Classification of Yarn Faults and Possible Source of Origin
The yarns used could be in two different forms: a twisted assembly of continuous filaments or staple fibers, or a parallel assembly of filaments. The yarns are interlaced or looped together to form woven, knitted, braided or knotted products. Sometimes, the slender filaments are first transformed into a bulky yarn and then used in this form in some applications.
Classification of Yarn Faults:
Faulty yarns produce due to a number of factors like type of raw material used, process parameters adopted, processing conditions maintained etc. Defective yarns not only affect the appearance of yarn but also have a significant influence on postspinning operation.
Broadly we can classify yarn faults into the following categories:
Broadly there are three basic subcategories of the imperfection index that are given here:
1
Yarn diameter = -------------------- inch
√28 count
Yarn diameter can also be calculated by optical or capacitive method. The USTER Tester 5 uses the capacitive method to determine the yarn diameter. If the diameter of any place along the length of the yarn is 50% higher than the actual diameter of the yarn then it is considered as a thick place, and if the diameter is 50% less than the yarn diameter then it is counted as a thin place. If the diameter of any place is so high that it becomes 200% of the yarn diameter then such a place is considered to be a nep of yarn. The IPI tells us about the evenness of the yarn; the greater the value of the IPI, the greater will be the evenness. The IPI of the yarn is determined by following the standard test method ASTM D 1425. The USTER Tester is used to determine the unevenness of yarn and is based on the capacitive method. In this method, the yarn is passed through two capacitive plates and on the basis of capacitance changes the diameter of the yarn passing through the plates is analyzed.
Coefficient of Variation of Mass (CV%):
CV percentage can be defined as the standard deviation expressed as a percentage of average:
SD
CV% = --------------- x 100
Average
Where
x are the individual values of mass of specific length over which unevenness is being measured.
n is the number of readings.
ASTM D 1425 also determines the CV% of the yarn.
Hairiness Index (H):
This is the accumulated length of hairs in centimeters in the unit length. It is denoted by H and has no unit because it is the ratio of two lengths:
Total length of all protruding fibers (cm)
Hairiness index (H) = -------------------------------------------------------------------------
One cm of the yarn
The hairiness range for the traditional yarn is 2–12. In the case of finer yarn, there are less fibers per unit cross-section and normally longer fibers are used so they have less tendency to move outward, which results in low hairiness. Normally ring spun yarn has a higher H value than air vortex and rotor yarn because of the friction that occurs between the traveler and the yarn and also the higher mobility that is observed. There are many techniques by which hairiness can be measured, such as optical, capacitive, and image analyses as well as the theoretical method. In most cases, hairiness is measured by the optical method, normally an USTER or Zweigle Hairiness Tester.
Periodic faults:
These are the faults that arise periodically and appear as a wood pattern or as stripes or streaks in the fabric. The appearance of periodic faults in yarn is shown in Figure-2. After dyeing such faults result in shade variation.
Classimate faults:
On the base of the USTER Classimate, yarn faults are classified into the following categories, most of which can be removed with the help of any yarn clearer in the auto cone department during the winding process.
Yarn slub test:
Slub yarn or fancy yarn have a variety of applications in textiles. All the slubs are calculated on the base of the reference level, which is on the level of the base yarn. The mass increase is the amount of mass that is increased from the base level/reference level, which is 0%. The maximum length of the slub at the bottom is named the slub length and the distance between the two consecutive slubs is known as the slub distance. The ratio T/P (top length to bottom length) is also a very importance factor and it tells us about the steepness of the slubs present in the yarn. We can produced a fancy yarn with two or more populations, this means that there are at least two different slub sizes regarding for example different mass increases or slub lengths or a combination of both in a slub yarn. A mass decrease of a slub is an important quality parameter because mass decrease before and after a slub produces weak places in the yarn, so it is very important to maintain the setting of the spinning machine or the slub yarn device. The count of the fancy yarn is normally given as the overall nominal count that describes the weight per unit length. It is also possible to describe the base yarn count and slub count separately. A yarn slub test is performed by the USTER Tester 5 and works on the capacitive principle in which the diameter of the yarn passing through the dielectric plates is determined by the change in the capacitance.
References:
Classification of Yarn Faults:
Faulty yarns produce due to a number of factors like type of raw material used, process parameters adopted, processing conditions maintained etc. Defective yarns not only affect the appearance of yarn but also have a significant influence on postspinning operation.
 |
| Figure-1: Different yarn faults |
- Imperfection index (IPI)
- Coefficient of variation of mass (CV%)
- Hairiness index
- Periodic faults
- Classimate faults
Broadly there are three basic subcategories of the imperfection index that are given here:
- Thick place (+50%)
- Thin place (−50%)
- Neps (+200%)
1
Yarn diameter = -------------------- inch
√28 count
Yarn diameter can also be calculated by optical or capacitive method. The USTER Tester 5 uses the capacitive method to determine the yarn diameter. If the diameter of any place along the length of the yarn is 50% higher than the actual diameter of the yarn then it is considered as a thick place, and if the diameter is 50% less than the yarn diameter then it is counted as a thin place. If the diameter of any place is so high that it becomes 200% of the yarn diameter then such a place is considered to be a nep of yarn. The IPI tells us about the evenness of the yarn; the greater the value of the IPI, the greater will be the evenness. The IPI of the yarn is determined by following the standard test method ASTM D 1425. The USTER Tester is used to determine the unevenness of yarn and is based on the capacitive method. In this method, the yarn is passed through two capacitive plates and on the basis of capacitance changes the diameter of the yarn passing through the plates is analyzed.
Coefficient of Variation of Mass (CV%):
CV percentage can be defined as the standard deviation expressed as a percentage of average:
SD
CV% = --------------- x 100
Average
Where
x are the individual values of mass of specific length over which unevenness is being measured.
n is the number of readings.
ASTM D 1425 also determines the CV% of the yarn.
Hairiness Index (H):
This is the accumulated length of hairs in centimeters in the unit length. It is denoted by H and has no unit because it is the ratio of two lengths:
Total length of all protruding fibers (cm)
Hairiness index (H) = -------------------------------------------------------------------------
One cm of the yarn
The hairiness range for the traditional yarn is 2–12. In the case of finer yarn, there are less fibers per unit cross-section and normally longer fibers are used so they have less tendency to move outward, which results in low hairiness. Normally ring spun yarn has a higher H value than air vortex and rotor yarn because of the friction that occurs between the traveler and the yarn and also the higher mobility that is observed. There are many techniques by which hairiness can be measured, such as optical, capacitive, and image analyses as well as the theoretical method. In most cases, hairiness is measured by the optical method, normally an USTER or Zweigle Hairiness Tester.
Periodic faults:
These are the faults that arise periodically and appear as a wood pattern or as stripes or streaks in the fabric. The appearance of periodic faults in yarn is shown in Figure-2. After dyeing such faults result in shade variation.
 |
| Figure-2: Appearance of the yarn periodic faults in the fabric. |
On the base of the USTER Classimate, yarn faults are classified into the following categories, most of which can be removed with the help of any yarn clearer in the auto cone department during the winding process.
- Neps
- Short thick
- Long thick or double yarn
- Long thin
Yarn slub test:
Slub yarn or fancy yarn have a variety of applications in textiles. All the slubs are calculated on the base of the reference level, which is on the level of the base yarn. The mass increase is the amount of mass that is increased from the base level/reference level, which is 0%. The maximum length of the slub at the bottom is named the slub length and the distance between the two consecutive slubs is known as the slub distance. The ratio T/P (top length to bottom length) is also a very importance factor and it tells us about the steepness of the slubs present in the yarn. We can produced a fancy yarn with two or more populations, this means that there are at least two different slub sizes regarding for example different mass increases or slub lengths or a combination of both in a slub yarn. A mass decrease of a slub is an important quality parameter because mass decrease before and after a slub produces weak places in the yarn, so it is very important to maintain the setting of the spinning machine or the slub yarn device. The count of the fancy yarn is normally given as the overall nominal count that describes the weight per unit length. It is also possible to describe the base yarn count and slub count separately. A yarn slub test is performed by the USTER Tester 5 and works on the capacitive principle in which the diameter of the yarn passing through the dielectric plates is determined by the change in the capacitance.
References:
- Advanced Textile Testing Techniques Edited by Sheraz Ahmad, Abher Rasheed, Ali Afzal, and Faheem Ahmad
- Technical Textile Yarns by R. Alagirusamy, A. Das
- http://fashion2apparel.blogspot.com/2016/12/yarn-faults-spinning-types-yarn-fault.html
