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Crawler Loader

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2005 Caterpillar 963C Crawler Loader
The crawler loader combines the stability of the crawler tractor with the abilities of a wheel loader. However, to construct a reliable crawler loader it requires more than simply attaching a loader bucket onto a crawler tractor. It must be designed with its specific purpose in mind to ensure it has the strength to withstand heavy excavating.

The introduction of hydraulic excavators diminished the market for the crawler loader because it was unable to match the excavator's lifting power and flexibility. However, crawler loaders are capable of maneuvering across the entire construction site under its own power, whereas most hydraulic excavators require towing or transport. While crawler tractors are still being manufactured today for niche markets, they reached their peak of popularity in the 1960s.


[edit] History

Modern crawler tractors are built as integrated units to provide the correct balance and strength for excavation. However, the first crawler loaders were manufactured as loader shovel attachments for specific tractors.

As early as the 1930s, loader attachments were being constructed for tractors. Incapable of carrying large loads, the buckets were operated by simple cables and latches.

[edit] Trackson's Developments

One of the first companies to design crawler loader shovels was the Milwaukee-based Trackson Co. Founded in 1922, the company began designing tractor equipment for Caterpillar in 1936. A year later, Trackson had constructed a vertical-lift cable-operated loader attachment designed specifically for Cat tractors. Together, with the loader and tractor, they were called "Traxcavators". These heavy attachments were mounted over and above the tractor hood, creating a fairly unstable machine. The first shovels had capacities ranging from half a cubic yard to two cubic yards (0.4 to 1.5 m3). They were controlled from the tractor's power take-off by a series of cables and winches.

The introduction of hydraulics into Trackson loader attachments was received with great support. The simpler hydraulically powered loader replaced the complicated cables, winches and latches. Trackson was also able to get rid of the heavy frame mounted on the tractor hood, creating a lighter attachment.

[edit] Caterpillar Acquires Trackson

Caterpillar loved the hydraulic changes so much that it bought the Trackson Co. in 1951, adopting the Traxcavator name for all its crawler loaders. Soon, Caterpillar decided the only way to manufacture a truly reliable machine was to build a crawler loader from the ground up for the specific purpose of heavy excavating. In 1953, Caterpillar released its first integrated hydraulic crawler loader, the No. 6 Traxcavator.

1999 Liebherr LR632 Crawler Loader

[edit] Contributing Companies

While Trackson and Caterpillar were certainly pioneers in the crawler loader industry, they were not the only companies that realized its potential. A Chicago-based company, Tractomotive Corp., designed the first hydraulically powered bucket in 1946. It was supplied to the tractor company Allis-Chalmers. Allis-Chalmers eventually bought out Tractomotive and went on to build some of the largest crawler tractors.

Bucyrus-Erie built hydraulic attachments for International Harvester tractors in the 1940s. However, IH made its mark on the crawler loader industry with Drott Co., who was responsible for designing the four-in-one clamshell bucket. This new bucket increased the versatility of an otherwise one-purpose machine. The crawler loader could now be used for loader, scraper, dozer, or clamshell duties.

Hoover Machine Co. Ltd. teamed with Caterpillar to manufacture the Overhead Dozer, which required the vehicle to excavate from the front then lift the material over the top of the machine and release it on the other side. The operator was equipped with overhead cab protection or falling debris could have been life threatening.

In the 1970s, the full range of hydraulics was instituted with the introduction of hydrostatic motors into crawler tractors. While hydraulic loaders eliminated the cables and winches, hydrostatic motors removed the steering clutches, brakes, transmissions, and drivetrains. All control was now done through two simple joysticks, one for the tractor and another for the loader.

The U.K.-based company JCB produced the first rear-engine hydrostatic crawler loader in 1971. It set the standard for all crawler loaders that followed.

Sales of the crawler loader have decreased significantly since the 1970s with the emergence of the hydraulic excavator. However, many hydraulic excavators are so large they require assistance to move to different areas of the construction site. So, companies requiring a more maneuverable excavator/loader still purchase the crawler loader for specific tasks.

[edit] Features/How it Works

As its name intimates, crawler loaders travel on crawler tracks. However, the tracks can be manufactured with varying number of grousers or can even be made of rubber. The type of track depends on the surface it will be driving upon.

The tractor is hydrostatically driven, meaning the entire motor is powered by hydraulics instead of transmissions, drive chains, and clutches. This increases the simplicity of operation by controlling all movement with joysticks. The lifting arms and buckets are also all powered by hydraulics. Size of the tractor and bucket varies entirely upon the manufacturer and model.

[edit] Common Manufacturers

[edit] Additional Photos

See also Crawler Loader (Photo Gallery)

[edit] References

Haddock, Keith. Giant Earthmovers. MBI Publishing Company:1998.