Mumbai University > Civil Engineering > Sem 8 > Construction Engineering

Marks: 10Marks

Scrapper are the devices to scrap the ground and load at simultaneously, transport it over the required distance, dump and then spread the dumped materials over the require area to be required thickness level and return to the pit for the neat cycle. The Scrapper are designed to dig, load, halt, dump, and spitted and sometime called as carry all.

Scrapper are 3 types:

1.Towed Scrappers

2.Self Propelled or Motorized or Conventional Types

3.Self loading or Elevating Scrapes.

The Towed Scrappers are provided with either cables or hydraulic control.

Self propelled or motorized or conventional scrappers are most popular nowadays.

These are generally manufactured in ranges from 10 to 25 wheeled metres.

Wheeled scrapers have more hauling speed and hence are suitable for long distances hauling while crawler towel scrappers travel at slower speed and can be used for short hauls only.

Construction:

Bowl:

The bowl is a span to hold the scrapped list. It is hinged at the rear corners to the rear axle inside the wheels, and is capable of tilting down for digging or ejecting. The bowl size is specified. It indicate the size of scrappers.

Cutting Edge:

The bowl has a cutting edge attached at the bottom. The cutting edge is lowered into the first to make a shallow cut.

Apron:

This is wall in front of the bowl, which opens and closes to regulates the flow of earth in and out of bowl

Tail Gate or Ejector:

These are rear of pan which is capable of forward and backward movement inside the bowl. During loading, it remains at its rear wall, while mains forward to help in ejecting the load during dumping.

Operations:

Loading or Digging:

Operator moves to the act with the ejector at the rear and the apron raised approximately to 40cm.The bowl is then lowered to desired depth at art increase engine speed, move, forward to first gear, keep optimum depth of cut, when the bowl is full the apron is closed and the bowl is then raise.

Transportation:

The bowl is transported in high rear in raised position to provide sufficient clearance. During transporting, apron should be fully closed to present loss of materials and the ejector should remain in rear position.

Unloading:

Unloading in a scrapper is also termed as ‘dumping’ and ‘spreading’. The bowl should be positioned to spread the material to the desired depth during this operation. A partial opening of apron during the initial unloading will help in even spreading, when the dump is complete, the tail gate is fully retracted, the apron dropped and the ‘bowl’ raised to transporting position. The finishing touch during spreading is done by grading it with cutting edge, and the unit then hurried back and starts next cycle.

For better efficiency, the following points should be taken care of:

Depth of cut should commensurate with the power available for the cut.

Keep the haul road maintained.

Pushes should utilize their waiting time in dressing the out.

Loading operations should be carried out downhill wherever possible.

Excessive turning of a pusher should be avoided and scrapper pushes balance should be maintained.