Lock-stitch embroidery has been the centre of much interest as a versatile and precise method of producing conductive tracks in the fabrication of wearable electronic devices. However, improper fabrication parameter settings could result in the nonconformity of the conductive tracks and damage the conductive coating of the conductive yarns. In this study, we evaluate the appearance quality, dimensional stability and electrical resistance of conductive tracks by taking into account the embroidering speed (ES), stitch length (SL), needle thread pre-tension (NTP) and embroidering direction (ED). The conductive tracks are embroidered onto knitted fabric in different directions with silver-coated polyamide yarn as the needle thread. The results show that stitching the conductive tracks in the wale direction results in a more uniform stitch lines in comparison to the other directions. To resolve the problem of floated stitches, it is recommended that an SL of 4 mm and a higher NTP are used. The percentage of shrinkage in the wale direction is lower than in the course direction. The electrical resistance of the conductive tracks increases with a higher ES and shorter SL. It is also found that a thicker yarn is more sensitive to the NTP and some of the silver coating is rubbed off with an NTP of 50 gf. We also carry out an overlay plot analysis, through which we predict and validate the optimal embroidery parameters that balance appearance quality and electrical resistance. The technique parameters in this study can be used to embroider conductive tracks for smart clothing.
Yarn tension is an important parameter which affects fabric properties and quality. An on-line tension measurement system was developed in which a Denkendorf yarn tension tester (DEFAT) was used to record and evaluate yarn tensions on an air-jet weaving machine. In dynamic warp and filling yarn tension measurements, the measuring head was put in continuous contact with the yarn during weaving. In warp tension measurement, the measuring head was placed in the warp sheet slightly ahead of the back rest roller on the weaving machine. One yarn from the center heddle was fed into the head to produce a trace. In filling tension measurement, the measuring head was placed closest to the pick insertion point at the machine as filling yarn was inserted from a package. Different cotton yarns were used as filling yarn.
In the second part of the study, 3/1 left-hand twill denim fabrics were woven with different filling yarns. The yarn characteristics are correlated to filling tension. Experimental results have shown that yarn count, twist multiplier, hairiness, friction coefficient and other yarn properties have effects on filling tension and filling tension affects the fabric properties. Fabric properties — fabric weight, thickness, air permeability, dimensional stability, abrasion resistance, drapeability, stiffness, wrinkle recovery, tear strength and tensile strength — were tested. It was found that tension had significant effects on some fabric properties. The relationships between fabric properties and filling tension were established.
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