Hydraulic control of a roll gap for a roll stand

A roll stand with at least two working rolls for rolling strip material and with a hydraulic arrangement for controlling a roll gap of the roll stand, comprising:

• at least one hydraulic adjusting unit for adjusting the roll gap, the hydraulic adjusting unit comprising a cylinder and an adjusting piston, the adjusting piston dividing the cylinder into a first chamber and a second chamber;
• a first valve arrangement for variably controlling the adjusting unit;
• a second valve arrangement for variably controlling the adjusting unit, which is connected in parallel with the first valve arrangement and has a larger nominal volume flow than the first valve arrangement;
• wherein the first valve arrangement is hydraulically connected to the first chamber and the second chamber for double-acting actuation of the adjusting unit,
• wherein the second valve arrangement is hydraulically connected to the first chamber and the second chamber for double-acting actuation of the adjusting unit, and
• wherein the hydraulic adjusting unit is capable of being subjected to a working pressure greater than 200 bar from a pressure medium source.

A method for controlling a roll gap of a roll stand with the roll stand comprising at least two working rolls for rolling strip material, a hydraulic arrangement for controlling the roll gap, at least one hydraulic adjusting unit for adjusting the roll gap, the hydraulic adjusting unit comprising a cylinder and an adjusting piston, the adjusting piston dividing the cylinder into a first chamber and a second chamber, a first valve arrangement for variably controlling the adjusting unit, a second valve arrangement for variably controlling the adjusting unit, which is connected in parallel with the first valve arrangement and has a larger nominal volume flow than the first valve arrangement, wherein the first valve arrangement is hydraulically connected to the first chamber and the second chamber for double-acting actuation of the adjusting unit, wherein the second valve arrangement is hydraulically connected to the first chamber and the second chamber for double-acting actuation of the adjusting unit, and wherein the hydraulic adjusting unit is capable of being subjected to a working pressure greater than 200 bar from a pressure medium source;

• the method comprising:
• determining an actual roll position of a working roll of the at least two working rolls;
• determining a nominal roll position of the working roll;
• and
• controlling an opening degree of the first valve arrangement and an opening degree of the second valve arrangement depending on the actual roll position and the nominal roll position, wherein the roll gap is changed during rolling,
• wherein for at least one thickness change of a thickness profile to be rolled, the adjusting unit is controlled in a first section of a stroke between the actual roll position and the nominal roll position by the first valve arrangement and the second valve arrangement, and in a second section of the stroke only by the first valve arrangement.