Method for changing the rolls on a rolling mill

A method for changing rolls, the method being carried out in an installation having:

• a rolling mill configured to roll a metal strip, the rolling mill including:
• a roll stand,
• a set of the rolls having substantially parallel axes, the set of rolls being superimposed thereon one another, the set of superimposed rolls including
• a lower work roll and an upper work roll, the lower and upper work rolls defining a nip through which the metal strip passes, and
• a lower backup roll and an upper backup roll configured to respectively bear against the lower and upper work rolls on an opposite side to a side of the nip,
• each of the lower and upper work rolls and the lower and upper backup rolls having two ends mounted such that the ends rotate, each of the ends being on a bearing supported by a chock comprising a protruding portion,
• a guide between the chocks of the lower and upper work rolls and the lower and upper backup rolls and the roll stand along a clamping plane of the rolling mill,
• a force applicator configured to apply a clamping force between the chocks of the backup rolls, the force applicator comprising hydraulic cylinders,
• locking members and grooves configured to clamp the chocks of the lower and upper work rolls and the lower and upper backup rolls, locking the chocks in position relative to the roll stand along an axis of the respective roll of the lower and upper work rolls and the lower and upper backup rolls, and allowing the chocks to slide along the guide, along the clamping plane,
• a motor configured to drive the backup rolls, on a drive side of the roll stand of the rolling mill at which the motor is disposed, and
• a bracket;
• and
• an extraction system configured to extract the lower and upper work rolls and the lower and upper backup rolls provided on the drive side of the rolling mill, the extraction system comprising:
• an actuator configured to push the lower and upper work rolls and the lower and upper backup rolls out of the roll stand of the rolling mill when the lower and upper work rolls and the lower and upper backup rolls are extracted, or conversely to pull the lower and upper work rolls and the lower and upper backup rolls into the roll stand when the lower and upper work rolls and the lower and upper backup rolls are inserted, and
• a coupling head secured to the actuator, the coupling head being situated at an intermediate height between the lower work roll and the lower backup roll when the roll stand is in an open condition in which the upper and lower work rolls and the upper and lower backup rolls are distanced from each other, the coupling head being configured to move in a direction parallel to the lower and upper work rolls and the lower and upper backup rolls, from a first retracted position in which the coupling head is located on the drive side, to a second deployed position in which the coupling head passes through the roll stand and is located on an operator side opposite to the drive side relative to the roll stand, the coupling head comprising:
• a rigid hook configured to drive the chock or one of the ends of the lower work roll on the drive side of the rolling mill, and
• at least one coupling hook configured to drive the chock of the lower backup roll on the drive side of the rolling mill, the at least one coupling hook having a retracted state in which the at least one coupling hook does not drive the chock of the lower backup roll and a deployed state in which the at least one coupling hook drives, by a pushing action, the chock of the lower backup roll, the chocks of the upper and lower work rolls having at least one connector on the operator side creating a mechanical connection between the chocks on the operator side,
• the method according to the following successive steps when the roll stand of the rolling mill is in the open condition:
• extracting, in a first extraction step, the upper work roll and the lower work roll by the pushing action from the actuator on the chock of the lower work roll, on the drive side, the coupling head passing from the first retracted position to the second deployed position, the upper work roll being driven together with the lower work roll via the created mechanical connection, on the operator side, between the chocks of the lower and upper work rolls, the at least one coupling hook of the coupling head being in the retracted state, in which the at least one coupling hook does not drive the chocks of the backup rolls during the pushing action;
• passing the at least one coupling hook from the retracted state by manual action on the at least one coupling hook, the coupling head in the first deployed position being accessible on the operator side of the rolling mill;
• returning, in a return step, the coupling head back from the second deployed position towards the drive side into the first retracted position;
• extracting, in a second extraction step, the lower backup roll from the roll stand by the pushing action from the actuator on the chock of the lower backup roll on the drive side, the coupling head passing from the first retracted position to the second deployed position, the at least one coupling hook being in the deployed state driving the pushing of the chock of the lower backup roll;
• positioning, in a positioning step, the bracket on the lower backup roll, the bottom portion of a bracket bearing against the chocks of the lower backup roll, a top portion of the bracket being configured to support the chocks of the upper backup roll, the bracket being configured to be inserted into the roll stand;
• inserting, in an inserting step, the lower backup roll and the bracket into the roll stand, by a pulling force exerted by returning the coupling head towards the drive side, from the second deployed position into the first retracted position, the bracket having a clearance through which the metal strip passes when the metal strip is inserted into the roll stand;
• depositing, in a depositing step, the upper backup roll on the top portion of the bracket, by an action of lowering the upper backup roll;
• and
• extracting, in a third extraction step, the lower backup roll, the bracket, and the upper backup roll by the pushing action from the actuator on the chock of the lower backup roll, on the drive side,
• wherein the lower work roll and the lower backup roll are distanced from the upper work roll and from the upper backup roll when the metal strip is present along a through feed plane of the rolling mill.