Study on Weft Knitted Fabric Faults and Remedies-1

UNIVERSITY OF DHAKA

COLLEGE OF TEXTILE TECHNOLOGY

TEJGAON, DHAKA-1208 B.Sc. IN TEXTILE TECNOLOGY, EXAM-2008

Project Report On

Study On Weft Knitted Fabric faults and Remedies SUPERVISING TEACHER:

Prof. Mashud Ahmed Principal of COLLEGE OF TEXTILE TECHNOLOGY,TEJGAON, DHAKA-1208

NAME

SUBMITTED BY: EXAM.ROLL

A.S.M RAHAT KHAN

137

SESSSION 04-05

1

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DEDICATTED TTO THO OSE WHO ARE INTEERESTED TO O LEARN



















ACKN NO OWLEDGEM MENT College of Textile engineering & Technology has given us the opportunity to perform the project project work. We obliged to Prof. Mashud Mashud Ahmed principal in charge our supervising teacher for his kind co-operation. We also thank Shah Allimuzzaman, Associate Professor and and Head Head of of Fabric Manufacturing Department for his important advice. Heartfelt thanks goes goes to textile engineers of various various industries (Reedisha knit tex Ltd, Epylion group , Matrix sweater industry,AKH,Mondol,Padma Polycotton) from whom we have collected samples. Above all we thank all the teachers of FMT Department for their kind inspiration and help, which remains as a backdrop of all of our efforts. Finally I would like to acknowledge that I remain responsible for the inadequacies and errors, which doubtlessly remain.



















ABSTRACT First we collected some defected fabric samples samples both from the circular knitting section , flat knitting section and wet processing section of different industries to commence our project work.then we also separate our collected Samples into three different sections so that we can analyse the collected fabrics very effectively and establish an acceptable result which will be enough to evaluate the grade of different fabrics and in further time it can help us to cary out further activities depending on the establish form of work. During our industrial attachment program we managed to see and collect different fabric samples and analyse them very effectively to find out and track the source of those problems and tried how to solve solve those problems. problems. We have tried our best to give our complete effort on the kniited fabric defects which was caused by fabric manufacturing manufacturing processes and wet processing processes.



















TTA AB BLLEE O OFF CCO ON NTTEEN NTTSS No

Title

Page No

Chapter-I

Introduction

6-8

Chapter-II

Fabric Inspection

9-12

Chapter-III

Yarn processing faults

13-18

Chapter-IV

Weft Knitted fabric Fault due to Yarn & knitting fault

19-40

Chapter-V

Weft Knitted fabric Fault due to Dyeing & Finishing

41-55

Chapter-VI

Flat bed knitted Fabric Fault

56-64

Chapter-VII

Conclusion

65-67





















Chapter-I Introduction



















Introduction: Due to the increasing demand for quality knitted fabrics, high quality requirements are today greater since customer has become more aware of “Non -quality” problems. In order to avoid fabric rejection, knitting mills have to produce fabrics of high quality, constantly. Detection of faults during production of knitted fabric with circular knitting machine is crucial for improved quality quality and productivity. productivity. Any variation to the the knitting process needs to be investigated and corrected. The high quality standard can be guaranteed by incorporating appropriate quality assurance. Industrial analysis indicate that product quality can be improved, and defect cost minimised, by monitoring of the circular knitting process. Fine gauge knitted fabric faults are very different in nature and appearance and are often superimposed. They can be attributed not only to the knitting, but also to the quality of yarns, dyeing and finishing. Some faults can be easily avoided by respecting some fundamental pre-requisites on the circular knitting machine such as the use of positive yarn feeders and the respect of rigorous machine maintenance and cleaning schedule. Other faults are much more difficult to expect because they are not related to just one cause New generation circular knitting machines are conceived with auxiliary equipment that ensure less fabric faults during knitting such as filter creel, lint removal, thread survey, precise oiling and fabric faults detector detec tor devices. Nevertheless, some fabric faults are not



















Many researchers have applied computer vision to improve inspection method of human vision in textile products. In most of them, the image of a knitted garment had been considered to specify the fault features. Other works aimed to classify defects in knitted fabric by using image analysis and neural network algorithm or Fuzzy logic. All theses methods are not completely reliable because image analysis of knitted fabrics involves difficulties due to the loop structures and yarn hairiness, compared to woven fabrics consisting of neat warp and weft yarns. Knitted fabric faults can also be detected by inspecting yarn input tension and loop but only few types of faults are concerned by theses methods. Human inspection by using knitted fabric inspection machines remains today the most used way to classify faults after knitting and after finishing. Generally, faults are classified by type and by frequency in the inspected knitted roll. The inspection assessment permits to appreciate fabric quality. The judgement of fabric quality depend on faults tolerance levels fixed by each knitter and could be in some cases subjective because it is often based only on the number of faults and not on fault size and gravity

“Our aim of this project is to study on weft knitted fabric

fault. To do so we collect various faults from many industries and classify them in a systematic manner.” Faults in circular knitting production can be caused in various ways and quite a few of them cannot be just related to just one cause.The following explanations are expected



















Literature review: The practice in the industry in assessment of hosiery yarn quality is on the lines with the established norms for weaving or for general understanding of yarn grade rather than anything specific specific to knitting.The purchase of yarn is based on the general parameters like count, U%, imperfections,strength imperfections,strength and elongation and TPM. Most of the knitters test only the count for setting the GSM of the fabric.The knit structure and knitting process have got some specific requirements compared to the weaving.the knit fabrics and their process requirements are definitely much different from weaving. It has not been appreciated so far, may be due to lack of proper tools to assess them. A number of demands placed today on knit yarns for flowless processing,must processing,must also be satisfied by yarns for weaving.But there are several properties,which have to be rated differently for knit yarns.The process of waxing,e.g, used to reduce the coefficient of friction of a knit yarn, is an important factor,wheares a weaving yarn is not waxed.in the last years the quality of raw metarials for jersey yarns has been to a large



















There are some specific difference between woven and knit fabric.They are different in construction and their raw materials that is Yarn used in woven & knit also have technical difference. As a result the fault found in Yarn used for woven and knit fabric production are widely widely different from each other.

The main difference between woven & Knit yarn:

Woven Yarn Have high twist High Strength Higher TM (4-4.5) Higher Elasticity Sized Yarn

Knit Yarn Low twist Low strength Lower TM (3.5-3.8) Lower Elasticity Unsized Yarn

So we have seen that a lot of wide varities between woven and Knit yarn and also between their structure & manufacturing process so the fault in woven & knit fabric are also different. Here in this paper we tried to put light on Knitted part.





















Chapter-II



















There are mainly two systems of inspected fabric grading: 1. 4-point system (Approved by AAMA and AAQC) 2. 10-point system But these systems do not take shade variation, handle, biasi problems into consideration. Now these are shortly described below:-

1. 4-point system: In this system fabric faults are identified with defect points in the scale of 4. i.e. maximum defect point is 4. 2

According to this system, if the total defect point per 100 yard of fabric is 40 or



















For holes and openings the pointing system is as follows:

SIZE OF HOLE Less than 1” More than 1” Knot(4 types) less than 3” Slubs- less than 3”

PENALTY POINTS 2 points 4 points 1 point 1 point

Some general rules of this inspection are: i) Not one metre of clothe is penalised more than 4 point. ii) Any defect occurring repeatedly throughout the entire piece is marked second. [Second is a cloth quality which implies that clothe contains minor defects. A trade discount of 8-15% is allowed in this category] iii) Combination of warp and weft defects running in one metre should not be penalised more than 4 points in them.



















WARP DEFECT Up to 1” From 1” to 5” From 5” to 10” From 10” to 36”

PENALTY POINTS 1 point 3 points 5 points 10 points

In case of weftway defects the penalty points are shown below:-

WEFT DEFECT Up to 1” From 1” to 5” From 5” to full width Full width

PENALTY POINTS 1 point 3 points 5 points 10 points

Some general rules of inspection are as below:-



















Chapter-III





















yarn processing faults 

yarn unevenness/Irregularity: unevenness/Irregularity:

the mass per unit length variation due to variation in fibre assembly is known as “irregularity” or “unevenness”.irregularities are seen in the yarn in the form of thic place,thin place,neps.





















For obtaining smooth curvature to loop and its uniformity the yarn should be uniform in thickness and imperfections should be minimum. The thin place in yarn receives more twist resulting in compact structure i.e. high torsional rigidity or sharp bends in loop while thick place receives less twist and forms a large curvature at loop. The coefficient of friction at thin places might be higher due to increased twist, which might be further aggravated by probable low wax pick-up. This variation in bending, twisting and surface friction can vary tension in yarn during loop formation. This





















Dry yarn: Dry yarns does not have a required amount of moisture which will not facilitate the yarn to have enough extension during knitting process. 

Causes:storage under extreme temperatures must be avoided under all circumstances.at circumstances.at high temperatures the danger is present that t hat paraffin























Unexpected high twist:

Twist in hosiery yarn should be less, a fact known to all technologists. Still in few cases one finds yarn of higher twist being preferred on the ground that it performs well in knitting in terms of lesser yarn breakages.





















As a result the effective twist in each loop arm may change to the extent of 400 to 600 tpm (10 to 15 tpi) e.g. in a 20s cotton yarn (29.5 tex) of 3.6 TM (34 tpc.tex½ of TF) twisted in ‘Z’ direction, or of 633 tpm (16tpi), would have a reduction in twist to the extent of 400 to 600 tpm (10 to 15 tpi) in left arm and an addition of the same amount in right arm of the loop. Such a great change in twist or strain in yarn at loop arms in association with strains experienced in the formation of loops would lead to deformation of













































List Of weft Knitted Fabric fault : 1)Barre























BARRÉ : The noun "BARRÉ" is defined by ASTM* as an unintentional, repetitive visual pattern of continuous bars and stripes usually parallel to the filling of woven fabric or to the























Raw Material Fiber : 1. Failure to control fiber diameter diame ter (micronaire or denier) from laydown to laydown.























Yarn Formation/Supply 1. Variations in carding; i.e., different amounts of non-lint content removal from card to card. 2. Poor blending of fiber in opening through finisher drawing.

























































































































































































































































































































































































































































































































































Loss of elastic properties in Cotton

Causes:

Improper processing method

Remedies:    

Elastane are sensitive to highly acidic pH Avoid Chlorinated Bleaching High tension & excessive heating should be avoided in finishing Pretreatment sequence adopted should be - Relaxation- heat settingdemineralization- scouring-bleaching- dyeing- finishing- compacting

Bowing :

Usually caused by finishing. Woven filling yarns lien in an arc across fabric width: in knits the course lines lie in an arc across width of goods. Critical on stripes or patterns and not as critical on solid color fabrics



















Wrong Slitting: Its causes due to operator carelessness.sometimes workers doesnt slit fabric through slitting mark. Operators have to slit fabric through slitting mark or fed fabric in slitting m/c in proper way so that m/c can slit fabric through slitting mark .

Lycra burn: Due to improper heat set.

Heat set be done carefully .



















Chapter-V Fault in V-bed knitted Fabric



















List of Fault in V-bed kniting kniting m/c: m/c:

1. Pilling 2. Hole 3. Curling 4. Width variation 5. Loop missing marks 6. Wax mark. 7. Needle missing mark



















Needle missing mark

Causes: 

1.because of partial opening of needle cap



2.deflection of need cam trick



3.dirty needle path



4.clogging with brush

Remedies: 

1.clearing needle position



2.confirming the optimum opening of needle



3.clean needle path



4.replacing defective needle





















Hole Causes: 

1.broken latch



2.cam box deflection



3.broken needle butt



4.damaged needle

Remedies: 

1.replacing broken & defective needle



2.confirming the opening of the needle



3.clean cam box



















Curling Causes: 

1.uneven tension on the take down



2.side needle deflection



3.uneven loop length

Remedies: 

1.proper & even tension



2.optimum & clean opening of every needle



















Width variation Causes: 

1.uneven tension at different points of the body part



2.weight variation at the tensioning device



3.improper tension in take down down



4.unequal loop lengths



















Loop missing marks Causes: 

1.improper running of cam box because of dirty needle trick



2.cam box deflection



3.uneven knock over of latch needle



4.uneven plies of yarn

Remedies:



















6.Wax mark. Causes: To prevent the friction between cam box and needle trick,wax is been used in needle trich,during knitting this wax penetrate into the yarn of the fabric,whenever the finshed fabric is washed in hot liquor the wax is been molten and creates a wax mark on the fabric.the wax is also been used to increasing the pliability of the yarn.

Remedies: 

1.Prevent using wax in cam trick & yarn



2.by using pliable yarn



3.ensure the smooth running of the cam trick & opening of needle





















7.Pilling Causes: 

1.using of different plies of yran



2,.excess tension



3.foreign fibres & materials

Remedies: 

1.using same ply of yarns



2.prevent of flying of foreign fibres



3.Ensuring correct tension, tension should not too less or to high.



















Chapter-VII Conclusion



















Conclusion: Detection of faults during production of knitted fabric is crucial for improved quality and productivity. productivity. This paper will present present and discuss discuss the detection detection of faults faults and malfunctions during the production remedies of weft knitted fabric. The use of mechanical tension tension tracking device we we can solve the most widely seen fault like barreness at every feeders. But few years back optical device for tracking these faults was introduced which can track these faults far more effectively then the mechanical sensors. But introduction of this optical optical sensors sensors coul dn’t sort out the widely seen problem patta in the knitting production production process cause cause it is created due to problem or breakage of yarn at every feeder . so tracking of YIT(yarn input tension) by the introduction of of mechanical sensors sensors at the feeding system system of the circular knitting m/c m/c is the only most effective effective way of solving the the patta problem in the industrial area



















Bibliography: # Fibre2Fashion.com # The Indian Textile journal # SaarcZone.com # Circular Knitting , By Meisenbach Bamberg Bamberg # Understanding Textiles for a merchandiser,By Engr.Shah Alimuzzaman Ali muzzaman # Wood Head Publication. # Cotton Incorporated. # Incampus.com #scribd.com

Study on Weft Knitted Fabric Faults and Remedies-1

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