Quality
Assessment of Sewing Threads
Aravin Prince Periyasamy
Assistant Professor- Textile
Chemistry, DKTE’S Textile Engineering Institute, Ichalkaranji, MH, India
ABSTRACT
Sewing thread is considered to have
been the first textile material. History tells us that some 25000 years ago
sewing threads were made by the persons living in caves and jungles by rubbing and
twisting together the long fur fibers pulled from animal skins. The crude
threads, by means of needle, were used to join animal skins to form the
primitive clothing of the early civilization. The most affected was the textile
industry especially the textile fabrication and sewing thread industry. In
India till 1990 we are used cotton threads only, but technical developments
have given us a wide range of synthetic threads which are for most purpose now
superior to cotton threads
TESTING ON SEWING THREADS
In generally the sewing threads are
tested by 2 methods .There is,
Ø
Physical Test
Ø
Chemical test
PHYSICAL TESTS:
THREAD COUNT:
Count or number of sewing thread is
in general measured by the ASTM test method designated D-1059 for short-length
specimen and skein method (ASTM-1907) for long specimen length. The direct
system of thread number is based on measuring the weight per unit length of a
yarn, where as the indirect system is based upon the length per unit weight of
a thread. In the short-length method, the specimens of prescribed length,
usually 1m or less, are cut from a conditioned sample, which is under
prescribed tension, and weighed. For skein method, the specified lengths of
thread are wound on reels as skeins, and weighed. The count or thread number is
then computed from the mass and length of thread.
THREAD DIAMETER:
The diameter of sewing thread is an
important parameter for effective sewability. It must be appropriate to the
size of the needle eye. If the thread diameter does not match with the size of
the needle eye, the thread may break during sewing deteriorating the appearance
of the seam. When the diameter of the thread is large enough, it displaces the
yarn in a fabric, resulting seam puckering. Generally the width of the needle
eye is about 40% of the size of the needle. Sewing thread must not occupy more
than 60% of the width of the eye to avoid the fraying of thread during sewing. Sewing
thread diameter is also a consideration in selecting sewing thread for
embroidery, contrast stitching, or other decorative applications, since cover
is important with such threads. So, diameter of a sewing thread is an important
parameter to measure.
THICKNESS GAUGE METHOD:
A thickness gauge with standard
pressure foot diameter (9.52+0.02mm) is used. The pressure foot and other
connected moving parts shall be weighted to apply a total force of 1.67+0.03N
equivalent to a pressure of 23.4kPa. For measuring the diameter, the thread is
to be drawn from the side of the holder without disturbing the twist. Then four
such strands of the thread are to be placed side by side on the anvil and
approximately mid-way between the sides of the pressure foot of the thickness
gauge. Then, the thickness to the nearest 0.02mm is to be measured and to be
recorded as the diameter of the thread. The next reading is to be taken after
removing at least 300mm of thread from the holder and 10such readings to be
taken along the length of the threads to calculate the average diameter of the
sewing thread.
OPTICAL METHOD:
In this method, a microscope, having
a stage that can be rotated to bring the thread parallel to the movable cross
hair in the eyepiece, is used to measure the diameter of the threads. The
mounting plate, with clip or other means is used for holding the thread at a
constant tension sufficient to remove any slackness in the thread without
stretching it. Before measuring the diameter, the thread is drawn from the side
of the holder without disturbing the twist. Then the thread is to be mounted on
the movable stage of the microscope using the mounting plate and the stage is
rotated until the thread is parallel ti the movable cross hair. The diameter of
the thread is measured to the nearest 0.02mm, as the difference in the
micrometer settings when the cross hair is moved from the one edge of the
thread to the other. The next reading is taken after removing atleast 300mm of
thread from the holder and 20 such readings to be taken along the length of the
thread to calculate the average diameter of the sewing thread.
SHRINKAGE:
Measurement of shrinkage of sewing
thread is very important because it may cause puckering along seams and thus
adversely affect the seam appearance. The following combinations may change the
influence of sewing thread shrinkage on the seam: the construction and mass of
the seamed fabric, the nature of the seam assembly, or the tension on the
sewing thread during sewing.
Shrinkage testing of thread due to its
Exposure to;
Ø
Dry heat
Ø
Boiling
water
DRY HEAT SHRINKAGE:
After preheating the drying oven to 176+3oc,
the specimen is suspended freely from a stationary rack side the oven
away from the side walls. After the oven returns to the original temperature,
the specimen is then exposed for 30+2min. Then the specimen is removed,
conditioned and the loop length is measured.
BOILING WATER SHRINKAGE:
The specimen is wrapped in
cheese-cloth. The wrapped specimen is immersed in boiling water and allowed to
boil for 30+2min and then the cheese cloth along with the specimen is removed
from the bath. The excess water is squeezed out from the cheese cloth and the
specimen is then removed from the cheese cloth and dried in a drying oven at 65oc for 1hr and conditioned. The loop
length is then measured.
DETERMINATION OF RESIDUAL SHRINKAGE:
Mounting Device-The device shall be
such that a test specimen of at least
100cm length can be mounted on it, with one of its ends in a fixed clamp
under the desired dead weight tension.
a.
Exposed to a temperature of 150oc or 180oc
b.
Immersed in water at 100oc
The shrinkage of
each test sample is to be calculated using the following equation;
Shrinkage% = I1-I2 / I1 X 100
Where,
I1 = original length of the loop
I2 =length of loop after exposure
LENGTH PER PACKAGE:
Measurement of length per package is
very important because the sewing thread is sold on length basis. This test
method is used to measure the total length of thread in a package. The length
of thread on a package is measured by winding the thread from the package to a
reel of known perimeter into skeins. The total length is measured by counting
the number of complete skeins of specified length, number of wraps in last
partial and by measuring the length of the last partial wrap.
Length
of thread in the package=I1+I2+I3
Where in,
I1=
number of whole skeins times length per skein,
I2= number of complete wraps in last partial skein times
meters per wrap,
I3= length of last partial wrap
on the reel
TICKET NUMBERING SYETEM:
The ticket number is the “number
assigned to a sewing thread to designate its approximate linear density, in
other way it denotes the thread sizes. But there has always been lot of
confusion over the thread ticket number in one way or the other. Ticket number
is determined on the basis of finished thread. Various finishing process like
Scouring, Bleaching, Dyeing, Stretching, Mercerizing, Bonding, Polishing,
Lubricating significantly change the apparent thread size of the unfinished
thread. Type and number of finishing processes required for different types of
threads vary from one type of thread to another type of thread. That is one
thread size or ticket number is determined on unfinished thread. The count of
the finished sewing thread does not depend only on its single input yarn count
and ply but also on amount and type of color/finishes applied on it.
HAIRINESS:
The hairiness of sewing thread is an
important property for its effective and efficient performance during sewing.
Too high hairiness of thread restricts its smooth run through the needle eye
and other thread path of a sewing machine resulting in thread breakage, high
heat generation or many other defects in seam. Measurement of hairiness is
important for sewing thread made out of staple fibers. Hairiness is defined as
the tendency for component fibers to stand out from the surface of the yarn
into the surrounding air. Hairiness of yarn or thread is commonly measured
optically in two different methods. In one of the method the overall length of
the hair present in unit length of yarn is measured. And in another method the
number of hair protruding above certain lengths are counted. The hair is
classified in a number of classes.
THREAD FRICTION:
Frictional property plays very important
role for effective sewability of a sewing thread. A controlled level of both
static and kinetic friction is required; the frictional force should not be too
high, which could cause thread breakage, and not too low, which could cause
improper thread control and seam slippage.
In its simplest form as illustrated
the yarn is merely hung over the rod, so that it becomes (π) radians. In that
case the equation becomes:
1n (T2/T1)
µ
= ----------------
Q
Where,
µ =
coefficient of friction,
1n = natural logarithm, to base e (2.718)
T1 = mean input tension
T2 = mean
output tension, and
Q = wrap angle, 3.14radian
Lawson Hemphills Constant Tension
Transport is an instrument which can be used for testing of yarn to metal/
ceramic or yarn to yarn friction. The thread withdrawal at constant tension is
utilized here to measure the friction coefficient applying capstan method. With
the precisely controlled input tension, thread drag over the standard pins or
on itself is monitored with a tension meter in thread path to calculate
coefficient of friction.
UNEVENNESS AND IMPERFECTIONS:
Unevenness is a degree of uniformity
of a sewing thread either in terms of mass per unit length or in terms of
diameter. Sewing performance can be affected by unevenness of yarn because the
thread is required to pass smoothly through the needle eye and tension disks.
More uniform the thread is better is a sewing performance thus resulting in
better seam quality. Unevenness of yarn is generally measured by two different
testers i.e. instrument having capacitance type sensor and the instrument
having photoelectric type sensor. Unevenness in terms of mass per unit length
is measured by capacitance type tester and diameter irregularity is measured by
photoelectric type tester. However he variation in diameter is more useful for
characterizing the uniformity in the sewing thread, because the actual diameter
of a particular portion of a sewing thread is important for effective sewing
performance and uniform seam quality. The imperfections such as thin place,
thick place, and neps are also measured by unevenness tester. Details of
testing parameters, setting etc. Vary with the type of instrument. However it
is common that testing is performed almost in every yarn manufacturing unit.
TENSILE STRENGTH AND ELONGATION:
Measurement of strength and
elongation is very important because the loop properties, the most important
characteristics of a sewing thread, are strongly dependent on tensile strength
and elongation. Also the performance of seam is very much dependent on the
tensile strength and elongation properties of a sewing thread. The tensile
properties of almost all types of sewing thread can be measured by any of the
following principles. Any single strand tensile testing machine working on one
of the following principles can be used:
Ø
Constant
rate of loading
Ø
Constant
rate of extension
Some testing instruments based on CRE principle, has the provision of
moving the top jaw in order to operate the load-indicating mechanism. The
movement of top jaw relative to movement of bottom jaw prevents the extension
of sample at an absolutely constant rate. The fact is that bottom jaw traverses
downwards at a constant rate and that is why such tensile testing machines are
referred to as constant rate of traverse testers.
LOOP AND KNOT STRENGTH:
The loop breaking strength is
measured to assess the ability of a sewing thread to contribute to seam
performance. It bears a direct relationship to stitch breaking strength and
hence to seam breaking strength. The loop elongation of a sewing thread is also
one important parameter contributing to elongation of a seam, along with the
stitch and seam type, the number of stitches per inch, and the nature of
material stitched. The knot strength of a sewing thread is considered a measure
of the brittleness of the thread. Reduction in knot strength reflects the
performance of a thread after stitching. The thread, after proper conditioning
is withdrawn from the thread holder very carefully to avoid any change in twist
or any stretching of the specimen. For measuring loop strength and elongation,
two pieces of a thread are taken from one thread holder or end. Then both ends
of one piece are fixed in one clamp of a tensile testing instrument without a
change in twist. The length of the loop is approximately one half the gauge
length. One end of the second piece is then passed through the loop formed by
first piece and both the ends of a second piece are fixed in the other clamp of
the machine. The loop breaking strength and elongation is then measured in the
same way as that of tensile strength and elongation.
ABRASION RESISTANCE:
A sewing thread is subjected to
vigorous abrasion during sewing operation while it moves through needle eye and
different parts of a sewing machine. In a garment or any other finished goods
the sewing threads need to withstand a great deal of abrasion while in use.
Abrasion resistance of sewing thread is thus very important quality parameter
of a sewing thread. There are different methods available for assessment of
abrasion resistance.
Before testing, the sewing thread is
conditioned in standard atmosphere condition. In Sweigle Abrasion Tester, an
appropriate grade emery paper and pretension weights are used and the results
are recorded as the number of strokes required breaking the specimen as
calculated. The average value of number of strokes required to break the
specimen. The average value of number of strokes is then converted in terms of
Relative Resistance Index. In this rubbing method the interpretation of
abrasion data is some what difficult. While some yarns may break after few
strokes, others may endure higher number of strokes. The suggested formula for
relative index is
Average number of strokes
to cause break*Pretension of thread (g/den)
RRI= ---------------------------------------------------------------------------------------
(Linear density, denier)1/2
Apart from the
above method, measuring the reduction in weight or strength of samples after
subjecting a thread to a definite amount or rubbing, is also a measure of
abrasion resistance.
CHEMICAL PROPERTIES:
Testing of some important
chemical properties are briefed here;
1.
Color fastness to washing
2.
Color fastness to dry cleaning
3.
Color fastness to water migration
4.
Color matching
COLOR FASTNESS TO WASHING:
Use of colored sewing thread is a
very common practice. The colored sewing thread is used either as per matching
with the color of fabric or some with a contrasting color for some special
effects. If the color fastness of sewing thread to washing is not up to the
mark, then the sewing thread may spoil the garment by color bleeding. The
alteration in shade and staining by sewing thread under conditions similar to
that experienced in domestic washing of apparel and other textile end products
is determined
COLOR FASTNESS TO DRY CLEANING:
Delicate stitched materials are
normally dry cleaned. It is important that he sewing thread should retain its color
or does not stain the adjacent fabric during. Alteration in shade and of
staining by sewing thread dry cleaning is determined by this test method. A
50mm square multifibre test fabric is stitched with a sewing thread in a
similar way as described earlier. Then the specimen is dry cleaned as per the
procedure under test method ASTM D2724. The alteration in shade of sewing
thread and the degree of staining of the multifibre test cloth after dry
cleaning is then graded as per standard procedure.
COLOR FASTNESS TO WATER MIGRATION:
Color fastness to water migration of
a sewing thread is very important so that color doesn’t create staining of the
garment or any finished product through water migration. Level of staining by a
sewing thread under home care conditions similar to those experienced when items
are left in a wet condition for a specific period of time is measured by this
test method.
A 50mm square multifibre test
fabric is sewn with three parallel lines of stitching space 10mm apart with the
first line 15mm from the test fabric edge. Using the sewing thread to be
tested. Generally the stitch length is 8 stitches per inch. Then the standard
polyester/cotton terry cloth is cut with 50mm *150mm dimension.
The specimen and strips of
terry cloth are then home laundered as per the standard method mentioned in
AATCC test method 143. The specimen is then rolled in the terry cloth strip and
inserted into a test tube. The test tube is then allowed to stand for 4hr at
ambient temperature. After 4hr the specimen is then removed from test tube and graded
immediately for change in degree of staining.
INDIAN STANDARD SPECIFICATIONS FOR COTTON
SEWING THREADS (REQUIREMENTS FOR COLOUR FASTNESS ETC.) (IS: 1720-1978)
|
S.No
|
Agency
|
Rating
|
Method of test
|
|
1
|
Color fastness
to
|
5 or better
*6 or better
4 or better
4 or better
|
IS 2454-1967
-do-
IS 765-1966
IS 971-1966
|
|
2.
|
Cupramonium
fluidity
|
Should not
exceed 8 rhes
|
IS 244-1969
|
|
3.
|
Length/mass of
sewing thread
|
Max. tolerance
-2%
|
_
|
CONCLUSION:
The quality of sewing is of great
importance even though it usually represents much less than 1% by mass of a
garment. The quality requirement of sewing thread is very stringent, both
during the sewing process itself, and during the subsequent life of the end
product. The most important quality requirements of a sewing thread are that
the thread must pass freely the small eye of the needle; consequently it must
be uniform, knot-free, non-torque, and fault free. Therefore, testing of sewing
thread is important from the point of view of quality control, process control,
product development and process optimization.
REFERENCE:
- Prof V.K. Kothari, Progress in textiles : Science & Technology, Vol 1, Testing and quality management, IAFL Publications
- Dr. J.V. Rao & Rajendra Kr. Gaur, Sewing threads, NITRA Publications.
- Pradeep V.Metha, An introduction to quality control in apparel industry.
- http://www.textileinfo.com
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