civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...

, a wheel tractor-scraper (also known as a Tournapull) is a type of

heavy equipment Heavy equipment or heavy machinery refers to heavy-duty vehicles specially designed to execute construction tasks, most frequently involving earthwork operations or other large construction tasks. ''Heavy equipment'' usually comprises five e ...

used for

earthmoving Earthworks are engineering works created through the processing of parts of the earth's surface involving quantities of soil or unformed rock. Shoring structures An incomplete list of possible temporary or permanent geotechnical shoring structur ...

. It has a pan/hopper for loading and carrying material. The pan has a tapered horizontal front cutting edge that cuts into the

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

like a carpenter's plane and fills the hopper which has a movable ejection system. The

horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

of the machine, depth of the cut, type of material, and

slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

of the cut area affect how quickly the pan is filled. When full, the pan is raised, the apron is closed, and the scraper transports its load to the fill area. There the pan height is set and the lip is opened (the lip is what the bottom edge of the apron is called), so that the ejection system can be engaged for dumping the load. The forward momentum or speed of the machine affects how big an area is covered with the load. A high pan height and slow speed will dump the load over a short distance. With the pan set close to the ground, a higher speed will spread the material more thinly over a larger area. In an "elevating scraper" a conveyor moves material from the cutting edge into the hopper.

Design

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

hopper Hopper or hoppers may refer to: Places *Hopper, Illinois * Hopper, West Virginia * Hopper, a mountain and valley in the Hunza–Nagar District of Pakistan * Hopper (crater), a crater on Mercury People with the name * Hopper (surname) * Grace H ...

(also known as the bowl) with a sharp horizontal front edge. The hopper can be

hydraulically Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...

lowered and raised. When the hopper is lowered, the front edge cuts into the

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

like a plane and fills the hopper. When the hopper is full ( 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 Robert Gilmour LeTourneau (November 30, 1888 – June 1, 1969), born in Richford, Vermont, he was a prolific inventor of earthmoving machinery and the founder of LeTourneau Technologies, Inc. His factories supplied LeTourneau machines which rep ...

in the 1930s. His company called them Tournahoppers. This concept was further developed by LeTourneau Westinghouse Company.The Wabco Archive Wheel-Tractor Scrapers (Global General Publishing Pty Ltd,2011) 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 . Multiple scrapers can work together in a push-pull fashion but this requires a long cut area.

Configurations

* Open bowl: usually requires a push-cat (bulldozer or similar) to assist in loading. * Elevating scraper: self-loading as it uses an elevator to load material; requires no push-cat. * Tandem scrapers: separate tractor and scraper engines provide greater power, and better traction in steep or slippery areas * Tandem Push-Pull: concentrates the combined horsepower of two such machines onto one cutting edge. The push-pull attachment allows two individual scrapers to act as a self-loading system, typically loading both machines in less than a minute, one after the other. * Auger: uses vertically mounted auger in the bowl to pull material upwards. * Pull type scraper: uses agricultural tractor, articulated dump truck, or bulldozer to pull. Pull type scrapers can be utilized individually or two or three units can be pulled behind a single tractor.

References

{{Authority control Engineering vehicles

Design

Configurations

See also

References