Extrusion Failure
Extrusion failures occurring when the molten polymer stream snaps at the exit of a spinning die result in significant production downtime and yarn inconsistencies. A spinneret capillary break happens when the tension or the viscosity of the liquid polymer is not properly balanced, causing the filament to pull apart as it is being drawn. This event disrupts the entire bundle of fibers and often requires the machine to be stopped so the spinneret can be cleaned and rethreaded.
In a high speed spinning mill, even a single break can cause the loss of hundreds of meters of yarn and reduce the overall efficiency of the plant. Monitoring the stability of the extrusion process is a primary task for the technical staff on the floor.
Breakage Mechanism
Physical separation of the polymer melt is often caused by the presence of impurities, air bubbles, or sudden fluctuations in the temperature of the spinning head. When a spinneret capillary break occurs, the molten stream loses its continuity and forms a globule at the face of the die. This is frequently triggered by a microscopic particle of degraded polymer or a metal fragment that partially blocks the small hole.
The high pressure required to force the melt through the capillary makes the stream very sensitive to any disturbance. Once the break happens, the surrounding filaments can become entangled with the broken end, leading to a massive knot that can damage the drawing rollers. Preventing these breaks requires the use of high quality melt filters and a very stable power supply for the heaters.
Operational Consequence
Recurring issues with filament stability can indicate a deeper problem with the quality of the raw material or the maintenance of the spinning equipment. A spinneret capillary break not only stops production but also creates a defect in the final yarn known as a slub or a thick spot. These defects are often not detected until the yarn is woven into fabric, where they appear as visible bumps or weak points.
Finishing plants may reject entire rolls of cloth if the frequency of these defects is too high. Mills use automated sensors to detect a break the moment it happens, allowing for a quick intervention to minimize the waste. Analyzing the cause of each break helps the engineering team adjust the processing parameters and improve the reliability of the line.
Prevention Strategy
Maintaining a clean and controlled environment for the extrusion process is the only way to minimize the occurrence of these costly interruptions. Spinneret capillary break frequency is used as a key performance indicator for the quality of both the polymer resin and the spinning operation. Regular cleaning of the spinnerets using ultrasonic baths or vacuum calcination furnaces ensures that the capillaries remain smooth and free from carbon buildup.
The polymer melt must also be degassed to remove any volatile components that could form bubbles in the stream. Upgrading to more advanced spinning heads with improved flow dynamics can also help stabilize the filaments at higher speeds. Final yarn quality depends on the ability to maintain a continuous and uniform extrusion for thousands of hours without a single failure.
