Why does yarn need to be sized? What are the requirements for sizing?

Why does yarn need to be sized? What are the requirements for sizing? During weaving, the warp yarns have to withstand a variety of forces and undergo complex deformations. From the basics of t...

Why does yarn need to be sized? What are the requirements for sizing?

During weaving, the warp yarns have to withstand a variety of forces and undergo complex deformations. From the basics of the loom For movement:

(1) When the opening moves, the warp The generally straight heddle line is bent into a fold line at the heddle eye, and elongation occurs in proportion to the square of the shed height. At the same time, due to the asymmetry in the length of the front and rear parts of the shed, the warp slips in the heddle eye. Friction occurs. 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, the edge warp is squeezed to a great extent. Causes bending, elongation and friction, and the weft guide components of shuttleless looms also have considerable friction on the warp yarns.

(3) During the beat-up movement, the front of the shed The warp yarns 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 weaving beam The upper warp yarn 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 a warp elastic-plastic deformation system together with let-off, beating-up and shedding.

It can be seen that the force and deformation experienced by the warp yarns during the weaving process It is mainly formed by tension (required not to cause breakage), elongation (recovery from cyclic deformation) and friction (required not to cause fluffing, pilling, or wear).

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, causing Unclear openings cause defects such as yarn skipping, skipping, and warp drop that are difficult to eliminate. In weft insertion of air-jet looms, unclear openings cause weft yarn blocking, which is the main factor affecting efficiency. Therefore, reducing hairiness is an important factor. Indicators.

In view of the above situation, in order to improve the weaving performance of warp yarns, An effective method in the weaving preparation process is sizing, which is to apply a slurry with adhesive material as the main body to the warp yarns, which acts on the surface of the warp yarns to a certain depth, and after drying, a sizing structure is formed in which the slurry and the yarn are integrated.

The improvement of warp performance 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 yarn breaking strength. 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 the wear resistance rate. Since the wear resistance test has not yet been standardized, the wear resistance rates of various slurry formulations also vary greatly.

(4) Hairiness reduction rate. Use YGl7lB type yarn hairiness tester and BT-2 type online hairiness test According to the comparison of yarn hairiness before and after sizing, the advanced index of hairiness reduction rate is more than 75%.

(5) The weaving beam has a good axis rate. 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) The number of warp breaks of 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 finishing, 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. The type of sizing, oil and sizing must be Rates and other aspects will be appropriately adjusted.

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