QC in Knitted ProductionQC in Knitted ProductionPart 2: Process ControlPart 2: Process Control

Jimmy LamJimmy Lam

Institute of Textiles & ClothingInstitute of Textiles & Clothing

Learning ObjectivesLearning Objectives

What are the major elements for processes control?What are the major elements for processes control? Fabric properties and loop lengthFabric properties and loop length Relationship between loop length and yarn tensionRelationship between loop length and yarn tension On machine controlOn machine control

– Yarn speed meter, yarn tension meter and yarn length meterYarn speed meter, yarn tension meter and yarn length meter Positive Feed devicePositive Feed device

– Trip-tape positive device, multi-coil positive feed,Trip-tape positive device, multi-coil positive feed,– Positive feed with intermittent yarn consumptionPositive feed with intermittent yarn consumption

Storage Feed deviceStorage Feed device

Remember this modelRemember this model

PROCESS

INPUT OUTPUT

CONTROL

What are the major control elements for process control

Closed-loop Control ModelClosed-loop Control ModelQuality Control ProcessQuality Control Process

KNITTING

YARN FABRIC

INSPECTION

Knitting ControlKnitting Control

This is a process control starting from yarn This is a process control starting from yarn feeding to fabric manufacturing.feeding to fabric manufacturing.

Please name the factors that will affecting the knitting Please name the factors that will affecting the knitting fabric quality during production stagefabric quality during production stage

Loop Length Control (I)Loop Length Control (I)

The loop length is the basic element (cell) in the The loop length is the basic element (cell) in the knitted fabric and is defined as the amount of knitted fabric and is defined as the amount of yarn used to form one unit loopyarn used to form one unit loop

Loop length = course length / no. of loopsLoop length = course length / no. of loops Loop length will affect the following parametersLoop length will affect the following parameters

– stitch density; tightness factors; fabric weight;stitch density; tightness factors; fabric weight;– Fabric width; panel length; dimensional stabilityFabric width; panel length; dimensional stability

Loop Length and Fabric PropertiesLoop Length and Fabric Properties

Loop Length Control (II)Loop Length Control (II)

Experiment shows that fabric thickness, weight, tightness Experiment shows that fabric thickness, weight, tightness factor and stitch density are INVERSELY factor and stitch density are INVERSELY PROPORTIONAL to the loop lengthPROPORTIONAL to the loop length

Setting of stitch cam (loop length control) and variation:Setting of stitch cam (loop length control) and variation:» Loop length is controlled by the setting of stitch cam in the Loop length is controlled by the setting of stitch cam in the

cylinder machine. However,how accurate is the indicator on cylinder machine. However,how accurate is the indicator on the stitch cam is the common question most knitters will askthe stitch cam is the common question most knitters will ask

– ConclusionConclusion» The variation on poor machine setting, yarn input tension The variation on poor machine setting, yarn input tension

and knitting tension, all account for loop length variationand knitting tension, all account for loop length variation

Yarn Knitting Tension ControlYarn Knitting Tension Control

Please show the relationship between the loop Please show the relationship between the loop length and knitting tensionlength and knitting tension

Please indicate what factors will affect the Please indicate what factors will affect the knitting tensionknitting tension

Knitting Tension & Package sizeKnitting Tension & Package size

Knitting Tension and InertiaKnitting Tension and Inertia

Knitting direction and yarn tensionKnitting direction and yarn tension

Knitting Tension (I)Knitting Tension (I)

Yarn unwinding methodYarn unwinding method– The yarn tension is different from the first layer to the The yarn tension is different from the first layer to the

bottom layerbottom layer

Package sizePackage size– The size of the package (cone diameter and cone height) will The size of the package (cone diameter and cone height) will

affect the winding tensionaffect the winding tension

Package densityPackage density– Unusual high package density will give higher friction to Unusual high package density will give higher friction to

yarn between coils, results in higher unwinding tensionyarn between coils, results in higher unwinding tension

Knitting Tension (II)Knitting Tension (II) Yarn faultYarn fault

– Yarn faults mean sudden increase yarn diameter with results in Yarn faults mean sudden increase yarn diameter with results in change of yarn tension in knitting processchange of yarn tension in knitting process

Spring wire on tensionerSpring wire on tensioner– This will affect on V-bed machine when the cam cartiage This will affect on V-bed machine when the cam cartiage

changing direction from RHS to LHS and vesa versa.changing direction from RHS to LHS and vesa versa.

DiagramsDiagrams– Relationship between package and unwinding tensionRelationship between package and unwinding tension– Change of knitting tension on V-bed machineChange of knitting tension on V-bed machine– Analysis on the peak tensionAnalysis on the peak tension

On machine Quality Control On machine Quality Control EquipmentEquipment

Knowing the factors affecting the fabric quality (loop Knowing the factors affecting the fabric quality (loop length variation), what possible equipment can be length variation), what possible equipment can be used to minimize it or to eliminate it ?used to minimize it or to eliminate it ?

If not, what equipment can be used to monitor any loop If not, what equipment can be used to monitor any loop length variation.length variation.

Yarn Speed MeterYarn Speed Meter

Yarn speed meter is used to Yarn speed meter is used to check the yarn consumption check the yarn consumption speed on the knitting feedersspeed on the knitting feeders

The results is good for The results is good for circular machine without circular machine without positive feeders.positive feeders.

Yarn speed is affected by Yarn speed is affected by loop length, structure and loop length, structure and machine speedmachine speed

Yarn Tension MeterYarn Tension Meter

Tension meter can be used to check the yarn winding Tension meter can be used to check the yarn winding tension, unwinding tension and knitting tension. tension, unwinding tension and knitting tension.

The usual tension (medium to fine gauge) on circular The usual tension (medium to fine gauge) on circular machine is 2-5 g/mmachine is 2-5 g/m– High knitting tension = smaller loop lengthHigh knitting tension = smaller loop length– Fluctuation in tension = variation on loop lengthFluctuation in tension = variation on loop length– Tension lower than 2 g = drop stitchesTension lower than 2 g = drop stitches– Low and even tension = good quality fabricLow and even tension = good quality fabric

What should we do if we find unusual high/low knitting What should we do if we find unusual high/low knitting tension ?tension ?

Yarn Tension MeterYarn Tension Meter

Yarn Length MeterYarn Length Meter

The yarn length meter The yarn length meter can be fixed on can be fixed on machine to record yarn machine to record yarn consumption for a consumption for a number of courses or number of courses or machine revolutions.machine revolutions.

The results can be used The results can be used to calculate the loop to calculate the loop length between machine length between machine of the same gauge.of the same gauge.

Dial Height Gauge ControlDial Height Gauge Control

The gap between the The gap between the cylinder and dial will affect cylinder and dial will affect the fabric quality on :the fabric quality on :– fabric thicknessfabric thickness

– fabric weightfabric weight

– dimensional stabilitydimensional stability

Now we found the way to measure Now we found the way to measure the loop length variation. But can the loop length variation. But can we actually to control or eliminate we actually to control or eliminate

such variation ?such variation ?

Can you suggest any methods ?Can you suggest any methods ?

Positive FeedersPositive Feeders

The function of positive feeders for circular The function of positive feeders for circular knitting machine is to regulate the yarn knitting knitting machine is to regulate the yarn knitting tension to desired value (low and even value) tension to desired value (low and even value) and results in better fabric can be producedand results in better fabric can be produced

The positive feeders are almost standard The positive feeders are almost standard equipment for high speed non-jacquard equipment for high speed non-jacquard machinemachine

(Why only non-jacquard m/c ?)(Why only non-jacquard m/c ?)

Yarn Tension with/without Positive Yarn Tension with/without Positive FeedersFeeders

Trip-tape Positive FeederTrip-tape Positive Feeder

Trip-tape positive feederTrip-tape positive feeder

It is the simple measured yarn speed feeding system. The It is the simple measured yarn speed feeding system. The yarn speed is controlled by speed tape pulley which in yarn speed is controlled by speed tape pulley which in turn, controlled by machine gearbox.turn, controlled by machine gearbox.

Two or three speed tapes are equipped which machine Two or three speed tapes are equipped which machine can have two or three yarn feeding speeds for the fabric.can have two or three yarn feeding speeds for the fabric.

When machine is properly adjusted, the yarn speed is When machine is properly adjusted, the yarn speed is equaled to tape speed, and the tape speed can control the equaled to tape speed, and the tape speed can control the suitable yarn tension and results in regular loop lengthsuitable yarn tension and results in regular loop length

Multi-coil Positive FeederMulti-coil Positive Feeder

Multi-coil positive feederMulti-coil positive feeder Due to the slippage between the tape and the yarn, the Due to the slippage between the tape and the yarn, the

efficiency of trip-tape positive feeder method is not efficiency of trip-tape positive feeder method is not 100%100%– yarn speed IS NOT EQUAL TO tape speedyarn speed IS NOT EQUAL TO tape speed

The multi-coil method is used to achieve this target.The multi-coil method is used to achieve this target. The yarn instead of directly driven by the tape, is first to The yarn instead of directly driven by the tape, is first to

the pin wheel for 10 coils before feeding to the needles.the pin wheel for 10 coils before feeding to the needles. The principle is the yarn coils on the wheel can The principle is the yarn coils on the wheel can

neutralize the yarn tension variation from cone and neutralize the yarn tension variation from cone and avoid and yarn slippage.avoid and yarn slippage.

Positive feed for intermittent yarn Positive feed for intermittent yarn consumptionconsumption

So far, the positive feed discussed is only used for So far, the positive feed discussed is only used for continuous yarn consumption, it cannot be used on the continuous yarn consumption, it cannot be used on the following machines:following machines:– Cotton’s fully fashion machine;Cotton’s fully fashion machine;

– V-bed machineV-bed machine

– Circular hoisery machine;Circular hoisery machine;

– Circular machine with stripersCircular machine with stripers

Please discuss WHY?Please discuss WHY?

Positive Feeder for stripping fabricPositive Feeder for stripping fabric

Positive Feed for intermediate yarn Positive Feed for intermediate yarn consumptionconsumption

A special positive feed has designed for circular machine with A special positive feed has designed for circular machine with stripers.stripers.

The working principle is to utilize the coil friction between the yarn The working principle is to utilize the coil friction between the yarn and the friction roller.and the friction roller.

When the yarn is not selected, the tension wire will bring the yarn When the yarn is not selected, the tension wire will bring the yarn away the roller and thus, it cannot contact with the tape and remain in away the roller and thus, it cannot contact with the tape and remain in idle positionidle position

When the yarn is selected, the yarn tension will increase and pull the When the yarn is selected, the yarn tension will increase and pull the torsion wire towards the yarn guide, and this friction in the coil will torsion wire towards the yarn guide, and this friction in the coil will move the yarn to roller speed.move the yarn to roller speed.

However, the slippage for this type of feeder is about 5-8%However, the slippage for this type of feeder is about 5-8%

Storage FeederStorage Feeder

Positive feeder device is an important device to Positive feeder device is an important device to control the yarn tension and thus to minimize control the yarn tension and thus to minimize the loop variation in knitting.the loop variation in knitting.

However, positive feeder can only be used on However, positive feeder can only be used on non-jacquard fabric such as interlock, pique non-jacquard fabric such as interlock, pique but not on jacquard fabricbut not on jacquard fabric

Please discuss WHYPlease discuss WHY

Storage FeederStorage Feeder

Storage FeederStorage Feeder Positive feeder is designed for regular loop fabric. For Positive feeder is designed for regular loop fabric. For

fabric with different loop length in each course, a new fabric with different loop length in each course, a new concept of storage feed has employedconcept of storage feed has employed

To eliminate the yarn tension variation, all yarns are To eliminate the yarn tension variation, all yarns are rewound onto a drum of equal diameter, under equal rewound onto a drum of equal diameter, under equal tension and speed.tension and speed.

The amount of yarn on drum is automatically controlled so The amount of yarn on drum is automatically controlled so there will be no difference in package diameter.there will be no difference in package diameter.

The yarn is consuming by the knitting needles at variable The yarn is consuming by the knitting needles at variable speeds, thus different loop length in each course is possiblespeeds, thus different loop length in each course is possible

DiscussionDiscussion

What are the major objectives for process What are the major objectives for process control ?control ?

Why loop length variation cannot be avoided Why loop length variation cannot be avoided during knitting processduring knitting process

What are the difference between positive feeder What are the difference between positive feeder and storage feederand storage feeder

Process ControlProcess ControlThe process control is to maintain a regular loop length

for the whole production process.

Multi-coil Positive FeedMulti-coil Positive Feed

Positive Feed for striping fabricPositive Feed for striping fabric

Storage Feed for Jacquard FabricStorage Feed for Jacquard Fabric

Where is the positive feederWhere is the positive feederin this diagram ?in this diagram ?