Download - Slings & D/d Ratio - · PDF fileSlings & D/d Ratio Wire Rope Slings Radius of contact should at least be equal to one rope lay. ... BUNCHING FOLDED SLING Slings & D/d Ratio

10/5/2011

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Copyright ©2011 Rigging Institute, LLC All rights reserved.1

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Slings & D/d RatioSlings & D/d Ratio

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No part of this presentation may be reproduced or distributed

without the written permission of Rigging Institute, LLC


� 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



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


6”

1”


� Softeners are often used to help create betterD/d ratios.


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.


DL

� It is recommended that the pin inthe eye be no less than 2 times thesling diameter.


� 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.


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 .


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


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.


― 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.


� Chain is different than wire rope.

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Deformation at Proof Test load Odd # of links.


D/d = 4

D/d = 3

D/d = 2Odd # Links.


Deformation at Proof Test load, even # of links.


D/d = 4

D/d = 3

D/d = 2Even # Links.

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NACM D/d De-rating Recommendations of Basket Hitch


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


� 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


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


888888--416416--19651965

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

Download - Slings & D/d Ratio - · PDF fileSlings & D/d Ratio Wire Rope Slings Radius of contact should at least be equal to one rope lay. ... BUNCHING FOLDED SLING Slings & D/d Ratio

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