Ply & Lay

From expert yarn, rope and rope machinery manufacturers, we understand there is no such thing as a standard in jute rope, and that tight and loose lay are subjective.

Subtle differences in jute filament colour (1. Grade 3 Tossa, 2. Grade 2 White, 3. Grade 1 Tossa, 4. Grade 2 Tossa, 5. Grade 2 Tossa, 6. Grade 4 Tossa, 7. Grade 3 Tossa)

A larger number of fine filaments can be twisted together tighter into a yarn of an equal count than can be made with coarse, low quality jute, due to the relationship between coherence and obliquity. As filaments are rotated, strength increases up to an optimum twist. With further rotation, obliquity decreases as fibres lay increasingly more perpendicular than parallel to the length of the yarn, losing linear orientation. Lower grade jute will have a lower optimum twist. The direct effect is lower overall longitudinal strength.

Yarn ply – left: single ply 14/1, middle: 2–ply 14/2, right: 2–ply 10/2

Yarn twist sets the optimum counter–twist when wound together into strands. If twist dynamics of yarn and strand counter each other, they will hang straight and true. Strands must then be twisted together to make rope. The twist dynamics of the yarns in one direction, the strands in the opposite, and then the rope back in the original direction must match to prevent recoil and corkscrewing.

With these dynamics at work, there is room to balance one against the other, and this is where lay ratio is set. While not as aggressive as over–twisting the yarn, strands or rope tightened too excessively will pass an optimum point of strength, and be more prone to filament breakage.

Yarn ply in rope – (left to right): single ply 14/1, 2–ply 14/2, 2–ply 10/2, single–ply 48/1

Tightly laid rope becomes very hard and more difficult to work with. When still within a ratio for structural integrity, a loose laid rope will feel very soft, but is easier to damage.

Lay ratio – left: looser, middle: medium, right: tighter

Multiple–ply yarns introduce a fourth twist dynamic. Relatively loose 2 and 3–ply yarns can feel very soft, and have an impact on the resulting twist dynamics of the strands and rope, and therefore lay. Tightly wound multiple yarns can make the rope tight, hard and feel uncomfortably knobbly.

Coating – left: rope made from coated yarns, right: rope made from uncoated yarns.

Amatsunawa no longer specifies lay ratio, but through education in precisely how our ropes will be used, we teach machine operators to sense the feel of the final rope, and pay specific attention to quality control.

©AMATSUNAWA GmbH 2021