A good seam is the key factor in a quality garment. The strength, flexibility, stability and appearance of a properly made seam depend on the type of seam, sewing thread, sewing needle, seam density and seam tension.
Fibers Used in Sewing Thread Production
Different types of natural and artificial fibers are used in the production of sewing threads. Some of them are used frequently, while others are used more limitedly. In addition, yarns that are combinations of staple fiber yarns or endless filaments are also produced.
Linen:
Although the threads obtained from flax fibers have a hard handle, they are used for products that require solid sewing due to their very high strength. They are especially preferred in the manufacture of shoes, tents and awnings and sewing buttons. However, in recent years, these yarns have been replaced by yarns obtained from artificial fibers.
Silk:
Silk threads are used as continuous filaments or as staple fiber threads obtained by spinning the plucked fibers. However, they are not widely used in planting operations due to their high cost. For this reason, it is used in evening dresses, special orders and buttonholes.
Cotton:
The most used natural fiber in the production of sewing threads is cotton.. Cotton threads generally provide good sewing performance. However, their strength and abrasion resistance are lower than a synthetic yarn of the same thickness. However, cotton yarns are more stable at high and dry temperatures than synthetics. For this reason, it is less affected by the needle heating that occurs during the sewing process. Due to this feature, they do not need to be processed with finishing agents.
The use of regenerated fibers in sewing threads is very limited. The tenacity and breaking elongation of yarns obtained from regenerated fibers are lower than those obtained from synthetic fibers. These threads are especially preferred in embroidery because of their high shine. The low strength and abrasion resistance of these threads, which are generally used in filament form, not only create problems in sewing or embroidery, but also create problems in washing finished products.
Synthetic sewing threads are generally obtained from polyamide and polyester fibers. Synthetic yarns are used as filaments or spun from staple fibers. Synthetic yarns are not affected by bacteria, mold and fungi. Especially since they are used in filament form, they have high breaking strength and abrasion resistance.
Polyamide and polyester are highly resistant to chemical effects.
Polyamide is more resistant to alkalis and polyester to acids. But both are adversely affected by the sun's rays.
Filament yarns can be used directly as well as converted into staple fiber yarn. Polyester and polyamide filaments to be used as sewing thread have a bright appearance as they have circular cross-sections.
Polyester fibers are the most preferred synthetic fiber in sewing thread production due to their low cost, favorable chemical properties, suitable elongation properties and high dye fastness.
Although polyamide fibers have high strength, their elongation properties are not suitable for sewing threads. Because they have more extensibility against stresses. This can cause seam puckering due to the stresses that may arise during sewing.
Aromatic polyamide fibers such as Nomex are very expensive. However, it is an ideal material for sewing threads used in the production of fire resistant clothing. PTFE (polytetrafluorethylene) sewing threads are also very expensive. However, they have very special industrial uses due to their incombustibility, insolubility and high resistance to chemicals.
Basic Factors Forming Yarn Structure
spinning
All conventional sewing threads begin the production phase as a single ply thread. These single yarns are produced by spinning staple fibers or very fine continuous fibers. Thanks to the fineness of the fibers, they support each other with the spinning process and form a strong structure.
twist
Twisting process is applied to the single-ply yarns obtained after the spinning process as double or multi-ply. The purpose of the twisting process is to hold the yarn layers together and to give the yarn strength and sewability. A thread that does not have enough twist cannot be controlled at the seam, its plies are separated one by one and eventually break. The yarn that has been twisted more than necessary will cause tangling and clumping and cause negative results in sewing. In order to determine the ideal number of twists, factors such as yarn raw material, yarn thickness, sewing conditions in which the yarn will be used should be taken into account.
Twist Direction
The sewing thread is affected by Z-twist as it passes through the machine parts during sewing. For this reason, the twist direction at the last stage of the sewing thread must be Z. Even at a very short stitch distance, a yarn with an S twist direction in its final stage is untwisted, a single ply wears out and breaks. As the twist direction in the last step of the sewing thread should be Z, the twist direction of the single ply should also be S.
When twisting a single yarn into multiple layers, the twist direction should also change. Otherwise, if the single-ply yarn spinning direction is S and the multi-ply yarn twisting direction is applied as S, the yarn plies will not merge with each other and a smooth structure cannot be formed. When the twist direction is requested as Z in the last step, the spinning direction of the single yarn should be.
Thickness
Various numbering systems are available to indicate the finished thickness of sewing thread. The most used systems were determined as Tex, Nm, Ne and Denier. These systems are specified by weight or length..
Yarn Types According to Production Methods
Staple Fiber Yarns
The raw material of yarns with this structure is cotton or polyester. They are produced by twisting fiber groups of certain lengths together. Before twisting, the yarn is combed. This process ensures that the existing short fibers are separated and the remaining long fibers are parallel to each other. Thus, the strength and smoothness of the yarn increase.
Corespun (Looped) Yarns
Threads in this group are produced with a special production method by gaining all the necessary advantages for sewing. Core yarns are produced by coating staple fiber polyester on continuous fiber polyester (poly/poly) or by coating cotton on endless fiber polyester (poly/cotton).
The core yarns gain high strength from the endless fiber polyester in the middle and a natural structure and stitching behavior from the staple fiber on the outside. Thus, they have the desired thinness and high breaking strength. In addition, with the aerodynamic feature of the hairy structure on the outer surface, needle cooling and less wear of the machine parts are provided.
Endless Fiber Yarns
Endless fiber yarns produced from polyester or polyamide raw materials are produced from 100% artificial fiber. The yarns produced in this structure are produced as single-ply by twisting the very fine endless fiber groups coming out of the multi-hole head, and as multi-ply by the next production stage. It has high tensile strength and wear resistance. These threads are generally used for sewing materials that will be exposed to heavy conditions.
Trilobal Polyester Yarns
One type of endless fiber yarns are trilobal yarns produced from triangular cross-section filaments. These threads are used in embroidery processes with their bright structure gained by their triangular sections.
Textured Yarns
Texturing is the process of giving a permanent crimped or wavy form to straight filament yarns with the help of various methods (false twist, air jet, stacking chamber). Thus, the yarn gets longer and gains a voluminous structure and a soft handle. Depending on the usage area of the yarn, its elongation and bulk properties may change. Textured threads are used especially in hemming and overlock stitches, and partially in chain stitching machines. Since these yarns are opened and spread over a wide surface, they give good results in edge closures.
Air Jet Yarns
These yarns, produced by air-jet texturing of endless filaments, are produced from multi-filament single-ply yarns, which can be characterized by loops of filaments that give small surface irregularities. These irregularities ensure good locking of the loop. At the same time, these yarns come into contact with machine parts less than flat filament yarns. In this way, the friction between the air-jet yarn and the surface it is in contact with is reduced. Texturing reduces the high strength achieved with filaments. But these yarns have higher extensibility.
Monofilament Yarns
It is a single filament, in desired yarn count, textured, untwisted, thick, coarse filament. Monofilament yarns are made of Nylon 6 or Nylon 6,6. Since they have only one surface to reflect light, they are translucent and show the color of the fabric being sewn. The yarn produced from a single filament is harder than the multi-filament yarn of the same number, and this difference is even more pronounced in thick yarns. It is generally used for sewing coarse fabrics.
Properties of Sewing Threads
No matter how good the material to be sewn and the sewing machine used during sewing are, if the sewing thread is not of the desired quality, the resulting product will not be at the desired level.
We can list the features sought in a good sewing thread as follows:
- thread number,
- high tenacity,
- suitable elasticity,
- Low yarn friction coefficient,
- heat resistance,
- yarn evenness,
- low hairiness,
- Softness and slipperiness,
- High abrasion resistance,
- Twist and twist balance,
- Color fastness, light fastness, dry cleaning and other fastness values are high,
Resistance to chemical processes
When making a decision about sewing thread, the features sought in a good sewing thread should be taken into account and checked. For example, if the slip feature is not good and the unevenness is high, high strength of the sewing thread will not be sufficient. Thus, the sewing thread gains the ability to be sewn and the performance after sewing with the optimal combination of all desired properties.
Numbering of Sewing Threads
There are various numbering systems used to determine yarn thicknesses in the world. Most used systems Tex, Nm, Ne and Denier has been determined. These systems are determined on the basis of weight or on the basis of length.
Label No. of synthetic yarns. When calculating water, the total thickness value in Tex is taken into account. Calculation; It is done by dividing 1000 by this value and multiplying by 3. For cotton, the number 590 is divided by the Tex value found.
Example calculation table for polyester and cotton sewing threads is shown below:
Sewing needle
Sewing needles have been used since ancient times. They were originally made of ivory, bone, wood and horn. Their shape has not changed since then. During the 15th century, iron needles began to be used for hand sewing. in Germany in 1800 Balthasar Krems started to use the needle for the chain stitch machine it developed for the first time.. With the sewing machines that started to be produced on a large scale after 1840, there have been great developments in the manufacture of sewing machine needles.
Sewing needles are made of steel and are polished at the final stage of manufacture. Then they are electroplated for corrosion resistance, mechanical wear resistance, reduction of friction during sewing and good appearance.
The coating material is usually chrome or nickel. Another important feature expected from the surface coating of the needles is that the molten particles that occur in synthetic fabrics and threads as a result of excessive needle heating during sewing are prevented from sticking to the needle to some extent. Teflon or PTFE coated needles have been developed for this purpose and are used for special applications.
To use on a particular machine, the needle must match that machine in diameter and length. Also, various needle manufacturers have needed to develop needles with a finer diameter to reduce the needle heating that occurs at high speeds and to prevent fabric damage and shrinkage problems. Sewing needles are produced in various numbers and are selected in accordance with the fabric and thread structure. Since fabrics are woven in a thinner and denser structure today, needles and threads should also have finer dimensions. If the needle is chosen thinner than the fabric and thread to be sewn, it bends and breaks during sewing. If the needle is too thick for the thread, loop formation is difficult to control and leads to skipped stitches. In addition, the thick needle opens large holes in the fabric, causing the sewing appearance to deteriorate and the fabric to be damaged. Different needle manufacturers use their own systems to define needle sizes. But the simplest numbering is the metric system. In this system, the needle number is determined by multiplying the diameter measure taken from the middle of the needle shaft by 100. If the diameter is 0,9 mm, Nm is 90, and if the diameter is 1,1 mm, Nm is 110.
Various needle numbering systems are seen below.
sewing process
The sewing process is applied in order to make the two-dimensional fabric surface three-dimensional. Only in this way can the depth dimension of the human body be achieved. While hand sewing was used at the beginning of the 18th century, the increasing population and the corresponding need for clothing led to the production of sewing machines. Thus, it has reached a shape formed by the quartet of sewing, needle, thread, fabric and machine. In the sewing process in the sewing machine, in one revolution of the machine, the sewing needle sinks into one or more layers of fabric with the sewing thread and is tied with a second thread under the fabric, and a loop is formed by pulling this connection into the fabric.
Basic Stitches on the Sewing Machine
Hand Sewing
Special sewing machines have also been developed for this hand-made sewing with a sewing needle. In this machine, which is called a point sewing machine, the two-edged needles go back and forth between the two gripper jaws on the top and bottom of the fabric, creating the sewing process. It is a flexible stitch type that is generally used for basting, printing and decoration. Since it is a special machine, it is used in expensive production. Especially this stitch is used for men's jacket collar and pocket edges and trousers side seams. It is necessary to change the thread constantly and special wax thread is used.
Straight Stitch
In this type of machines, the sewing thread coming from the upper bobbin with the help of the needle sinks into the fabric and forms a loop under the fabric. This loop catches the hook and enlarges it, passing it around the shuttle with the lower thread wound on the bobbin. While the upper thread is pulled upwards, it is knotted with the lower thread to form a seam.
Chain Stitch
In chain stitch machines without shuttle, a looper running underneath creates the stitch by passing the thread from the needle through itself. Performs sewing with the upper thread coming from the looper needle in single thread chain stitch. After the thread passes through the fabric, the looper forms a loop by holding this thread, and in the second insertion of the needle, the upper thread passes behind this loop and is knotted.
All stitch types are derived from these three main stitches. Overlock and hemlock machines are types of stitches derived from chain stitch.
There are international standards for many stitch types.
Aşağıda The system used by British and American standards can be seen.
- Class 100: Single thread chain stitches
- Class 200: Hand stitches
- Class 300: Lock - straight seams
- Class 400: Locked chain stitches
- Class 500: Overlock type seams
- Class 600: Covering seams (covering).
Sewing performance
The most important factor that determines the appearance and usage quality of a garment is the quality of the fabric. However, the quality of the fabric alone is not sufficient to create a garment with the desired properties. One of the most important factors affecting the quality during the creation of the garment is the sewing performance. The seams that make up the garment must be adequate both aesthetically and functionally. Even if a garment's fabric is in an extremely good condition during use, any seams or seams that break or open will render it unusable. When the causes of these and similar problems related to sewing in clothes are examined, three situations are mostly encountered.
- Sewing thread fraying or breaking before the fabric,
- The threads that make up the fabric are broken or damaged by the sewing needle during the sewing process and as a result, small holes are formed in the fabric,
- Stitch slippage, i.e. slippage of weft or warp threads adjacent to stitch loops and the occurrence of seam opening.
In order to prevent these problems from occurring, effective parameters such as sewing machine, sewing type, sewing speed, needle number, needle tip shape, sewing thread, seam allowance, stitch density and tension should be selected in accordance with the fabric during the creation of the garment.
Sewing performance It was described by Carr and Latham as strength, flexibility, durability and the creation of a comfortable seam. In another source, it is stated that sewing performance depends on the flexibility of sewing, strength and adaptability to the body, and these properties depend on the characteristics of the fabric, sewing technique, sewing type, sewing thread type and number and stitch density. There are many components of the seam, when they are all correctly balanced with each other, the seam can perform efficiently.
Sewing Strength
Seam strength is the resistance of the seams to breaking as a result of a force applied perpendicular to the sewing direction in sewn fabrics. Elongation at break is the % elongation value at the time the seam breaks.
The seams are also exposed to the forces that fabrics are exposed to during use. As a result of the application of these forces, damage to the seam instead of the fabric is preferred in terms of repetition and repair. For this reason, it is recommended that the seam strength be 80-85% of the fabric strength.
When two pieces of fabric are joined by a seam and an increasing force is applied at right angles to that seam line, breaks occur at and near the seam line. These breaks occur with a force less than the force required to break the unstitched fabric. These also create sewing mistakes.
seam strength Thread properties are affected by fabric type, stitch type and stitch density. Variations in thread properties and wear resistance during sewing affect sewing strength. It has been observed as a result of the researches that the sewing strength increases as the thread becomes thicker. In addition, synthetic threads create higher sewing strength than natural threads.
Stretching of the fabric to be sewn, its arrangement, tight weave, finishing processes affect the strength of the seam and cause the seam to break before the fabric. When the stitch types are examined, it has been determined that the chain stitch, which creates more connections by using more thread, has a higher stitch strength, but the multi-row stitches show an increasing strength with the increase in the stitch order. Changes in seam density is another parameter that affects seam strength. The higher the seam density, the higher the seam strength. This lasts until the point where the material begins to weaken due to pinholes. Stronger thread should be used with lower stitch density. This requires a thick needle and as a result needle damage to the fabric increases.
In thin fabrics, as the stitch density increases, the seam strength becomes almost equal to the fabric strength, and therefore, when a force is applied to the seam area, instead of breaking the sewing thread, tearing occurs in the fabric along the seam line.
Variations in seam type also affect seam strength. In lockstitch machines, large force losses occur that affect the needle thread. Needle threads are under a stitch geometry that imposes more tension than chain stitches. For this reason, chain stitch and overlock stitch are stronger than lock stitches.
Seam Elasticity
When the seam is stretched in the longitudinal direction, seam distortions occur due to thread breaks, depending on the stitch type, fabric properties, thread type and stitch density, and the amount of tension in the thread.
The use of seams that will keep up with the strains during use and return to their original state when the force is removed is essential for flexibility. Generally, the tension in woven fabrics is less than in knitted fabrics. Elongation values differ depending on the stitch type used. However, the elongation values of the stitches can be approximated by changing the thread tension settings. If you don't have to worry about seam snagging, chain stitching with low tension helps with the extra elongation. In case of stretching of the seam, the threads are pulled towards the fabric and return to their original form when the force is removed. However, this tends to cut the fabric threads, which means seam breakage.
504 three needle overlock stitch
It gives the maximum flexibility achievable. The coverstitch also performs well in terms of flexibility and also provides less bulk. High elongation and strength can be achieved by using the lock stitch with zig-zag steps. The chain stitch is more flexible because it uses more thread per unit length than the straight stitch.
As the stitch density increases, the stitch flexibility increases up to a certain point, as the amount of thread per centimeter will increase. This is made possible by adjusting the thread tension very well as the stitch is shortened. By adjusting the tension according to the density of the seam, the seam of the seam will remain the same in the case of different seam densities and more than 70% stretching can be achieved.
Increasing the stitch density above a certain limit in order to provide flexibility causes the fabric to be compressed, the stitch to gather and the fabric to not fully relax after elongation, weakening and deteriorating.
Sewing thread type is also important in terms of stitch elongation. Cotton threads stretch by 6–8%, medium-thick synthetic threads stretch 15-20% without losing their good sewing performance, and thick synthetic threads stretch 25%. If a large increase in elongation is desired, spun polyamide yarns with 30% elongation can be used. However, these threads can be used not as needle thread, but as lower thread in straight and chain stitches to provide maximum elongation, smooth stitching and sewing flexibility. Discharge of the thread from the bobbin with minimal tension is necessary for a full seam elongation potential.
Sewing Strength
The seam life of a garment should be as long as any other material and should be suitable for its expiry time. If there is a shrinkage in the thread or fabric at an earlier time, this may be considered a seam breakage. Jeans, work clothes, underwear and school clothes are subject to a great deal of wear. Therefore, the seams should be formed to meet this wear. The first abrasive effect on the clothes is the sewing process itself and the loss of strength in the needle threads during sewing. Strength of a thread during sewing; stitch type, stitch balance, stitch tension, stitch pitch, thread type and structure of the material to be sewn dependent on many factors, including
Stitches sewn under high tension are less delicate than those sewn under low tension. In addition, the life of the loop threads in chain stitches increases as the stitch balance is achieved. So the ratio between needle thread and loop thread should be 1:1. All these effects ensure that the thread is better bedded in the material and the seam is protected. As the increase in the density of the seam will increase the friction, it decreases the abrasion resistance.
In densely woven and coated fabrics, the wear will be more as the seam will remain on the surface. Depending on the place of use, the wear resistance of the threads to be used in special effect sewing and fabrics should be high.
Synthetic threads, spun polyester coated cotton thread and polyester coated core thread show better sewing performance. Since the number of fibers exposed to abrasion in thick yarns will be higher, the abrasion resistance will increase. Thin and highly twisted yarns will have less wear.
To increase the abrasion resistance of the threads and thus the sewing; It will be beneficial to lubricate the threads during sewing, to use long fiber and high-resistance raw materials in thread production, and to apply gauze treatment to the thread.
Sewing Safety
Sewing security can be thought of as the seam not breaking as a result of thread or fabric breakage or stitch slippage. Sewing safety; It also includes factors such as stitch pitch safety, stitch pitch type and quality.
In one sewing step, the threads can pass through each other in 3 different ways. All these types affect sewing safety, and each type is described with different degrees of safety.
In a lockstitch sewing process, a thread breakage may occur during other sewing steps, depending on the longitudinal and diagonal tensions, fabric elongation and thread surface. In terms of sewing safety, it is important to strengthen the seams by basting from the back at the end of the sewing process.
The least secure stitches in practice are single thread chain stitches. Because these stitches are formed by passing a loop of thread through another loop of the same thread. For this reason, if the last stitch is not properly locked, it is very easy to untie the stitch with a thread break and stitch slippage. Careful thread selection can increase the internal friction of each stitch, reducing the tendency to run-back. There is still a tendency to run back in the type of stitches in which needle threads are formed by passing through single or multiple loops formed by one or more different threads. However, with the increase in internal friction and the smooth yarn surface condition, a mixture occurs in the seam, often before the yarns run too far. Another important point is that the ends of weak seam lines are reinforced with cross stitch and the ends of the threads are taken to the sewing line with bartack stitch.
As will be understood, the stitch type is the first possibility to affect the thread breakage in a sewing line and determines the degree of future opening of the seam.
Stitch slippage is caused by a fault in the bobbin traveler or when the loop structure pulls the loop in the needle thread. Crooked needles, unsuitable needles for thread size and type, incorrect thread tension, weak presser foot, and large needle hole and opening affect stitch slippage. In this case, the fabric moves up and down with the needle, which is undesirable.
Sewing Comfort
This factor will emerge depending on the application of the first four factors. The sutures may be tied around, across the body, and may give the body a feeling of bulge or stiffness. This is due to improper stitch pitch, stitch or sewing thread selection. Thread ends or label corners can also cause local discomfort.
If a seam is tied across the body, there is a high probability of thread breakage and the fabric elongation will be greater than the seam elongation. If a seam creates an uncomfortable ridge, it's because it creates a bulkier and safer seam line than a closed overlock or open seam. An alternative to this, an open seam, will be more costly and will have insufficient elongation in terms of stitch pitch types. A rough handle stitch can be softened by using textured thread as the loop thread in overlock and coverstitch to smooth edges.
Sewing problems encountered
Sewing Thread Breakage
The sewing thread breaks from its weak place with the increase of the tension on it for any reason. Sewing thread breakage may be caused by not selecting the appropriate sewing machine, sewing type and sewing thread. Apart from these, high thread tensions, defective needle point and needle eye, and using a very thick needle may also cause the sewing thread to break.
In industrial flat sewing machines, sewing threads are damaged during high-speed sewing and this causes a decrease in strength. In scanning electron microscope (SEM) shots, it is seen that the damage mostly occurs at the connection point of the needle thread. In the fibers of the sewing thread, slits are formed as a result of periodic tensions and as a result, thread breaks occur.
Sewing Slip
Stitch slippage (opening) is the name given to the situation where the seams in the fabric open under the influence of load. Seam slippage mainly depends on the fabric structure. Stitch slippage is not very common. However, it is more common in loose fabrics. Stitch slippage normally occurs when a stitch is stretched at right angles to its direction. If the seam opening is conspicuous, it is counted as a seam defect.
Studies on seam slippage based on fabric mechanical properties showed that seam slippage is affected by the bending, tearing and deformability properties of the fabric.
Low bending stiffness is detrimental to the appearance of the seam. However, the very low formability prevents the fabric from adapting to the forces generated during sewing, causing shear deformation of the fabric due to the mass of the sewing thread at the point where the seam is formed in the seam area. Fabric shear deformation caused in this way results in fabric elongation in the seam formation area.
Seam slippage is a seam deformation that occurs due to the interaction between shear forces and fabric elongation in the seam formation area.
Seam Grinding
When two pieces of fabric are joined with a straight stitch and that stitch is forced at right angles, a slit can be made between the two fabrics before the stitch breaks.
This is the seam crease and can be controlled with the stitch tension and density settings.
As a result of the researches; shows that the amount of stitching increases with decreasing stitch density and increasing yarn flexibility. The load applied to the fabric causes fabric deformation and then stitch deformation. Therefore, if the fabric elasticity is increased, the amount of seam squeaking will decrease.
Skip Stitch
Failure of one or more stitch steps to occur at the seam line is known as skipped stitches. Stitch skipping occurs in stitch formation because the gripper or looper cannot catch the needle thread loop.
In a good stitch, it is desirable that there are no skipped stitches as well as thread damage and breakage. This is even more important in chain stitch and automatic sewing machines. Infrequent stitch skips may not be noticed by the eye. However, if these jumps are not repaired, they can later lead to complete removal of the seam. The most important causes of skipped stitches are improper distance between the needle and the gripper point and the needle hole on the stitch plate. Incorrect needle system, incorrect threading, too low presser foot pressure, and misalignment of the gripper tip or looper can also cause skipped stitches. To correct the skip stitch problem, it is necessary to adjust the timing of the sewing machine, replace the faulty parts, and clean the machine.
Seam Shrinkage
Shrinkage in garment technology is the wavy appearance along the seam line on a flat fabric.. Shrinkage either occurs immediately or it does not appear at first and can be seen after processes such as ironing and washing of the garment.
Seam shirring is determined by measuring the percent increase in thickness of the fabric sewn on the original fabric under a constant load.
Each time the sewing needle sinks into the fabric, it pushes the weft and warp threads, causing them to displace, and during this time it is exposed to some tension. This voltage; It depends on the fabric's structure, thickness, mechanical properties, sewing needle spacing and stitch length. When the sewing needle is separated from the pieces in the stitch formation direction, partial or complete relaxation of the weft and warp threads occurs in the needle hole opening area. This depends on the elastic properties of the weft and warp threads. Therefore, the workpieces are jammed at the time of seam formation due to abrasion forces in the locking area of the needle and bobbin thread. The deformation in the seam center direction, which occurs in this way, may cause an increase in the tension of the weft and warp threads. During repeated punctures, the sewing needle has to orient itself between the fabric weft and warp threads, and the threads are pushed back between each other. Structural deformation occurs on the textile surface due to the repetitive displacement of the weft and warp threads. If the tension is higher than the elasticity limit, it will manifest as plastic deformation in the fabric.
This deformation is reflected as seam gathers. This has a negative effect on the sewing quality.
One of the important reasons for the sewing pucker is that the needle-thread tension of the sewing machine is not adjusted well. In general, sewing puckering occurs in sewing machines with high needle-thread tension. In such sewing machines, hard threads are more suitable than soft threads in reducing puckering. In machines with low needle-thread tension, soft threads are more suitable than hard threads.
Another important factor that causes seam shrinkage is washing. The vast majority of fabrics produced today are of fixed size. They do not shrink from width and length during use. Because the raw materials of these fabrics are mostly synthetic or a mixture of synthetic-natural fibers. When yarns made from natural fibers absorb moisture, they expand in diameter and shorten in length. Gathering and seam puckering occur in the fabric sewn with cotton thread that is more moist than normal. When the fabric dries, the shrinkage on the fabric does not disappear, even if the threads return to their original length. Cotton thread in the wet condition draws between 4 and 7%. This rate is 3% in mercerized cotton yarns. The degree of hardness of the washing water also affects the shrinkage rate.
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