What are the characteristics of nylon fabric
Nylon fabric can be divided into three main categories: pure spun, blended, and woven fabrics, each of which contains many varieties. Pure nylon fabrics are various fabrics woven solely from nylon silk, such as nylon taffeta and nylon crepe. Nylon blended and woven fabrics are obtained by blending or weaving nylon fibers with other fibers, such as viscose/nylon wool.
Nylon has excellent strength and abrasion resistance, ranking first among all fibers. This is one of the reasons why nylon is used as a material for mountaineering clothing and winter garments. Clothes made from nylon are generally durable and not easily worn out.
The elasticity and elastic recovery of nylon fabric are very good, but they are prone to deformation under small external forces. Therefore, during wear, nylon clothing is likely to wrinkle, affecting its appearance.
Nylon has poor ventilation and breathability, and is prone to static electricity. Therefore, it is advisable not to wear underwear made from nylon to prevent harm to the human body.
The moisture absorption of nylon fabric is among the better varieties in synthetic fiber fabrics, making clothing made from nylon more comfortable to wear than polyester clothing.
Nylon has good resistance to moths and corrosion, making it relatively easy to store.
Nylon's resistance to heat and light is not very good, and the ironing temperature should be controlled below 140 degrees. During wear and use, care must be taken regarding washing and maintenance conditions to avoid damaging the fabric.
Nylon fabric is lightweight, second only to polypropylene and acrylic in synthetic fiber fabrics, making it suitable for making mountaineering clothing and winter garments.
Introduction to air-packed and machine-packed spandex yarn
Spandex covered yarn (Covered Spandex Yarn) generally has single-covered and double-covered forms. Among them, nylon spandex and polyester spandex are mostly single-covered. Air-covered yarn (referred to as air pack, abbreviated as ACY) is yarn created by simultaneously stretching outer packaged filament and spandex through certain nozzle specifications, with high-pressure air regularly spraying densely to form rhythmic network points. Its fabric feels soft and smooth; mechanical covered yarn (referred to as machine pack, abbreviated as SCY) is yarn created by continuously rotating the outer packaged filament around uniformly stretched core spandex, possessing a twist (abbreviated as TPM), and the fabric style is flat and crisp which is its main characteristic.
Air pack and machine pack yarn each have their advantages and disadvantages when woven into downstream weaving mills. Generally, air pack needs to be sized when warping on air jet looms; otherwise, the fabric tends to fuzz and break the yarn, but it can be used directly for weft insertion. Simply from a cost perspective, air pack production capacity significantly exceeds machine pack capacity, making the price lower and easier to reduce costs for downstream weaving mills. Although machine pack does not expose the core yarn, quality problems during spinning and weaving are not easily generated, except for uneven twisting, but its output is low, making its price more than RMB 5000/T higher than the same specifications of air pack, even fine denier covered yarn prices exceed RMB 10000/T higher than the same specifications of air pack, thus greatly increasing the cost of using machine pack.
During the spinning process, the pre-stretching multiple (Spandex Stretch) of spandex is an important process parameter that affects the elasticity of covered yarn and fabric, as well as the strength and uniformity of covered yarn, and the creep performance. If the pre-stretching multiple of spandex is too small, it cannot fully utilize the advantage of elasticity in elastic fabric, and if the stretching is too high, spinning becomes difficult, leading to breakage and a decrease in product quality; additionally, the percentage content of spandex also affects the elasticity of covered yarn, with higher content generally providing better elasticity. With a fixed spandex specification, increasing the stretch ratio leads to a decrease in the percentage content of spandex, meaning that the pre-stretching multiple of spandex is inversely proportional to the percentage content of spandex in the yarn.
The strength of covered yarn increases with an increase in the pre-stretching multiple of spandex, and after reaching a certain value, the recovery of spandex causes the outer packaged fibers to curl, while the spandex core is pulled straight; appropriately increasing the pre-stretching multiple reduces the percentage content of spandex, significantly increasing the degree of curl in the outer packaged fibers. However, when the stretching is excessive, the deformation amplitude of spandex approaches the critical value of deformation, causing a decrease in the strength of covered yarn, but benefiting the uniformity of the covered yarn. The phenomenon where deformation varies over time under constant stretching force is called creep. The covered yarn has the best anti-creep performance when the spandex is pre-stretched to 3.5 times.
The twist of the machine pack affects the quality of the yarn, strength, and the uniformity of the covered yarn. Increasing the twist can enhance the adhesion between the outer packaged fibers and the spandex, improving the strength of the covered yarn. The elongation of machine pack mainly depends on the properties of the spandex core, while excessive twisting can cause the outer fibers to be wrapped too tightly, preventing the elasticity of the spandex from being fully realized, thus decreasing the elongation rate. As the twist increases, the uniformity of the covered yarn improves. If the twist is too small, the outer fibers may loosen, and slightly move along the yarn axis during spinning due to friction and other reasons, thus deteriorating the uniformity of the yarn.
The presence of spandex in machine pack can weaken the adhesion between the outer packaged fibers, and if the twist is too low, the outer packaged fibers become loose affecting the covering effect, leading to exposure of the core, thus the twist during mechanical covering should be relatively high. However, if the twist is too high, the fabric’s hand feel becomes stiff, and its drape is poor. Generally, the twist should be adjusted according to the yarn's denier, for example, N40D+20D machine pack is best at 600 twists, while N70D+40D or T150D+40D machine pack can be controlled at about 480 twists. Some small spinning mills, considering delivery times and reducing production costs, may choose to lower the twist or increase the equipment speed to improve yield, which is detrimental to the quality of the covered yarn.
Nylon production process flow
Nylon 6 mainly uses PA6 dry chips to produce various specifications and purposes of stretched yarn through melt spinning, stretching, and winding. Due to different characteristics of the polymer, the spinning process differs from other fibers. The basic process for our company’s PA6 products is: dry chips -- feed hopper -- intermediate material warehouse -- screw extruder -- spinning box -- melt metering pump -- spinning components spinneret -- winding machine stretching roll -- winding head winding forming -- finished product inspection -- finished product -- packaging and warehousing.
Feeding and extrusion: PA6 dry chips are unpacked and added to the feed hopper, then controlled by a pneumatic valve to enter the intermediate material warehouse, continuously sent into the screw extruder for melting, mixing, and metering. The screw extruder has a heating element, and the temperature zone is adjusted according to process requirements, and the screw is driven by an AC motor with variable frequency control to achieve the required extrusion pressure.
Spinning: The melt enters the distribution pipeline under pressure from the screw head and is evenly sent to each spinning position according to the equal distance principle, each spinning position has a high-precision melt metering pump, and the melt is precisely metered by the pump before being evenly sent to each spinning component, and filtered through metal sand and mesh before being extruded through the spinneret. The molten yarn coming out of the spinneret is cooled in an optimized side-blown wind device using laminar side-blown wind. The yarn solidifies, and the fiber structure undergoes molecular orientation change. The oil application device uses a high-precision oil pump to supply oil, ensuring the yarn has the required oil content for the process. The spinning box and melt pipeline are insulated to a certain temperature.
Winding forming: The yarn spun downward passes vertically into the winding space, is directed by the filament guide roller, and then after passing through the heated stretching roll (HOY is a cold roll), enters the high-speed winding head to automatically wind onto a bobbin.
Finished product: The finished yarn cake is inspected for quality, dyed, graded, and then enters packaging as the final product.
