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The two most commonly used slings in material handling applications with single-part six-strand wire rope are the mechanical spliced Flemish Eye Sling and the mechanical spliced Returned Loop Eye Sling, sometimes referred to as the Turnback Eye Sling.
Visually, these termination methods exhibit slight differences when compared side by side. The Flemish Eye Sling typically features a swaged steel sleeve that tapers down on one end, while the Returned Loop Eye Sling utilizes one or more straight non-tapered steel or aluminum sleeves. However, due to variations in fabrication methods and sleeve types used by different sling manufacturers, these distinctions may not always be readily apparent to untrained observers.
Although both sling types involve the use of one or more metal sleeves swaged over the rope juncture, the fabrication methods employed for each differ.
The Wire Rope Technical Board Sling User's Manual describes the fabrication method for the Returned Loop Eye Sling as follows: "The returned loop is created by forming a loop at the end of the wire rope, sliding one or more metal sleeves over the short end of the loop eye, and pressing these sleeves to secure the rope end to the sling body." (See picture below.) It is common practice to have one metal sleeve at each eye.
On the other hand, the fabrication of the Flemish Eye Sling involves opening or unlaying the rope body into two parts: one part with three strands and the other with the remaining three strands and the rope core. The rope is unlayed to create a loop or eye by looping one part in one direction and the other part in the opposite direction, and then re-laying the rope back together. The strands are rolled back around the rope body. Subsequently, a metal sleeve is slipped over the splice ends and pressed (swaged) to secure them to the sling body.
It is important to note that the termination (splice) efficiency, which refers to the strength retained by the wire rope sling after the fabrication process, is typically 90% or higher if the correct fabrication methods are followed for each type of sling. The actual efficiency depends on factors such as the rope diameter and other variables involved in producing the splice. For instance, a nominal splice efficiency of 94% means that 94% of the minimum breaking force (MBF) of the wire rope remains intact after the termination or swaging process is completed.
Now, let's explore a few key considerations applicable to both types of slings being discussed.
The Flemish Eye Sling is the more widely favored option among the two wire rope slings. This is primarily due to its robust capabilities and ability to endure rough handling. Users also prefer the presence of a backup splice beneath the swaged sleeve.
Typically, a steel sleeve is swaged onto a steel wire rope, ensuring that no dissimilar materials come into contact that could accelerate corrosion.
According to ASME B30.9 standards, a proof test for Flemish Eye Slings is not mandatory unless specifically requested by the user.
The Flemish Eye termination features a streamlined profile that is less prone to snagging on obstructions. These slings are typically faster and less expensive to manufacture, excluding the time and costs associated with proof testing.
The strength of the sling relies entirely on the integrity of the swaged sleeve. If the sleeve fails, there is an immediate loss of load, so users in the field should closely inspect the sleeves before each use.
When aluminum sleeves are utilized with carbon steel wire rope, there may be a higher risk of deterioration due to electrochemical reactions between the different metals. Environments with saltwater and corrosive elements can be particularly damaging.
In contrast, ASME B30.9 regulations mandate that all Returned Loop Eye Slings (also known as Turnback Eye Slings) undergo proof testing by the sling manufacturer or a qualified individual.
These are just a few key distinctions between the two most common types of wire rope slings.
Flemish Eye Sling
Returned Loop Eye (Turnback Eye Slings)
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