The spinning process and control method of spandex core-spun yarn are explained in detail

2020-09-07 | 669Hit

In recent years, more and more enterprises produce spandex core-spun yarn, and its application is very common. However, the design method, quality standard and test method of spandex core-spun yarn vary greatly among enterprises, which are all the enterprise standards set by each enterprise itself. Enterprises with more than ten years of production history of spandex core-spun yarn have found out some experience in the production of spandex core-spun yarn through years of practice, which is introduced as follows for peer reference.



1. Performance characteristics of spandex filament

The biggest characteristic of spandex filament is its high elasticity, its elastic elongation can reach 6 ~7 times, the elastic recovery rate can reach 95%~98%, and it has the characteristic of repeatedly stretching, that is, in the range of 50%~250%, the stretching force is large and then shrink back, which is the unique characteristic of spandex filament. The fabric with spandex filament has no sense of restraint, no sense of pressure and no sense of relaxation, which is incomparable with other elastic fibers. The elastic recovery of spandex filament decreases at 170℃~180℃. However, since spandex filament exists in the fabric in the form of other fibers, it can be processed under the high temperature of 180℃~190℃. The elasticity of spandex filament decreased only after 40h of uv irradiation, while the strength of rubber filament decreased by 50% after only 10h of irradiation. Spandex filament is acid-resistant, cold-resistant, resistant to organic solvents and most chemicals, but it is sensitive to chlorine reaction, so it cannot be processed with chlorine bleaching. The strength of spandex filament was 0.45cN/dtex~1.18cN/ Dtex, which was 5 ~7 times that of rubber filament.



2. Spandex filament conveying mechanism and drafting mechanism

Spandex filament has the characteristics of low load and high elongation. When spinning spandex core-spun yarn, a set of conveying rollers should be installed at the lower part of the roving spindles of the spinning frame, which can be driven by chains. The linear speed of the conveying drum is lower than that of the front roller, so that the predraft of the spandex filament can be obtained, and its elongation can be controlled as a constant value, that is, the content of the spandex filament in the spandex core yarn can be controlled. The collector behind the rubber roller before feeding the spandex filament into the spinning frame is combined with the drawn whiskers of the cotton roving and twisted to form a spandex core-spun yarn. Generally, the pre-draft multiple of spandex filament is 125.38Zb/(Za×Zc).



If the outer diameter of the conveying drum is 40mm, Za has several specifications of 40 teeth, 45 teeth, 50 teeth, 55 teeth and 60 teeth, Zb has several specifications of 30 teeth, 35 teeth, 40 teeth, 45 teeth and 50 teeth, and Zc has several specifications of 34 teeth to 45 teeth, which are used for the adjustment of pre-draft multiple.



3. Process design of spandex core-spun yarn



3.1 Spandex filament content and Pre-draft multiple

In the design of spandex core-spun yarn, when determining the amount of spandex filament, we should not only pay attention to the yarn strength, but also consider the final use and cost of the fabric. (1) The single sliver of spandex core-spun yarn is generally 1.05-1.1times as much as the same pure cotton sliver, and the drawing in the rear area of the designed spinning yarn is too small to be controlled. (2) The strength of spandex core-spun yarns is close to that of pure cotton yarns. In general, the strength is more than 95% of that of pure cotton yarns of the same size, and the breaking strength of single yarns can reach about 85% of pure cotton yarns of the same size. However, as the yarn number becomes smaller, its strength also decreases. The elongation of spandex core-spun yarns is higher than that of pure cotton yarns of the same size, which is generally about 10% higher, and the breaking work of spandex core-spun yarns is also greater than that of pure cotton yarns. These properties are very beneficial to post-processing and weaving processes.

Spandex core-spun yarn, single yarn breaking strength with thinner yarn number and decrease, the reason is that after thinner yarn, spandex filament content is relatively increased, especially the content of spandex filament in more than 10%, the single yarn strength will be larger, so in the design of spandex core-spun yarn, spandex filament yarn of different yarn number should choose appropriate content and predraft multiple.



When spinning spandex core-spun yarn, the specifications of spandex filament are 231Dtex, 154Dtex, 110Dtex, 77Dtex, 44Dtex, 33Dtex and 22Dtex. And so on. Clothing fabrics are generally 77Dtex and 44dtex., fine yarn 44Dtex., 33 Dtex and 22dtex, medium yarn 77Dtex, coarse yarn 154Dtex and 110Dtex. If spinning the same yarn, the elastic force is required to choose 154Dtex or 110Dtex, and the elastic force is required to choose 77Dtex or 44dtex.



When spinning spandex core-spun yarn, it USES Changzhou Gill spandex spinneret. Generally, the predraft of spandex filament is about 3.8 times. At this time, the elasticity of elastic fabric can be controlled between 25% and 35%. The spandex core yarn of 14.5 Tex ~18.2 Tex is commonly used in knitted underwear and stretch socks. The spandex filament is usually 77Dtex, and the predraft multiple of spandex filament is 3.5-3.7 times. The drawing times of spandex core-spun yarns used for weaving warp stretch denim are larger, generally about 3.8~4 times. Generally, the predraft times of spandex filament are 4 times ~5 times for 154DTEX, 3.5 times ~4 times for 77DTEX, and 3 times ~4 times for 44Dtex.

The amount of predraft should be left when selecting spandex filament. For example, the spandex filament with 77DTEX is broken when the elongation is 400%, and its fineness at the time of fracture is 77/(1 400%)=15.4dtex. In this case, its fracture strength is (1cN/dtex× 77Dtex) / 15.4Dtex =5cN/dtex. For this reason, only 5 times can be used. If it is more than 5 times, if 6 times is used, then the fracture strength is (1cN/ Dtex × 77Dtex) / [77DTEX /(1 500%)] =6CN/dtex, which has exceeded the fracture strength of spandex filament 5CN/ Dtex and will cause spandex filament to break. Therefore, the pre-draft multiple should be less than 5 times.

The fineness of spandex core-spun yarn is determined by the fineness of yarn number, fabric elasticity and yarn shrinkage. Generally, the spinning number is [yarn number × (1 fabric elasticity)]/ (1- yarn shrinkage), and the elasticity of elastic fabric is about 25%~30% at this time. Table 1 shows the conversion relation between the metric number and the inch count of cotton and spandex core-spun yarn.



Note: The common fixed moisture regain rate of spandex filament is 1%

When the spandex filament content is 3%~10%, the conversion factor is 583.23~583.73, and the decimal part has little influence, so the conversion factor can be generally used 583.5.



3.2 Design of spinning number of spandex core-spun yarn

The calculation formula of spandex core-spun yarn number Cs is Cs=H S/9D×K, the fineness (denier) of The H-outsourcing fiber spinning number S-spandex filament D -- The pre-draft multiple K -- coefficient of spandex filament. The data of dupont company in the United States is 1.16, and that of China is 1.0

From the calculation formula of spinning number of spandex filament, it can be seen that S/9D·K is the coefficient of spandex filament. SK/(Cs·D·9) is the content of spandex filament in core-spun yarn.

When spinning spandex core-spun yarn, the speed of spinning frame should be lower than that of pure cotton yarn of the same size. Under normal circumstances, the front roller rotation speed is within the range of 180r/min~190r/min. In order to fully improve the utilization rate of the strength of the outsourcing fiber, it is necessary to enhance the friction resistance between the fibers when the core-spun yarn is under stress, that is, the axial component force of the broken fiber and the friction resistance of the slipping fiber. Therefore, the twist design of spandex core-spun yarn should be on the high side to make the outsourcing fiber

The dimension produces a large centripeal pressure, which makes the spandex core-spun yarn obtain a higher strength. In general, it should be about 2 twist /250px more than the cotton yarn of the same size.



4. Heat setting

The setting temperature of spandex core-spun yarn is generally 60~80℃,15min~20min, and it is shaped by vacuum twice to control its elasticity to avoid setting at high temperature for a long time, so as to avoid damaging the elasticity of core-spun yarn. If steam, the temperature is 75~80℃, and the time is 40min. If the twist coefficient is not large, thermal setting may not be used.



5. Matters needing attention in the selection of spandex core-spun yarn spinning equipment

(1) The lower opening collector is selected. The opening of the collector should be slightly larger, so as to avoid the breakage of the strip and the diameter being too small, which will affect the yarn evenness.

(2) The selection of the wire ring should be slightly heavier than the same number of pure cotton yarn No. 1 ~ no. 2, the cross-section of the wire ring to choose a small friction coefficient, will not damage the spandex filament is better. According to Japan's Shemin Industrial Plant, the elongation of 44dtex spandex filament is 3.66 times, the spindle speed is 11000r/min, when the diameter of the steel collar is 45mm, the optimum weight of the wire ring is 4.864g/ (100 pieces) [namely 75 green/(100 pieces)], too heavy will increase the fracture, too light will appear a larger air ring. In addition, the replacement cycle of the wire coil should be shortened by 1/3 than that of pure cotton yarn of the same number. The steel collar is 3.2mm with wide edge.



6. Common defects in spandex core-spun yarns and matters needing attention in joints

Whether the common defects in spandex core-spun yarns are covered with outer fiber, without core and with poor coating effect (partial coating), etc. When spinning fine spandex core-spun yarns or when the spandex filament is thicker, the defects are easy to occur, because the number of single yarn fibers on the cross section of the cotton fiber strand is less, and it is easy to break during drafting.

If the content of spandex filament exceeds 20%~25%, the roving strand is interrupted or cannot be supplemented in time in the spinning process, or part of the cotton fiber is sucked away by the cotton flute, then the quality of spandex core-spun yarn is poor and its elasticity is also greater than that of normal spandex core-spun yarn. Core-less spandex yarns are often caused by the spandex filament breaking, which is usually caused by improper configuration of the wire ring and steel collar, heating or wear of the wire ring with gaps, resulting in the spandex filament breaking, while long segments without cores are often caused by improper operation and technology. The poor coating effect of spandex core yarn is that the spandex filament is not covered in the yarn body but exposed outside the yarn body. This defect is caused by the improper relative position of spandex filament and cotton roving strand or the spandex filament does not pass through the collector and is out of control.

When spinning spandex core-spun yarn, the joint quality of spandex core-spun yarn is particularly important, especially to control such defects as "hollow core" and "naked core tail", which is the key to the joint quality of spandex core-spun yarn. Because of spandex core-spun yarn with spandex filament as the core, beheaded output of the first roller fiber filament and outsourcing in the cotton suction pipe, the longer the time, the more long inhalation of spandex silk, cotton and outsourcing for the single fiber intake, filament suction pressure is greater than the short fibers, causing the collapse of both central spandex filament fiber can't stay in outsourcing, so the connector to the first roller pipe mouth of bare wire dew outside the yarn body, namely into "tail" naked core; The twist of the part wound on the bobbin after breaking is small and loose, which makes the spandex filament shrink back, which is the main reason for the "empty core" of the spandex core-wrapped joint. Attention should be paid to the problem of spandex core-spun yarn joint.



(1) Joint length. Use both hands and joint method namely one hand joint, one hand with scissors to cut the filament core. According to the test, when the joint length of spandex core-spun yarn is about 40mm~45mm, it can ensure that the strength of the joint section is close to the normal yarn. In addition to emphasizing the use of both hands, the joint of spandex core-spun yarn should also emphasize the strengthening of daily mechanical maintenance, so as to ensure the uniformity of the height of cotton flute pipe and the unification of the front and middle cots, so as to ensure the standard of joint length.

(2) Prevent "naked tail". Before the two-hand joint, the filament should be precut so that the filament loses its suction instantaneously and springs back to the center of the outsourcing fiber. If you can master the quick recovery elastic energy of the filament, you can eliminate or significantly reduce the "naked tail" caused by the joint.

(3) Prevent joint hollow core. After repeated practice, the "empty core" of the joint can be eliminated by using the method of twisting again after untwisting, that is, 20mm untwisting of the broken yarn segment wound on the bobbin, to make the spandex filament freely rewind and draw out the outer fiber, and then use your hands to properly twist the untwisted yarn end to make the joint with better quality.

In a word, when spinning spandex core-spun yarn, it needs standard design method and test means to spin the spandex core-spun yarn that meets the requirements. The production process should be strictly managed, the quality inspection should be strengthened, the spinning process should be optimized, and finally the spandex core-spun yarn that meets the requirements of users can be produced