Manufacturing of Denim

Manufacturing of Denim
For manufacturing Denim and Grey Fabric, the process is same up to the level of weaving, but in case of Denim Fabric, dyeing is done at the stage of sizing where as for Grey Fabric it depends upon the finished product. The details of each process are given below:
1. Fabric Weaving
a. Grey Yarn on ConesNormally yarns received for weaving in cone forms are either from ring spinning or from open end spinning in single or double fold as required. For weaving, yarn used is categorised into:
o Warp yarn
o Weft yarn
Normally for Weaving, yarn used as warp should be sufficiently strong to withstand stress and strains exerted during weaving operations. Hence they are having Count Strength Product(CSP) and further sized to increase its strength. The weft yarn is directly used on weaving machines and in some cases, if required, is rewound also so as to enhance its performance in weaving.
b. Warping on Sectional/ Direct Warping
The warp yarn is required to be fed into a sheet form to the weaving machines. At warping, the individual cones are put into the creel (the number of cones depends upon fabric construction) and yarn from individual cones is pulled together in sheet form, wound on a barrel called warping beams (for Direct warping) or on weaving beams (for Sectional Warping). Normally if warp sheet is with patterns of different coloured yarns it is processed on sectional warping machine.
c. Sizing of yarn in Set/ Beam to Beam Position
The object of Sizing is to improve the strength of yarn by chemically binding the fibres with each other and also improve upon its friction resistance capacity by chemically coating the surface of yarn/fibres. Further, number of threads in warpers beam sheet is very less against number of threads required in whole width of fabric. Hence multiplication of sheets by drawing yarns together from many warp beams and again making one sheet is also performed on sizing machine. On sizing, normally, 8-12 % size material on warp thread is applied. This improvement in strength and frictional resistance characteristic of warp yarn is essential because during weaving, yarn has to undergo severe strain & stress as well as frictional operations.
d. Drawing–in
Weaving is basically interlacement of two sets i.e. warp and weft threads in desired sequence and pattern. To obtain this interlacement, warp yarn sheet is bifurcated & opened in the form of two layers/ sheet and weft thread is inserted between so opened two warp sheets. This operation is called shedding. to perform shedding the warp yarn needs to be passed through heald eyes of the heald shafts, this operation is called as drawing-in.
e. Beam Gaiting or Knotting on Loom
The drawn weavers beams are fixed on weaving machines, threads are tied and heald shafts are coupled. This operation is called Beam Gaiting. If undrawn warp threads are directly knotted to the threads of finished beams, it is called Knotting. These operations are essential because normally weavers beam can carry only certain length of warp sheet on it and when so woven, whole length is converted to the fabric by weaving machine. Further warp length is required to be fed which can be done by knotting or gaiting other beams on weaving machine.
f. Weaving
As stated earlier, weaving is interlacing two sets of yarn and making fabric. One set is called warp thread which is in sheet form, the other one is called weft thread which is inserted between two layers of warp sheet by means of a suitable carrier i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending upon the type of the weaving machines. The different types of technologies available for weaving machines are briefly explained as below:
o Conventional Shuttle Weaving System by Ordinary Looms or Automatic Looms.
o Shuttle less Weaving System by Airjet /Waterjet/Rapier/Projectile
Shuttle loom is a conventional Technology with much less production on account of slow speed and excessive wear and tear of machinery. This shuttle loom technology has now become obsolete. Denim is woven through Shuttle less Weaving System by using 96 ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile looms. These looms are distinguished by weft insertion method, which is briefly discussed hereunder.
Airjet Looms
These types of looms adopt the latest development in Weaving Technology where weft insertion is done with the help of compressed air. A very high weft insertion rate up to 1800 metre per minute is achieved. Compared to rapier and projectile looms, these looms are less versatile but are economical and are used in mass textile production unit like denim.
Finishing
a. Grey Fabric
The finally woven fabric or Grey Fabric, as it is popularly called, wound on a cloth roll is taken out from weaving machines at certain intervals and checked on inspection machines for possibilities of any weaving fault. If such faults are seen anywhere in fabric during inspection, certain corrective steps are taken at weaving, warping, sizing, etc so that they can be minimised in subsequent product. This is a quality control exercise.
b. Denim Fabric
Denim Fabrics woven of 100% cotton would be very strong and durable.
Traditionally Blue Denim is warp faced cotton fabric with 3 x 1 twill construction with warp being dyed in a solid colour and weft left un-dyed. The look and quality of the Denim Fabric shall improve after dyeing, the process of which differs from plant to plant. Normally the process of dyeing dictates the technology of Denim manufacturing.
The dyeing for Denim Fabric happens at the sizing stage. Generally there are two most popular methods of dyeing Denim Fabric. They are:
o Rope Dyeing
o Sheet Dyeing
A company can adopt any of the methods. In countries like India Sheet Dyeing Method is commonly used for manufacture of its Denim Fabrics, which has following advantages over Rope Dyeing Method:
o The technology is less capital intensive.
o The technology is a proven one.
o The cost of production is lower.
o The process time is lower.
o The Sheet Dyeing machines are very easy to operate.

The only defect in Sheet dyeing is that their is a problem of center to selvedge shade variation.
c. Sheet Dyeing Process
This process eliminates a few intermediate processes of the rope dyeing. The yarn sheet is washed with chemicals such as caustic and washing soda and after squeezing the excess water; the yarn sheet is allowed to pass through Dyeing Troughs one time for oxidation and development of dye on yarn. After dyeing, the dyed yarn is washed again with fresh water for two-three times and finalIy squeezed before allowing it to pass through six drying cylinders. The dyed yarn enters the starching device and sizing is done. After sizing, the sized warp beam goes for weaving. After weaving, the woven Denim Fabrics goes for various finishing processes consisting of brushing, singeing, washing, impregnation for dressing and drying. Brushing and singeing should eliminate impurities and help to even the surface of the fabric. Dressing regulates the hand and rigidity of the fabric while compressive shrinking regulates its dimensional stability.
Even today Denim Fabric without Indigo Dyeing is not called authentic Denim. Initially when Denim Fabric entered the fashion market, Denim manufacturers were using Natural Indigo Dye, which was costly and giving a natural finish. Though Synthetic Indigo Dye has gradually replaced Natural Indigo Dye, some unorganised manufacturers still prefer the latter and attract premium after branding them “Natural Dye Used”.
d. Making-Up
Weaving of fabrics on such multi sizes is not economical, hence a standard width fabrics is then sent to making up. Fabrics are cut into the desired width as per size required on this machine. Denim Fabric and Grey Fabric are thoroughly checked for various types of defects such as:
o Weaving Defects
· Uneven Dyeing
o Bleaching and Dyeing Defect
o Oil Stain
o Patches
Here the final product is categorised quality-wise. The products then found okay are segregated and sent to packaging department whereas defective ones are sent for correction. After inspection, the sets are wrapped with polythene covers and sent for despatch as per buyer’s specifications.
Despatch
Rolls and sets so formed and packed as per buyers’ requirements are then sent for final despatches.

Properties of Viscose Rayon

Properties of Viscose Rayon

Moisture Absorption

It absorbs more moisture than cotton. Moisture Content of Coton is 6% at 70 deg F and 65% RH, and for Viscose Rayon it is 13% under the same conditions.

Tensile Strength

The Tensile Strength of the fibre is less when the fibre is wet than when dry. It is 1.5-2.4 gpd in the dry state and 0.7-1.2 gpd in the wet state. For high tenacity variety the values are 3-4.6 gpd and 1.9 to 3.0 gpd.

Elasticity

The elasticity of Viscose Rayon is less than 2-3%. This is very important in handling viscose yarns during weaving, stentering etc when sudden tensions are applied.

Elongation at Break

Ordinary Viscose rayon has 15-30% elongation at break, whule high tenacity rayon has only 9-17% elongation at break.

Density

The density of Viscose rayon is 1.53 g/cc. Rayon filaments are available in three densities: 1.5, 3.0 and 4.5

Action of Heat and Light

At 300 deg F or more, VR loses its strength and begins to decompose at 350-400 deg F. Prolonged exposure to sunlight also weakens the fibre due to moisture and ultraviolet light of the sunlight.

Chemical Properties

Viscose rayon consists of cellulose of lower DP than cotton cellulose. Also amorphous region of Viscose rayon is present to a greater extent, therefore, Viscose rayon reacts faster than cotton with chemicals. Acids like H2SO4 HCL breaks the cellulose to hydrocellulose. Oxidising agents like Na(OCl)2, Bleaching powder, K2Cr2O7, KMnO4- form oxycellulose. Cold acid solutions for a short time do not attack viscose rayon.

Action of Solvents

Textile solvents can be used on Viscose rayon without any deteriorating effect. Viscose rayon dissolves in cuprammonium hydroxide solution.

Effect of Iron

Contact with iron in the form of ferrous hydroxide weakens viscose rayon yarns. Therefore staining, marking or touching of rayon to iron or iron surface should be avoided.

Action of Microorganisms

Microorganisms ( moulds, mildew, fungus, bacteria) affect the colour, strength, dyeing properties and lustre of rayon. Clean and dry viscose rayon is rarely attacked by moulds and mildew.

Longitudinal View

The longitudinal view of these fibres show many striations running parallel to the long axis of the fibre. The cross section of viscose has striated periphery, having many sharp indentations, and cross sectional contours vary from circular and oval to ribbon-like forms.

Textile Softners

Textile Softners

Softness of fabric depends upon several factors, these are:

1.       Composition of the Fiber: The more crystalline region a fiber has, the less soft will be the fabric. Thus viscose is more soft than cotton as it has less crystalline region than cotton.

2.       Softness of Yarn: It depends upon the twist. The higher the twist, the less soft will be the yarn and hence less soft will be the fabric.

3.       Weave: Loose weave give more softness to the fabric than closer weave. Thus a fabric made with satin or twill weave will be more softer than that made with plain weave. 

Chemical softening is done by using chemicals which act as a lubricating agent and permits sliding of the fibers in the fabric. However, washing can eliminate these chemicals. Therefore they are applied during the final stage of the treatment.

The most common type of Chemical Softeners are:

1.       Non Ionic softeners: These are less efficient than anionic or cationic softeners, but they can withstand the effects of hard water. They can also sustain themselves in acid and basic environments and thus are most suitable for normal washing.

2.       Anionic Softeners: These are very good and give the fabric a full hand. However they cannot sustain hard water and acid environment. They can also cause yellowing at certain  temperatures.

3.       Cationic Softeners: They are amongst the best of the softeners. However they can cause dye toning. Also they can affect the color fastness to light.

4.       Silicone Based Softeners: These are insoluble in water and therefore must be applied on the fabric after dissolution in organic solvents. They have good fastness to washing. They create a lubricating film on the surface and give fabric a velvety silky hand.

5.        Reactive Softeners: These products have to be cross linked and provide permanent softness and water repellency.              

Northern University Bangladesh Textile Engineering Department

Northern University Bangladesh Textile Engineering Department

Introduction (Textile Engineering):
The B.Sc in Textile Engineering degree course of the Northern University Bangladesh has been designed for students to acquire sufficient understanding of the principles and techniques of the Textile Science. It will provide students with a coordinated understanding, comprehensive knowledge and expertise in all disciplines of Textile. Lectures along with practical classes, seminars, in-plant training, interactive small group teaching and tutorials will be part of the Bachelor of Textile Engineering Program. Presently the engineers and managers of the industrial concerns are under constant pressure of time, cost and maintaining the quality of products and services. The research and development of a product, its manufacturing and marketing have to be achieved within a short period. Thus engineers are now facing diverse challenges. New generations of engineering graduates are therefore on demand. Besides engineering and technological skills, they must posses leadership and managerial capabilities. ‘Hi-Tech’ is an accurate description of today’s textile industry, with output embracing not only clothing and household items, but also an increasing range of diverse industrial and leisure products. Highly specialized advanced textile materials are rapidly becoming crucial components in a wide range of applications for the emergency services (fire-fighting, air, sea rescue etc.), medical science, civil and mechanical engineering, marine exploration, sport, recreation and aerospace. In fact, textiles are involved in just about every facet of modern life. In today’s rapidly changing fashion scene with seasons measured in weeks rather than in months, a quick response to demand is vital. This has been made possible by the continuing development of new fibers and innovative manufacturing methods. The advent of computerization and microelectronic technology has brought about a second revolution in the textile industry, introducing sophisticated high speed manufacturing systems capable of keeping pace with rapidly evolving world markets. There are in addition, many special applications of textiles, which stem from the heightened public awareness of environmental factors. Textile products, made at low energy cost from renewable resources are now making a considerable impact around the world, combating soil erosion by substrate stabilization, providing communication infrastructure in remote areas and supporting irrigation systems in developing countries

Bangladesh Textile Mills Corporation

Bangladesh Textile Mills Corporation was brought into existence on March 26, 1972 with the promulgation of the Bangladesh Industrial Enterprises (Nationalization) Order, 1972 (President’s Order No.27 of 1972 ) and started its formal function from July, 1972.

hs shutle loom

The general direction and administration of the affairs and business of the Corporation are vested in a Board of Directors. The exact administrative approach of the Corporation towards the enterprises placed under it and the range of functions to be performed by the corporation are contingent upon the policies perused by the Government.However, Article 17of the Nationalization Order sets the general tone in the following words

" It shall be the function of a Corporation to control, supervise and co-ordinate, subject to any regulation made in this behalf, the activities, business and affairs of the scheduled industrial enterprises placed under it by clause ( i ) of Article 10 or, as the case may be, the industrial enterprises placed under it by an order under that clause, and to establish and develop new industrial enterprises within their respective fields. The corporation shall, in respect of any scheduled industrial enterprise, (or as the case may be, the industrial enterprises placed under it) also exercise such of the power of the Government as the Government may be notification in the official Gazette delegate to the Corporation." The role of BTMC within Bangladesh Textile Industry has been substantially altered since denationalization of large number of public sector textile mills that took place over the last 30 years. Prior to denationalization, BTMC enjoyed nearly monopoly within the yarn and cloth market of Bangladesh and there was no competitive source for the yarn product of BTMC. Consequently the Corporation was an alert to dispose of its entire output to the domestic market. Since demand for the domestically manufactured cloth products was such that BTMC lacked the capacity to supply yarn requirement of the industry. As a result of the denationalization the market situation has changed dramatically. At present 18 Textile Mills (22 units) of which 6 Textile Mills (8 units) are in operation under service charge system and producing different counts of Cotton yarn/Polyester yarn in the form of 32/1 to 80/1. Another 11 mills are under process in operation, and 1 mill earmarked for setting up textile palli. Service Charges System in the mills has been introduced on contract basis. In this system contracted parties supply of Raw Materials to respective mills at their own cost. BTMC mills produces different counts of yarn/woolen fabrics within the available technical facilities prevailing in the mills as per requirement of the parties. The mills get only a certain rate of service charge per bale from the parties. The responsibility of the marketing of finished products lies with the parties Among the 18 mills, The Valika Woolen mills Ltd., Nasirabad, Chittagong is only specialized mills under BTMC, producing knitting wool, woolen suiting, Gents & Ladies woolen Shwal & woolen blanket. Most of the buyers of finished product of this mills are Govt. , Semi Govt. & Autonomous bodies of the country. Biman Bangladesh Airlines are the main buyers of the woolen Blanket.