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
| FMDZ