جرافة

الجرافة بالإنجليزية Bulldozer ، هي مركبة معدنية ثقيلة جرارة ، ومجهزة بلوحة معدنية مثبت عليها ما يعرف بالشفرة ، تستخدم لدفع كميات كبيرة من التراب و الرمل ، أو إستخراج ما تحت الأنقاض في عمليات البناء والهدم. وتسخدم كذلك في الأغراض العسكرية وتعرف تلك بالجرافة المصفحة.

A Caterpillar D10N bulldozer

A Liebherr bulldozer with ripper at the back

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 التاريخ

نشأت أول الجرافات من جرارات مزرعة هولت التي كانت تستعمل في حراثة الحقل. وبملاحظة قدرة هذه المركبات على الحركة بإستقرار على الأرض الناعمة أو الطينية بالإضافة إى إمكانياتها للقيام بوظائف عديدة في مجالات البناء أو تمديد الطرق ، تم تطويرها وعمل الجرافة المدرعة والتي أستخدمت في الحرب العالمية الأولى لأول مرة.

 الوصف

A Liebherr bulldozer with a straight blade

The same bulldozer's multishank ripper

Typically, bulldozers are large and powerful tracked heavy equipment. The tracks give them excellent traction and mobility through very rough terrain. Wide tracks also help distribute the vehicle's weight over a large area (decreasing ground pressure), thus preventing it from sinking in sandy or muddy ground. Extra-wide tracks are known as swamp tracks or low ground pressure (lgp) tracks. Bulldozers have transmission systems designed to take advantage of the track system and provide excellent tractive force.

These traits allow bulldozers to excel in road building, construction, mining, forestry, land clearing, infrastructure development, and any other projects requiring highly mobile, powerful, and stable earth-moving equipment.

A variant is the all-wheel-drive wheeled bulldozer, which generally has four large rubber-tired wheels, hydraulically operated articulated steering, and a hydraulically actuated blade mounted forward of the articulation joint.

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

 الشفرات

Bulldozer blade

Komatsu bulldozer pushing up to 7 m³ with semi-U tilt dozer

Bulldozer blades come in three types:

• straight ("S blade"), short with no lateral curve or side wings. Can be used for fine grading.
• universal ("U blade"), tall and very curved, with large side wings to maximize load.
• combination ("S-U", or semi-U), shorter, with less curvature and smaller side wings. It is typically used for pushing large rocks, as at a quarry.

Blades can be fitted straight across the frame, or at an angle. All can be lifted, some, with additional hydraulic cylinders, can be tilted to vary the angle up to one side.

Sometimes, a bulldozer is used to push or pull another piece of earth-moving equipment known as a "scraper" to increase productivity. 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 an area being cut and depositing where needed as fill. Dozer blades with a reinforced center section for pushing are known as "bull blades".

Dozer blades are added to combat engineering vehicles and other military equipment, such as artillery tractors such as the Type 73 or M8 Tractor, to clear battlefield obstacles and prepare firing positions. Dozer blades may be mounted on main battle tanks to clear antitank obstacles or mines, and dig improvised shelters.

 Ripper

Multishank ripper

A Caterpillar D10N bulldozer equipped with a single-shank ripper

A ripper is a long, claw-like shank that may be mounted singly or in multiples on the rear of a bulldozer to loosen hard and impacted materials. Usually a single shank is preferred for heavy ripping. The ripper is equipped with a replaceable tungsten steel alloy tip, known as a boot.

Ripping can not only loosen soil (such as podzol hardpan) in agricultural and construction applications but break shaly rock or pavement into easily handled small rubble.

A variant of the ripper is the stumpbuster, a single spike protruding horizontally used to split a tree stump.

 التعديلات

لقد طرأ على الجرافات تعديلات كثيرة مما أعطاها المقدرة على العمل في المجالات المختلفة وعلى القيام بمهام كانت تعجز عن عملها الجرافات الأصلية في الماضي.

 التعليم

الرابطة الوطنية لمدارس تدريب المعدات الثقيلة (nahets) ، والتي أنشئت عام 2002 ، تستخدم أسلوب التدريب والتعليم المزود بمناهج دراسية كوسيلة لإختبار وتدريب مستخدمين الجرافات.

 الإستعمالات

نجد الجرافات موجودة في معظم المجالات ، في مواقع البناء الكبيرة والصغيرة ، مشروعات التعدين ، مصانع الصناعات الثقيلة ، و المشروعات البيئية الكبيرة.

 الجرافات المصفحة

جرافة مصفحة Caterpillar D9 تستعملها إسرائيل في جيش الدفاع

Bulldozers employed for combat-engineering roles are often fitted with armor to protect the driver from firearms and debris, enabling bulldozers to operate in combat zones. The most widely documented use is the Israeli Military militarized Caterpillar D9, for earth moving, clearing terrain obstacles, opening routes, and detonating explosive charges. The IDF used armoured bulldozers extensively during Operation Rainbow where they were used to uproot Gaza Strip smuggling tunnels and destroy residential neighbourhoods, water wells and pipes, and agricultural land to expand the military buffer zone along the Philadelphi Route. This use drew criticism against both the use and the suppliers of armoured bulldozers from human-rights organizations such as the EWASH-coalition and Human Rights Watch, the latter of whom urged Caterpillar to cease their sale of bulldozers to the IDF. The use of bulldozers was seen as necessary by Israeli authorities to uproot smuggling tunnels, destroy houses used by Palestinian gunmen, and expand the buffer zone.

Some forces' engineer doctrines differentiate between a low-mobility armoured dozer (LMAD) and a high-mobility armoured dozer (HMAD). The LMAD is dependent on a flatbed to move it to its employment site, whereas the HMAD has a more robust engine and drive system designed to give it road mobility with a moderate range and speed. HMADs, however, normally lack the full cross-country mobility characteristics of a dozer blade-equipped tank or armoured personnel carrier.

Some bulldozers have been fitted with armor by civilian operators to prevent bystanders or police from interfering with the work performed by the bulldozer, as in the case of strikes or demolition of condemned buildings. This has also been done by civilians with a dispute with the authorities, such as Marvin Heemeyer, who outfitted his Komatsu D355A bulldozer with homemade composite armor to then demolish government buildings.

 انظر ايضا

• هندسة مدنية
• مركبات هندسية
• Demining - used for landmines clearance
• National Association of Heavy Equipment Training Schools - US educational organisation
• Mining Simulation

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 إستعمالات الكلمة بمعاني أخرى

• كلمة بلدوزر تطلق على مشروب كوكتيل كحولي ويطلق عليه أيضا Jäger Bomb.
• جمبري البلدوزر هز إسم يطلق على نوع من الجمبري يعيش في البحار الإستوائية.
• النقل القاطرة يطلق عليها أحيانا خطأ إسم بلدوزر.

 معرض الصور

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  A Caterpillar D10N bulldozer at work

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 وصلات خارجية

• Bulldozer Specifications and Comparisons
• Bulldozer Specifications
• Construction Equipment and Methods Photographs
• Construction Vehicles Reference CD
• The mechanism of a bulldozer (Short illustrated explanation, with GIF animations, fit for kids)
• Quick Reference Equipment Specs
• Van Natta Bulldozers
• Configure a Caterpillar Bulldozer - from the official website
• Tractor Mounted Dozer Blades - from the Degelman website
• Dozer Simulation
• Bulldozers and GPS Technology
• Pictures and photographs
  • Old bulldozer traversing a cocoa plantation in Ghana
  • Modern CAT D8 bulldozer
  • Small old bulldozer with open cabin
  • CAT largest conventional bulldozer: the D11 dozer
  • Pictures of used bulldozers

http://www.mcaninchcorp.com/ENR_04_10_2006_v6.pdf