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Post on 07-Mar-2015
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Characteristics of Cotton | Cotton CharacteristicsCotton Staple Length If the length of fiber is longer, it can be spun into finer counts of yarn which can fetch higher prices. It also gives stronger yarn. Cotton Strength Stronger fibers give stronger Yarns. Further, processing speeds can be higher so that higher productivity can be achieved with less end-breakages. Fiber Fineness Finer Fibers produce finer count of yarn and it also helps to produce stronger yarns. Cotton Fiber Maturity Mature fibers give better evenness of yarn. There will be less end - breakages . Better dye absorbency is additional benefit. Uniformity Ratio If the ratio is higher. Yarn is more even and there is reduced end-breakages. Cotton Fiber Elongation A better value of elongation will help to reduce end-breakages in spinning and hence higher productivity with low wastage of raw material. Non-Lint Content Low percentage of Trash will reduce the process waste in Blow Room and cards. There will be less chances of yarn defects. Sugar Content Higher Sugar Content will .create stickiness of fiber and create processing problem of licking in the machines. Cotton Moisture Content If Moisture Content is more than standard value of 8.5%, there will be more invisable loss. If moisture is less than 8.5%, then there will be tendency for brittleness of fiber resulting in frequent yarn breakages.
Cotton Feel If the feel of the Cotton is smooth, it will be produce more smooth yarn which has potential for weaving better fabric. Cotton Grade Cotton having better grade in classing will produce less process waste and yarn will have better appearance. Grey Value If the reading of calorimeter is higher it means it can reflect light better and Yam will give better appearance. Yellowness When value of yellowness is more, the grade becomes lower and lower grades produce weaker & inferior yarns. Cotton Neppiness Neppiness may be due to entanglement of fibers in ginning process or immature fibers. Entangled fibers can be sorted out by careful processing But, Neps due to immature fiber will stay on in the end product and cause the level of Yarn defects to go higher. Cotton parameters It is better if quality parameters are established for different varieties so that buying decisions are easy for buyers Following standards have been found to be appropriate for Strict Middling Grade Cotton of staple 1.3/32". Staple Length ( 2.5% Spun Length) - Minimum 1.08" or 27.4 mm Micronaire : Minimum 3.8, Maximum-4.6.Variation within bulk sample should not be more than 0.1 Colour : Readingd not less than 75 not more than 10 Nep Content: Less than 150 per gram Strength : More than 30 grams/tex Length Uniformity Ratio: Not less than 85% Elongation : More than 8% Short Fiber Content: Less than 5% Seed Count Fragments : Less than 15 per grams
Cotton and Yarn Quality Co-Relation | Cotton Yarn Properties | Cotton QualityThe Cotton Yarn Properties which can be directly Attributed to Cotton Quality are Cotton Yarn Count Higher Count of Yarn can be produced by longer, finer and stronger fibers. Coefficient of Variation of Count Higher Fiber Uniformity and lower level of short fiber percentage will be beneficial to keep C.V. (Coefficient of Variation) at lowest. Cotton Yarn Tensile Strength This is directly related to fiber strength. Longer Length of fiber will help to produce stronger yarns. C.V. of Strength This is directly related to CV of fiber strength. Cotton Yarn Elongation Yarn elongation will be beneficial for weaving efficiently. Fiber with better elongation have positive co-relation with Yarn elongation. C.V. Of Yarn Elongation C.V. of Yarn Elongation can be low when C.V. of fiber elongation is also low. Cotton Yarn Hairiness It is due to faster processing speeds and high level of very short fibers Cotton Yarn Brightness Yarn will have brighter appearance if cotton grade is higher.
Yarn Testing | Coefficient of VariationYarn occupies the intermediate position in the manufacture of fabric from raw material. Yarn results are therefore essential, both for estimating the quality of raw material and for controlling the quality of fabric produced. The important characteristics of yarn being tested are: Yarn Twist Linear Density
Yarn Strength Yarn Elongation Yarn Evenness Yarn Hairiness Yarn Twist Twist is defined as the spiral disposition of the components of yarn, which is generally expressed as the number of turns per unit length of yarn, e.g turns per inch, turns per meter, etc. Twist is essential to keep the component fibers together in a yarn. The strength, dyeing, finishing properties, the feel of the finished product etc. are all dependent on the twist in the yarn. With increase in twist, the yarn strength increases first , reaches a maximum and then decreases. Depending on the end use, two or more single yarns are twisted together to form "plied yarns" or "folded yarns" and a number of plied yarns twisted together to form "cabled yarn". Among the plied yarns, the most commonly used are the doubled yarns, wherein two single yarns of identical twist are twisted together in a direction opposite to that of the single yarns. Thus for cabled and plied yarns, the direction of twist and the number of turns per unit length of the resultant yarn as well as of each component have to be determined for a detailed analysis. Direction of twist is expressed as "S"-Twist or "Z"-Twist. Direction depends upon the direction of rotation of the twisting element. Twist take up is defined as, The decrease in length of yarn on twisting, expressed as a percentage of the length of yarn before twisting. Coefficient of Variation of Twist In handling large quantities of data statistically, the coefficient of variation (C.V.%) is commonly used to define variability and is thus well-suited to the problem of expressing yarn evenness. Coefficient of Variation is currently probably the most widely accepted way of quantifying irregularity. It is given by coefficient variation (C.V.%) = (standard deviation/average) x 100 The coefficient of variation for twist per metre shall be not more than 7% when tested. Linear Density or Count of Yarn The fineness of the yarn is usually expressed in terms of its linear density or count. There are a number of systems and units for expressing yarn fineness. But they are classified as follows Direct System English Count (Ne) Metric Count (Nm)
French Count (Nf) Indirect System Tex Denier English Count (Ne) No of 840 yards yarn weighing in One pound Metric Count (Nm) No of one kilometer yarn weighing in One Kilogram French Count (Nf) No of one kilometer yarn weighing in 0.5 kilogram Tex Weight in grams of 1000 meter(1 kilometer) yarn
DenierWeight in grams of 9000 meter(9 kilometer) yarn For the determination of the count of yarn, it is necessary to determine the weight of a known length of the yarn. For taking out known lengths of yarns, a wrap-reel is used. The length of yarn reeled off depends upon the count system used. Another factor which determines the length of yarn taken for testing is the type of balance used. Some balances like quadrant balance, Beesley's blanace have been specially designed to indicate the yarn count directly from tests on specified short lengths of yarn and are very useful for determining the counts of yarn removed from the fabrics. The minimum accuracy of balance required is 0.001mg One of the most important requirements for a spinner is to maintain the average count and count variation within control. The term count variation is generally used to express variation in the weight of a lea and this is expressed as C.V.%. This is affected by the number of samples and the length being considered for count checking. While assessing count variation, it is very important to test adequate number of leas. After reeling the appropriate length of yarn, the yarn is conditioned in the standard atmosphere for testing before it's weight is determined. The minimum number of sample required per count is 20 and per machine is 2. Yarn Strength and Elongation Yarn Breaking strength, Yarn elongation, Yarn elastic modulus, resistance abrasion etc are some important factors which will represent the performance of the yarn during actual use or further processing. Yarn Strength testing is broadly classified into two methods single end strength testing skein strength or Lea strength
Yarn Strength - Tensile Strength of Single Strands of Yarn During routine testing, both the breaking load and extension of yarn at break are usually recorded for assessing the yarn quality. Most of the instruments record the load-elongation diagram also. Various parameters such as initial elastic modulus, the yield point, the tenacity or elongation at any stress or strain, breaking load, breaking extension etc can be obtained from the loadextension diagram Two types of strengths can be determined for a yarn Yarn Strength - Tensile Strength Load is applied gradually Yarn Strength - Ballistic Strength Applying load under rapid impact conditions Tensile strength tests are the most common tests and these are carried out using either a single strand or a skein containing a definite number of strands as the test specimen. An important factor which affects the test results is the length of the specimen actually used for carrying out the test. The strength of a test specimen is limited by that of the weakest link in it.If the test specimen is longer, it is likely to contain more weak spots, than a shorter test specimen. Hence the test results will be different for different test lengths due to the weak spots. The amount of moisture in the yarn also influences the test results. Cotton yarn when fully wet show higher strength than when dry, while opposite is the case with viscose rayon yarns. Hence, to eliminate the effect of variation due to moisture content of the yarn, all yarn strengrth tests are carri