Stretching is the thinning of a thread or wick by sliding fibers over each other. The numerical value of the E-stretch is given by the relationship between the final length of the and the primitive length prior to stretching. It's an abstract number, and it's always positive.
For example, if you have a thread with initial length 1m, feeding a machine that makes a stretch, and you get a thread with length 6m, then the produced stretch is calculated:
Stretching increases the output length, as a result, the thickness of the thread decreases, but the weight of the material on both sides of the machine remains constant. There is no reduction in the machine. Following the example, then the thread output has a length that is 6 times longer, but its diameter is one-sixth of the original thread.
As the purpose of the spinning is to obtain a thin mass of fibers (thread), it is expected that the material is fine-tuning its thickness during its pass in each of the processes, then, you must infer that every spinning machines perform a stretch. This is true and is one of the core principals of spinning.
Another important consequence of stretching is the parallelization of the fibers in the tape: Theoretically the thread could be taken directly to the spinning machine, but as the fibers are not yet parallel, would have a large number of ruptures, so it is necessary to carry out the thinning of mass of fibers in succession, in several stages. In this way, gradually the fibers straighten up when they slide over each other thanks to them being stretched.
The total stretching depends on:
- the type of material
- the content of short fibers
- the length of fiber