Event: Bending-Balancing Cylinders - Retract (Using Servo Valves)

See the event “HPU – On” for previous steps in this sequence.

 

Note that this event describes the sequences for Mill Stand F1. Also, this event describes the sequences for the Drive Side cylinder circuits. The same sequences apply for stand F2 through F6, though the component numbers will change. Refer to the relevant schematic for each stand for the appropriate component number.

 

When there isn’t a strip, the Bending-Balancing Cylinder balances the work roll upward. When a strip is present, the Bending-Balancing cylinder goes into the bending mode forcing upward against the AGC. The backup roll forces downward to achieve the desired deflection of the work roll. The emergency circuit is there in case the servo valve circuit fails. The Bending-Balancing Cylinder acts on a chock (bearing carrier) to lift the work roll up against the backup roll.

 

1)    The Bending-Balancing Accumulator Stand supplies pressurized hydraulic fluid to Accumulator 242.07 via Pressure Header Line P3, keeping the rod ends of Operator Side Bending-Balancing Cylinders 713.01 and 713.02 pressurized at all times.

2)    Directional Control Valve 303.23 is energized to the crossover flow pattern to deliver pilot pressure to the pilot pressure ports of Pilot Operated Check Valves 153.11 and 153.12. When 153.12 is piloted open pressurized hydraulic fluid may flow to the pressure port of Servo Valve 354.13. When 153.11 is piloted open exhaust fluid from the cap ends of Operator Side Bending-Balancing Cylinders 713.01 and 713.02 may flow to the A-port of the servo valve.

3)    Servo Valve 354.13 is energized to the crossover flow pattern. Pressurized hydraulic fluid flows through the valve passing from P to B. The fluid then deadheads at a blocked B-port.

4)    Exhaust fluid from the cap ends of the cylinders flows through Pilot Operated Check Valve 153.11, which was piloted open in step 2, above. Next, the exhaust fluid flows through the servo valve, passing from A to T, and then back to tank through Check Valve 125.08 and Duplex Return Line Filter 045.02. Note that the servo valve controls the retraction speed of the cylinder. The mass of the cylinder piston and rod, along with the mass of the machine parts as well as the pressure in the rod end of the cylinder, aids in forcing the exhaust fluid through the servo valve.

5)    Pilot Operated Check Valve 167.31, which is vented closed as Directional Control Valve 305.01 is de-energized, prevents pressurized hydraulic fluid from flowing toward the A-port of Directional Control Valve 301.01. Pressure Relief Valve 291.01 protects the cap ends of the cylinders from overpressure.