The appearance and shape characteristics of yarn
The influence on fabric
The appearance performance of yarn mainly refers to the fineness of yarn, that is, the relative thickness of yarn.The thickness of yarn directly determines the specifications, varieties, styles, uses and physical and mechanical properties of fabrics.The thickness of yarn can be expressed by relative thickness or geometric thickness.Because the yarn cross-section is irregular and easy to deform;spun fiber yarn has more hairiness, and the deformed yarn is puffed, making the yarn boundary unclear;plus the tedious and inconvenient geometric shape test, it is usually described by relative thickness, referred to as "fineness".
There are many ways to express the fineness of yarn, such as size, metric number, English number, denier, etc.The twist of yarn is expressed by the number of twists per meter or per inch.The direction of twist is divided into S twist and Z twist.Within a certain twist range, the strength of yarn increases with the increase of twist.The twist of single yarn and the twist of stock line are selected according to the purpose of stock line.Usually, single yarn and stock line are opposite twist, namely ZS or SZ. There is an optimal ratio of single yarn and rib twist. Within this range, rib strength increases with rib twist, but decreases when it exceeds the critical value.
Fiber properties and spinning methods play a decisive role in yarn performance.In the twisting process of ring spinning yarn, due to the transfer of fibers, from the inner layer to the outer layer of yarn, and then from the outer layer to the inner layer, the fibers are spiral around the axis of the yarn, and the spiral radius increases or decreases alternately along the axial direction.At this time, the long fiber tends to the axis of the yarn, and the short fiber tends to the outer layer of the yarn.The fine fiber tends to the axis of the yarn, and the coarse fiber tends to the outer layer of the yarn.The fibers with smaller initial modulus are mostly located in the outer layer, and the fibers with large initial modulus are mostly located in the inner layer.Reasonable selection of fibers with different properties can be spun into different styles of yarns to adapt to different fabric uses or improve wear performance. The effect of yarn hairiness on yarn performance Yarn hairiness refers to the fibers stretching out from the surface of the yarn body. Mainly due to the failure to control the fiber movement well during spinning, the fibers stretching out from the surface of the yarn body are shaped in arc or other shapes to expose the surface of the yarn body.The yarn hairiness affects the appearance of the fabric and the production and processing of the fabric. Hairiness is an important attribute of yarn, which plays a major role in evaluating yarn quality, especially in export trade.Hairiness not only affects the appearance of fabric, but also affects other properties of fabric.Whether it is for woven fabrics, knitted fabrics and printing and dyeing products, the cross section of the fabric is a defect.This defect occurs in the weft direction, and shows great differences due to the difference of the weft hairiness index.Yarn hairiness not only affects the performance of fabric, such as fabric permeability, pilling, water absorption, etc., but also affects some sensory parameters of fabric, such as surface roughness, hand feel and friction performance. Hairiness will have the following effects:
(1) the utilization coefficient of fiber strength is low, which affects the strength of yarn.
(2) warping, sizing and winding are not clear, weaving weft insertion resistance is large, and the opening of the loom is not clear;affects the surface finish and clarity of fabric, the hand feel is not smooth, the fabric wear resistance is poor, easy to pilling;leads to uneven dyeing;for high-grade fabric yarn, it is necessary to burn hair first, which will increase the loss rate. Three, the influence of yarn twisting characteristics on fabric .Twisting is a necessary means for staple fiber side growth yarn.The twisting of yarn is to make the two cross sections of the yarn rotate relatively, and then the fibers in the yarn that were originally parallel to the yarn axis are inclined into spirals. The twist and twist of yarn and the twist and twist of yarn in the fabric have a greater impact on the physical properties and wearing properties of the product.
3.1 physical and mechanical properties Through twisting, the binding force between fibers increases, the breaking strength and elongation at break increase, and the crease resistance and wear resistance increase. However, the twist can not exceed a certain value, otherwise the textile fabric is stiff, the fold is easy to break, and the strength decreases, and the dye is difficult to penetrate, and the dye is easy to fade or "whiten".The requirements for twist of yarns for different purposes are also different.Generally, on the premise of meeting the requirements of strength, the smaller the twist of yarn is, the better, because the increase of twist will make the yarn feel harder, the elasticity decreases, and the shrinkage increases.For example, filament yarn should not be twisted or twisted as little as possible; the twist of woven and knitted puff fabric yarn should be smaller, so as to facilitate the puffing; the twist of warp yarn should be properly increased to adapt to the requirements of weaving process with large tension and more friction; the twist of flax yarn fabric should be large to have a stiff and smooth feeling. In addition, the arrangement of warp and weft yarns in the fabric organization: the same twist and different twist will also have a greater difference. This is because when the warp and weft yarns are arranged with the same twist, the twist direction on the contact surface of the warp and weft yarns is the same, so that the yarns of the two systems can be embedded into each other, resulting in increased holding force.The embedding also makes the fabric with the same twist arrangement appear thinner than the fabric with different twist arrangement. Therefore, the puffy, thick and soft fabric should be chosen with different twist arrangement.At the same time, because the fabric with the same twist arrangement looks like the twist direction is just 90 degrees vertical from the front, so the yarn reflects light inconsistently, resulting in a gloss that is not as good as that of the different twist fabric.Some fabrics with hidden strips and hidden lattice effect on the surface are woven by using the gloss inconsistent with the different twist.Twisting direction is also related to the twill direction of twill fabric. For example, the left twill is often used when the warp is Z twist, and vice versa.
3.2 Wearing performance Twist has an effect on the volume weight and diameter of the yarn. Twisting reduces the diameter of the yarn, increases the density, and increases the unit weight of the same yarn gap.After twisting, the gap between the fibers becomes smaller, and the air in the gap is squeezed out.The size of the insulation of the fiber mainly depends on the size of the air content. The larger the air content is, the better the insulation is. Therefore, when the static air between the fibers becomes smaller, the insulation of the fabric will become worse. The gap between fibers is also related to the moisture absorption and permeability of the fabric. The fabric with large gap has good permeability and fast moisture absorption and permeability. Twisting can improve the resistance of yarn to pilling and pilling.The greater the twist, the greater the friction and cohesion between fibers. The fiber ends are difficult to slide to the surface of the fabric, which is difficult to entangle.In addition, the greater the twist, the tighter the yarn, the better the hooking resistance. Twisting can also make the flexural stiffness of the yarn larger, the softness of the fabric decreased, and the drape feel worse.Because the more fiber ends are exposed on the surface of the yarn, the better the softness of the fiber is.For towels, underwear and cotton socks, the twist should be smaller to make the finished product feel soft and comfortable. The twist of the yarn is related to the surface texture of the fabric.The so-called gloss is actually determined by how much light the naked eye can see from the object.Take cotton yarn as an example. When combed cotton yarn is without twist, the light is reflected on the surface of each fiber. The surface of the yarn appears dark and dull. When the twist of combed cotton yarn reaches a certain value, the light is reflected from the smooth surface, and the reflection reaches a maximum value. However, when the twist continues to increase, the light is diffusely reflected and absorbed between the convex and concave surfaces of the yarn, so the reflected light weakens with the increase of twist, so the fabric woven with high twist yarn has a soft reflective surface and a hard feel. Four, the impact of yarn defects on fabric With the development of society and the progress of textile science and technology, people's requirements for the use of fabric performance and grade are becoming higher and higher. While requiring durable and comfortable textiles, the requirements for clean and defect-free appearance are also higher and higher.This is an urgent need to produce high-quality yarn to meet the needs of the market and consumers. How to improve the quality of yarn to meet the needs of fabric?
4.1 The impact of major yarn defects on fabric For pure cotton combed high-count yarn, from the degree of harm and the frequency of occurrence, the harmful defects affecting the fabric surface are mainly coarse knots, details, uneven drying, flying flowers, cotton knots and abnormal defects.The following first introduces the impact of these defects on the post-processing process.
4.1.1 Coarse knots and details Coarse knots, the fabric surface is a prominent knot, affecting the appearance of the fabric, and even causing the degradation of the fabric.The cloth factory can improve the appearance by manual picking and repairing, but the operation is difficult and time-consuming. Details, because than normal yarn fine, will form a yarn strong weak ring, causing preparation and weaving process of breaking, affect the efficiency of preparation and weaving, even if there is no breakage, will also form on the cloth surface is thinner than the normal yarn details defects, and can not repair, when the number will cause the cloth surface degradation.
4.1.2 Uneven drying affects the appearance of the fabric, causing the cloth surface degradation, especially serious in the fabric cloth surface performance for a shadow or wood grain, lighter in the case of cloth surface appearance turbidity, not smooth like clouds, uneven drying will also cause uneven dyeing.
4.1.3 Cotton knot cloth surface performance as cotton dots or white stars, stars and dots distributed on the cloth surface, such as color spots affect the girl's face beautiful affect the appearance of the fabric.The cloth factory can be through manual repair to reduce cotton dots, but the number of excessive repair can not achieve good results, and time-consuming.When this kind of defects are more or larger in the preparation and weaving of yarn breaking rate will increase, affect the preparation and weaving efficiency, affect the appearance and smoothness of the fabric, causing the cloth surface degradation.
4.1.4 Flying flower cloth surface performance between coarse section and big cotton knot, shorter than coarse section, fiber loose, affect the cloth surface cleanliness.Through manual repair can be improved.
4.1.5 Abnormal defects Mostly long fragments, low frequency, such as double yarn in single yarn, three and four yarns in stock yarn, as well as long rough section and long details.Such defects seriously affect the appearance of fabric, resulting in fabric degradation. Garment factories generally need to do avoid cutting treatment, which will reduce the utilization rate of cloth.In more serious cases, it will even delay the delivery of orders and compensate for the loss of customers.It can be seen that yarn defects have a greater impact on the post-processing, especially the fabric's fabric effect.From the perspective of the product types of cloth factories, different cloth types have different requirements for the quality of yarns, such as:Net color cloth (plain fabric with the same color or different colors of the warp and weft yarns): according to the size of the color contrast of the warp and weft, the cotton knot requirements of the yarn are different. The greater the color contrast of the warp and weft, the higher the requirements for the cotton knot, especially the special post-processing cloth types have higher requirements for the rough section and cotton knot.Meter strip cloth (fabric with different colors of the warp and weft or adjacent yarns in both directions): the greater the color contrast of the yarn, the higher the requirements for the rough section, cotton knot and dry evenness.White cloth varieties (white or extra white cloth in both warp and weft): the requirements for the rough section and cotton knot are relatively low.Striped cloth: wide strips are higher than narrow strips (at the same color contrast) for the cotton knot. Mosaic (ordinary plain weave fabric embedded with a single or several yarns with large color contrast): usually mosaic yarns have higher requirements on yarn roughness, cotton knot and uneven dryness.
4.2 Cause analysis and improvement measures of major yarn defects Different cloth has different requirements on yarn quality. An effective quality data sharing and exchange mechanism can be established between yarn factories and cloth factories, so that cloth factories can use different cloth according to the specific quality of each batch of yarn.At the same time, cloth factories can also put forward grade requirements for yarn according to the requirements of different cloth, so as to reasonably control the quality cost according to the quality status of raw materials and spare parts.Of course, in order to effectively meet customer requirements and control the quality cost, yarn factories must find out the causes of these defects in the spinning production process, and take effective measures to control and reduce defects, so as to improve the quality of yarn.