Measuring Wire Rope

Wire rope is designated by its diameter in inches, as shown in figure 6-38. The correct methods of measuring wire rope is to measure from the top of one strand to the top of the strand directly opposite it. The wrong way is to measure across two strands side by side.

To ensure an accurate measurement of the diameter of a wire rope, always measure the rope at three places at least 5 feet apart. Use the average of the three measurements as the diameter of the rope.

Wire Rope Safe Working Load

The term safe working load (SWL) of wire rope means the load that can be applied and still obtain the most efficient service and also prolong the life of the rope. For the safe working load of wire rope, refer to the manufacturer's certification of published breaking strength or the actual breaking strength of a piece of wire rope taken from the reel and tested.

Wire Rope Failure

Some of the common causes of wire rope failure are the following:

Using incorrect size, construction, or grade

Dragging over obstacles

Lubricating improperly

Operating over sheaves and drums of inadequate size

Overriding or cross winding on drums

Operating over sheaves and drums with improperly fitted grooves or broken flanges

Figure 6-38. - Correct and incorrect methods of measuring wire rope.

Jumping of sheaves

Exposing to acid or corrosive liquid or gases

Using an improperly attached fitting

Allowing grit to penetrate between the strands promoting internal wear

Subjecting to severe or continuing overload

Using an excessive fleet angle

Handling and Care of Wire Rope

To render safe, dependable service over a maximum period of time, you should take good care and upkeep that is necessary to keep wire rope in good condition. Various ways of caring for and handling wire rope are described below.

COILING AND UNCOILING. - Once a new reel has been opened, it may be coiled or faked down, like line. The proper direction of coiling is counterclockwise for left lay and clockwise for right lay wire rope. Because of the general toughness and resilience of wire, it tends now and then to resist being coiled down. When this occurs, it is useless to fight the wire by forcing down the turn because it will only spring up again. But if it is thrown in a back turn, as shown in figure 6-39, it will lie down properly. A wire rope, when faked down, will run right off, like line; but when wound in a coil, it must always be unwound.

Wire rope tends to kink during uncoiling or unreeling, especially if it has been in service long. A kink can cause a weak spot in the rope that wears out quicker than the rest of the rope.

Figure 6-39. - Throwing a back turn.