Backhoe comprises a bucket on the end of an articulated boom, set on a pneumatic tyred or crawler tractor unit. The boom, bucket arm and bucket are usually controlled by hydraulic rams. Back-acters operate by digging towards the machine in an arc from a small distance above the surface on which the machine stands to a position vertically below the outer edge of the machine. The maximum depth of excavation is related to the length of the boom and machines with depth capacities between 2.6 and 6 m are in common use. Long reach machines with nominal reach and depth capacities up to 18 to 14m respectively are also available. Buckets are available for back-acters in different sizes up to 3cum., depending on the power of the machine and the use. Loading is generally carried out by lifting the bucket and swinging the boom away from the working face to the awaiting haulage vehicle. Alternatively, material can be dumped adjacent to the machine.
2. Face, Front or Loading Shovel
Face, front or loading shovel is constructed in a similar manner to a back-acter except the boom; bucket arm and bucket operate in the opposite direction, i.e. up and away from the machine. Generally used for excavating faces upto about 8m high and stockpiles. Buckets are available in different sizes upto 4cum (heaped) depending on the power of the machine. Loading is carried out in a similar manner to the back-acter, although some machines have bottom dump buckets to increase the speed of loading. It is useful in excavating soils, weak rocks and blasted rocks from faces in cutting etc. some larger excavators can be converted from back-acters to face shovels.
3. Forward Loader
Forward loader consists of a pneumatic tyred or crawler tractor at the front of which is mounted a wide bucket that can be moved in a vertical plane. Excavation is carried out by driving the machine towards and the bucket into the material; the bucket is then turned and lifted upwards, thus catching and excavating the material. The hauling vehicle is loaded by driving the loader to and emptying the bucket into the body of a vehicle. Loaders are generally used to excavate the materials at and for a distance above ground level and can be used to push or haul material in the bucket over a short distances. Modern loaders have hydrostatically powered buckets and the smaller units may be equipped with a back-acters (i.e. backhoe loader)
General characteristics of forward loader
Used for loading, backfilling, grabbing and light dozing
Set on pneumatic tyres with wide bucket on front
Payload capacity-700 g
Breakout force at bucket edge-3500 kg
Overall length-5.23 m
Overall width-2.00 m
Dump angle-41 degree
Max height-4.165 m
Dump height-3.365 m
These machineries are used for various earthwork puposes such as excavation of earth and loading etc. its excavating and loading capacities are given in the following table
Max operating height
Reach from side
Reach at ground
Reach from swing
Reach from rear side
Rollback at GL
Height max fully raised
Max dump angle
Bucket breakout force
Loader arm force
Lift capacity to full height
Dragline equipment is operated from cranes or similar plant with a long boom. Excavation is done by pulling a bucket suspended on a cable towards the machine by a second cable. Thus, draglines are especially suited for the excavation of soft and loose materials from a distance at a level beneath or slightly above their tracks and may be used to excavate under water. Excavated material can be removed directly to a stockpile or loaded into haulage vehicles or conveyer hoppers by rotating the machine with the bucket in the upward position.
Grab consists of a cable or hydraulically controlled bottom-opening bucket suspended from a crane or a lifting arm. The bucket is opened and dropped on to a material to be removed. It is then closed and the material caught between the jaws lifted in the grab bucket and discharged onto stockpiles or into waiting haulage vehicles. Grabs are typically used for the excavation of pits or trenches and loading to and from stockpiles.
Graders are used to spread fill and finely trim the subgrade. They consists of a blade which can rotate in a circular arc about a sub horizontal axis and which is supported beneath a longitudinal frame joining the front steering wheels and the rear drive wheels. The front wheels are generally articulated whilst the rear wheels are set in tandem beneath the motor and control units. The blade is used to trim and redistribute soil and therefore graders usually operate in the forward direction.
8. Road Lorries
Road lorries are available in sizes up to 38 tonne gross vehicle weight and generally have steel or steel/aluminum sheeted bodies. Such vehicles require to be loaded by other plant but are generally unloaded by side or rear tipping.
Dump trucks or dumpers generally vary in size from 1 to about 80 tonne capacity. Large capacity machines are also available but are generally used in mines, quaries or open cast sites. In recent years articulated dump trucks with capacities upto 35 tonne have become popular as they are versatile and are especially suitable for hauling on softer sub grades. The speed of tipping in increased over a road lorry by the absence of a tailgate. Small dumper units are available for work on small sites and mounted dump trucks are also available with load capacities upto about 20 tonne.
Conveyers are built up with a number of units of endless flat belt conveyers placed in series and major changes in direction can be made at transfer points where material from one belt falls and is channeled on to next. Loading is generally carried out via a hopper, which may be designed to screen out over size material. The conveyer may end either above a stockpile or in a stacker, which allows the material to be spread over a large area. Conveyers are generally used in quarries and pits in areas of very steep or poor access.
Bulldozer is a tractor equipped with affront pusher blade, which can be raised and lowered by hydraulic rams. An angle dozer has a blade that is capable of being set an angle to push material sideways whilst the tractor moves forward. The tractor unit is usually mounted on crawler tracks thus allowing it to travel over and push off a wide variety of ground conditions although wheel mounted units is available. Blades are manufactured in a variety of styles but are all of heavy duty construction with a hardened steel basal leading edge driven into the ground to cut and push the material to be excavated. Dozers have a wide variety of roles including excavating soils and weak rocks, ripping moving excavated material over short distances spreading materials, trimming earthworks and acting as a pusher to boost the effective power of scrapers and other plants. Wide ranges of crawler units are available ranging from 45 to 575 kW.
Scraper can excavate load and deposit material in one cycle and may be towed or self propelled. It consists of a centrally mounted bowl, the bottom, leading edge of which can be controlled. Both towed and self propelled scrapers are effectively articulated between the front motorized or towing unit and the bowl and larger self propelled scraper may second engine mounted on the rear.