Ch 7 A

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25 Νοε 2013 (πριν από 4 χρόνια και 5 μήνες)

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Unit 5 A

Hoists & cranes

Industrial hoists & cranes

Overhead hoists

slung cranes

running cranes

jib cranes

Overhead manual chain hoists

Hand chain turns a
pocket wheel

1/2 to 60 ton capacity

suspended trolley

Overhead powered hoists

Electric or pneumatic powered

chain hoist or wire rope

reeving (wire rope)
passing a rope over the
sheaves , gains mechanical advantage

single reeved
1 rope, block moves horizontally
as the hook

double reeved=1 rope, both ends attached to
drum, load stays centered as hook
, can use
smaller rope, drum & sheaves

Overhead hoists 2


the number of rope lengths between
the drum & the hook

More parts = more mechanical advantage

generally a push button control
pendant with

and an emergency stop

speed control,

brake system

limit switch

Jib cranes or hoists

Can be wall mount or pedestal mount

fixed, partial rotation or full rotation

top braced, under
braced or cantilever

rotation type have bearings

Safety 1

Only 1 operator per hoist

only 1 boss per hoist


Do not side pull a load, this is very dangerous
do vertical lifts only

Overload limit devices

Keep hook from going too far up

prevent damage to unit when exceeding lift

are not a guarantee of safety

Bridge Cranes

A Bridge Crane system consists of three major

the Bridge Crane, which traverses across the

the hoist & trolley, which traverses across the
bridge and lifts up and down

the runway, which is tied to the building


slung cranes

Hoist is suspended from 1 or more bridge
beams fitted with end trucks

smaller lift capacity than top
running cranes

used where ceiling space is limited

Top running cranes

Cranes are mounted on top of support beams,
run on rails

gantry cranes

gantry cranes or half gantry cranes

cab operated, pendant control,
radio control

the crane operator is

the rigger!!!!

Top Running or Under Running?

Top Running vs. Under Running is primarily
determined by two factors:


Although under running can be up
to 25 ton capacity, the practical limit is more
like 15 tons and the economic sweet spot is 1
to 7.5 ton range.

Support Structure

Under running can be
suspended directly from the overhead steel
(for lighter cranes). Top running cranes will
require a bracket off the building support steel
(up to 10 tons capacity) or independent
columns for heavier capacities.

Top Running or Under Running?

The top running configuration is best used in
cases where the end user has issues with
headroom. The most space efficient
configuration is the double girder, top running
crane system. When headroom is not an issue
a top or under running configuration can be
used with either the double or single girder
bridge crane.

Top Running or Under Running?


Inspect & service

trained personnel

as required by OSHA

hooks, cable, drum,
sheaves, contacts,
gear boxes, limit
switches, controls,
brakes, lube

Hand signals

between rigger &
crane operator

very important

only 1 rigger per job
except for STOP