Yarn Quality Parameters for Knitting

Yarn Quality Parameters for Knitting

Yarn Quality Parameters for Knitting

Yarn Quality Parameters: 

For the best knitting we have to choose the best yarn or ideal yarn for knitting to fault free fabric or quality full fabric. So we have to careful about the yarn properties or for ideal yarn. The following yarn properties should have to be said textile yarn as a ideal yarn-

• The yarn in circular in cross-section and is uniform along its length.
• Yarn is composed of concentric layers of different radial.
• Each fiber follows a uniform helical path around one of the concentric cylinder so that its distance from yarn axis remains constant.
• A fiber at the centre will follow a straight line of the axis.
• The axis of circular cylinders coir sides with yarn axis.
• The number of filaments or fibers crossing the unit area is constant; that is the density of packing. Fibers in the yarn are constant throughout the model.
• Every filament in the yarn will have the same amount of twist per unit length.
• The yarn consists of very large number of filaments.

If the above mentioned yarn properties is absent on any yarn than the yarn should not be allowed on knitting to make fabric. Because it will not be able to give you perfect knitting where the yarn’s parameter is mandatory to be maintained.

Yarn quality requirements for knitting such as

• Evenness,
• Yarn Count
• Breaking strength,
• Elongation,
• Twist,
• Moisture contents,
• Yarn winding,
• Yarn lubrication,
• Yarn hairiness.

Yarn evenness: 

Yarn evenness is a measure of the level of variation in yarn linear density or mass per unit length of yarn. In other words, it refers to the variation in yarn count along its length. It is the evenness of staple spun yarn that is of concern here. Continuously filament yarns have virtually no variation in linear density so evenness is not an issue for those yarns. A yarn with poor evenness will have thick and thin places along yarn length, while an even yarn will have little variation in mass or thickness along length. While a yarn may vary in many properties, evenness is the most important quality aspect of a yarn, because variations in other yarn properties are often a direct result of yarn count irregularity. We already know that twist tends to accumulate in the thin places in yarn, so irregularity in yarn linear density will cause variations in twist along yarn length. This preferential concentration of twist in thin places along a yarn also exacerbates the variations in yarn diameter or thickness, which often adversely affects the appearance of the resultant fabrics. An irregular yarn will also vary in strength along the yarn. 

Yarn counts (tex) and twist (turns/cm): 

The responsibility for the accuracy of the yarn count and the tolerance levels for variation in yarn count and twist (turns/cm), as well as the type and level of lubricant/finish, lie with the spinner and are normally declared in the terms and conditions of sale. For highly critical end-uses such as military items and technical textiles, special yarn quality specifications and variability limits will be required and must be negotiated with the spinner. 

Selection of suitable yarn count should be based on:

Machine gauge, Yarn Tex = {100/G}2

Machine types which are having varied needle strength hook sizes and dial and cylinder distances

. 

Knitted structures which are produced with from one feeder (Plain, rib etc.,) to 3 or 4 feeders (blister and multicolor jacquards). More number of needles/inch necessitates the use of finer counts.

Breaking Strength & Elongation of Yarn:

Tensile property of textile yarns is a prime important parameter in determining the suitability for any particular application. It is therefore of utmost importance to determine this characteristic accurately. There are three basic principles for measuring yarn tensile strength. But for measuring single yarn tensile strength mainly constant rate of extension (CRE) and constant rate of loading (CRL) principles are used. A single yarn shows two different results of breaking load and elongation value in these two methods due to the difference in measuring system.

Winding: 

Winding, which is the transfer of the yarn from the primary or 'spinners' package to a secondary conical package (cone) more suitable for weft knitting, provides an opportunity to monitor the yarn electronically for a number of faults, including:

• Knots
• Thin places
• Slubs or thick places
• Weak places

The tension employed in winding causes weak places to break and results in knots. Slubs and thin places are cut out by the electronic clearer and also replaced by knots. All knots, including those generated by the clearing process, are placed on the nose of the cone where they may be counted prior to packing. An agreed maximum limit of knots per cone will be set and any cone that exceeds this limit will be rejected. 

Yarn lubrication: 

The type and level of yarn lubrication determine the coefficient of friction of the yarn. In weft knitting in particular, the coefficient of friction is a key factor in determining the quality of the knitted product as it has a direct influence on the peak yarn tension in the knitting zone and thus on the number of yarn breakages, as well as the extent to which dropped stitches will ladder. 

Objectives of yarn lubrication 

• The main aim of yarn lubrication is to reduce yarn friction. Added advantages include:
• Reduced abrasion effects on guide surfaces and needles - this is important with hard synthetics (PA, PE)
• Dissipation of static charges - this is important with 100% synthetic yarns
• Better cohesion of the filaments
• Improved yarn pliability. Due to lubrication, yarn becomes softer and more pliable offering less resistance to the loop formation 

Yarn Hairiness:

Fibres protruding out from the main body of the yarn are called hairiness. The number of hairs exceeding 3mm in length as a percentage of the total number of hairs is found to be linearly related to the count of the yarn, i.e. there are more hairs in a fine yarn than a coarse one of the same type.