Yarn Construction

Introduction-

Yarns are composed of textile fibers. A yarn can either be a spun yarn (from staple fibers) or a filament yarn (from filament fibers).

The different ways in which fibers can be joined together aid in providing the variety of structures that in turn create a wide variety of fabrics.

Yarn is an assemblage of fibers twisted together. A yarn composed of a group of fibers laid in parallel & kept together by twisting.

Yarn Twist-

The fibers & yarns are strengthening by giving them twist.

The spiral deposition of the components of a twist is the measure of the spiral turns given to a yarn in order to hold the constituent fibers or threads together.

The amount of twist is measured by the number of twists given to staple yarns per inch. It is also called (tpi). Low twist is- 0-3tpi

Medium twist is 4-7 tpi

High twist is 8-12tpi

Twist Direction-

The direction of the twist at each stage of manufacture is indicated by the use of letters S or Z in accordance with the following convection:

A single yarn has S twist if, when it is held in the vertical position, the fibers inclined to the axis of the yarn conform in the direction of the slope to the central portion of the letter S.

The yarn has Z twist if the fibers inclined to the axis of yarn conform in the direction of slope to the central portion of the letter Z.

As twist increases, yarn strength and yarn stiffness increase up to a point, level off, then begin to fall at very high twist levels.

Yarns with extremely high levels of twist are called “crepe yarns”. Crepe yarns, have a high tpi (turns per inch).

Yarn Number/ Yarn count-

A measure of the fineness or size of a yarn expressed either as ‘mass per unit length' Or length per unit mass depending upon the yarn numbering system used.

This relation indicates the thickness of the yarn.

Yarn Formation-

The following are the main steps for natural fibers (making yarn from staple fibers) - Ring spinning

Opening/Blending-

Opening is necessary in order to loosen hard lumps of fibers & disentangle them.

Cleaning is required to remove trash –The fibers must be sorted ,based on grade, cleaned to remove particles of dirt, twigs, and leaves, and blended with fibers from different bales to improve the consistency of the fiber mix.

Blending is necessary to obtain uniformity of fiber quality.

Sorting and cleaning is performed in machines known as openers.

Carding-

To better align the fibers into thin, parallel sheets to prepare them for spinning.

The sheet of carded fibers is removed through a funnel into a loose rope like strand called a sliver.

Combing-

In this operation, fine-toothed combs continue straightening the fibers until they are arranged with such high degree of parallelism that the short fibers called ‘noils’ are combed out and completely separated.

Several card slivers are fed to the combing machine and removed as a finer, cleaner, and more aligned comb sliver.

Drawing –

Several slivers are combined into a continuous, rope like strand and fed to a machine known as a drawing frame.

This action pulls the staple lengthwise over each other, thereby producing longer & thinner slivers.

During drawing, slivers from different types of fibers (e.g., cotton and polyester) may be combined to form blends. Once a sliver has been drawn, it is termed a roving.

Roving-

Roving is the final product of several drawing out-operation.

These bobbins are placed on the roving frame, where further drawing out and twisting take place until the stock is about the diameter of a pencil lead. To this point, only enough twist has been given to hold the fibers together.

Spinning-

The ring spinning frame completes the manufacture of yarn. Ring Spinning draws; twist & winds in one continuous process.

Man Made Fiber Formation-

Man-made fibers are polymeric forms that are produced by some type of chemical or by the regeneration & natural polymers in a new physical form.

The liquid polymer is extruded through a spinneret. Each spinneret has a number of holes, and each hole produces one filament.

As they exit the spinneret the filament fibers are solidified by cooling of melted polymers, by evaporating the solvent, or by precipitating the polymer from solution.

Most spinnerets are made with round openings, some may use other shape is order to produce fiber with special characteristics.

Chemical Spinning’s to convert Synthetic Fibers into Yarns-

Wet Spinning.

Melt Spinning.

Dry Spinning.

Note- Prepare Assignment on Chemical Spinning.