Yarn density, linear

Yarn type Linear density, dtex/filament number Tenacity, Ntex Breaking strain, % Hot air shrinkage at ISO C, %... 

Nominal linear density of the yarn measures the coarseness of the yarn in units of dedtex, i.e. mass per unit length. In the metric system, 10 000 m of 1 dtex yam weighs 1 g. Higher decitex value indicates a coarser yarn. Filament linear density, ), is calculated using following equation ... 

ISO 1889 1997 Reinforcement yarns - Determination of linear density ISO 1890 1997 Reinforcement yarns - Determination of twist ISO 2113 1996 Reinforcement fibres - Woven fabrics - Basis for a specification ISO 2113 1996/Cor 1 2003... 

FIG. 13.94 Generalised stress-strain diagram for nylon 6.The tex is a standardised symbol for the linear density of a yarn 1 tex = 1 g per 1000 m. Divided by the density it is proportional to the cross-section of the yarn (after Herwig, 1970). 

Twist in the yarn Most yams have filaments that are twisted. The main reason for this is that an untwisted yam is difficult to weave or knit. Two types of twists can be given to the yam, a counterclockwise twist or S twist and a clockwise twist or a Z twist. Figure 2.1 shows these twists. We can also make a ply yam by using reverse twist directions. This serves to balance out residual stresses. We can also twist together two or more plies to make a cord. Commonly, yam designation on a fiber spool provides information such as name, linear density, number of fibers and fiber type. 

It can be seen from this that different fiber types of the same linear density but of different densities can have different fiber diameters, so a fiber with a higher density will have a smaller diameter than a fiber of the same linear density but a lower density. This highlights another area where fiber (filament) diameter is also important, and that is in calculating cover factor. Cover factor is simply a number that gives an indication of the extent to which the area of fabric is covered by one set of threads or as a measure of the relative density of packing (i.e., looseness or tightness) of the yarn in the fabric. It is calculated, in the case of woven fabrics, from the equation... 

However, as stated above, the description of fiber fineness by reference to its diameter tends to be in the minority, and usually fiber fineness is expressed in terms of linear density. There have been many systems of yarn measurement throughout the world, not to mention the variations in the cotton spinning, worsted, and woollen industries, but for present purposes only the SI system will be used (tex = g km), as this is universally recognized and is the system employed in international standards after 50 years of gestation it is now being widely used across the globe. 

If however the linear density of the fiber was 2 dtex, then clearly the number of fibers in the cross section would only be 125, and as a consequence the yarn regularity would be worse (i.e., the CV% would be higher). 

The coefficients of variation of linear density for. short staple yarns specified in ASTM D 2645 95 are 5% for carded yarns and 4% for combed yarns. ISO 10290 does not differentiate between carded or combed yarns and has the CV% for linear density as 4% for both, but this is clearly the result of optimism. A method for the indirect measure-... 

As mentioned above, the usual or common means of describing fiber finenc.ss is by-reference to its mass, unit length or linear density, The standard SI unit for this measure is tex, which is the number of grams per unit length of 1.000 m (i.e.. g, km), or its multiples such as kilotex (for the extremely coarse measures such as ropes > 4 mm counting systems sec ASTM D 861 or ISO 1144 and ISO 2947. 

Gravimetric Method. This method determines the average linear density of the sample, irrespective of the variability of the density of fibers within the sample. It is therefore unsuitable for fiber blends in which the linear densities of the fibers are markedly different. This does sometimes happen, and blends of fibers having different crimp rigidities are sometimes processed to permit changes in yarn properties or fabric properties to be developed later, but generally speaking the staple yarn spinner will try to blend fibers of the same linear density, as this creates fewer problems in production. 

Note 1. In testing textile fibers and yarns, tensile force is normally measured in Newtons (or multiples or submultiples thereoO and linear density in tex (or decitex). Thus... 

Figure 17 Force linear density vs. extension curves for the yarns shown in Figure 16.

ASTM D 861 95 Use of the Tex system to de.signate linear density of fibres, yarn intermediates, and yarns. 

Impregnated yams are considered as composites with unidirectional reinforcement (twist of the yarns used in composite reinforcement is normally negligible) with the given fibre volume fraction Vj this value is determined by the dimensions of the cross-section of the yam (which can differ from point to point in the unit cell, but most often assumed to be constant) and the amount of fibres inside the yam, given by the fibre count or yam linear density ... 

Glass strand is normally measured by the number of 100 yards in 1 lb weight (for example, a 130 s count contains 13,000 yards per pound weight or the number of grams per kilometer, imder the international unit tex. Tex is a unit for expressing linear density equal to the mass of weight in grams of 1000 m of strand, fiber, filament, yarn, or other textile strand. 

Fiber tex A unit for expressing linear density equal to the mass of weight in grams of 1000 m of fiber, filament, yarn, or other textile strand. 

The linear density of the individual fibers making up the network is given little consideration, despite the importance of this characteristic in staple fibers, where it is a major factor controlling the levelness of the spun yarn. Adhering bark increases the linear density of the fiber and makes subjective assessment difficult. 

From an extensive series of correlations between fiber properties and yarn properties, Mather concluded that the tensile properties of a yarn could be predicted from two measurements only on the raw fiber, namely, the linear density and the ballistic work of rupture of uncarded strands of fiber. 

The linear density was measured by an air-flow method using a modification of apparatus designed for cotton and wool. A sample of fiber weighing 27 g was used, and care was taken to include in the sample a similar amount of nonfibrous matter as was contained in the bulk. The nonfibrous component effectively increased the linear density, and a less regular yarn resulted when spun to a fixed count. 

The fiber linear density is a measure of the average number of fibers in the cross section of a given yam, and this controls the yarn irregularity. The more fibers in the cross section, the more uniform is the yarn thickness from point to point. As yams break at their thinnest points, the breaking load is greater, irrespective of the intrinsic fiber strength. 

Under mercerizing conditions, the fibers lose considerable weight (15% or more) and give the appearance of being opened up. It is commonly said that there is a considerable reduction in diameter, which implies a lower linear density and hence the production of more regular yarns. However, just as in natural jute, there appears to be a limit below which the diameter does not fall as with mercerized fiber. 

Agricultural developments to breed Corchorus or Hibiscus plants containing fibers of significantly lower linear density would allow yarns of lower count to be spun than is feasible at present, and therefore enable lightweight fabrics to be produced. Such fabrics could have increased potential for decorative and furnishing use, especially if the constraint of instability of color could first be removed and some process then devised to produce additional elasticity on a more permanent basis than is done by the woolenizing process. 

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