WEAVING OF DENIM FABRIC

WEAVING

INTRODUCTION

The process of producing a fabric by interlacing warp and weft threads is known as weaving. The machine used for weaving is known as weaving machine or loom. Weaving is an art that has been practiced for thousands of years. The earliest application of weaving dates back to the Egyptian civilization. Over the years, both the process as well as the machine has undergone phenomenal changes. As of today, there is a wide range of looms being used, right from the simplest handloom to the most sophisticated loom.

BASIC WEAVE DESIGNS

There are three basic weaves:

1. Plain weave
2. Twill weave
3. Satin Weave

DENIM WEAVING:

Denim is a fabric traditionally woven with what is known as a twill weave. This is simply a weaving pattern that produces parallel diagonal ribs. The weaving process interlaces the warp, which are the length-wise indigo dyed yarn and the filling, which are the natural-colored cross-wise yarn. The warp thread is in the form of sheet. In denim, the warp-faced twill pattern calls for passing the weft yarn over one and under two (1/2), or over one and under three warp (1/3) yarns. Because there are fewer lacings in twills than in plain weaves, the yarns are freer to move when being worn resulting in a fabric that is both flexible and resilient. The weft thread is inserted between two layers of warp sheets by means of a suitable carrier, such as Shuttle, Projectile, Rapier, Air current, Water current, etc. The selection of carrier depends upon the type of weaving machinery used. The two different technologies available for weaving machines are - Conventional Shuttle Weaving System which is done by Ordinary Looms or Automatic Looms; and the Shuttle less Weaving System which is done by Airjet, Waterjet, Rapier, or a Projectile weaving machine. The Conventional Shuttle loom results in lesser production due to slow speed and excessive wear and tear of machinery. As such, now denim is generally woven through Shuttle less Weaving System namely, Airjet looms, rapier looms or projectile looms. The most common twill used for jeans is a 3x1. A 2x1 twill is used in lighter weight denim.
The yarns used in making denim have a very high twist, a process which gives the yarn much greater resistance both to tensile stress and to abrasion.

Typical Denim Constructions, Weaves, and Weights

The classical construction of a bottom weight 14.5-ounce denim is 60-64 warp yarns per inch and 38-42 filling yarns per inch. The number of warp yarns per inch is sometimes referred to as the fabric sley. The weight is influenced by the size of the yarn used, the fabric weave design, and the fabric tightness. Also influencing the fabric weight is the amount of size left on the finished fabric. Other denim fabrics and denim “look-a-likes” may vary in construction from 52 to 70 warp yarns per inch and from 36 to 52 picks per inch. As a rule, denim is woven as 3/1 twill, 2/1 twill, 3/1 broken twill, or 2/2 broken twill. The weights of these finished fabrics can vary between 3.5 and 16.5 ounces per square yard. The weight of the fabric usually determines what the final garment application will be. Numerical notations for different denim designs, such as 3/1, denote what each warp yarn is doing relative to the filling yarns that it is interlacing with. In this case, each warp yarn is going “over” three picks and then “under” one pick. This would be verbally stated as “3 by 1” twill or “3 by 1” denim. At the next end, moving to the right, the same sequence is repeated but advanced up one pick. This advancing upward sequence continues, giving the characteristic twill line. In this case, the twill line is rising to the right, and the fabric is classified as a right- hand twill weave. If the twill line is made to rise to the left, then the design is left-hand twill. Broken twills are designed by breaking up the twill line at different intervals thus keeping it from being in a straight line.

Left Hand Twill:

This refers to the direction that the denim is woven. Left hand twill denim is softer to the touch than right hand twill, and was originally used by Lee denim. Left hand twill is easy to spot, as the weft threads appear to move upward and to the left as opposed to upward and to the right.

Right Hand Twill:

This refers to the direction that the denim is woven. The opposite of Left Hand twill, this weave is much more common, as almost all jeans are woven with right hand twill. The weft (filler) threads will be visible in upward-right diagonal lines on right-hand twill jeans.

Broken Twill:

Instead of the twill running to the right or left, broken twill jeans (traditionally considered the cowboy-preferred denim) contain no distinct direction of weave. The weave is instead alternated right and left - the end effect resembles a random zig-zag. Broken Twill was designed to combat the twisting effect that was a characteristic regular twill (and considered a 'fault' by many at the time). By going on both directions, the tension in the yarns is balanced in Broken Twill.

Non-conventional Denim Fabric Constructions

Indigo-dyed yarns have been woven in plain weaves known as chambray, oxfords, baskets, herringbones, bedford cords, and combinations of 3/1 and 1/3 twills. Jacquard designs and dobby weaves have also been incorporated into denim designs to produce new looks and textures.

Twill Weave

Twill Weave is produced in a stepwise progression of the warp yarn interlacing pattern. The interlacing pattern of each warp yarn starts on a different filling yarn and follows the same formula. These results in the appearance of a diagonal line called twill line in the fabric, which is then characteristic of this design. Depending on the direction of the twill line, the twill weaves are called right-hand or left-hand twills. The sum of the digits in the formula determines the unit cell of the design, which also gives the minimum number of harnesses, requires weaving the design; at least three harnesses are required for a twill weave. Common twill, Steep twill, Reclining twill and Broken twill are the different variations of the twill weave.