A method for controlling the position of at least one roller for shaping a face of an annular part to be shaped within a circular rolling mill that comprises:
- a fixed main frame;
- an internal cylindrical roller intended to shape an internal radial face of the annular part and an external cylindrical roller intended to shape an external radial face of the annular part and rotated by a first driving electric motor, the internal cylindrical roller and the external cylindrical roller being supported by a first auxiliary frame mounted on the fixed main frame;
- an upper conical roller intended to shape a front face of the annular part and a lower conical roller intended to shape an opposite front face of the annular part, the upper conical roller and the lower conical roller being each rotated by a second driving electric motor and supported by a second auxiliary frame mounted on, and movable with respect to, the fixed main frame;
- at least a first rack and pinion assembly, including a first rack and a first pinion, to move the external cylindrical roller or one of the conical rollers relative to the fixed main frame;
- at least a second rack and pinion assembly, including a second rack and a second pinion, to move one of the conical rollers relative to the second auxiliary frame;
- a first supply system for supplying a first variable volume chamber, integrated into a first discharge mechanism interposed in a first kinematic force transmission chain between the first rack and the external cylindrical roller moved by the first rack, with fluid under a pressure greater than or equal to 100 bars, the first supply system including a first pipe, a first pump that delivers oil at an input pressure, a first tub, a first tared non-return valve that connects the first pipe to the first tub and a second non-return valve, mounted in the opposite direction from the first non-return valve, at the outlet of the first pump, to prevent the pressurized fluid from circulating through the first pump from its outlet toward its inlet;
- a second supply system for supplying a second variable volume chamber, integrated into a second discharge mechanism disposed in a second kinematic force transmission chain between the second rack and the conical collar, with fluid under a pressure greater than or equal to 100 bars, the second supply system including a second pipe, a second pump that delivers oil at an input pressure, a second tub, a third tared non-return valve that connects the second pipe to the second tub and a fourth non-return valve, mounted in the opposite direction from the third non-return valve, at the outlet of the second pump, to prevent the pressurized fluid from circulating through the second pump from its outlet toward its inlet;
- and
- at least one electric geared motor, different from the first and second driving motors, to drive at least one of the first and second pinions of the first and second pinion and rack assemblies,
- wherein this method comprises the following steps:
- a) supplying pressurized fluid to the first variable volume chamber, to stiffen the first kinematic chain during normal operation of the rolling mill in order to absorb a temporary overload transmitted to the first kinematic chain in case of irregularity of the surface shaped by the roller, and
- b) absorbing the temporary overload, without moving the first rack, by discharging at least part of the pressurized fluid from the first variable volume chamber into the first tub via the first tared non-return valve, by reducing the volume of the first variable volume chamber, in case of irregularity on the face of the annular part that is shaped by the roller.