The amount of twist imparted to a yarn during the spinning process determines not only the strength, size etc of the yarn but also its appearance. Thus if the twist in nominally identi-cal yarns varies from bobbin to bobbin when the yarn is woven the eye sees the difference and the material is considered faulty. For this reason both the spinning and weaving sides of the textile industry place great emphasis on the determination of the twist in a yarn by including tolerances in contract conditions.
With regard to written standards it appears that for ring spun yarns there are adequate national and international (ISO) standards. In the case of yarns produced by the so-called open end spinning process (DE) however, there is no approved method. There is therefore a need for prestandardization work in the case of OE yarns to allow a twist measurement method acceptable to all to be agreed.
The participants will test three types of yarn by the so called twist untwist method and will then compare results.
ITF Mulhouse has fabricated and tested 18 batches of threads, including:
1. 3 materials (VIS/CO 67%/33%; PES/CO 67%/33%; PES 100%)
2. 2 titles (20 tex and 50 tex)
3. 3 twist coefficients (115, 125, 135).
The results of the tests indicate important differences in the measured twist values from the actual ones:
a 40-45% for VIS/CO, using the simple twist/untwist method;
b 10-15% for VIS/CO, 15-30% for PES, 20-30% for PES/CO, using the method with double counter try (NF G 07-09).
It was concluded from this preliminary work that no method is as yet sufficiently developed to be proposed as a standard and thus the intercomparison will not be carried out.