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Transcript
BASIC RIGGING
MSHA REGULATIONS
• 56/57.16007 Taglines, Hitches, and Slings


(a) Taglines shall be attached to loads that may
require steadying or guidance while
suspended.
(b) Hitches and slings used to hoist materials
shall be suitable for the particular material
handled.
• 56/57.16009 Suspended Loads

Persons shall stay clear of suspended loads.
TOOLS OF RIGGING
•
•
•
•
Hoists
Cranes
Slings
Special
lifting
devices
HOISTS AND CRANES
• Different types of
hoisting equipment
– Manual and
powered devices
– underhung and top
running cranes
– monorails
– various types of jig
cranes
SLINGS
• Main purpose is to suspend a load from a
hoist
• Commonly made of wire rope or welded
link chain
• Can be constructed from fiber
rope,synthetic webbing or metal mesh
• Most slings are assembled by sling
manufacturers
• Can be assembled at the job site
The rigging system
•
•
•
•
Load
Sling
Hoisting equipment
Rigger (Designer and
Operator of the
system)
• = Single, complex
rigging system
The Rigger
• Must apply intelligence, common
sense and experience
• Anticipate what will happen when the
load is moved
• Thought process must take place
before the work is started
• Must answer the following
questions…..
Questions that must be
answered by rigger
• What is to be done with the
load?
• What tools are needed?
• Do the tools have the
capacity to handle the loads
and forces involved?
Questions that must be
answered by rigger
• How can the hookup be made?
• What will happen when the load
is first moved?
• What will be the travel path of
the load to reach the desired
location?
Questions that must be
answered by rigger
• How will the load be set down at the
desired location?
• What other factors are involved
(weather, electrical wires, sloping
grades, visibility)?
• Are additional personnel needed to
control the load safely during the
process?
Planning a rigging system
• Determine the weight of the load
• Locating the center of gravity of a load
• Distinguishing the force components
(horizontal and vertical) at work in a
diagonal force(loads at some angles other
than 90 degrees to the horizontal)
• Limitations of each component of the
rigging system
Determining the weight of
the load
• Shipping paper
• Manufacturers information attached
to the load
• Catalogs or blueprints
• Tables of weights from
manufacturers or handbooks
• Make sure the weight has not
changed
Volume & Area Formulas
Calculating an allowable
load
• Determine the breaking strength of
the rope
– Load which will cause the rope to break
– Refer to standard tables in rigging
handbooks
– Listed according to the diameter and
kind of rope
– Design or safety factor usually 5
Calculating an allowable
load
• Find the load limit by dividing the
breaking strength of the rope by the
design factor
• Example– If the table indicates that the breaking
strength of the rope you are using is
27,000 pounds. Dividing this figure by
the design factor of 5 gives you a 5400
pound maximum allowable load.
Determine the center of
gravity
• The point at which the load will balance
• Whole weight of the load is considered
concentrated at this balance point
• When suspended from a point, the load
tends to move so that the center of gravity
is directly below the point of support.
• Make sure the center of gravity is located
directly below the hoisting hook
Determine the center of
gravity
• Stable load
– Balanced about its center of
gravity
– Directly below the hoisting hook
• Unstable load
– has a tendency to tip or topple
– Creates a hazard to personnel and
equipment
Before Lifting any load
check for hazards
• If not directly below
the hook the load is
unstable
• If the sling is free to
slide across the hook
the center of gravity
will shift directly
below the hook
• If two slings are used
one will assume the
greater share of the
load
Before Lifting any load
check for hazards
• The sling must not be
attached to the load at
a point lower than the
loads center of gravity
– Exception to this
rule when lifting
loads on pallets or
skids
– Then apex of sling
must be above the
center of gravity
Determining the center of
gravity
•
•
•
•
Marked on the load by manufacturer
Located in catalogs or blueprints
Some objects have lifting lugs
Calculate or estimate it
– Make an educated guess and
correct through trial and error
before making the lift
Procedures to determine
center of gravity
• Connect slings and hoist based on
estimate of object’s center of gravity
• Take up slack in slings or hoist
• Lift the load just enough to check stability
• If stable, continue to lift
• If unstable, lower load and adjust the
rigging
– Lift point should be moved closer to
end that dips
• Repeat until load is stable
Horizontal Force
• Very often sling legs are attached at
an angle less than 900
• Then a horizontal force is added to
the vertical force
• Resulting Combined force is greater
than the weight of the load
• Horizontal force increases as the
angle becomes smaller
Horizontal Force
• When a sling
angle is 300 the
total force is
twice that of the
load
• Sling Angles of
450 are not
recommended
Horizontal Force
• Horizontal forces act
on the load causing
damage by
compression or
buckling
• Horizontal forces are
absorbed by using a
spreader beam making
the sling legs between
beam and load vertical
Sling Components
•
•
•
•
•
Hooks
Coupling Links
Fittings
Sling Legs
Can be assembled at the job site but must
use recommended components and
assembly procedures
– May also require some sort of weight test
Hook Hazards
• Attachments should never be field welded to a
hook
• Heat should not be applied in an attempt to
reshape a hook
– Can reduce strength of hook
– Could result in hook failure at loads lower than the
rated load
• If handles or attachments are required they
should be obtained from the hook
manufacturer
Purpose of a latch?
• Purpose is to retain slings in the hook
– Not intended to support the load
– Should be sturdy enough to retain the sling
if the moving load should catch on
something
• Latches are used to close the throat opening
• Must be provided on hoist and crane hooks
Reasons For Removing a
Hook From Service
• Hook throat has increased by
more than 15%
• Wear exceeds 10% of the
original hook section
dimension, or there is a bend
or twist of more than 10%
from the plane of the unbent
hook
• Hook shows cracks,
excessive nicks, or gouges
Factors Affecting Wire-Rope
Strength
• Three major signs of loss of strength
– Flat spots worn on outer wires
– Broken wires
– reduction of rope diameter
• Other factors that can reduce strength
–
–
–
–
Bending the rope over a curved surface
Temperature
Corrosion and environment
Rope fittings or terminations
Bending The Rope Over A
Curved Surface
• Normal curved surfaces that ropes are
curved over include sheaves, pins and
other curved surfaces
• The rope is subjected to bending stress
• Reduces rope efficiency/nominal strength
by a certain percentage
• Efficiency depends upon the:
– D = Diameter of curved surface
– d = Nominal diameter of rope
Example (You will need to refer
to Fig. 2-5 and Table 2-1)
• Fiber-core 6 x 37
wire rope, 1” in
diameter (d)
• Sheave with a 30”
diameter (D)
• D/d ratio is 30/1
• Efficiency is 95%
• Load Rating
dropped 95% from
83,600 lb. To 79,420
lb.
Wire Rope Clips
•
•
•
•
•
•
Two basic designs
U section contacts dead end of the rope
Tends to crush some wires
Affects strength if u-bolt clip is installed wrong
Fist Grip can be installed either way
Use only forged steel for lifting slings
Removal From Service
• Rope Distortion such as
kinking, crushing,
unstranding, birdcaging
or core protrusion
• Heat Damage from any
source
– Look for damage from
weld and weld splatter
• Cracked or deformed
end fittings(hooks
particularly)
• Corrosive failure of one
wire adjacent to end
fitting
Removal From Service
• One broken or cut strand
• Pitting due to corrosion
• For Single Wire Rope Either:
– 10 broken wires in a section the length of one
rope lay
– 5 broken wires in one strand within a distance
of one rope lay
Chain Hazards
• Similar force acts on
the links if the chain
is knotted or twisted
• Never shorten a
sling by twisting or
knotting
• Never use bolts and
nuts or other
fasteners to shorten
a sling