Fleet Angle

A fleet angle is the angle between the rope leaving the sheave and the centerline of the sheave groove. The fleet angle is important when winding a wire rope on a drum. As the rope is being wound on a drum, it wanders from one side of the drum to the other. Make sure the sheave groove is aligned with the center of the drum to minimize the maximum fleet angle. The maximum fleet angle determines the uniformity of the rope wound on the drum. If the fleet angle is small enough, the rope will wind on uniformly. If the fleet angle is too large, it will leave gaps between wraps. These gaps encourage the rope to cut into the underlayers resulting in crushing and pinching of the rope during winching operations. This situation is aggravated by the use of softer synthetic fiber lines. Large fleet angles can also cause excessive abrasion of the rope against the inner surface of the sheave groove and cause the rope to rotate forming hackles and kinks. A levelwind device may be required to ensure uniform winding if a small fleet angle cannot be achieved. This device is usually sold as an option of a deck winch. It consists of a moving sheave mounted on a shaft with diamond-shaped grooves. The shaft rotation is synchronized with the drum rotation such that the diamond grooves push the sheave to align with the wraps on the drum to achieve uniform winding. When using a deck winch with a levelwind, the sheave fleet angle is restricted only by the abrasion and rotation problems mentioned above.

Where space limitations are unrestricted such as on mine hoists, the fleet angle is sometimes as small as 1/2 of 1 degree. This is equivalent to a distance of 115 feet between the drum and the first fixed sheave for each foot of drum width. It represents the minimum below which the rope will not properly wind back from the drum flange after completing one layer.

Most installations do not permit this much distance between the drum and sheave and for average conditions it is considered good practice to keep the fleet angle within 2 degrees for a grooved drum and 1-1/2 degrees for a drum with a smooth face. Two degrees is equivalent to a distance of 29 feet and 1-1/2 degrees is equivalent to 38 feet for each foot of drum width either side of centerline of sheave as illustrated.

1-1/2° fleet angle centerline of ropes

1-1/2° fleet angle centerline of ropes

Was this article helpful?

0 0

Post a comment