This article is developed from four aspects: the basics of fabric shrinkage (definition, principle, common…
In the spinning process, yarn hairiness is an inevitable phenomenon, so what is yarn hairiness? What effect does it have on the spinning system? How does yarn hairiness occur and how can it be controlled? And how to calculate the yarn hairiness? Today, the TESTEX blog will answer these questions.
Table of Contents
What is yarn hairiness?
As the fibers located on the surface of the yarn are not closely enough connected with the yarn itself, the fibers on the surface of the yarn will stick out as hairiness when the yarn is subjected to friction and other external forces during spinning.
Hairiness is generated by twisting and friction during the spinning process, mainly referring to the twisting triangle and component friction. Its morphology is different and the pattern of appearance is also different. Depending on the morphology, yarn hairiness is divided into three types: end hairiness, loop hairiness and floating hairiness.
1 End hairiness: One end of the fiber sticks out of the surface of the yarn body, while the rest is caught in the yarn body. This kind of hairiness has a larger proportion below 4mm in length and is mainly caused by short piles, especially harmful 3mm hairiness mostly belongs to end hairiness.
2 Loop hairiness: Both ends of the fiber are rolled into the yarn body at the same time, and the middle part sticks out of the yarn surface. Loop hairiness often forms 8mm~9mm hairiness after friction, especially after winding, the increase of 9mm hairiness value is extremely closely related to the number of loop hairiness.
3 Floating hairiness: Loose hairiness attached to the surface of the yarn body. This type of hairiness is mostly caused by the impurity fibers in the yarn, which will cause flying during the subsequent processing by strong friction.
Hairiness is one of the basic structural characteristics of the yarn. It determines the appearance of yarn together with yarn evenness, yarn irregularity, yarn impurities, etc. Yarn hairiness has positive effects, such as wind protection, warmth, softness and water absorption. However, in most cases, yarn hairiness not only affects the breathability, pilling and abrasion, clear appearance and pattern and evenness of the fabric, but also affects the effective utilization and strength of the fibers in the yarn.
What does yarn hairiness affect?
First of all, we need to understand that hairiness is the basic structure of the yarn, which is inevitable. Reasonable hairiness is acceptable, but what brings problems are those poor yarn hairiness, and poor hairiness mainly has the following phenomena.
1 The overall value of hairiness is high, and the fabric surface is not clear, which seriously affects the dyeing effect.
2 High CV value of hairiness, the fabric surface is not flat and causes dyeing difference.
3 A few dense yarn hairiness, resulting in the formation of cotton balls and knots in the weaving channel affects the head breakage and fabric quality.
Poor yarn hairiness will affect the subsequent process, such as leading to unclear warp opening during the weaving process, increasing head breakage and reducing productivity. In addition, poor yarn hairiness will also have a negative impact on the appearance, feel and use of the finished product, such as uneven distribution of hairiness will make the fabric appear horizontal file, stripes and other defects. In particular, hairiness of more than 3mm will make the yarn tangled in the weaving to form defects, seriously affecting the subsequent production.
The effect of yarn hairiness is mainly reflected in several aspects.
Warping: During the rewinding process of the cylinder yarn, there will be head breakage caused by too long sticky hairiness.
Sizing: dry state warp sheet splitting in sizing will cause the fabric surface weaving defects, the fabric surface effect is blurred.
Weaving: Hairiness entanglement leads to unclear loom opening causing warp and weft breakage.
Other: affect the fabric breathability, pilling and abrasion, etc., resulting in dyeing horizontal stripes.
Causes of formation and control methods of yarn hairiness
Due to the irregularity of yarn hairiness form, it is randomly distributed on the surface of the yarn. Therefore, how to analyze and evaluate the condition of yarn hairiness, establish and strengthen the quality management of yarn hairiness is the key to preventing the poor hairiness phenomenon. The following is a brief analysis of the factors affecting yarn hairiness.
1 The influence of fiber characteristics on yarn hairiness
During the spinning process, the length, fineness, staple rate, and impurities carried by the fibers will have a direct impact on the production of yarn hairiness.
Long fiber, good uniformity, good adhesion between fibers, small chance of hair formation. When the fiber is short, the fiber in the spinning process can not be normal wrapping, so that one end of the fiber is exposed on the surface of the yarn body, thus forming yarn hairiness.
The higher the staple rate of the fiber, the more floating fibers in the drafting process, the greater the chances of forming hairiness. The impurities carried by the fiber itself in the spinning process is easy to produce defects, affecting the normal operation and straightening parallel of the strip, so that increase the fiber exposed to the body of the opportunity and produce hairiness.
Control method: The quality of fibers should be strictly controlled during the production process, and slender fibers should be selected as much as possible to improve the consistency and stability of fiber materials.
2 The effect of the pre-spinning process on yarn hairiness
Carding: Generally speaking, the carded yarn has 30%~40% more hairiness than combed yarn. Through the combing process, a large number of short fibers in the whiskers are excluded and the fiber straightening parallelism is improved, so the yarn hairiness will be reduced.
The combing preparation process should pay attention to reducing the phenomenon of sticky roll, combing appropriate to increase the cotton drop, keep the top comb, tin and brush in good working condition, the entire cotton channel should be clean and free of sarcasm.
Drawing: Pay attention to the drafting distribution, to promote the straightening of the fiber, so as to reduce the formation of hairiness, the pressure bar should be checked regularly to ensure good condition.
Roving: The yarn hairiness will decrease as the twist of the roving increases. The more hairiness of the roving, then the more hairiness of the spun yarn will increase. It is important to keep the yarn polished in all places where sliver passes.
3 The effect of spun yarn process on yarn hairiness
Spun yarn is the key process of spinning, the quality of the spinning frame has a greater impact on yarn hairiness, mainly as follows.
3.1 The ring rail, bad roundness, flatness, or ripples, burrs, unevenness and unpolished, uneven ring rail or walking deformation, up and down movement is not vertical, will cause the fluctuation of spinning tension and friction effect increase, resulting in increased yarn hairiness.
3.2 A poor fit between the ring rail and the balloon control ring can cause a significant increase in yarn hairiness.
3.3 The guide eye grooves, friction on the yarn, will increase hairiness.
3.4 The speed of the spindle is also an important factor affecting hairiness, the faster the speed, the more hairiness in the finished yarn.
3.5 In the twisting part of the spinning frame, the process conditions and equipment are not in good condition, the yarn is scratched, which will damage the yarn structure and increase the hairiness. During the twisting process, the flying and short pile are attached to the yarn body and partially twisted in the yarn, which will also form hairiness.
3.6 The draft of the ring frame has a particularly strong influence on hairiness, which increases with a higher draft. In addition, the hairiness decreases as the twist factor of the yarn increases.
3 The effect of the winding process on yarn hairiness
The winding process has a great impact on hairiness and is a key factor in the growth of hairiness, mainly in the following ways.
4.1 When all components in the winding channel are burrs, grooves, broken and the surface at the contact yarn is not smooth, the cotton yarn will be subjected to greater friction during the movement and static electricity will be generated, leading to an increase in cotton yarn hairiness.
4.2 When the pagoda tube, tube and groove tube are not well matched, the yarn will jump and slip during the movement, all of which will lead to the local aggravated friction of the yarn and the cotton yarn hairiness will increase significantly.
4.3 The higher the speed, the greater the friction between the yarn and the groove tube, the more the yarn is damaged and the number of hairiness increases. With high winding tension, the friction between the yarn and the components of the winding channel increases, and the cotton yarn hairiness becomes longer and increases. The amount of cylinder yarn winding also has a certain influence on the cotton yarn hairiness. If the winding is too large, the weight of the cylinder is large, the friction between the cylinder and the grooved cylinder is large, the yarn is damaged, and the cotton yarn hairiness will increase.
5 Temperature, humidity and other effects
Theoretically, humidity is one of the main reasons affecting the change of hairiness, but in actual production, it is difficult to quantify its effect on hairiness due to the instability of various condition changes, and the trend of its effect on hairiness can be seen only from long-term monitoring.
If the humidity is high, the fiber volume expands, the air permeability is poor, the single fiber strength increases, the yarn tolerates higher strength under the same conditions, the friction resistance increases, and the hairiness has a tendency to decrease. Therefore, it is beneficial to increase the humidity of the environment in the process of spinning and falling barrels to reduce hairiness, which increases sharply when the relative humidity in the spinning workshop is below 50%.
In addition, the yarn itself will also produce hairiness by rubbing against each other, and the tube yarn falling from the ring frame or the wound cylinder yarn will also produce hairiness by rubbing against each other during rewinding, transportation and storage. Therefore, during the production process, care should be taken to minimize the chance of hairiness by taking the yarn lightly.
How to calculate the yarn hairiness?
In the spinning process, the fibers undergo mechanical action such as carding and drafting to produce pre-tension, so once the fibers are stretched out into hairiness, they are bound to be in a complex spatial state. At the same time, the shape of hairiness is unstable and changeable, and will change with the changing conditions, thus bringing many difficulties to the accurate determination of hairiness.
The characteristic indexes of yarn hairiness: total number of hairiness N, the total length of hairiness L, the average length of hairiness , hairiness index η, etc.
The total number of hairiness N is the total number of hairiness present in the unit length of the yarn (number/m) and the total length of hairiness is the total length in the unit length of the yarn (mm/m), then: L = N *
Set length l. The hairiness index η is the number of hairiness in a unit length of yarn that extends beyond the set length, i.e.
The figure below shows the measured regression curve of 14.5tex single yarn hairiness index h and hairiness length l. Obviously, h conforms to the exponential curve, the larger η is, the worse the appearance quality is, and the longer length is, the more harmful it is to the weaving.
There are many methods to measure yarn hairiness, such as the weighing method, projection counting method, photoelectric test method and electrostatic method, etc. However, the most commonly used laboratory test is the photoelectric test method, and the more practical one is the burnt hairiness weighing method.
The photoelectric test method uses an optical microscope system to automatically detect the number of hairiness per unit length of yarn. The working principle is to measure the set length of hairiness according to the light projection and count them, and calculate the characteristic index of hairiness according to the above formula. The burnt hair weighing method uses burnt hair to remove yarn hairiness and assesses the amount of yarn hairiness by how much the weight difference is compared to the original yarn.
With the increasing application of computer technology in the field of textile expertise, the use of computer image analysis and processing technology for yarn hairiness testing has become the direction of development.