Drag line (or dragline) excavators are very heavy machinery which is used for different purposes. These purposes include surface mining, civil engineering and excavation. The smaller types of this machinery are used for the roads and ports construction in the field of civil engineering. On the other hand, the larger machines of drag line excavators are used for heavy operations like coal mining extraction and mining operations. Dragline excavators are the largest type of moving equipments and their weight is up 10,000 tons.
The bucket system of dragline excavators consist of large buckets which are suspended from a boom. This bucket is moved with the help of many chains and ropes. The pulling rope, powered by either an electric or large diesel motor, holds up the bucket and raises the coupler assembly from the boom. Another drag rope which is present on the assembly helps to draw the bucket horizontally. This bucket can be controlled in order to perform different types of operations through the skilful use of hoist and drag rope.
This bucket is positioned high above the material being operated during the typical excavation cycle. This bucket is then brought down and the drag rope is used to drag it all along the surface of material. After this, the bucket is lifted by using the hoist rope. Bucket is then placed at the point where the material is placed and this is done by a swing operation. Thus, bucket will be inclined by releasing the drag rope. This will make the material of bucket to fell down. This felling of material from bucket is commonly known as the dump operation.
Same dragline excavator is then used to throw the bucket by winding up and then releasing the clutch of drag cable. This will make the bucket to swing like a pendulum. If it is operated by a skillful worker, he can make the bucket to about half the length of jib away.
The drag line excavators can dump the waste material only according to the length of their boom and this is a great limitation or disadvantage of the drag line. It is very effective in excavating the material below the level of their tracks. These are not useful in loading the piled up material. This also adds to its disadvantages.
Despite all their disadvantages and capital, they have a very high demand and they are used in many mines because they are efficient in whatever they do and their operating cost is very low. They are also considered to have a best performance and high reliability. Their cost of removing the waste material is very low. They have very different and unique cutting sequences. Among its cutting sequences, the first is the method which uses offset benches which is a side casting method. In this method, the overweight material is thrown on the blasted material in order to make a bench.
Second method of cutting sequence is the key pass. In this method, the pass will cut the key at the toe of the wall which is new and high and this will shift the bench towards the wall. If the wall is blocky, this can also require chopping pass. This chopping pass means that the bucket will be dropped on a high wall and this will help in scaling the surface.
The third and the slowest method of cutting is known as the block pass. This will move most of the material. This can move the biggest material which is even bigger for the holes in ground and this can also maximize and minimize the productivity.