V Parthasarathi, R Praveena, S Saranya and S Revathy reveal the results of an investigation of knitted fabric sewability, percentage of rejection and rework involved and loss incurred in the apparel industry due to the sewability problem.
Knit fabrics are having wider use in time since they can be produced more easily for a lower cost, and they are more flexible. However, knit fabrics are less than woven fabrics since they are produced with low twist yarn and have a slack construction, as a result of which they have a low abrasion resistance. The sewing needle penetration force, sewing thread tension, the feed of the sewing material, as well as selection of the sewing thread, sewing needle size and shape of the sewing needle point are very important parameters during the sewing of knitted fabric.
Sewing thread plays an influential role in seam design; it should be stretchable since knitted fabric has elastic properties in the direction of courses and Wales. The size of the needle eyelet and thread thickness should be mutually adjusted in order for the thread to pass through the eyelet with as little friction as possible. The quality of a sewn seam depends on these factors, therefore it is necessary to match the thickness and density of the knitted fabric with the fineness of sewing thread and needle.
The penetration force of a sewing needle is mostly based on the friction occurring between the sewing work pieces and sewing needle. The sewing needle penetration force is one of the most significant technical parameters in the sewing process affected by various factors such as: type, number of layers of the sewing material, and needle size. Better identification of sewability problems, control and proper operator training in sewing and finishing departments are necessary to reduce the probability of rejection.
Factors affecting sewability
Influence of elastane yarn type
Two types of yarns are taken to analyse the sewability of elastane yarn type. In the first case polyester/elastane covered yarn is taken as warp and air covered PET is taken as weft whereas in the second type polyester/elastane covered yarn is taken as warp and twisted elastane yarn is taken as weft.
Plain and twill fabrics were produced for testing from both sets of yarn. Needle penetration force were determined on L&M sewability tester which are 64 CN and 370 CN respectively, the needle damage index was calculated as 18 and 79 per cent[1].
Influence of scouring with enzymes
Raw cotton is hydrophobic in nature. So scouring with NaOH increases hydrophilicity, but decreases strength and DoP. It also damages the loop of knit, which causes the needle penetration force, and dynamic tension of sewing thread. Scouring with enzymes help to overcome the above mentioned problems[2].
Influence of stitch length in weft knitted fabric
The importance of sewing of knitted fabrics are sewing needle penetration force, feed of the sewing material and sewing needle size. If stitch length of 100 per cent cotton single jerky fabric increases, then sewability decreases. Coarser yarn count gives higher needle penetration. Hence coarser yarn and shorter stitch length gives high functional performance characteristics by increasing the sewability[3].
Influence of multifunctional cotton knit pretreatment
Multifunctional cotton knit fabric pretreatment has significant influence on sewability property. Cotton knit fabric wet treatments increase the value of the fabric, but results in shrinkage which in turn leads to fabric mass per unit area increment and increase in needle penetration force. In addition to this, fabric layer increment also<