ASTM D1422-99

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D1422–99
Standard Test Method for
Twist in Single Spun Yarns by the Untwist-Retwist Method
This standard is issued under the fixed designation D 1422; 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 and health practices and determine the applicability of regu-
2 latory limitations prior to use.
1.1 This test method describes the determination of twist in
single spun yarns when only an approximation of the true twist
2. Referenced Documents
is required.
2.1 ASTM Standards:
NOTE 1—For a more accurate method see Test Method D 1423.
D 123 Terminology Relating to Textiles
D 1059 Test Method for Yarn Number Based on Short-
1.2 This test method is applicable to spun single yarns in
continuous lengths, and also to spun yarns raveled from Length Specimens
D 1423 Test Method for Twist in Yarns by the Direct-
fabrics,providedspecimensatleast200mm(8in.)longcanbe
obtained. Counting Method
D 2258 Practice for Sampling Yarn for Testing
1.3 The values stated in either inch-pound or SI units are to
be regarded separately as standard.Within the text, the SI units
3. Terminology
are shown in parentheses. The values stated in each system are
3.1 Definitions:
not exact equivalents; therefore each system shall be used
3.1.1 direction of twist, n—the right or left direction of the
independently of the other. Combining values from the two
helix formed in a twisted strand as indicated by superimposi-
systems may result in nonconformance within this test method.
tion of the capital letter “S” or “Z.”
1.4 This test method has been found satisfactory for use in
3.1.1.1 Discussion—Yarn has S twist if, when the yarn is
determiningtwistinallsingleringspunyarnsand100%cotton
held in a vertical position, the visible spirals or helices around
open-endyarns.Forallopen-endspunyarnsthatarenot100 %
its central axis conform in direction of slope to the central
cottonthistestmethodhasnotbeenfoundtobesatisfactoryfor
portion of the letter“ S,” and Z twist if the visible spirals or
determining twist but may be used to measure deviation from
helices conform in direction of slope to the central portion of
an average value.
the letter “Z.” When two or more yarns, either single or plied,
1.5 This specification shows the values in both inch-pound
are twisted together, the letters “S” and “Z” are used in a
units and SI units. The “inch-pound” units is the technically
similar manner to indicate the direction of the last twist
correct name for the customary units used in the United States.
inserted.
The “SI” units is the technically corrected name for the system
ofmetricunitsknownastheInternationalSystemofUnits.The
3.1.2 single yarn, n—the simplest strand of textile material
values stated in either acceptable metric units or in other units
suitable for operations such as weaving, knitting, etc.
shall be regarded separately as standard. The values expressed
3.1.2.1 Discussion—A single yarn may be formed from
in each system may not be exact equivalents; therefore, each
fibers with more or less twist; from filaments with or without
system must be used independently of the other, without
twist; from narrow strips of materials such as paper, cello-
combining in any way.
phane, or metal foil; or from monofilaments. A yarn which is
1.6 This standard does not purport to address all of the
either twistless or can be rendered twistless in a single
safety concerns, if any, associated with its use. It is the
untwisting operation. When twist is present, it is usually all in
responsibility of this standard to establish appropriate safety
the same direction.
3.1.3 spun yarn, n—in a staple system, a continuous strand
of fibers held together by some binding mechanism.
ThistestmethodisunderthejurisdictionofASTMCommitteeD13onTextiles,
3.1.3.1 Discussion—The binding mechanism most com-
and is the direct responsibility of Subcommittee D13.58 on Yarn Test Methods,
monly used in spun yarns is twist. Other useful mechanisms
General.
Current edition approved Nov. 10, 1999. Published January 2000. Originally
that are used are chemical additives, wrapping, entanglement,
published as D 1422 – 56 T. Last previous edition D 1422 – 92.
This test method is commonly designated by the less precise term“ Untwist-
Twist Method.” 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.
D1422
or some combination of these. Test Method D 1422 is appli- 5. Significance and Use
cable only to yarns which have twist.
5.1 This test method is used for acceptance testing in the
3.1.4 twist, n—in textile strands, the helical or spiral con-
trade for economic reasons even though it is less accurate than
figurations induced by turning a strand about its longitudinal
the direct method, Test Method D 1423.
axis.
5.1.1 If there are differences or practical significance be-
3.1.4.1 Discussion—Twist is usually expressed as the num-
tween reported test results for two laboratories (or more),
ber of turns about the axis that are observed in a specified
comparative tests should be performed to determine if their is
length either metres (tpm) or inches (tpi).
a statistical bias between them, using competent statistical
3.1.5 twist factor, TF, n—the product obtained when the
assistance.As a minimum, the test samples should be used that
twist expressed in turns per centimetre is multiplied by the
are as homogeneous as possible, that are drawn from the
square root of the yarn number expressed in tex:
material from which the disparate test results are obtained, and
Twist factor ~TF!5 tpcm 3 T (1) thatareassignedrandomlyinequalnumberstoeachlaboratory
=
for testing. Other materials with established test values may be
where:
used for this purpose.The test results from the two laboratories
T = yarn number expressed in tex.
should be compared using a statistical test for unpaired data, at
3.1.5.1 Discussion—Twist multiplier and twist factor are a
a probability level chosen prior to the testing series. If a bias is
measure of the “twist hardness” of yarn because they are
found, either its cause must be found and corrected, or future
approximately proportional to the tangent of the angle between
test results must be adjusted in consideration of the known
fibers on the outer yarn surface and the axis of the yarn; the
bias.
larger this angle, the harder the twist. Furthermore, this angle
5.2 The “setting” of twist in some fibers causes excessive
is a function of both the twist content (turns per unit length)
contraction when the yarn is retwisted in the reverse direction.
and the number of fibers per yarn cross section (yarn number).
Therefore, the number of turns required to bring the specimen
Hence, twist content alone cannot provide a measure of the
back to its original length may be less than the number of turns
twist hardness of a yarn. Twist multiplier and twist factor are
removed in untwisting. This effect may be partially offset by
proportional to each other and differ only in the units used.
the use of higher pretensioning loads; but this increases the
The two are related by Eq 2 and Eq 3:
danger of stretching the yarn. Little information is available on
TF 5 k 3 TM (2)
the correct tensions to use for yarns made from different fibers
k 5 277.29/ L (3)
= or with different amounts of twist.
5.3 In addition to being less tedious, this test method
requires fewer specimens than the direct-counting method and
where:
the results may be sufficiently accurate for certain purposes.
L = length in yards of the hank used to define the indirect
This test method can be useful in those cases where the main
yarn number of the type,
objective is to measure variations from an average value.
N = hanks/lb. In particular for cotton count,
Another possible application is where a large amount of twist
k = 9.567 so that Eq 2 becomes Eq 4:
testing is required on yarns of similar type and twist. In this
TF 5 9.567 3 TM (4)
case preliminary tests comparing this method and the direct
3.1.6 twist multiplier, TM, n—the quotient of the twist
method could be used to determine the correct pretension.
expressed in turns per inch and the square root of the yarn
5.4 Twist has important effects on the physical properties of
number in an indirect system.
yarn. Low-twist yarn is lofty and is usually preferred for
Twist multiplier ~TM!5 tpi/ N (5)
=
knitting because of its softness, covering power, and warmth.
Increasing the amount of twist causes an increase in yarn
where:
strength by increasing fiber cohesion, but as the twist angle
N = yarn number in an indirect system, the cotton system
increases beyond an optimum point, strength decreases due to
unless otherwise specified.
a loss in effective fiber contribution. Maximum yarn strength is
3.1.7 yarn, n—a generic term for a continuous strand of
obtained by inserting a medium amount of twist to obtain an
textile fibers, filaments, or material in a form suitable for
optimum balance between these two opposing forces. High
knitting, weaving, or otherwise intertwining to form a textile
twist produces yarns of high density (“hard” or “wiry”) and
fabric.
high elongation and may improve the abrasion and impact
3.2 For definitions of other textile terms used in this test
resistance of fabrics.
method, refer to Terminology D 123.
5.5 The optimum twist for either manufacturing efficiency
4. Summary of Test Method
or physical properties usually increases as staple length de-
creases.
4.1 A specimen is untwisted and then retwisted in the
opposite direction until it contracts to its original length. It is 5.6 The twist in a yarn before it is packaged may be
assumedthatthesameamountoftwisthasbeeninsertedaswas different from that of the yarn after it has been withdrawn from
originally present. Twist, as turns per unit length, is calculated the package because of changes in tension and the effect of the
ashalfthenumberofturnsregisteredonthecounterdividedby method of withdrawal. If the yarn is withdrawn over-end, a
the specimen length. slight increase or decrease in twist will take place, depending
D1422
upon the direction of the twist in the yarn, the direction of not cut the specimen free from the package or from the yarn to
windingonthepackage,andthelengthoftheturn(orwrap)on be discarded until after the yarn is secured in the clamps of the
the package. twist tester. When possible, take the specimen from near the
center of the traverse and not at the traverse reversals.
NOTE 2—The difference in twist between unwinding from the side and
7.3.3 For woven fabric, take warp specimens from separate
over-end is 1/pd, where d is the diameter of the package. Thus, for a
25-mm (1-in.) diameter package, the difference would be about 13 tpm or ends, since each represents a separate package. Because the
about one third tpi.
fabric may have been woven on any of a variety of looms
which are random quilling, sequential quilling or shuttleless,
5.7 When a yarn is taken from a more complex yarn
take filling specimens at random through the whole laboratory
structure or from a fabric, the resultant twist should be
sample to obtain as representative data as possible. If a strip
consideredonlyanapproximationoftheoriginalvaluebecause
about2m(2yd) long is used as a source of specimens.
of alterations that may have occurred as a result of the effects
ofunwinding,handling,andmechanicalstrainsmetinprocess-
7.3.4 For weft-knit fabric known to be multi-feed, take
ing.
specimensfromsuccessivecoursesinoneportionoflaboratory
sample. For weft-knit fabric known to be single-feed or for
6. Apparatus
which the type of feed is not known, take specimens at random
6.1 Twist Tester,consistingofapairofclamps,oneofwhich
from the whole sample.
is rotatable in either direction and positively connected to a
7.3.5 For warp-knit fabrics, cut a walewise strip from which
revolution counter. The tester may be hand- or power-driven.
specimens can be raveled for testing as needed (Note 3). Cut
The position of one clamp (or both clamps) shall be adjustable
strips from which the test specimens can be raveled for testing
to accommodate specimens having the length prescribed in
as needed (Note 4). Cut these strips to provide yarn specimens
10.2. The tester shall be provided with a variable tensioning
at least 75 mm (3 in.) longer than the specimen length and to
devicesoconstructedthataspecificforcemaybeappliedtothe
contain more than the required number of specimens for test. If
specimen at the beginning and end of the test and removed
several strips are cut, divide the number of specimens among
completely during the intervening untwisting and twisting
the strips as nearly equally as possible. Use care to avoid loss
operations.
of twist prior to testing.
6.2 Dissecting needle or stylus.
6.3 Metal ruler to verify gage length (accurate to 2 mm or
NOTE 3—In order to minimize changes in twist, specimens should not
be unraveled from the strips until they are to be placed in the twist tester.
0.1 in.).
7.4 Number of Specimens:
7. Sampling
7.4.1 Spun Yarn Singles—Take 25 specimens from each
7.1 Lot Sample—Select one or more shipping units taken at
laboratory sampling unit of spun yarn singles.
random to represent an acceptance sampling lot and used as a
source of laboratory samples.
8. Conditioning
7.2 Laboratory Sample—For packaged yarns, take a mini-
mum of five packages for the laboratory sample unless
8.1 Conditioning is not required for this test method.
otherwise agreed upon between purchaser and seller. For yarns
from woven or knitted fabrics, the sample must be large
9. Procedure
enough to furnish specimens of the length and number speci-
9.1 To Determine Twist:
fied in 7.3.3.
9.1.1 Check the twist tester to be sure that the longitudinal
7.3 Selection of Specimens:
play and radial play of the clamp assemblies are small enough
7.3.1 As nearly as possible take an equal number of speci-
to secure the required precision.
mens from each package or unit of the laboratory sample.Take
9.1.2 Determine the twist with the precision stated in the
the specimens from each package in a random manner to
minimize the effect of cyclic variations introduced during following table:
manufacturing processes. When preparing specimens, condi- Turns of Twist in Test Specimen Precision, in
(tpm or tpi) 3 Length (metres or inches) revolutions
tioning them, or inserting them in the tester, take care to avoid
any change in twist.
5 or less 0.1
7.3.2 For packaged yarns, r
...