hydraulic pressure accumulator,
• feeding, at least partially, the hydraulic fluid previously stored in the at least one hydraulic pressure accumulator to the hydraulic drive for a short-term supply of hydraulic fluid,
• determining a roll gap setting of a roll stand adjacent the roll arrangement;
• and
• controlling the valve arrangement in addition to the strip tension of the metal strip based on the roll gap.

An apparatus for controlling a strip tension during flexible rolling of metal strip, the apparatus comprising:

• a roll arrangement with at least one dancer roll, a position of said dancer roll being adjustable for controlling the strip tension of the metal strip,
• at least one hydraulic drive coupled to the dancer roll for adjusting the dancer roll,
• a hydraulic tank being fluidly connected to the hydraulic drive via a hydraulic supply line delivering hydraulic fluid to the hydraulic drive from the hydraulic tank and via a hydraulic return line returning hydraulic fluid from the hydraulic drive to the hydraulic tank,
• a hydraulic pump for supplying hydraulic fluid from the hydraulic tank to the hydraulic drive,
• a controllable valve arrangement disposed in the hydraulic supply line between the hydraulic pump and the hydraulic drive for controlling the hydraulic drive and disposed in the hydraulic return line between the hydraulic drive and the hydraulic tank,
• a pulsation damper arranged in the hydraulic return line between the controllable valve arrangement and the hydraulic tank,
• at least one hydraulic pressure accumulator for temporarily storing hydraulic fluid previously delivered by the hydraulic pump, the hydraulic pressure accumulator being arranged between the hydraulic pump and the valve arrangement, and
• a pressure sensor for determining a hydraulic pressure arranged in the hydraulic drive.