Weft knitted fabrics are separated in one direction due to the particularity of their coil structure and knitting process. Therefore, in the process of wearing, using or washing knitted products, if a yarn breaks or the coil loses the string connection, the coil will be separated from the broken yarn along the longitudinal line under the action of external force. Eventually, the holes will occur and gradually expand, which will seriously affect the strength and appearance of knitted fabrics and reduce their use value.
In weft knitted fabrics, the weft flat needle and double reverse side are easy to separate. They can be separated in the reversible weaving direction or along the weaving direction. Even when a coil is broken, it will be separated continuously along the longitudinal line. Due to the introduction of yarn and decolor, the additional change of yarn structure or composite structure is small. The quality and variety of yarns used are different, such as the friction coefficient, bending stiffness and coil length between yarns, and the detachability of knitted fabrics will also be different.
During the sewing process of knitwear, when the machine needle is running at high speed, it stabs the fabric coil, causing the yarn to break and the stitch hole to expand, resulting in coil separation and holes in the suture. The main causes of sewing needle holes can be summarized from the installation of sewing machine parts, the selection of sewing needles and threads and the characteristics of fabrics:
(1) The shape of the needle tip is improperly selected, or the needle tip becomes blunt for a long time, or the needle tip is too sharp to stab and scratch the fabric yarn; Improper or over sized needle; The needle bar diameter is too small to match with the needle plate hole diameter, or there are burrs on the edge of the needle plate hole, crushing or scraping the fabric yarn.
(2) Improper installation and commissioning of machine parts, such as dense needle code; If the sewing needle is installed too low, the cone part of the needle handle enters the sewing material and breaks; The needle bar is loose or the needle is not aligned with the needle plate hole, breaking the cloth yarn; If the presser foot pressure is too high, the coil yarn cannot be transferred; The cloth feeding teeth are too sharp and bite the cloth yarn
(3) The suture is too thick or the twist of the suture is too large, too thick and hard, and the suture is not smooth enough
(4) Knitted fabrics feel bad and hard; The fabric structure is relatively compact; The moisture regain of fabric grey cloth and the temperature and humidity of sewing workshop are too high or too low; The temperature of sewing chemical fiber products is too high.
