Fleet Angles on Wire Rope
An important topic in any wire rope reeving system, this article looks at fleet angles both at the drum and at the sheave.
Fleet Angle at the Drum
Fleet angle has a significant influence on the spooling of rope on to a smooth drum.
Fleet Angle is usually defined as the included angle between two lines, one which extends from a fixed sheave to the flange of a drum and the other which extends from the same fixed sheave to the drum in a line perpendicular to the axis of the drum.
When spooling wire rope onto a smooth/plain drum it is generally recommended that the fleet anlge is limited to between 0.5 and 2 degrees. If the fleet angle is too small, ie less than 0.5 degrees, the rope will tend to pile up at the drum flange and fail to return across the drum. In this situation, the problem may be alleviated by increasing the fleet angle through the introduction of a sheave or spooling mechanism.
If the rope is allowed to pile up it will eventually roll away from the flange, creating a shock load in both the rope and the drum assembly, thus creating an undesirable and unsafe operating condition.
Excessively high fleet angles will return the rope across the drum prematurely, creating gaps between wraps of rope close to the flanges as well as increasing the pressure on the rope at the cross-over positions.
Where drum grooving is provided, large fleet angles will result in wear taking place to the drum grooving which may then result in the rope miss-spooling on the drum. When spooling onto a grooved drum, it is recommended that the fleet angle is limited to between 0.5 and 4 degrees for 6&8 stranded single layer construction wire ropes and between 0.5 and 2 degrees for rotational resistant and parallel laid construction wire ropes. Note, for high speed spooling of wire rope in excess of 8m per second it may be necessary to reduce the fleet angle to 0.5 to 1.5 degrees especially at high D/d ratios.
Where possible, fleet angles can be reduced by:
- reducing the width of the drum and/or increasing the drum diameter
- increasing the distance between wire rope sheaves and drums
Level winding/spooling mechanisms can be positioned in front of a wire rope winch drum to guide the rope across the face of the drum to provide superior spooling utilising fleet angles between 0.25 and 1.5 degrees
Fleet Angle at the Sheave
Where a fleet angle exists as the rope enters a sheave, it initially makes contact with the sheave flange. As the rope continues to pass through and around the sheave it moves down the flange until it sits in the bottom of the groove. In doing so, even when under tension, the rope will actually roll as well as slide. As a result of the rolling action the rope is twisted, ie turn is induced into or out of the rope, either shortening or lengthening the lay length of the outer strands which can damage the rope and cause ‘birdcages’ or similar distortions within the rope. A s the fleet angel increases so does the amount of twist
The fleet angle within the reeving system should be limited to 4 degrees for 6 & 8 stranded single layer construction wire ropes and 2 degrees for rotational resistant and parallel laid construction wire ropes. However, for some applications such as overhead hoists, it is recognised that for practical reasons it is not always possible to comply with these general recommendations, in which case the rope life can be affected.
Please do not hesitate to contact the team at Crane Ropes Australia if you would like more clarification or would like to work through some technical issues you may be having with your wire rope.