process control in wet processing

Process Control in Wet Processing

Process Control in Wet Processing

1.Introduction

The introduction of comprehensive process control techniques in the textile industry is a comparatively recent phenomenon. The concept of process control measures in the local textile industry is catching up very fast for the two main reasons, namely, growing competition and increasing cost of production. Today, a textile manufacturer is faced with stiff competition not only from within the country, but also from overseas manufacturers. This, in turn, has offered a wider choice of material to the consumer. Under these circumstances, price and quality become important criteria in the process of purchasing. Process control within the mill has therefore become essential for achieving over all success.

2.Role of process control.

In order to achieve overall profitable results and operate effectively, certain management tools are needed to control various phases of production. Process control is one such tool. The main functions of a process control laboratory comprise the following :

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Obtaining and maintaining optimum processing conditions

Establishing correct operative procedures

Carrying out adequate machinery maintenance

Controlling Production yield and waste

Setting up to testing sequences

Providing for through documenting system

Assessing the department's effectiveness

Today in the textile industry, increasing costs are a matter of grave concern. For any product, there is always a minimum cost of production; but, in practice the actual cost is higher than the minimum one due to excessive production of waste, processing, difficulties, incorrect procedures, etc. Thus, in today's context, one of the most important functions of the process control laboratory is to reduce overall cost besides ensuring the production of goods conforming to the standards / specifications laid down.

3.Approach of process control

As far as the choice of processing conditions for a given product is concerned, generally, some guidelines are always available. However,

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the optimum levels of various processing parameters differ from mill to mill for obvious reasons. Thus, mills have to carry out their own experiments to identify their optimum processing levels. In order to achieve these levels, it is recommended to adopt the 'Evolutionary Operation Technique'. In this technique, experiments are carried out by the process control personnel during the various production stages and small changes are made in the process variables in a systematic manner, till optimum operating levels are reached. Every change in the processing parameters is introduced in such a manner that in case of a failure, the financial losses due to higher rejects or degradation of product are minimal. It is also important to thoroughly review the results of each change before deciding upon the next set of experiments.

Once the processing conditions are standardised, it becomes necessary to ensure that these conditions are rigorously followed during the normal course of production and adequate records of the process control checks are maintained. During process control rounds, it may not be possible to check all the process parameters in one go and hence separate lists for each process should be prepared for those parameters to be checked regularly and for those to be checked randomly, depending on the bearing of the individual parameter on the effectiveness of the

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process. However, it is important that the selected regular inspection checks ensure that the particular process is doing precisely what it is supposed to do.

4.Process control in wet processing

Textile wet processing comprises several unit operations, namely, desizing, scouring, bleaching, dyeing, printing and finishing. During the course of wet processing, the goods are subjected to various chemical / mechanical treatments employing widely varying process conditions. Since most of these operations are carried out in a sequential order, the efficiency of the preceding operation has direct bearing on the success of the following one. Further, some of the steps involved in wet processing of textiles are not specific and while accomplishing one desired property in the textile material, an undesired effect may also result, if the processing conditions are not rigidly controlled. again, for consistent performance, reduced damages and increased machine efficiency, regular checks at each strategic point are absolutely essential.

In the wet processing department, process control starts with the inspection of grey cloth meant for processing and follows right upto the final finishing. Various important process control measures to be

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implemented at the different stages of processing are discussed with the help of Tables 10.1 - 10.12 which cover in general, all the unit operations. It is important to note that regular checking of all the parameters listed in the Tables is not required. hence the mills should prepare two sets of formats for each unit operation; one of which should cover the checks to be carried out regularly and the other should cover the checks to be carried out randomly.

Table - 10.1 : Process control in grey inspection

Sr.

No.ParameterCheck PointMethod of checkingStandard / frequency of checkNecessary action(s)

1.ConstructionBefore stitchingPick glassRandomSegregate odd pieces

2.Crey widthBefore stitchingMeasurement by tape+ 1 cm / random during each roundSegregate odd pieces

3.Mechanical damageBefore stitchingVisual}

}

} Once a shift

} between the

} rounds

}

{Segregate the pieces for full bleached / dyed / printed sorts depending upon the extent of damage

4.Manufacturing damageBefore stitchingVisual

5.Piece lengthBefore stitchingMeasurement by tapeSegregate short length piecs mainly in the case of export orders.

6.Stain mildewBefore stitchinguv lampNo stains / mildew / once in a daySpot clean for stains, give damage note for mildew affected goods.

7.MendingBefore / after stitchingVisual-Take necessary action for correcting and subsequent segregation of damaged goods.

8.Mix up of warp yarnbefore stitchingStrip dyeing if not done at beam stageNo mix up of wrap yarnsConvert to full bleached sorts.

9.Blend variationBefore stitchingSpotting with Shirlastation or similar staining agentsNo variation in blend / randomIf any variation is found, then convert to full bleached sort or pigment printed sort

10.Reedinessbefore stitchingStreak analyser-Correct to full bleached or printed sort.

11.Selection of thread for stitchingBefore stitchingCount/ply/blend determination-Ensure that proper thread is used for stitching.

12.End to end stitchingBefore stitchingVisualNo bowingTear and restitch

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Table - 10.2 : process control in shearing / cropping

Sr.


1.Metal detectionDuring shearing / croppingMetal detectorNo metallic particles should be presentEnsure efficient working of metal detector.

2.Seam detectionDuring shearing / croppingSeam detector-Ensure efficient working of seam detector

3.Loose threadsDuring shearing / croppingVisualNo loose thread should remainAdjust the position of ledger blades and sharpen (honing)

4.AbrasionDuring shearing / croppingVisualNo abrasion / random checkDisengage emery rolls

5.Long threadsduring shearing / croppingVisualOnce a shiftCheck for proper functioning of suction.

6.Cut / hole formationDuring shearing / croppingVisualNo cuts or holes / random checkEnsure proper adjustment of brushes and blades

7.Overall shearing efficiencyAfter shearing / croppingVisual assessment80 - 90%Ensure proper working of the machine

8.Machine efficiencyDuring shearing / croppingProductivity assessment70 - 75 % once a dayMake sure of optimum speed and also assess the feasibility of running two ends to increase production.

Table 10.3. : Process control in singeing

Sr.


1.SpeedDuring singeingSpeedometer reading90 - 135 m/min as per make / during each round Run the machine at optimum speed

2.Flame heightDuring singeing-4 - 7 inches as per qualityAdjust the length of the flame

3.Sooty flameDuring singeingVisualNo sooty flames / during each roundMix Gas and air property

4.Uneven flameDuring singeingVisualNo uneven flame / during each roundClean choked up orifices

5.ThreadingDuring singeingVisualAs per machine constructionEnsure that both faces of the fabric are signed

6.Crease free flowDuring signeingVisualNo creases / random checkingEnsure proper functioning of expanders

7.Quenchingduring signeingVisual - examination of the extinction of sparksNo sparksEnsure proper quenching

8.Singeing efficiency After drying / singeinghazy dyeing pilling test feel visualRandomEnsure efficient singeing of the goods

9.Machine efficiency-Production record70 - 75 % once a dayTake corrective measures

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Table - 10.4 : Process control in desizing

Sr.


1.Nature of sizePrior to desizingLaboratory testing of sized sample-Select corresponding desizing agent

2.Percentage wet pick upDuring desizingpercentage pick up determination by laboratory analysisAbout 110% as per quality / once a shift

Nip pressure during each roundEnsure proper nip expression

3Concentration of desizing agent / salt / wetting agentDuring desizingCheck recipeAs per requirementTake corrective measures to adjust recipe

4.Impregnation / dwell timeDuring DesizingThermometer reeading3-5 sec. As per nature of the desizing agentEnsure optimum penetration and reaction time

5.Temperatureduring desizingThermometer readingAs per desizing agent characteristics during each round per Regulate steam supply

6.pHDuring desizingpH indicator / pH paperAs per desizing agent characteristics during each roundMaintain the required pH

7.Desizing eficiencyAfter desizinglaboratory testing< 85% / once a shiftControl process parameters adequately

Table - 10.5 : Process control in scouring.

A. Kier

Sr.


1.Kier liningPrior to filing of kierVisualNo chipping of interior wall / once a weekEnsure proper cementing of the interior wall of the kier

2.Pilingduring filing of the kierVisualUniform piling / once a dayDo uniform piling

3.Air removalBefore taking pressureVisualNo entrapped airEnsure complete removal of air in the kier by passing steam for some time and then closing the cock for pressure build-up

4.CirculationDuring processFlow rateSmooth circulationEnsure proper cleaning of heat exchanger tubes

5.Recipe Before scouringCheck recipe with respect to the amount of cloth to be scoured and quality of clothAs per quality / once a dayTake corrective measures

6.Concentration of scouring liquorBefore / During scouringTitrationAs per quality / once a dayAdjust the concentration

7.TemperatureDuring scouringThermometerAs per quality during each roundRegulate steam supply

8.Steam pressureDuring scouringpressure gauge readingAs per quality during each roundRegulate steam supply

9.Time During scouringTime recordAs per quality / once a dayGive optimum dwell time for treatment

10.concentration of drain liquorAt the end of scouringTitration< 10% of original concentration / once a day

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Table - 10.5 :Process control in scouring ( Contd. )

B. J - box.

Sr.


1.Recipe checkingPrior to scouringCheck the requisitionAs per quality / once a dayTake corrective measures

2.Concentration of chemicals in the saturatorDuring scouringTitrationAs per quality / once a shiftEnsure proper concentrate of chemicals in stock tank feed liquor / saturator

3.Flow of chemicals in the saturatorDuring scouringFlow rate measurementsAs per quality / once a shiftAdjust flow of chemicals and maintain constant level in the saturator

4.Pick-up During saturationlaboratory analysisAbout 15-20% positive pick - up / once a shiftAdjust nip pressure

5.Steam pressureDuring scouringpressure gauge readingAs per quality / once a shiftEnsure proper steam pressure, inform boiler house if necessary

6.TimeDuring scouringDwell time recordAs per quality / once a shiftGive optimum dwell time

7.TemperatureDuring scouringThermometerAs per quality / once a shiftRegulate steam supply

Table - 10.5 : Process control in scouring ( Contd. )

C. Jigger

Sr.


1.TimeDuring ScouringRecord time by counting no. of endsAs per quality / once a dayEnsure optimum treatment time by giving optimum number of ends

2.Temperatureduring scouringThermometerAs per requirement / during each roundRegulate steam supply

3.Concentration of chemicalsDuring scouringTitrationAs per quality once a shiftMaintain optimum concentration of chemicals

4.Residual alkaliAfter scouringTitration< 10% of chemicals / once a dayMaintain concentration of seouring liquor

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Table - 10.6 : Process control in chemicking /

perioxide bleacing

Sr.


1.Metal contaminationCheck stock solution and while in processLaboratory analysisNo metal contamination / once a weekAdd sequestering agent Use Filters

Replace silicate by metasilicate

Resort to souring prior to bleaching

2.RecipePrior to bleachingCheck requisition slipAs per requirement / once a dayTake corrective measures

3.Concentration of chemicalsDuring processTitrationAs per requirement / once a shiftAdjust concentration of chemicals

Adjust feeding concentration.

Regulate flow rate

4.Quantity of stock solutionPrior to peroxide bleachingComparison of level of stock solution and quantity of cloth to be bleachedFull consumption of prepared stock solution / once a dayEnsure full consumption of prepared chemicals

5.TemperatureDuring bleachingThermometerAs per requirement / during each roundRegulate steam supply

6.TimeDuring bleachingDwell time recordAs per quality / once a shiftGive adequate treatment time

7.pHDuring bleachingpH indicator / paper9.5 - 0.5 (chemick)

10.5-11.5 (peroxide)

during each round Maintain required pH

8.Concentration of drain liquorAfter bleachingTitrationOnce a dayEnsure optimum utilisation of peroxide

9.Na2O : sio2 ratio for sodium silicatePrior to preparation of peroxide stock solutionLaboratory analysisNa2 : SiO2 : 1:1Replace by metasilicate

Add soda ash / caustic to maintain the ratio

Table - 10.7 : Process control in souring / acid desizing / neutralisation

Sr.


1.Concentration of acidPrior to souringTitrationAs per requirement / once a shiftMaintain the

2.Flow rate during feedingDuring souringFlow meterAs per requirementRegulate flow of acid during feeding

3.TemperatureDuring souringThermometerRoom temperature / during each roundPlug all steam leakages

4.TimeDuring souringDwell time recordAs per requirement / once a shiftEnsure optimum dwell time

5.Localised dryingDuring storageVisualNo localised dryingEnsure proper covering of the acid treated goods during storage

6.pH during washing / neutralisationAfter acid treatmentpH indicator paperNo acidity after washing / once a shiftTake corrective measures

7.Pick - upDuring souringLaboratory analysis Positive pick-up 15-20% once a shiftAdjust nip presure

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Table - 10.8 : Process control in drying ( cylinder drying )

Sr.


1.Steam pressureDuring dryingPressure gauge readingAs per quality / during each roundRegulate steam supply

2.Guide rollsDuring dryingVisual-Ensure smooth rotation and alignment of guide rolls

3.Scroll / Rolls / expandersDuring dryingVisual-Ensure crease free flow of cloth

4.Nip pressureDuring dryingLaboratory analysisMinimum possible expression / once a dayAdjust nip pressure

5.Steam trapsDuring dryingVisualAtleast once a shiftEnsure no air / water / steam condensate inside the cylinder, prior to taking steam pressure

6.Cleaning of cylindersDuring dryingVisualRandom checkingEnsure efficient heat transfer from the surface of the cylinders

7.Alignment of cylinderDuring dryingVisual-Adjust the alignment of cylinders for crease - free drying.

Table - 19.0 : Process control in mercerising

Sr.


1.Moisture contentBefore mercerisationLaboratory testingEither dry or with uniform moistureDry the fabric on a drying range or squeeze the fabric on a padding mangle or a water mangle which is running in tandem with mercerising machine

2.Caustic soda solution at paddingConcentrationTwaddle meter / titrationAccording to treatment desired / during each roundAdjust the concentration and control the temperature

TemperatureThermometerRoom temperature / during each round

3.Time of mercerisationImpregnation zoneStop watch / speed indicator45 - 60 sec / during each roundAdjust speed

4.Wet pick up of caustic sodaFabric after last padding with caustic soda solutionPick-up study120-135% Random checking for each qualityAdjust nip pressure

Adjust concentration of caustic soda solution

5.WashingConcentration of wash liquorTwaddle meter8-10' TW / during each roundAdjust rate of flow of water

6.RecuperatorTemperatureThermometerMore than 900C (coloured fabric 600C) / during each roundAdjust steam flow

7.Caustic soda left on the fabricFabric at delivery endLaboratory testingLess than 1% once a shiftCheck the washing procedure, take necessary action to effect thorough washings

8.Souring and washingAcid additionLaboratory testing and pH indicatorpH near neutral / random checkArrange for overhead tank and pipe line.

Concentration of feed liquor

Concentration of acid in the tankAdjust the concentration of acid

Adjust the rate of flow

9.Fabric after washingpH of fabricpH indicatorAbout 7.0 / during each roundAdjust rate of flow of water

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Table - 10.10 : Process control in dyeing

A. yarn deying

Sr.


1.Package densityPrior to loadingBITRA package density meter0.3g/c/c/ 1 or 2 packages at random per shiftEnsure uniform package density both within the package and among the packages.

2.Shape of the cheesePrior to loadingVisual-Take corrective measures

3.Checking of angle of windingPrior to processVisualCross wound for cheese and parallel for beam random checkSegregate defective wound goods and rewind them

4.Variation in packagePrior to loadingActual weighingRandom checkEnsure uniform package size

5.Perforation of spindlesPrior to mounting on spindlesVisualRandom checkEnsure no choking of the perforation of spindles.

6.MLRDuring processBy Dip-stick measurementAs per makeEnsure proper MLR

7.Pump pressureDuring processpressure readingChange in pressure after reversal of the cycle should not be more than 41b/in.2Take necessary action for smooth reversal and choking of pump

8.Recipe-colour / chemicalsPrior to dyeingScrutinising of colour / chemical issue slipsOnce a dayEnsure conformity with standard recipe

9.Colour dissolutionprior to dyeingSpotting on filter paperonce a dayEnsure proper dissolution of dyes

10.pHDuring processpH indicatorAs per class of dyesMaintain the desired pH

11.TemperatureDuring ProcessThermometerDuring each roundRegulate steam supply

12.TimeDuring processProcessing cycle record-Maintain optimum processing time

13.Entrapped airPrior to pressure build-upCheck air vent valveNo entrapped airEnsure complete air removal

14.Steam leakagesDuring processVisualNo leakage, keep vigilance / during roundPlug steam leakages

15.Variation in package density during processAfter dyeing of polyester component of ployester / cellulosic blended goodsFeel after dryingRandom checkCorrect package density after drying and rewinding

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Table - 10.10 : Process control in dyeing

B. H.T.H.P. dyeing : beam / jet dyeing

Sr.


1.Fabric pretreatmentBefore dyeingAbsorbency Uniformity of treatment.

Degree of heat settingLaboratory analysis / each bleached lotEnsure good pretreatment of the fabric

2.Package densityDuring batchingFeel-Ensure uniform batching resulting in neither too tight nor too loose a batch

3.Overlap on beamDuring batchingVisualAs per quality / random checkMaintain desired overlap

4.Wrapper cloth lengthBefore batchingVisualMinimum 8-10 layers / random checkEnsure proper length of wrapper cloth being used for avoiding perforation marks

5.Overloading dye becksPrior to during loadingBy yardage measurement-Restrict batch size as per machine specification

6.Air entrapped Before pressure build upWater outlet valveNo entrapped airRemove entrapped air completely.

7.Flow reversalDuring processPressure guage readingDifference of > 41b/in2 between reversals / once a shiftCheck for proper batching and air removals

8.MLRPrior to dyeing-As per makemake desired changes

9.Jet pressureDuring dyeingJet pressure gauge readingRandom checkAdjust jet pressure according to quality

10.RecipePrior to dyeingChecking of batch size, shade number and corresponding colour / chemical issue sliponce a dayEnsure conformity with standard

11.PHDuring dyeingpH paper / pH meterpH 4.5 - 5.5Adjust concentration of acid buffer solution

12.TemperatureDuring dyeingDial thermometerAs per requirement / during each roundEnsure uniform heating rate as per standard programme

Maintain uniform steam pressure

Check proper working of thermostat

13.Dyeing timeDuring dyeingTime recordingAs per requirementEnsure desired holding time and rate of cooling

14.Steam pressureDuring dyeingpressure gauge readingDuring each roundEnsure optimum steam supply.

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Table - 10.10 : Process control in dyeing ( Contd. )

C. Jigger dyeing

Sr.


1.Fabric preparationPrior to dyeingAbsorbency

Uniform whiteness pH of cloth

Body creases / selvedge creaseGood absorbency

Uniform whiteness

Near neutral

No creases / each bleached lot

Random checkEnsure good fabric preparation

2.BatchingDuring batchingVisualRandom checkKnife edge batching

Ensure no slippage while running Proper working of expander

Uniform tension at the time of batching

3.Batch sizeDuring batchingMeasurement of yardagemaximum permissible load as per make / random checkEnsure that jigger is not overloaded

4.MLRPrior / during dyeingCheck for water level in jigger

Check for weight of fabric loadedOnce a shiftMaintain constant MLR for consistent results

Water level marking in jigger must be done in accordance with capacity and not by approximate level (height) of water in the jigger.

Prevent water / steam leakages

5.Selection of end clothPrior to dyeingLength of the cloth

Colour of end cloth should be compatible with the shade to be dyedRandom checkEnsure proper selection and length of the end cloth.

6.Creasefree working of jiggersDuring dyeingVisualDuring each roundAdjust alignment of expanders

Adjust roller alignment

Remove crease manually, if possible

7.RecipePrior to dyeingScrutinising of chemical / colour issue slip with respect to batchsize, shade number, sort numberOnce a dayTake corrective measures

8.Colour preparationDuring colour preparationVisual / spotting on filter paperRandom checkEnsure proper dissolution of dye

Strain the colour prior to dyeing

Investigate the method of dissolution

Ensure proper vatting of vat dyes

9.Colour / chemical additionDuring DyeingVisualRandom checkuse splash board during additions

Carry out colour addition in equal parts

Effect proper stirring after colour addition

Predissolve all solid chemicals added

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Sr.


10.Concentration of chemicalsDuringdyeingCheck hydrose / caustic by using vat yellow / congo red paper

The concentration of chemicals should be on volume / depth basis irrespective of batch size whereas the dyes should be calculated on the fabric weight basisDuring roundsEnsure proper concentration

11.TemperatureDuring dyeingThermometerAs per standard dyeing procedure / during each roundRegulate steam supply

Carry out heating at the end of turn

Prefer dial thermometer to cup type thermometer for precise temperature control

12.pHDuring dyeingpH paperAs per class of dyestuffTake corrective measures

13.TimeDuring dyeingTime record, number of ends-Give adequate time / number of ends

14.Addition of colour for correction of shareDuring processVisualWherever possibleEnsure that when additions are made half the liquor containing unexhausted dye is drained so as to maintain MLR and help in exhaustion

15.After treatmentsAfter dyeingLaboratory analysisAs per class of dye / random checkCheck if the following treatments are given

Sulphur black-sodium acetate / soda ash treatment or sodium dichromate treatment

Azoic - thorough soaping with dispersing agent

Reactive - thorough soaping, dye fixing treatment and ensure no tinting of colour in final wash

Direct - dye fixing treatment.

Disperse - reduction clearing treatment

16.RedyeingDuring processProduction recordsminimum redyeing / once a dayInvestigate the reasons of for redyeing

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Table - 10.10 : Process control in dyeing ( Contd. )

D. Semi continuous / Continuous methods of dyeing

Sr.


1.Fabric preparationPrior to dyeingUniform absorbency

Crease - free cloth

Even width

Proper stitching of the end piecesEach bleached lotEnsure good fabric preparation

2.Nip pressurepadding rolls

Squeeze rolls (soaper)Percentage expression determination

Hardness of bowls

Carbon impressionOnce a shiftEnsure optimum pick-up

3.ThreadingProcess :

padding

drying

soapingVisualOnce a ShiftEnsure optimum pick-up

4.ExpandersDuring dyeingVisual-Ensure smooth working and crease - free run of the material

5.Guide rollsDuring dyeingVisual-Ensure smooth working of guide rolls

6.Colour preparationDuring colour preparationAs per recipe

Proper dissolution

StrainingRandom checkEnsure proper colour preparation

7.PHDuring processpH paperAs per class of dyeMaintain recommended pH

8.SpeedDuring dyeingSpeedometerDuring each roundMaintain required speed

9.Dwell timeDuring dyeingStop watchAs per requirementAdjust speed

10.Temperature in drying zoneDuring drying of padded goodsDial thermometerDuring each roundEnsure slow, uniform and progressive drying to avoid migration

11.Uniform colour concentration in padding troughDuring dyeingVisualRandom checkEnsure continuous circulation of the dye liquor if possible or use shallow padding trough

12.Temperature of padding liquorDuring dyeingThermometerAs per the class of dyestuffMaintain desired temperature throughout the padding process

13.Flow feeding liquorDuring dyeingFlow meter-Adjust flow and ensure uniform feeding of dye liquor through out the width of the fabric

14.BatchingAfter batchingVisualRandom checkmake proper arrangement for rotation of padded batches to avoid seepage of dye liquor and stoppage marks Ensure low padding expression

15.Covering of batches (pad - roll/pad batch)After batchingVisualIsolate from atmosphere by proper covering / random checkProperly wrap with polythene sheet

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Table - 10.11 : Process control in printing

A. Actual printing

Sr.


1.Fabric preparationBefore printingVisual / laboratory testingGood absorbency

Uniform whiteness

Creasefree fabric

pH of the cloth

Uniform width

Appropriate sort number

Correct face for printing / each bleached lotTake corrective measures and batch the material for printing on correct face

2.Gum preparationDuring gum preparationVisual / visocosity measurementAs per requirement / once a dayEnsure adequate working time and temperature

Ensure the preparation of free flowing gum devoid of lumps

3.Colour preparationDuring colour preparationVisual and random checking of issue slips for colours and chemicalsAs per standard recipe / once a day- Ensure correct pH,

- Add ingredients in the desired order only after dissolution and straining

Use prefiltered gum and also filter the print paste

4.Design checkingBefore printingVisualRandom checkTake corrective action.

5.Sample checkingBefore printingComparison with sketch or approval sampleOnce a dayTake corrective action

6.Expanders / guide-rollsDuring printingVisual-Ensure creasefree run of the cloth

7.Squeezee pressure / design roll pressureDuring printingVisualNo selvedge - to - selvedge variation / during each roundEnsure uniform pressure throughout the fabric width

8.BackgreyDuring printingVisualCreasefree feeding of dried backgreyEnsure proper drying and creasfree feeding of back grey

During each roundEnsure the use of longer length pieces with minimum stitches

9.Lapping of guide rolls on printing machineDuring printing of discharge or resist stylesVisualRandom checkTake necessary action and change lapping at regular intervals.

10.Drying During printingBy feelDuring each roundEnsure uniform and complete drying

11.Crease free dryingDuring printingVisualDuring each roundEnsure proper working of fans / alignment and free rotation of guide rolls in the case of hot flue

12.Stability of print pasteBefore printingSample printingRandom checkEnrich the print-paste with the required ingredients to take care of depleted strength

13.left over pringt pasteColour kitchenVisual random checksonce a shiftEnsure proper recording of actual print paste consumption on the machines and effective reutilisation of loft - over print paste

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Table - 10.11 : Process control in printing ( Contd. )

B. Polymerising

Sr.


1.TemperatureDuring polymerisationDial thermometer / thermopaperAs per requirement during each roundEnsure adequate and uniform temperature throughout the width of the machine

2.TimeDuring polymerisationStop watchAs per requirement / during each roundMaintain proper speed

3.ExhaustDuring polymerisationVisualAs per requirement / once a shiftSee that all exhaust fans work mainly for pigment printing when kerosene is used

4.Free movement of guide rollsDuring polymerisationVisualAs epr requirementEnsure creasefree run of cloth

Table - 10.11 : Process control in Printing ( Contd. )

C. Ageing

Sr.


1.TimeDuring ageingStop watchAs per requirement / during each roundMaintain speed / holding time

2.Guide rollsDuring ageingVisualNo creases / if possible, during each roundEnsure crease - free flow of cloth

3.Water levelDuring ageingVisualAs per style of printing / once a shiftEnsure optimum water level

4.Acid InjectionDuring ageingVisualOnce a shiftEnsure optimum quantity of acid injection

5.Steam pressureDuring ageingPressure guageAs per requirement / during each roundRegulate steam supply and correlate with temperature

6.LeakageDuring ageingVisualNo leakages, keep vigilancePlug all steam leakages

7.CondensationDuring ageingVisualNo water dropping / random checkEnsure proepr heating of steam jackets / shoes, lid and roof and use of completely dried back grey

8.Making offAfter ageing VisualNo marking off / random checkChange back grey on pressure ager at desired internally.

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Table - 10.11 : process control in printing ( Contd. )

D. Carbonising / Silicate padding / Soaping

Sr.


1I.Carbonising

1.Checking of concentration of sulphuric acidprior to carbonisingTwaddel meter / titration70% ( w/w ) once a shiftMaintain proper concentration of sulfuric acid

2.Concentration of chemicalsPrior to processScrutinising of the issue slipsOnce a dayMaintain the required concentration of chemicals.

3.Nitrogenous impurities in sulphuric acidPrior to carbonisingDiphenyl amine test / brown ring testFor each lot of sulfuric acidAdd urea or sulphamic acid in carbonising bath

4.Dwell timeDuring carbonisingStop watchAs per quality minimum 45 min. / once a shiftEnsure optimum dwell time.

5.CarbonisingAfter carbonisinglaboratory analysis99.7% once a dayEnsure optimum carbonising efficiency

6.neutralisingAfter carbonisingpH indicatornear neutral / check each lotEnsure complete neutralisation and washing

7.Local dryingDuring carbonisingVisualNo local drying / random checkincrease acid pick-up and avoid undue exposure

II.Silicate Padding

1.Concentration of silicatePrior to silicate padingTwaddel meter102-106 Tw/ during each roundmaintain optimum concentration of silicate

2.Na2O : SiO2Prior to silicate paddinglaboratory analysis 1:2 I/once a shiftAdd sodium hydroxide to maintain the ratio

3.Nip pressure During processlaboratory analysisRandom checkEnsure optimum nip pressure and uniform application

4.Dwell timeAfter paddingStop watch, time record16 hr. for cold pad batch and 8-12 sec. for hot silicate / random checkGive optimum dwell time

5.TemperatureDuring processThermometerRoom temperature

(cold process) 85-900C, (hot process) during each roundRegulate steam supply in hot silicate process

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Table - 10.11 : Process control in printing ( Contd. )

D. Carbonising / Silicate padding / Soaping

Sr.


6.Proper coveringAfter processVisualRandom checkTake necessary action to avoid local drying and exposure to atmosphere

III.Soaping

1.Water jetsDuring washingVisualNo choking of jets / once a dayEnsure proper functioning of jets

2.Water supplyDuring washingVisualRandom checkEnsure adequate supply of water for overflow washes

3.ThreadingPrior to processVisualProper threading / once a dayTake corrective measures

4.Guide rollsPrior to / during processVisual-Ensure smooth working of guide rolls also check for alignment of guide rolls

5.Squeeze pressurePrior to / during processVisualDuring each roundEnsure proper and uniform expression at each nip

6.Temperatureprior to / during processThermometerAs per treatment / during each roundRegulate steam supply to maintain the temperature

7.Concentration of chemicalsPrior to / during processBy known test methods for individual chemical for reduction clearing and developing bathsAs per treatment / during each round while reduction clearingMaintain optimum concentration.

Table - 10.12 :Process control in finishing

A. Stenter

Sr.


1.Nip pressureDuring processPick-up studyOnce a shiftAdjust the compressor valve or weights on lever

Check the surface of padding mangle

2.Chamber temperature During processDial thermometerAs per requirement / during each roundRegulate steam supply

3.Dwell timeDuring processStop watchAs per requirement / during each roundRegulate speed

4.overfedDuring processmeasurementAs per requirement / during each roundEnsure optimum overfeed in the case of heat setting

5.Expanders / uncurlersDuring ProcessVisualNo crease / during each roundTake corrective measures

6.BlowerDuring processVisualProper air circulation / once a shiftEnsure proper working and the direction of fans

7.WidthDuring process at delivery endTape measurementAs per requirement / during each roundMaintain desired width

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Sr.


8.Steam leakagesDuring processVisualNo leakages, keep vigilancePlug all steam leakages

9.Concentration of chemicalsPrior / during processChecking chemical issue slips and actual verification during preparingRandom checkMaintain the required concentration

10.Stability of procondensate in resin finishingPrior to resin finishingVisualRandom checkEnsure proper stability / selection of resin precondenstates

11.Temperature / viscosity of starch pastePrior / during starch finishingThermometer / viscometerDuring each roundMaintain optimum temperature / viscosity of starch paste

12.Drying eficiency During / after processTextometer or by feel at stitchesNo overdrying /.during each roundEnsure optimum drying efficiency

13.Steam pressureDuring processpressure gauge readingDuring each roundRegulate steam supply

14.Random inspection of clips / pinsPrior to processVisualOnce a week Ensure proper functioning of clips / pins

Table - 10.12 : Process control in finishing

B. Pre-shrinking

Sr.


1.DampingPrior to Palmer stretcherFeel-Adjust the spray intensity

2.TemperatureDuring pre - shrinkingdial - thermometerDuring each roundRegulate steam supply

3.WidthAfter pre - shrinkingTape measurementAs per fabric sort / random checkAdjust the dwell time and percentage shrinkage

4.SpeedDuring pre-shrinkingSpeedometerDuring each roundAdjust speed regulator

5.Belts / BlanketsPrior to pre - shrinkingVisual / Feelonce a week Ensure correct surface of the belts / blankets by regular grinding

6.ShrinkageAfter pre - shrinkingShrinkage testAs epr fabric sort / check for each lotEnsure optimum shrinkage percentage

7.Cooling water nozzleDuring pre - shrinkingVisualDuring each roundCheck the choking of nozzle heads

8.StampingDuring pre - shrinkingVisualDuring each roundEnsure

Stamping as per quality

Correct position of stamping

Adequate ink application resulting in clear imprint.

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Table - 10.12 : Process control in finishing

A. Calender / Schriener

Sr.


1.Nip pressurePrior / during processNip presure reading-Regulate the compressor valve or correct the lever arrangement

2.ThreadingPrior / during processVisualAs per requirement / random checkEnsure proper threading

3.DampingPrior to calenderingFeel-Adjust water spray intensity

4.SpeedDuring processSpeedometerDuring each roundRegulate speed

5.WidthDuring processTape measurementAs per sort / during each roundEnsure desired width at the delivery end

6.Roll surfacePrior to processVisualNo grooves / cracks / holes or surface deposition / once a shiftEnsure proper maintenance and cleaning of calender bowls.

5.Benefits of Process control

Clariant has been stressing the need for adequate process control measures in textile wet processing for over a decade. It has guided its customers in successfully introducing the concept of process control in process houses. The various advantages that have accrued to the member industry by the implementation of these process control measures recommended by Clariant are as follows :

Increased production efficiency as a consequence of more stable speeds and in certain cases even higher processing speeds, besides better machine utilisation.

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Reduced chemical consumption ( it is not uncommon to discover that chemicals are not only frequently overused but also under utilised ).

Reduced energy and water consumption.

Reduced labour cost per unit of production.

Improved consistency of chemical treatments and consequent standardisation of a product's performance particularly in the case of repeat orders.

Precise prediction of chemical processing costs for a given product, eliminating the risk of undercosting of products by taking hypothetical averages.

Predictability in quality of the products.

Significant reduction in percentage reprocessing.

6.Summing up

From the foregoing, it can be said that process control is one of the most effective managerial tools. Its important and positive role towards maintaining the quality and increasing the margin between production cost and sales price cannot be undermined. In the past and even today, in some of the mills, the process control department is considered non

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productive and is hence neglected. Over the years, Clariant has been helping its member mills in implementing process control measures and the mills have derived considerable advantage in terms of reduced value loss and improved quality. In some of the cases, the mills have been able to reduce processing costs by way of optimising the various unit operations and standardising chemical recipes. The mill have also succeeded in reducing the extent of reprocessing on account of the vigilance of the process control personnel in maintaining the processing parameters at a desired level. In a nutshell the need of the hour is total exploitation of the concept of process control.

Before concluding, it would be worthwhile to mention that the personnel working in the area of process control must have good rapport with other personnel engaged directly or indirectly in the production line, elicit their co-operation and acquire the confidence of shop-floor personnel. They must also have thorough knowledge of the process involved and be able to discuss the problems with others in a language that they can understand.

process control in wet processing

Documents

process control laboratory

wet processing process

process control personnel

process control checks

process control rounds

role of process control

approach of process

process variables