If you work with wire ropes, you're probably familiar with the term fleet angle. If not, there's a good chance you've never heard of it. It's a technical term used specifically in the wire rope industry. But what exactly is a fleet angle? What problems can it cause? And how can you prevent or correct it? In this video podcast, wire rope specialist Frits van Boetzelaer explains everything you need to know.
Watch the video podcast
Frits begins by explaining what a fleet angle is:
"A fleet angle occurs when a wire rope does not run in a straight line from a drum to a sheave, or from one sheave to another. Instead, the rope approaches the sheave or drum at an angle, causing it to enter via the flange before rolling down into the groove. As a result, the rope twists slightly, creating a rotational effect."
The Consequences of an Excessive Fleet Angle
In the podcast, Frits demonstrates several examples of the problems that an excessive fleet angle can cause. These include kinks in the wire rope, the formation of a birdcage, and even core protrusion. All of these can significantly reduce the service life of the wire rope and should be avoided.
Prevention Is Better Than Cure
So, how can you prevent these issues?
Frits explains:
"For a standard six- or eight-strand wire rope, the maximum permissible fleet angle is 2.5 degrees on either side, giving a total of 5 degrees. For a rotation-resistant wire rope, the maximum is 1.5 degrees on each side, or 3 degrees in total. These limits should be taken into account when designing an installation. However, a fleet angle is not always easy to detect. In practice, it's almost impossible to prevent it completely."
Possible Solutions
In the podcast, Frits discusses several ways to reduce or partially correct the effects of an excessive fleet angle:
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Use a plastic-impregnated wire rope (plastic-filled wire rope).
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Install a wire rope with the opposite lay direction.
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Install a swivel in the dead end of the wire rope.
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Fit a travelling sheave that can move laterally along its shaft.
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Install an additional sheave.
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In some applications, a plastic sheave may be a suitable alternative.
Take Action Immediately
Frits concludes the podcast with three important recommendations:
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If you notice a fleet angle developing, take action immediately. The sooner you respond, the greater the chance of preventing permanent damage.
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Loosen the wire rope or install a wire rope swivel where appropriate.
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Never install a swivel on a six- or eight-strand wire rope. A swivel should only be used with a rotation-resistant wire rope.
Podcast Summary: What Is a Fleet Angle and How Does It Occur?
A fleet angle occurs when a wire rope approaches a sheave or drum at an angle instead of running in a straight line. As the rope enters the sheave or drum, it creates a rotational effect that remains throughout the operating cycle. When the tension is released, this can result in damage such as a kink or birdcaging. These defects reduce both the service life of the wire rope and the efficiency of the lifting system.
A fleet angle can occur in a variety of applications, including mobile cranes and at end terminations. In these situations, the wire rope may shift or begin to rotate. The maximum permissible fleet angle depends on the type of wire rope being used. For a standard six-strand wire rope, the recommended maximum fleet angle is 2.5 degrees on either side (5 degrees in total). For a rotation-resistant wire rope, the maximum is 1.5 degrees on either side (3 degrees in total).
Although it is difficult to eliminate a fleet angle completely, several measures can help minimise its effects. These include using a plastic-filled wire rope, which provides greater rope stability and reduces rotation. Additional sheaves or wire rope swivels may also be used to limit rotational forces. However, keep in mind that adding extra sheaves may reduce the fleet angle but can also increase rope wear and shorten the service life of the wire rope.
If you notice a fleet angle developing, it is important to act immediately. Measure the angle to determine the severity of the problem and select the most appropriate solution. Depending on the situation, this may involve replacing the wire rope, installing an additional sheave, or relieving the rope's tension and rotational forces before further damage occurs.
