In an act described by some as a miracle, five gold miners trapped underground for 41 days have been rescued in Tanzania and 12 others are still missing.
The miners had gone underground to rescue a group of 11 other miners and they “survived by eating roots, soil, frogs and cockroaches and are receiving treatment at hospital,” the BBC reported.
Efforts to rescue the miners by the community members were abandoned last month after a fruitless week-long rescue operation.
However, the rescue operation resumed after faint cries were heard by other miners working near the accident site, which confirmed the miners were still alive.
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| mine hoist |
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Friction (or Koepe) hoists are the most common type of hoist used in Europe, Asia and Australia. The friction hoist was invented in 1877 by Frederick Koepe. Friction hoists are mounted on the ground above the mine shaft, or at the top of the headframe. Friction hoists utilize tail ropes and counterweights and do not have the haulage rope fixed to the wheel, but instead passed around it. The tailropes and weights offset the need for the motor to overcome the weight of the conveyance and hoisting rope, thereby reducing the required horsepower of the hoisting motor by up to 30%, with the overall power consumption remaining the same. Friction hoists, unlike drum hoists, can and normally do use multiple ropes giving them a larger payload capacity, however since they require a larger safety factor, they are impractical for very deep shafts.
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 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).
Advantages
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 etc. Because drum hoists do not have tail ropes, the hoisting system is more suited to slinging beneath a conveyance.
Disadvantages
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.
This series hoisting winch are mainly used for mine shaft and inclined shaft to lift coal,ore,waste rock as well as lifting personal,materials,tools and equipment.The principle axis unit used split or intergral type flexible struction drum and the drum suffers force uniformly with big strength.Disc brakes are rear mounted fuel tank with flexible action.The hydraulic can delay secondary brake, and it can be automatically released in wellhead.Double drum hoisting machine has rope adjusting cluth with radial teeth.Transmission parts can be equipped with planetary reducer or parallel axis hardened reducer.Electrical parts has necessary protection and interlock device,and user can choose PLC electrical controller and frequency speed changing electrical controller.Dynamic braking is also available on request.
