A load haul dump truck (LHD), also known as a scoop tram, is a specialized loading machine manufactured for the underground mining industry. LHDs are used to scoop extracted ore, such as coal, with a bucket, load it into the cart, and dump it in the bottom of the mine to undergo primary crushing before being hoisted to the surface out of the mine.[1]
LHDs are used in more than 75 percent of underground mines throughout the world and are suitable for small and large tunnels, chambers, and stopes.
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[edit] History
[edit] Early Ore Carts
The first form of ore carts did not follow a singular style. Ore carts were constructed in an assortment of designs, some with end dumps, side dumps, and rotating dumps. Even the way carts were transported varied from cart to cart. The earliest forms used in the 1800s were likely hauled by mules and ponies or pushed by men. They were equipped with wheels and later mounted on a set of rails, while later versions were hauled by electric trains.
The early ore carts were constructed in an adaptable, flexible manner and miners made use of them in as many mining conditions and methods as possible. The construction of these cart were so efficient that essentially every component of the car could be easily replaced including the wheels. This was because the flimsy materials used to build the early carts would suffer wear and tear after so much use, probably in part because they were made with wood frames and sides. Later, the carts upgraded to steel frames and cast iron wheels, equipped to give the cart a longer life.
Carts were commonly built in the one-ton size. A mucker would load it the old-fashioned way, with hand tools such as shovels, as much as 16 carts could be loaded during a single shift.[2]
[edit] Loaders and LHDs
As the modern world became increasingly mechanized, loading evolved from the shovel. Miners were now operating heavy equipment to complete this difficult and taxing task. Scrapers were used to pull the rock onto ramps and conveyor systems to be loaded into mine cars and transported out of the mine. The carts also became more modern, with inventors such as Joseph Francis Joy, the founder of Joy Mining Machinery, who devised mechanical loading and digging device in the early 1900s that could be used in underground mining applications.[3]
A singular ore cart could not keep up with the evolving equipment that a mechanized and industrialized society could produce. The 1930s saw the use of cars running on locomotives to load the ore. By now, a range of manufacturers had begun developing machines and carts that were multifunctional, making the arduous task of mucking a mine much easier and simpler.
When Wagner Tractors developed a rubber tired, front end loader for underground mining at the request of Phillips Petroleum in 1958, it marked the beginning of a new market for them. Wagner Mining Scoop Co., founded in 1958, began manufacturing underground mining loaders. The company shipped its first mining scooptram, featuring an articulated center joint known as the MS-1, that summer.
Wagner’s vision led to several inventions, including the first rear dump truck in 1960, the first horizontal discharged truck, the Teletram, in 1961 and the first LHD vehicle in 1963. The first LHD, the ST-5, featured a full reversing 4-speed power transmission, a side seat for the operator to drive in any direction with supported visibility and comfort. Wagner Mining Equipment Co. was acquired by Atlas Copco AB, a manufacturer of mining equipment, compressors and power tools in 1989.
[edit] Present Day LHDs
Wagner’s early inventions paved the way for many progressive features in its future scoop trams and LHD vehicles. Most of the features and progressive models were manufactured throughout the 1990s, including a diesel scooptram with a Z-bar boom linkage, which appeared in 1992, and a fully integrated electronic powertrain with split cap pin retention assembly in 1996.[4]
Just as early carts came in a variety of forms, so too does the modern day LHD or scooptram. Depending on the needs of the mining contractor, LHDs can range in different sizes to carry more volume of ore; they utilize the latest technology in scooping ore with bucket capacity and articulation, and are run by the most powerful powertrains and motors built to date.
The future of LHDs may lie in remote-control technology, which uses a transmitter and radio receiver to control and monitor the operations of the LHD. This enables the operator to control the LHD steering and accelerator system via control. The remote control functions by moving the machine forward into the muck pile and ore is extracted with the bucket. Meanwhile, the engine speed is adjusted to ensure the machine is operational without additional stress being placed on it. When the bucket has scooped a sufficient amount of ore, the operator reverses the machine until it reaches the mine’s opening.[5]
Other developments include an Eject-O-Dump (EOD) bucket, offered by select manufacturers. The EOD positions the bucket in front of the tires. This type of bucket has an extended reach that is made possible by a smaller bucket size and is designed for mines with difficult-to-reach ore. The EDO is useful for loading material into higher trucks.
Automatic tramming is another new feature being explored. The Sweden-based Toro LHD, capable of producing 70,000 tons of ore per day, comprises an automatic tramming system that is capable of loading and dumping 8,000 tons of ore.
[edit] Features/How it Works
The LHD is a machine that travels at modest speeds and consists of internal and external components. The internals of the LHD consist of a bucket, a small engine, an emission exhaust, a long and narrow profiler, a diesel exhaust treatment device, tires and tire accessories, and ventilation systems.
The LHD was modeled to fit under restricted heights and narrow areas within a mine. It consists of a long, low and narrow profiler, which makes it adaptable to mines of all sizes. Because of its size, maneuvering the LHD is awkward but beneficial as it evenly distributes the axle weight of the vehicle to allow for a larger bucket size.
[edit] LHD Internal
The standard for LHD is a diesel engine with horsepower ranging from 78 to 145, but smaller LHDs are outfitted with electric motors. The engine of the LHD are cooled either by water or air and located on the chassis along with emergency and parking brakes, and hydraulic fluid resistant to fire.
Other internals of the LHD include a diesel exhaust treatment device that uses water, catalyctic fume diluter, or similar substances to spray or bathe the exhaust device with water. The LHD is also commonly equipped with a device that automatically shuts off the fuel supply to the engine in emergency situations such as exceeding temperatures of exhaust gases.
A ventilation system is required for the LHD to counter the excessive exhaust fumes it creates inside a confined space. Ventilation systems are also incorporated into safety laws and regulations defined by many countries. To accomplish a healthy working environment, it is recommended that the velocity of air should be more than 98.4 feet (30 m) per minute.
[edit] Buckets and Tires
The externals of the LHD include the bucket, loading and dumping mechanisms and tires. Buckets can come in a variety of sizes, from 1.04 to 13.1 cubic yards (0.8 to 10 m3) with payloads of 1.5 to 17 tons. The standard type ranges from two to five cubic yards (1.53 to 3.83 m3).
The tires can be treaded or smooth and may be fitted with chains. Most mines tend to remove the chains if the LHD includes them because they can prove dangerous in some conditions. Tires account for 10 to 20 percent of the total operation cost because they have to be re-treaded or replaced every 75 to 1,000 hours when they wear down. Tire experience such wear and tear as a result of wet ground, too much wheel spin, and the unstable and sometimes ragged condition of the road they run on.
[edit] Types
Another type of loader is the autoloader, which is used for mucking and delivering. The LHD is used for mucking and transporting. The autoloader is similar to the LHD but features a hopper where the coal is loaded. Once full, the autoloader makes its way either to the ore pass, waste pass, or mill hole to dispose of its contents.[6]
[edit] Common Manufacturers
- Atlas Copco
- Caterpillar
- Dux
- Eimco Elecon India Ltd.
- Equipment Miner
- GHH Fahrzeuge
- Joy
- Schopf
- Tamrock
- Sandvik
[edit] References
- ↑ Mucking. Rock N'Metal. 2008-09-25.
- ↑ Pearson, David W. and Bommarito, Ron. Antique Mining Equipment and Collectibles. Schiffer Publishing: Atglen, 2002.
- ↑ History. Joy. 2008-09-25.
- ↑ Timeline and Milestones. Atlas Copco. 2008-09-25.
- ↑ Load Haul Dump Equipment. Berlet Electronics. 2008-09-25.
- ↑ Tatiya, Ratan Raj. Surface and Underground Excavations. Taylor and Francis: 2005.
