Handbook of value addition processes for fabrics (2024)

73 Handbook of value addition processes for fabricsSố trang: 469 trangNgôn ngữ: English--------------------------------------- The purpose of this book is mainly to guide new entrants in the textile field who would like to supervise and manage the various processes involved. Chemicals and chemical reactions are not discussed however, as the process parameters and chemicals used vary and this needs to be decided by senior technical personnel. This book does however give general guidelines that are applicable for all and which can be used as a guide for training technical staff. It is not possible to list all the value addition processes practiced worldwide in one book, and hence, an attempt is made to collect details of some of the commonly practiced value addition processes, especially for apparel purposes. The functional treatments given for various technical textiles like medical textiles, protective textiles, industrial textiles, agrotech materials, geotextiles, and sport tech, etc are not covered in this book.This book is aimed mainly to guide the new entrants in the textile field, who would like to supervise the processes and manage them. The chemicals and chemical reactions are not discussed in this book as the process parameters and the chemicals used vary depending on the processes which needs to be decided by the senior technical person in the section considering the fabric in use, the effect required, the machinery and chemicals available. This book gives general guidelines that are applicable for all which can be used as a guide for training technical staff. It is not possible to list all the value addition processes practiced world over in one book, and hence, an attempt is made to collect details of some of the commonly practiced value addition processes, especially for apparel purposes. The functional treatments given for various technical textiles like medical textiles, protective textiles, industrial textiles, aggrotech materials, geotextiles, and sport tech and so on are not covered in this book.

Handbook of Value Addition Processes for Fabrics

B Purushothama

New Delhi, India

Daryaganj, New Delhi - 110002, Indiawww.woodheadpublishingindia.com

First published 2018, Woodhead Publishing India Pvt Ltd.© Woodhead Publishing India Pvt Ltd., 2018

This book contains information obtained from authentic and highly regarded sources Reprinted material is quoted with permission Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book.

Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfi lming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing India Pvt Ltd The consent of Woodhead Publishing India Pvt Ltd does not extend to copying for general distribution, for promotion, for creating new works, or for resale Specifi c permission must be obtained in writing from Woodhead Publishing India Pvt Ltd for such copying.

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Woodhead Publishing India Pvt Ltd ISBN: 978-93-85059-44-5

Woodhead Publishing India Pvt Ltd Master E-ISBN: 978-93-85059-92-6

Preface xxiii

1 Value addition processes and pretreatment 1

1.1 Various value additions done on fabrics 11.1.1 Grey fabric inspection 4

1.3 Machinery for textile value addition processes 9

2.2 Purpose of singeing the fabrics 14

2.3 Purpose of desizing 142.4 What singeing should and should not do? 15

singeing and desizing machine (example—Osthoff

singeing cum desizing machine) 182.8 Precautions to be taken for singeing and desizing 202.9 Control points and checkpoints 20

2.12 Responsibilities and authorities of supervisor in

Contents vii

3.2.4 Signifi cance of different steps in kier boiling cycle 313.2.5 Precautions to be taken for kier boiling 313.2.6 Control points and checkpoints for kier boiling 323.2.7 Normal problems in kier boiling 343.2.8 Dos and don’ts for kier boiling 353.2.9 Responsibilities and authorities of

supervisor in kier boiling 363.3 Continuous scouring using J-box 37

4.1 Mercerization purpose and systems 474.2 Chain mercerizing using caustic soda 484.2.1 What chain mercerization should and should not do? 494.2.2 Quality of mercerizing 494.2.3 General activities in fabric mercerizing

4.2.4 Typical operating procedure of a chain

mercerizing machine using caustic soda 514.2.5 Precautions to be taken for mercerizing

4.2.6 Control points and checkpoints in chain

mercerizing using caustic soda 584.2.7 Dos and don’ts for chain mercerizing using

4.3 Liquid ammonia (LA) mercerizing of cellulose fi bres 62

4.3.1 Benefi ts of LA mercerizing 634.3.2 Standard operating procedure for LA mercerizing 664.3.3 Dos and Don’ts for LA mercerizing 674.3.4 Normal problems in fabric mercerizing 684.4 Responsibilities and authorities of supervisor in mercerizing 68

6.5.1 What jigger should and should not do? 866.5.2 Dyeing process using a jigger 866.5.3 The factors controlling the rate of dye

absorption in jigger dyeing 876.5.4 Typical operating procedure of dyeing on a jigger 876.5.5 Some typical problems that may be

encountered in jig machines 896.5.6 Precautions to be taken for jigger dyeing 906.5.7 Control points and checkpoints 906.5.8 Limitations of jigger 926.5.9 Dos and Don’ts for jigger dyeing 936.5.10 Responsibilities and authorities of

supervisor in jigger dyeing 936.6 Continuous dyeing system 946.6.1 Problems in continuous dyeing 100

7.4.1 Overfl ow dyeing machine 1047.4.2 Soft fl ow dyeing machine 1067.4.3 Airfl ow dyeing machine 1107.5 Process steps in jet dyeing 1127.6 Control points and checkpoints 1137.7 Normal Problems in Jet Dyeing 115

8.2 Principle of operation 1188.3 Various activities that can be done using airfl ow machines 1218.4 Typical work procedure for softening cotton fabrics 1238.5 Control points and checkpoints 124

Contents xi

9.8.1 Drying of hanks using hot air chamber 135

9.10 Radio Frequency Drying (RFD) 136

11 Radio frequency dryers 163

11.1 What is radio frequency (RF) drying 16311.2 Advantages of RF drying 165

11.6 Typical working procedure 171

13.6 Control points and checkpoints 191Control points

15.6 Process recommendation for 100% polyester processing using jet dyeing machine for weight

reduction (as recommended by Rossari) 208

19.4 Decatizing machines 25819.4.1 Kier decatizing 25919.4.2 Continuous decatizing 26019.4.3 Finish decatizing 26219.5 Some commercially available decatizing machines 262

19.5.1 KD Minimat HQ model manufactured by

Biella Shrunk Process (Italy) 26219.5.2 KD Gigante—machine for ‘KD’ permanent

fi nishing and for atmospheric decatizing 26319.5.3 Thermo Duplex 90—continuous decatizing

Contents xvii

21.1 Purpose and concepts 28121.2 Principle of operation 28121.2.1 Main characteristics of ‘KD Suprema 95’ 28221.2.2 Technical characteristics 28321.3 Typical operating procedure 28521.4 Control points and checkpoints 28921.4.1 Control points 289

23 Calendering of fabrics 315

23.1 What is calendering? 31523.2 Objectives of calendering 31623.3 Components of calendering machine 31623.4 Different types of calendering 317

press calendering machine 32423.4.7 Friction calender 32423.5 Typical working procedure for a friction calender 32524.5.1 Terminating the production of calender machine 32623.6 Control points and checkpoints 32723.6.1 Control points 327

(high-density printing process) 33324.2.4 Sequence of discharge printing process on

cotton: discharge printing style 333

25 Digital printing of textile fabrics 353

25.6 Digital printing solutions 37525.7 Problems/limitations associated with digital printing 376

26.1 Evolution of garment washing techniques 37726.2 Types of garment washing 378

26.4 Objects of garment washing 38026.5 Advantages of garment washing 38126.6 Different washing methods 381

27.11 Folding 41027.11.1 Fabric inspection and roll folding 410

28.10.1 Problems with reactive dyes 43728.10.2 Problems in dyeing with direct dyes 43828.10.3 Problems in sulphur dyeing 44028.10.4 Problems in dyeing with vat dyes 44028.11 Factors affecting dyeing performance 44428.11.1 Reproducibility and right-fi rst-time dyeing 44428.12 Factors affecting dye selection and evaluation 448

Fabrics taken out at loom state cannot fetch good price as they are not attractive and do not have a good hand Also, they are not suitable for wearing or for any kind of use at all.

The size present in the fabrics need to be removed (desized), if sized, and the impurities in the materials are to be removed by treatments such as scouring and various treatments such as bleaching, dyeing, printing and different fi nishes are to be given In a number of processes, chemicals are involved and; hence, people call these processes as chemical processing of textiles As water is invariably used in number of processes, these processes are also termed as wet processes There are a number of processes which neither use chemicals nor water and; hence, the terms chemical processing or wet processing might not suit all the time All these processes add value to the fabric and; hence, term ‘value addition processes’ is more appropriate.

It is not possible to list all the value addition processes practiced in the world in one book In this book, an attempt is made to collect details of some of the commonly practiced value addition processes, especially for apparel purposes The functional treatments given for various technical textiles like medical textiles, protective textiles, industrial textiles, aggrotech materials, geotextiles and sport tech, etc are not covered in this book.

This book has aimed mainly to guide the new entrants in the textile fi eld, who would like to supervise the processes and manage them The process parameters and the chemicals used vary depending on the processes that need to be decided by the senior technical person in the section considering the fabric in use, the effect required, the machinery and chemicals available Therefore, the chemicals and chemical reactions are not discussed in this book This book gives general guidelines that are applicable for all This book can be used as a guide for training technical staff.

I hope the readers shall get a fair idea by which they can start their career.B Purushothama

Value addition processes and pretreatment

1.1 Various value additions done on fabrics

The fabric coming from the loo m does not have properties such as absorbency, softness and so forth, and the appearance of the fabric is dirty or pale yellow They are not undesirable and cannot be used directly for making apparels or clothing Therefore, it is necessary to follow some processing of the material to make it wearable These processes add value to the fabrics and; hence, are

referred as value addition processes.

There are innumerable value addition processes in textile industry The purposes are different for each value addition process They are all done as per the requirement of the customers Although the value addition processes done on fabrics have different purposes and the processes, they can be broadly grouped as follows:

Pretreatments • Singeing• DesizingScouring/

• Kier boiling• Bleaching• Mercerizing

• Scouring and milling of wool fabrics• Rotary drum washing

Dyeing • Padding process• Jigger dyeing• Jet dyeing

Drying • Drying ranges—cylinder drying• Hot-air drying.

• Air-fl ow processing of fabrics• Hot-air stenters

• Radio frequency dryers• Relax dryers

2 Handbook of Value Addition Processes for Fabrics

Shrink-proof fi nishing

• Suprema KD Biella• Formula-1, KD Biella• Sanforizing

• Zero–zero fi nish• Comfi t

• Steam relaxing• Jet air

• Relax shrinkingSpecial

• Emboss printing—pub printing• Glitter printing

• Inkjet printingPrinting

• Block printing• Burnout printing• Blotch printing• Digital printing• Duplex printing• Engraved roller printing• Electrostatic printing• Flock printing• Inkjet printing• Jet spray printing• Photo printing• Photographic printing

• Screen printing—fl at screen• Rotary screen printing• Stencil printing• Spray printing• Transfer printing• Warp printing

• Special methods—tie and dye, Batik printing, space dyeingGarment

• Wet process/chemical process

• Normal wash/garment wash/rinse wash• Pigment wash

• Caustic wash• Enzyme wash

• Stonewash with or without bleach• Stone enzyme wash

• Tinting (tie) and overdyeing (dip dyeing)• Super-white wash

• Bleach wash• Acid wash• Silicon wash• Soft wash• Whitening• Metal wash

Dry process/mechanical process• Sandblasting

• Hand scraping• Overall wrinkles• Permanent wrinkle• Broken and tagging• Grinding and destroy

• PP spray, PP sponging and so forth.

It is practically impossible to list all the value addition processes practiced worldwide We shall be discussing some of the processes, especially those used for apparel purposes There are a number of value addition processes for garments normally referred as garment washing, which are discussed in brief.

The value addition processes for fabrics to be used for apparels are arranged as per the requirement of the customers A general fl ow chart shall be as follows.

4 Handbook of Value Addition Processes for Fabrics

Grey fabric inspectionDelivery

ScouringBleachingSewing or stitchingFinal inspection

After manufacturing of grey fabric on loom, it is inspected using an inspection table During this inspection, defects such as knots, broken and loose warp ends, broken weft ends are removed In case of holes, either it is mended or the fabric is cut off depending on the position of the hole and its severity.

Figure 1.1 Batch inspection machine.

1.1.2 Batching

Batching is the receiving section of grey fabric, where the fabrics which should be dyed and processed for a particular lot of a particular order are grouped, assembled together and the length is increased (Fig 1.1) From batching section, the grey fabric is sent to the dyeing section for dyeing.

Flow chart of batching section is given as follows:

Fabric received and stored

Send for bleaching and/or dyeingSupervisor batches the fabric according to

• Type of fabrics (100% cotton, polyester cotton, chief value cotton, etc.)• Emergency

The grey fabric is sent to the dyeing fl oor with a batch card providing details of the fabric rolls, the processes to be carried out and the sales contract against which the process is taking place Records are maintained for the same The criteria for proper batching are:

1 To use maximum capacity of existing dyeing machines.

2 To minimize the washing time or preparation time and machine stoppage time.

3 To keep the number of batches as less as possible for same shade.4 To use a particular machine for dyeing same shade.

6 Handbook of Value Addition Processes for Fabrics

1.1.3 Stitching

Stitching is done of different fabrics of the same variety undergoing same process to increase the length of the fabric, making it suitable for processing It is done by plain sewing machine.

Brushing is done to remove the dirt, dust, loose fi bre and loose ends of the warp and weft threads If brushing is not done, the impurities obstruct the absorption of chemicals in next processes.

The shearing or cropping is the process by which the attached loose ends of the warp and weft thread is removed by cutting by the knives or blades After this, the fabrics undergo singeing process.

In singeing process, the protruding and/or projecting fi bres are removed from the fabrics by burning and/or heating to increase the smoothness of the fabric If required, both sides of the fabric are singed This process is optional.

Desizing is the process in which the sizing materials are removed from the fabric This must be done before other wet processes of bleaching, mercerizing, dyeing, printing or fi nishing are carried out.

The process by which the natural impurities (oil, wax, fat, etc.) and added/external/adventitious impurities (dirt, dust, etc.) are removed from the fabric is called scouring It is done by strong alkali like caustic soda (sodium hydroxide).

bleaching cotton, using hydrogen peroxide (H2O2) is most common In addition to an increase in whiteness, bleaching results in an increase in absorbency, levelness of pretreatment and complete removal of seed husks and trash.

Mercerizing is the process by which the cellulosic materials are treated with highly concentrated sodium hydroxide (NaOH) to impart properties such as strength, absorbency capacity and lustre This process is optional.

Dyeing is the process of colouring fi bres, yarns or fabrics with either natural or synthetic dyes Dyeing imparts beauty to the textile by applying various colours and their shades onto a fabric Dyeing can be done at any stage of the manufacturing of textile such as fi bre, yarn, fabric or a fi nished textile product including garments and apparels The property of colour fastness depends on two factors, selection of proper dye according to the textile material to be dyed and selection of the method for dyeing.

Colour is applied to the fabric by different methods and at different stages of the textile manufacturing process.

• In stock dyeing, the fi re is dyed even before it is spun.

• Top dyeing is the process of dyeing the slivers, that is, the fi bre is dyed at the stage just before the appearance of fi nished yarn This process is more popular in combed wool and in the production of melange yarns.• Yarn dyeing may be done in hank form or in package form The package

dyeing may be done for yarn cheeses or yarn beams.

• Space dyeing consists of dyeing the yarn at intervals along its length.• Piece dyeing consists of dyeing fabrics in small batches according to

the demands for a given colour.

• In solution pigmenting or dope dyeing, the dye is added to the solution before it is extruded through the spinnerets for making synthetic fi laments.

• In garment dyeing, the dye is applied to fi nished products such as apparels and garments.

1.1.13 Printing

Printing is the process for producing a pattern on yarns, warp, fabric or carpet by any of a large number of printing methods The colour or other treating

8 Handbook of Value Addition Processes for Fabricsmaterials, usually in the form of a paste, are deposited onto the fabric which is then usually treated with steam, heat or chemicals for fi xation.

1.1.14 Finishing

There are numbers of fi nishing treatments to give special effects The fi nishing treatments are carried out according to buyer requirements, which are followed by folding, packaging and delivery.

1.2 Pretreatment

Satisfactory preparation of the substrate before any value addition process such as bleaching, dyeing, printing and fi nishing makes major contributions to consistent attainment of the desired end-product quality In order to get the best results, we should conduct right pretreatment right at fi rst instance.

Successful preparation depends on four factors:• The amounts of the various impurities present• The purity of the water supply

• The chemicals used in the various preparation processes• The machinery available for processing of the goods

It is necessary to remove the unwanted materials from the fabric which hinder the value addition processes They may be referred to as impurities from the point of view of value addition processes Let us see the normal unwanted materials in a fabric that hinders value addition processes.

• Cotton impurities and preparation chemicals

• Pectins are polygalacturonic acids and their calcium, magnesium and iron salts

• The inorganic ash containing calcium, magnesium and potassium phosphates and carbonates

• The spin fi nish and knitting oil containing mineral oil and surfactants applied to decrease friction on machinery parts

• Sizing agents, which are fi lm-forming polymers applied to warp yarns before fabric weaving in order to minimize yarn breakage

• Metallic ion contamination, particularly iron and copper, is of serious concern during oxidative bleaching processes

Important factors to select and use of surfactants in preparation are as follows:

• Wetting agents used in the desizing stage must be compatible with the enzyme preparation.

• Detergents selected for scouring must be stable at the temperature and concentrations of alkali and electrolyte required.

• Surfactants added to bleach liquors must be stable at strong oxidizing conditions.

• Residual surfactants which are retaining must not cause problems in subsequent printing or water-repellent fi nishing.

• The cloud point of any non-ionic surfactants used must be high enough to avoid impairing the wetting or detergency performance.

• Surfactants must be low-foaming to avoid risks of pump cavitation in circulating liquor systems and loss of traction in conveyor or roller-bed steamers.

• The viscosity of the surfactant solution should allow satisfactory performance in automatic dosing systems.

The various pretreatments are singeing, desizing, scouring, bleaching, mercerizing for cotton fabrics The degumming is a special pretreatment for natural silk fabrics.

1.3 Machinery for textile value addition processes

Textile machinery used for value addition processes can be classifi ed as batch, semi-continuous and continuous one While semi-continuous and continuous machineries are generally used for textile fabrics, batch machines are available for fi bre, yarn as well as fabrics and garments.

The examples of batch machines used in value addition processes are kiers, jiggers, winch, jet dyeing machine, drum washers, HDHP dyeing machines for yarns and so forth Semi-continuous and continuous machines include chain mercerizing machine, stenters, J box, sanforizing machines and so forth.

The hairs on the grey fabrics produce fuzzy effect when dyed by absorbing more dyes at hairy portions Hence for high-value products, it is suggested to remove the hairs Singeing is the process of removing protruding fi bres from the fabric by burning them out (Fig 2.1).

Figure 2.1 Techniques of singeing.

Singeing and desizing can be done on a single machine or on two different machines depending on the requirement (Fig 2.2).

There are three types of singeing machines available for fabric singeing They are:

a) Plate singeing machineb) Roller singeing machinec) Gas singeing machine

Gas singeing is normally practiced in majority of the mills as fl ames can penetrate the gaps in the fabric and singeing can be more effective.

There are three types of techniques in desizing and four methods of desizing that has been used in wet processing Desizing techniques are different depending on the kind of sizing agent to be removed.

Natural starch, starch ethers, cellulose ethers and polyacrylates are usually used as sizes Economical starch-based formulations are effective for cotton yarns Polyvinyl alcohol is often preferred for sizing polyester/cotton blends Waxy plasticizers may be added to the size mix Considering the sizing chemicals used, the desizing chemicals are to be decided.

Factors to be considered for removing the size are:• Concentration and viscosity of the size formulation• Nature and amount of plasticizer present

• Fabric construction

• Ease of dissolution of the size

• Washing-off procedure and temperature

Singeing machine without desizing (Osthoff)

Singeing cum desizing machine (Osthoff)

Figure 2.2 Singeing machines.

Singeing and desizing of fabrics 13

Desizing involves impregnation of the fabric with the desizing agent, allowing the desizing agent to degrade or solubilize the size material and fi nally to wash out the degradation products The major desizing processes are:

• Enzymatic desizing of starches on cotton fabrics• Oxidative desizing

• Acid desizing

• Removal of water-soluble sizes• Bioscouring

Enzymatic desizing: Enzymatic desizing is the process of degrading starch

size on cotton fabrics using enzymes Enzymes are complex organic, soluble biocatalysts formed by living organisms that catalyze chemical reaction in biological processes Enzymes are quite specifi c in their action on a particular substance A small quantity of enzyme is able to decompose a large quantity of the substance it acts upon Enzymes are usually named by the kind of substance degraded in the reaction it catalyzes.

Amylases are the enzymes that hydrolyze and reduce the molecular weight of amylose and amylopectin molecules in starch, rendering it water soluble enough to be washed off the fabric Amylase enzymes are highly effective catalysts for the hydrolysis of the amylose and amylopectin components of the starch.

Effective enzymatic desizing requires strict control of pH, temperature, water hardness, electrolyte addition and choice of surfactant Normal types are applied for several hours at 65–70°C.

Thermostable hydrolytic enzymes have been introduced, allowing brief dwell times at temperatures up to 120°C Common salt and calcium ions increase the rate of hydrolysis but amylase is deactivated by copper or zinc ions, as well as most anionic surfactants.

There is some interest in the use of pectinases as scouring agents and lignases to degrade the lignin in bast fi bres, but as yet no commercial processes have been developed.

Oxidative desizing: In oxidative desizing, the risk of damage to the cellulose

fi bre is very high, and, hence, its use for desizing is rare Oxidative desizing uses potassium or sodium persulphate or sodium bromite as an oxidizing agent.

Oxidative desizing reduces the number of fabric preparation stages minimizing the overall energy consumption The oxidant can be added to the hot caustic scour liquor and little or no magnesium silicate or organic stabilizer is needed Rapid desizing treatments require more critical control

of alkali and oxidant concentrations Increased oxidant above the quantity necessary for effective desizing and increasing the alkalinity for a given oxidant concentration both tend to increase the degree of chemical damage Persulphate promotes desizing rather than bleaching and requires more critical control of concentration than does hydrogen peroxide.

Acid desizing: Cold solutions of dilute sulphuric or hydrochloric acids are

used to hydrolyze the starch; however, this has the disadvantage as it also affects the cellulose fi bre in cotton fabrics.

Removal of water-soluble sizes: Fabrics containing water-soluble sizes can

be desized by washing using hot water containing wetting agents (surfactants) and a mild alkali The water replaces the size on the outer surface of the fi bre, and get absorbs within the fi bre to remove any fabric residue.

Bioscouring: Bioscouring is a process in which alkali-stable pectinase as

the enzyme is applied to selectively remove pectin and waxes from cotton fi bres By hydrolyzing the pectin material between the waxes and the fi bre surface, the enzyme exposes the waxes to emulsifi cation when the scouring bath temperature exceeds their melting range Bioscouring does not eliminate motes (cottonseed fragments) or the natural colour of the cotton, which can be benefi cial when scouring for a natural look.

2.2 Purpose of singeing the fabrics

The basic purpose of singeing the fabrics is to remove the hairs projecting out of the fabric by burning them out and making the fabric surface smooth This helps in improving lustre of the fabric and also in getting good printing effect The fabrics may be singed either on one side or on both the sides.

Singeing is an optional process It is performed only on the fabrics where the presence of protruding hairs is a hindrance for processing and is not attractive to the customer.

2.3 Purpose of desizing

The size applied during sizing is required only while weaving, and has no function once the fabric is woven The size, if remains in the fabric, does not allow the dyes and chemicals to penetrate inside the fi bres Hence the purpose of desizing is to remove the size applied to the warp yarn and make the fabric suitable for further wet processing such as scouring, bleaching, dyeing, printing and/or fi nishing.

Singeing and desizing of fabrics 15

2.4 What singeing should and should not do?

d) Singeing should not lead to fi re accidents in the factory.

2.5 What desizing should and should not do?

c) Desizing should not result in water pollution.

d) Desizing should not result in uneven patches on fabrics.

2.6 General activities in singeing and desizing offabrics

The general activities in singeing and desizing can be listed as follows Gas singeing operation (Figs 2.4 and 2.5) is considered in the illustration.

a) The fabrics to be singed are opened and prepared so that they can be fed to singeing machine without any hindrances Normally the fabrics are batched and rolled.

b) The fabrics are fed in open width without any slackness or wrinkles Singeing cannot be done in rope form.

c) The cloth is exposed to fl ame from a twin gas burner where the gas comes through the fi lter at a pressure of 100–140 mbar.

d) The ratio of gas to air mixture is maintained at 1:4 The fabric is brushed using special brush roller Different types of brush rollers are developed for different type of fabrics.

e) As the cloth runs at a high speed, only protruding fi bres are burnt out The cloth passes in water after burning to avoid chances of fi re.

Figure 2.4 Gas singeing of fabric.

Singeing and desizing of fabrics 17

f) In singeing cum desizing machine, the singeing is done fi rst followed by desizing The desized materials are wound on the batch, and kept for rotating slowly Minimum 8 h rotation is needed to complete desizing activity (breaking of sizing materials to microfi ne level so that they can be washed off in the next process) and to get the uniform effect so that the further processes give uniform results.

g) There are three different positions to get varied effect of singeing (Fig 2.6).

Figure 2.5 Schematic diagram of singeing machine with desizing attachment.

Delivering on BatchDesizing

UnitSingeing

UnitFeeding

i The singeing fl ame meets the free-guided fabric at right angles as the fabric passes between two guide rollers This position is recommended for materials made of 100% natural fi bres and for blended fabrics which have been thoroughly beaten, with weights over 125 g/m2.

ii The singeing fl ame meets the fabric at right angles as it is bent over a water-cooled roller The choice of this position is recommended for qualities of fabric composed of temperature sensitive fi bres, open-weave blended fabrics and those with weights of less than 125 g/m2.

iii The singeing fl ame passes close to the fabric with the jet direction being at a tangent to the fabric surface This singeing process is recommended for all materials which cannot tolerate direct exposure to fl ame Tangential singeing can also equalize protruding fi bres and repair fi lament breaks However, at present, this facility is not available on our machines.

Figure 2.6 Different positions of fl ame to get different singeing effect.

2.7 Operating instructions for operating a

combinedgas singeing and desizing machine (example—Osthoff singeing cum desizing machine)

Following is a typical operating instruction for working on Osthoff singeing cum desizing machine.

1 Clean the machine with compressed air and wipe with clean cloth before starting

2 Clean the desizing chamber with pressure water3 Clean the brushing units and remove the threads

4 Clean the double jet burners by using the gauge provided with the machine5 Clean the ducting unit and dust collecting airbags once in a shift or

whenever the bag becomes half full6 Clean all the chemical preparation tanks

7 Bring the material to be fed to the machine and keep at the feeding place8 Prepare the desizing recipe as needed Take the required chemicals by

weighing, mix them appropriately and fi ll them in the overhead tank.9 Open the air valve, water supply valve and gas supply valve

10 Following is an example of recipe for desizing• Water—1000 L

• Bactasol PHC 3 g/L• Acetic Acid 1 g/L

Chemicals taken for 5000 Litres

Take 200 Litres of stock Solution in stock tank Heat up to 60˚C, and then fi ll the tank to 1000 Litres

Add Chemicals one by one, while stirring continuously and add 500 Litres of water

Fill half the overhead stock tank with water i.e around 2500 Litres

Fill the water to complete 5000 Litres

Singeing and desizing of fabrics 19

11 Maintain pH at 5.5–6.0 and saturator temperature at 60°C12 Check the pickup per cent of mangles

13 Discuss with process house head and set the parameters such as speed, fl ame intensity, as per the fabric requirement and the intensity of singeing required

14 When singeing is done onto a cooled roller, verify and ensure that inlet and outlet of water is working and water is fl owing smoothly

15 Open the manual gas stop valve and allow the gas16 Ensure that the brush rollers are set properly

17 Start the Mangle motor, brush motor and batcher motor18 Run the machine at the desired speed

19 Take the burner at its positions

20 Check the working of discharge fan and ensure that all smoke and residual fuel are discharged out safely in time

21 While desizing check the pH from lot-to-lot

22 Separate the designs by putting a polythene sheet at the end of each design to prevent colour migration from one design to another23 While taking the processed material out of the machine to the batcher,

put polythene sheet on the fabric

24 Keep the singed and desized material at rotating station (Fig 2.7) as instructed by the supervisor.

25 While working if you fi nd any quality problem in the cloth, inform the superiors immediately

Figure 2.7 Rotating station.