Problems of fabrics distortion can be discussed under following headings Seam Stretch and grinning Seam slippage and fraying Seam Pucker
Seam Stretch & Grinning It is essential for a seam to be able to extend adequately along its length in use without the sewing thread reaching its breaking extension and cracking.
Where the stitch balance is not properly adjusted (stitch too loose) and can see the seam opening up or seam grin . To check for Seam Grin, apply normal seam stress across the seam and then remove the stress. If the seam remains opened, then the seam has too much "grin through". SOLUTIONS: • To correct, readjust the sewing machine thread tensions so that the proper stitch balance is achieved. • Too much tension will cause other problems including seam failures ("Stitch Cracking"), excessive thread breakage, and skipped stitches.
Seam Slippage Woven fabrics of open construction, particularly those made from smooth, continuous filament yarns, and weaves with long floats, are liable to develop slippage in those seams of a garment which are stressed during movement. Threads running parallel to the seam are liable to slip. Where the yarns in the fabric pull out of the seam from the edge. This often occurs on fabrics constructed of continuous filament yarns that are very smooth and have a slick surface. Also caused by loosely constructed fabrics. MINIMIZING SEAM FAILURES - SEAM SLIPPAGE: • Consider changing the seam construction to a French seam construction • Seaming at an angle to the cloth thread • O/L edges • Increase the seam width or width of bite; • Optimize the stitches per inch; • Contact your fabric supplier.
What is seam pucker? • A gathering of the material to produce and uneven, distorted or crinkled seam. • More common in woven fabrics than in knitted fabrics, and prominent in tightly woven fabrics. This disturbs the appearance of seam
Main problem areas? • Lightweight fabrics Shirts Blouses Skirts • Fine woven fabrics Ladies dresses
Understanding the causes! • So that its occurrence is avoided during making up. • Pressing is not a reliable solution. • It is costly and the effect is frequently short lived. • Take your time when analysing.
Seam Pucker! • Is apparent on one or both sides of the seam. • It shows immediately after sewing or shortly afterwards. • It shows after several laundering • The degree of seam pucker is usually measured by visual comparison of photographic standards. • The degree of pucker is marked on a scale of 1 to 5 (1= no pucker, to 5 = very badly puckered).
Basic causes? • Machine Puckering or Feed pucker ( Uneven fly feeding) • Yarn displacement (or inherent pucker or Structural jamming) • Tension Puckering (Excessive Thread Tension) • Pucker due to mismatched patterns • Stitch density and fabric type
Feed Pucker (differential fabric stretch) • Occurs when one of the fabric plies is fed at a different rate the other ply or plies. This causes a gathering effect in the overfed ply. • The bottom ply is usually fed more positively by the feed dogs while the top layer is only held and guided by the presser foot.
Prime requirement of a feeding system is it should move plies of fabric past the needle and that all the plies should move together. • In drop feed system • Lower ply is positively engaged with a feed dog • Lower ply moves same amount as feed dog moves • For the upper fabrics, lower fabric acts as feed dog and exerts a frictional force tending to move it forward. • Friction between fabric and fabric lower than that of between feed dog and fabric. • In general upper fabric would tend to move less than the movement of the lower one.
Feed Pucker Contd • The opposing force generated on the top ply of fabric by the base of the presser foot can cause the ply to be stretched against the bottom ply • It can be viewed as bottom ply being gathered against the top ply • The shortening of one of the fabric layers (usually the bottom one) creates a wavy appearance on one side and results in what is known as “feed pucker”
Identification Method 1 Make two perpendicular cuts across a sewn seam where the puckered condition is the greatest. Remove the thread in the seam and see if the two plies are of equal length. If one is longer than the other then the puckering is being caused by uneven ply feeding.
Identification Method 2 Cut two pieces of fabrics (either in warp or weft direction) Mark about 25 marks in 1cm interval at right angles to the edge Place two pieces together with marks face to face Pinned at one end, and then stitched If differential stretch has occurred marks will gradually loose their register
Improvements can be made Use the minimum presser foot pressure that will maintain uniform feeding. Set the feed dogs at their proper height and check for back-feeding. Use the correct presser foot and needle plate for the material and operation being sewn. Use machines equipped with a needle feed or compound feed mechanism where the needle moves with the feed as the fabric is being sewn.
Improvements cont: Whenever possible, use machines equipped with auxiliary top feeding mechanisms such as: walking foot, puller, top driven roller feed, upper belt feed, etc. On machines equipped with differential feed systems, set the differential action to slightly stretch the bottom ply to match the top ply so they are fed evenly into the seam. Use automatic machines equipped with material clamping systems that prevent the fabric from moving as it is being sewn. Observe operator handling for proper fabric movement to and through the machine. If the plies have different stretch characteristics, position the ply with the greatest amount of stretch are against the feed if possible.
Choosing the correct feed dog • Feeds with finer teeth gauge set. • Ensuring the feed is not set too high or too low. • If feed is set too high, back feeding can occur causing the fabric to be held back slightly. • If the feed dog is set too low, slippage of the fabric plies can occur causing pucker.
Presser foot pressure • Reduce pressure to a minimum in order to provide adequate feed without fabric slippage • With lightweight fabrics it can be very difficult to set the foot pressure adequately to prevent the fabric from slipping • Reducing machine speed is a possible helpful factor but only as a last resort • Use automatic machines equipped with material clamping systems
Presser foot pressure Contd • Observe operator handling for proper fabric movement • Lamination material, and membrane fabrics often cling to the presser foot, making it virtually inevitable that slippage will occur when a drop feed mechanism is used. • Machines with a specific top feed can be of benefit. • PTFE coated presser foot can be a temporary remedy.
Sewing thread pucker(Tension Pucker) Threads used must. • Suit the seam position. • Give the required strength. • Produce the required visual affect (decorative seams)
Factors affecting tension pucker • Extension properties of the sewing thread. • Shrinkage due to moisture and heat. • Surface structure and running properties.
Tension Pucker If a thread is sewn into the seam with heavy machine thread tension so that it has been elongated or stretched as the stitch is being set. The thread will try to recover or return to its original length If the fabric is going to stretch or contract by the same amount there will not be any visible effect. This can cause the seam to pucker immediately as the seam is coming out from under the presser foot.
Shrinkage of sewing thread • Can occur under low humidity conditions • Absorption of moisture by natural fibres e.g. cotton will cause the fibre to swell and to increase in diameter and thus decrease (that is shrink) in length • Pucker in the seam will result
Other properties that could affect tension pucker Surface properties • Twist properties • Friction properties • Fine long staple polyester sewing threads give a vastly superior stitch
Stitch density and material type • Must also be considered when studying tension pucker. • It is directly linked with the required thread tension and the length of thread required by the seam. • Increasing the thread consumption in the seam increases the seam strength. • In a lock stitch for example- A 3% increase in stitch consumption can give almost 60% increase in seam strength.
Stitch Density Contd • A stitch is only complete after the fabric has moved past the needle. • The fewer stitches per cm, the greater the distance the fabric must be moved for the next stitch insertion. • Consequently a greater force is required to present the correct thread length for a perfect stitch. • Higher thread tension in the seam is caused and puckering induced that could have been avoided.
Seam appearance Left = 6 stitches / cm Right = 3 stitches / cm
Identification Method 1 Carefully clip the thread between adjacent needle penetrations along the seam and observe if the puckering is reduced in the fabric. If it is, then excessive thread tension is the probable cause of the seam puckering.
Identification Method 2 A seam is sewn joining two pieces of fabrics, using the thread in question using the previously used tension. If this seam shows pucker, re sewn with a sheet of paper on top of it. After sewing torn away the paper along the needle holes. If the pucker is due to tension this seam should be free of pucker. Paper ensures that the extra length of thread is fed on to the each stitch.
Improvements can be made Use a thread with a low elongation or high initial modulus to minimize stretching during sewing. Use a thread with good lubricity characteristics that will allow it to be sewn with minimum thread tension. Use very light machine thread tensions. Reduce the thread size matching the requirement If structural jamming does not appear to be a problem, increase the needle size or use a needle with a ball eye needle to open up a larger hole in the fabric so the stitch can be set with the lightest tension possible. On some machines the thread control guides and eyelets can be adjusted to control the thread more efficiently so less tension is required.
Inherent Pucker(Structural Jamming) Caused by the displacement of the warp and weft yarns by the needle penetration and thread insertion onto the fabric. If sewn in the warp direction the warp threads will be displaced laterally causing an inevitable shortening of their length relative to adjacent yarns. The term structural jamming is given to this type of pucker because it results directly from the act of jamming extra threads into the structure.
yarn sewing thread Structural jamming pucker showing crimping and hence shortening of yarns adjacent to the seam
Inherent Pucker Contd The fabric structure becomes jammed resulting in swelling and puckering of the seam.
Inherent Pucker Contd The use of finer needles and finer threads is vital if inherent pucker is to be avoided
Identification This is visible on both plies Carefully clip the thread between adjacent penetrations along the seam where puckering is visible. Observe if the puckering remains or goes away. If puckering is still remain then yarn displacement is a probable cause.
Improvements can be made The use of fine holed needle plates are essential for reducing seam pucker The use of stitch type also plays a very important part in reducing pucker Operator handling also needs to be addressed The sewing direction is also very important
Shrinkage puckering Shrinkage puckering can be caused when one of the components sewn into a seam shrinks at a different rate than other components. Typical components include the shell fabric, interlining, zipper tapes, stay tapes, and the thread. All these components should have minimum shrinkage to produce the flattest pucker-free seam.
Identification Using an permanent ink pen, make two perpendicular lines exactly 10 inches apart across a seam that usually exhibits excessive seam puckering after laundering. Connect the marks with a line running parallel to the seam. Now, subject the garment to finishing and pressing cycles and then check the length of the seam again. If there is seam shrinkage, the distance between the two marks will be less than 10 inches.
Other factors causing seam pucker • Fabric finish and structure. • Seam planning. • Changes to garment construction. • Operator handling. • Influence of accessories. • Influence of seam type. • Influence of knives.