Siamak Shirzadeh Ajirloo - Department of Textile Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Saeed Shaikhzadeh Najar - Department of Textile Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.
Mehdi Varsei - Department of Textile Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Abosaeed Rashidi - Department of Textile Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.

The aim of this study is to provide a method toevaluate the intermingled nip stability. For this purpose,polypropylene (fully drawn yarn) FDY with three types ofintermingling Heberlein jet inserts (P۴۱۲, P۲۱۲, and S۱۶) andthree air pressure values of ۲, ۳, and ۴ bar was subjected tothe texturing process. In measuring the nip stability in theprevious methods, i.e. using the nip number, it was observedthat in some long nips with special structures, a nip withcertain length under the stretching process may becomeseveral nips with a less total entanglement length. This cancause an error in evaluating the nip stability. Therefore, inorder to evaluate the nip stability, it is suggested to use the niplength in the ۳۶۰° study around the yarn axis to evaluate theeffect of the change in the length of the intermingled areas dueto stretching. Using the method presented in this research andafter performing experiments, the maximum and minimumnip stability with considering the nip length were ۹۷.۳% (forP۴۱۲ jet insert and ۴ bar air pressure) and ۴۸.۵۵% (for S۱۶ jetinsert and ۲ bar air pressure), respectively. However, the nipstability in the same test conditions based on nip density was۷۴.۴۷ and ۵۲.۹۴%, respectively.

nip length, Nip Stability, false twist textured yarn, Nip Structure, intermingling