Shrinkage

Factors influencing sewing thread shrinkage:

• The sewing thread itself:
  • Raw material
  • Construction

  • Manufacturing process (stretching/drawing, heat setting, dyeing)

     

• Thermal or hydrothermal exposure
  • Treatment temperature
  • Exposure time
  • Type of medium (water, steam, hot air, etc.)
  • Stress state

AMANN conducts shrinkage testing in accordance with DIN 53 866. Length measurements are taken before and after treatment in the respective medium using simple suspension and measuring devices. The test is carried out using the so-called strand measurement method and with a preload force that depends on the linear density. 

AMANN tests both thermal and boiling shrinkage using the following parameters:

• Thermal shrinkage:  180°C, 15 min., in a thermal cabinet
• Boil shrinkage:  95°C, 30 min., in boiling water

The thermal shrinkage parameters simulate a finishing treatment, while boiling shrinkage simulates the stress of the washing process. These results help to coordinate the respective thermal and mechanical parameters for sewing thread production. This enables AMANN to ensure compliance with the lowest shrinkage values.

A distinction is made between disruptive defects, i.e. those that hinder the sewing process, and non-disruptive defects. Thread consistencyis particularly important for the qualitative assessment of spun threads and core spun threads, as these, due to their construction, exhibit sporadic irregularities and thick spots even under optimal manufacturing conditions.

For optimum thread consistency, a smooth production process from the spinning mill to the finished thread is essential. AMANN examines both the consistency of the yarns used and the threads themselves. This quality feature is tested and monitored in the laboratory and during production.

An Elcometer is used for laboratory testing, which mechanically scans the sewing threads with a probe and detects defects (diameter deviations of a specified size). Defects are cut out and displayed on defect cards.
The faults are divided into fault classes. These are linked to the various causes that lead to the formation of thick and thin spots. They can be caused in the spinning or twisting process, by nubs, impurities, fibre deposits, loops, knots or poor splice points.

Thread consistency is checked during production using optical sensors on the winding machines. Unlike in laboratory testing, defects are not cut out but simply recorded as part of quality control. This allows goods with an excessive number of defects to be identified and separated.