Hoist (mining)

In underground mining a hoist or winder is used to raise and lower conveyances within the mine shaft. Modern hoists are normally powered using electric motors, historically with direct current drives utilizing Ward Leonard control machines and later solid-state converters (thyristors), however modern large hoists use alternating current drives that are variable frequency controlled. There are three principal types of hoists used in mining applications: Drum hoists are the most common type of hoist used in North America, South Africa and South America. When using a drum hoist the hoisting cable is wound around the drum when the conveyance is lifted. Single-drum hoists can be used in smaller applications, however double-drum hoists easily allow the hoisting of two conveyances in balance (i.e. one skip being lifted while a second skip is being lowered). Drum hoists are mounted on concrete slabs within a hoistroom, the hoisting ropes run from the drum, up to the top of the headframe, over a sheave wheel and down where they connect to the conveyance (cage or skip). Drum hoists require less routine maintenance than a friction hoist, because the haulage cable is fixed to the drum, and therefore have less downtime, and the maintenance regime is less sophisticated. Drum hoists can continue to operate if the shaft bottom gets flooded and less shaft depth is required below the loading pocket, unlike friction hoists where such flooding could cover the tail ropes and so on. Because drum hoists do not have tail ropes, the hoisting system is more suited to slinging beneath a conveyance. Drum hoists take up more space than a friction hoist for the same service as all of the haulage cable must be accommodated on the drum when the hoist is fully raised. Drum hoists require rapid fluctuations in power demand, which can pose a problem if power is generated on site rather than provided through the main power grid. Friction (or Koepe) hoists are the most common type of hoist used in Europe, Asia and Australia.