Wheel tractor-scraper

In civil engineering, a wheel tractor-scraper is a piece of heavy equipment used for earthmoving. The rear part has a vertically moveable hopper (also known as the bowl) with a sharp horizontal front edge. The hopper can be hydraulically lowered and raised. When the hopper is lowered, the front edge cuts into the soil or clay like a cheese slicer and fills the hopper. When the hopper is full (8 to 34 m³ (10 to 45 yd³) heaped, depending on type) it is raised, and closed with a vertical blade (known as the apron). The scraper can transport its load to the fill area where the blade is raised, the back panel of the hopper, or the ejector, is hydraulically pushed forward and the load tumbles out. Then the empty scraper returns to the cut site and repeats the cycle.



On the elevating scraper the hopper is filled by a type of conveyor belt with cutting edges.

Scrapers can be very efficient on short hauls where the cut and fill areas are close together and have sufficient length to fill the hopper. The heavier scraper types have two engines ('tandem powered'), one driving the front wheels, one driving the rear wheels, with engines up to 400 kW (550 horsepower).
A Caterpillar towed scraper parked up

Self propelled scrapers were invented by R. G. LeTourneau in the 1930s. His company called them Tournahoppers.



Two scrapers can work together in a push-pull fashion but this requires a long cut area.

From http://en.wikipedia.org/