Workers involved in hoisting and rigging must exercise care when selecting and using slings. The selection of slings should be based upon the size and type of the load, and the environmental conditions of the workplace.
Slings tend to be placed into three groups: chain, wire rope and mesh, fiber rope and synthetic web. Each type has its own particular advantages and disadvantages. Factors to consider when choosing the best sling for the job include size, weight, shape, temperature, and sensitivity of the material being moved, and the environmental conditions under which the sling will be used.
The following information may be useful in selecting the appropriate sling:
1. Chains- Alloy steel chains are strong and able to adapt to the shape of the load. Care should be taken when using chain slings because sudden shocks will damage them. Chain slings must be visually inspected prior to use. During the inspection, pay particular attention to any stretching, nicks, gouges, and wear in excess of the allowances made by the manufacturer. These signs indicate that the sling may be unsafe and must be removed from service immediately.
2. Wire Rope -Wire rope is composed of individual wires that have been twisted to form strands. Strands are then twisted to form a wire rope. When wire rope has a fiber core, it is usually more flexible but less resistant to environmental damage. Conversely, wire rope with a core that is made of a wire rope strand tends to have greater strength and is more resistant to heat damage.
When selecting a wire rope sling to give the best service, there are four characteristics to consider: strength, ability to withstand fatigue (e.g., to bend without distortion), ability to withstand abrasive wear, and ability to withstand abuse.
Wire rope slings must be visually inspected before use. Slings with excessive broken wires, severe corrosion, localized wear, damage to end-fittings (e.g., hooks, rings, links, or collars), or damage to the rope structure (e.g., kinks, bird caging, distortion) must be removed from service and discarded.
3. Fiber Rope – Fiber rope and synthetic web slings are used primarily for temporary work, such as construction or painting, and are the best choice for use on expensive loads, highly finished or fragile parts, and delicate equipment.
Fiber rope slings deteriorate on contact with acids and caustics and, therefore, must not be used around these substances. Fiber rope slings that exhibit cuts, gouges, worn surface areas, brittle or discolored fibers, melting, or charring must be discarded. A buildup of powder-like sawdust on the inside of a fiber rope indicates excessive internal wear and that the sling is unsafe. Finally, if the rope fibers separate easily when scratched with a fingernail, it indicates that the sling has suffered some kind of chemical damage and should be discarded.
4. Synthetic Web Synthetic web slings are commonly made of nylon, polypropylene, or polyester and have the following properties in common:
- Strength – Depending upon their size, synthetic web slings can handle loads of up to 300,000 pounds.
- Convenience and Safety – Synthetic web slings adjust to the load contour and hold it with a tight, non-slip grip.
- Load Protection – Unlike other sling materials, synthetic web is less likely to mar, deface, or scratch highly polished surfaces.
- Shock Absorbency – Regardless of the construction material, shock loading (e.g., excessive speed, rapid acceleration or deceleration) of slings should be minimized. However, it should be noted that synthetic web slings can absorb heavy shocks without damage.
- Temperature Resistance – The lifting capacity of synthetic web is unaffected by temperatures up to 180 degrees Fahrenheit.
- Economy and Long Life – Synthetic web slings have a low initial cost and a long service life. They are unaffected by mildew, rot, or bacteria, resist some chemical action, and have excellent abrasion resistance.
Synthetic web slings must be inspected before use and should be removed from service if found to have acid or caustic burns, melting or charring of any part of the surface, snags, tears, or cuts, broken stitches, distorted fittings, or wear or elongation beyond the manufacturer’s specifications.
Overall the selection of the sling is only the first step in the rigging process. The next step is learning how to safely use it to hold and move a suspended load. The load size, weight, and center of gravity, number of legs and angle with the horizontal, rated capacity of the sling and the history of care and use of the sling must be taken into consideration. This requires specialized training in hoisting and rigging operations so that riggers.
If you want more information on rigger or crane signaler training contact Randy Free. 407-353-8165 or email him at rfree[at]safetylinks.net