Wheel tractor-scraper
In civil engineering, a wheel tractor-scraper is a piece of heavy equipment used for earthmoving. The rear part of the scraper has a vertically moveable hopper with a sharp horizontal front edge which can be raised or lowered. The front edge cuts into the soil, like a carpenter's plane cutting wood, and fills the hopper. When the hopper is full it is raised, closed, and the scraper can transport its load to the fill area where it is dumped. With a type called an 'elevating scraper' a conveyor belt moves material from the cutting edge into the hopper.
The scraper is a large piece of equipment which is used in mining, construction, agriculture and other earthmoving applications. The rear part has a vertically moveable (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 plane and fills the hopper. When the hopper is full (8 to 34 m3 or 10 to 44 cu yd 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 bowl is filled by a type of conveyor arrangement fitted with a horizontal flights to move the material engaged by the cutting edge into the bowl as the machine moves forward. Elevating scrapers do not require assistance from push-tractors. The pioneer developer of the elevating scraper was Hancock Manufacturing Company of Lubbock, Texas USA. Self-propelled scrapers were invented by R. G. LeTourneau in the 1930s. His company called them Tournahoppers. This concept was further developed by LeTourneau Westinghouse Company. Most current scrapers have two axles, although historically tri-axle configurations were dominant.
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 (536 hp). Multiple scrapers can work together in a push-pull fashion but this requires a long cut area.
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