The purpose of fabric raising processing is to improve the style and appearance of the fabric, and to increase the wool texture and warmth on the surface of the fabric. The fabric becomes bulky and thick, feels soft, improves the taking effect, and increases the added value of the fabric.
The principle of raising
The steel wire raising machine is equipped with two types of raising rollers on one drum. One kind of pile roller is equipped with metal needles that bend in the same direction as the movement of the fabric, and the other kind of pile roller is equipped with metal needles that bend in the opposite direction of the movement of the fabric, which are what we usually call carding and brushing rollers. When the fabric is running on the raising machine, the rotating carding and brushing rollers have a relative movement to the fabric at the same time. It is this relative movement that causes the needle tip of the raising roller to scrape the fabric in one direction and then in the opposite direction. Scratching causes the velvet of the fabric to rise, thereby achieving the purpose of raising. This is the principle of fabric raising.
Common problems and solutions during fluffing
There are three main reasons for the problems that occur during the fabric raising process: the fabric itself and its processing methods are not suitable, the raising machine is not suitable or perfect, and the raising operation technology is incorrect. The problems that often occur during the fabric raising process are mainly uneven raising and damaged fabrics. Excessive weft strength reduction, excessive pile reduction, yarn scratches, insufficient thickness, etc. The reasons for uneven velvet are very complex and extremely troublesome to solve. Other problems can be avoided as long as sufficient attention is paid during raising. Pilling defects originating from the fabric itself are caused by fiber, yarn or fabric preparation, weaving and pre-treatment (scouring, dyeing, finishing) and other processes.
1. Problems caused by fibers and yarns and their solutions
(1) The weft strength is affected by the fiber type. The shorter the fiber length or the smaller the yarn twist, the greater the weft strength decrease. This type of fabric does not have high strength before raising, and there is a lot of waste during the raising process, so the raising effect is poor. The fiber length used must be more than twice the length of the pile pulled out of the fabric, and the best average length should be more than 10mm.
(2) Yarns with long fiber length and small twist are suitable for raising even if the strength is not strong. On the contrary, when using yarn with long fiber length and strong twist, it is difficult to raise the yarn, but beautiful, uniform and neat pile can be obtained. When the twist of the weft yarn is too strong, not only is it difficult to raise the yarn, but the suede effect is also unsatisfactory.
It can be seen from the above conclusion. If yarns of the same count from different manufacturers or twists are woven into the same weave specifications, uneven pile will inevitably occur. Even if we work hard on raising methods, it is almost impossible to change the current situation. If the blended yarn is unevenly blended, fluffing defects will also occur.
If the yarn tension during weft winding is uneven, its moisture content will be different, and weft defects will occur during raising. This reason is caused by the different shrinkage rates of the weft yarns after weaving. After the yarn with small shrinkage is raised, small groove-shaped raising defects will occur in the warp direction. Uneven thickness of weft yarn is a fatal flaw of pile. Hard yarn is more difficult to nap than soft yarn. Uneven yarn count and twist also have a serious impact on raising. Generally, the same yarn has a small twist in the thick part and a large twist in the thin part, which causes uneven pile.
Different dyeing conditions also affect the raising effect to a greater or lesser extent. The amount of dyeing auxiliaries and softeners remaining in dyed fabrics can also cause uneven nap. Cotton staple fiber fabrics are dyed with direct dyes. Light colors are difficult to nap, while dark colors are easy to nap. Uneven raising caused by dyeing will be improved as long as proper softening treatment is performed before raising.
2. Problems caused by fabric structure specifications and weaving and their solutions
The structure and organization of the fabric have a great influence on the raising effect. Uneven fabrics are not easy to detect at first and are mostly exposed after dyeing or raising. The key is that the tension of the warp and weft yarns should be uniform. The most difficult problem to solve is that the edges of the fabric are sometimes tight and sometimes loose. At this time, the fabric needs to be finished again. Uneven pile occurs due to uneven weft tension, which is related to weft rolling and weaving. If the weft yarn tension in a certain part of a fabric is small, the result is that this part will have groove-shaped pile in the warp direction. Uneven weft density will not only cause uneven pile, but also the parts with low density will be strongly piled, and the strength will be significantly reduced. Generally, when fabrics with many weft floating points are raised, a short dense raising method that reduces the raising force and increases the number of raisings is often used to improve the raising effect.
3. Defects caused by fabric preparation methods
(1) Improper moisture content
For light raising or raising that requires a reduced amount of raising, the expected effect cannot be achieved if the moisture content is inappropriate. Uneven moisture content will cause uneven fluff. Cotton fabrics are always dry-naped, but fabrics that are over-dry will experience increased pile loss. If the moisture content is too high, creases will easily occur in the warp direction of the pile, making it difficult to pull out the pile.
(2) Unreasonable pre-processing of fluffing
The fabric before fleece must not have warp wrinkles.If warp wrinkles appear, they need to be soaked in water and then dried before they can be raised.
(3) Improper seam head
The seam head needs to be straight and firm. If the seam head appears corrugated or the front and rear fabric connections are skewed, a large section of fabric at both ends of the seam head will be unevenly raised. When the seam head is not strong, the seam head is easily scratched during the raising process, causing the fabric to get entangled in the card clothing roller, which not only damages the card clothing but is also dangerous.
4. Problems caused by raising machines and raising methods
(1) Problems caused by the centrifugal force of the drum
The speed of the raising machine is high. Due to the centrifugal force generated by the high-speed operation, the middle part of the drum is convex, which makes the central part of the fabric strongly raised.
(2) Problems caused by improper raising methods
If two narrow-width fabrics are raised for a long time and then wide-width fabrics are raised, the central part of the fabric will appear to be strongly raised, resulting in striped uneven raising. Therefore, when raising narrow-width fabrics, the contact position between the fabric and the card clothing must be frequently moved.
If the normally open medium-width fabric is piled with wide-width fabric, the pile will be weak on both sides of the wide-width fabric. The middle part has strong fluff. Because the tension on both sides of the fabric is large, the tension in the middle part of the fabric is slightly smaller, causing the middle part of the fabric to be hairier than both sides. Therefore, it is necessary to move more when opening medium-width fabrics to prepare for wide-width fabrics.
If the winding tension of the card clothing is too high, the card clothing will lose its elasticity, scratch the weft yarn, excessive pile reduction, uneven pile and other problems. When some fabrics first start to pile, the fabric tension between the running card rollers is out of balance, which affects the pile operation. The relationship between the fabric tension and the speed between the carding and brushing rollers is very critical. Once the balance is obviously lost, the weft tension increases, causing the weft to scratch or cut the warp. The tension of the fabric is small, and the needle is inserted deeply into the fabric, which is prone to long lint and even uneven weft pile. If the fabric tension is too high, the belt of the card roller will slip, which will not improve the raising efficiency and easily cause the edges of the fabric to be damaged.
Postscript
In short, it is necessary to choose fibers, yarns, etc. that are evenly processed, have small twists and strong strength, so that the expected raising effect can be achieved after being woven into fabrics. Increasing the cloth speed may not necessarily improve the pile efficiency, and speeding up the drum speed may not necessarily improve the pile effect. If the speed is raised too high, the contact time between the needle and the fabric will be shortened, and the brushing effect will be reduced.
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