In recent years, two-for-one twisted yarn has been widely used due to its excellent softness, wear resistance, and tensile strength. However, since the spindle-by-spindle monitoring technology of two-for-one twisters is not yet mature, more than 80% of quality issues still require manual control. Therefore, it is essential to establish and improve a quality management system, standardize employee operations, and comprehensively and effectively implement all tasks according to actual production conditions in order to ensure the quality of yarn after twisting.

1.1 Power Unit
Includes the motor, secondary transmission shaft, spindle speed change pulley, electrical control box, operating components, and display.

Twisting Unit
Includes spindle braking devices, spindle components, and yarn winding devices. This unit is the core of quality control.

  1. The spindle braking device includes the spindle drive belt, tension pulley, spindle brake pedal, etc.
  2. The spindle components include a yarn storage and guiding disk, yarn can, yarn tension device, spindle bushing, balloon cover, balloon guide hook, and yarn break auto-stop device.
  3.  The yarn winding device includes the drum, overfeed roller, transverse yarn guide nozzle, creel device, and bobbin chuck.

1.3 Transmission Unit
Includes the power transmission system, anti-overlap device, and electromagnetic clutch.

  1. Power transmission system: The motor drives the spindles through pulleys, belts, and the spindle tape; the spindle tape transmits power via toothed belts and a reduction device to the winding roller and overfeed roller. At the same time, the cam motion is converted into a reciprocating slider motion to drive the transverse yarn guide.
  2. Anti-overlap device: Prevents the formation of band-shaped winding patterns on bobbins.
  3. Electromagnetic clutch: Controls pulses and periodically changes the speed of the transverse yarn guide.

02 Basic Equipment Management

Unsynchronized winding or twisting anomalies in two-for-one twisters may cause batch quality issues. The transmission and twisting units are key to quality control; therefore, daily preventive measures and periodic closed-loop management are required.

  • 2.1 Machine Cleaning and Overhaul Cycles
    We set the cleaning cycle at 45 days and the overhaul cycle at 2 years. Using a combined cleaning/overhaul management method, we inspect the twisting and transmission units, calibrate relative component positions, replace worn parts, and verify process parameters.
  • 2.2 Assigned Responsibility Management
    Implement position-based responsibility management so that in case of equipment issues, accountability can be traced to the specific operator, ensuring effective supervision of maintenance quality.
  • 2.3 Daily Inspection Requirements
    Maintenance workers must conduct 30 minutes of self-inspection daily on their assigned machines, checking different items each day. The equipment manager also performs random inspections to ensure timely and thorough rectification.
  • 2.4 Spare Parts Management
    Maintain detailed spare parts records for effective control of key quality points. For example, to reduce twistless yarn, keep detailed replacement records of twisting-related parts, including issue date, material name, specifications, quantity, unit, and machine used.
  • 2.5 Fault Logbook
    Establish categorized logbooks for faulty machines, recording causes of failure and downtime. Analyze and implement corrective measures, adhering to the principle of “no problem left unresolved” until completely solved.
  • 2.6 Maintenance Responsibility System
    Assign machines to specific maintenance personnel, encouraging proactive work. Evaluation indicators include spare parts costs, faulty machines, operator feedback, etc. Combined with performance evaluation, this ensures high-quality equipment operation.

03 Equipment Inspection Management

  • 3.1 Spindle Inspection
    Conduct spindle sweeping once a week to reduce twist differences between spindles and machines. The actual spindle speed difference must not exceed 50 r/min.
  • 3.2 Process Consistency Check
    Processes for the same machine model and product must remain consistent, with a 100% qualified rate.
  • 3.3 Spindle Oiling and Cleaning
    Lubricate spindles regularly and remove entangled yarn from spindle disks.
  • 3.4 Bobbin Chuck Inspection
    Regularly check the flexibility of bobbin chucks to avoid uneven twist caused by poor rotation.
  • 3.5 Yarn Twist Unevenness Test
    Every 45 days, test the twist unevenness of 20 randomly selected bobbins.

04 Quality Control of Two-for-One Twisting

  • Process Design Sheets and Gear Management
    The technical department must archive complete process design sheets for all products and strengthen gear management with proper storage, classification, and accurate issuance. Establish a process change procedure, ensuring quality requirements are met. Random checks should be conducted on machines by quality personnel.
  • Periodic Checklists
    The operating team must establish periodic checklists (tension checks, process changes, two-yarn-per-spindle checks, yarn checks, component consistency checks, etc.) to monitor critical quality points.
  • Doubling Quality Control
    Doubling quality directly affects breakage rate and twist unevenness. Consistent tension and speed are key control points.
  • Multi-Product Management
    Combine inspections with training. For example, daily production information is shared in work groups; operators and yarn handlers check machines, and supervisors monitor compliance. Different product types should be arranged in separate areas, with regular training sessions.
  • Internal Quality Inspection System
    Establish a clear defect-catching system with rewards and penalties. Implement internal mutual checks between operators and maintenance workers to ensure final product quality.
  • Workshop Humidity Control
    Humidity significantly impacts yarn quality. Maintain good working conditions, reduce dust, improve softness, and reduce yarn breakage and hairiness. Relative humidity should be kept between 60–70%.

05 Common Issues and Solutions in Two-for-One Twisting

  • High Breakage Rate
    Causes: improper yarn tension, deformed spindle wing, poor spindle wing rotation, balloon too small, yarn contacting burrs or dirt, damaged yarn guides, entangled yarn, poor bobbin rotation, weak single yarn strength, etc.
    Solutions: adjust yarn tension, correct spindle wings, clean/replace parts, adjust balloon height, lubricate bearings, maintain proper doubling tension, etc.
    Case: On machine #998, 50D yarn had high breakage. Adjusting the balloon rod seat increased balloon size, preventing yarn from hitting the can edge; using the smooth side of the friction plate improved spindle wing flexibility.
  • Uneven Twist (Loose or Tight Twist)
    Causes: wrong gears, worn belts, spindle brake issues, damaged spindles, unstable bobbin position, burrs on parts, tension issues, or poor operator handling.
    Solutions: use correct gears, adjust belts, repair brakes, replace spindles, check bearings, clean guides, and strengthen operator training.
    Case: At TS20, spindle #18 had wrong twist gear installed, causing low twist.
  • “Braided” Yarn Defect
    Occurs due to inconsistent tension, poor yarn unwinding, burrs on rollers, or improper settings.
    Solutions: ensure tension consistency, clean and replace worn parts, adjust process settings, standardize splicing, and straighten yarn before restarting.
  • Uneven Yarn Strength
    Caused by balloon rubbing the can edge, damaged guides, poor spindle wing motion, or uneven single yarn strength.
    Solutions: correct balloon height, replace damaged parts, ensure smooth spindle motion, and maintain cleaning devices.
  • Poor Bobbin Formation
    Caused by poor bobbin rotation, misaligned rollers, improper pressure adjustment, worn parts, or guide misplacement.
    Solutions: adjust pressure, check positioning, inspect rollers, and mark bobbins when removed to avoid mismatching.

07 Conclusion

In two-for-one twisting, factors such as humidity control, equipment maintenance, and standardized employee operations significantly affect final product quality. By combining periodic equipment management, status checks, operational quality control, and personnel management, effective quality control in two-for-one twisting can be achieved.