Aravin Prince. P
MDP, TEXPORT SYNDICATE (I) LTD
There are large number of tests available for assessing the quality of sewing threads and the most common tests conducted by the manufacturers and users are physical and fastness properties. However, the most critical test for sewing thread is the �sewability� in the dynamic conditions. The principles and methods for evaluating some of the important sewing thread properties are discussed in this paper.
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 are
� Physical Test
� Chemical test
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.
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.
1. Prof V.K. Kothari, Progress in textiles : Science & Technology, Vol 1, Testing and quality management, IAFL Publications
2. Dr. J.V. Rao & Rajendra Kr. Gaur, Sewing threads, NITRA Publications.
3. Pradeep V.Metha, An introduction to quality control in apparel industry.
Aravin Prince. P
I done my diploma in textile processing ( sandwich) from S. S. M.Institute of Textile technology, After that I was work one year in Production supervisor as a Dyeing Field in M. S. Dyeings Thirupur, Then I joined B. Tech in R. V. S. College of Engineering and Technology, after complete my degree I join Texport Syndicate India Ltd in Bangalore, I am publishing some articles either websites and journal. and I am attending more national and international textile conference
AREA OF INTEREST
Technical Textiles, Garment Processing
Contact no : +919916738343
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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.
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.
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;
� Dry heat
� 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 150�c or 180�c
b. Immersed in water at 100�c
The shrinkage of each test sample is to be calculated using the following equation;
Shrinkage% = I1-I2 / I1 X 100
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
I1= number of whole skeins times length per skein,
I2= number of complete wraps in last partial skein times meters per wrap, and
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.
INDIAN STANDARDS FOR DETERMINING THREAD TICKET NUMBERS:
For cotton sewing threads
It relates to 3 ply construction as a base: the number denotes the single yarn count (Ne). For eg, Tkt. No. 60, means 3/60s or 2/2/80s or 3/2/120s of which resultant count is 20s
It is also based on a 3 ply metric single yarn count(Nm) e.g. Nm 70/3 thread, ticketed as 70 and Nm 120/4 is ticketed as 90.
British standards also published guidelines for determining thread ticket numbers of cotton as well as synthetic threads. Some attempts have been made to over-come the confusion over determining the thread ticket number by using same system of yarn numbering by British standards by issuing its separate standard giving formulae for calculating the thread ticket number for cotton as well as synthetic threads.
Synthetic sewing thread ticket number for following threads (as per IS 9543-1980)
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 are classified in a number of classes.
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 (�) radians. In that case the equation becomes:
� = 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:
� Constant rate of loading
� 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.
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 to break the specimen as calculated. The average value of number of strokes required to break the specimen. The average value of number of strokes are 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
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.
Ultra-violet rays are a part of spectrums of electro-magnetic radiation emitted by sun. They severely damage the thread if exposed continuously for long periods.
What happens when seams are exposed to sunlight:
Base polymer of sewing thread is irradiated by ultraviolet/visible light. And this results in change in the physical and chemical properties of polymer of sewing thread due to absorption of energy. This energy absorption promotes the degradation of the polymeric chain and ultimately the strength loss to the sewing thread. Not only this, UV radiations also attack the dyes present thread leading to spotting and fading of color of sewing thread.
Though, UV degradation of thread takes place at different rates depending upon the type of polymer of which thread is made of. Such degradation does not happen at a time. UV impacts the thread life by gradually deteriorating its strength. There are several factors that can be made accountable for UV degradation of sewing thread.
Fiber characteristics with regard to UV radiation:
Natural pigments, pectin�s and waxes are the good UV absorbers, hence protect grey cotton. Since above components are removed during scouring and bleaching, bleached cotton fabric has low UV protection.
UV PROTECTION OF SEWING THREAD BY GLASS:
Though it is not possible to put a variety of sun protection glasses to protect the seams of garments from UV radiation, simple understanding of the methods of UV protection would help to decide for the type of sun protection glasses to be used for controlling the damages.
� Ordinary glass filters out radiation between 290 and 320nm
� Tinted glass absorbs radiation below 340nm
� Laminated glass filters out virtually all UV radiation below 380nm
In general, polyester thread is more resistant to UV degradation and light, better than nylon thread. Not only this, polyester also posses better dimensional stability, lower elongation5, very good abrasion resistance and better shrink resistance.
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.
The thread, under test, is laundered in contact with a multifibre test cloth with the help of home laundry and drying equipment. The laundering can be done with or without bleach, depending on the conditions one tries to reproduce the effect of home laundering on sewing thread. The change in shade of the sewing thread and the degree of staining of the multifibre test cloth are graded with the help of standard Grey scale.
Three parallel lines are stitched on a 50mm square multifibre test fabric using thread from a thread holder. The direction of stitch should be perpendicular to the strips and completely across the multifibre fabric. The stitch density is normally kept at 8 stitches per inch and stitch lines are placed approximately 10mm apart and the first line starts about 15mm from the edge of test fabric.
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.
Matching of colors of a sewing thread and piece goods is very important where seams are to be inconspicuous. Whether a thread can be matched to the color of particular piece goods may depend on the dyeability of the fibers in the thread. Some fibers take certain colors better than others, and some dyestuffs have better colors in certain hues.
Testing of color matching is generally done in two different ways viz visual matching and computerized color matching. The success of visual color matching depends on the type of light, nature of the surroundings, and the viewer�s ability to see color differences. Colors that appear to match in one environment may not appear to match in another; thus , standardized conditions in terms of type of light, angle of viewing, and color of surroundings must be used for reliable visual matching. So, while matching the color visually, it is very important to mention the type of light and other conditions. Only an experienced person with very good eye sight and without color blindness can perform the color matching test visually.
Instrumental color measurements with a spectrophotometer and computerized shade recipes are used for dyeing thread to common color standards for various fiber contents, thread structures, and dye stuffs. These systems may also may create dye recipe formulations for custom matching to particular piece goods although the apparel manufacturer would probably be required to buy the entire lot.
INDIAN STANDARD SPECIFICATIONS FOR COTTON SEWING THREADS (REQUIREMENTS FOR COLOUR FASTNESS ETC.) (IS: 1720-1978)
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.