Slings & D/d Ratio - · PDF fileSlings & D/d Ratio Wire Rope Slings Radius of contact should...
Transcript of Slings & D/d Ratio - · PDF fileSlings & D/d Ratio Wire Rope Slings Radius of contact should...
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Slings & D/d RatioSlings & D/d Ratio
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� D/d Ratio – the diameter of curvature around which
a sling is bent affects its capacity.
– The upper case ‘D’ refers to thediameter of the object to which thesling hitch is applied.
– The lower case ‘d’ represents thediameter of the sling.
Slings & D/d RatioSlings & D/d RatioD/d RatiosD/d Ratios
D
d
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� To determine the D/d ratio, divide the diameter of
the wire rope sling into the diameter of the load.
� A good rule to follow with wire rope slings, is to keep
at least a 6:1 ratio which results in an 80% efficiency
of the sling.
� A 1:1 ratio results in only 50% efficiency of the wire
rope sling.
Slings & D/d RatioSlings & D/d RatioWire Rope SlingsWire Rope Slings
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Slings & D/d RatioSlings & D/d RatioWire Rope SlingsWire Rope Slings
D/d RATIO FOR WIRE ROPE ON SHEAVES & DRUMS
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D/d
Ratio
Wire Rope Sling
Strength Efficiencies
25:1 100%
20:1 92%
15:1 88%
10:1 86%
8:1 84%
6:1 80%
4:1 75%
2:1 65%
1:1 50%
1” wire rope sling
D/d ratio = 6” ÷ 1” = 6
6: ratio = Approx. 80% efficiency
Slings & D/d RatioSlings & D/d RatioWire Rope SlingsWire Rope Slings
6”
1”
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� Softeners are often used to help create betterD/d ratios.
Slings & D/d RatioSlings & D/d RatioWire Rope SlingsWire Rope Slings
Radius of contact should
at least be equal to one rope lay.
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� The diameter of the pin or hook inthe eye of the sling should be nogreater than 1/2 the eye length.
Slings & D/d RatioSlings & D/d RatioWire Rope SlingsWire Rope Slings
DL
� It is recommended that the pin inthe eye be no less than 2 times thesling diameter.
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� When using multi-part slings follow themanufacturer’s requirements for D/d ratioreductions.
Basket capacity on this multi-part wire
rope sling is based on the D/d ratio of
the component wire diameter. The pin
diameter in the eye is based on the
slings finished diameter .
Slings & D/d RatioSlings & D/d RatioMultiMulti--Part Wire Rope SlingsPart Wire Rope Slings
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� When using multi-part slings follow themanufacturer’s requirements for D/d ratioreductions.
Slings & D/d RatioSlings & D/d RatioMultiMulti--Part Wire Rope SlingsPart Wire Rope Slings
Basket capacity on this multi-part wire
rope sling is based on the D/d ratio of
the sling’s finished diameter. The pin
diameter in the eye is also based on
the slings finished diameter .
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D/d RatioSlingmax® (9-prt) Sling
Strength Efficiencies
5:1 100%
4:1 92%
3:1 84%
2:1 73%
1:1 65%
0.5:1 50%
Slingmax® Gator 9-Part
Slings & D/d RatioSlings & D/d RatioMultiMulti--Part Wire Rope SlingsPart Wire Rope Slings
D
d
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Slings & D/d RatioSlings & D/d RatioAlloy Chain SlingsAlloy Chain Slings
D
d
� D/d Ratio – the diameter of curvature around which
a sling is bent affects its capacity.
– The upper case ‘D’ refers to thediameter of the object to which thesling hitch is applied.
– The lower case ‘d’ represents thediameter of the chain link of thesling.
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― Flexible inter-link.
― Rigid intra-link.
― Based on link length also. However,
inside length to wire diameter is
relatively constant for alloy chains.
– therefore D/d works.
Slings & D/d RatioSlings & D/d RatioAlloy Chain SlingsAlloy Chain Slings
� Chain is different than wire rope.
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Deformation at Proof Test load Odd # of links.
Slings & D/d RatioSlings & D/d RatioAlloy Chain SlingsAlloy Chain Slings
D/d = 4
D/d = 3
D/d = 2Odd # Links.
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Deformation at Proof Test load, even # of links.
Slings & D/d RatioSlings & D/d RatioAlloy Chain SlingsAlloy Chain Slings
D/d = 4
D/d = 3
D/d = 2Even # Links.
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NACM D/d De-rating Recommendations of Basket Hitch
Slings & D/d RatioSlings & D/d RatioAlloy Chain SlingsAlloy Chain Slings
Alloy Chain D/d Ratio Efficiency
D/d Ratio % of Rated Capacity
Less than 2 Not Recommended
2 60
3 70
4 80
5 90
6 and greater 100
D
d
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� D/d ratios are NOT a concern for synthetic web slings.
Slings & D/d RatioSlings & D/d RatioSynthetic Web SlingsSynthetic Web Slings
Is this a diameter issue?
NO
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� Spatial issues of web slings reduce its efficiency.
BUNCHING FOLDED SLING
Slings & D/d RatioSlings & D/d RatioSynthetic Web Slings BunchingSynthetic Web Slings Bunching
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RS90 Roundsling with a vertical work
load limit of 8400 lbs. is connected to the
rounded bow end of a 5/8in. Shackle.
The shackle has an inside opening of 2
inches and a stock diameter of 0.62.
A force of only 6000 lbs. is applied,
noticeably less than the work load limit.
Is the shackle suitable?
Sling Load Value (Lbs.)
Load Bearing AreaBEARING STRESS
5/8 IN
2 IN
=
RS90
8400 lbs.
Vertical 6000 lbs.
Force
Slings & D/d RatioSlings & D/d RatioRoundsling Bearing StressRoundsling Bearing Stress
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Effective Contact Width
Curved – 75% of Actual Inside Width
.75 x 2 inches = 1.5 inch
Load Bearing Area
EffectiveContactWidth
LoadBearing
Area=X
Hardware Thickness or Diameter
.62 1.5 = .93 INX
BEARING STRESS(Not to exceed 7000 PSI)
6451 Lbs. / IN
=
=
Sling Load Value
Load Bearing Area
6000.93 IN
Slings & D/d RatioSlings & D/d RatioRoundsling Bearing StressRoundsling Bearing Stress
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Slings & D/d RatioSlings & D/d Ratio
CANADACANADA
No part of this presentation may be reproduced or distributed
without the written permission of Rigging Institute, LLC