LHD (load, haul, dump machine)

LHD (load, haul, dump) loaders are similar to conventional front end loaders but developed for the toughest of hard rock mining applications, keeping overall production economy, safety, and reliability in consideration. They are extremely rugged, highly maneuverable, and exceptionally productive. 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 drive train technology, heavy planetary axles, four-wheel drive, articulated steering, and ergonomic controls. Their narrower, longer, and lower profile make them most suitable for underground application where height and width are limited. As the length is not a limitation in a tunnel and decline, LHD loaders are designed with sufficient length. The length improves axial weight distribution and bucket capacity can be enhanced. The two-part construction with central articulation helps in tracking and maneuverability. In mining, there is a limitation for shifting heavy equipment, and sometimes, an LHD has to be shifted through a shaft while dismantled.[1]

Capacity

An LHD tramming capacity varies from 1 to 17-25 metric tonne. Their bucket size varies from 0.8 to 10 m³. 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 power drive of 75 to 150 HP or more. Engines are either water- or air-cooled.

LHD with electric motors as drives have a general capacity of 75 to 150 HP. These are operative 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 signal, backup alarm, and portable fire extinguisher are provided. 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 electric shock safety, these LHDs' power source (gate end box) are equipped with earth conductivity protection using pilot core[3] in electric trailing cable, which isolates complete power when earth continuity is broken.

Latest developments

LHDs are available with remote controls. These are essential to remove the material where the stope is unprotected from the top and loose muck can fall off. There are LHD available with the remote tramming facility and these can handle 8000 tons of ore per day.[4]

Footnotes

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