Bulldozer and Scraper

Bulldozer

A bulldozer is often referred to simply as a dozer. It is a tractor with a pusher blade attached 10 the front portion. The tractor is the diesel-operated power unit equipped with either crawler chains or rubber tyred wheels for flitting. The pusher blade can be raised or lowered or tilted through small angles horizontally by rams operated through hydraulic pressure or by ropes. The dozer blade is used for pushing loose material or for digging in earth, sand and soft weathered rock. The machine is also engaged for levelling or spreading earth, for levelling of rock spoil in the dumping yard, grading and compacting temporary roads, pushing mineral into sub-ground level bunkers through grizzly, for towing dumpers, etc. It also serves the purpose of pushing boulders, pulling down trees, and is an essential equipment to push scrapers. A dozer equipped with a fork like attachment is known as ripper and operates like a plough to loosen moderately hard rock. The loosened rock may be loaded by a scraper. A dozer can dig 1.2 m to 1.5 m below ground in earth or weathered rock. (Fig 5.2)

                      

 

Scraper

This machine is diesel-operated with pneumatic tyred wheels and has at the centre a bow! fitted with a cutting blade at bottom.

The blade is reversible and can be replaced when blunt. Its working may be compared to that of a lawn mower. As a scraper is pushed forward by a dozer, its blade cuts a thin slice of earth usually between 75 mm and 225 mm thick over a distance of nearly 30 m. The earth is automatically collected in a central bowl whose capacity ranges from 3 m³ to 22 m³ and it takes nearly one minute for loading. When the scraper is fully loaded its bottom opening is closed by the operator through manipulation of a cable (rope) and the loaded scraper, with the bowl lifted, travels to the dumping yard on its own power. At the dumping yard, as the scraper moves, the bottom opening of the bowl is opened and the contents are unloaded in a layer 150 mm to 250 mm thick, over a distance of 30 to 70 m. The bowl is always bottom discharging. Scrapers are unsuitable in soils with stumps, large boulders and hard rocks. When the ground is hard, it is necessary to rip the surface with the help of a ripper before loading by a scraper. Sandy soil is best for a scraper which has to be stopped during rains, if engaged in alluvium. (Fig. 5.3).

Scrapers are used in coal mines for cutting and transporting weathered sandstone as well as coal. The coal excavated by it is however smaller in size.

A Scraper may take 5 to 6 minutes for a complete cycle of loading and unloading if the total up-and-down distance of a trip is nearly 300 m. One-way traffic of loaded and empty scrapers is desirable for good results. One dozer is normally sufficient for every two scrapers used.   

The scraper manufactured by BEML has the following main specifications.

Flywheel H.P. of engine 332 at 2100 rpm;

Capacity: payload 23000 kg; struck 11.5 m³, heaped 16 m^:

Max. Travel speed (forward) 44 km/hr

Overall dimensions mm: length 12600; width 3470; height 3890.

Net weight (no load): 26584 kg.