How to assess the tension of fabrics -- a popular science about textile tensile testing…
Diverse fabrics vary from each other in appearance due to the difference in numerous performances, such as texture, the arrangement of dyed yarns, the raw material of yarn, yarn count, yarn density, twist direction, yarn twist, yarn structure as well as the post-treatment methods and so on. Fabric analysis comes to the stage for the need of testing them.
It is essential to learn about the texture structure of fabrics, the technological environment of operation, and so on for the production, innovation, and counterfeiting of products. As a result, we need to analyze fabrics thoroughly and carefully so as to obtain a convincing outcome and provide pertinent information for the design, transformation, and counterfeiting of fabrics.
In order to analyze results in an accurate way, the items to be analyzed and their sequence should be planned before the analysis. Besides, during the operation process, we should be meticulous about every procedure, use less cloth sample material as much as possible and satisfy the condition needed by the analysis test at the same time.
Table of Contents
The fabric analysis is generally performed in the following order.
There are some provisions about the sampling methods for the fabric analysis because the accuracy of information is associated with the location of sampling and the area size of samples. Additionally, we should select samples based on a concrete situation in the actual operation due to the considerable types of fabrics and the huge difference between them.
Subject to the warp and weft yarn tension equilibration, the fabric removed from the machine will acquire a new width and length with a slight alteration that causes a difference in fabric density on its two sides, the marginal and the central area. In addition, there is little difference in changes that occur in the two sides, the marginal and the central area of fabrics in the dyeing and finishing process. Considering this situation and eagerness for more precise and representative data, some regulations are proposed as follows: when sampling from textiles, the distance between sample and selvage should be a minimum of 5cm. Besides, for the cotton fabrics, the distance between its two sides should not be less than 1.5m and more than 3m. For the wool fabrics, the distance between its two sides should be at least 3m. As for the silk fabrics, the distance between its two sides should be kept in a range of about 3.5 to 5m. Furthermore, the sample is required to maintain its natural form without any significant blemishes with the purpose of ensuring the accuracy of the analysis results.
Sample area size should vary with the types of fabrics and structures. As the test to analyze fabrics is deemed to be consuming, we should spare no effort to reduce the sample size on the premise of ensuring the correct analysis information, upholding the principle of saving cost. Generally, the area size of samples of the simple-structure fabric should be 15cm * 15cm, which can also be smaller while the area size of samples of dye yarn fabrics with large repeats needs to be 20cm * 20cm. The area size of samples of dye yarn fabrics, such as bed sheets, should be the same as the area occupied by one repeat at least.
For large jacquards, such as quilt and carpet, the testers are required to analyze part of the representative structure due to its large repeats of the warp and weft direction. Therefore, the area size of samples is generally 20cm *20cm or 25cm *25cm. If the sample with small dimension, we need a part of it slightly over 5cm*5cm.
2 The determination of the front and back sides of fabrics
Secondly, we should determine the front and back sides of fabrics in the fabric analysis. The front and back sides of the fabric are generally judged from their appearance effect. Here are some common methods for testing them.
(1) Towel fabric: the side with a large density of terry is the front of the fabric.
(2) Gauze fabric: the side with a distinct pattern and prominent twisted warp is the front side of the fabric.
(3) For convex and convex fabrics, the surface of its front side is close and delicate with stripes or convex patterns, while the backside is relatively rougher with a long floating line.
(4) Pile fabrics: for single-sided pile fabric, its pile side is taken as the front side of the fabric. For double-sided pile fabric, the side with a clean and neat cloth edge is regarded as the front side.
(5) Observe the edge of the fabric: the surface of the edge area of fabric that is clean and neat is the front side of the fabric.
(6) For double, multi-layer, and multiple fabrics, the front side of fabrics is characterized by relatively large density or made of materials of high quality when there is a difference between the warp and weft density of the front side and back side of fabrics.
(7) The front pattern of the fabric about a plant with a lattice outlook and color-matching mold pattern is bound to be discernible and aesthetically pleasant.
(8) Generally speaking, the front side of fabrics has a clearer and more beautiful pattern, color, and luster than the back side does.
For the majority of fabrics, there are obvious differences between the front and back sides. However, there are several fabrics with extremely similar front and back sides. Therefore, it is not a must to distinguish its front and back side for such kind of fabric.
3 The measurement of the warp and weft direction of fabrics
After determining the front and back of the fabric, the next step of the fabric analysis is to figure out the warp and weft yarn direction. Only when we successfully do that, can we test the fabric density, the warp, weft yarn count as well as fabric structure, and so on. If the fabric meets the following requirements, its wrap and weft yarn can be recognized and identified. If the sample of the analyzed fabric is taken from its selvage, the yarn parallel to the selvage is the warp yarn while the yarn perpendicular to the edge of the cloth is the weft yarn.
(1) The warp yarn contains the pulp white weft yarn is the one without the pulp.
(2) The warp yarn fabric is generally characterized by its large density while weft yarn is by its small density.
(3) For the fabric with a prominent reed mark, its warp direction is the direction where the reed mark lies.
(4）If the fabric is made of strands and single yarns, its warp yarns are the strands and its weft yarns are the single yarns in general.
(5）If there is a difference in the yarn twist direction of fabrics woven with single yarns, Z-twist yarn is the warp direction while S twist yarn is the weft direction.
(6）If there is a difference in the yarn twist of fabrics, the warp yarns are the ones with large yarn twists while the weft yarns are the ones with small yarn twists.
(7）If there is almost no difference in the warp and weft yarn counts and the yarn twist, the warp yarns are those with evenly strips and relatively good luster.
(8）For towel fabric, its yarn with terry is warp yarn, and the yarn without terry is weft yarn.
(9) The direction of the strip woven in the strip fabric is usually a warp direction.
(10) If the fabric has a system of yarn with a variety of counts, this direction can be considered to be the warp direction.
(11) For saree fabrics, twisted yarn is the warp yarn while the non-twisted yarn is the weft yarn.
(12) For fabrics interwoven with general cotton wool and cotton linen, cotton is the warp yarn. For fabrics interwoven with wool and silk, silk is the warp yarn. For fabrics interwoven with wool, silk, and cotton, the silk and cotton are warp yarns. For fabrics interwoven with natural silk and spun silk, natural silk is the warp yarn. For fabrics interwoven with natural silk and man-made silk, the natural silk is the warp yarn.
Because fabrics can be widely used in many areas, the requirements of raw materials and structures of fabrics are also varying. In all, we must find out the warp and weft direction according to the actual situation.
4 The assessment of warp and weft yarn density in the fabric analysis
The number of warp and weft yarns arranged in the unit length of the fabric is called the warp and weft density of the fabric which is needed to be tested in the fabric analysis. The calculation unit of fabric density applying the metric system refers to the number of warp and weft yarn arranged within 10cm. The density not only directly affects the appearance, touch feeling, thickness, strength, folding resistance, breathability, abrasion resistance as well as warmth performance, and other physical and mechanical indicators of the fabric, but also the cost of the product and the production efficiency.
There are two ways to determine the warp and weft density.
(1) indirect test method
This method is applicable to fabrics with large density, small yarn count, and regular texture. First of all, we must analyze the fabric texture to find out the following equation. The amount of repeat warp or weft yarn*the number of repeats in the structure with a length of 10cm=the warp or weft yarn density
(2) direct test method
Following the direct measurement method, the test about density is completed by virtue of the cloth lens or analysis mirror of fabric density. The analysis mirror of fabric density is characterized by the scale length of 5cm. There is a red line engraved in a piece of a long strip of glass under the lens of the analysis mirror. When analyzing the density of fabrics, we need to move the lens and align the red line on the glass and the scale at the same time between two yarns. Then take it as a starting point and count the number of yarn roots while keeping moving the lens until the scale reaches 5cm. Finally, the number of yarn roots is multiplied by 2, which is the density value of fabric with a length of 10cm.
We need to count yarn roots from the middle area between the two yarns. If the number of final yarn roots exceeds 0.5 but less than 1, it should be recorded as 0.75. If the number of final yarn roots is less than 0.5, it should be recorded as 0.25. For obtaining the fabric density, generally, we should measure 3 or 4 data, and then take its arithmetic mean as the measurement results.
5 The testing of warp and weft yarn shrinkage rate in the fabric analysis
In the fabric analysis, warp and weft yarn shrinkage rate is regarded as one of the parameters to evaluate the fabric structure. By determining the warp and weft yarn shrinkage rate, we can calculate the yarn count and the amount of yarn used in the fabric. Since the yarn will be interwoven and flexed in the weaving process of textiles, the length of yarns used at the beginning of weaving the textiles will be larger than that in the finished textiles. Therefore, the ratio of the difference value with the original length of fabrics is called shrinkage rate, shown as ａ（％）in the application.
shrinkage rate =100%* (length of elongated specimen – length of the specimen)/ length of the elongated specimen
The warp and weft yarn shrinkage rate is an important reference for the process design, putting a great influence on the amount of yarn, the physical and mechanical properties, and the appearance of the fabric.
There are numerous factors affecting the shrinkage rate, including fabric texture, raw materials, count of warp and weft yarns, warp and weft yarn density as well as the tension of yarns in the weaving process, and so on.
When analyzing the fabric, we need to take a sample with a length of 10cm from the edge of the fabric along the warp or weft direction the determination of the shrinkage rate. If the fabric area is very small, we can take a sample with a length of 5cm. Then put a marker on it and cut short the yarn coma on the side of the fabric so as to reduce the elongation of fabrics that occur at the time when they are pulled out from textiles. Next, gently pull out the warp or weft yarn from the textile with fingers pressed on the end of the yarn and softly straighten the yarn with another hand. Keep in mind that the tension should maintain in an appropriate range to avoid the expansion of the textile. Finally, we measure the length of the warp and weft yarn between the markers ten times and take the average value of the ten consecutive numbers. The average value needs to be substituted into the formula to get the shrinkage rate of warp and weft yarn. This method is easy to use but with less accuracy. Determining the shrinkage rate contributes to measuring the yarn count and the amount of yarn used in the fabric.
The following points should be noted in the determination of the shrinkage rate.
（1）When pulling out and straightening the yarn, we should ensure that the yarn is not twisted or untwisted. For some yarns with a small twist or very poor strength, some measures should be taken to prevent accidental elongation.
（2）When analyzing scraping and shrinking fabrics, we should remove the surface lint with scissors or matches before carefully pulling the yarn out of the fabric.
（3）Since the viscose fiber is more prone to expand in the wet environment, we should prevent the yarn from wetting by sweat when carrying out the test.
6 The measurement of warp and weft yarn count in the fabric analysis
Count refers to the fineness of yarns which is also an important indicator. The yarn count is equal to the weight in grams of yarn with a length of 1000m at conventional moisture regain. The formula is as the following: tex=1000G/L
Tex refers to the warp or weft yarn count; G represents the weight (g) at conventional moisture regain; L represents the length (m).
There are two methods commonly used to determine the yarn count.
Comparative determination method: put the yarn under a magnifier and compare it with yarns of known counts carefully and then determine warp and weft yarn count. The accuracy of this method mainly relates to the experience of the tester. Factory testers usually tend to apply such a method as it is easy to work, spending less time on the operation.
Weighing method: before testing, we must check whether the warp yarns of the sample have been in size. If so, we should perform the desizing of the yarns. When testing, take out 10 warp and weft yarns from the fabric with an area of 10cm*10cm. If the actual moisture regains in fabrics and the warp and weft shrinkage has been measured, warp and weft yarn count can be calculated according to the following formula.
G means the actual weight of 10 warp or weft yarns; a represents warp or weft yarn shrinkage rate; W refers to the actual moisture regain of the fabric; W~ points to the conventional moisture regain of the yarn.
The followings are the conventional moisture regain for a variety of yarns (measured by the unit of %).
|Combed wool yarn||16|
|Coarse combed wool yarn||15|
7 The determination of raw materials of the warp and weft yarn
In the fabric analysis, it is of great importance to choose the raw materials used to manufacture various fabrics in a correct and reasonable way, which can satisfy the various demands. Therefore, we need to analyze the raw materials of the warp and weft yarn from the following aspects.
Quantitative analysis of the composition of blended textiles
It is used to measure the content of the fabric, generally adopting the dissolution method which applies an appropriate solvent to dissolute the fibers in blended textiles. And finally, we can measure the mixing proportion on the basis of the weight of remaining fibers and the weight of dissolved fibers. The specific method is the same as the analysis method for the blended yarn content.
Qualitative analysis of raw materials of the warp and weft yarn
It is used to analyze the type of raw materials of which the fabric yarn is composed, pure fabrics, mixed fabrics, or interwoven fabrics. Generally speaking, we need to take the following steps when identifying the fiber. Firstly, we should figure out the fiber category to check whether it belongs to natural cellulose fibers, natural protein fibers, or chemical fibers. Next, we should determine the fiber species. To measure them, we commonly use some identification methods, such as the handle and visual measurement method, combustion method, microscopy method as well as chemical dissolution method, and so on.
8 The measurement of fabric weight in the fabric analysis
Fabric weight refers to the pulp-free gram of the fabric per square meter, which is an important technical indicator of the fabric and is also used to measure the economic calculation of the fabric. There are two test methods that are based on the size and other concrete information about the fabric sample.
It is necessary to use the torque balance, analytical balance, and other tools according to this method for the fabric weight. For the determination of the weight per square meter, we need to take the sample with an area of 10×10 (CITi2) from the fabric. The larger the area, the more correct the result is. Before weighing, the desizing fabric will be dried in the oven until its weight keeps constant and then weigh its weight by the following forum. G (g / m2) = gxl0000 / (L x b)
G means the pulp-free dry weight of the sample per square meter(g / m2). S means pulp-free dry weight (g) of the sample. L refers to sample length (cm) while b refers to sample width (cm).
In the case of a small sample area and an inaccurate weighing method, you can calculate the weight of fabrics on the basis of the warp and weft yarn count, warp and weft yarn density, and warp and weft yarn shrinkage rate. The formula is as follows.
In conclusion, the above information can help you to learn how to start manufacturing a fabric.
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