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Scraper – Construction, Operataion and Specification

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Scraper

It(Scraper) is a diesel-operated four-wheel-drive rubber tyred tractor or a crawler tractor having a bowl attached with a cutting blade at the bottom.

The scraper can cut a thin slice of unconsolidated material solt rock on soil (thickness of the slice is approximately varying from 70 mm to 250 mm) and can nicely be used within a radius varying from 150 m to 1500m.

The size of the material which it can handle varies from very fine to more than 550 mm in good and dry ground condition. However wet ground condition hampers the scraper efficiency.

It is very much flexible under wide varied conditions and can handle a wide rate of production ranging from very small to very high total tonnage.

Maximum efficiency is achieved at a very flat gradient but it can negotiate a gradient even more than 15°. Scraper cut and load or simply load, haul, dump and return back for recycling of operations.

Construction And Operation Of Scraper

Scraper can also be used for hauling blast fragmented hard rocks or minerals. The scraper should be used for removal of topsoil or unconsolidated rocks or minerals of thickness 2m to 3 m.

The speed of a tractor wheel-mounted scraper is around 60km/h to 65 km/h. Because of higher mobility, the wheel-mounted scraper is preferred over the crawler track-mounted scraper.

However where steep gradient, seasonal variations, etc., are to be encountered and where mobility is not a factor of selection the crawler track-mounted tractor will yield a very good result.

The tractive effort of the scraper depends on power, the weight of the machine, gear efficiency, type and size of the tyres, condition of the surface topography over which it moves, etc. During cutting most of the times a bulldozer is necessary to push the scraper the backside.

The scraper may be used over a ripped or hard mineral or rock surface for loading and transporting purposes. It is also used for leveling purposes. However, it requires a very good traveling way. It is unsuitable in hard ground conditions and sites having big boulders.

Types Of Scraper

The scrapers are basically divided into two categories

  • Sell propelled type
  • Towed type.

Rubber tired self-propelled scrapers are available as four-wheel units or as two-wheel overhung units. Because of the stability, smoothness of movement, ease of operation, higher speed (around 45 km/h to 50 km/h), higher safety, four-wheeled scrapers are widely used.

Of course sometimes due to lower investment, lower operating and maintenance cost, a greater degree of maneuverability two-wheeled overhung scrapers are also selected.

The pusher tractor or bulldozer provides the extra tractive effort in it during cutting and loading operations.

The towed scrapers are mounted over a four-wheeled machine body and attached to the rear side of the tractor. A scraper consists of the following main units and components: bowl, apron, cutting blade, steering system, power transmission system, cable or hydraulic type of control unit, braking system, etc.

After retracting the tailgate to the extreme position, the apron is opened partially and the bowl is lowered till the cutting blade touches or penetrates the loose ground with high hydraulic pressure.

The scraper thereafter moves forward taking a slice of 100 mm to 200 mm of the soft, unconsolidated and loose ground material which fed into the bowl till it is filled up.

Thereafter bowl is raised up and the excavated material is hauled and dumped to the required place.

Whilst operating on a bench, a scraper should not approach within 2 m of the bench crest. No scraper should be permitted to move backward downhill when unloading.

Scrapers hauled by wheeled tractors should not be permitted to negotiate access roads having a gradient greater than 15° in the case of a loaded machine or 25° in the case of an empty machine.

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