Method for changing the rolls on a rolling mill

Method for changing the rolls on a rolling mill for rolling a metal strip, which is carried out in an installation (1) having:

• a rolling mill comprising:
• a roll stand (2),
• a set of superimposed rolls having substantially parallel axes, comprising two work rolls (3, 4), one lower and one upper, defining the nip through which the strip passes, and two backup rolls (5, 6), respectively one lower and one upper, intended to bear respectively against the work rolls on the opposite side to the side of the nip,
• each roll having two ends mounted such that they rotate, each of which on a bearing supported by a chock (30, 40, 50, 60),
• guide means between the chocks of the rolls and the roll stand along the clamping plane,
• means for applying a clamping force between the chocks of the backup rolls, comprising hydraulic cylinders (VS),
• a clamping system (9) for clamping the chocks of the rolls, locking the chocks in position relative to the roll stand, along the axis of the roll, while allowing the chocks to slide along the guide means, along the clamping plane,
• drive means (10) for driving the backup rolls, on one side of the roll stand of the rolling mill, referred to as the drive side,
• a system for extracting the work rolls and the backup rolls provided on the drive side of the said rolling mill and comprising:
• an actuator (70) configured to push the rolls out of the roll stand (2) of the rolling mill when the rolls are being extracted, or conversely to pull the rolls into the roll stand (2) when the rolls are being inserted,
• a coupling head (8) secured to the said actuator (70), situated in an open position of the roll stand (2) at an intermediate height between the lower work roll (4) and the lower backup roll (6), capable of moving in a direction parallel to the rolls (3, 4, 5, 6), from a first retracted position (P1) wherein the coupling head is located on the drive side, to a second deployed position (P2) wherein the coupling head (8), having passed through the roll stand (2), is located on the operator side, the said coupling head (8) comprising:
• first coupling means configured to drive the chock (40) or the end of the lower work roll (4), on the drive side of the rolling mill,
• second coupling means configured to drive the chock of the lower backup roll (6), on the drive side of the rolling mill, having a retracted state wherein they do not drive the chock of the lower backup roll (6) and a deployed state wherein they drive, by a pushing action, the chock (60) of the said lower backup roll (6),
• and wherein the chocks (30, 40) of the upper and lower work rolls have connection means (11), on the operator side, opposite the drive means, creating a mechanical connection (12) between the said chocks on the operator side,
• and wherein the work rolls (3, 4) and the backup rolls (5, 6) are extracted, after opening the roll stand of the said rolling mill, during which step the lower work roll (4) and the lower backup roll (6) are distanced from the upper work roll (3) and from the upper backup roll (5), when the metal strip (B) is present along the through feed plane of the said rolling mill by implementing the following successive steps:
• a first extraction step (E1) wherein the upper work roll (3) and the lower work roll (4) are extracted, by a pushing action from the said actuator (70) on the chock (40) of the lower work roll (4), on the drive side, the coupling head (8) passing from the first retracted position (P1) to the second deployed position (P2), the said upper work roll (3) being driven together with the lower work roll (4) via the mechanical connection (12) created, on the operator side, between the chocks (30, 40) of the lower and upper work rolls, the said second coupling means (81, 82) of the coupling head (8) being in the said retracted state, in which they do not drive the chocks of the backup rolls during the said pushing action,
• a return step (E2) wherein the coupling head (8) is brought back from the second deployed position (P2) towards the drive side into the first retracted position (P1),
• a second extraction step (E3) wherein the lower backup roll (6) is extracted from the roll stand (2) by a pushing action from the said actuator on the chock (60) of the lower backup roll (6) on the drive side, the coupling head (8) passing from the first retracted position (P1) to the second deployed position (P2), the said second coupling means being in the said deployed state driving the pushing of the chock (60) of the said lower backup roll (6),
• a positioning step (E4) wherein support equipment (13) is positioned on the lower backup roll (6), the bottom portion whereof bears against the chocks (60) of the lower backup roll (6), and the top portion whereof is intended to be used to support the chocks (50) of the upper backup roll (5), the said support equipment (13) being capable of being inserted into the roll stand (2),
• an insertion step (E5) wherein the lower backup roll (6) and the said support equipment (13) are inserted into the roll stand (2), by the pulling force exerted by the return of the coupling head (8) towards the drive side, from the second deployed position (P2) into the first retracted position (P1), the said support equipment (13) having a clearance (14) through which passes the metal strip (B) when inserted into the roll stand (2),
• a depositing step (E6) wherein the upper backup roll (5) is deposited on the top portion of the support equipment (13), by an action of lowering the said upper backup roll (6),
• a third extraction step (E7) wherein the group constituted from the lower backup roll (6), the support equipment (13) and the said upper backup roll (5) is extracted by a pushing action from the said actuator (70) on the chock (60) of the lower backup roll (6), on the drive side.
• and wherein the second coupling means are passed from the retracted state wherein they do not drive the chock of the lower backup roll (6) to the deployed state wherein they drive the pushing of the chock (60) of the said lower backup roll (6) by manual action on the said second coupling means, subsequently to the said first extraction step (E1), the coupling head (8) being in the said second deployed position (P2), accessible on the operator side of the said rolling mill, and prior to the said return step (E2).