Wheel tractor-scraper
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In civil engineering, a wheel tractor-scraper is a piece of heavy equipment used for earthmoving. The rear part has a vertically moveable hopper 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 like a cheese-cutter 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. The scraper can transport its load to the fill area where the blade is raised, the back panel of the hopper is hydraulically pushed forward and the soil load tumbles out. Then the empty scraper returns to the cut site and repeats the cycle.
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).
Scrapers were invented by LeTourneau in the 1930s.
Two scrapers can work together in a push-pull fashion but this requires a long cut area.
