What is a dragline?
The dragline, or dragline excavator, is a mechanized excavator and crawler that is used in large-scale works.
It operates with a shovel or scoop attached to the machine only with cables, which offers it a wide range of action and load. However, it reduces power, so the dragline is ideal for excavating and hauling materials that are not very hard.
What elements make up a dragline, and how does it work?
- Machine body: this is the location of the engines and operator’s cabin. The other elements of the machine are assembled off of this main body. The body can have continuous tracks or be situated on pontoons, as the case may be.
Depending on its type and size, the dragline can have different amounts of displacement, drag, and rotation motors with various powers.
- Mast or boom: the metal structure which rises from the body of the machine and from which the lifting cable hangs, holding the shovel.
- Shovel or scoop: the toothed container that performs the tasks of scraping and loading materials. It moves up and down via the lifting cable, and it moves forward (digging) and backward via the drag wire. With both cables and the operator’s expertise with the machine, the shovel can move, excavate, load and unload materials, etc. Depending on the machine’s dimensions, the working conditions, and the materials’ characteristics, various techniques for operating the shovel are used.
- Lifting cable: the cable that hangs from the tip of the mast. It holds the scoop or shovel and makes it go up and down.
- Drag wire: it is fixed to the shovel and the machine body. It is shortened or lengthened to move the shovel forward or backward, as well as to change its inclination as needed, in coordination with the movement of the lifting cable.
Draglines are among the largest machines ever built. Smaller ones weigh about 8,000 tons, while larger ones can weigh 13,000 tons.
How is a dragline transported?
Draglines are composed of detachable parts that make it possible to move them. According to their sizes, draglines are classified into two major types that condition the way they move and are transported:
- Lifting cranes: smaller in size, and their body rests on continuous tracks, which allow them to get around on the job site. They are traditionally designed to be transported on platform cargo vehicles after their moving parts have been disassembled.
However, the modern dragline’s design has evolved to create lighter, more portable machines that can, once the moving parts have been disassembled and loaded onto the machine body, travel the main roads and land routes. This way, time and costs are optimized, thereby increasing profitability.
- Heavy units: these are the largest draglines whose parts must be transported by cargo vehicles and assembled entirely at the work site. Due to their own weight and what they reach with their load, these draglines don’t rest on any type of wheel or track system but are equipped with feet or pontoons.
Draglines of these dimensions have a large range of action, so they don’t need to move as much as the small ones to carry out their tasks. When moving around a construction site, the dragline moves just a few meters per minute because the feet on which it is supported have to be repositioned. When the dragline needs to move a medium distance (up to about 100 km) within the work itself, dragline transport vehicles are typically used. To move the machine over longer distances, disassembly is always indispensable.
What are the main uses of a dragline?
Small draglines are typically used for building roads and ports, foundations of bases, and other civil works. Larger draglines are fundamental for mining operations in open-pit quarries.
Who can operate a dragline?
As is the case with all construction machinery, draglines can only be operated by specialized staff. However, these large machines present an added difficulty: it would be too expensive to assemble a machine to properly train an operator. Fortunately, technology has made it possible to use simulators during the training process, thereby guaranteeing greater safety at very contained costs.
What is the maximum digging and load capacity of a dragline?
The largest, most powerful draglines that exist today can have:
- 2,500 HP engines.
- 120 m3 shovels.
- Load capacity of 150,000 kg.
- Maximum excavation depth of almost 80 meters.