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Fashion Merchandising (eBook)



Fabric Assurance by Simple Testing (FAST)

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Fabric Assurance by Simple Testing (FAST)

  1. 1. FAST FABRIC ASSURANCE BY SIMPLE TESTING [ FAST has been developed by CSIRO in Australia which is designed to predict the properties of wool and wool blended fabrics that affect their tailoring performance and the appearance of the tailored garments in wear. [ These instruments also give information which can be related to the fabric handle. [ Unlike KES-F system, FAST only measures the resistance of fabric to deformation and not the recovery of the fabric from deformation. [ However, the FAST system is much cheaper, simpler and more robust than the KES-F system, and, as such, perhaps more suited to an industrial environment.
  2. 2. N FAST can predict how a fabric will perform when made up into a garment – an information of importance for fabric manufactures, suppliers, finishers and garment makers. N FAST consist of three instruments and a test methods: ž FAST – 1 : Compression Meter ž FAST – 2 : Bending Meter ž FAST – 3 : Extension Meter ž FAST – 4 : Dimensional Stability Test N Test results from FAST – 1, - 2 and – 3 can be recorded instantly and automatically, FAST – 4 results are recorded manually. N The results are plotted on a control chart to provide a Fabric Fingerprint, which indicates weather the tested fabric will be suitable for the intended end use.
  3. 3. Parameters Measured and Calculated on the FAST system Instrument Measurement Parameters Symbol Units Predicts Problem In Fabric Thickness T mm Pressing (Finish Stability) FAST 1 Compression Fabric Surface thickness ST mm Released Surface thickness STR mm Warp bending length W1 mm Cutting Weft bending length W2 mm Automated Handling FAST 2 Bending Warp bending rigidity B1 uNm Weft bending rigidity B2 uNm Formability F mm2 Seam Pucker Warp extensibility E100 -1 % Laying up, pattern FAST 3 Tensile Weft extensibility E100 -2 % Matching, Moulding Extension Over feed seams, Shear rigidity G N/m Sleeve insertion Warp relaxation shrinkage RS – 1 % Sizing, Seam pucker, Weft relaxation shrinkage RS – 2 % Pleating FAST 4 Fabric Dimensions Warp Hygral expansion HE – 1 % Weft Hygral expansion HE – 2 % App. Loss, Pleating Chemical Weight Fabric Weight per unit area W g/m2 Balance
  4. 4. COMPRESSION METER FAST - 1 FAST-1 is a compression meter which measures the thickness of the fabric under two fixed loads. First the fabric is measured under a load of 2g/cm2. and then again under a load of 100g/cm2.
  5. 5. z The fabric thickness is measured on a 10cm 2 area at two different pressures, firstly at 2gf/cm2 (19.6mN/cm2) and then at 100gf/cm2 (981mN/cm 2) using the apparatus shown. z This gives a measure of the thickness of the surface layer which is defined as the difference between these two values. z The fabric is considered to consist of an incompressible core and a compressible surface. z The fabric thickness measurements are repeated after steaming on an open Hoffman press for 30s in order to determine the stability of the surface layer. Fabric Surface Thickness (ST) = Difference betn thickness measured at 2 & 100 g/cm2 Released Surface Thickness (STR) = Difference betn relaxed ST & ST
  6. 6. The difference between these two thicknesses is a measure of the amount of compressible fibre, or "pile" on the surface of the fabric and is know as the Surface Thickness of the fabric. Further measurements are taken after the fabric has been steamed to obtain a value known as Released Surface Thickness œ Thickness and Surface Thickness do not themselves have any great impact upon the tailoring performance of a fabric but are useful indicators of any change or variation in fabric handle. œ If however the value of Surface Thickness is assessed against the value of Released Surface Thickness, then the results assume much greater significance œ A big difference between, thickness measured at 2 & 100 g/cm 2, these two values indicates that the finish on the fabric is unstable and is likely to come off during the final pressing operation.
  7. 7. BENDING METER FAST - 2 ± FAST-2 is a bending Meter which is used to measure the stiffness or conversely, the flexibility of a fabric. ± The instrument works on the cantilever principle, which involves pushing a fabric over a vertical edge until it has bent to a specified angle (41.5o). ± Stiff fabric will need pushing further to bend to this angle, whereas a flexible, or limp one will fall quickly.
  8. 8. ♪ The bending rigidity, which is related to the perceived stiffness, is calculated from the bending length and mass/unit area. ♪ Fabrics with low bending rigidity may exhibit seam pucker and are prone to problems in cutting out. ♪ They are difficult to handle on an automated production line. ♪ A fabric with a higher bending rigidity may be more manageable during sewing, resulting in a flat seam but may cause problems during moulding, as it is stiffer . where C is bending length and M is mass per unit area.
  9. 9. EXTENSION METER FAST - 3 ! FAST-3 is an extension Meter which measures the amount (in per cent) that a fabric will stretch under three fixed low loadings (5, 20 & 100g/cm). ! Fabrics are measured at all three loads in the warp and weft directions and (at the lowest load only) in a bias direction of 45o. ! Bias extension is converted to Shear Rigidity which is directly related to fabric looseness. ! Both high and low values of Extensibility can have serious consequences if the Garment Maker is not aware of them.
  10. 10. Low Extensibility can lead to: d Difficulties in producing Overfed Seams d Problems in Moulding d Seam Pucker High Extensibility can lead to: d The fabric being stretched during laying-up, causing the cut panels to shrink when they are removed from the cutting table. d Problems in matching patterned fabrics, such as checks
  11. 11. DERIVED PROPERTIES y Some values of produced by FAST are not measured directly but are calculated using a combination of values from different FAST instruments and in some cases using Mathematical Constants. y These properties are known as Derived properties because they are not directly measured by any one instrument. y Bending Rigidity, described earlier, is a derived property because in addition to the Bending Length, fabric weight is brought into the calculation. y The measurements obtained from FAST-3 are important in calculating two further derived values, Formability and Shear Rigidity. y Extensibility is used in conjunction with the value for Bending Rigidity to calculate the Formability of the fabric. y Shear Rigidity is a measure of the ease with which a fabric can be distorted in a "Trellissing" action and is calculated from the Bias Extensibility measured on FAST-3.
  12. 12. FORMABILITY »Formability is calculated using values obtained from both FAST-2 and FAST-3. » It can be described in scientific terms as "a measure of the ability of a fabric to absorb compression in its own plane without buckling". » In practical terms, this type of compression is imposed upon the fabric by a combination of thread size, needle size, thread tension and stitch rate; a fabric which buckles easily under these types of force will form Puckered Seams. » Formability is a direct indicator of the likelihood of Seam Pucker occurring either during or after sewing. Low Formability = Tendency to
  13. 13. SHEAR RIGIDITY Shear Rigidity is a measure of the ease with which a fabric can be distorted in a "Trellissing" action and is calculated from the Bias Extensibility measured on FAST-3. S Low Shear Rigidity means that the fabric will be easily distorted in laying-up, marking and cutting. S High Shear Rigidity means that the fabric will be difficult to form into smooth three-dimensional shapes, causing problems in moulding and sleeve insertion. Drape may also be affected.
  14. 14. DIMENTIONAL STABILITY TEST FAST - 4 X FAST-4 is not an instrument but a test method, used to calculate the Dimensional Stability of the fabric. X In the test (which requires a laboratory oven), the fabric is subjected to a cycle of drying, wetting and then drying again. X After each stage the fabric’s dimensions in both warp and weft are measured. X The results give valuable information to the garment maker as to how the dimensions of a fabric will change when exposed to moisture. X The test method enables the Dimensional Stability properties of the fabric to be split into to clearly identifiable components whose cause and effect are quite different. XThese are: Relaxation Shrinkage and Hygral Expansion.
  15. 15. HYGRAL EXPANSION Hygral Expansion is the reversible change in the dimension of the fabric that occurs when the moisture content of the fibres is altered. Using FAST, Hygral Expansion is defined as the percentage change in dimensions of the relaxed fabric from wet to dry. ¹ This effect displays its most serious consequence as loss of appearance. Panels constrained by seams try to grow but have nowhere to grow into, with resultant loss of shape and in extreme cases, bubbling and delamination of fused panels. ¹ This type of problem typically occurs when garments are made in areas of low humidity, such as the UK, and exported to or worn in very humid climates such as those in much of Asia. Fabrics with high levels of Hygral Expansion also cause problems in pleating.
  16. 16. RELAXATION SHRINKAGE © Relaxation Shrinkage is the irreversible change in fabric dimensions (shrinkage or expansion) that occurs when a fabric is wet out or exposed to steam. © Relaxation Shrinkage is caused by the release of cohesively set strains which are imposed on fabrics during the late stages of finishing. © In the FAST system, Relaxation Shrinkage is defined as the percentage change in dry dimensions after release in water at room temperature. Where : L1 = Length of dry fabric L2 = Length of wet fabric L3 = Length of dry fabric
  17. 17. F During finishing, most fabrics are dried under tension, which is not released until the fabric is next exposed to moisture. F This typically takes place at the final pressing stage of garment manufacture. F The result is that the fabric reverts to its original dimensions and shrinkage takes place. F If this shrinkage is excessive, cut panels may well change their original dimensions, leading to garment sizing difficulties. F In addition, excessive Relaxation Shrinkage may well result in the formation of puckered seams in final pressing. F Most garment makers require a small amount of Relaxation Shrinkage to be present in a fabric in order to shrink out any residual fullness in the garment during final pressing. F If a fabric is to be pleated then a certain amount of relation shrinkage must be present in the fabric in order to prevent bubbling in the pleat formation process.
  18. 18. FAST Chart The whole of the results are plotted on a chart, shown in Fig., which is similar to the chart produced by the KESF system. The shaded areas show regions where the fabric properties are likely to cause problems in garment manufacture. These limits have been determined from experience and apply only to the worsted suitings for which the system was originally designed.
  19. 19. USES OF FAST FAST can tell how a fabric will perform. Fabric Fingerprints can be used for.. ♠ fabric specifications ♠ developing new fabrics ♠ comparing fabric finishing routs ♠ assessing stability of finished fabric ♠ predicting tailoring performance & ♠ predicting final garment appearance. Abnormal Fabric Fingerprints point to potential problem areas. Fast can pin-point these areas and enable one to adjust the procedures before the problems become serious.
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