The photo above shows four of the 20 groups of cylinders for lifting the dragline. Each cylinder has a lifting capacity of 100 tons. Inset shows an ariel view of all 20 cylinder groupings. Note how the work site dwarfs the men at the bottom of the photo.
The 3500-ton dragline at the Curragh mine, prior to bearing replacement on the turret. The dragline was not only synchronously lifted but also tilted to apply comparable loads to simulate actual operation.
Draglines just might be the largest land-based equipment moving across the earth, typically weighing in at 2500 to 6500 tons. Throughout Australia, draglines "walk" across the surface of the land, progressing a few feet at a time as they stop to scoop huge masses of earth to expose resources being mined.
Machines this large and heavy can't go into the maintenance shop when service is needed. All maintenance must be performed on site, which usually does not pose any extraordinary challenge. But having to replace bearings that allow the dragline to pivot poses a huge challenge. First, you must raise a load weighing thousands of tons. Second, you must keep it level for obvious safety reasons. However, it must also be kept level to prevent damaging the machine itself.
This monumental challenge was presented to G&S Engineering Services, Queensland, Australia, at the Curragh coal mine in the Bowen-Basin area. Their task was to raise the turret of a 3500-ton dragline 8 in. so the turret bearings could be replaced.
G&S Engineering chose to use 80 hydraulic cylinders — each with 100-ton lifting capacity — to raise the turret. The PLC-controlled hydraulic system was supplied by Enerpac, Milwaukee. Lifting such a massive load is not unusual for hydraulics. But synchronizing the motion of 80 cylinders required careful engineering to prevent damaging the machine and to en-sure safe operation.
The Enerpac synchronous hydraulic lifting system kept motion of all cylinders within 0.02 in. of each other while lifting a load of more than 3500 tons. They raised it a total of 8 in. to allow machining between the upper and lower rails on which a bearing is placed. The bearing surfaces could then be precisely machined to accommodate different loads and maximize the lifespan of the bearing surfaces.
The cylinders, controlled in groups of four around the perimeter of the dragline's base, lifted it 0.4 in. at a time to maintain tight control. The system simulated actual loading on the dragline to maximize and accurately predict the life of the bearing.
Basin area. Their task was to raise the turret of a 3500-ton dragline 8 in. so the turret bearings could be replaced.
The synchronous system provided pinpoint accuracy by minimizing the difference between leading and lagging lifting points, ensuring optimum safety and stability throughout the entire lift. In addition to great safety and stability, the high-pressure (10,000 psi) cylinders offered great weight and space savings compared to the much larger lower-pressure types of hydraulic cylinders previously used.
On-site benefits of these smaller and lighter cylinders translate into more space under and around the job, permitting G&S Engineering Services to employ uninterrupted use of the latest laser-guided machining systems to machine the upper rail on which the dragline rotates. The precision achieved by Enerpac's synchronous system is so great that it can be used to safely tilt massive objects during lifting to enable exact aligning of upper and lower bearing surfaces.
Features of the Enerpac Synchronous Hydraulic Lifting system for this project include:
- stroke control between unevenly distributed load points,
- automatic stop at pre-set stroke,
- PLC control with user-friendly touch screen,
- stroke and load control in all hydraulic circuits with real-time dis-play of relative stroke and load,
- continuous data recording of time, relative stroke, and load
- progressive lift control to allow tilting an object,
- center of gravity calculation, and
- 10,000 psi operating pressure, allowing full cylinder capacities with standard Enerpac hydraulic component.