INSTALLATION OF STEEL WIRE ROPES
Steel Wire Rope Installation Guide: Safety and Efficiency
CRANE ROPES
INSTALLATION OF STEEL WIRE ROPES
Objective: The rope should be introduced into the reeving system of the application without tension, twisting or damage.
INCORRECT UNWINDING
The work operation shown creates a torsion for each winding in the rope that can result in loops. If this rope is then pulled tight, it causes irreparable kinks. The rope must be discarded.
Removal from coil from the side – Removal from reel from the side
CORRECT UNWINDING FROM THE COIL
The rope should be rolled out on a turntable or like a tyre on the ground. However, when rolling out, make sure that the ground is clean so that the rope lubricant cannot pick up dirt and form an abrasive paste.
Unwinding with a turntable – Rolling out on the ground
CORRECT UNWINDING FROM THE REEL
A turntable can also be used when unwinding the rope from a reel. However, the use of a frame or winding block to neatly unwind the rope is recommended for large reels and thick ropes.
Unwinding with a turntable – Unwinding with a frame
Correct winding in bending direction
Incorrect winding opposite to bending direction
WINDING THE ROPE FROM A REEL TO A DRUM
CAUTION
During the manufacturing process, every steel wire rope receives its preferred bending direction. Make certain that it bends in the same direction when it is wound from the reel onto the drum. For this reason, the rope winding on the drum and the rope unwinding from the reel must always hold the same position, i.e. bottom to bottom or top to top.
If the rope is pulled diagonally, i.e. winding in the opposite direction to the preferred bending direction, it will either try to twist between reel and drum or it will later try to regain its preferred position when in practical service. In both cases, structural changes to the rope may occur.
THE FLEET ANGLE
The fleet angle (β) describes the lateral deflection of a rope on the drum or, in the reeving system, the deflection that a rope experiences, which spools from a fixed sheave from one edge of a drum to the other. Here it must be taken into account that the fleet angle for a typical arrangement with the sheave central to the drum naturally has its maximum at the drum edges. In addition the rope grooves on the drum itself also describe an angle, the so-called pitch angle (α), that must be subtracted from the fleet angle (β) or added to
it.
CAUTION
Generally the rope fleet angle causes the rope to not wind to its lowest point but instead the sheave first touches an edge and then rolls into the bottom of the groove. This so-called “forced torsion of the rope” increases with the fleet angle. The authoritative ISO standard 16625 limits the fleet angle to 4° for non-rotation-resistant ropes and 2° for rotation-resistant and low rotation ropes. This narrow restriction for low rotation and rotation-resistant ropes results from the fact that ropes with steel cores closed in the
opposite direction respond more sensitively to forced torsion than conventional ones. Lateral deflection can of course arise during rope installation. Here, the specified maximum fleet angle from ISO 16625 must also be complied with to prevent twisting developing during rope installation. The fleet angle can be minimised by establishing as large a distance as possible between the reel and drum or head pulley sheave.
THE GROOVES OF DRUMS AND SHEAVES
Naturally, each component of a crane that comes into direct contact with the rope has an effect on the service life. This also includes the grooves of the sheaves and the drum whose quality and dimensional accuracy have a significant influence on the service life of the rope. Here, the grooves should have a diameter that is slightly larger than the effective diameter of the rope. ISO 16625 prescribes that the diameter of the grooves must be a minimum of 5% and a maximum of 10% more than the rope diameter. As an optimum value, the standard specifies a groove diameter of 7.5% more than the rope diameter.
CAUTION
If the diameter of the sheave is too small for the rope (Fig. A), the rope is compromised when winding on the sheave or drum. This can lead to wire breaks in the inside of the rope caused by so-called arch pressure. An additional effect is excessive length of the outer strands in respect of the reduced rope diameter. This excessive strand length is typically shifted to a point and results in strand loosening or even birdcage deformation.
A rope groove that is too large results in a greater surface pressure of the rope in the bottom of the groove as the support at the edges is missing and therefore the contact area is reduced (Fig. C). The increased pressure in the bottom of the groove and the additional tensions due to the intensified rope deformation (ovalisation of the rope) lead to a reduction of the service life. In general, falling below 5% has significantly more serious consequences for the service life of the rope than exceeding 10%.
To determine the diameter of the rope grooves of sheaves and drums, so-called groove gauges are used. These are pressed into the rope groove and should be well positioned over broad sections of the circumference. The rope groove is then OK.
