GB/T 3292.1-2008 English PDF (GBT3292.1-2008)

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GB/T 3292.1-2008: Textiles -- Unevenness of textile strands -- Part 1: Capacitance method
GB/T 3292.1-2008
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 59.080.20
W 04
Replacing GB/T 3292-1997
Textiles - Unevenness of textile strands - Part 1:
Capacitance method
(ISO 16549:2004, Textiles - Unevenness of textile strands - Capacitance
method, MOD)
ISSUED ON: JUNE 18, 2008
IMPLEMENTED ON: MARCH 01, 2009
Issued by: General Administration of Quality Supervision, Inspection
and Quarantine;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 5 
2 Normative references ... 5 
3 Terms and definitions ... 5 
4 Principle ... 8 
5 Apparatus ... 9 
6 Standard atmosphere ... 10 
7 Sampling ... 10 
8 Procedure ... 11 
9 Calculations and expression of results ... 12 
10 Test report ... 12 
Textiles - Unevenness of textile strands - Part 1:
Capacitance method
1 Scope
This Part of GB/T 3292 specifies the method for determining the unevenness
of linear density along the length of textile strands (including yarns, rovings and
slivers) by using capacitance method.
This Part applies to staple-fibre strands and continuous filament yarns. The test
range, for staple-fibre strands, is 4 tex ~ 80 ktex; the test range, for filament
yarns, is 10 dtex ~ 1 670 dtex. This Part does not apply to fancy yarns and
yarns containing conductive materials (such as metal wires); the latter can be
measured by the photoelectricity method (see Part 2 of GB/T 3292).
This Part describes the generation process of the CVm-length curve, as well as
the determination of periodicities of linear density. This Part also includes the
counting of imperfections in the yarn (namely thin places, thick places and neps).
2 Normative references
The terms in the following documents become the terms of this Part by
reference to this Part of GB/T 3292. For dated references, all subsequent
amendments (not including errata content) or revisions do not apply to this Part.
However, parties to agreements that are based on this Part are encouraged to
study whether the latest versions of these documents can be used. For undated
references, the latest edition applies to this Part.
GB/T 6529, Textiles - Standard atmospheres for conditioning and testing
(GB/T 6529-2008, ISO 139:2005, MOD)
3 Terms and definitions
The following terms and definitions are applicable to this Part of GB/T 3292.
3.1
Unevenness
The unevenness of linear density along the length of the sliver.
One of the time-domain representations of yarn linear density changes. The
abscissa represents the length that is calculated from the starting end of the
tested yarn; the corresponding ordinate represents the relative size of the linear
density of the tested yarn at that point.
3.13
CVm-length curve
The CVm value under normal circumstances, which refers to the CVm value of
the capacitor length. Use the electronic method to extend the length of the
measuring field; calculate the CVm value under different cutting lengths (this
method corresponds to the early cutting and weighing method). Several CVm
values under different cutting lengths constitute the CVm-length curve.
4 Principle
4.1 When the sample passes through two capacitance plates, the rate of
change of capacitance is linear with the rate of change of mass of the sample.
The evenness tester calculates these changes and reports them as CVm or Um.
4.2 The fibre dielectric constant is also a factor that determines the capacitance
change. As long as the dielectric constant does not change (non-blended
strands or perfectly uniform blending), the dielectric constant has no influence
on the unevenness value, which completely depends on the variation of mass.
If the dielectric constant is different due to the fibre type or irregular mixing in
the blend, the unevenness value will be greater than the true value. Therefore,
this difference in results requires attention.
4.3 Compared with the test results of the evenness tester, the unevenness
value that is obtained by the cutting and weighing method has a very high
consistency; other studies in recent years also reach this conclusion, so, the
result of the evenness tester can be used as the true unevenness value.
4.4 The unevenness value is only valid when both Lb and Lw are known. In
principle, they are always reported together. A more preferable method of
expression is CVm (Lb, Lw), such as CVm (8 mm, 1 000 m). In practice, Lb and
Lw are usually not marked, and are assumed to be the most frequently used
conditions in the unevenness tester, namely:
-- Lb: 8 mm for yarns, 12 mm for rovings, 20 mm for slivers and tops;
-- Lw: total length of the tested yarn on the package.
-- calculates and displays the value of CVm or Um, and can also calculate
the CVm-length curve, and provides a graph of the periodic variations
of linear density;
-- calculates and displays the number of imperfections of each level.
Note: Imperfections are usually divided into the following levels:
Neps: +400%, +280%, +200%, +140%.
Thick places: +100%, +70%, +50%, +35%.
Thin places: -60%, -50%, -40%, -30%.
c) Printer (optional), which:
-- provides yarn linear density index and graphic output.
d) Twisting device for testing untwisted or low-twist filament yarns, so that
the filament yarns pass through the capacitance detection area with an
approximately round cross-section. No twisting device is required for the
test of monofilaments.
5.3 For calibration, use the procedure built into the instrument as much as
possible. Or use a standard signal of known unevenness provided by the
instrument manufacturer. If the instrument manufacturer does not have an
available standard, a sample of known and low unevenness can also be used.
6 Standard atmosphere
The standard atmosphere for preconditioning, conditioning and testing shall be
in accordance with the standard atmosphere specified in GB/T 6529. Generally,
unsupported packages shall be conditioned for 24 h; supported packages shall
be conditioned for 48 h.
7 Sampling
7.1 Select laboratory samples according to one of the following methods:
-- according to the relevant specification of the product standard;
-- by agreement between the relevant parties.
7.2 Recommended sampling amount:
-- slivers and tops: 3 packages;
Generally, select the running speed according to the yarn bearing capacity and
the needs of test analysis. The following running speeds are recommended.
Other speeds, if used, shall be stated in the test report:
-- slivers and tops: 25 m/min;
-- rovings: 50 m/min;
-- yarns: 400 m/min.
8.5 Guiding facilities
Before the test, adjust the guiding and the tensioning devices to provide a
pretension that does not extend the yarn (or otherwise distort the material), to
ensure that the sample passes through the condenser detection area without
fluttering, which would produce an error of measurement.
8.6 Twisting device
Low-twist strands or non-twisted filament yarns need to pass through a twisting
device.
8.7 Operate according to the prescribed procedures in the instrument manual.
9 Calculations and expression of results
9.1 The test results of yarn unevenness mainly include the following indicators:
coefficient of variation unevenness CVm, yarn imperfections per kilometer,
evenness diagram, spectrogram, CVm-length curve, etc.
9.2 When testing a batch of samples, calculate the CVm and yarn imp...