Li�ing mechanisms
in mines- Hoists
Hoist by de nition means to haul or to raise an object to higher altitudes. Hoists are mechanical or electromechanical devices used to move an object from one point to another, which would be otherwise physically challenging. �e object can be raised, lowered or moved depending on the necessity. �e hoist work on the basic principle of balance of forces where an equal and opposite force is applied on the load force. �e applied force can be reduced by using a pulley system. �e hoist technology is believed to originate from the lever system where a large force can be countered using small force by proper placement of the fulcrum. �e block and tackle pulley invented by Archimedes allowed sailors to move heavy objects with ease that would otherwise be very difficult. �is invention is considered as a precursor to the modern hoist technology.
TYPES OF HOIST �e hoists can be classi ed based on the li�ing medium, and the source of powering the hoist. Li�ing medium:
1. Manual: �e load is hoisted using manual operation. It is the oldest type of hoist where humans, and animals where used to haul the loads. Such schemes where used during ancient period for the construction of buildings. Nowadays these hoists are used to li� light loads.
2. Electric: Electric power is used to hoist the load. �is technology overtook the manual operation during the industrial development. Such hoists are faster and more powerful and thus forms a huge percentage of the hoists used in the industries. 3. Pneumatic: �e powering of these hoists is through pneumatic medium. Compressed air is used to run the motor or the engine to deliver a li�ing torque. �ese hoists have an advantage of being lighter, safer and use less energy to do the same task.
Powering source: Chain: Utilizes link or roller chain as its li�ing medium. Wire rope: Utilizes wire rope as the li�ing medium Strap: Utilizes polyester or nylon straps as the li�ing medium �e hoist can be further classi ed into drum, friction, and Blair multi-rope type.
Drum type:
Page34 | Jan- Feb 2016
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