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The complete process for producing Ne 21 open-end spun cotton yarn is a complex systems engineering undertaking that entails the precise control of multiple operational stages. Ne 21 counts fall within the medium-to-coarse yarn range and are widely utilized in open-end spinning applications. The following provides a detailed breakdown of this typical end-to-end manufacturing process:Core Objective: To efficiently and economically process raw cotton (or cotton-type fibers) into Ne 21 open-end spun cotton yarn that meets specified quality standards.
Key Stages of the Complete Process:
Raw material preparation and cotton opening
Opening:
The process of breaking down tightly compressed cotton blocks or tufts into smaller tufts or individual fibers, thereby creating the necessary conditions for subsequent impurity removal and uniform blending.
Key Point: Opening must be performed with moderation; excessive mechanical impact should be avoided to prevent fiber damage and an increase in short fibers.
Impurity Removal: Utilizing components such as dust bars, airflow, and beaters to extract the majority of impurities (e.g., leaf fragments, cotton seed hulls, sand, etc.)—as well as a portion of the short fibers—from the raw cotton. Key Point: Adjust parameters such as beater speed and dust bar settings based on the impurity content of the raw cotton to strike a balance between impurity removal efficiency and the minimization of fiber damage.
Blending: The thorough and uniform mixing of raw materials from different batches or with varying characteristics, ensuring the ultimate uniformity of the yarn's linear density and consistency of its color.
Raw Material Selection: Typically, Grade 3 or Grade 4 cotton is utilized. Depending on the intended application of the yarn and cost constraints, a certain proportion of "reprocessed waste" (e.g., comber noils, draw frame waste, roving waste), reclaimed cotton (after processing), or synthetic fibers (such as polyester) may be blended in. Regarding raw cotton specifications, the short fiber content should not be excessively high (generally <18%), and the impurity level should be moderate.
Opening and Impurity Removal: Achieved through the use of various machinery—including bale breakers, blenders (multi-bin or automatic types), openers (axial-flow, porcupine-roller types, etc.), and cleaners (single-beater or multi-beater types)—to accomplish the following:
Output: The formation of a uniform, clean, and well-opened cotton lap (in traditional processing lines) or the direct supply of a loose cotton stream to the carding machine (in integrated blow-room-to-carding systems).
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Carding：
Cylinder-Flat Setting: Influences carding intensity, impurity removal efficiency, and fiber damage. For Ne 21 yarn, a moderately tight setting (e.g., 0.18–0.25 mm) is typically employed.
Delivery Speed: Affects production output and carding quality. The objective is to maximize efficiency while ensuring quality is maintained.
Sliver Linear Density: Generally falls within the range of 4.0–6.0 g/5m and must be harmonized with the subsequent drawing process.
Fine Carding: Thoroughly breaks down fiber tufts into individual fibers.
Impurity Removal: Further eliminates fine impurities, neps, and a portion of short fibers (<16 mm).
Uniform Blending: Further blends the fibers during the carding process.
Fiber Straightening and Parallelization: Aligns the fibers as straightly as possible and orients them along the longitudinal direction of the fiber web.
Sliver Formation: Condenses the carded fibers into a continuous, structurally uniform strand (sliver), which is then coiled into a sliver can.
Core Function: Performs fine carding on fibers that have undergone the opening and cleaning processes; it is a critical stage that significantly impacts both yarn quality and production output.
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Drawing (Typically 2 Passages)：
Number of Doublings: 6 or 8 ends for the 1st passage (Breaker Drawing); 8 ends for the 2nd passage (Finisher Drawing).
Total Draft Ratio: Slightly greater than the number of doublings (to account for drafting efficiency). The total draft is approximately 6–8 times for the 1st passage and 6–8 times for the 2nd passage. Total Draft Ratio = Number of Doublings / (Finisher Sliver Linear Density / Breaker Sliver Linear Density).
Draft Distribution:The back zone employs a higher draft ratio (1.7–2.2 times) to preliminarily straighten the fibers; the front zone serves as the primary drafting zone (handling the majority of the draft) to ensure stable fiber acceleration.
Roller Settings (Nip Distances): Adjusted according to fiber length (commonly referencing Micronaire values or effective fiber length) to ensure effective control over fiber movement. The setting in the front zone is critical.
Finisher Sliver Linear Density:** Determined based on the feeding requirements of the rotor spinning machine and the target yarn count. If the linear density is too high, it impairs carding efficiency and increases end breakage; if too low, it reduces production output.
Doubling:The process of combining multiple breaker slivers into a single strand, subsequently attenuating it through drafting, and utilizing the "doubling effect" to significantly reduce long-term linear density variations.
Drafting:The process of attenuating the combined, coarse strand to the designed linear density (finisher sliver), while simultaneously further straightening, paralleling, and separating the fibers to improve short-term linear density variations.
Blending: The combination of multiple strands through doubling achieves more thorough fiber blending.
Core Functions: To improve sliver evenness, enhance fiber straightening and parallelism, and thoroughly blend breaker slivers from different sliver cans.
Process Flow: Generally requires two drawing passages (1st Passage/Breaker Drawing and 2nd Passage/Finisher Drawing). The 1st passage typically employs 6 or 8 doublings, while the 2nd passage employs 8 doublings. These two stages of doubling can significantly reduce the coefficient of variation in linear density.
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Rotor Spinning：
Opening Roller Speed: Influences the degree of fiber opening, impurity removal efficiency, and fiber damage. Excessive speed increases short fiber content and fiber damage; conversely, insufficient speed results in inadequate opening, negatively impacting yarn quality. For Ne 21 counts, the common operating range is 8,000–10,000 rpm.
Rotor Speed: One of the most critical parameters, directly affecting production output and yarn quality. For Ne 21 counts, the common operating range is 70,000–90,000 rpm.
Rotor Diameter: Influences the fiber condensation effect, twist transmission, and the upper limit of rotor speed. A smaller diameter allows for higher speeds (yielding higher output), but the smaller condensation circumference places stricter demands on yarn uniformity; a larger diameter entails relatively lower speeds, yet the larger condensation circumference is beneficial for improving yarn evenness. Common diameters range from Φ40 mm to Φ54 mm.
Twist (Twist Coefficient):Another critical parameter that determines yarn strength and handle (tactile feel). Insufficient twist results in inadequate yarn strength; excessive twist leads to a harsh handle and reduced production output. The twist coefficient in rotor spinning is generally 10–20% higher than that in ring spinning. For Ne 21 cotton yarn, the common twist coefficient range is 400–480 (metric system).
Feeding Coefficient: The ratio of the linear density (weight per unit length) of the fed sliver to the linear density (count) of the output yarn. It influences the thickness of the fiber layer within the rotor and the manner in which fibers are stripped from the opening roller. This parameter requires optimization based on the specific rotor diameter and yarn count being produced.
Feeding and Opening: The sliver is fed uniformly into the machine via a feed roller and feed plate, where it is opened into individual fibers by a high-speed rotating opening roller (saw-tooth roller), which also removes a portion of fine impurities and short fibers.
Stripping and Transport: The fibers on the opening roller are stripped away by a high-velocity airflow and transported into the rotor through a fiber transport channel.
Condensation: Inside the rotor, under the influence of centrifugal force, the fibers accumulate on the sliding surface (condensation groove) of the rotor's inner wall, forming a ring-shaped fiber strand (the rotor condensation strand).
Stripping and Twisting: The yarn tail (starter yarn) enters the rotor through the doffing tube and makes contact with the accumulated fiber strand. Winding: The twisted yarn passes through a twist blocker (false-twist disc) to attenuate the transmission of twist, is then drawn out by a delivery roller, and finally wound onto a yarn tube to form a yarn package.
Core Process: Directly spinning the finished sliver into fine yarn. This process utilizes the centrifugal force and negative airflow generated by a high-speed rotating rotor to accomplish the stages of condensation, twisting, and winding.
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Summary of Process Characteristics and Key Points for 21s Rotor-Spun Yarn:
High Raw Material Tolerance: Rotor spinning imposes relatively looser requirements on raw materials compared to ring spinning, allowing for the effective utilization of lower-grade cotton, cotton waste, and recycled cotton.
Short Process Flow: The roving stage—a necessary step in ring spinning—is eliminated.
High Production Output: The rotational speed of the rotor is significantly higher than that of a ring spindle, resulting in a high production rate per unit.
Unique Yarn Structure: The yarn features a high twist in the core and a lower twist in the outer layer (a layered structure); consequently, the yarn is bulky, soft, and abrasion-resistant, though it tends to have higher hairiness. It also exhibits excellent moisture absorption and breathability. While its tensile strength is typically lower than that of ring-spun yarn of the same count, it possesses a higher elongation at break.
Process Core Lies in the Spinning Stage: The rotational speeds of the opening roller and the rotor, along with the yarn twist level, are the most critical parameters influencing both yarn quality and production output; therefore, optimizing and balancing these factors requires focused attention.
