The yarn doubling machine is one of the core equipment in the post spinning processing stage. Its function is to combine two or more single yarns into strands through twisting, meeting the requirements of fabric strength, elasticity, and appearance. Due to long-term high load operation, improper parameter settings, or lack of maintenance, the double twisting machine is prone to faults such as breakage, uneven twist, abnormal tension, and abnormal noise, which directly affect production efficiency and product quality. This article combines equipment principles and practical experience to systematically sort out the troubleshooting logic and solutions for common faults.

1、 Overview of Core Structure and Working Principle of Double Twisting Machine

Understanding faults requires first mastering the core components and workflow of the equipment. The double twisting machine mainly consists of the following parts:

-Feeding system: including yarn frame, yarn guide hook, tensioner, responsible for stable output of single yarn;

-Twisting unit: The core is a rotating spindle (driven by a motor through a dragon belt), which obtains twist in the yarn through high-speed rotation;

-Winding system: composed of a groove tube, a yarn guide rod, and a transverse device, the twisted strands are wound into tubes according to certain forming rules;

-Control system: including frequency converter PLC、 Sensors (such as yarn breakage detection and tension sensing) enable parameter setting and automatic protection.

Its working principle is: after being adjusted by a tensioner, the single yarn enters the spindle tank and completes twisting with the rotation of the spindle (producing 2 twists per rotation, hence called "double twisting"), and finally winds into a tube through a groove tube. Any abnormality in any link may lead to yarn quality or equipment malfunction.

2、 Common fault classification and troubleshooting methods

（1） Broken end fault: the main cause of production interruption

Broken ends are the most common problem of double twisting machines, which can be divided into "occasional broken ends" and "batch broken ends". It is necessary to analyze the fracture morphology and occurrence location in combination.

1. The fracture surface is loose and filamentous (non violent fracture)

-Possible reasons: Insufficient strength of the single yarn itself (such as short raw material fibers and poor dryness of the fine yarn); Or if the feeding tension is too low, the yarn may relax before twisting, resulting in local stress concentration.

-Troubleshooting steps:

① Check the quality of single yarn: Extract untwisted single yarn and test its strength (normally ≥ 300cN). If the strength is too low, trace the fine yarn process;

② Verify tension setting: Use a handheld tension meter to measure the feeding section tension (the standard value is adjusted according to the yarn count, such as about 8-15cN for 10s-30s yarn). If it is lower than the set value, increase the tensioner spring pressure or replace the worn porcelain hole;

③ Check the yarn guide path: Confirm that the yarn guide hook and tensioner ceramic groove are free of burrs (sharp edges can be lightly sanded off with sandpaper) to avoid scratching and damaging the yarn.

2. The fracture surface is neat (like a knife cut) and concentrated near the spindle

-Possible reasons: Abnormal state of the spindle (such as bearing wear, spindle tip hooking) or additional friction on the yarn during the twisting process.

-Troubleshooting steps:

① Shutdown inspection of spindle: manually rotate the spindle and feel whether the resistance is uniform (normally there should be no jamming); Observe whether there are dents or scratches on the tip of the ingot (which can be cleaned with alcohol swabs); If the spindle shakes significantly, the bearing or spindle body needs to be replaced;

② Check the inner wall of the spindle can: If there are scratches or rust, it will cause the yarn to scratch and break during operation, and the spindle can needs to be polished or replaced;

③ Check the spindle speed: Measure the actual spindle speed with a tachometer (recommended spindle speed for T/C40s yarn is 8000-10000rpm). If it is lower than the set value (possibly due to loose dragon belt or motor aging), adjust the dragon belt tensioner or replace the motor.

3. Batch cutting of heads concentrated in a certain section of spindle or area

-Possible reasons: Uneven transmission of the dragon belt (local slippage) or abnormal electrical control (such as unstable output of a frequency converter).

-Troubleshooting steps:

① Observing the operation of the dragon belt: The normal dragon belt should be tightly attached to the spindle without any jumping or deviation; If local wear is found on the dragon belt (such as thinning at the edge of the spindle), the dragon belt needs to be replaced and the tension wheel adjusted;

② Detecting the output of the frequency converter: Use a multimeter to measure the voltage of the corresponding spindle motor (normal fluctuation should be ± 5%). If the voltage fluctuation exceeds 10%, it may be due to damage to the frequency converter module and requires repair or replacement;

③ Check the carbon brush of the spindle motor: If the carbon brush wears down to one-third of its length, it will cause poor contact and needs to be replaced with a carbon brush of the same model.

（2） Uneven Twist: A Key Defect Affecting the Quality of Strands

Uneven twist is manifested as a large difference in twist between the inner and outer layers of the tube (commonly known as "twist difference") or local areas of the same tube with excessively high/low twist, mainly due to the transmission of twisting power and the stability of yarn tension.

1. The overall twist is lower than the set value

-Possible reasons: Insufficient spindle speed or yarn obstruction in the twisting zone (such as excessive tension limiting spindle load).

-Solution:

① Calibration of spindle speed: Check the deviation between the set spindle speed and the actual speed (measured with a laser velocimeter) through the human-machine interface (HMI). If the deviation is greater than 5%, the frequency converter parameters need to be recalibrated;

② Reduce feeding tension: Properly reduce the pressure of the tensioner (adjust 1-2 grids each time, observe the change in twist), to avoid excessive stretching of the yarn in the spindle can;

③ Check the contact between the dragon belt and the spindle: If the dragon belt slips due to oil, use a clean cloth dipped in alcohol to wipe the surface of the dragon belt, and ensure that the tension wheel pressure is sufficient (generally, a dragon belt sag of 2-3mm is normal).

2. There is a large difference in twist between the inner and outer layers of the tube (loose outer layer, tight inner layer)

-Possible reason: Improper setting of winding forming parameters resulted in changes in the stacking angle of the yarn on the tube, affecting the release of twist during unwinding.

-Solution:

① Adjusting the groove drum speed ratio: Double twisting machines usually control the forming through the "winding ratio" (groove drum speed/spindle speed), which is generally set to 0.95-0.98 (refer to the machine manual for details). If the ratio is too small, the outer yarn winding will become loose and the ratio needs to be increased;

② Check the lateral device: If the reciprocating motion of the lateral yarn guide rod is not smooth (such as wear on the guide rail), it will cause uneven arrangement of the yarn, and the guide rail needs to be lubricated or worn parts need to be replaced;

③ Correct the pressure of the cylinder bracket: If the bracket pressure is too high, it will cause deformation of the cylinder, and if the pressure is too low, the winding will become loose. It is advisable to adjust it until the cylinder is lightly pressed by hand and there is no obvious depression.

（3） Abnormal tension: a cause of breakage and poor forming

Tension fluctuations can cause yarn shaking, tube grooving, or edge collapse, and it is important to focus on the stability of dynamic tension.

1. Fluctuations in tension (periodic fluctuations)

-Possible reasons: Wear of tensioner components (such as non-circular ceramic holes) or poor yarn passage path (such as offset of yarn guide hooks).

-Troubleshooting method:

① Replace the tensioner ceramic hole: Observe the surface of the ceramic hole with a magnifying glass. If there are cracks or grooves, replace them immediately (it is recommended to check every 3 months);

② Adjust the yarn guide position: Ensure that the yarn enters the tensioner ceramic hole vertically (deviation ≤ 1mm) to avoid sudden tension changes caused by diagonal pulling;

③ Check yarn quality: If a single yarn has coarse knots (+50% or more) or details (-30% or less), it will get stuck when passing through the tensioner, and feedback should be given to the previous process to remove defects.

2. The overall tension is too high

-Possible reasons: Fatigue of the tensioner spring (decreased elasticity) or excessive winding resistance (such as winding yarn in a groove tube).

-Solution:

① Replace tension spring: Compare the free length of the new spring with the old spring (such as the original length of 50mm, the elastic force should be 20cN when compressed to 30mm). If the elastic force decreases by more than 20% after compression, it needs to be replaced;

② Cleaning the groove: After stopping the machine, use tweezers to remove the waste yarn (especially at both ends) in the groove of the groove to avoid the yarn being forcibly pulled;

③ Check the weight of the tube: If the tube is overweight (exceeding the maximum design weight by 5%), it will increase the winding resistance and shorten the tube replacement cycle.

（4） Mechanical noise and vibration: signals of equipment loss

Abnormal sounds (such as metal impact sounds, sharp friction sounds) or increased body vibration are usually signs of mechanical component wear or loose installation.

1. The spindle produces a buzzing sound accompanied by vibration

-Possible reasons: lack of oil or wear of spindle bearings, or imbalance of spindle discs.

-Processing steps:

① After stopping the machine, remove the spindle cover and inject high-speed lubricating oil (such as 7014-1 grease) into the bearing. If there is still abnormal noise, the bearing needs to be replaced (it is recommended to maintain it every 6 months);

② Check the spindle: Use a dial gauge to measure the radial runout of the spindle (normal ≤ 0.05mm). If it exceeds the standard, correct the position of the spindle or replace it;

③ Tighten the screws of the spindle base: Use a torque wrench to tighten according to the instructions (usually 20-25N · m) to avoid resonance caused by looseness.

2. The dragon belt squeaks and screams during operation

-Possible reasons: There may be foreign objects (such as flying flowers, oil stains) on the contact surface between the dragon belt and the spindle, or the dragon belt may have aged and hardened.

-Solution:

① Clean the dragon belt and spindle: Use a soft bristled brush to remove surface flying flowers, and then wipe with alcohol to remove oil stains;

② Adjust the tension wheel of the dragon belt: If the dragon belt is loose, rotate the tension wheel handwheel clockwise (1/4 turn each time) until the sag of the dragon belt meets the standard;

③ Replace the dragon belt: If the dragon belt cracks (crack depth>1mm) or delaminates, it is necessary to replace it with a dragon belt of the same specification (note that the length of the dragon belt should match the number of ingots).

（5） Electrical Failure: The "Central Nervous System" Issue in the Control System

Electrical faults often manifest as equipment failure to start, uncontrolled spindle speed, sensor false alarms, etc., which need to be gradually investigated in conjunction with circuit diagrams.

1. A certain section of the spindle cannot be started

-Possible reasons: The fuse of the spindle motor is blown, the circuit contact is poor, or the motor is burnt out.

-Troubleshooting process:

① Measure the voltage at both ends of the fuse with a multimeter (normally 220V). If there is no voltage, replace the fuse with the same specification (pay attention to distinguishing between fast melting and slow melting types);

② Check the motor wiring: remove the motor end cover and observe whether the terminal posts are loose (tighten with a screwdriver), whether the insulation layer is damaged (measure the insulation resistance with a megohmmeter, which should be>2M Ω);

③ Test motor winding: Use a multimeter to measure the resistance of the three-phase winding (balance error ≤ 5%). If the resistance of a certain phase is infinite, it indicates that the motor has burned out and needs to be replaced.

2. The touch screen displays "broken yarn" but it is actually not broken

-Possible reasons: The sensitivity of the yarn breakage sensor is too high or it is obstructed by flying flowers.

-Solution:

① Clean the sensor: Use compressed air to blow away the flying flowers on the sensor window (at a distance of 10cm to avoid high pressure damage);

② Adjust sensitivity: Enter the HMI parameter interface and lower the "yarn breakage detection threshold" from the default 5cN to 3cN (depending on the actual yarn tension);

③ Check the installation position of the sensor: Ensure that the sensor is aligned with the yarn running path (deviation ≤ 2mm) to avoid misjudgment caused by positional deviation.

3、 Daily maintenance and preventive measures

The key to troubleshooting is to prevent problems before they occur. It is recommended to develop the following maintenance plan:

-Daily inspection: Check the operation of the conveyor belt, spindle vibration, yarn tension, and clean the surface of the equipment for flying flowers;

-Weekly maintenance: Add lubricating oil to the spindle bearings and check the wear of the tensioner ceramic holes;

-Monthly calibration: calibrate the spindle speed and tension parameters with a tachometer and tension meter, record and archive the data;

-Quarterly overhaul: Disassemble key components such as spindles and troughs, clean and inspect for wear, and replace if necessary.