Shrinkage of yarn is a decrease in yarn length due to heating processes. Yarn length before and after the process is measured under certain stress and is expressed as a percentage of the initial yarn length. The results of the measurement of this characteristic can be used to predict the dimensional stability of the fabric after washing and heating processes at high temperatures.
Shrinkage of yarn test – Sirang quality control Lab
Yarn shrinkage can be applied, measured, and reported in a variety of conditions, including boiling water, hot and dry air, saturated steam, or even superheated steam.
In the laboratory of Sirang Company, shrinkage is performed in boiling water and hot and dry air. The equipment required in this test is a wrap reel machine, boiling water bath, high-temperature oven, and a device for measuring the length of yarn samples.
Video of the steps of performing this test in the laboratory of Sirang Co.
Existing standards in this field include ASTM D2259, ISO 18066, ISO 18067, and domestic standards such as ISIRI 20095 and ISIRI 20096.
To prepare yarn samples (skein), an automatic wrap reel machine is used. The boiling water bath has a suitable width and depth and using a holder, the sample is fixed in it.
The high-temperature oven can provide hot air up to 200°C. The sample length measuring device automatically applies certain stress to the yarn samples and determines their length with a resolution of 0.05 mm and shrinkage is calculated based on the lengths measured by the machine software.
In general, yarn shrinkage can manually and automatically be determined in skein or single-end yarn.
For example, to determine the shrinkage of 100% polyester FDY yarn with a linear density of 500 dtex in the form of skein, after preparing the yarn samples using the formula mentioned in the relevant standards and a wrap reel machine (skein with 10 turns), the skein are placed on the holder and the initial length of the samples is measured using the shrinkage tester and stored in the device memory. Then, depending on the test conditions, the samples are placed in a boiling water bath at 100±3 °C for 30±5 minutes or in an oven with dry and hot air at 190±3 °C for 15±1 minutes.
Then, the samples are taken out and after reaching the temperature equilibrium, the secondary length of the yarns is measured using the shrinkage tester.
It is noteworthy that the applied stress for this yarn is set at 0.05 cN/dtex. Yarn shrinkage is calculated by the machine software as a percentage using the primary and secondary lengths.
According to Iranian National Standard No. 925, the maximum shrinkage percentage of FDY yarn is 15%.