The fact that rotor-spun yarns contain significantly fewer yarn defects than ring-spun yarns has made a major contribution to the success of the rotor spinning system. A comparison of Uster Statistics shows that the numbers of thick places, thin places and neps are significantly below the level of ring-spun yarns, even at delivery speeds that are up to 10 times higher. And the finer the yarn counts, the greater the differences. The reasons for this are back-doubling in the rotor (which balances variations in mass) (refer to section Fiber collection in the rotor groove (back-doubling) and fiber guidance and monitoring without a cylinder drafting system. Furthermore, a package of rotor-spun yarn contains only a fraction of the yarn joints (piecings) compared with a cross-wound package of ring-spun yarn. A 4 - 5 kg cross-wound package in the rotor spinning mill contains no more than 3 - 5 spinning related piecings at normal ends down rates. However, a 3 kg cross-wound package of ring-spun yarn produced on the winder already contains some 30 - 40 piecings due to system-related cop joints plus a certain number of additional piecings due to cleared yarn defects. This very soon adds up to more than 50 piecings (splices or knots per package).
This was also a major reason why rotor-spun yarns could for many years be processed further without cleaning. However, today‘s quality standards no longer permit this; quality requirements for rotor-spun yarns have increased considerably. For example, manufacturers of branded denim products (jeans, shirts, etc.) stipulate precise specifications for yarn and fabric quality which are so strictly formulated that only quality-tested yarns can be considered for processing.
Quality control systems have therefore very soon become integral components of high-performance rotor spinning machines. While contract spinning mills were the first to cite quality-tested yarns as a product advantage, in the meantime increasing numbers of vertically integrated mills are also starting to used quality-tested and cleaned yarns in downstream processing, especially for high-quality woven or knitted fabrics.
Leading global suppliers of quality control systems (e.g., Uster Technology with the Uster Quantum Clearer2® and Barco with the BarcoProfile) employ different measuring systems in some cases, but offer a largely comparable range of performance:
- detecting, counting and clearing disturbing yarn defects in accordance with adjustable clearing limits;
- counting uncleared (non-disturbing) yarn defects in defect classes;
- detecting and eliminating extraneous substances;
- measuring the main physical textile yarn attributes: yarn irregularity, imperfections and Classimat values (not yarn tenacity and elongation).
Quality data from each spinning position for all running batches are available to operating personnel on request at any time. Necessary interventions in the event of variances can be made immediately if required, and thus without any loss of time.