Ancient ancestors evolved the technique of sewing with needles and threads, creating various types of sewing threads; in clothing production, a needle and a thread, along with continually improving craftsmanship, have created numerous brands. It goes without saying, the thread plays a crucial role in clothing.
Sewing threads include pure cotton, nylon, poly-cotton, blended, polyester, and rayon, usually composed of two, three, four, or six strands twisted together. The twisting direction can be classified into s-twist and z-twist. Regular sewing machines generally use z-twist threads, but high-quality s-twist threads can also be applied to other sewing machines. Cotton sewing threads perform well in sewing but shrink more during washing compared to synthetic fibers, and have lower strength, chemical resistance, and abrasion resistance than synthetic fibers. High-quality mercerized cotton threads are expensive and thus less commonly used nowadays. Short fiber polyester sewing threads are low-cost with excellent sewing stability, durability, and sewing performance, making them suitable for all regular clothing sewing. Sewing threads used in overlock machines are generally cotton, but due to the high cost of cotton fibers, they are now usually replaced by poly-cotton threads.
Below are characteristics of various threads:
(1) High Strength Polyester Thread: Currently one of the most commonly used and widely adopted sewing threads in the market, characterized by good luster, no elasticity, good color fastness, and strong tensile strength. It is extensively used for sewing PVC, thicker fabrics, nylon leather products, etc.
(2) Fishing Line (Transparent Thread): Transparent threads can be classified into nylon and polyester monofilaments, differing in stretchability, hardness, tensile strength, and usage. They are often used for weaving, sewing labels, suit trousers, sewing transparent materials, and various crafts.
(3) Pure Cotton Thread (Polyester Short Fiber Thread): Polyester short fiber thread is widely used as a conventional thread with slightly hairy surface, lower breaking strength, gloss, and abrasion resistance than other threads. It is used for thinner fabrics. Pure cotton thread is made from natural cotton, combed, and singed, designed specifically for sewing pure cotton fabrics.
(4) Waxed Thread (Horse Line): Waxed thread comes in nylon and polyester materials, with flat shape preferred, and very strong tensile strength. After waxing, it becomes waxed thread, often used for thick leather sofas, outdoor equipment, casual shoes, leather clothing, and other thick products for machine or hand sewing.
When choosing the thickness of the thread, priority should be given to using finer sewing threads, considering the following aspects:
① Finer threads can also minimize prominent seam marks, embedding within the fabric’s inner layer and reducing abrasion impact.
② During the sewing process, to form correct stitches, it is essential to ensure the specifications of the needle, thread, and fabric match. Additionally, attention should be paid to the following two points:
③ Firstly, during sewing, the twist of the thread must be considered. Twisting increases strength and elasticity, but excessive twisting can cause thread curling, affecting loop formation. Typically, when holding a 1-meter-long thread from both ends and making the strands meet, the natural twist count should not exceed 6, to prevent skipping stitches.
④ Secondly, when sewing thin and soft fabrics, fine needles must be used while increasing the needle's lift amount. Smaller friction between the thread and fabric will reduce loop width if the lift distance remains unchanged, affecting normal hook formation and causing skipped stitches. The opposite applies to thick and stiff fabrics.
While the thread is chosen, the needle selection is also crucial in sewing. The nature of the machine determines the needle type. Different machines require different needle specifications, such as 96'1 or 88'1 for plain sewing machines, and 18'1 for overlock machines. Regardless of the machine type, the needle’s specification or number should be chosen based on the fabric's nature and thickness. Generally, needles for textiles and knits have conical tips, while needles for leather and similar materials use special-shaped tips like spear, triangular, or reverse twist to increase strength and achieve good sewing results.
Many garment factories face the problem of a large accumulation of various sewing threads, whether newly developed or in stock, which invisibly wastes costs. To avoid thread waste during production, here are methods and the significance of calculating thread usage: Firstly, for garment cost calculation, thread usage forms part of the total production cost, requiring accurate calculation for comprehensive cost accounting. Secondly, for planning and management: knowing the thread usage aids in procurement and preparation, ensuring timely delivery and quality assurance. Thread usage can be estimated using two methods: the "ratio method" and the "formula calculation method."
Thread usage is determined by many factors, such as fabric thickness, softness, stitch type, stitch density, thread thickness, thread tension, and machine presser foot pressure. These factors often change, making precise calculation challenging. Currently, the ratio method is commonly used.
The "ratio method" involves deriving the thread consumption per unit length of fabric sewn under various conditions from experiments. This ratio e=l/c represents the thread consumption ratio, with l as the thread length (m) and c as the fabric length (m). e can then be used to estimate practical thread usage.
In the formula l=c·e, l is the thread length(m), c is the sewing length(m), and e is the thread consumption ratio. To estimate usage using the ratio method, e must be experimentally determined. Methods include the fixed-length thread method and the fixed-length stitch method.
① Fixed-Length Thread Method
Prepare for the experiment by selecting a well-performing sewing machine, adjusting all parts to the actual process requirements, and preparing the specified fabric and thread. Measure a fixed length of thread (e.g., 1m), leaving 0.5m at the front. Clearly mark this segment with color, wind it on the spool, and sew on the selected fabric until the marked thread is used up. Measure the sewn fabric length to calculate thread usage per meter of stitch, obtaining e: e=marked thread length(m)/stitched fabric length(m).
② Fixed-Length Stitch Method
Preparation is the same as the above method. Then, directly sew with the specified thread and fabric, stitching over 0.5m. Measure a fixed stitch length (20cm or more) in the middle of the stitch, cut it out, and carefully unravel the thread without breaking it, measuring the actual thread length. Calculate thread usage per meter of seam to get e: e=actual thread length(m)/measured stitch length(m).
For lockstitch seams, where the upper and lower thread structures are the same and using the same thread, only estimate the upper thread usage—total thread usage is double. For other seams with different upper and lower thread structures, experiment separately to determine the upper and lower thread consumption ratios. For example, assume a lockstitch seam, stitch density 8 stitches/2cm, fabric thickness 1mm, thread 9.8tex×3 (60/3), total sewing length 6.5m, and e=2.73. Calculate thread usage: l=e·c=2.73×6.5=17.745m.
This method calculates the thread usage of a unit seam based on stitch geometry and derives a formula for practical applications.
The formula derivation involves three steps: One, idealize the stitch's geometric shape, assuming a regular shape like a rectangle or ellipse for lockstitch loops. Two, calculate thread usage for a unit stitch, including one thread loop and junctions between loops. Three, using the unit stitch formula and stitch density, derive a practical formula for the thread usage per meter of seam.
For example, lockstitch seam (301):
l1=2+0.2dt+0.26d/(nm*δ)1/2; l2=1.57+0.16dt+0.36d/(nm*δ)1/2
Where l1 - formula for rectangular lockstitch seam thread length (m) per meter of fabric. l2 - formula for elliptical seam. d - stitch density (stitches/2cm). t - fabric thickness (mm). nm - thread metric number. δ - thread density, cotton δ≈0.8-0.9g/cm^3, poly-cotton δ≈0.85-0.95g/cm^3.
Example: Lockstitch seam, stitch density d=9, fabric thickness t=1.2mm, thread 60/3 poly-cotton, total length 6.5m. Calculate thread usage.
Calculation: Assume rectangular loops, nm=1.693ne=1.693603 =33.86
l1=2+0.2×9×1.2+0.26*9/(33.86*0.9)1/2 =4.58m; total thread length l1×6.5=4.58×6.5=29.77m.
Assume elliptical loops, l2=1.57+0.16dt+0.36d/(nm*δ)1/2 =1.57+0.16×9×1.2+ 0.36*9/(33.86*0.9)1/2=3.88m; total thread length l2×6.5=25.22m.
In fact, common domestic threads cost around 3 yuan each, while imported threads cost around 20 yuan each, several times more. However, imported threads outperform in color fastness, shrinkage, etc. High-quality garments costing thousands need perfect details, prioritizing quality over thread cost to avoid “penny wise, pound foolish.”
In garment manufacturing, choosing needles and threads seems simple but requires satisfying technical and aesthetic demands. Consideration of needle-thread-fabric compatibility, thread-fabric color matching, and fine thread selection achieves the best results.
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