civil engineering Civil engineering is a regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads ...

, a wheel tractor-scraper (also known as a land scraper, land leveler, tournapull or simply called a scraper) is a type of

heavy equipment Heavy equipment, heavy machinery, earthmovers, construction vehicles, or construction equipment, refers to heavy-duty vehicles specially designed to execute construction tasks, most frequently involving earthwork operations or other large con ...

used for earthmoving. 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, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

like a carpenter's plane or cheese slicer 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 (mathematics), line is a number that describes the direction (geometry), direction of the line on a plane (geometry), plane. Often denoted by the letter ''m'', slope is calculated as the ratio of t ...

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.

History

R.G LeTourneau conceived the idea of the self-propelled motor scraper while recovering from a near-fatal auto accident. He was an earth moving contractor dealer in bulldozer accessories and envisaged a pulled trailer that could excavate and pick up earth as it moved. He approached bulldozer manufacturer

Caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...

in the mid-1930s with his idea, but it was turned down, so he founded his own company. The first Tournapull, called the Model A, was rolled out of his factory and into trials in 1937. 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.

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 (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

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

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. Scrapers can be very efficient on short hauls where the

cut and fill In earthmoving, cut and fill is the process of constructing a railway, road or canal whereby the amount of material from cuts roughly matches the amount of fill needed to make nearby embankments to minimize the amount of construction labor. ...

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. Smaller scrapers may be towed by a

bulldozer A bulldozer or dozer (also called a crawler) is a large tractor equipped with a metal #Blade, blade at the front for pushing material (soil, sand, snow, rubble, or rock) during construction work. It travels most commonly on continuous tracks, ...

Configurations

Challenger tractor with a scraper pan behind

* 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

History

Design

Configurations

See also

References