By H-Lift | 13 March 2023 | 0 Comments
Shackle
There are, in the main, three types of shackle used for lifting: the bow, dee and grab types. They are normally forged from various grades of steel, the higher quality alloy steels giving, size for size, a higher working load limit than those made in higher tensile steels, and correspondingly higher tensile steel shackles have a higher working load limit than those made in mild steel.
A shackle is regarded as a lifting accessory consisting of a body and pin. The nomenclature used for parts of the shackle is as shown in figure 19.1.
Dee shackle
All shackle standards specify dee shackles, with some specifying both a large dee and a small dee shackle. A large dee shackle is a shackle which has ample internal clearances in the body and jaw, and which is appropriate for general engineering purposes. A small dee shackle is a shackle which has moderate internal clearances in the body and jaw but, size for size, has a SWL higher than that of the large dee. It is suitable for use with hook eyes, eyebolts, egg links, wire rope thimbles, etc. and for the head fittings of ships’ blocks.
Bow shackle
All shackle standards specify bow shackles, with some specifying both a large bow and a small bow shackle. A large bow shackle is a shackle which has ample internal clearances in the body and jaw and which is appropriate for general engineering purposes. A small bow shackle is a shackle which has moderate internal clearances in the body and jaw but, size for size, has a SWL higher than that of the large bow. It is suitable for use with the eyes and bodies of hooks, eyebolts, egg links, wire rope thimbles, etc. and for the head fittings of ships’ blocks.
Grab shackle
A grab shackle is a dee shackle having a screwed countersunk pin, designed for use with grabs where the shackle must pass through a circular aperture of minimum diameter.
Working Load Limit
A shackle must have a working load limit at least equal to the total load to be imposed upon it; alloy steel shackles will be dimensionally smaller load for load than those of higher tensile steel. The shackle pin and body are designed to be of equal strength. To attain this condition, the pin normally has a slightly larger diameter than the material of the body. If the load on the pin is distributed over its length, or part of its length, the load bearing capacity of the pin is effectively increased but that of the body is not. Distributing the load right across the pin will NOT INCREASE THE STRENGTH OF THE SHACKLE. Standard shackles are designed to take the SWL between the centre of the pin and the bearing point(s) in the crown. (See figure 19.15)
Choice of Body Shape
The selection of the shape of the shackle body will depend on the intended use. It is desirable to use a shackle with as small a jaw opening as is consistent with adequate articulation of the connection. Dee shackles are, in general, used to join two pieces of lifting equipment. Bow shackles are, in general, used where more than one attachment is to be made to the body, or to allow freedom of movement in the plane of the bow. (See figure 19.16)
The necessity for the eye of a shackle to pass through another fitting may have to be considered. Where a shackle does not have to be dismantled, or where it is required to remain captive, it may be permanently attached by forming a link or thimble round the shackle body. (See figure 19.17)
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