An excavator is a cyclic -moving earth moving machine designed to separate the soil from the massif, move it and load it. The main working body of special equipment is a bucket, which is loaded, moving relative to the developed rock with the help of traction mechanisms of the machine.
The excavator can be of the “straight shovel” type (designed to develop rock above the standing site), “backhoe” (used to extract earth mass below the support surface) and dragline excavator with a “scraper” bucket. The latter type is indispensable for the development of large volumes of soil, during overburden operations, in land reclamation and hydraulic engineering, for cleaning the bottom of rivers, lakes and other bodies of water.
Dragline excavator
The first schematic diagram of a dragline excavator was developed back in the 16th century by the great scientist of the Renaissance - Leonardo da Vinci. On an industrial scale, this type of equipment has been used since 1884 in the United States. In Russia, this type of earth moving machinery first appeared in the post-war years. They were used to develop mineral deposits.
A dragline excavator, unlike other models of special equipment, separates the rock from the massif by dragging the bucket along the surface, and not by the action of a hydraulic or cable-block system. Thanks to the flexible rope mounting of the bucket to the boom, the dragline performs its work at a much greater distance and greater depth from the traction mechanism than other types of machines. This is both an advantage and the main difference between this type of earth moving equipment.
Design and principle of operation
Dragline consists of several basic systems - a machine that creates traction, boom, cable system and bucket. The rope system includes traction and hoisting cables, which are fastened with a bucket using chains. The first is necessary to move the working body in a vertical plane, and the second pulls the bucket to the machine, due to which both cutting of the rock and loading of the soil occur.
After that, the dragline excavator simultaneously pulls both the hoisting and traction cables, because of which the distance between the tipping block and the connecting link grows, and the unloading rope is pulled. As a result, the front edge of the bucket lifts up, which prevents the soil from getting enough sleep.
After moving the soil mass to the place of unloading, the force on the traction and lifting ropes is sharply reduced, due to which the tension of the unloading cable is weakened - the bucket loses its balance, turns over, rock is shipped.
Operational Features
The bucket is buried in the ground only under its own weight. Therefore, in order to provide a high digging force, the rocks must be sufficiently loose. Therefore, dense and hard ground rocks, which are planned to be developed using a dragline excavator, are first loosened by wedge-shaped baking powder or blasting.
During operation, both the traction and hoisting ropes must be in constant tension, which is necessary to avoid overlap. Raising and lowering the boom also occurs due to the operation of the cable mechanism. Therefore, when working with hard and dense rocks of the soil, smaller buckets are installed so as not to exceed the maximum load capacity.
Advantages and disadvantages
Unlike conventional excavators, in which the tractive effort is created by hydraulic or cable-block systems, and the bucket is rigidly connected to the boom, the dragline working body moves freely relative to the main machine. This allows you to lower it to a greater depth (several times greater than conventional models can allow).
Thanks to the light and long boom, excavation by a dragline excavator can be carried out at a considerable distance from the standing point. This increases the productivity of this type of equipment and reduces the cost of excavation. In addition, judging by the reviews, a simple and durable bucket control mechanism can reduce costs associated with the current maintenance of the equipment.
The disadvantages of the dragline excavator are due to the flexible bucket suspension. Because of it, the accuracy of digging and unloading is reduced. As a result, shipping rocks directly to vehicles is difficult. Most often, soil is poured into a dump - from where it is transported to dump trucks. Therefore, the development of the land mass without additional special equipment - ordinary excavators, loaders - is impossible.
Technical features
In order for the excavator with dragline equipment to show maximum performance, the site of excavation should be located directly in front of the machine. Moving the bucket to the bottom can take place in a pendulum way - an experienced driver, having swinged the working equipment, can “cast” it to a greater distance than the boom allows.
Depending on the model of this type of earthmoving equipment, the characteristics of the machine will be in the ranges:
- boom length - from 15 to 100 meters;
- the capacity of the main bucket - from 6.3 to 168 m 3;
- maximum scooping radius - 15.3 and more meters;
- ground pressure - 0.06-0.255 MPa.
A distinctive characteristic of the dragline excavator is the working mass. The weight of the lightest cars is several times more than special equipment with a hydraulic drive or a cable-block system. This greatly limits their scope.
Application area
Reviews say that dragline excavators are most often used in places of large-scale development of the soil mass. They are actively used during stripping operations, as well as mining and quarrying of large radius and depth.
A dragline with a perforated bucket is used for mining rocks from the bottom of reservoirs, as well as for cleaning rivers, lakes or during the construction of
hydraulic structures. They are also widely used in land reclamation works. In urban environments, such earthmoving machines are extremely rare.
Excavator Drive Type
Recently, walking dragline excavators have been increasingly used . They are delivered to the place of work in disassembled form, where they are subsequently assembled. Such a machine most of the time is located on a flat platform. If necessary, to move to a new place, the driver of the dragline excavator lowers special shoes that take weight and raise the machine.
After that, the support platform moves, and the equipment "sits" on it again. The shoes are set in a new place, and the whole process is repeated. As a rule, walking excavators have a large mass that a caterpillar mover cannot withstand .
Crawler or pneumatic wheel dragline excavators are now almost never found. Usually they are small machines with low productivity, which is why it is impractical to use them on construction sites. Almost all representatives of this species are replaced by hydraulic and cable block machines.
Global manufacturers
Uralmash is a domestic engineering company from which a dragline excavator is purchased in different parts of the world. The technical characteristics of the models are in a wide range, which allows each client to choose a machine according to their needs. Judging by the reviews, this is one of the most reliable stepping representatives of special equipment.
The competition of the domestic company is only a diversified Japanese concern, which promotes tracked models on the world market. As a rule, this is a lighter technique that is used in the development of relatively small massifs of soil.