21 Defects in Knitted Fabrics PDF

Knitting Technology  Skew or Bias ►Skewing: Skewing effect is seen as a line or design running at a slight angle across the cloth.  Bowing or Twisting ►A line or a design may curve across the fabric. This bowing is the distortion caused by faulty take-up mechanism on the...

Knitting Technology  Skew or Bias ►Skewing: Skewing effect is seen as a line or design running at a slight angle across the cloth.  Bowing or Twisting ►A line or a design may curve across the fabric. This bowing is the distortion caused by faulty take-up mechanism on the knitting machine. Bowing Knots Thick and Thin Yarn Uneven Yarn Structure Course Yarn Slub Slub  Needle Lines ►Needle lines or vertical lines is due to a wale that is either tighter or looser than the adjacent ones. ►This is caused by needle movement due to a tight fit in its slot or a defective sinker.  Needle Run ►Bent needles - stem, ►Broken needles ►Dirty needles ►Dial and cylinder needle misalignment needles rub ►Improper setting of yarn guides ►Machine vibration ►Wrong needle ►Mixed needle lots  Fabric Run ►Dropped Stitch: This is an unknitted stitch caused either by the yarn carrier not having been set properly or the stitch having been knitted too loosely. ►Run or ladder: A run or ladder indicates a row of dropped stitches in the wale.  Ladder Wales Collapse in straight line  Holes ►A large hole or a press off is the result of a broken yarn at a specific needle feed so that knitting cannot occur. Yarn or mechanical in nature High friction - between yam and guides Insufficient wax or oil Poor quality (strength, elongation) Too much yam tension Knots Improper yam size for gauge  Holes Snarling of yarn (twist lively) Slubs, trash Lint (low twist, extreme hairiness, poor cleanliness) Low humidity Static Improper setting of yam guides Feeder problems (tight, rough places) Faulty height adjustment of sinkers Hole Hole Needle hole  Holes by defective machine elements  Cloth Fall Out ►It can occur after a drop stitch especially when an empty needle with closed latch runes into the yarn feeder and removes the yarn out of the hooks of the following needles. Cloth Fall Out  Bunching Up ►This is largely influenced by the fabric take-up and whether it functions properly.  Shade Bar/ Barre ►A barre effect has the appearance of a stripe with shaded edges. It is horizontal in weft knits and vertical in warp knits.  Barre ► Yarn related causes of barré: Yarn count variations. Yarn twist variation. Wrong yarn - size, color, blend level, twist direction. Mixed yarn lots. Mixed shipment dates of same dye lot. Uneven waxing or oiling of yarn. Improper conditioning.  Barre ► Knitting Machine related causes of barré include: Different stitch settings (stitch lengths). Improper tension at a feed. Faulty cylinder or dial cam settings. Malfunctioning of storage or tape feeders. Improper threading of yarn. Variations at take-down or spreader system.  Barre Machine vibration. Dirt, lint, and/or yarn fragments in the camming system, tricks, needles, or sinkers. Variation in oil content. Worn needles, which generally produce length direction streaks. Uneven cylinder height needles (wavy barré). Worn cylinder and/or dial.  Barre ► Recommendations to minimize barré include: Knit an entire dyelot from the same knitting machine. Use only yarn from the same spinning lot. Use only from the same shipment date if possible. Determine through laboratory analysis and experience if the preparation procedures are sufficient or can they be modified to eliminate the problem. Fly Yarn Contamination Fabric Weight out of Tolerance Fabric Elongation not as Approved Dye Mark  Stain Excessive oil, dirt  Missing Plush Loop Mulfunctioning of loop  Pin Marks Poorly adjusted stenter pin  Spirality ►This is a very common problem in single jersey knits and it may exist in grey, washed or finished state and has an obvious influence on both the aesthetic and functional performance of knitwear. ►However, it does not appear more in interlock and rib knits because the wale on the face is counter balanced by a wale on the back.  Spirality Over twisted yarn  Spirality ►Spirality is a regular deformation (skewing) of the knit structure due to the yarn twisting within the structure, so that the vertical lines of stitches (the wales) are no longer at right angles to the horizontal lines of stitches (the courses).  Spirality ►Spirality in knitwear is caused by using an “unbalanced” yarn. ►When spirality occurs in a fabric there is little or nothing which can be done in finishing to alleviate it and usually the only option is to use replacement yarn having balanced twist.  Spirality ►However, sometimes spirality can be prevented by steam setting an unbalanced yarn when knitted in a single bed structure, and also some yarns which cause spirality can usually be knitted in a rib structure, since skewing tendency on the front and back beds should cancel out.  Spirality ►Weft knitted fabrics tend to undergo certain dimensional change that causes distortion in which there is a tendency of the knitted loops to bend over, causing the wales to be at diagonal instead of perpendicular to the courses.  Spirality ►Some of the practical problems arising out of the loop spirality in knitted garments are: displacement or shifting of seams, mismatched patterns and sewing difficulties.  Spirality ►These problems are often corrected by finishing steps such assetting/treatment with resins, heat and steam, so that wale lines are perpendicular to the course lines. ►Such setting is often not stable, and after repeated washing cycles, skewing of the wales normally re- occurs. Spirality  Spirality ► Calculation: Percent change in spirality can be represented as follows: X = 100 x (AA’/AB) Where, X = % change in spirality  Facing-up ►Facing-up can be defined as the generation of unwanted surface fibres leading to a change in the appearance of the garment. ►Fabrics and knit made from Woollen spun yarns generally are finished to create a fuzzy or hairy surface and during wear/abrasion the reverse effect is sometimes an issue.  Facing-up ►Facing up can occur all over a garment or in localised areas. ►It is caused by the gradual withdrawal of fibres from the surface layer of yarns (migration) and can in many cases lead to Pilling.  Facing-up ►The migration of surface fibres from the body of the fabric to the surface is due to frictional forces applied to the fibres on contact with other surfaces which might also include the same fabric. ►Consequently facing up tends to occur when surface abrasion forces are high such as during tumble drying.  Facing-up ►The tendency to facing up depends on several factors, very similar to those associated with pilling, and include: Fibre length Short or broken fibres are less well anchored in the yarn structure and migrate more easily Fibre diameter Finer fibres tend to be shorter and thus more likely to migrate Yarn twist Low or irregular twist permits fibre migration  Facing-up Cover factor Higher densities increase inter-fibre friction and slow down fibre migration. Fabric Softener Too much softener reduces inter-fibre friction and permits fibre migration. ► To avoid the potential for facing up the above factors should be considered in the design of the fabric/garment.  Cockling and Loop Distortion ►Cockling has been defined as “an irregular surface effect caused by loop distortion”. ►In general it appears as localised groups of distorted knitted loops which have twisted out of the symmetrical configuration. ►The fault is usually found in the plain knit structure, which is relatively unstable, and especially in yarns spun from animal fibres such as wool or mohair.  Cockling and Loop Distortion ► Wool knitwear made from worsted yarns is more prone to cockling/loop distortion because, unlike woollen knitwear, no milling is carried out during finishing which helps to conceal faults under a surface fuzz.  Cockling and Loop Distortion ► There are three types of cockling:- ►a) Rib/plain interface cockling caused by a difference in the relaxed widths of the two structures.  Cockling and Loop Distortion ►Panel-edge cockling caused by a difference in the relaxed dimensions of neighboring structures. ►Panel edge loops are stretched in length when fashioning takes place and this tends to result in the contraction of the adjacent plain knit fabric, allowing cockling to take place.  Cockling and Loop Distortion ►Random all-over cockling. Almost always this can be assigned to using unsuitable yarn. ► Yarns which cause random all-over loop distortion also tend to cause rib/plain and panel edge cockling as well.  Cockling and Loop Distortion Factors affecting Cockling/Loop Distortion ►The main factors which have been linked to cockling/loop distortion include: Fibre Diameter There is a direct relationship between an increase in fibre diameter and increase in loop distortion/cockling. Cockling and Loop Distortion Method of Dyeing Package dyeing increases loop distortion/cockling because it creates a ‘setting effect’ on the fibre and yarn, making it more rigid and hence resistant to loop formation on knitting. Cockling and Loop Distortion Yarn Count Regularity Although yarn count has little effect, yarn count regularity does influence loop distortion/cockling. Yarn Twist Regularity Generally accepted that large variations in twist can lead to loop distortion/cockling. Cockling and Loop Distortion Yarn Rigidity The more rigid the yarn the greater will be the tendency for loop distortion/cockling. However, the flexural rigidity of a yarn is usually dependent upon the diameter of the fibres. Cockling and Loop Distortion Yarn Steaming Steaming causes setting and increased rigidity particularly in the case of shrink-resist yarns. Cover Factor The lower the cover factor, the less stable the resultant fabric, and the greater possibility of loop distortion/cockling. Cockling and Loop Distortion Fibre Crimp Inconclusive, but it is believed that the higher the fibre crimp the less the tendency for loop distortion/cockling to occur. Top Chlorine/Hercosett Treatment Although some opinions have been somewhat diverse, it is generally regarded that it has no significant direct effect on the tendency for the occurrence of cockling/loop distortion.  Cockling and Loop Distortion Avoiding cockling/loop distortion ►Where possible the above factors should be considered and if feasible: Use a wool with a finer mean fibre diameter Improve the regularity of the yarn Avoid package dyeing – top or piece dye instead Avoid steam setting the yarn on package Use a wool with more crimp