Denim Washing

Denim washing is the aesthetic finish given to the denim fabric to enhance the appeal and to provide strength. Much of the appeal of dry denim lies in the fact that with time the fabric will fade in a manner similar to that which artificially distressed denim attempts to replicate. With dry denim, however, such fading is affected by the body of the person who wears the jeans and the activities of their daily life.This creates what many feel to be a more natural, unique look than pre-distressed denim.

HOW DOES WAHING CREATE UNIQUE LOOK?

Washing of the denim cause it to fade which result its unique look. There are at least three fundamental reason that indigo dyed denim washes down to produce lighter and more attractive shades during washing the outer more heavy dyed yarn surfaces loses dyed through abrasion by stones,enzymes and chemical effect.Indigo dye has intrinsic chemical instability to strong oxidizing agent such as chlorine bleach. Some of the undyed fiber in the interior of the yarn migrate to the yarn surface diluting the color of the yarn.

There are two process involved in DENIM WASHING.

1. DRY PROCESS
2. WET PROCESS

Read More

FAULTS IN DENIM PRODUCTION

FALUTS IN MACHINE:

• • Stop motion does not work on creel and on warping drum as a result broken ends are not traceable for knotting.
• • Chain breakages
• • If frictional drum should not be kept in a polished state, then thermal damages occur due to abrasion.
• • Brake could be inefficient.
• • Sprockets are jammed.
• • If comb do not move properly then there is a chance of cutting of comb due to friction with yarn.

FALUTS IN RAW MATERIAL:

• • Neps
• • Long thick places (in case of non slub yarn)
• • Short thick places (in case of non slub yarn)
• • Thin places
• • Weak places
• • Count variation
• • Hairiness

FALUTS IN PRODUCT:

• • Misalignment of yarn sheet if the yarn sheet is not properly adjusted
• • Uneven package density
• • Too soft package winding
• • Package could not be in uniform density

FALUTS IN MACHINE:

• • leakage of steam in drying cylinders
• • wear and tear of rollers if bearing is jammed
• • Improper working of load cell on squeezing roller. Which causes entanglement of warp sheet as pressure is not properly distributed.
• • Faults in dosing system can cause serious problem of shade variation.
• • If the accumulator do not work properly than the machine is stopped.
• • If speed of the machine is kept greater than the yarn` s bearable strength

FALUTS IN RAW MATERIAL:

The main causes of the dye ability variations in yarn are:

• • Immature fibres
• • Dead fibres
• • Vegetable matter or other foreign matter
• • Wrong twist
• • Bad splice
• • Neps
• • Count variations

SIZING FAULTS:

• • pressure rolls do not work properly
• • squeezing rollers do not work properly

WEAVING FAULTS:

• • dropper will not fall
• • sensors do not work properly
• • Problem in electrical panel
• • Problem in electronic card
• • wear and tear of temple
• • if dust comes in nozzles
• • improper working of solenoid valves

Read More

TOPPING & BOTTOMING DURING DENIM DYEING

Topping & Bottoming

Bottoming:

In this case another dye is applied before dyeing with indigo. First the warp sheet is dyed with sulfur and then it is washed and then dyed with indigo.

Topping:

In this case the warp sheet is dyed with indigo in start and then it is washed and then it is dyed with another dye (normally with sulfur).

Bottoming indigo Topping:

In this case the warp sheet is firstly dyed with some dye and then after washing with indigo and then after washing with other dye like sulfur.Washing is done after each bath in order to remove unfixed dye. Dyeing of indigo occurs at low temperature and that of sulfur at high temperature. Firstly the warp sheet is dipped in the dyeing liquor and then airing is done in order to do fixation as indigo and sulfur dyes are in reduced form in liquor than they are oxidized by giving air. Which is necessary because if airing is not proper than immature oxidation occurs. For this purpose an airing zone of about 40 m is provided after each bath. The airing process is also known as dwelling time.

Read More

DENIM DYEING

DENIM DYEING:

The classical jeans were produced out of indigo-dyed Denim fabric. The special character of this fabric only the warp thread is dyed makes it necessary to carry out dyeing in yarn form. The yarns applied for Denim were exclusively produced on ring spinning machines in former times. The development of OE (open end) yarns by applying smaller rotors with a spinning speed of up to 200 m/min - has led to the application of OE rotor yarns both for warp and weft. The yarns applied for weaving must be of high quality: a high fiber for strength, regularity as well as a small part of short-stapled cotton fibers belong to the basic features of the denim yarn. For regular jeans qualities the warp yarns are spun in a fineness of 50 to 90 tex, for the weft yarn the fineness ranges are mainly 75 to 120 tex. If Denim is made out of Tencel or Modal especiallyfor jeans shirts the finenesses are up to 25 tex.
Indigo, sulphur and indanthrene are mainly used in the dyeing process. Two methods are applicable for continuous dyeing with indanthrene dyes: rapid dyeing and vat dyeing. While processing the basic colored denim, reactive dyes are used and fixed with hot caustic soda solution. The dyeing process is mainly influenced by the dyestuff characteristics, dyeing temperature and necessary chemicals used in the process. Indigo dye is the most popular choice as it has good depth of shade and suitable rubbing and washing fastness. When cotton yarn is dyed with indigo, it leaves a ring-dyeing effect, because of which the outer layer of warp yarn is coated with indigo, and the core of the yarn remains undyed. This gives the denim garment a unique ‘faded look’ and a rich blue shade after repeated use and wash. Originally, the warp yarns or ends were put through the dye bath side by side to form a sheet of yarn, which passed continuously through several dye baths, squeeze rollers or airing sequences. However, if there were breaks in the yarn (and there would be, as each yarn had to take the tension of being pulled through these processes virtually on its own),the dyeing process had to be stopped. The yarns would be then mended, or else it would lead to very bad tangling. These stoppages would in turn cause large shade variations, and the yarn breaks would show up as bad faults in the fabric. Now, an infinitely more efficient system has been introduced. Special attention shall be paid here to Indigo, the „king of dyestuffs” since it plays an important role in obtaining the jeans effect. Indigo belongs to the category of water-insoluble dyestuffs. It was first mentioned in a book 13 BC; at that time the name Indian blue indicated the country the color came from. It is said to have been used for dyeing in India and China 2000 years BC already. The Indigo plant is used for preparing Indigo.
Nowadays, yarn dyeing with indigo is done continuously. Here the various dyeing processes with different concentrations of chemicals as well as the subsequent yarn sizing exert an influence on the quality and the appearance of the ready fabric. There are two processes in the practice for continuous dyeing:

• • Rope Dyeing
• • Slasher or Sheet Dyeing

ROPE DYEING

Indigo Rope Dyeing When dyeing according to the rope dyeing or cable dyeing method.350 - 400 warp threads are bound on the ball warper to very thick cables of 10000 - 15000 m length. On the continuous dyeing installation, 12 to 36 cables are led side by side, wetted, dyed and dried after the dyeing process on cylinders and put into cans. Then the cables are dissolved to warps on the long chain beamer. The warps are added to the sizing machine, sized and then led together to warp depending on the total numbers of threads. In practice, this method has proven to be very good through obtaining an optimum indigo dyeing. However it is important that the cables have a constant tension in order to avoid warp stripes. The disadvantage compared to other methods is that yarn breakages do occur more often. Size of the dyeing unit is between 60 - 80 m. Normally, 6 dyeing vats are in use. There are nevertheless variations with 3 to 8 dyeing vats.

SLASHER DYEING

Indigo Sheet or Double Sheet Dyeing (Slasher Dyeing).When dyeing according to the sheet dyeing method, instead of cables the warp threads are fed to the machine parallel next to each other. These are much smaller compared to the rope dyeing machines. Another advantage is that the cables don’t need to be open after dyeing. Moreover, each yarn wets much faster and in this way reduces the dipping and wetting times during dyeing. All in all, each thread has a larger surface compared to a dyeing cable and this requires somewhat more hydrosulphite to prevent a premature oxidation of the indigo. Whereas during rope and sheet dyeing the yarns are always led in succession to the dyeing baths, the fabric of the loop dye method is led several times through the same dyeing bath. The machine is then much shorter and the hydrosulphite consumption is lower. Depending on the number of dyed passages and the concentration of indigo in the dyeing vats, different dyeings of the yarn.

WORKING PRINCIPLE OF SLASHER

Warp beams are brought to the dyeing and sizing section in sheet form as per requirement. The warp sheet is taken to wetting tank (like mercerize, semi mercerize and causticize tanks depends upon the dyeing methods) which swells the fiber and increases its dye uptake. It is then taken to a hot washing tank whose temperature is maintained at 850C. It is then taken to cold washing tank whose temperature is maintained at 600C.
Warp sheet is then taken to dyeing tanks where dye is reduced to soluble leuco form by using sodium hydrosulfite, yarn is then contacted with the reduced dye, and the dye is adsorbed by the fibers. The fixed leuco indigo in the yarns of the warp sheet was oxidized to form pigment during transport of the warp sheet in the air space following the dwelling chamber, taking approximately 60 seconds. It is taken to two hot washing tanks for fixation. Following rinsing, warp sheet is dried on cylinders dryers prior to the application of sizing agent.

OXIDATION REACTION

Na2S2O4 + O2 + 2NaOH → Na2SO4 + Na2SO3 + H2O + C16H10O2N2Na2 + . O2 + H2O + Sodium Hydrosulfide C16H10O2N2 + 2NaOH

OXIDIZED INDIGO

During the slashing process, the sheet of yarns is passed through the size box which contains the hot water solution or mixtures of sizing agents. The yarns pick up the required quantity of size solution in the size box, excess size is squeezed off as the yarns pass through squeeze rolls. After the size box, the yarns go through the dryer section. The wet yarns are dried by using drying cylinders. Cylinder drying is done using steam heated hot rolls. The Teflon coating is done on all the cylinders to prevent sticking of yarns. Accumulator stores 150 meters of warp sheet. Due to the nature of sizing, the yarns in the sheet may be stuck together at the exit of the dryer section. They are separated into individual sheets by leasing rods and individual ends of yarns are separated by passing through comb then the yarns are wound on to a loom beam for weaving.

Read More

SHEDDING SYSTEM

SHEDDING SYSTEM

There are four shedding systems used to provide manipulation to the warp yarns:

1. Crank Shedding
2. Cam Shedding
3. Dobby Shedding
4. Jacquard Shedding

CRANK SHEDDING:

This is the simplest shedding system. In this system, the crankshaft of the weaving machine provides the harness motion. This system is used only for plain weave and its derivatives.

CAM SHEDDING:

A typical cam system can handle weave patterns with up to 14 different harnesses. Cam shedding mechanisms are relatively simple. A pair of cams is sufficient to weave plain fabric. A cam is a disk that transforms a rotational motion of its own to a reciprocating motion of a follower. The transfer is done by means of the cam’s edge or a groove cut in its surface.

DOBBY SHEDDING:

Dobby mechanisms are more complicated than cam systems. They are normally built to control up to 30 harnesses. Picks per repeat are virtually unlimited in dobby. Basically there are two separate functions in dobby mechanism: 1) power transmission, 2)connection and disconnection of the harnesses from the power source at the proper time. Dobby mechanisms are classified as negative, positive and rotary dobby. They can be mechanical or electronic.

JACQUARD SHEDDING:

Jacquard Shedding offers unlimited patterning possibilities. The Jacquard machines offer the highest level of warp yarn control. This versatility is due to the separate control of each warp end or groups of similarly interlacing warp ends within the pattern repeat across the fabric width. They enable the most sophisticated patterns, such as pictures, to be produced in the woven fabrics. Jacquard machines can be mechanical or electronic with single lift or double lift mechanisms; the new machines are all double lift. Most Jacquards heads generally are equipped to handle over 2000 harness cords or hooks with pattern repeating on about on about 9000 picks and multiple heads can be employed over a single weaving machine to increase the weave pattern capability. Jacquard systems are placed on top of the weaving machine.

Read More

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.

Read More

SIZING BEFORE DENIM WEAVING

SIZING

Although the quality and characteristics of the warp yarns coming out of the winding, warping and dyeing processes are quite good, they are still not good enough for the weaving process for most of the yarns. The weaving process requires the warp yarns to be strong, smooth and elastic or extensible to certain degree. To achieve these properties on the warp yarns, a protective coating of polymeric film forming agent (size) is applied to the warp yarns prior to weaving; this process is called slashing or sizing. The main purposes of slashing are as follows:

1. To increase the strength of the yarns
2. To reduce the yarn hairiness that would cause problems in weaving process
3. To increase the abrasion resistance of the yarn against other yarns and various machine elements
4. To reduce fluff and fly during the weaving process for high speed weaving machines.

One sizing tank is provided after the drying zone. The capacity of the size box is about 400 liters. Sizing material is provided automatically by dosing system or it can be manually added.

DRYING ZONE

After the size box the yarns go through the dryer section. The wet yarns are dried by using cylinder drying. Cylinder drying is done using steam heated hot rolls called the drying cylinders. The cylinders are coated with Teflon to prevent sticking of the yarns on the cylinders. The drying zone contains 14 cylinders.

ACCUMULATOR:

Accumulator is also known as compensators. After drying two accumulators are provided on the machine. Whose function is to minimize chance of stoppage of machine because of the change of beam on the head stock and insertion of rods in the leasing zone they accumulate the extra warp when the speed is reduced from the headstock by moving assembly to upward direction. When the head stock is moved with a greater speed the excess warp is removes from the accumulator.

LEASING ZONE

Due to the nature of sizing, the yarns in the sheet may be stuck together at the exit of dryer section. Therefore they are separated into individual ends using leasing rods. The individual sheets of yarns from each section beam are separated.

EXPANSION COMB

Pins in the expansion comb separate the yarns within each sheet. With the expansion comb the warps are spread according to the required width of the weaver’s beam.

BEAMING

The yarns are wound on to weaver’s beam at the headstock. Maximum beam width of 4000 mm can be used, usually 3600 mm is used. A pressing roller is pressing the warp yarn for uniform tension winding. A guide roller guides the yarns to the weaver’s beam. A pressing roller is pressing the warp yarn for uniform tension winding. A machine speed of 100-110 m/min. is used.

TRANSPORTATION OF BEAMS:

After the winding of dyed warp beams the from the head stock the samples of the yarn are taken to laboratory for testing and then it is transported to the weaving department.

Read More