Abstract
The physico-mechanical properties of cotton and staple viscose open-end yarns were studied in connection with layer depth. It was observed that there are systematic trends, more visible for cotton yarns, for the parameters considered here, dependent on bobbin build. Thus, breaking strength and extension, resistance to repeated extensions, abrasion resistance, and short-term irregularity tend to deteriorate more or less as bobbin build increases.
These phenomena are related to both material and rotor cleanliness, the spectrograms of the yarns being a valuable index to the existence of certain zones in the bobbin where the yarn presents anomalies in the shape of transient periodic irregularities together with deterioration of mechanical properties, yarn irregularity, and yarn defect content. Such anomalies gradually appear in cotton bobbins from spinning rotors in which no end break has occurred, culminating in the outer layers (full bobbin). But in the staple viscose bobbins they appear in the central layers and then disappear, which is thought to be related to the accumulation of impurities in the rotor and to the eventual break of the yarn and subsequent cleaning operation. The fact that there should be less difference between the beginning and the end of the bobbin for staple viscose yarns is attributed to the greater cleanliness of this fiber as compared with cotton. Other yarn parameters such as diameter and hairiness are affected by the phenomena mentioned above, but the nature of the fiber can offset, to some 'extent, some of the observed effects.
The differences observed, while significant in some cases, are usually not great, but the existence of yarns with fluctuations in their irregularity, fault content, and hairiness, can originate defects and patterning in the woven fabric; it is thus concluded that the cleanliness of the rotor is a factor of major importance is open-end spinning.
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