ASTM D1425-96

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Designation:D1425–96
Standard Test Method for
Unevenness of Textile Strands Using Capacitance Testing
Equipment
This standard is issued under the fixed designation D 1425; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers the indirect measuring of 2.1 ASTM Standards:
unevenness of textile strands from tow, top, sliver, roving, and D 123 Terminology Relating to Textiles
yarn produced from staple fibers and filament yarns by means D 2258 Practice for Sampling Yarn for Testing
of continuous runs using capacitance testing equipment.
3. Terminology
1.2 Thetestmethodprovidesavalueof“short-termuneven-
3.1 Definitions:
ness,” a single value expressing the complicated strand prop-
erty that is unevenness. 3.1.1 coeffıcient of variation unevenness, CV%, n—in tex-
tiles, the standard deviation of the linear densities over which
1.3 The test method is applicable to all yarns, rovings,
slivers, and tops, except as indicated below. unevenness is measured expressed as a percentage of the
average linear density for the total length within which
1.3.1 Low twist filament yarns should be tested only if
additional twist is inserted during testing. unevenness is measured. (See also unevenness, mean deviation
unevenness.)
NOTE 1—In many cases, low twist yarns tend to flatten to a ribbon
3.1.2 integrator, n—in textile unevenness testing, a device
while passing through the condenser of the instrument, and the recorded
that calculates the coefficient of variation unevenness or the
value of unevenness is increased above the true value.
mean deviation unevenness.
1.3.2 Strands made from fiber blends should be tested only
3.1.2.1 Discussion—The terms “integrator” and “integra-
if blending is uniform along the strand.
tion” as applied to textile unevenness testing do not imply
NOTE 2—Nonuniform blending may cause a higher reading of uneven- integration in the strict mathematical sense. The type integra-
ness than the true value if the component fibers differ in dielectric
tor, linear or quadratic, must be carefully selected depending
constant. The magnitude of the increase of unevenness readings due to
upon a known irregularity of the material; that is, purely
nonuniform blending cannot be stated in general terms.
random or purely periodic.
1.4 The values stated in either acceptable metric units or in
3.1.3 length between, L , n—in textile unevenness testing,
b
other units shall be regarded separately as standard.The values
the length between which unevenness is measured; the equiva-
stated in each system may not be exact equivalents; therefore,
lent of the length of strand segments weighed in a direct
each system must be used independently of the other, without
method of measuring unevenness.
combining values in any way.
3.1.4 length within, L , n—in textile unevenness testing, the
w
1.5 This standard does not purport to address all of the
length over which unevenness is measured.
safety concerns, if any, associated with its use. It is the
3.1.4.1 Discussion—The total length of the strand from
responsibility of the user of this standard to establish appro-
which the segments weighed were sampled in a direct method
priate safety and health practices and determine the applica-
of measuring unevenness. For indirect methods, the maximum
bility of regulatory limitations prior to use.
value of length within is the tested length from the specific
package.
3.1.5 linear integrator, n—in textile unevenness testing,an
integrator that operates continuously and reports unevenness
ThistestmethodisunderthejurisdictionofASTMCommitteeD-13onTextiles
for a certain, and unchanging, time past.
and is the direct responsibility of Subcommittee D13.58 on Yarn Test Methods,
General.
Current edition approved Feb. 10, 1996. Published April 1996. Originally
published as D1425 – 56 T. Last previous edition D1425 – 89. Annual Book of ASTM Standards, Vol 07.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D1425
3.1.5.1 Discussion—Theinputtotheintegratorimmediately 4.4 Theunevennesstestinginstrumentsmeasurethoseprop-
preceding the moment of taking a reading receives greater erties of the strand which change the capacitance when the
“weight” than the prior input, and this “weighting” gradually strand passes between the plates of a capacitor.
decreases with the lapse of time. (Syn. fading memory integra- 4.5 Anumber of mathematical concepts are used to express
theunevennessofastrand.Theyareallbasedonthecoefficient
tor)
of variation or its square. There is, therefore, some advantage
3.1.6 mean deviation unevenness, U%, n—in textiles, the
in using an unevenness testing instrument that gives the
average of the absolute values of the deviations of the linear
coefficient of variation and thereby fits into the general
densities of the integrated lengths between which unevenness
mathematical scheme.
ismeasuredandexpressedasapercentageoftheaveragelinear
4.6 If the method is followed exactly and the testing
density for the total length within which unevenness is mea-
instrument has been adjusted to eliminate bias in the results,
sured. (See also unevenness, coeffıcient of variation uneven-
then unevenness values obtained on different instruments will
ness.)
agree for the same strand, or will be comparable for different
3.1.7 quadratic integrator, n—in textile unevenness testing,
strands, provided that the following are the same in all cases:
anintegratorthatoperatescontinuouslyandreportsunevenness
(1) the measure of unevenness used (see 3.1.5 and 3.1.6); (2)
for the time during which it has been active, giving equal
thelengthbetween, L (see3.1.3);and(3)thelengthwithin, L
b w
weight to all portions of the input. (Syn. compensated-memory
(see 3.1.4). When different models of instruments are used,
integrator)
then one or more of the three items are often not identical and
3.1.8 strand, n—(1) a single fiber, filament, or monofila- the test results may differ from instrument to instrument.
ment, (2) an ordered assemblage of textile fibers having a high
5. Summary of Test Method
ratio of length to diameter and normally used as a unit,
5.1 A strand is passed through the sensing device of the
including slivers, rovings, single yarns, plied yarns, cords,
evenness tester at constant speed and a momentary value
braids, ropes, etc.
proportional to the linear density of the strand is recorded. The
3.1.9 strand irregularity, n—in textiles, variation in a prop-
instruments are equipped with an integrator that calculates the
erty along a strand.
unevennessautomaticallyandthevalueisreadwhilethestrand
3.1.10 unevenness, n—in textiles, variation in the linear
ispassingthroughtheinstrumentafter40m50ydofyarnhave
density of a continuous strand or of a portion of a strand. (See
been tested.
also coeffıcient of variation unevenness, mean deviation un-
evenness.)
6. Significance and Use
3.1.11 unit length of instrument, L , n—in textile uneven-
c 6.1 Test Method D 1425 for the determination of uneven-
ness testing, the length of strand being measured between the
ness of textile strands is considered satisfactory for acceptance
sensing elements at any moment.
testing of commercial shipments of filament or spun yarn,
3.1.12 For definitions of other textile terms used in this test roving, sliver, tow, or top since the method has been used
method, refer to Terminology D 123. extensively in the trade for acceptance testing.
6.1.1 In case of a dispute arising from differences in
4. Basic Principles of Test Method reported test results when using Test Method D 1425 for
acceptance testing of commercial shipments, the purchaser and
4.1 Properties of a strand vary along its length and these
supplier should conduct comparative tests to determine if there
variations are termed strand irregularity. The variation of one
is a statistical bias between their laboratories. Competent
specific property, linear density, is termed unevenness. This
statistical assistance is recommended for the investigation of
method is concerned with measuring the unevenness of a
bias.As a minimum, the two parties should take a group of test
textile strand.
specimens that are as homogenous as possible and that are
4.2 Unevenness is always expressed as between successive
from a lot of material of the type in question. The test
lengthsandoveratotallength.Whenthelengthbetweenwhich
specimens should then be randomly assigned in equal numbers
unevenness is measured (L ) is very short, 8 mm (0.3 m) for
b
to each laboratory for testing. The average result from the two
yarn and roving and 12 mm (0.5 m) for slivers, then reference
laboratories should be compared using appropriate statistical
is often made to short-term unevenness.
analysis for unpaired data and an acceptable probability level
4.3 Unevenness can be measured by direct method or
chosen by the two parties before the testing is begun. If a bias
indirect methods. The direct method consists of cutting and
is found, either its cause must be found and corrected or the
weighing strand segments of length L and is the reference purchaser and the supplier must agree to interpret future test
b
method of determining unevenness. Unevenness testing instru-
results with consideration to the known bias.
ments, as covered in Method D 1425, use the indirect method 6.2 The interpretation of results of unevenness tests is a
where unevenness is determined by the measurement of strand
complex matter and a detailed discussion is outside the scope
properties closely related to and dependent on linear density. of Method D 1425. Unevenness is a fundamental feature of
The accuracy of the indirect method and of an instrument
yarn construction and influences many properties of the yarn.
utilizing it can be judged by a comparison of the value of Unevenness cannot be fully expressed as a single number and
unevenness it gives with one obtained by the direct method of various methods exist for a more complete presentation. The
cutting and weighing. value for short-term unevenness determined as directed in this
D1425
method provides a single number of either CV% or U% which fore be stable and the strand must be in equilibrium with the
is related to the unevenness of the strand. prevailing atmosphere. To satisfy this condition, testing should
6.3 A value of short-term unevenness is useful in quality be carried out after thorough conditioning in the standard
control, in research, and in a first appraisal of a strand, namely atmospherefortestingtextiles.Preconditioningisgenerallynot
filament or staple yarn, staple roving, sliver, or top, that is an advisable as it prolongs the time required for conditioning.
article of commerce. A low unevenness is, in general, pre-
10.2 Thetimerequiredforconditioningdependsonthefiber
ferred. Higher unevenness is generally associated with more
andonthesizeandcompactnessofthepackage.Also,ashorter
difficult processing, lower yarn strength, and poorer fabric
conditioning time is sufficient if only the outside layer of a
appearance. Experience has shown, however, that the relation-
package is to be tested for unevenness than if the whole
ship of short-term unevenness to performance of the yarn or to
package is to be used for testing.As a general guide, condition
fabric appearance is not a simple one. A value of short-term
tightly wound packages for 48 h and strands in loose form for
unevenness must, therefore, be used cautiously and should, if
24 h.
possible, be supplemented by additional information on un-
evenness, such as chart evaluation and spectrogram analysis.
11. Selection of Testing Parameters
11.1 Measure of Unevenness—A choice between CV% and
7. Apparatus
U% is possible only when the chart is used for the evaluation
7.1 Capacitance-Type Unevenness Testing Instruments—
of unevenness. When unevenness is evaluated automatically,
All models of unevenness testing instruments use automatic
then the selection of CV% or U% depends on the type of
integrators. Certain models of instruments are provided with a
integrator that is available with the unevenness testing instru-
standardizing tape for checking the functional operation of the
ment.
equipment, and certain models of instruments contain a built in
electronic checking system. NOTE 4—Unevenness values are not comparable unless the same
expression for unevenness is used. Conversion factors between CV% and
NOTE 3—The length between, L , is usually equal to unit length L ;
b c
U% have been proposed, but they are approximations only and their use
however, a damping circuit permits, L , to be increased above, L .
b c
is not recommended.
7.1.1 Package Holders, Guides, Tension Devices, and
11.2 Length Between and Length Within—The possibilities
Take-Up Mechanism, which allow for, or assist in, uniform
of selecting L and L are limited by the design of the
b w
delivery of the strand at the specified speed without undue
unevenness testing instrument. The unevenness value obtained
acceleration or deceleration and at a reasonably constant
from testing depends on both L and L ; unevenness decreases
b w
tension.
rapidly when L increases and increases slowly when L
b w
7.1.2 Recorder, to give a permanent chart record of the test
increases. Therefore, if unevenness values are to be compa-
details and to depict the unevenness. It is a means to record all
rable, L and L must be the same for all the tests to be
b w
unevenness.
compared.
7.2 System for imparting false twist into low-twist filament
11.2.1 Length Between—L is usually equal to L (unit
b c
yarnwhileitpassesbetweenthesensingelementsandprovides
length of the instrument) and is determined by the instrument
a constant tension on the yarn.
used. In all evenness testing instruments, the circuit allows L
b
to be increased above L . The use of a longer L frequently
8. Sampling
c b
assists visual inspection of an autographic unevenness chart by
8.1 Unless otherwise agreed upon, as when specified in an
the suppression of short-term peaks, since the longer term
applicable material specification, take a lot sample and labo-
periodicities can be observed more readily. Such an increased
ratory sample as directed in Practice D 2258.
setting of L is referred to as a dampened or inert setting.
b
9. Number of Specimens
NOTE 5—When unevenness is determined by cutting and weighing,
9.1 Test one specimen from each package. The recom-
then L can be selected at will.As an example
...