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Long Reach Excavator

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Construction Equipment
Case CX240 Long Reach Excavator
The long reach (LR) excavator is a digging machine with an extended boom that is longer than the typical excavator, approximately more than 20 feet (6.1 m) high. Part of the excavator family, the LR excavator is used primarily in demolition projects but can be used in a variety of construction applications. Although it is not known which manufacturer is responsible for inventing the LR excavator, it was brought about when contractors needed to reach further heights than could be achieved with the typical excavator. Reaching more than 20 feet (6.1 m) and sometimes as high as 150 feet (46 m), the LR excavator continues to aspire to new heights.

Contents

[edit] History

[edit] The Otis Shovel

Excavators are among some of the oldest and most essential pieces of earthmoving equipment in history. Deriving from the shovel, the first modern excavator was developed by William Otis in Canton, Massachusetts, 1835. The Otis Shovel consisted of an arm and a bucket that produced a half-slew and was powered by steam. Mounted on a set of cast iron wheels, its mobility was limited, but the efficiency of the machine led manufacturers to experiment with how it could be improved and what other applications it could be used for.

[edit] Developments and Advancements

Other types of excavators quickly followed. Excavators were made mobile with the development of the mobile excavator, as well as larger and capable of digging more materials with the bucket wheel excavator. Excavators were developed for literally any and every excavation project required.

The excavator experienced a series of changes in the years after its initial invention. After the Second World War, manufacturers began powering excavators with hydraulics. The first hydraulically operated model, the TU hydraulic excavator was developed by Poclain in 1951.[1]

What gives the long reach excavator its significance is the height to which it can reach, as implied by the name, but also how it excavates materials. A British company called the Priestman Brothers, now owned by R-B International, produced a long reach excavator that could reach as high as 82 feet (25 m) and was capable of excavating 7,238 pounds (3,283 kg) of materials from sites, whether on land or in ponds. The VC long reach excavator, made in the 1980s, was distinct in that it had a variable counterweight where the typical excavator had a counterweight that was fixed. This feature meant that the excavator boom could reach further heights without running the risk of tipping over the weight of the boom. This type of excavator became very efficient on sites where water was present, such as ponds. [2]

LR excavators were still not widely used and some companies found that in order to satisfy the demand for a product not yet developed, they had to create it themselves. That is what Long Reach Excavations Pty Ltd. did. Its first LR excavator was based on a Komatsu PC220-5. [3]

Similarly, Kocurek Excavators built its first LR as a result of a demand from another company. This product resulted in a demand that led the company to build its first LR excavator for demolition in 1992. [4]

[edit] Safety Issues

Because of the height long reach excavators aspire to reach, the base of the excavator can sometimes risk tipping the machine. Current manufacturers of long reach excavators are focused on producing machines with a long reach but also with a stable base. Excavators with a boom longer than 20 feet (6.1 m) could risk tipping over if this is not taken into consideration. Case Construction has built long reach excavators that operate under a speed that will ensure safe movement to keep the machine stable.

Similarly, Liebherr has developed an Automatic Reach Limitation, a technology that calculates when the boom has exceeded its optimum length and proceeds to shut down to avoid tipping catastrophes. Liebherr LR excavators also consist of a protective cab, designed for demolition projects, where a lot of materials are being broken by the thrust of the arm’s bucket.

Caterpillar has an ultra-high demolition excavator which contends with heights as much as 120 feet (37 m). The UHD has a variable gauge undercarriage that provides stability of for the excavator’s base. Caterpillar also provides warning technology to ensure that the boom doesn’t exceed the height it has been designed for.

[edit] Volvo's LR Excavators

While some manufacturers are specific about the LR excavators that they produce—whether they are for demolition or construction purposes, soft or hard terrain—others, such as Volvo, prefer to keep options available. Volvo produces excavators that can be fitted with an implement. The Volvo EC Series come with different size capacities, depending on the project and application. [5]

[edit] Features/How it Works

Link-Belt 700 LX Series
The LR excavator contains a cab, a base, a boom, and a bucket. The cab is a protective cover for the operator and the controls. The window of the cab normally has bulletproof glass that it is five times stronger than normal glass, to protect the operator from any falling debris. The base of the LR excavator has to be heavy enough to act as a counterweight for the long height of the boom (arm of the excavator), which is in turn connected to the bucket.

Once the boom of the excavator reaches past 20 feet (6.1 m), stability measures have to be in place to ensure the excavator is safe and stable. The capacity of the bucket and how much material it can collect is also determined by the weight of the base.

The base of the excavator is available with crawler tracks or rubber-wheeled tires, dependent upon whether it is rough or soft terrain. Crawler tracks enable the excavator be sufficiently mobile in mud and softer terrain with a conveyor-belt mechanism, whereas rubber tires are ideal for harder, defined surfaces, such as concrete and asphalt.

Modern excavators are normally powered by hydraulics.

Some companies provide implements or attachments that can make the normal excavator a long reach one. Paul Wever Construction Equipment Co., for example, manufactures an apparatus that adds eight to 20 feet (2.4 to 6.1 m) to the excavator. This implement is adaptable to 99 percent of equipment.

Some companies rely on outriggers to stabilize the machine. Typically any machine reaching more than 50 feet (15 m) should have base weighing 120 tons.

[edit] The Arm

The arm moves in two parts just like a human arm would: at the wrist and the elbow. The end holding the bucket can move in directions up and down and is also capable of pivoting.

Inside of the hydraulic cylinder is a rod, which is the inner part of the cylinder, and a piston, which is at the end of the cylinder and enables the arm to move with the help of oil. If there were no oil in the cylinder, the piston would drop to the bottom, but because of the nature of oil, its volume always stays the same.

Oil is pumped through the end of the piston and in turn pushes the rod through the cylinder, thus creating movement of one or both parts of the arm. By controlling the amount of oil that is pumped through the valve, the accuracy of the arm can be easily manipulated. This movement is activated by the use of control valves that are positioned inside the cab where the driver seat is. [6]

One of the functions of this machine is slewing. The swing of the excavator enables it to turn. The swing circle comprises several components: an outer race, an inner race, ball bearings, and a pinion. As the outer race turns, the pinion runs alongside the unmoving inner race. The ball bearings work to ensure that this is done smoothly. [7]

[edit] Demolition Excavator

A demolition excavator is essentially an LR excavator adapted for demolition purposes. They are used on demolition projects when explosives cannot be used. It raises the boom and uses the bucket to strike or cut material as it stands, normally a tower block or building. In the past, a wrecking ball performed this function, but the excavator is preferred as it can offer more precision and control. The excavator can be fitted with shearing or cutting attachments to achieve this. The jaws of the shearing device can be removed and replaced by crushing and cutting implements. In demolition jobs the excavator is normally fitted with a pulverizing attachment so it can break hard material such as concrete. [8]

[edit] Common Manufacturers

[edit] References

  1. Haddock, Keith. The Earthmover Encylopedia. Motorbooks: St. Paul, 2002. 225-263.
  2. What Can You Do with an Excavator. Grading and Excavation Contractors. 2008-09-24.
  3. History. Long Reach Excavation.s 2008-09-24.
  4. A Short History. Kocurek. 2008-09-24.
  5. What Can you Do with an Excavator. Grading and Excavation Contractors. 2008-09-24.
  6. The Mechanism of a Hydraulic Excavator. Kenkenkikki. 2008-09-24.
  7. The Mechanism of a Hydraulic Excavator. Kenkenkikki. 2008-09-24.
  8. The Mechanism of a Hydraulic Excavator. Kenkenkikki. 2008-09-24.