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      You are here:Home>News>Technical journal

      MEBON Instrument technical journal-second issue

      分類:Technical journal  發布日期:2017-03-10 05:02:49  瀏覽次數:1636  [返回]
      Study on air permeability of fabric - second issue
      Release time: 2017-03-10
      Subject: Discussion on the air permeability of fabric
      1. The significance of air permeability test of fabric
       In addition to ornamental beauty, the main purpose of the body wearing clothing is to maintain the balance of energy exchange between the body and the surrounding environment. When the surrounding environment changes, the energy balance can be adjusted by adding or reducing clothing, which can keep the environment temperature of the human skin relatively stable. 
       In order to study the important adjustment of fabric in the body clothing environment system, it is necessary to measure the permeability of the fabric. The so-called permeability refers to the heat, wet (liquid phase gas phase), air (air) and so on through the difficulty of the fabric, this performance varies with the purpose of use. The body is an organism that constantly metabolisms to maintain a constant surface temperature of the skin. At this point, the surface of the skin is constantly emitting heat and moisture to the environment. The moisture content includes two aspects. One is the moist gas (gas phase) evaporated into the environment under the condition of human body's static condition, and the other one is to emit wet gas (liquid phase) through the environment without human sweat under the condition of human movement. Therefore, it is necessary to determine the warmth, water permeability, hygroscopicity and air permeability of the fabric, which are in turn to reflect the comfort performance of the clothing in the clothes. 
       With the improvement of people's living standard, the comfort and performance requirements of fabrics are increasing. Therefore, permeability is becoming more and more important as an important part of fabric comfort performance, and its performance detection and evaluation methods are more important.
      2. Factors affecting the permeability of fabric
       There are many factors that influence the permeability of fabrics. There are many details, such as fiber cross-section shape, yarn fineness and volume weight, fabric material, structure, surface characteristics, processing methods and dyeing and finishing process conditions, etc., as shown in Table 1.
       Influence factors of permeability of Table 1 fabric

      3. Research status of air permeability of fabric at home and abroad
       The air permeability of the fabric refers to the volume of air that passes through the unit area of the fabric in a unit time under a certain pressure difference (its unit is m2s). The general clothing material has the certain air permeability, because the human body is breathing at all times, and the clothing material permeability just provides the channel for the human body skin and the outside to carry on the gas exchange. At the same time, the air permeability of the fabric is also beneficial to the heat of the body to diverge, thus keeping the body comfortable.
       Another important factor affecting the comfort of the fabric is the permeability of the fabric. Sports clothes, winter clothes on the windproof fabric permeability have higher requirements. Some industrial textiles, such as airplane parachute and filter cloth, have special requirements for the permeability of fabric. Fabric permeability is determined by the number and size of warp and weft yarns and fiber gaps, and also related to factors such as warp and weft density, yarn number of warp and weft, yarn twist and so on. In addition, it is also related to the properties of fiber, yarn structure, fabric thickness and volume weight. The air permeability of fabric in clothing is also influenced by external atmospheric factors. Generally, air temperature increases, air permeability decreases, and wind speed increases, which increases air permeability.
       The study of fabric permeability began in nineteenth Century for the application of sanitary fabrics. By studying the results of permeability in porous media, Darcy established a linear relationship between air pressure and air permeability based on pressure drop. The first Rubner to study fabric permeability is based on the rule of Darcy. The following research is carried out by Rekk, Florinskii, Fochheimer, Khanzhonkov and Zelenko to explore the passing rate of airflow through porous materials. This study shows that permeability determined by pressure difference no longer presents linear change with the increase of filtration rate. Applied to textile materials, this phenomenon is reflected in the study of Rakhmatullin and the equation he proposed. Arkhangel did a lot of systematic research on the permeability of textile materials. A commonly used characteristic value air permeability coefficient was introduced, and textile classification was put forward according to their different air permeability. The effects of different fabric features on their permeability have been studied by Clayton, Keswell, Hearle and others.
      4. Test standards and methods for air permeability of commonly used fabrics at home and abroad
      (1). Introduction of air permeability test standard
       The air permeability of textiles is one of the most important factors affecting fabric performance. There is a great relationship between the comfortability of the fabric and the comfortability of the fabric. Some industrial textiles, such as aircraft parachutes, filter cloth and airbag fabrics, must also comply with certain air permeability requirements to better play its role.
       At present, the permeability detection methods abroad are: ISO 9237-1995 (mainly used in textile fabrics, industrial fabrics, nonwoven cloth); ISO 7229-1997 (mainly used in rubber or plastics coated fabrics); ASTM D737-2004 (2012) (mainly used in textile fabric; BS (5636-1978) is mainly used in textile fabric; JIS (L1096-1999) is mainly applied to textiles). Among them, the two standard methods of ISO 9237 and ASTM D737 are most widely used.
      我們國內對織物透氣性的測定方法,應用較為廣泛的標準是GB/T 5453-1997(等效采用ISO 9237-1995),該標準適用于多種紡織織物,包括產業用織物、非織物布和其它可透氣的紡織產品。在測試時通過不同的壓降對服用織物與產業用織物進行了細微區分,服用織物壓降選擇100Pa,產業用織物壓降為200Pa。GB/T 5453-1985《織物透氣生試驗方法》中以透氣量(是指織物兩面在規定的壓力差下,單位時間內流過織物單位面積的空氣體積)衡量織物透氣性的指標,修訂標準GB/T 5453-1997采用透氣率(是指在規定的試樣面積、壓降和時間條件下,氣流垂直通過試樣的速率)表示織物的透氣性能。 
        而ASTM D737與上述兩項標準在適用范圍、溫濕度、測試面積、壓力差等方面有所差異??紤]到進出口紡織品貿易的實際情況,擬選用不同的樣品對ISO 9237和ASTM D737的具體溫濕度、測試面積、壓力差,等條件進行對比探討,選擇出最具適用性和代表性的條件,建立適合進出口貿易的行業標準。 
      2. 透氣性測試標準比較 
        目前,常用的透氣性測試標準主要有ASTM D737-2012《紡織品透氣性測試方法》,ISO 9237-1995《紡織品織物透氣性的測定》,GB/T 5453-1997《紡織品織物透氣性的測定》和JIS L1096-1999《紡織品透氣性測試方法》。其中,GB/T 5453-1997等效于ISO 9237-1995。JIS L1096-1999分為A法和B法,A法采用弗雷澤型(Frazir)透氣度測試儀,壓差為125Pa,測量5次求平均值;B值采用格利型(Gurley)透氣度測試儀,測量在特定壓差下,300ml空氣透過織物所用的時間,透氣率用時間來表達,單位為秒,此法適用于毛織物。由于JIS L1096要求采用特定的儀器,因而在日常檢測中并不常用在下文的條件探討中,不考慮該標準。 
        對于進出口貿易來說,抽樣的代表性至關重要,因此系統內部也對紡織品和服裝的抽樣均制定了行業標準,為了更好的適應進出口紡織品的具體情況,抽樣的原則引用SN/T 3702《進出口紡織品質量符合性評價抽樣方法》,該標準包括7個部分分別為: 
        可以滿足各種需求,比ASTM D737-2012和ISO 9237-1995的規定更為具體和全面。 
        在取樣方面,ISO 9237-1995的規定較為籠統,僅表示測試部位隨機選取。ASTM D737-2012的規定具體但是特別規定了樣品的裁剪。從透氣性測試本身的需要和客戶成本需求,進行無損檢測更為合適,沒有必要對樣品進行裁剪。 
        織物透氣性測試儀器國際上主要有FF-12(匈牙利),VPTM-2(俄羅斯),Shirley透氣儀(英國),其中VPTM-2適用于研究氣體透過織物的流動特征。VPTM-2和Shirley透氣儀測得結果的一致性已經確定。在這些儀器中,透氣性結果測量的比率范圍0.83≤BVPTM/BShirley≤1.07,BVPTM/BShirley的平均值約等于0.96。從FF-12和Shirley透氣儀測得的結果比率范圍0.93≤BFF/BShirley≤1.61,BFF/BShirley的平均值約等于1.32。數據的相關系數值是:RFF and Shirley=0.98,RVPTM and Shirley=0.99。 
        國內透氣儀主要有Y561、YG461A、KESF-AP1、YG(B)401D-Ⅱ、FX 3300型。YG461系列主要用于測試一般的機織物,針織物,特種工業用織物及非織造織物的透氣性,可也用于測試造紙行業中空氣濾芯紙,工業濾紙,復膜材料等非紡織物,及其它片狀材料的透氣性。其測試原理是:使用織物透氣儀測定織物在一定壓力差條件下,單位時間內通過織物的空氣量,從而求得織物的透氣性能。一般透氣儀測定織物在一定壓力差條件下,單位時間內通過織物的空氣量,從而求得織物的透氣性能。一般透氣量越大,織物的透氣性越好;在透氣量相等的情況下,織物兩端的壓力差越大,織物的透氣性越差。 

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