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.
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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.
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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
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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.
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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
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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.
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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.
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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.
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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.
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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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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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