Yarn Twist Parameters PDF

Yarn Parameter 2: YARN TWIST Yarn Twist Yarn Twist Specifications: Twist Direction – S or Z Twist level – turns per metre (t/m) or turns per inch (tpi) Twist Angle/Twist Factor or Multiplier Twist Direction for Single & Folded Yarns Most manufactured single ply yarns are spun with a Z twi...

Yarn Parameter 2: YARN TWIST Yarn Twist Yarn Twist Specifications: Twist Direction – S or Z Twist level – turns per metre (t/m) or turns per inch (tpi) Twist Angle/Twist Factor or Multiplier Twist Direction for Single & Folded Yarns Most manufactured single ply yarns are spun with a Z twist. To ply these Z-spun singles together they are spun with an S twist to give a balanced plied yarn. Almost all yarns available for commercial knitting are made with a Z twist if they're single ply Generally, higher twist yarns for and having a final S twist if they're weaving and lower twist yarns for plied. knitting. Combinations of twist directions in spun plied yarns Some Reasons for Yarn Folding Yarn folding for: Improved yarn regularity; Improved yarn strength; Balanced or twist-lively yarn; Novelty effects. For example: shadow effects can be produced in finished fabrics by the use of yarns combining opposing twists, producing differing light reflections. Twist level – turns per metre (tpm) or turns per inch (tpi) TPI/TPM (twists/turns per inch or metre) expresses the number of twists per inch/metre in a yarn. For example, the tpi of a yarn can be calculated by counting the number of twists in an inch of a yarn.  Amount of Twist given to a Yarn The amount of twist given to a yarn varies depending on the fibre length and preparation (carded or combed), thickness of yarn, spinning methods, and the desired yarn properties. Effect of Level of Twist on Properties of Single Yarn Strength and extensibility of yarn – increase with twist Stiffness of yarn – increase with twist Compactness – increase with twist Dimensional stability such as spirality/distortion/liveliness Effect of yarn twist and twist direction on fabric properties, for example: Fabric handle: higher twist yarns give harsher feel and vice-versa; Fabric appearance such as lustre is affected by the twist directions of warp and weft; Fabric pilling and abrasion resistance: a high level of twist helps to resist abrasion and pilling Moisture absorption: high level of twist gives low water absorbency fabric Some examples of the use of yarns of different twist level and direction in fabric construction Crepe yarns, producing a crinkled effect in fabrics, are made with a very high degree of twist, producing kinks and twist liveliness in the yarns. Additive twist is given by S on S or Z on Z, producing compact and twist-lively folded yarns. Crêpe, or crepe, is a silk, cotton, wool, or synthetic fabric that has a distinctive wrinkled and bumpy appearance. Fabric handle and appearance are altered Crepe fabric Chiffon fabric How to Determine the Direction & Level of Yarn Twist? Using Visual and Instrumental Methods Twist Factor/Multiplier  Twist Angle It is known that the surface twist angle determines the twist dependent character of the yarn, regardless of its diameter and tpm. The surface twist angle is the angle the surface fibres make with respect to the yarn axis. Although the two yarns have the same tpm, they do not have the same surface twist angle. Same tpm but Therefore their twist dependent properties different twist such as handle, bending stiffness, and angle strength will NOT be similar. In general, thinner yarns are given higher twist than thicker yarns to achieve similar twist angle. Twist Factor or Multiplier, an empirical parameter Since same tpm may give different twist angles for yarns of varying fineness, tpm is not a good measure of the yarn properties. Twist angle is. But since twist angle is difficult to measure, we use twist factor to define the twist characteristic of a yarn. Analogy: Yarn tenacity and Yarn strength  Twist Factor, k Twist angle affects the twist-dependent properties of yarn; Staple Yarn: strength increases with twist level up to an optimum value; Twist angle expressed by twist factor, k; k = tpi/(count)1/2 (3.0-8.0), (indirect system); k = tpcm(linear density)1/2 (29-77), (direct system); low value = soft feel; medium values for good to optimum strength Tutorial Question Statement: In general, for same surface twist angle, thinner yarns are usually given higher twist than thicker yarns to achieve similar twist dependent yarn properties such as strength. Use the twist factor, k, to support the above statement. k = tpi/(count)1/2 (3.0-8.0), (indirect system); Answer: Let’s, say, a cotton spun yarn A has a count of 40s and another yarn B has a count of 80s. Assuming the twist factors of both yarns are same; i.e. they have the same surface twist angle or factor, k = 4.0. This means they are expected to have similar twist dependent properties such as tensile strength. For yarn A, the tpi = k*(count)1/2 = 4.0 *(40)1/2 = 25.3; this means that yarn A has 25.3 turns per inch For yarn B, the tpi = k*(count)1/2 = 4.0 *(80)1/2 = 35.8; this means that yarn B has 35.8 turns per inch Yarn B, which is thinner (higher count value of 80s), has more twist per unit length than yarn A which is thicker (lower count value of 40s) and has lower twist level. So we can conclude that thicker yarns have lower twist levels than thinner yarn for similar twist dependent property such as tensile strength. Other Yarn Parameters which gives further information about the yarn: Yarn Strength/Tenacity Yarn Elongation Yarn Evenness Yarn Hairiness These parameters are sometimes useful when specifying the yarn for certain applications. All of the above may be measured and quantified instrumentally. End of Lecture