dbyd ratio slings

8/12/2019 Dbyd Ratio Slings

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Copyright 2011 Rigging Institute, LLC All rights reserved.1

888888--416416--19651965

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.


Wire Rope SlingsWire Rope Slings


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.

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.



DL

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


When using multi-part slings follow themanufacturers 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 pindiameter 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 themanufacturers requirements for D/d ratioreductions.


MultiMulti--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 slings finished diameter. The pin

diameter in the eye is also based on

the slings finished diameter .


D/d RatioSlingmax (9-prt) SlingStrength 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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Alloy 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 the

sling.


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.



D/d = 4

D/d = 3

D/d = 2Odd # Links.


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



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


Synthetic 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

HardwareThicknessor 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


Roundsling Bearing StressRoundsling Bearing Stress


888888--416416--19651965


CANADACANADA

No part of this presentation may be reproduced or distributed

without the written permission of Rigging Institute, LLC

dbyd ratio slings

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