Replace any link that shows cracks, distortion, nicks, or cuts. However, if a chain shows stretching or distortion of more than 5 percent in a five-link section, discard and destroy the entire chain.
Remove chains from service when any link shows signs of binding at juncture points. This binding condition indicates that the sides of the links have collapsed as a result of stretching.
Before lifting with a chain, first place dunnage between the chain and the load to provide a gripping surface. For hoisting heavy metal objects with a chain, always use chaffing gear around the sharp comers on the load to protect the chain links from being cut. As chafing gear, use either planks or heavy fabric. In handling rails or a number of lengths of pipe, make a round turn and place the hook around the chain, as shown in figure 6-23.
In addition to block and tackle, slings, and chains, hooks, shackles, and beam clamps are also used for lifting objects and material.
There are two types of hooks available: the slip hook and the grab hook (fig. 6-24).
Slip hooks are made so the inside curve of the hook is an arc of a circle. They are used with wire rope, chains, and fiber line. Chain links can slip through a slip hook so that the loop formed in the chain can tighten under a load.
Figure 6-24. - Hooks: A. Slip; B. Grab.
Grab Hooks Grab hooks have an inside curve that is almost U-shaped so that the hook will slip over a link edgeways and not allow the next link to slip past. Grab hooks have a much more limited range of use than slip hooks. They are used exclusively when the loop formed in the chain is not intended to close around the load.
As a rule, a hook should always be moused as a safety measure to prevent slings or line from coming off. Mousing also helps prevent the straightening of a hook but does not add to the strength of the hook. To mouse a hook (fig. 6-25) after the sling is on the hook you should wrap the wire or small stuff 8 or 10 turns around the two sides of the hook. Mousing is then
Figure 6-23. - Chain sting.
Figure 6-25. - Mousing a hook.Continue Reading