Page 237 - DMGT551_RETAIL_BUSINESS_ENVIRONMENT

Retail Business Environment

Notes Overhead Cranes and Hoists

A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around
which rope or chain wraps. It may be manually operated, electrically or pneumatically driven
and may use chain, fiber or wire rope as its lifting medium. The load is attached to the hoist by
means of a lifting hook.

Common small portable hoists are of two main types, the chain hoist or chain block and the
wire rope or cable type. Chain hoists may have a lever to actuate the hoist or have a loop of
operating chain that one pulls through the block which then activates the block to take up the
main lifting chain.

The basic hoist has two important characteristics to define it: Lifting medium and power type.
The lifting medium is either wire rope, wrapped around a drum, or load-chain, raised by a
pulley with a special profile to engage the chain. The power type can be either electric motor or
air motor. Both the wire rope hoist and chain hoist have been in common use since the 1800s.

Gantry Cranes are used for overhead materials handling where existing columns do not have
overhead brackets to support gantry and rails or in open areas where columns cannot be
accommodated. The top main girder is mounted on two A shape columns which are further
resting on wheel mounted end carriages.

Main Girder: The girder is designed considering the class, the frequency of operation and the
duty cycle. The girder could be RSJ type, plate box type or truss type for single girder with its
bottom flange as path for trolley of hoist.
The girder could also have a double girder design for heavy duty applications, where a suitable
track is provided on top of the girders for travel of crab wheels.
Overhead cranes and hoists are used to move heavy objects through a plant. They are used for
the movement of material in a fixed route and fixed area of operation. They come in a variety of
sizes, and many are able to lift twenty-five tons or more. Moving steel slabs is an example of an
overhead crane application. Overhead cranes are efficient at moving small parts only if the parts
can be put together in a large batch and moved in one trip.

Conveying Equipment

Conveyors are used to transport material form one fixed point to another fixed point. Some
conveyors have belts that can move parts or granular material; others have a series of hooks that
can move parts through a paint system. Some use gravity or a powered device to carry material.
Some of the conveyor systems are portable which may be moved from time to time, but generally
these are fixed. These are used for the following applications:

 Moving homogeneous material
 Fixed route of movement

 Constant rate of material movement
 Mass production units
A belt conveyor consists of two or more pulleys, with a continuous loop of material — the
conveyor belt — that rotates about them. One or both of the pulleys are powered, moving the
belt and the material on the belt forward. The powered pulley is called the drive pulley while
the unpowered pulley is called the idler.

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