Right laid wire should be taken right-handed around catheads and capstans to avoid kinking. A hard strain on a wire with a kink in it is even more disastrous than a strain on a kinked line. Kinks in wire must be avoided.
Wire that has been subjected to long usage wears like any other metal. The outer parts of the strands begin to flatten out, and as a result the diameter of the wire decreases. Individual strands of wire begin to wear through, and fishhooks appear here and there. A wire with an overstrain also shows a great many fishhooks, besides a marked decrease in diameter where the strain occurred. A wire containing fishhooks should never be used in boat falls, cargo whips, or other weight-carrying device for handling cargo, where so much depends on the strength of the wire.
Wire rope should be inspected frequently, checking for fishhooks, kinks, and worn out corroded spots. Worn spots show up as shiny flattened surfaces. To watch the wear you must know (1) the original diameter of the wire rope; (2) the present diameter of the wire rope at the worn area; and (3) the diameter of a single wire in one of the strands of the wire rope. The actual diameter is found by measuring with a micrometer or vernier caliper. Now, subtract the measured diameter of the wire rope from the original diameter. If the difference is half the diameter of the single wire, the safe working load of the wire rope is materially reduced. If the differences is equal to or greater than the diameter of the single wire, replace the rope. Even if no worn spots are apparent, wire rope should be measured occasionally to determine the overall wear. Take three or four measurements at intervals of several feet and find the mean. The same rule applies here as with worn spots: Replace the rope if the outer wires are worn to one half their original diameter.
Rusting and corrosion of the wires and deterioration of the fiber core sharply decrease the strength of a rope. It is impossible to estimate accurately the loss in strength from these effects.
Wire rope should not be stored in places where acid is or has been kept. The slightest trace of acid coming in contact with wire rope will damage it at that particular spot. Many times wire rope that has given away at one point has been found to be damaged by acid.
Prior to storage, wire rope should always be cleaned and lubricated. If the lubricant film is applied properly and the wire is stored in a dry place, corrosion is virtually eliminated.
The importance of lubricating wire rope is because wire is really a mechanical device with many moving parts. Each time a rope bends or straightens, the wires in the strands and the strands in the rope must slide upon each other, so a film of lubricant is needed on each moving part. Another important reason for lubrication is to prevent corrosion of the wires and deterioration of the hemp core.
Used wire ropes should be cleaned before they are lubricated. They may be cleaned with wire brushes, compressed air, or by superheated steam. The object is to remove all foreign material and old lubricant from the valleys between the strands and from the spaces between the outer wires. Lubricant may be applied with a brush and worked in well. Another method is to pass the wire rope through a trough or box containing the lubricant.
Commercial lubricants may be obtained. The best is a semiplastic compound, applied hot in a thinned condition. It penetrates while hot, then cools to a plastic filler, preventing the entrance of water. If a heavy strain was put on a wire rope with a kink in it, the rope can no longer be trusted. Cut out the kinked part and splice the ends together.
Frequently, abrasion or reverse or sharp bends cause individual wires to break and bend back. These breaks are known as fishhooks. If several occur at a point near each other, or several wires are broken along the wire rope's length, the safe working load is reduced greatly. When 4 percent of the total number of wires in the wire rope are found to have breaks within the length of one wire rope lay, the rope is unsafe for use. Consider the rope unsafe if three broken wires are found in one strand of 6x7 rope, six broken wires are found in one strand of 6x 19 rope, or nine broken wires are found in one strand of 6x37 rope.
Some common causes of wire rope failure include the following:
1. incorrect size, constuction, or grade.
2. Allowed to drag over obstacles.
3. Improperly lubricated.
4. Operated over sheaves and drums of inadequate size.
5. Overriding or crosswinding on drums.
6. Operating over sheaves and drums out of alignment.
7. Operating over sheaves and drums with improperly fitted grooves or broken flanges.
8. Permitted to jump sheaves.
9. Subjected to moisture or acid fumes.
10 Improperly attached fittings.
11.Permitted to untwist.
12. Subjected to excessive heat.
13. Destroyed by internal wear caused by grit penetrating between the strands and wires.
14. Subjected to severe overload because of inefficient operation.
15. Kinked condition.
