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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
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In civil engineering, a wheel tractor-scraper (also known as a land scraper, land leveler, tournapull or simply called a scraper) is a type of heavy equipment 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 like a carpenter's plane or cheese slicer and fills the hopper which has a movable ejection system. The horsepower of the machine, depth of the cut, type of material, and slope 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 (bottom edge of the apron) is opened, 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.
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 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.[1][2] [3] This concept was further developed by LeTourneau Westinghouse Company.[4] Most current scrapers have two axles, although historically tri-axle configurations were dominant.
The wheel tractor-scraper is a large piece of wheeled equipment which is used in mining, construction, agriculture and other earthmoving applications. The front (tractor) portion is articulated to allow a relatively small turning radius. The rear (scraper) portion 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 plane and fills the hopper. When the hopper is full (8 to 56 m3 or 10 to 73 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 under the bowl while the machine is moving. Then the empty machine returns to the cut site and repeats the cycle. Suspension between the tractor and scraper ends typically uses a hydraulic cushion hitch design which can accommodate large load changes between empty and loaded.
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 to load material. 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 areas are close together and have sufficient length to fill the hopper. Smaller scrapers may be towed by a bulldozer, articulated truck, or tractor. The larger scraper types have two engines ("tandem powered"), one driving the front wheels, one driving the rear wheels, with engines up to 469 kW (629 hp) on tractor end, plus up to 353 kW (473 hp) on scraper end. Multiple scrapers can work together in a push-pull fashion using a bail and hook arrangement, or are commonly pushed by track type tractors to assist in loading more quickly.
Modern scrapers can also be factory equipped with Grade Control systems that use GPS Global Positioning System guidance combined with precise hydraulic controls to achieve desired grade in cut and fill areas with millimeter accuracy. [5] Onboard payload systems can also use hydraulic cylinder pressures to estimate payload weight carried by the scraper for each load.
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
In civil engineering, a wheel tractor-scraper (also known as a land scraper, land leveler, tournapull or simply called a scraper) is a type of heavy equipment 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 like a carpenter's plane or cheese slicer and fills the hopper which has a movable ejection system. The horsepower of the machine, depth of the cut, type of material, and slope 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 (bottom edge of the apron) is opened, 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.
The Caterpillar 740 Ejector Articulated Truck is Caterpillar's second generation of articulated haulers (dump truck) to have a system that pushes material out the back of the body. It is the largest articulated haul truck offered by Caterpillar; larger trucks use a rigid frame system. The ejector uses a 4-cylinder hydraulic ram and blade to dump the material out, a similar system to Cat's wheel tractor-scrapers. The 740 Ejector is sold as separate model from the usual 740. Total power is 436 hp (325 kW), total operating weight is 162,280 lb (73,610 kg), with the load being 42 short tons (38 tonnes), 37.3 yd3 (28.5 m3) at a 1:1 heap. Top forward speed is 34 mph (55 km/h).
The Euclid Trucks was a manufacturer which specialized in heavy equipment for earthmoving, particularly dump trucks, loaders and wheel tractor-scrapers. Known for its distinctive bright 'highlite green' paint scheme, it operated in the United States from the 1920s to the 1950s, when it was purchased by General Motors. The firm was later bought by Hitachi Construction Machinery.
A loader is a heavy equipment machine used in construction to move or load materials such as soil, rock, sand, demolition debris, etc. into or onto another type of machinery (such as a dump truck, conveyor belt, feed-hopper, or railroad car). There are many types of loader, which, depending on design and application, are variously called a bucket loader, end loader, front loader, front-end loader, payloader, high lift, scoop, shovel dozer, skid-steer, tractor loader or wheel loader.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
