Linear Density of Yarn | Measurement of Linear Density
Linear Density of Yarn:
Among the other parameters of a yarn, yarn's diameter is a significant factor. But determining the diameter is impossible by any means due to the fact that it varies significantly as the yarn is squeezed. Besides the optical technique, all other methods involve compressing the yarn during testing. Due to this compressive character of yarn, the measured diameter varies with the pressure applied.
Optical techniques for determining diameter have the difficulty of specifying where the peripheral edge of the yarn lies as its surface can be unclear or rough due to hairiness on it. That is why the determination of the yarn’s edges is subject to the operator’s understanding. Due to these problems a system must be designed to ascertain the delicacy of a yarn by weighing its predefined length. This quantity is called the linear density or yarn count and it can be determined with accuracy if the tested amount of yarn is sufficient. There are two main systems for assessing the linear density of yarn: the direct and the indirect.
Direct System:
In this system we determine the weight per unit length. The most well known direct systems are
* Tex: This is the number of grams in 1000 m of yarn.
* Decitex: This is the number of grams in 10,000 m of yarn.
* Denier: This is the number of grams in 9000 m of yarn.
Indirect System:
In this system we determine the length per unit weight. This linear density is also called a count, due to the fact that it is established by determining the hanks of a specified length. It is the most widely used system of measuring a yarn’s linear density. A conversion table for different systems is shown in Figure.
The most well-known direct systems in use are:
* Yorkshire skeins woollen (Ny) Count: This is the number of hanks per pound (where one hank = 256 yards).
* Worsted count (New) Count: This is the number of hanks per pound (where one hank = 560 yards).
* Cotton count (Nec)*** Count: This is the number of hanks per pound (where one hank = 840 yards).
[***In these systems the fineness and count of a yarn are directly proportional to each other.]
* Metric count (Nm) Count: This is the number of kilometers per kilogram.
Measurement of Linear Density:
Yarn linear density is often measured using standard test method ASTM D1907. Specified lengths of yarn are wound on reels as skein, and then weighed. From this the linear density is calculated from the weight and length of the skein. In some options, the skein is scoured before weighing, or the mass of the skein may be determined after oven drying or after conditioning.
A reel having a length between 1.0 and 2.5 m or between 1.5 and 3.0 yards may be used with a tolerance of ±0.25%. The tension on the reel is adjusted to 0.5 cN/tex with an adjustable tension device. The yarn sample is preconditioned for a minimum of 3 h before drying in an oven. A ventilated oven with the ability to control the temperature at 105°C ± 3°C is required to dry the skeins. After oven drying, the weight of the sample is measured by a weight balance having a sensitivity of 1 part in 1000 to measure the linear density. This sample is then conditioned for a minimum of 24 h at a standard condition of 20°C ± 2°C and 65% ± 4% relative humidity then weighed to measure the linear density at the standard moisture regain, from which the linear density is calculated.
(100 + Standard regain)
Weight at correct condition = Dry weight x ----------------------------------------------
100
Among the other parameters of a yarn, yarn's diameter is a significant factor. But determining the diameter is impossible by any means due to the fact that it varies significantly as the yarn is squeezed. Besides the optical technique, all other methods involve compressing the yarn during testing. Due to this compressive character of yarn, the measured diameter varies with the pressure applied.
Optical techniques for determining diameter have the difficulty of specifying where the peripheral edge of the yarn lies as its surface can be unclear or rough due to hairiness on it. That is why the determination of the yarn’s edges is subject to the operator’s understanding. Due to these problems a system must be designed to ascertain the delicacy of a yarn by weighing its predefined length. This quantity is called the linear density or yarn count and it can be determined with accuracy if the tested amount of yarn is sufficient. There are two main systems for assessing the linear density of yarn: the direct and the indirect.
Direct System:
In this system we determine the weight per unit length. The most well known direct systems are
* Tex: This is the number of grams in 1000 m of yarn.
* Decitex: This is the number of grams in 10,000 m of yarn.
* Denier: This is the number of grams in 9000 m of yarn.
Indirect System:
In this system we determine the length per unit weight. This linear density is also called a count, due to the fact that it is established by determining the hanks of a specified length. It is the most widely used system of measuring a yarn’s linear density. A conversion table for different systems is shown in Figure.
 |
| Figure: Conversion table of yarn count |
* Yorkshire skeins woollen (Ny) Count: This is the number of hanks per pound (where one hank = 256 yards).
* Worsted count (New) Count: This is the number of hanks per pound (where one hank = 560 yards).
* Cotton count (Nec)*** Count: This is the number of hanks per pound (where one hank = 840 yards).
[***In these systems the fineness and count of a yarn are directly proportional to each other.]
* Metric count (Nm) Count: This is the number of kilometers per kilogram.
Measurement of Linear Density:
Yarn linear density is often measured using standard test method ASTM D1907. Specified lengths of yarn are wound on reels as skein, and then weighed. From this the linear density is calculated from the weight and length of the skein. In some options, the skein is scoured before weighing, or the mass of the skein may be determined after oven drying or after conditioning.
A reel having a length between 1.0 and 2.5 m or between 1.5 and 3.0 yards may be used with a tolerance of ±0.25%. The tension on the reel is adjusted to 0.5 cN/tex with an adjustable tension device. The yarn sample is preconditioned for a minimum of 3 h before drying in an oven. A ventilated oven with the ability to control the temperature at 105°C ± 3°C is required to dry the skeins. After oven drying, the weight of the sample is measured by a weight balance having a sensitivity of 1 part in 1000 to measure the linear density. This sample is then conditioned for a minimum of 24 h at a standard condition of 20°C ± 2°C and 65% ± 4% relative humidity then weighed to measure the linear density at the standard moisture regain, from which the linear density is calculated.
(100 + Standard regain)
Weight at correct condition = Dry weight x ----------------------------------------------
100
