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By Ma Chunqin, Chen Yufeng, Lu Rongsheng
Abstract:
This paper summarizes the difficulties and control measures in the carding process of Lyocell fiber. In response to issues such as fibrillation, poor transfer, excessive hard slubs, and static electricity during Lyocell fiber carding, a series of technical measures have been adopted. The process follows the principles of “heavy weight, multiple carding and cleaning, high transfer, high tension, no floating or falling, sufficient carding, and reduced damage.” The selection and matching of card clothing aim to improve transfer, reduce fibrillation, and minimize static electricity. Carding speed is optimized with high speed for the cylinder, doffer, and hopper beater, and low speed for the licker-in and flat tops, enhancing carding while minimizing fiber damage. Reasonable carding gauge design helps eliminate hard slubs while balancing lint removal and fiber damage. Temperature and humidity management combines humidification and moisture retention to reduce static electricity. In practice, these measures effectively solve the carding difficulties of Lyocell fiber and improve carding quality and production efficiency.
Keywords: Lyocell fiber; Carding; Fibrillation; Gauge; Card clothing; Process; Fiber damage; Temperature and humidity
Due to the eco-friendly and biodegradable characteristics of Lyocell fiber, its domestic production scale has been increasing year by year. Compared with traditional cellulose fibers, Lyocell fiber, with its skin-core structure, circular cross-section, and fast moisture absorption and release properties, presents certain challenges in carding process and quality control.
Due to its circular cross-section, Lyocell fiber has poor cohesion and is prone to fibrillation due to its skin-core structure. It contains many hard and soft slubs that are difficult to remove. Unstable oil content can cause quality fluctuations, and the fiber’s fast moisture absorption and release make it prone to static electricity during production. These factors lead to issues such as web edge breakage, poor web clarity, difficulty in sliver formation, poor carding quality, residual hard slubs, high lint loss, and thick flat waste, ultimately affecting yarn quality and fabric appearance. Therefore, designing a reasonable process based on the carding capacity of the carding machine is key to improving the spinning quality, yield, and production efficiency of Lyocell fiber.
The degree to which fiber bundles are separated into single fibers on the carding machine is closely related to yarn strength and evenness. The carding process gradually opens fiber bundles and removes impurities, decomposes fiber bundles into single fibers, and improves fiber parallelism and straightness. Due to the cross-sectional shape and structural characteristics of Lyocell fiber, friction and beating during carding can cause fibrillation and fiber damage. Therefore, the carding process should follow the principle of “strong carding, fast transfer” to reduce fibrillation caused by friction. The process gauge should be designed to be smaller than the diameter of the impurities.
Soft slubs, hard slubs, and glue lumps are common in Lyocell fiber production. The diameter of these impurities generally ranges from 0.3mm to 1.2mm. They are small in volume and stick to fibers, making them difficult to remove. Glue lumps are small and hard, and tend to carbonize and embed impurities when exposed to high temperatures. Process design should follow the principles of “gradual opening, minimal rubbing, full exposure, and thorough separation,” utilizing the high-speed centrifugal force of the cylinder and licker-in, combined with airflow boundary layers, to remove impurities.
In practice, there are significant performance differences between batches of Lyocell fiber. Therefore, process design should focus on fiber blending to avoid fabric streaks and color differences. Due to its circular cross-section, Lyocell fiber easily slips off the needle surface during carding. The carding force varies greatly in different zones, leading to poor transfer and doffer web return. Blending process design and card clothing configuration must consider fiber control, release, transfer, and blending.
During carding production, due to the high friction coefficient of Lyocell fiber, beating and carding by various rollers can intensify fibrillation and increase short fibers. In downstream processes, short fibers affect sliver evenness and fabric appearance, and fibrillation can cause fabric pilling. Therefore, the carding process must control the increase of short fibers to reduce their impact on downstream processes.
The mechanism of fibrillation is that the lateral force between fibrils becomes weak in the wet state, causing fibrils to split under external shear and form small hairs detached from the fiber body. This is especially likely to occur in wet conditions. Excessive carding can also affect fiber transfer and cause hairiness. From a carding perspective, controlling fibrillation should focus on improving transfer, reducing friction, minimizing repeated carding, and maintaining stable relative humidity.
When producing Lyocell fiber, the carding process follows the principles of “heavy weight, multiple carding and cleaning, high transfer, high tension, anti-wrapping and anti-embedding, reasonable speed, no floating or falling, sufficient carding, and reduced damage.” Multiple carding means strengthening carding, designing reasonable gauge based on fiber impurity diameter, increasing fiber separation, and improving carding effect. Multiple cleaning means removing hard slubs, soft slubs, glue lumps, and sticky fibers through card clothing selection. High transfer means smooth transfer from licker-in to cylinder and cylinder to doffer, preventing wrapping and reducing friction and fibrillation. High tension mainly increases the tension draft between doffer and pressure roller to prevent falling and blocking. Anti-wrapping and anti-blocking prevent wrapping around rotating parts and blocking sliver tubes. Anti-embedding prevents impurities from embedding in fixed and movable flats. Reasonable speed means setting cylinder and licker-in speed based on weight. Reducing lint means minimizing spinnable fiber loss while ensuring quality. No floating or falling means ensuring the web does not float or fall, with low breakage and normal production.
Cylinder clothing should shift from strong to gentle fiber support, reduce flat waste, improve transfer, and reduce carding load. Thin base and increased lateral density enable fine carding, exposing impurities and short fibers. A large working angle of 35°–40° improves penetration and reduces fiber damage. Tip thickness is reduced from 0.060mm to 0.035mm to minimize fiber damage. Cylinder density is increased from 800 to 1000 points/(25.4mm)² to improve carding. Tooth depth is reduced from 0.35mm to 0.30mm to aid transfer and reduce embedding. Base thickness is reduced from 0.50mm to 0.35mm to improve carding. A commonly used model is AC2035×01645TR-3.
Doffer clothing requires strong control, high transfer, reduced hooks, and improved straightening. A larger working angle of 30°–35° improves transfer rate. High tooth density (505–551 points/(25.4mm)²) enhances fiber control and reduces web dropping. Increased tooth depth (1.9–2.3mm) improves fiber capacity and transfer. Straight tooth profile reduces hooks and resistance, ensuring fiber straightness and reducing A1 yarn defects. Low shoulder height (1.0mm) improves transfer and fiber control. Thin base (≤0.70mm) limits fiber movement and improves straightness. A commonly used model is AD4030×02065.
Licker-in clothing requires high penetration, minimal damage, reduced short fibers and lint, no wrapping or embedding, and fibrillation control. Selection principles: large angle (10°–20°), thin tip (≤0.17mm), large longitudinal pitch (6.0–8.0mm), and thin base (≤2.0mm). A commonly used model is AT5020×06015V.
Fixed flat clothing should not embed impurities, cause minimal damage, and provide strong carding. High tooth density (230–1075 points/(25.4mm)²), large working angle (10°–20°), shallow tooth depth (0.6mm), large pitch (≥2.0mm), and thin base (≤0.50mm) are recommended.
Flexible flat clothing should not embed impurities, enhance lateral interception, and remove hard slubs and glue lumps. Lateral needle distance ≤0.317mm, short needle height (7.5mm), high density (450–600 points/(25.4mm)²), and large working angle (76°–78°) are recommended. A commonly used model is MCH55-78.
Due to its nearly circular cross-section, Lyocell fiber has poor cohesion and loose fiber-to-fiber contact, which is unfavorable for transfer. If the card sliver weight is too low, web formation becomes difficult, leading to issues such as floating web, web dropping, and return of fibers. Therefore, a relatively heavy card sliver weight is recommended for Lyocell fiber. Generally, the sliver weight should be controlled above 25 g/5 m to improve and stabilize carding quality.
When processing Lyocell fiber, carding speed design follows the principle of “sufficient carding, thorough cleaning, reduced fiber damage and fibrillation.” The traditional “four highs and one low” approach is adjusted to “three highs and two lows.” The “three highs” refer to high speeds for the cylinder, hopper beater, and doffer, which enhance carding intensity and transfer rate, and use greater centrifugal force for impurity removal and transfer. The “two lows” refer to low speeds for the licker-in and flat tops. Flat speed affects the residence time of each flat in the carding zone; higher speed increases lint loss but reduces carding time and effectiveness, while lower speed improves carding quality and lint control. Low licker-in speed and a high cylinder-to-licker-in speed ratio reduce fiber damage and improve transfer. Compared with traditional processes, the carding speed design for Lyocell fiber is shown in Table 1.
Table 1 Comparison of Main Process Conditions for Carding Speed
| Parameter | Cylinder Speed (r/min) | Licker-in Speed (r/min) | Flat Speed (mm/min) | Doffer Speed (r/min) | Hopper Beater Speed (r/min) |
|---|---|---|---|---|---|
| Traditional | 670 | 280–330 | >180 | 20–35 | <800 |
| Lyocell | ≤840 | 360–450 | <160 | 40–70 | >1000 |
When processing Lyocell fiber, carding gauge design follows the principle of “sufficient carding, improved transfer, full straightening, reduced fibrillation and fiber damage.” The cylinder-flat fine carding zone should have tight gauge for strong carding, while the pre-opening zone should have larger gauge to reduce rubbing and improve transfer. The rear fixed flat pre-carding zone should reduce opening zone positive pressure, release airflow, lower operating temperature, and reduce fiber damage and rubbing. The front fixed flat carding zone should have tighter gauge to enhance single-fiber alignment. The front web cleaner gauge should prioritize lint removal to exclude short fibers, hard slubs, and glue lumps. The rear web cleaner gauge should be larger to reduce lint loss and release airflow. The rear licker-in zone should follow the principle of tight gauge and small zone to reasonably distribute lint removal, remove more impurities and hard slubs, and reduce spinnable fiber loss. Lint removal distribution: front web cleaner > flats > rear web cleaner > licker-in rear waste zone > licker-in suction and cylinder under suction. Cylinder-doffer and licker-in-cylinder gauges should be tight to improve transfer. Stable negative pressure inside the card and controlled lint removal reduce fiber fly and prevent floating or choking.
Main carding gauge settings:
Due to the low crimp of Lyocell fiber, the draft between doffer and calendar roller should be higher than for cotton, around 1.06×. When using a stripping apron, the draft can be 1.20–1.30×. Due to the low crimp and near-circular cross-section, Lyocell fiber is not easily gripped. To improve licker-in carding efficiency, the feed roller pressure should be increased by 20–50% compared to cotton to enhance grip and prevent fiber clumping, which aids licker-in carding and reduces lint loss. However, excessive pressure increases power consumption and roller deformation, which is unfavorable for gripping.
Due to the high friction coefficient and oil content of Lyocell fiber, sliver may clog the coiler tube or fail to form. Therefore, oil residues in the sliver path must be cleaned, and the sliver diameter should be moderately compressed (increased pressure at the calendar roller).
Environmental temperature and humidity greatly affect spinning quality and efficiency. When relative humidity is too low, Lyocell fiber becomes stiff, prone to static electricity, increased lint loss, fiber damage, reduced yarn strength, and worsened fibrillation. When relative humidity is too high, Lyocell fiber swells radially, reducing lateral cohesion and making fibers softer and easier to card, but fibrillation increases. In carding, temperature should be controlled at 26–30°C, relative humidity at 60–70%, and sliver moisture regain at 10–11%. Fiber raw material should be fully conditioned before feeding. Humidification should be even to effectively control fibrillation.
Lyocell fiber specification: 1.33 dtex × 38 mm. Siro compact spinning technology is used to produce 14.6 tex yarn. The blowroom-carding line process:
JWF1018 auto bale plucker → JWF1026 multi-mixer → JWF1116 fine opener → JWF1176 feeder → JWF1216 carding machine.
Original clothing configuration:
Optimized clothing configuration:
Optimized carding parameters:
For 14.6 tex Lyocell siro compact yarn:
Table 2 Comparison of Main Quality Indices Before and After Optimization
| Parameter | Before | After |
|---|---|---|
| Production (kg/h) | 26 | 53 |
| Delivery speed (m/min) | 100 | 190 |
| Yarn evenness CV (%) | 10.2 | 9.38 |
| Thin places (/km) | 0 | 0 |
| Thick places (/km) | 11 | 7 |
| Neps (/km) | 29 | 11 |
| A1 defects/100 km | 103 | 67 |
| Slub removal rate (%) | 86 | 95 |
Traditional Lyocell carding uses light weight, large gauge, and low speed, with clothing borrowed from conventional synthetic fiber types, leading to conflicts between quality and output, poor carding and fiber damage, and high lint loss with low yield. Based on Lyocell fiber characteristics, optimization with heavy weight as the foundation, high cylinder-licker-in speed ratio, reasonable lint distribution, and optimized carding gauge is carried out. Clothing selection prioritizes transfer, sufficient carding, reduced short fiber damage, increased yield, and reduced defects. In practice, reasonable selection of new clothing and optimized process design based on fiber characteristics increases hard slub removal rate to over 95%, improves fibrillation, boosts production to over 50 kg/h, and achieves quality indices and defect levels better than USTER 2023 5% level, realizing high-efficiency carding.
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