Influence of Needle Heat during Sewing Process on Tensile Properties of Sewing Thread

In this work, the tensile properties of a sewing thread, i.e. tenacity, breaking elongation and initial modulus of two common industrial sewing polyester-polyester core spun threads, were studied at four sewing stages. Firstly, the needle heat was measured at different speeds from 1000 rpm to 4700 rpm of an industrial lockstitch sewing machine with the inserted thermocouple method. Secondly, the tensile properties of a thread were compared at different predefined sections of the sewing thread in the sewing process. The results show that the needle heat and bobbin thread interaction has a great impact on the sewing thread tensile strength, while the tensile strength is minimal at the point when the machine stops and the thread is in direct contact with the hot needle. Tenacity, breaking elongation and initial modulus decrease substantially with a higher speed of the machine as the needle temperature increases. At 4000 rpm of the sewing speed, the sewing thread loses 50% of its tenacity as the needle temperature reaches nearly 250 degrees C, the impact being higher for higher count (linear densities) threads.