• Pattern alignment in relation to the grain of the fabric: Pattern pieces normally carry a grain line. When pattern pieces are laid down on the piece of cloth, the grain line should lie parallel to the line of the warp in a woven fabric or the wales in a knitted fabric. When pattern pieces are laid across the piece, the grain line should lie parallel to the line of the weft in a woven fabric or the course in a knitted fabric. In bias cutting, which is often used in large pattern pieces as part of the apparel style in ladies dresses and lingerie, as well as in small pattern pieces such as pocket facings and undercollars in menswear as a requirement of satisfactory apparel assembly, the grain lines will be at 45 °C to the warp. The designer or pattern cutter may define a tolerance that allows the marker planner to swing the grain line a small amount from parallel. If the marker planner lays down a pattern outside the stated rules for grain lines, then the finished apparel will not hang and drape correctly when worn.

• Mixed pattern parts: Parts not correctly labelled in marker, therefore a marriage of wrong-sized parts

• Line definition poor: Poor line definition (e.g. chalk too thick, indistinctly printed line, perforated lay not fully powdered), leading to inaccurate cutting

• Skimpy marking: Either the marker did not use the outside edge of the pattern or the pattern was moved or swung after partial marking to squeeze the pattern into a smaller space in the interests of fabric economy. Alternatively, the pattern is worn around the edges and should be replaced.

• Marker too wide: Apparel parts at the edge of the lay are cut with bits missing

• Frayed edges: May impede cutting time by clogging the knife action and/or spoil the fabric with rips or pulled yarns. The amount of fraying depends on fabric construction and finish. Improper cutting tools or dull knives cause excessive fraying in a pattern as the section is cut.

• Fuzzy, ragged, or serrated edges. The result of poor cutting implements. Such edges will impede sewing and/or diminish sewing quality. Such a condition is caused by faulty knife edges such as burrs, chips, or dullness.

• Ply-to-ply fusion: More common and troublesome. Adjacent plies in a block are fused together, which makes it difficult for the sewing machine operator to pick up a single ply quickly. Fusion occurs due to heat created by excessively high speed of cutting or by the friction of a dull knife. To prevent fusion, check knife speed, keep knives sharp, place wax paper between fabric plies, and lubricate the cutting blade.

• Single-edge fusion. Consists of a single ply whose cut yarn ends are fused to form a hard brittle rim on the cut edges. Sometimes, this is desirable to prevent fraying; however, hardness and brittleness are undesirable if they impede sewing manipulation or may result in seams uncomfortable to the consumer.

• Pattern precision. Misshaping or distortion of the pattern perimeter as cut. Whether it is under or overcut is due to poor manual control of the cutting machine and poor lines on the marker. To assure precision in a pattern, check markers before cutting, use tensionless spreading, or allow time for the fabric to relax. After a cut, check the top, bottom and middle plies against the pattern.

• Notches . Notch size refers to the depth of a notch. If the depth is too great, the notch may show after sewing. If the notches are too small, sewing operators may have difficulty locating them quickly, resulting in decreased efficiency. Misplacement of a notch may be due to an improperly spread marker, poor control of a cutting machine with the cutter's notching tool stroking diagonally instead of vertically, incorrect marker in that the notches formatting parts do not coincide. Check notch placement against matching pieces. Quality control in stitching may be a problem if notches are not aligned (Fig. 16.1).

• Drilling. The drill hole may be too small in diameter. In addition, a drill may become too hot due to high speed or wrong size, causing the plies to fuse at the drill hole. The drill must stroke vertically to the table for uniform placement throughout the bundle. Sometimes fabric properties are such that the slight movement of yarns in a fabric would close a drill hole. In such cases, it is necessary to drill holes with a marking fluid. The drill used for such a purpose is hollow and carries marking fluid (ink) that is deposited at the drill point on the fabric as the needle is withdrawn. Such marks should last long enough so that further processing can be finished without difficulty, but should be easily removable after processing or in case of an error.

General

Seam pucker (Fig. 16.7) is a wrinkled appearance along the seam, which influences the apparel appearance to a considerable degree. Seam pucker, identified as a sewability problem about 70 years ago, has been regarded as one of the most important parameters of quality control in apparel manufacturing industries (Anon, 2010; Hati and Das, 2011). It is usually caused by improper selection of sewing parameters and material properties, which results in unevenness on fabrics being stitched together, thus impairing their aesthetic value. In severe cases, seam pucker could appear like a wave front, originating from the seam and extending through the entire garment. In less severe cases, the wave formation is less pronounced, but nevertheless discernible. Indeed, apparel exhibiting pronounced seam puckers is certainly unwelcome by customers. Table 16.6 summarises the causes and solutions for seam pucker.

Structural jamming

During seam formation, stitches are made by interloping of bobbin and needle thread. These sewing threads displace the fabric yarns from its original position. Fabric yarns attempt to return to original position and they are prevented from doing so by the sewing threads. This causes the fabric layers to displace in a plane perpendicular to fabric plane and results in seam puckering (Fig. 16.8). This kind of pucker is visible mostly in tightly constructed fabrics that do not have enough space to accommodate sewing threads. The problem can be avoided or reduced by using a thinner thread and a small needle point; a needle plate and a presser foot with a smaller needle hole; fewer stitches per unit length; and stitching in a direction which allows the different yarns in the construction of the fabric to be displaced. This kind of pucker is visible on both sides of the fabric (Crum, 1983; Dorkin and Chamberlain, 1961).

Differential feed

Differential feed of the feed dog produces feeding pucker (Fig. 16.9). During sewing operation, bottom layer fabric is moved forwarded by the feed dog positively. But the movement of the top layer fabric is effected through frictional contact between top and bottom fabric. Thus movement to top fabric is not a positive one. The velocity of the top layer fabric is generally lower than that of the bottom layer fabric. This causes accumulation of bottom layer fabrics and produces feeding pucker, which is visible at one side only. Use of an appropriate feed dog, presser foot pressure and sewing speed may help to reduce this kind of pucker (Hati and Das, 2011).

The feed dog should have the optimum number of teeth and rows of teeth for the operation and fabric being sewn. Sometimes, pucker occurs when the material is not held down flat as it is being fed through the machine, creating a rippled appearance as the plies conform to the feed dog teeth. Generally, light weight, wrinkle-resistant fabrics should be sewn with feed dogs having 20–24 teeth per inch. Medium and heavy weight fabrics should be sewn with feed dogs having 14–18 teeth per inch and 8–12 teeth per inch respectively. The pressure exerted by the presser foot against the needle plate causes the fabric to spread. Therefore the dimensions of the seam produced on a fabric have been momentarily altered. When the fabric returns to its normal dimensions, waviness occurs. Reducing the pressure of the presser foot can prevent or at least reduce waviness. High sewing speed requires high presser foot pressure in order to control the feed and prevent the presser foot from bouncing under the impact of the feed dog movement. The bouncing of the pressure foot disturbs the fabric feed, leading to a puckered seam and uncontrolled sewing conditions (Fan and Hunter, 2009).

Sewing thread tension

Tension pucker occurs when the sewing thread is under very high tension (Fig. 16.10). Sewing thread extends due to very high tension, and afterwards attempts to relax. If elastic recovery of thread and shrinkage of fabric coincides, pucker does not occur. But in most situations recovery of thread is more than fabric shrinkage causing fabric to pucker. This is inevitable from the point of view of the sewing operation, which requires higher needle thread tension than bobbin thread tension to snatch the latter for stitch formation. Although sizing or resin on the fabric can prevent or reduce this problem, the seam will still become puckered after laundering. Thread tension pucker can be minimised by reducing the thread tensions on the sewing machine or using a thread with a low elongation or high initial modulus to minimise stretching during sewing. If structural jamming does not occur, it is beneficial to increase the needle size or use a needle with a ball eye to open up a larger hole in the fabric so the stitch can be set. The take-up spring, thread control guides and eyelets should also be properly set to avoid undue tension of the sewing thread during sewing (Fan and Hunter, 2009; Hati and Das, 2011)

Sewing thread shrinkage

High shrinkage potential of fabrics is another source of seam pucker. Threads made of cotton and other natural fibre often shrinks when wet. This may cause seam pucker when fabric shrinkage and thread shrinkage differs. This problem can largely be overcome with the use of synthetic sewing threads. These threads are normally dry heat stabilised to withstand up to 110 °C. They may also cause seam pucker during pressing, if the pressing temperature is above heat-set temperature (Dorkin and Chamberlain, 1961).

Fabric shrinkage

Different shrinkage of plies of fabric causes seam pucker that is visible only after few washing cycles (Fig. 16.11). The component that has the lower shrinkage rate will buckle, resulting in a shrinkage pucker. They will never occur during the sewing operation. They are concerned with dimensional stability of plies of fabric. To prevent or reduce this type of pucker, it is necessary to use compatible components that have similar dimensional stability (Anon, 2010; Hati and Das, 2011)

Mismatched patterns

If the patterns of fabric that are to be matched are of unequal length, the experienced tailor will feed more length of the longer pattern. This compensates for extra length, but fabric accumulates in the form of wrinkles and seam pucker appears (Fig. 16.12).

Generation and loss of heat in the needle

Heat is generated in the machine needle as a result of friction between the needle passing at high speed through the substrate and the thread passing at high speed through the needle eye. Heat retained by the needle is concentrated in a small mass of metal and the temperature may reach 300–350 °C. During the stitching operation heat is also dissipated from the needle. Heat is transferred by conduction through the needle-bar to other machine parts, to fabric surrounding the needle and to thread in the needle eye. Heat loss by conduction may be higher when materials of high thermal conductivity are used and when the needle size (diameter) is also increased. Conduction is the most important means of heat loss from needles. Movement of air around the needle allows heat loss by convection, with air currents created by moving machine parts and by movement of the sewing thread. Radiation has only a minor role in heat loss from needles. Conduction, convection and radiation are heat-loss processes which occur naturally but, by altering conditions of sewing, heat loss can be increased, though modifications to machine parts may be necessary (Laing and Webster, 1998).

Use of a bulged-eye needle provides for only a single line of contact between needle and material at the needle eye. Using a bulged-eye needle, as compared with a normal needle, results in a drop in needle temperature. Heat loss is also increased by using an air-cooler on the needle. Lubricants applied directly to needles may lower friction between the needle and thread, or they may be applied to thread. Absorption of energy by a vapour spray (i.e. a coolant atomised or directed straight to the needle, with heat being removed by vaporisation of the solvent), offers further scope for temperature reduction. Water may be a satisfactory coolant, but a rust inhibitor is required. Temperature losses achievable in this way can be up to 90 °C.

High needle temperatures and their effects

Few fabrics were damaged seriously by needle heat prior to the 1940s. Since then fabrics and sewing threads manufactured from thermoplastic fibres have become common, and the maximum stitching speed of sewing machines has increased markedly from around 1000 to 6000 stitches/min. Thermoplastic sewing threads, such as nylon and polyester, may be heated by the needle, soften, melt, and break. Nylon and polyester threads melt at 240–260 °C. Cotton and silk are not thermoplastic, but degrade at around 400 °C. Thread breaks decrease production levels because of discontinuity in stitching, assuming that the partly-formed seam is not unpicked and fully restitched (Laing and Webster, 1998).

Softened polymer from either the sewing thread or the fabric being stitched (or both) may be deposited in the needle eye. The needle eye cools when machining stops, and the polymer hardens, thus clogging the eye. On restarting the machine, the sewing thread cannot move though the eye and so breaks. During the down stroke part of the stitch formation cycle a crease may form in the sewing thread at the needle eye. If the needle temperature is sufficiently high, this crease may be set in the thread by heating followed by rapid cooling. Any loop subsequently formed in the sewing thread (required during formation of ISO 301 for example), is improperly shaped when the thread is creased and the rotary hook may not enter the loop. This would result in missed or skipped stitches and seam performance is adversely affected. More generally, any thermal damage to the fabric may affect the properties, performance or appearance of a seam. Table 16.7 summarises the causes and solutions for thermal damage (Carr and Latham, 1994, 2000).

Machine variables affecting needle-heat

Sewing speed has greater influence on needle temperature than any other single factor. Keeping other variables constant, the higher the speed the higher the temperature, up to an equilibrium point for any particular combination of variables. Equilibrium is reached when the heat generated is equal to that lost by conduction, convection and radiation. The actual temperature at equilibrium is specific to stitching conditions, for example the number of fabric plies, fabric properties, needle size and thread type. The time and number of stitches formed before the equilibrium may be quite short (Laing and Webster, 1998).

Needle size (Fig. 16.13) has been identified as an important variable. With lower temperatures typical of fine needles, less work is required for penetration of the cloth. Where needle diameter is larger, greater force is required for penetration of cloth and higher temperatures are observed. Needle temperature increases with increasing needle size but the magnitude of the effect is small, other variables being more significant (Hurt and Tyler, 1971, 1972b).

Needle-point shape (Fig. 16.14) and surface finish are also significant variables. Sewing with a heavy-ball needle usually results in temperatures at the higher end of the range. Bulged-eye needles operate at lower equilibrium temperatures than cloth or set point needles, the reduction being 11–30 °C. The surface finish of the needle also affects generation of heat. The highest temperatures are with dark matt surface needles, nickel, plain steel and chrome finishes giving progressively lower temperatures. The main parts in contact with material being stitched, the top of the blade and the needle point appear to have most effect on heat generated.

Any form of restraint on the movement of fibre and yarns in fabric might be expected to lead to an increase in the force required for the needle to penetrate the fabric. Machine parts such as the presser foot and throat plate affect the extent to which fabric is restrained. With respect to the throat plate, its hole size appears to be a critical variable. Movement of the fabric during the stitching operation is three dimensional with a glove of yarns/fibres forming around the needle as it passes down through the throat plate. If the throat plate hole is too small the fabric cannot be depressed and yarns are displaced temporarily. This may cause some fibres in the yarn to break. It has been shown that increasing the diameter of the throat plate hole decreases the equilibrium needle temperature (Laing and Webster, 1998).

Material variables affecting needle-heat

Needle heat generated during stitching depends on fabric-needle surface characteristics, fabric frictional characteristics, and fabric tightness (Laing and Webster, 1998).

Fabric density is a critical determinant of needle temperature. Any reduction in the ease with which fibre and/or yarns can be deflected from the path of the needle increases the force required for needle penetration. For example, woven fabrics with high cover factor and knitted fabric constructed of short stitches will be associated with elevated needle temperatures (Hurt and Tyler, 1971, 1972b; Laing and Webster, 1998).

Fabric finishing treatments (cleaning processes and solvents used to extract fats/waxes from the cloth, dyeing for colour change, resin finishes used to impart a different hand to cloth or to alter creasing characteristics) because of their effect on the frictional properties of the fabric, are the most important material variable influencing thermal damage. The amount and type of finish determines whether the needle temperature is raised or lowered. A decrease in needle temperature occurs with addition of lubricants or softeners – commonly long-chain fatty acid radicals that are hydrophilic. Softeners are applied primarily to improve the handle of fabric, but simultaneously may improve its sewing characteristics. Some softener is transferred from the fabric to the needle, the needle thus being lubricated, which reduces the friction thereby lowering equilibrium needle temperature. Fibres and yarns are stiffened by the application of many forms of resin and the handle and some other properties of the finished fabric are usually altered. These effects increase the resistance of yarns and fibres to movement by the needle, resulting in higher frictional forces and equilibrium needle temperatures (Hurt and Tyler, 1971; Laing and Webster, 1998).

The influence of sewing thread on needle temperatures is complex. Thread is able to cool the needle by conducting heat away (transfer occurring between the hot needle and the cold thread) and by increasing convective losses due to the cooling air stream created by the moving thread. The influence of both effects is greatest at the eye of the needle. Heat is also generated by the thread passing rapidly through the eye of the needle and against machine parts. Equilibrium needle temperature in a test run without sewing thread was lower than that obtained when subsequently stitching with a thread. A needle carrying thread, but without interacting with any fabric, heats by about 50 °C when running at high speed (Hurt and Tyler, 1971, 1972b; Laing and Webster, 1998).

The type of thread appears to affect the equilibrium needle temperature. Continuous filament thread results in higher needle temperatures than staple fibre thread. With continuous filaments, there is a greater area of contact between the thread and needle, and in addition less air is carried along with the thread on account of its smooth surface. Sewing threads of bulked or textured yarns have both a reduced surface area for contact between thread and needle, and facilitate air movement through the needle eye. Staple sewing threads also transport more cooling air to the needle, allowing the sewing speed to be increased by up to 10%, relative to that with comparable continuous filament thread, without adverse needle-temperature effects (Dorkin and Chamberlain, 1961; Laing and Webster, 1998).

The damage process

Inclusion of a seam in fabric generally reduces the fabric breaking load. Mechanical damage of yarns adjacent to the stitching may be a contributing factor. Rapid rupture of a yarn during stitching may occur as a result of extension to its breaking extension, or by cutting. The needle or the sewing threads may cut through the yarns of the material, but the mechanical damage outlined below appears largely independent of the presence of sewing threads.

When the needle point strikes a spun and/or multi-filament yarn and passes through its centre, a diamond-shaped opening is formed and some fibres/filaments are extended to accommodate the thickness of the needle. Twist will be displaced. Where the yarn has a low twist, fibres/filaments can move easily, but as twist level increases, twist displacement become increasingly problematic. fibre/filament failure will occur if the fibres are stretched to their breaking extension (Laing and Webster, 1998).

Many fabrics, especially those made from cotton and/or viscose, are treated with a stiffener, starch or crease-resistant resin finish. With the addition of starches and dextrins, the extensibility of individual fibres may not be affected but the fibres adhere to one another laterally. Adhesion prevents fibres slipping. With a resin finish, the extensibility of the fibres generally decreases. The effect of any finishing agent depends on the yarn’s initial twist level, with low-twist yarns not being adversely affected by more severe finishing processes.

Interstitial spaces in the fabric, sufficient to accommodate a needle or to facilitate yarn redistribution, are necessary if mechanical damage is to be avoided. If the fabric (woven or knitted) has a high cover, yarn relocation is impeded. With needle penetration of a fabric with maximum cover, the fabric tends to buckle from the horizontal plane. As a result warp/weft yarns in a woven fabric are pushed together, and where the fabric is near its maximum cover, this is possible only if the fabric buckles from the horizontal plane. The action of the presser foot and the throat plate tend to inhibit buckling, and yarn breakages may result. Damage to knitted fabrics needs also to be considered as a three dimensional phenomenon. Yarns are stretched in the plane of the fabric with yarn robbing, and also stretched in the direction of the needle axis with deformation of the fabric by the needle point. In some fabrics, the length of yarn in a knitted loop is less than the circumference of the needle, so yarn robbing from adjacent loops occurs. The case with which any one loop can draw from adjacent loops is critical. Two separate frictional forces are in operation: that generated between the needle surface and the yarn around it: and that generated as the yarns in the fabric move over each other changing their configuration to accommodate the needle. As yarns are forced out of the path of the needle, they are stretched. If the extension forces are equal to or exceed the breaking load of the yarn, it will break and result in a hole in the fabric at the seam (Laing and Webster, 1998).

Fabric is controlled in a horizontal plane during stitching by the feed dog and the spring-loaded presser foot. The needle acts vertically on the cloth and filaments/yarns may form a glove around the needle point. Yarns may be forced into the throat plate hole. With knitted fabric, only those loops or parts of loops not held by the presser foot are free to move. Cotton interlock, which is often badly damaged in machine sewing, is not damaged at all if the fabric is held freely in the hand and hand stitched, thus illustrating the detrimental effect of clamping.

Strike-through and strike-back

During fusing, three parameters must be considered: the fusing method; the fusing machine; and the condition of the fusing (viz. temperature, time pressure and cooling). If the parameters are not properly selected and/ or adjusted fusing problems (e.g. strike-through and strike-back, colour changes and fusing distortion) can occur. Strike-through means that the adhesive resin appears on the outside of the fabric being fused. Table 16.9 summarises the causes and solutions for strike-through. Strike-back means that adhesive resin appears on the non-adhesive side of the fusible interlining after fusing. Table 16.10 lists the causes and solution of strike-back (Anon, 2010; Fan and Hunter, 2009; Galuszynski and Robinson 1986).

Colour changes during fusing

Inappropriate fusing can cause temporary or permanent colour changes (shine/glazing and/or discolouration) in fabrics. Colour changes during fusing are caused by the action of heat on certain dyes. The causes and solutions for this phenomenon are listed in Table 16.11 (Anon, 2010; Fan and Hunter, 2009; Galuszynski and Robinson 1986).

Fusing distortion

Fusing distortion means that panels are distorted during the fusing process. This problem should be prevented, as such distorted panels cannot be corrected and must be discarded as waste. Fusing distortion may be caused by inadequate fusing conditions, improper handling of fusing panels, poor stability of the fabric and wrong fusing directions. The cause and solutions of fusing distortion are summarised in Table 16.12 (Anon, 2010; Fan and Hunter, 2009; Galuszynski and Robinson 1986).

Preparation and handling

Before pressing, remove all the tacking threads and pins so as to avoid any marks on the garment. In order to prevent scorching, melting, hardening or shrivelling, first test the heat (temperature) of the iron prior to pressing so as to ensure that it is suitable for the garment to be pressed. Test the heat on a spare piece of the actual fabric before applying the iron to the apparel, so that a suitable heat can be found. When placing a garment onto a pressing machine, make sure the grain of the fabric is not pulled out of line, so as to ensure that it is not unnecessarily creased. Keep all seams in a straight line. To avoid shine or iron marking on the right side, press on the wrong side of the apparel. If necessary, slip a strip of paper underneath seam turnings to prevent their marking the right side of the fabric or apparel (Butler 1972; Fan and Hunter, 2009).

Pressing conditions

In practice, pressing can be conducted either with industrial or domestic irons (with or without steam) or else with a heavy press. Whatever the pressing method chosen, pressing consists of five components namely, heat (temperature), moisture (usually as steam), pressure, time and equipment. When pressing low-volume, high-fashion or highly structured apparel, an industrial flat iron is usually used, similar to those used by the consumers at home. For pressing performed on high-volume, ready-to-wear apparel, presses or pressing machines, such as flatbed, buck presses, form presses and upright presses are normally used, these being more efficient than hand pressing. Generally, the apparel is slipped over the machine; steam and pressure are applied automatically and then a vacuum extracts any excess moisture. Ideal pressing conditions vary for different types of fabrics and apparel (Brown and Rice, 2001; Fan and Hunter, 2009; Crowley, 1978).

Effect of fabric properties on pressing performance

Different fabrics have different properties, which require different pressing conditions. For example, microfibre apparel has poor resistance to heat and can be hard to press and finish without any shine, marks or glazes. In order to solve this problem, it is recommended that apparel comprising microfibres or extremely light fabrics be pressed from inside using foam finishes. If they need to be pressed from the 'right side' of the fabric, the temperature has to be very low, whilst the steam has to be perfectly dry since synthetic cannot take any moisture. The press duration and ambient relative humidity for both preconditioning and post conditioning of the fabrics also has a significant influence on the pressing performance (Fan and Hunter, 2009).

• Fabrics are more extensible in the low-load region than in the higher-load region.

• The property in this region is closely related to the tailoring process and the comfort of a wearer.

KES-F1 (tensile and shear tester)

The principle of KESF-1 system is shown in Fig 16.16. The fabric specimen is clamped between two jaws (one attached with drum for tensile force application, and the other attached with slide for shear force application) and subjected to a constant tension of 10 gf/cm by a weight attached to the drum on which one jaw is mounted. Tensile force is applied by allowing the drum to rotate freely. The tensile force is measured by the tensile force detector by measuring the torque and the tensile strain is measured by tensile strain detector from the data of rotational angle of the drum. The shear force is measured by a transducer connected to the other jaw (attached with slide) which moves sideways to apply shear deformation. The shear force is measured by the shear force detector by measuring the force required to slide, and the shear strain is measured by shear strain detector from the resulting displacement of the slide.

KES-F2 (bending tester)

The principle of the KESF-2 system is shown in Fig. 16.17. The fabric specimen is gripped by two jaws. One jaw is attached with the bending arrangement, which moves in a circular direction to apply bending force. The other jaw is connected with the torque sensor, which detects the torque value of steel wire during bending of specimen. The curvature of bending is obtained from the drive to the bending arrangement. The fabric specimen is bent with the help of bending arrangement between the curvatures of − 2.5 cm^− 1 and + 2.5 cm^− 1.

KES-F3 (compression tester)

The working principle of KESF-3 system is shown in Fig. 16.18. The fabric specimen is compressed between two plates, that is anvil and pressure foot. The fabric specimen is placed on the anvil and pressure is increased with the help of the pressure foot, while continuously monitoring the sample thickness with a thickness detector. The compressive pressure is detected by the compressive force detector. The pressure foot is driven from the drive arrangement.

KES-F4 (surface tester)

Friction and surface roughness characteristics of fabrics are measured by KESF-4 system. The working principle is shown in Fig. 16.19, where the surface roughness and surface friction of the fabric specimen are being measured at the same time. The fabric specimen, kept at constant tension by a hanging dead weight, gets to-and-fro motion from a drum that rotates intermittently clockwise and anticlockwise. The frictional force between the fabric specimen and the friction surface at the friction point is detected by a frictional force detector. The surface roughness of the fabric is measured by a detection system that is basically a displacement sensor. The probe of the displacement sensor is in touch with the fabric surface. When the fabric moves in the horizontal plane, due to the surface roughness the probe is deflected vertically. This vertical deflection of the probe measures of the surface roughness of fabric.

From all the above parameters, which are obtained from KESF instruments, the total handle value (THV) can be calculated, which is the indicator of fabric handle behaviour of fabric.

FAST-1 (compression meter)

A schematic diagram of FAST-1 system is shown in Fig. 16.20. It measures the fabric thickness over a range of loads, the variability and the durability of the thickness of the fabric surface layer. It can measure fabric thickness to micrometre resolution at two predetermined loads, and thereby enables the accurate measurement of surface layer thickness. The fabric thickness (T) is measured at a pressure of 2 gf/cm². Surface thickness (ST) is the difference in thickness of a fabric measured at pressures of 2 and 100 gf/cm².This gives information about the hairiness or surface bulk of the fabric (closely related to surface treatment like brushing, singeing, finishing etc). Released surface thickness (STR) is the measure of the ST after the fabric is exposed to steam or water. The increase in fabric ST obtained by this steaming process simulates the actual change in surface characteristics that occur during actual use of the apparel.

FAST-2 (bending meter)

A schematic diagram of the FAST-2 system is shown in Fig. 16.21. FAST-2 measures the bending length (BL) and bending rigidity (B) of fabric. The fabric BL simulates the draping behaviour of fabric and B is related to the quality of stiffness when a fabric is handled. B is particularly crucial in the tailoring of lightweight fabrics as a very flexible fabric (low B) may cause seam puckering while a high B fabric can be more manageable in sewing and so produce a flat seam. Operator error in aligning the sample is eliminated with the use of an optical sensor. BL is displayed automatically, so chances of the error due to the operator's judgement are eliminated.

FAST-3 (extension meter)

A schematic diagram of the FAST-3 system is shown in Fig. 16.22. It measures extensibility of fabric at various loads as well as its shear rigidity. It is capable of measuring the fabric extensibility in warp, weft and bias directions over a range of loads, with direct reading of extension as a percentage of the initial gauge length. The fabric extension is displayed as a percentage with a 0.1% resolution. Extensibility is measured at three loads 5 gf/cm (E5), 20 gf/cm (E20) and 100 gf/cm (E100). The difference between fabric extensibilities at between E5 and E20 is used to calculate fabric formability (F), which is a parameter related to the incidence of seam pucker. Fabric extensibility is combined with bending rigidity to calculate F, which is a measure of the ability of a fabric to absorb compression in its own plane without buckling. E100 is used in FAST control chart (FAST fabric fingerprint) as the measure of fabric extensibility. If the value is below approximately 2%, then the fabric will be difficult to extend during seam overfeed. Apart from the fabric extensibility, another important fabric handle related parameter, shear rigidity (G), is measured in the FAST-3 system. The bias extension is converted to G, which is directly related to fabric looseness. For G below 30 N/m, the fabric deforms so easily that it may give problems in handling, laying up and sewing. Conversely if it is above 80 N/m then the fabric can be difficult to overfeed, mould, etc.

FAST-4 (dimensional stability test method)

Poor dimensional stability of fabrics is one of the main causes of poor appearance in apparel. This is a test method for measurement of relaxation shrinkage (RS) and hygral expansion (HE), which can test these parameters in less than an hour as compared to the conventional one-day test. The drying is done in a forced convection oven. A template and a ruler are the only equipment required to do the test. The results from this method simulates the change in fabric dimensions that may occur during the actual wear as the fabric is subjected to washing and changing humidity conditions. RS is mainly due to the recovery of fabric structure that became strained during manufacturing, while HE (and hygral contraction) is caused by the swelling or de-swelling of hygroscopic fibres. Very high RS results in the problem of change of size, puckering, etc. Similarly, higher HE may result in seam pucker, fabric waviness, buckling and overall poor appearance.

The testing is completed in following three difference steps (Fig. 16.23):

RS and HE are calculated from the above dimensions, using following relationships:

The FAST data analysis software, included as part of the FAST system package, automatically plots the appropriate values and joins the various plotted points together to form a fabric 'FAST control chart', which is unique to each particular fabric. Figure 16.24 shows a typical FAST control chart. Each value has a separate scale showing a graphical representation of the range of values in the appropriate units that we expect for each of the various measurements. For example relaxation shrinkage 'RS-1' represents the warp value and 'RS-2' that of the weft. In addition to the values for the various measurements, each scale contains one or more shaded zones. If the fingerprint falls into one of these zones, a potential problem with the particular aspect(s) of fabric performance influenced by that property is indicated.

Durability of finish of zippers to laundering

The durability of the finish of zippers to laundering is evaluated by laundering the test specimen in a Launderometer (AATCC test method 61).

The effect of the test on the zipper coating is evaluated by noting the loss of coating on the zipper chain or components or both (ASTM D2051).

Colourfastness of zippers to dry-cleaning, light and crocking

The colourfastness of a zipper to dry-cleaning is tested by subjecting the zipper stringer (tape) to commercial dry-cleaning with a multifibre fabric. The dry-cleaned specimen is compared with the original specimen and any change in the colour of the specimen or staining of the multifibre fabric is then assessed using the AATCC gray scale for colour change or the chromatic transference scale. The colourfastness of zippers to light and crocking is tested in the same way as the colourfastness of fabrics to light and crocking (ASTM D2052, ASTM D2053 and ASTM D2054).

Colourfastness of zippers to laundering

The colourfastness of zippers to laundering is tested by subjecting the zipper with a multifibre test fabric to home laundering according to the intended care instructions for the apparel on which this particular zipper would be used. The alteration in shade of the zipper stringer (tape) and the degree of staining of the multifibre test fabric are evaluated by the AATCC gray scale for staining and colour change or the chromatic colour transference scale (ASTM D2057).

Durability of finish of zippers to dry-cleaning

The durability of the finish of zippers to dry-cleaning is tested by subjecting the zipper to dry-cleaning, as in AATCC test method 86, but the zipper is air-dried rather than hot-pressed. The specimen is then evaluated visually for any exposed base metal compared to a new zipper or compared to a sample illustrating an acceptable degree of coating loss (ASTMD 2058).

Resistance of zippers to salt spray

Sometimes, due to corrosion, a zipper will not operate smoothly and its crosswise strength may be reduced. Such deterioration in a zipper can be evaluated by subjecting the zipper to a salt spray test. Of course, plastic/ nylon zippers do not corrode, and therefore, this test applies only to metal zippers. In this test method (ASTM D2059), specimens are subjected to salt spray (5% salt solution at 33 °C to 36 °C) for 24 h continuously. The exposed specimens are then visually evaluated for any sign of corrosion and tested for case of operation and crosswise strength, and the results are compared with the case of operation and crosswise strength of the original specimens (ASTM D2059).

Operability of zippers

The operability of zippers is tested by pulling the slider with a force indicator (such as a pull gauge) along the zipper chain alternately in the opening and closing directions and recording the force required to maintain each movement. This force is a measure of the case with which the zipper will operate in end-use applications (ASTM D2062).

Strength tests of zippers

The usefulness of a zipper in service can be evaluated by the following strength tests. No test determines the suitability of a zipper for a specific end use. Since the tests are interrelated, more than one may be needed for a complete evaluation. Zipper strength is usually tested in the following areas (ASTM D2061):

Yarn diameter

Knowledge of thread diameter is important because it can affect sewing performance and seam appearance. Sewing performance can be influenced because thread is required to pass through restrictions, such as a needle's eye and tension discs. Seam appearance can be adversely affected when the diameter of a thread is large enough to displace fabric yarn and results in a puckered seam. Sewing thread diameter is also a consideration when selecting sewing threads for embroidery, contrast stitching, or other decorative applications. The diameter of a thread is determined either with a thickness gauge (preferred method) or optical method (alternative method).

The procedure (ASTM D204) for measuring sewing-thread diameter by a thickness gauge is given below. Draw the thread from the side of the sewing thread holder, taking care not to disturb the twists. Place four strands of the thread side by side on the anvil and approximately midway between the sides of the pressure foot of the thickness gauge. Measure the thickness to the nearest 0.0025 cm under 240 gm/cm² at 10 m points along the thread and calculate the average as the diameter of the sewing thread The optical method for measuring sewing thread diameter is not recommended because it is difficult to determine the exact boundaries of threads having hairy fibres on the surface.

Yarn number of a sewing thread

Yarn number is a measure of the fineness or size of a yarn, expressed either as mass per unit length or length per unit mass. There are two systems of expressing yarn number or yarn count: a direct system and an indirect system. Under the direct yarn-numbering system, yarn number is expressed in terms of mass per unit length. The most frequently used units of the direct system are denier (weight of 9000 m of yarn in grams) and tex (weight of 1000 m of yarn in grams). In an indirect yarn-numbering system, yarn number is expressed in terms of length per unit mass. The most widely used unit for expressing the yarn number of a sewing thread in the indirect system is cotton count, which is the number of 840-yard lengths of yarn per pound, generally used for yarns spun on a cotton system.

Yarn number based on short-length specimens can be determined by (ASTM D1059). In this method, a short length (25–50 cm) of yarn is taken from a spool, conditioned, and weighed. The yarn number is then calculated from the weight and the measured length of the yarn. This is a quick method for the determination of the approximate yarn number. Because any error present in the reported length of the yarn specimen is multiplied many times when calculating the theoretical yarn number, it is extremely important that the length be measured as precisely as possible. Another method (ASTM D1907) for determining yarn number uses a much longer yarn length. Under this method, specified lengths of yarn are wound on a reel as skeins and weighed. The yarn number is calculated from the mass and length of the yarn in the skein. For all practical purposes, the calculation of the yarn number of a sewing thread based on short-length specimen is adequate.

Yarn ply

For checking the number of plies in a sewing thread, simply cut a short length of the sewing thread from the spool, hold two ends in each hand and untwist the sewing thread to a point that one can count the number of yarns plied together to make that sewing thread unless it is single ply (Kothari, 1999b; Pradip and Satish, 1998).

Strength and elongation

The strength and elongation of sewing thread must be adequate for good sewing performance as well as good seam strength. Strength and elongation of sewing threads are determined by breaking a single sewing thread on a tensile testing machine and recording the force and elongation at break (ASTM D2256). Sometimes, it is necessary to measure loop strength and loop elongation of a sewing thread, as these properties are also very relevant to the performance. The loop strength and elongation of a sewing thread are a measure of the thread's ability to contribute to seam performance. The loop strength of a thread bears a direct relationship to stitch strength and hence to seam strength. Loop elongation is an indication of the degree to which a seam, under stress, can be stretched without a thread breaking. Besides loop elongation, the ultimate elongation of a seam is dependent on the material stitched, the stitch and seam type, and number of stitches per inch. In a loop strength and elongation test, each specimen consists of two pieces of yarn taken from one package or end. Both ends of one piece are secured in one clamp of the testing machine so that the length of the loop is about one-half the gauge length. One end of the second loop is passed though the loop formed by the first piece of the sewing thread, and both ends of the second piece are clamped in the other clamp of the tensile testing machine. The machine is started, and the force and elongation, when the loop breaks, are observed and noted, which are the values of loop strength and elongation.

Twist balance and number of twists

The determination of twist balance of a sewing thread is important in predicting the snarling tendency of the thread during actual sewing operations. In this method, about a metre of conditioned thread from a spool is withdrawn, in the same manner as that in which it is delivered to the sewing machine, and formed into a loop, positioning the ends of the threads so that they are 10 cm apart at the top of the loop. The twist balance is reported in terms of the complete rotations that the loop makes.

The number of twists per centimetre is measured by counting the number of turns of twist in a known length of sewing thread as they are being removed by rotating one end of the specimen while the other end remains fixed until the elements of the thread being tested are parallel and free from twist (ASTM D1423).

Shrinkage

Good shrinkage performance of sewing thread is important because shrinkage can cause puckering of a seam, thus adversely affecting seam appearance. A conditioned single end thread is measured under a prescribed tensioning force before and after exposure to boiling water for 1/2 h h or dry heat 152 ± 3 °C for 1 h. The change in length is expressed as a percentage of the length before exposure (ASTM D204).

Length per thread holder

The length of sewing thread on a thread holder is measured in metres or yards while being removed from the thread holder (ASTM D204 and D3693).