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Digital control hydraulics control lift of 400t turret

Huge ladles are used in US Steel’s Edgar Thomson plant to transfer molten steel from a blast furnace or basic oxygen process to a dual-strand continuous casting line. In addition, metallurgy is fine-tuned while material is in the ladle.

Part of the path of the ladles is a correspondingly massive double-arm turret capable of lifting ladles on each of its two arm sets simultaneously and rotating them to their intended stations. After years of service, the 400-ton turret’s main bearing came due for replacement.

The entire turret assembly rests on the large main bearing, so the turret had to be safely lifted to a height sufficient to remove and replace the bearing. Engineering consultant Dick Kelly of R.G. Kelly designed the necessary fixturing and wrote a procedure for the disassembly and bearing replacement. Major steps were installation of the bolted lift structure components as follows:

1) Two beams between turret arm tops to render the structure rigid for lifting
2) Pedestals around the turret base
3) Bolted base beam structure on pedestals
4) Lift beam assemblies along both sides
5) Carry beam assemblies and blocks under the arms.

Each of the two lift beam assemblies contains four inverted 150-ton, 32-inch (812.8mm) stroke hydraulic cylinders. The total weight lifted including the lifting hardware was about 550 tons, so the eight cylinders provided a 2:1 capacity margin. Additionally, Dick Kelly explains that he designed the structure to be stiff enough that in the unlikely event that a cylinder should fail, the remaining seven cylinders would be able to do the lift.

Hydraulic lifting was used because overhead crane service was not available during this shutdown and also due to clearance problems. But the key to uniformly and accurately lifting such a large, heavy structure is digitally controlled hydraulics. The lifting could have been accomplished in a traditional manner, using manually controlled jacks, but that’s more easily said than done. Manually raising each of the eight lift points in precisely equal amounts is tricky and extremely time-consuming. Too great a variance in the lifting at various points would tilt the turret and cause it to bind. And, unequal lifting can induce internal stresses in the object being lifted.The same remarks apply to lowering.

The word “digital” may bring to mind complicated, difficult-to-operate equipment, but Enerpac’s award-winning Synchronous Lifting System is elegant in its simplicity for the user. The SyncLift operating system receives electronic signals from position sensors that are attached to the load close to each lifting cylinder.

These signals are processed, and based on the results the computer switches hydraulic control valves on and off. The Sync-Lift position sensors utilize a thin cable that unwinds from a spool. The end of the cable is attached to the load and the sensor is attached to a stable reference surface (or vice-versa). The result is simultaneous load travel monitoring accurate to ±0.04 in.(1.0mm) at each jack. The operator control station provides readouts of individual cylinder load and total load as well as other parameters.

The bottom line is that the ESS Sync-Lift digital hydraulic system delivered accurate control, increased safety and allowed the project to be completed on time during a very tightly scheduled outage.
Enerpac technical staff assisted in testing the system at the lift frame fabricator and also provided training to on-site contractor personnel.

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