Yarn Testing in Textile:
Testing has never been more important in the textile industry than at present, with the increasing accent and premium on high-quality products, whether for domestic markets or export trade. Important characteristics of yarn quality being tested are discussed subsequently.
The yarn represents the final outcome of the fiber processing or yarn manufacturing part of the fiber to fabric textile pipeline. Prior to the yarn it is still possible, within certain limits, to take corrective action should problems or mistakes have occurred during the earlier processing stages. Once the yarn has formed, any corrective action is limited to yarn clearing (i.e. removal of gross or unwanted faults), uptwisting and singeing. The properties of the yarn largely determine subsequent fabric manufacturing performance and efficiency (also sewing performance) as well as the properties, aesthetic and functional, of the fabric and end-product. Yarn quality control, and the associated testing of those yarn properties which determine the yarn quality, are therefore crucial in ensuring that the yarn meets the requirements of the subsequent fabric manufacturing stages as well as of the fabric and end product.
The testing or monitoring of yarn properties can take place either on-line during spinning (e.g. rotor and air jet spinning) and winding, or more commonly off-line, such as measuring the yarn evenness and tensile properties, or both.
Yarns are often characterized by fineness, twist, tenacity, elongation, and crimp. A yarn’s thermal behavior and bending properties can also be important for certain applications. For nearly all products made from yarns, the yarn evenness is crucial. The respective testing devices often also determine yarn imperfections (thick and thin places, neps) and hairiness.
Different Types of Yarn Tests:
The important yarn tests are given below:
- Determination of yarn count
- Determination of yarn evenness
- Determination of yarn hairiness
- Tensile strength testing
- Twist testing
- Abrasion resistance
Determination of above yarn testing methods are described below:
A. Determination of yarn count:
Count is a fundamental structural parameter of a yarn. The fineness of the yarn is usually expressed in terms of its linear density or weight per unit length (count). A number of systems and units express yarn fineness and are classified as: Direct system (English count [Ne], metric count [Nm], and French count [Nf]) and Indirect system (Tex and Denier).
To determine the yarn count of a sample, it is needed to measure the length and weight of the sample. The equipment used for this purpose is Wrap reel and Analytical balance or Knowles balance or Quadrant balance etc. Beesley’s balance can be used to get the yarn count directly from the balance. When yarn specimen supplied is not sufficient to perform the tests on the above methods, Beesley’s balance can be used to examine the yarn count with reliability.
B. Determination of yarn evenness:
The uniformity of a yarn is expressed by the mass variation per unit length, known as evenness. The surface irregularity of yarn is of particular importance in relation to processing properties, as even with a well maintained mean count, the appearance of the fabric can sometimes be affected considerably. Yarn evenness is assessed basically by deriving either the variation along the length of a yarn in the mass per unit length (or number of fibers per cross-section) or the variation in diameter. Visual evaluation and electronic methods are used for this purpose.
C. Determination of yarn hairiness:
The occurrence of short fibers and loops protruding from the yarn’s surface is known as hairiness. Although hairiness is desirable in certain types of fabrics, notably soft knitteds, brushed fabrics and flannels, it is undesirable in other fabrics, such as shirting. Yarn hairiness affects the fabric surface appearance and properties, including fabric pilling, handle and comfort (thermal insulation). Yarn hairiness also plays an important role in weavability, since the protruding hairs tend to catch on adjacent yarns causing yarn breakages and loom stoppages. It is particularly important in air-jet weaving.
There are two major manufacturers of hairiness testing equipment on the market. Uster hairiness (H) is defined as:
H = total length (measured in centimetres) of all hairs within 1 cm of yarn.
Zweigle is a less well-known manufacturer of yarn testing equipment. Unlike Uster, Zweigle does not give averages. The number of hairs of different lengths are counted separately; these values are displayed on the equipment. In addition, the S3 value is given, defined as:
S3 = sum (number of hairs ≥ 3 mm)
D. Tensile strength testing:
The tensile properties of a yarn rank as one of its most important quality characteristics, since they largely determine the efficiency with which the yarn can be converted into fabric as well as the tensile properties of the final product. Particular importance is often attached to the tensile strength attained in a single or folded yarn of particular type and composition. Yarn extension also plays a considerable role in the processing of the yarn and in the end-use properties of the fabric produced. The range of instruments which are available for testing the strength of yarns is quite wide e.g. Single-thread testers operating on the principles of pendulum lever, inclined plane, Strained gauge, and Constant-tension hank testers of the pendulum lever or Ballistic type. Some of these instruments are relatively simple, some complicated, some have recording devices, and some are automatic. The choice of the best type to use is often difficult. Strength testing deals with the finding of load-elongation curve or stress-strain curve and breaking point or stress etc.
E. Twist testing:
Twist is one of the fundamental constructional parameters for yarns. The yarn twist (number of turns per meter of yarn) is also an important property for yarns and especially for ply-yarn yarns. Twist is a measure of spiral turns given to a yarn to hold the constituent fibers or threads together. Twist is generally expressed as the number of turns per unit length of yarn: for example, turns per inch or turns per meter. Twist in a yarn may be either in the S or Z direction. Strength, dyeing and finishing properties, the feel of the finished cloth, and so on depend on the twist in the yarn.
The most common term used to express a twist level is the twist multiplier, which is independent of the yarn count. It is used to compare certain yarn characteristics of yarns with different counts.
Generally, the Twist tester is used to determine the number of twist per unit length or tpi manually.
F. Abrasion resistance:
Abrasion resistance is the ability of a fibre to withstand the rubbing or abrasion it gets in everyday use. This property of yarn plays an important part in its processing e.g. it determines the friction occurring on thread guides. A measurement of abrasion resistance is the number of cycles required to break the test specimen at a given initial tension.
You may also like:
- Effect of Twist on Yarn Strength and Fabric Properties
- Yarn Count Measurement System
- Imperfection Index of Yarns (IPI) | Reasons for Increasing Imperfection Index of Yarn
- Yarn Strength | Measurement of Yarn Unevenness | Types of Yarn Irregularity
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.