An excavator is the oldest types of the machine which removes earth. It performs its work of moving the earth while unit stationary. The little effort is required to move dead weight of earth in a vertical plane. The excavated may be mounted on crawlers, wheels or trucks and may be provided with buckets of suitable sizes and capacitates.
The excavators in common use are of the following five type
- Back trench hoe excavators
- Clamshell excavators
- Power shovel excavators
- Dragline excavators
- Skimmer excavators
Back trench hoe excavators
This type of excavators is used for digging the foundation trenches below operating level. It can also be used for excavation of smaller area such as basements, footing and trenches. The material caught is suitable discharge.
This type of excavator is used for digging below, at or above operating level in a vertical range. The material removed is suitably dumped. The material to be handled should be relatively losses or soft to medium hard. The clamshell excavators are widely used for reading of material and for working in limited space as in case of foundation trenches for pipelines, etc. it is also used for jobs which require fairly accurate dumping and disposal of materials.
Power shovel excavated
This type of excavator carries shovel at its lower end. The shovel is provided with a sharp cutting edge. This type of excavator is used to dig at or above the operating level. It can handle the loose rock and the material caught in the shovel may be suitably disposed of. The boom of the hovel excavators is not placed where the sufficiently wide area is available for working space of the shovel and for the hauling equipment to gain access to the shovel.
This types of the excavator are used for or below operating level. The various type of dragline excavators is available.
It is useful under following conditions
- The bottom conditions are wet i.e. dredging in the river bed and clearing ditches.
- The digging is to be done well below the ground level. The dragline bucket is better filled by level. The dragline bucket is better filled by jerking i.e. by intermittent pulling.
- The ground to be excavated is soft or medium hard the thickness of the soil layer caught and removed from the bucket depends on the density of soil.
- The stuff is being dumped as far from the unit as possible.
There are three types of dragline excavators
Crawler mounted: it has a low travel speed and is suitable for soft ground
Wheel-mounted: it has a high travel speed and suitable for firm ground and for the scattered job.
Truck mounted: it has a high travel speed and suitable for the firm for scattered jobs
This type of excavators carries the skimmer at its lower end. It is used for surface excavation and levelling and it cuts the surface of the earth to a depth of about 200mm to 300mm. the skimmer excavator can also be used for loading the loose excavated material.