From Academic Kids

A bulldozer is a powerful crawler (caterpillar tracked tractor) equipped with a blade. The term bulldozer is often used to denote any heavy engineering vehicle although the term officially relates only to the dozer blade installed on a tractor. The most common usage of the term bulldozer is to denote a tractor (most often tracked) equipped with a blade, which is the meaning used in this article.

Caterpillar Inc. D9R tracked-type bulldozer.
Image:Cat D9.png
On the right side is the blade, on the left side is the rear-ripper.

The first bulldozers were adapted from farm tractors that were used to plough fields. In order to dig canals, raise earthen dams, and do other earthmoving projects, the tractors were equipped with a large thick metal plate. This thick metal plate (it got its curved shape later) is called a "blade". The blade peels layers of soil and pushes it forward as the tractor advances. Several specialised blades have been developed: for high volume loads such as coal, rakes to remove only larger boulders or blades with razor sharp edges to cut tree stumps.

Sometimes a bulldozer is used to push another piece of earthmoving equipment known as a "scraper". The towed Fresno Scraper, invented in 1883 by James Porteous, was the first design to enable this to be done economically, removing the soil from the cut and depositing it elsewhere on shallow ground (fill).

Over the years, when engineers needed equipment to complete large scale earthworks, firms like the Caterpillar Tractor Company, Komatsu, Fiat-Allis, John Deere, International Harvester, Case, Liebherr, Terex and JCB started to manufacture large tracked-type earthmoving machines. They were large, noisy, and powerful, and therefore nicknamed "bulldozer".

Through the years, the bulldozers got bigger, more powerful, and more sophisticated. Important improvements include more powerful engines, more reliable drive trains, better tracks, raised cabins, and hydraulic (instead of early models' cable operated) arms that enable more precise manipulation of the blade and automated controls. As an option, bulldozers can be equipped with a rear ripper claw in order to loosen rocky soils or to break up pavement (roads).

The best known maker of bulldozers is probably the Caterpillar Tractor Company, which earned its reputation for making tough, durable, and reliable machines. Although these machines began as modified farm tractors, they became the mainstay for major civil construction projects, and found their way into use by military construction units throughout the world. Their best known model, the Caterpillar D9, was also used to clear mines and demolish enemy structures.

Most often, bulldozers are large and powerful tracked engineering vehicles. The tracks give them excellent ground hold and mobility through very rough terrain. Wide tracks help distribute the bulldozer's weight over large area (decreasing pressure), thus preventing it from sinking in sandy or muddy ground. Extra wide tracks are known as 'swamp tracks'. Bulldozers have excellent ground hold and a torque divider designed to convert the engine's power into dragging ability - enabling the bulldozer to use its own weight to push very heavy things and remove obstacles that are stuck in the ground. The Caterpillar D9, for example, can easily tow tanks that weigh more than 70,000 kg. Because of these attributes, bulldozers are used to clear areas of obstacles, shrubbery, burnt vehicles and structures' debris.

The bulldozer's primary tools are the blade and the ripper.

The ripper is the long claw-like device on the back of the tractor. Rippers can come singly (single shank) or in groups or two or more (multi shank rippers). Usually, a single shank is preferred for heavy ripping. The ripper shank is fitted with a replaceable tungsten steel alloy tip.

Ripping rock allows the ground surface rock to be broken into small, easy to handle and transport rubble which can then be removed so that grading can take place. Agricultural ripping allows rocky or very hard earth to be broken up so that otherwise unariable land can be put to use in agricultural applications. For example, much of the very best land in the California wine country consists of old lava flows. With heavy bulldozers such as the Caterpillar D9 and the D11 the lava is shattered allowing practical agriculture for the wine industry. In another example, hard earth can be ripped and decompacted to allow the planting of orchards which otherwise could not grow on the land.

The dozer blade is a piece of heavy metal plate, installed on the front of the tractor, with the aim of pushing things, handle rough obstacles and shoving sand, dirt and debris. The dozer blade on front of the tractor usually comes in 3 varieties:

  1. A Straight Blade ("S-Blade") which is short and has no lateral curve, no side wings, and can be used for fine grading.
  2. A Universal Blade ("U-Blade") which is tall and very curved, and has large side wings to carry more material.
  3. A "S-U" combination blade which is shorter, has less curvature, and smaller side wings.

Bulldozers have been further modified over time to evolve into new machines which are capable of working in ways that the original bulldozer can not. One example is that loader tractors were created by removing the blade and substituting a large volume bucket and hydraulic arms which can raise and lower the bucket, thus making it useful for scooping up earth and loading it into trucks. Other modifications to the original bulldozer include the reduction in size of the machine to permit it to operate in small work areas where movement is limited such as in mining.

Nevertheless, the original earthmoving bulldozers are still irreplaceable as their tasks are concentrated in deforestation, earthmoving, ground leveling and road carvings. The heavy bulldozers are mainly employed at the leveling of the terrain in order to make it fit to construction. The construction itself, however, is mainly done by small bulldozers and loader tractors.

Bulldozers can be found on large and small scale construction sites, mines, roadsides, military bases, heavy industry factories, and large governmental projects.

Some bulldozers, especially bulldozers in military usage, have been fitted with armor in order to protect the driver from enemy fire, thus enabling it to operate in battle zones. The most famous armored bulldozer is probably the IDF Caterpillar D9, used by the Israeli Defence Forces for detonating explosive charges and demolishing terrorists' structures under fire. Some bulldozers have been fitted with armor by civilian operators in order to prevent bystanders or police from interfering with the work performed by the bulldozer. See: Marvin Heemeyer, Killdozer.

See also

External links

he:דחפור ja:ブルドーザー


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