"Core Curriculum: Introductory Craft Skills," Vocabulary from Module Six

Two common types of cranes are overhead cranes and mobile cranes. As with other types of equipment, cranes are available in many different configurations and capacities.

Sling: Wire rope, alloy steel chain, metal mesh fabric, synthetic rope, synthetic webbing, or jacketed synthetic continuous loop fibers made into forms, with or without end fittings, used to handle loads.

An identification tag must be securely attached to each sling and clearly marked with the rated capacity of the type of hitch used with that sling.

Here are some important characteristics for a sling:
•Manufactured grade of steel or type of synthetic material used
•Link size (diameter)
•Rated load and the angle on which the rating is based
•Sling reach (a measure taken from the master link of the sling, where it bears weight, to either the end fitting of the sling or the lowest point on the basket).
•Number of sling legs (the parts that reach from the attachment device around the object being lifted).

Here are some common designs for slings:
•Endless web slings, which are also called grommet slings.
•Synthetic web eye-and-eye slings, which are made by sewing an end of the sling directly to the sling body.
•Round slings, which are endless and made in a continuous circle out of polyester filament yarn that is covered by a woven sleeve (jacket).

Their elasticity also makes them flexible and able to mold themselves to the shape of the load.

Another warning sign is called a tattle-tail, which is a cord attached to the strands of an endless loop sling and protrudes from the jacket. When the tail has been pulled into the jacket, it indicates that the sling may have been overloaded.

Unlike synthetic web slings, which should not be exposed to temperatures above 180°F (82°C), most alloy steel chain slings can be used in temperatures up to 500°F (260°C) with little loss in rated capacity.

There are three basic types of supporting cores for wire rope:
•Fiber cores - Usually made of synthetic fibers, but can also be made from natural vegetable fibers, such as sisal.
•Independent wire rope cores - Made of a separate wire rope with its own core and strands; the core rope wires are much smaller and more delicate than the strand wires in the outer rope.
•Strand cores - Made by using one strand of the same size and type as the rest of the strands of rope.

It makes it less likely that the wires and the core will be damaged when the rope is placed at an angle during rigging or when it is bent around loads or sheaves (grooved pulley-wheels for changing the direction of a rope's pull; often found on a crane).

Here are some rejection criteria:
•Abrasions or cuts that have worn through or severed the outer jacket or exposed the loadbearing yarn of the sling, or the warning yarn of a web sling.
•A puncture.
•Broken or worn stitching in the splice or stitching of a web sling.
•A knot that cannot be removed by hand in either a web or round sling.
•Chemical damage, including discoloration, burns, and melting of the fabric or jacket.

Birdcaging - This damage occurs when a load is released too quickly and the strands are pulled or bounced away from the supporting core. The wires in the strands cannot compensate for the change in the stress level by adjusting inside the strands. The built-up stress then finds its own release out through the strands.

Rejection criteria for broken wires consider how many wires are broken in one lay length of rope, or one-rope lay. One-rope lay (identifying a single rope lay and not a rope lay made with one rope) is a term that defines the lengthwise distance it takes for one strand of wire to make one complete turn around the core.

Here are some signs that a wire rope's integrity may be broken:
•Kinks - Kinking, or distortion of the rope, is a very common type of damage.
•Unstranding - describes wire rope strands that have become untwisted.
•Crushing - This results from setting a load down on a sling or from hammering or pounding a sling into place.

Shackles are available in two basic classes, identified by their shapes: anchor shackles and chain shackles.

Unshouldered eyebolts are designed for straight vertical pulls only. Shouldered eyebolts have a shoulder that is used to help support the eyebolt during pulls that are slightly angular. Swivel eyebolts, also called hoist rings, are designed for angular pulls from 0 to 90 degrees from the horizontal plane of the load.

In order for the clamp to hold an item securely, the cam and the jaw must bite or grip both sides of a single item. An adjustable cam can be set and tightened to maintain a secure grip on the load.

A rigging eye hook has a large eye that can accommodate large couplers. Reverse eye hooks position the point of the hook perpendicular to the eye. Sliding choker hooks can be positioned anywhere along the sling body, and are used to secure the sling eye in a choker hitch. Grab hooks fit securely in the chain link, so that choker hitches can be made and chains can be shortened.

A block and tackle is a simple rope-and-pulley system used to lift loads. By using fixed pulleys and a wire rope attached to a load, a rigger can raise and lower the load by pulling the rope or by using a winch to lift the load.

The single vertical hitch allows the load to rotate freely. To prevent the load from rotating, some method of load control, such as a tag line, must be used.

The multiple-leg bridle hitch consists of three or four single hitches attached to the same hook, master link, or bull ring. Multiple-leg bridle hitches provide increased stability for the load being lifted.

The choker hitch is made by wrapping the sling around the load and passing it through one eye to form a constricting loop around the load.