1、Ch.15 Yarn Properties,Words list,Key words全部 New words 1，3-7，9，16-19，21，24，26，28。,In traditional textile manufacturing, it has been common to first make yarn from fibers, then produce a fabric from the yarn. Fabrics produced directly from fibers (skipping the yarn step) represent a growing textile m
2、arket segment, but traditional woven and knitted fabrics produced by intertwining（捻合，缠结） yarns still dominate the market. In addition to knitting yarns and weaving yarns, sewing threads, twine（绳，股线） for wrapping（包装） packages, and the rope（缆绳） used to tie a sailboat to the dock are made by combining
3、fibers.,Basic Terminology,ASTM D 123 defines yarn as a continuous strand（绳、线的）股；缕；单纱，须条，绞合 of textile fibers, filaments, or material in a form suitable for knitting, weaving, or other-wise intertwining(捻合，缠结) to form a textile fabric. Yarn structures used for purposes other than fabric production ma
4、y be referred to as cords（细绳，粗线), ropes（绳索） and thread（线）. Thread is a specific term for yarn used to join fabrics by the process sewing。,When short-staple fibers are twisted together by the process of spinning, the product may be referred to as a staple （短纤维） or spun yarn （短纤维）. Other binding mecha
5、nisms, such as wrapping short fibers with a continuous filament or using an adhesive to bind fibers together, are also used: their products also referred to as spun yarns.,A single spun strand, produced by one of the processes above, is referred to as a singles yarn（单纱，单丝). When two or more single s
6、trands are combined, the yarn becomes a ply yarn（股线） , with each single strand referred to as a ply.,It is possible to combine filaments and spun strands to form more complex yarns. Many types of strands may be combined to form novelty（新奇的、新颖的） yarns for design interest in a fabric, or several simpl
7、e strands may be combined to provide strength. A classification system for yarns is shown in Table 15.1.,YARN SIZE,The concept of relating linear density to the fineness of a textile strand was introduced with the discussion of fiber denier and tex in Chapter 3. denier, ex, and other related terms a
8、re also used to denote(表示） the yarn numbering systems（纱线细度计量制）that describe the linear density of yarns.,These yarn numbering systems（纱线细度计量制） have been developed to describe the relative size, or fineness, of a yarn as a mathematical relationship between the length of a strand of yarn and its mass.
9、 The mathematical equation used to calculate yarn number(纱线支数) may use length as a constant, making it a direct numbering system, or it may use mass as a constant, producing an indirect yarn number.,Designating Ply（股线表示方法）,A single-ply, or singles, yarn is designated with a slash mark and a numeral
10、one (/1) or the yarn number and the letter “s.” Thus, either “20/1” or “20s” could be used to refer to a 20 cotton-count singles yarn. A two-ply yarn is designated by “/2.” A 60/3 Ne sewing thread(线) is a yarn made by combining three 60-count cotton piles. If the three-ply yarn were measured and wei
11、ghed as a single yarn, it would appear to be a 20 Ne yarn.,YARN TWIST(纱线捻度),Fibers are usually twisted together by the process of spinning to produce a yarn that will withstand the rigors（剧烈、猛烈） of weaving or knitting. The direction in which the fibers are twisted and the amount of twist inserted af
12、fect the properties of yarns and the products that can be made from the yarns. Twist affects strength, luster， abrasion resistance, hand, absorbency（吸湿性）, and flexibility.,Direction,Twist is inserted by rotating fiber strands in either a clockwise（顺时针） or counterclockwise direction. The direction of
13、 twist is defined by the letter S or Z (Figure 15.1). An S-twist yarn is one in which the spiral（螺旋） of the yarn is parallel to the center bar（条） of the letter S: likewise（同样地） for a Z-twist yarn. A spindle rotating counterclockwise produces an S twist: a spindle rotating clockwise produces a Z twis
14、t.,FIGUBE 15.1 Diagram of S and Z twists in yarns,Most yarns spun on cotton systems have a Z twist. The tradition goes back to medieval times. The consumer protection laws of the craft guilds（手工业行会） decreed（颁布） that cotton and linen would be spun with an S twist. In modern times, because most of the
15、 people who operate and repair spinning frames are right-handed, the equipment is designed to spin Z-twist yarns to maximize their efficiency.,Amount,The amount of twist in a yarn is expressed as turns per inch (tpi) of yarn length. Yarns that have low levels of twist are softer and have more loft（厚
16、度）, or bulk（体积）: they are usually weaker than yarns with more twist. In general, the shorter the fiber being spun, the more twist is required to give strength. At some point, however, the optimum twist will have been inserted, and additional turns will decrease the strength of the yarn. Past the opt
17、imum, the fibers in the yarn are more perpendicular(垂直的） than parallel to the length of the yarn.,The optimum tpi in a yarn is directly related to its fineness. Fine yarns usually require a higher tpi than coarse（粗的） yarn. To achieve similar properties in yarns of various counts, the concept of the
18、twist multiple, or twist multiplier (TM捻系数), is used. The TM is the ratio of the tpi to the square root of the cotton count of the yarn, and it may be used as a measure（尺度、表征） of the hardness（紧密度、硬度） of twist in the yarn.,Stated as a formula TM=tpi/sqr(Ne) where TM=twist multiplier Tpi=turns per inc
19、h twist Ne=cotton yarn count Cotton knitting yarns are spun with a 2 to 3 TM; filling yarns （纬纱）for weaving may have a 3 to 4 TM; and warp yarns（经纱） for weaving may have a 4 to 5 TM. Hard twist yarns such as crepe yarns（绉纱） are spun with a 5 to 7 TM. When too much twist is added to these yarns, the
20、yarn may develop torque（扭转） and kink（扭结） and snarl（缠结）, making it difficult to weave or knit.,Liveliness（回弹性） and balance（平衡） are terms used to describe this tendency of yarns to develop torque. A balanced yarn (Figure 15.2) is one that will hang in a loop without kinking (扭结）, doubling（折叠）, or twis
21、ting（扭曲） itself. A lively, or unbalanced, yarn is one with enough twist to set up a torque effect. It will untwist（退捻） and retwist（再加捻） on itself, often snarling（缠结） or kinking(扭结）.,One method of controlling torque and using it to advantage is to combine plies twisted in opposite directions to form
22、a plied yarn. The final yarn has the properties described in a tightly twisted yarn, but the liveliness has been controlled. It is also possible to use a twist setting （捻度定形）finish, which allows miles to weave high-twist crepe yarns（绉纱）.,Other Properties,DURABILITY（耐久性）Tensile strength and abrasion
23、resistance are important in determining the durability of yarns for weaving and knitting and in predicting the performance of yarns in other end uses. Variations in yarn construction (for example, fineness and twist), in addition to fiber content, affect the durability of a yarn.,Fiber Cohesion（内聚力，
24、抱合力）,Yarn strength depends somewhat on fiber cohesion. If long fibers are made parallel (aligned) to provide maximum contact between fibers, it is possible to produce a cohesive yarn stronger than the yarn produced by spinning the same fibers without aligning them. Long fibers also produce a more co
25、hesive, and hence stronger yarn than short fibers.,Twist,Twist affects both strength and abrasion resistance. Low twist produces a yarn that pulls more easily. The fibers are not held in the strand as firmly, so with any disturbance (abrasion) more fiber ends protrude（突出、伸出） from the surface of the
26、yarn. They attract other bits（片） of fiber, producing pills on the surface of the yarn. Pilling caused by abrasion is often a problem with yarns manufactured from short fibers loosely twisted together.,As twist in a yarn increases, strength increases and pilling decreases. As a rule, strength and abr
27、asion resistance improve to a point and then begin to decline as the fibers become more perpendicular to the lengthwise axis of the yarn.,Ply(股数),A fine single yarn is weaker than a coarse yarn of the same TM（捻系数）. One method of increasing the strength of fine yarns is to produce a plied yarn of the
28、 same apparent count.,EVENNESS（均匀度）,If the diameter of a yarn is constant throughout its length, the yarn is perfectly even. Few yarns exhibit perfect evenness; most have an occasional thick or thin place in the strand, and in yarns there may be neps （棉结，毛结，麻粒） or knots（结头）of fibers that from thick
29、places. Such yarns may produce fabric defects that affect appearance and performance. When uneven places recur（重复）, an undesirable pattern（型式、图案） may be produced in a fabric. Control of evenness is an important component of yarn quality control (Figure 15-3).,In some cases unevenness is desirable. M
30、any novelty yarns are produced by including thick and thin places, or slubs（竹节） of within the yarn. To be effective， their recurrence（循环） must be controlled.,BLENDING FIBERS,It is possible to balance desirable and undesirable properties by blending generic（同类） fibers during the yarn manufacturing pr
31、ocess. Two or more fibers may be combined to form an intimate（固有的、最佳的、临界的） blend within a single strand. The procedures are described in Chapter 16. Intimate blending produces a more even distribution of the properties of all the involved fibers throughout the finished product.,Fibers can also be bl
32、ended by combining plies of different fiber content. In some production techniques, it is possible to wrap a strand of staple fibers around a core of filament fiber. Core-spun（包芯纱） sewing threads are made by this process.Control of blending is necessary to correctly balance fiber properties and to e
33、nsure accurate labeling of fiber content under the regulations of the TFPLA（纺织纤维产品鉴别法）. The descriptions of yarn-forming processes in the following chapters provide additional information on blending fibers.,HOMEWORK,Preparation of Knit Fabrics : （P158） Yarn size Translate the paragraphs into Chinese.,
