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    Technical Information  
  Use and Care of Wire Rope  
  Wire Rope is a Machine  
    Installation of Wire Rope:  
  Foreword, Measuring the rope diameter  
  If you have to cut a rope  
  Unreeling the rope  
  Connecting the old rope to the new rope  
  Rope lay direction versus Drum Grooving  
  Winding on to the drum  
  Installation of Wedge Sockets  
  Using your rope for the first time  
  Efficiency ratings of end terminations  
    Inspection of Wire Rope:  
  How to inspect Wire Rope  
  Crown- and Valley Wire Breaks  
  Number of broken Wire Discard Tables  
  Reduction of diameter, Rope Wear  
  Rope Stretch, Core Wire breaks  
  Mechanical damages  
  Corrosion, Rope Removal and Cause  
    Maintenance:  
  Inspection of Sheaves and Drums, Dimensions of Groove Radius  
  Cut and Slip Procedure, Lubrication  
    Rope Properties & Data:  
  Tensile Strength and Fill Factor  
  Strand- and Swage Compaction  
  Rotation Resistant and Non-Rotating Wire Rope  
  Sheave and Drum Dimensions  
  Relative Service Life, Loss of Strength over Pins, Why Multistrand Ropes  
Technical Information – Inspection of Wire Rope
     
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Rope Stretch
 
Constructional Stretch
All ropes will stretch to varying degrees when loads are initially applied. This stretch is known as the 'constructional stretch'.


This stretch occurs in three phases:

1) Initial or constructional stretch during the early period (Run-In) of rope service, caused by the rope adjusting to the operating conditions.

2) Following the run-in period there there is a extended period – the longest part of the ropes's service life – during which a slight increase in stretch takes place over an extended time. This results from normal wear, fatigue etc. On a graph this portion would almost be a horizontal straight line inclined slightly upward from its initial level.

3) Thereafter, the stretch occurs at a quicker rate. This means that the rope has reached the point of rapid degradation; a result of prolonged subjection to abrasive wear, fatigue, and inner undetected wire breaks, etc. This second upturn of the curve is a warning indicating that the rope should be removed to avoid sudden catastrophic rope failures.

  Elastic Stretch / Elastic Limit
Elastic stretch of wire rope occurs as soon as a load is applied. When the load is released the rope returns to it's initial length, hence the term 'elastic' stretch. This stretch is caused by the elastic deformation of the steel itself (the individual steel wires) and also by the lay of the rope which could be compared to resemble a coil spring. With other words, the longer the lay length of a rope becomes, the less elastic stretch it will develop. Elastic stretch in a wire rope is a desired feature. The ability of a rope to stretch under load means that the rope is capable to absorb enegry; the term here is 'energy absorption capability'.

In many instances it is not easy to clearly distinguish between (the remains of) constructional stretch and elastic stretch as they may occur together especially when the rope is new. The values for Elastic Stretch are dependent on rope construction, lay length and type, steel material, tensile strength of wires etc. An approximation is o.25% to o.6% at WLL (or lifting capacity). The E-module varies similarily from about 11 Million to 16 Million lbs/inch. For exact values please contact us for further information.

Elastic stretch turns into a 'permanent' stretch when the rope is loaded beyond 55%-60% of it's breaking strength (or beyond 2-1/2 to 3 times its WLL). At that point the steel material elongates and deforms permanently and renders the rope inoperable as the individual wires will have lost much of their mechanical properties to withstand material fatigue.

     
Core Wire Breaks

The most difficult to detect wire rope deterioration. Core wire breaks are more likely to appear in 6 & 8-strand and 19x7/19x19 ropes, rather than in multi-strand plastic coated core wire rope. We have had examples where 8x36 and 19x7 ropes broke showing no externally visible removal criteria, yet the core was completely broken to pieces. Once the core breaks, the resultant sudden shock load on the outer strands may cause the rope to fail in a catastrophic, unpredictable manner.

Core wire breaks in PYTHON™ plastic coated core ropes are not likely to appear due to the cushioning effect of the plastic layer. Field experience from customer returned plastic coated core PYTHON rope revealed no broken core wires without the outer strands having visible wire breaks in excessive numbers far beyond any removal criteria.

To inspect the core of a 6- or 8-strand wire rope, the rope must be completely unloaded. Carefully insert a spike through one or two strands and turn the spike with the rope lay. If the core is heavily lubricated you need good lighting to see broken wires! You may also wish to use a air gun to blow excessive lubricant off the core, but be sure to re-lube the core after your inspection.

As with any rotation resistant or non-rotating rope we recommend to leave such internal inspections to the expert as such inspections can permanently damage the rope.
     
     
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