Hoist by definition 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. The object can be raised, lowered or moved
depending on the necessity. The hoist work on the basic principle of
balance of forces where an equal and opposite force is applied on the
load force. The applied force can be reduced by using a pulley system.
The 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. The block and tackle pulley invented by
Archimedes allowed sailors to move heavy objects with ease that would
otherwise be very difficult. This invention is considered as a precursor
to the modern hoist technology.
The hoist can be further classified into drum, friction, and Blair multi-rope type.
Drum type: In Drum type hoisting devices, the lifting medium
is continuously wrapped around a drum. Unlike the friction type where
the load is directly hoisted from the top, in drum type hoist the
pulling mechanism is connected to a drum, which is to the other side of
load across the headframe and sheaves. The headframe and sheaves are
required to center the hoisting medium in the shaft compartment. Drum
hoists are the most common hoists used in North America, South Africa
and South America. They also require the least amount of maintenance
among all hoist types.
a. Single drum: In a single drum hoist, a rope is attached to a drum
and wound and is used to hoist the load through an overhead pulley.
Single drum hoists are found to be more efficient than double drum
hoists for most of the applications.
b. Double drum hoist: In a double drum hoist, a rope is wound around
two drums instead of one. Double drum hoists are preferred for lift
systems with multiple hoists.
You can find more information about drum hoists at this link.
Friction (Koepe) type: Unlike drum hoists, friction hoists are
economic options for shallow shafts. They are mounted right above the
mine shaft or at the top of headframe, thus requiring less space than
drum hoists. The lifting medium is passed over a pulley with the load
connected to the one end of the lifting medium. The friction between the
pulley and the lifting medium aids the hoisting. The friction between
the pulley and the lifting medium prevents the load from sliding in the
opposite direction when the weight is pulled up using gears and pulleys.
Developed by Frederick Koepe in 1877, the lifting medium is not wound
on a drum, and hence multiple hoists can be used near to each other.
Friction hoists require more routine maintenance than drum hoists and
are not suitable for hoisting from multiple loading pockets on different
horizons within a shaft.
Blair multi-rope type: The Blair multi-rope hoist system is
used for accessing much deeper mines and can be found in many of the
world's deeper mines, such as in South Africa. One of the mines that
uses this type is the Moab Khotsong Mine where it is used up to 3,150m.
It has a capacity to access a depth of up to 5,000m.
USAGE IN MINES
In mines hoist are generally used in transportation to and from the
underground mines. As very high power hoist controlled operation is
required, generally electric hoist driven by frequency controller are
used for precise movement of the hoist. The hoist can be either drum
type or friction type. There are various arrangements for drum type
1. Single Drum Unbalanced hoisting: These types of hoists are
generally used for single hoists. These hoists can be expensive if the
hoists are to be used for greater depths as high torque motors and high
tension lifting mediums will have to be used.
2. Single Drum Balanced hoisting: These hoists provide a cheaper
option by reducing the need of high torque motors and high tension
lifting mediums. In balanced hoisting, the hoisted load is balanced by
counterweight. It is mostly used for single level hoisting.
3. Divided Single Drum: This can be used for multi-level hoisting with multiple hoists.
4. Split Differential Diameter Drum: Split differential diameter
drums are used for reducing the problems of rope adjustment, which is
often faced in the divided single drum. Here one drum with smaller
diameter than the main drum is used to balance the hoist.
5. Double Drum, One Drum Clutched: This type of hoists helps in
making quick adjustments to the lifting medium. These hoists can be
efficiently used for multilevel operation.
6. Double Drum, One Drum Clutched: This type of has all the
advantages of one drum clutched with an extra capability of having an
uninterrupted hoisting even is the counter apartment is under repairs.
7. Multiple Drum, Blair Type: The conveyances are attached with two
lifting medium instead of one which is coiled on a drum. The advantage
of this type of hoist is that much thinner lifting medium and smaller
drums can be used.