During weaving, the warp yarns must withstand a variety of forces and undergo complex deformations. From the perspective of the basic movement of the loom:
(1) During the shedding movement, the warp yarn is bent from a generally straight heddle line into a fold line at the heddle eye, and the warp yarn is The elongation is proportional to the square of the mouth height. At the same time, due to the asymmetry in length between the front and rear parts of the shed, the warp slips in the heddle eye, causing friction. When the upper and lower warp yarns alternately rise and fall during the shedding movement, severe friction occurs between them.
(2) During the weft insertion movement, the shuttle of the shuttle loom relies on the shed and rubs through it, especially when entering and exiting the shed, it has a great impact on the edge warp yarns. A large degree of squeezing causes bending, elongation and friction. The weft guide components of the shuttleless loom also have considerable friction on the warp yarns.
(3) During the beat-up movement, the warp yarns in the front of the shed are rubbed by the reciprocating reed teeth. Due to the shrinkage of the weaving, the squeezing and friction between the reed teeth and the edge warp yarns is more severe. In the beat-up area of the cloth fell, the forward and backward movement caused by each beat-up will increase the friction between the warp yarn and the heald eye.
(4) During the let-off and take-up movements, the warp yarn on the weaving beam always has a certain braking tension when it is sent out. Most of the existing warp let-off mechanisms are tension-adjusted let-off mechanisms, which use sensor feedback of warp tension to control the amount of warp let-off. Therefore, warp yarns with weak joints begin to break when they pass through the back beam. The winding movement will also affect the warp tension, forming an elastic-plastic deformation system of the warp together with the let-off, beating-up and shedding.
It can be seen that the force and deformation endured by the warp yarn during the weaving process are mainly caused by tension (required not to cause breakage), elongation (recovery of cyclic deformation) and friction (required not to cause fluffing) , pilling, wear and tear) are formed.
At the same time, it is worth paying attention to the problem of hairiness. In the warp opening, the protruding hairiness will be entangled with each other, making the opening unclear. , causing defects such as yarn skipping, flower skipping, and warp hanging that are difficult to eliminate. In the weft insertion of air-jet looms, unclear openings cause weft yarn obstruction, which is the main factor affecting efficiency. Therefore hairiness reduction is an important indicator.
In view of the above situation, in order to improve the weaving performance of warp yarns, an effective method adopted in the weaving preparation process is sizing. That is, a slurry with adhesive material as the main body is applied to the warp yarns, which acts on the surface of the warp yarns to a certain depth. After drying, a sizing structure is formed in which the slurry and the yarn are integrated.
The improvement of warp properties after sizing should be enhancement, stretch retention, wear resistance, and adhering to hairiness. The filament is sizing to make the individual filaments stick to each other and have bundling properties, which prevents the filament from fluffing or breaking, and suppresses the elasticity of the filament, making it easier to operate. Short fiber warp elastic yarn and strong twisted yarn also need to be sized to inhibit shrinkage in order to be produced smoothly. The ultimate purpose of sizing is: good sizing shaft, few weaving defects, low number of broken ends, high weaving efficiency, and improved warp weavability. The specific requirements are:
(1) Increase the breaking strength of the yarn. It is necessary to increase the strength appropriately, but if you pursue the increase in sizing strength too much, it will inevitably make the yarn hard and brittle, lose elasticity, and easily break. The reinforcement rate of pure cotton yarn is generally controlled at 25% ~ 40%, polyester / cotton yarn 10% ~ 25%, pure polyester yarn 10% ~ 20%, polyester / viscose and pure viscose yarn > 25%.
(2) Maintain the yarn elongation at break. The elongation rate of cotton yarn raw yarn is generally 7%. After sizing, it should be maintained at 4%-5% to facilitate weaving, so the elongation reduction rate is ≤30%, polyester/cotton, polyester/viscose yarn ≤25%, pure viscose yarn ≤ 35%.
(3) Improve wear resistance. Since wear resistance testing has not yet been standardized, the wear resistance rates of various slurry formulations also vary greatly.
(4) Hairiness reduction rate. Using the YGl7lB yarn hairiness tester and the BT-2 online hairiness tester to compare the yarn hairiness before and after sizing, the advanced index of hairiness reduction rate is more than 75%.
(5) The rate of weaving beams is good. It is required that the sizing yarn has no broken ends, multiple ends, sticking, twisting, light sizing and pilling, and the weaving does not have defects such as edge pulling, and the good axis rate at the advanced level is above 60%.
(6) Number of warp breaks on the loom. The number of broken warps for shuttle looms should be less than 1 thread/(unit·h), and for shuttleless looms, the number of broken warps for 100,000 picks should be less than 10-15 threads.
As a gray fabric for printing and dyeing, in addition to the requirements of weavability, it also requires easy desizing, and the desizing waste liquid does not pollute the environment. It must be considered in the selection and proportion of slurry.
As a finished fabric, it is required to give the fabric a unique style and feel, and it must be appropriately adjusted in terms of the type of sizing, oil agent and sizing rate. </p
