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  Return to Wire Rope Main Page and Detailed Wire Rope Data  
    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  
Rotation Resistant and Non-Rotating Wire Rope
 
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When loaded, every wire rope will develop torque; that is it has the tendency to
unlay itself unless both rope ends are secured against rotation.
cause a lower sheave block to rotate and to spin the line parts together.
  Rotation resistant ropes can be divided into 3 categories:
Spin-Resistant
2-layer
(8 to 10 outer strands)
Rotation Resistant
2-layer
(11 to 13 outer strands)
Non-Rotating
3-layer
(14 or more outer strands)
     
Example of a 2-layer
rotation resistant construction
with 12 outer strands.
(19x7)
  The characteristic of these wire ropes are that the outer layer is twisted in the opposite direction of their inner layers. The sometimes confusing issue is that many 8-, 9- and 10 strand constructions are 2-layer types but their inner strands are NOT twisted in the opposite direction and therefore these rope are NOT spin-resistant; plus, for the untrained eye these ropes look very much alike their spin-resistant variants. These and regular 6-strand ropes will spin violently and unlay themselves when loaded, with one rope end allowed to spin freely. They may also develop a significant drop in breaking strength and an even larger drop in their fatigue life characteristic when used with one end allowed to rotate.

As already mentioned, to achieve any degree of resisting the tendency of a rope to spin and unlay under load, all such rope types (other than 4-strand ones) are constructed with 2 or more layers of opposite twisted strands.

2-layer ropes have a larger tendency to rotate than 3-layer ones (e.g. class 34x7). Furthermore, 2-layer spin-resistant and rotation resistant ropes will develop only about 55% to 75% of their breaking strength when one end is allowed to rotate freely. This number increases to between 95% to 100% for 3-layer non-rotating ropes.

Another important issue is that 2-layer rotation resistant and 2-layer spin-resistant rope types have shown to break up from the inside. The 8 (e.g. 8x25 spin-resistant) or 12 outer strands (19x7, 19x19) are not able to evenly distribute the radial forces and because of the inherent internal strand cross overs (which make the rope spin- or rotation resistant) the resultant severe notching stresses cause the rope core to break up premature (unless the core is plastic coated, e.g. Python® Multi). Unexpected and sudden rope failures may be the result. Moreover, 2-layer spin-resistant or rotation resistant ropes satisfy only low to moderate rotational resistance demands.

3-layer rope constructions (e.g. Python® Lift, Python® Compac 35) have many more outer strands which can much better distribute the radial pressures onto the reverse lay inner strands. These ropes should be selected for larger mobile- and ALL tower cranes.
     
     
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