User:Cheesetron246/Revision of LHD (load, haul, dump machine)

LHD (load, haul, dump) loaders are similar to conventional front end loaders. LHD loaders are used in hard rock mining applications, often underground. More than 75% of the world's underground metal mines use LHD for handling the muck of their excavations.^[1]

Constructional details

LHDs have powerful prime movers, advanced drivetrain technology, heavy planetary axles, four-wheel drive, articulated steering, and ergonomic controls. Their narrower, longer and lower profile make them suitable for underground application where height and width are limited. As the length of the vehicle is not a limitation in a tunnel, LHD loaders are designed with increased length as compared to conventional front end loaders. The length improves axial weight distribution and bucket capacity. The two-part construction with central articulation helps in tracking and maneuverability. In mining, there is a limitation for shifting heavy equipment, and sometimes a LHD has to be shifted through a shaft while dismantled.^[1]

Capacity

An LHD's carrying capacity ranges from 1 to 17-25 metric tonnes, their bucket size ranges from 0.8 to 10 m³, and their bucket height ranges from 1.8 to 2.5 m.

Drives

LHDs are available in both diesel and electric versions. The diesel version is easily transportable from one location to another and has diesel engines as the main power drive with around 75 to 150 horsepower. Engines are either water- or air-cooled.

Electric motor driven LHDs generally have 75 to 150 HP. These operate at a medium voltage of 380 to 550 volts. Flexible trailing cables are provided with a reeling/unreeling facility to feed power.

These drives operate hydraulic pumps and hydraulic motors for further operation of the various movements of buckets and vehicle traction and steering. The speed of the vehicle is controlled mechanically. The transmission is controlled by a hydrostatic drive; in hydrostatic transmission, the motor drives a variable displacement pump hydraulically connected to a hydro-motor driving the axle via a gearbox. The speed is controlled by changing the displacement volume of the axial pump. The power train consists of a closed-loop hydraulic transmission, parking brakes, two-stage gearbox, and drive lines.^[2]

Safety provisions

Service, emergency, and parking brakes with fire-resistant hydraulic fluid are used. Headlights, audible warning signals, backup alarms, and portable fire extinguishers are kept on board the vehicle. A special cabin is also provided for the safety of the operator. A safety device is provided to shut off the engine if exhaust gases exceed a temperature of 85 °C (or as per set value).^[1]

For safety from an electric shock, the LHD's power source (gate end box) are equipped with earth conductivity protection using a pilot core^[3] in the electric trailing cable, which isolates complete power when earth continuity is broken.

Latest developments

LHDs are available with remote controls. These are essential where the stope is unprotected from the top, as loose muck can fall, endangering anyone in the vehicle. There are LHDs available with a remote tramming device. Vehicles equipped with this can handle 8000 tons of ore per day.^[4]

Footnotes

^ ^a ^b ^c [1], Surface and Underground Excavations, 2nd Edition: Methods, Techniques and ..., By Ratan Raj Tatiya, p. 181
^ [2], Reliability modeling and performance, by B. Samanta*, B. Sarkar†, and S.K. Mukherjee‡[3]
^ [4]; Electrical Engineer's Reference Book, M A Laughton, M G Say - 2013 - Technology & Engineering, p.32/18 mining; [5]
^ [6], Surface and Underground Excavations, 2nd Edition: Methods, Techniques and ..., By Ratan Raj Tatiya, p. 183