Imperfection Index of Yarns (IPI) | Reasons for Increasing Imperfection Index of Yarn

Last Updated on 31/01/2021

Imperfection Index of Yarns (IPI) | Reasons for Increasing Imperfection Index of Yarn

Engr. Monirul Islam Shaikat
Dept. of Textile Engineering
Ahsanullah University of Science & Technology (AUST), Bangladesh


Imperfection Index of Yarns:
IPI stands for Imperfection Index of Yarns. Imperfections is the description for thin, thick places and neps in 1000m of yarn. Evenness Tester is required to calculate the IPI of yarns with the results of different yarn evenness parameters. It is a common fault of yarn. Imperfections have a decisive influence on the utility and market value of a yarn. Higher fiber openness results in less imperfection in yarn due to the fact that higher fiber openness results in better fiber individualization in card sliver, which in turn produces quality yarn. The carding process has a major impact on yarn imperfection.

Imperfection Index of Yarns
Fig: Imperfection Index of Yarns

For ring spun yarn imperfections in the yarn refer to the total number of thin places (-50%), thick places (+50%) and neps (+200%) present per 1000 metre of yarn.

For rotor spun yarns the number of (+280%) neps per 1000 meters of the tested yarns is considered instead of +200% neps.

*A thin place of -50% mean the cross-section of the yarn at the thick place is only 50% of its mean cross section or less.

**A thick place of +50% means the cross-section of the yarn at the thick place is 150% of its mean cross section or more.

***+200% Neps indicates the cross-section at the nep is 240% of the mean cross-section of the yarn or more.

****+280% Neps indicates the cross-section at the nep is 280% of the mean cross-section of the yarn or more.

Imperfections can both be the cause of ends down in downstream processing and also make a disturbing appearance in the fabric. The less imperfections in the yarn, the better the appearance of the fabric.

Reasons for Increasing Imperfection Index of Yarns:
For following reasons yarn imperfection index may increase.

1. The increase in break draft, the yarn imperfection increases.

2. The yarn imperfection also increases due to the increasing roving twist multiplier for the same yarn count.

3. Fiber rupture is critical that significantly affects yarn quality and processability. Fiber rupture will have a huge impact on imperfections and irregularity in the yarn.

4. The efficient opening at blow room stage not only improves fiber cleaning but also yarn properties such as yarn tenacity and total imperfections.

5. The increase in imperfections at higher openness is due to over beating than that which is necessary.

6. The yarn unevenness and imperfections increase with the increase in card production rate.

7. The increase in the delivery speed of the card will substantially increase unevenness and imperfections of the sliver. Incorrect break draft increases yarn U%, imperfections, and neps.

8. Yarn imperfections and hairiness index increase with thicker lap.

9. Yarn imperfections have increasing trend with an increase in the feed amount.

10. A higher noil% always improves the imperfections in the final yarn.

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