Core-spun yarn, a special type of yarn composed of a core yarn and an outer sheath fiber, is susceptible to defects during spinning if the outer sheath fiber is missing. These defects directly impact the fabric's feel, appearance, and durability. Such defects typically arise because the outer sheath fiber fails to adequately cover the core yarn, resulting in an exposed core. Their occurrence is closely related to factors such as raw material selection, process parameters, equipment condition, and operational procedures. To avoid these problems, a comprehensive approach is needed, encompassing raw material pretreatment, process optimization, equipment maintenance, and operational management.
Raw material pretreatment is fundamental to preventing these defects. The fiber length, fineness, and uniformity of the outer sheath fiber directly affect its cohesion with the core yarn. If the fiber length is too short or the uniformity is poor, it is prone to breakage during spinning, leading to core yarn exposure. Therefore, it is necessary to select suitable outer sheath fibers based on the core yarn characteristics and improve fiber flexibility and cohesion through a blending process. For example, when spinning cotton-polyester core-spun yarn, adding wool oil emulsion can reduce friction between fibers, prevent fiber damage caused by static electricity or mechanical action, thereby reducing breakage rate and improving coating effect.
Optimizing process parameters is the core of controlling yarn defects. During spinning, parameters such as roving twist coefficient, yarn twist coefficient, and draft ratio need to be precisely controlled. A higher roving twist coefficient can prevent fiber diffusion during untwisting in the back zone of the yarn, reducing sliver dispersion; a higher yarn twist coefficient can enhance the cohesion between fibers, preventing core filament exposure. For example, when spinning spandex core-spun yarn, using lighter travelers and selecting corrugated or thin-arched cross-sections can expand the yarn channel, preventing excessively heavy travelers from causing over-drafting or fraying of the spandex core filament, thus leading to core exposure. Furthermore, precise control of core filament positioning, using guide rollers with "V"-shaped guide grooves to ensure the core filament does not move during drafting, is also crucial to preventing core exposure.
Equipment maintenance is crucial for yarn defect control. Wear or malfunction of spinning machinery directly leads to yarn defects. For example, damage or aging of rubber rollers and rings increases friction, causing fiber breakage; sluggish or wobbly guide rollers cause unstable filament feeding, leading to core exposure. Therefore, worn rubber rollers and rings must be inspected and replaced regularly to ensure smooth guide roller rotation. Simultaneously, the uniformity and stability of the cradle pressure, the flexible operation of the center roller, and the integrity of the upper pin claws also require close inspection to avoid poor wrapping due to mechanical problems.
Strict adherence to operating procedures is the last line of defense against yarn defects. Operators must be highly responsible, patrol frequently, and promptly identify and address issues such as yarn breakage and core misalignment. For example, when spinning spandex core-spun yarn, the splicing length must be controlled within a reasonable range to avoid defects such as "bare core tails" or "hollow core splices." Furthermore, when changing spandex yarns collectively, the difference in yarn cake diameter must be minimized to prevent core exposure due to inconsistent drafting. For existing yarn defects, a second check using electro-cleaning equipment is necessary during the winding process to remove coreless yarn, exposed core yarn, and other defective products.
The cleanliness of the spinning channel is equally important. Impurities such as fly ash and short fibers, if adhering to the yarn, will damage the covering structure and lead to yarn defects. Therefore, it is necessary to regularly clean the roving slant, drafting area, channels, and rubber rings to ensure a clean spinning environment. At the same time, the correspondence between the core yarn channel and the spindle position must also be checked to avoid core yarn cross-winding or improper operation leading to double-core yarn.
Controlling the ambient temperature and humidity also plays a supporting role in preventing yarn defects. High temperature and high humidity environments easily cause fibers to absorb moisture and expand, increasing the risk of yarn breakage; while low temperature and dry environments may cause fibers to fly due to static electricity, affecting the covering effect. Therefore, it is necessary to reasonably control the workshop temperature and humidity according to fiber characteristics and process requirements to provide stable conditions for the spinning process.
