Air Permeability Tester

Research and Testing on Air Permeability Tester
The Significance of the Fabric Air permeability Test
People’s clothing, in addition to giving the decorative beauty, its main purpose is to keep the energy of the human body and the environment between the exchange equilibrium. When the environment changes, changes in the use of clothing to regulate energy balance, keeps skin ambient temperature is relatively stable.
In order to study the fabric important regulatory role for human - clothing - environment, it is necessary to measure the fabric permeability. The so-called permeability, refers to heat, moisture (vapor phase), air (air flow) and so the degree of difficulty through the fabric, with the purpose of this performance varies. The human body is an organism, constantly engaged in metabolism to maintain the skin surface temperature constant. At this time, the body surface of the skin to keep the environment dissipates heat and moisture. Humidity includes two aspects, one is static conditions in the human body, no sense of perspiration to the environment by evaporation of moisture (vapor); the other is under the conditions of human motion, distribute wet to the environment by not feeling perspiration gas (liquid). To do this, you need to determine the fabric warm, water permeability, moisture absorption, permeability, etc., in turn indirectly reflect comfort when wearing performance clothing
As clothing is required depending on the season, physical fitness, and hobbies, so different hobbies use different fabrics such as underwear moisture permeability and moisture absorption applications have warm fabrics and breathable outerwear should be used in small and an appropriate moisture-permeable fabric. As an industrial fabric, requiring good fabric permeability, and special-purpose products, such as parachutes products for higher breathability, umbrellas products require higher water permeability, in addition to Punta canvas should have a color fastness and durability, but also it should be waterproof features. The ability of air permeability called fabric permeability. It directly affects the administration and performance of the fabric. Fabrics such as summer want good permeability, and winter coat breathable fabric should be small in order to ensure a good wind performance clothing, to prevent the dissemination of a large number of heats. For some uses of fabric, breathable and more important in the sense of defense and industry, such as the permeability of the parachute should be moderate, excessive rate of decline is too large, too small, too slow decline. Therefore, taking the performance quality of the fabric and breathable fabric has a close relationship
Waterproof breathable fabric prevents liquid water penetration, while allowing water vapor pass. Such fabrics widely used, from the ordinary to the outdoor sportswear for medical and military professionals have protective clothing waterproof breathable fabric applications. In order to prevent the penetration of liquid water, such fabrics often require finishing, coating or laminate film processing, etc., but these processes may prevent the evaporation of sweat, causing the wearer discomfort and physical fatigue. Thus, breathable waterproof fabric is one of the main items of the test.
With the improvement of people's living standards, comfort performance of fabric requirements increasing gradually, therefore, as the fabric breathable comfort performance is also an important part of more and more important, their performance testing and evaluation methods are correspondingly more important.
Affecting Factors for Air permeability Test
There are many factors affecting the fabric air permeability, there is a cross-sectional shape of the fiber, yarn fineness and volume weight, tissue fabric material, structure, surface characteristics, as well as dyeing and processing methods and processing conditions, etc., see Table 1
Factors for Air permeability Test
Factors
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Result
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Fabric Materials
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Permeability decreasing order: linen> cotton> wool> Polyester> Nylon
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Fabric structure
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Permeability relationship: openwork> satin fabric> Twill> plain weave;
Weft yarn constant support, warp density or weft density increase, the permeability decreased;
Yarn twist increases, improved breathability.
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Finishing mode
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Fabrics were soft, soft, liquid ammonia, after iron, iron liquid ammonia, ammonia tide cross linking and three anti-such as finishing, its permeability sizes are: liquid ammonia treatment> Common soft and durable press finishing> finishing three anti
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Washing times
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5 times before the washing process, successively decreased permeability of the fabric; washed 5 to 100 times, permeable fabric
Gas changes less stable; which was washed 30 times or more, and permeability of the fabric slightly increasing trend.
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Baking
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After curing the fabric breathable than the rate increase before baking, because before curing padding on fabrics cross linking aid not covered between the fibers and yarns, impede air circulation.
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Domestic and Foreign Research Status on Air permeability Test
Air Permeability means that under certain pressure, time spent per unit volume of air in the fabric per unit area (in units of m2 • s). General fabric has certain permeability, because the human body all the time breathing, and breathable fabric exactly human skin gas exchange with the outside world provides the channel. Meanwhile, breathable fabric is also conducive to body heat divergence, so that the body maintains a comfortable
Another important factor affecting the comfort of the fabric is breathable fabric. Sportswear, winter clothes are windproof breathable fabrics have higher requirements. Some industrial textiles such as aircraft parachute, cloth and other fabrics for breathability with special requirements. Breathable fabric depends on the fabric between the weft yarn and fiber number and size of the gap, but also with the thread count, the number of special warp and weft yarn, yarn twist and other factors. In addition, the nature of the fiber, yarn structure, fabric thickness and volume weight and other factors. Wearing the clothing fabrics in gas permeability in the atmosphere is also affected by external factors, generally elevated temperatures, reduction in air permeability, wind speed increases, the permeability increases.
Research on Fabric Air permeability Test began in the nineteenth century applications. By results of the study permeability of porous media, Darcy establish a linear relationship based on the results of the pressure drop and permeability between the first research fabric breathable Rubner precisely to Darcy's law as the basis. Subsequent research by Rekk, Florinskii, Fochheimer and Khanzhonkov, Zelenko explored the air flow rate through the porous material, this study shows the permeability determined by the pressure difference is no longer with increasing filtration rate and exhibits a linear change. Applicable to the textile material, this phenomenon in his study and equations presented in Rakhmatullin reflected. Arkhangel study a lot of systemic for textile materials permeability, the introduction of a common characteristic value now - permeability coefficient, and propose different textiles are classified according to their permeability. They feature different fabric structure on the permeability has been studied out by the Clayton, Keswell, Hearle et al.
Theory Research on Air Permeability Test
There are gas pores and fibers interwoven between two ways slit through the fabric, generally intertwined porosity of the main way. Large pores between the yarns are penetrating pore cross-sectional shape is substantially a certain regularity, from one side to the other side of the fabric, the porosity was lean angle square, when the air through the fabric, similar to the fluid flow through porous media It flows. Pore structure of the fabric can be simplified into a parallel capillary array model, shown in Figure 1, so that the porous fabric structure may be modeled as a number of parallel capillary assemblies
Map 1 "capillary" parallel geometry model diagram
Press the hydrodynamic theory, the air through the pipe, the flow rate q laminar flow (m3 / s) available Hagen - Su Bo Ye (Hagen-Poiseuille) Law to calculate
(1)Δp is the pressure difference across the tube (Pa); L is the tube length (m); d is the diameter of the tube (m); μ is the dynamic viscosity of air (Pa • s).Calculated on the amount of Air Permeability Tester by Application (1), make two assumptions based on fabric: 1) in the yarn fibers and yarns closely evenly distributed in the fabric; 2) gaps between the yarns in the fabric cross section is rectangle.
Taking into account equation (1) there are n pores, the equation (1) becomes:
(2)There are 3 methods of estimating the Air Permeability among fabric,
——Calculation (method 1), the equation d = 0.0357 (T / ρ) 1/2 of the diameter of the yarn is determined, (1) is calculated using the linear density of the Pn average density and T, in the following equation transmittance Rs:
Rs=1-(dwa∏wa+ dwe∏we -10-2 dwa dwe∏wa∏we)
(3)Wherein, dwa warp diameter, dwa weft diameter, Πp the warp yarn between stomata perimeter, Πwe weft is between stomata perimeter.
——Precise calculation (Method 2): isolated from plants yarn diameter measured under an optical microscope, the transmittance calculated in Equation (3).
——Projection method (Method 3): Based on a scanning electron microscope micrograph of a fabric sample. Related pore diameter dh calculated famous hydraulic dynamics equation.
dh=4S/∏
(4)Wherein, S is the pore diameter,S=ab,a=100/∏wa- dwa,b=100/∏we- dwe,∏=2(a+b)
In determining the method of fabric pore size, RS and dh values obtained are significantly different and dh value, often by other methods than the value obtained is higher. This is because the structure of the fabric yarns are smooth and fluff factors not taken into account (using the method based on the yarn cross-section is circular vision), and the conventional average density value to calculate the yarn diameter, and the real value and Different
Based on Method 2 for determining RS and the dh value of the methodology is more reliable, but the measured results are also significantly different.
When the fabric breathable fabric and yarn cross-sectional size and yarn hairiness (does not affect the stoma) relevant, the method of the measured Rs 2 a small flaw is due to the different cross-sectional structures out of fabric and yarn diameter measuring yarn changing the cross-sectional switch, leaving the value has changed. Method 3 allows the fabric yarns in their plane compression and fluffing, the measurement of permeability of the true value, partially covered yarn surface pores of the individual fibers important resistance does not exist, so the Rs value obtained in this way than in the gas flow conditions fabric measured actual value is smaller
The international community that the current limitations of the Institute of breathable fabric that is mainly in three aspects: the description of a gas permeability model structure decision did not adequately take into account the structure of the material factors, its recognition in the field there is a certain limit; permeability test used the method does not guarantee that the material test conditions and their conditions of use consistent; people according to different requirements of air permeability of breathable fabric design is currently unlikely.
Basic Information of Air Permeability Tester
- Basic Principle
The so-called fabric air permeability refers to the case where a pressure differential exists on both sides of the fabric, the fabric permeable to air performance. That is under pressure on both sides of the fabric in a predetermined unit time per unit area of fabric flowing air volume, in units of L / (mm2 • s). Because the pressure is a necessary condition upon which the flow of air, measured only in both surfaces of the fabric to maintain a pressure differential in order to produce an air flow in the fabric.
The air permeability of the test is the reference pressure as a fixed amount of gas permeability test. International pressure test standards are not consistent, for example, US ANSI / ASTM, K773, FS191 / 5450 and regulations of Japan was JISL1096 127.4Pa (13mm water column); France NFG07-111 defined as 196Pa (20mm water column); the provisions of the German DIN 53387 clothing fabric is 100Pa (10mm water column), parachute fabric is 160PA (16mm water column), filtration fabrics and industrial fabrics to 200Pa (20mm water column); British BS5636 defined as 98Pa (approximately 10mm of water) and so on; our standard GB / T 5453- 1997 "Textiles - Determination of permeability" is defined as taking fabric 100Pa (about 10mm of water), industrial fabric is 200Pa (20mm water column).
- Testing Methods
There be very different from different Permeability requirements, even if the same fabric, due to the different requirements, the pressure on both sides of the fabric are often different circumstances, it should be based on the characteristics of their own fabric materials, different requirements, choose different pressure drop for testing
Common air permeability tester in the test is substantially certain pressure differential through the gas area has a fabric testing air flow, air permeability tester thus obtained. Most of the fabric may be considered to be taking relatively sparse use of stress testing requirements are relatively low at this level low pressure air out of the habit of using a vacuum pump to achieve the required pressure difference between the gas flow rate is read from the meter. Commonly used Gellowen G021 fabric air permeability tester on the use of this test method
Air Permeability Testerdiagram shown in Figure 2 as shown, two air chambers 1, 3, 5 samples placed in front of the air chamber 1. 4 when the exhaust fan is rotated, air is entering the air chamber 5 through the sample 1 and 3. 2 air through the pores due to the reduction of area, which is caused by the static pressure drop, its value can be read on the pressure gauge 7. Pressure on both sides of the fabric can be read from the pressure gauge 6. After the pressure gauge shows the number of stable, read the data, the look-up table, find the corresponding permeability values
Air Permeability Tester
Test principle fabric air permeability tester is based on different fabrics to choose the appropriate diameter, use an exhaust fan drawing air, so that both sides of the fabric to achieve the required pressure difference, resulting in a stable gas flow through the fabric, apply the principles of the throttle plate to test out gas flow, whereby the air permeability of the fabric. G021 type air permeability tester is tested under steady pressure through the fabric breathable air when the situation stabilized. Currently permeability tester upgrading, the new generation of digital permeability tester from the measurement accuracy and test pressure range have been improved, however, from the test method and principle point of view, is still quasi normal, static measurements
Key technology on Air Permeability Tester
Key technology on Air Permeability Tester is to measure the pressure and flow. G021 type air permeability tester which using an orifice meter measuring gas flow. U-tube pressure measurement
As orifice flow meter device has more than 100 years of history, many national and international standards promulgated are led to it. In the narrow pipe, it is suitable as blocking orifice plate is measured and forcing the substance being squeezed. Filled with a fluid conduit, when the throttling element within it through the pipeline, the stream will be formed at the orifice of the local contraction, the static pressure is reduced, so before and after the orifice will produce a differential pressure, the greater the fluid flow, generated the greater the pressure difference, which can be based on the size of the pressure to measure the flow. In many installations, the application orifice flow meter is very common. There is also some fabric air permeability test which used Venturi tube to measure the flow. Venturi orifice plate compared to the pressure loss is small, long life
Whether or throttling device orifice venturi throttle device, measuring methods are based on flow continuity equation (conservation of mass) and the Bernoulli equation (energy conservation law) basis for measuring steady stream of air. The following conditions must be met when using a standard flow measurement throttling device
(1) Measured media is full of all the pipe cross-section and along the inner diameter of the circular pipe flow of not less than 50mm; the Venturi tube, which should not be less than 100mm diameter should not be larger than 800mm.
(2) Stream within the pipe is stable, or may in fact considered stable (when the stream is stable, the same point on the flow rate and pressure does not change over time
(3) When measured media through the throttle device, phase change (for example: the liquid does not evaporate, superheated steam is still overheating, the gas dissolved in the liquid does not precipitate, etc.), it is also present in a single phase. For complex composition of media in order to use only similar media and the nature of a single component。
On fabric Air permeability tester, mercury manometer for measuring the gas pressure in the chamber size, until the pressure gauge shows the number of stable, read the value, each experiment can only come to a result. This pressure measuring device cannot achieve real-time measurement of the moment
Traditional Air permeability tester, both measuring gas pressure measurement is not a flow, are suitable for a given normal gas. Some fabrics in the application process (such as airbag fabric during deployment), the gas pressure is constantly changing, and large-scale change, short duration, at a given normal static testing permeability of the fabric does not reflect the performance of the fabric
In addition, the traditional method of Air permeability tester uses evacuated, on both sides of the fabric a certain pressure, pressure range is very small, when the pressure reaches or exceeds the level of the vacuum pump pressure, which approach seems powerless. Fabric Air pressure permeability test can only measure up to 3000Pa. Traditional measurement methods are difficult to reach some of the practical work of special fabric pressure.
Domestic and Foreign Testing standard & Methods for Air permeability tester
Air permeability tester Standard Introduction
Air permeability for textile is one of the important factors that affect the fabric performance. Taking, upholstery fabric and other comfort features and permeability of the fabric of a great relationship. Textiles play a role in some industries, such as aircraft parachute cloth and airbag fabric must also comply with certain requirements of permeability, in order to better
At present, the foreign Air Permeability testing methods are mainly:
ISO 9237-1995(Mainly used in the textile fabric, industrial fabrics, non-woven cloth);
ISO 7229-1997(Mainly used in rubber or plastic coated fabrics);
ASTM D737-2004(2012)(Mainly used in the textile fabric);
BS 5636-1978(Mainly used in the textile fabric);
JIS L1096-1999(Mainly used in textile)
Wherein, ISO 9237 and ASTM D737 standard method most widely used.
Our domestic method for measuring permeability of the fabric, the more extensive standard applications GB / T 5453-1997 (equivalent to ISO 9237-1995), which is applicable to a variety of textile fabrics, including technical textiles, non-woven cloth and other breathable textile products. When testing different pressure drop taking fabric and industrial fabrics subtle distinction, taking fabric selection drop 100Pa, 200Pa industrial fabric pressure drop through. GB / T 5453-1985 "breathable fabric raw test methods" to the amount of ventilation (refer to pressure on both sides of the fabric at a predetermined difference, the flow through the fabric per unit time per unit area of the volume of air) to measure the permeability of the fabric index, revised standard GB / T 5453-1997 adopted permeability (mean area of the sample under a predetermined pressure drop and time conditions, the vertical air flow rate through the sample) indicates the permeability of the fabric
The ASTM D737 with the above two criteria varied in application scope, temperature and humidity, the test area, pressure and poor terms. Taking into account the actual situation of import and export trade of textiles, intended for use in different samples to ISO 9237 and ASTM D737 specific temperature and humidity, the test area, differential pressure, and other conditions are discussed contrast, selected the most representative and applicability conditions, establish industry standards for the import and export trade
Comparison of Air permeability tester standards
At present, the commonly used Air permeability test standards are ASTM D737-2012 " Textile Air permeability test testing methods", ISO 9237-1995 "Determination of Air permeability of textile fabrics", GB / T 5453-1997 "Determination of Air permeability of textile fabrics" and JIS L1096-1999 " Air permeability textile testing methods." Wherein, GB / T 5453-1997 equivalent to ISO 9237-1995
JIS L'1096-1999 is divided into A and B Method law, A law adopted Frazier type (Frazir) Air permeability tester, a differential pressure of 125Pa, measuring 5 times averaging; B value using Gurley type (Gurley) air permeability tester measured at a specific pressure, 300ml of air through the fabric of the time used to express permeability with time, in seconds, this method is suitable for wool fabrics. Due to JIS L1096 require specific instrument, and thus are not commonly used in routine testing to explore the conditions below, it is not considered the standard
Mainly about ASTM D737-2012 and ISO 9237-1995,make comparison for two testing methods, difference of two kinds of standard refer to Table 2.
Detect differences table ASTM D737-2012和ISO 9237-1995
Testing Standard
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ISO 9237-1995
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ASTM D737-2012
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unit
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mm/s or m/s
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cm/s
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Application Scope
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For a variety of textile products, including textiles, nonwovens and other air permeability textile
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For most of textiles, including woven, non-woven fabric, inflatable bag with a cloth, carpets, fluff pile fabrics, knitted fabrics and multilayer fabric; fabric may be tested without finishing, it can be severe by sizing, coating , resin finishing or other finishing。
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Testing area/cm2
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5,20,50,100
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5,6.45,38.3,100
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Pressure difference
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50-500
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100-2500
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Common reference /Pa
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100Pa(Fabric),200Pa(Industrial fabrics),20cm2
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125Pa,38.3cm2
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Pre thermostat, the humidity test conditions
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(20±2)℃,65%±2%
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(21±1)℃
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Textiles air permeability test for non-destructive testing, ASTM D737-2012 and ISO 9237-1995 in selecting sample and getting sample were different rules, detailed in Table 3
Sampling Difference Table ASTM D737-2012和ISO 9237-1995
Standard
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Sample
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ISO 9237-1995
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ASTM D737-2012
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Standard
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Sample
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ISO 9237-1995
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Each sample from the batch in a length of at least 1m clip of the whole fabric is used as laboratory samples, it should be randomly selected at the end of cloth from 3m above the site, and which have a crease or obvious defects
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ASTM D737-2012
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As it can be seen from the table, in order to reduce the risk of trade, the test needs to extract a sufficient number of samples from sexually sample, ASTM D737-2012 and ISO 9237-1995 are on the samples taken were clearly defined, up from the batch See more stringent provisions ASTM D737-2012
For the import and export trade, a representative sample is essential, and therefore also the internal system of textile and apparel industry have developed a standard sample, in order to better adapt to the specific circumstances of the import and export of textiles, a reference to the principle of sampling SN / T 3702 "Quality conformity evaluation of textiles for import and export. Sampling method," seven parts for the standard including:
——Part 1: General rules
——Part 2: Textile Raw Materials;
——Part 3: textile yarn;
——Part 4: woven fabric;
——Part 5: Textiles;
——Part 6: Clothing;
——Part 7: Special Textiles.
Meet a variety of needs, more specific and comprehensive than ASTM D737-2012 regulations and ISO 9237-1995
In terms of the sample, the more general provisions of ISO 9237-1995, only that randomly selected test site. Specific provisions of ASTM D737-2012 are especially for the cutting of the sample. From the permeability test it needs and cost requirements of customers, non-destructive testing is more appropriate, there is no need for sample cutting.
Air Permeability Tester
There is FF-12 (Hungary), VPTM-2 (Russia), Shirley permeability tester (UK) fabric permeability testing equipment internationally, which VPTM-2 is suitable for studying the gas flow characteristics through the fabric. VPTM-2 and Shirley permeability tester measured consistency of results have been identified. In these instruments, the ratio range of permeability measurement results 0.83≤BVPTM / BShirley≤1.07, mean BVPTM / BShirley equal to about 0.96. From FF-12 and Shirley permeability tester measured results ratio range 0.93≤BFF / BShirley≤1.61, mean BFF / BShirley equal to about 1.32. Data correlation coefficient is: RFF and Shirley=0.98,RVPTM and Shirley=0.99
Domestic ventilation main instrument Y561, YG461A, KESF-AP1, YG (B) 401D-Ⅱ, FX 3300 type. YG461 series is mainly used for testing generally woven fabrics, knitted fabrics, special industrial fabrics and non-woven fabric breathability, it can also be used to test the paper industry, non-woven fabric air filter paper, industrial paper, laminating materials, and other air permeable sheet material. YG (B) 401D-Ⅱ digital breathable fabric measuring instrument is currently the use of more equipment, it is mainly used for all kinds of woven fabrics, knitted fabrics, non-wovens and industrial filter paper has an air permeability measurement requirements of the project. FX3300 type ventilation applications are more widespread, mainly applicable to closely coated fabrics, non-woven, felt very loose paper, glass fiber, air filter and so on. The test principle is: the use of fabric air permeability measured under conditions of a certain pressure difference, the amount of air per unit time through the fabric, so that air permeability of the fabric is obtained. Breathable fabric is generally measured under conditions of a certain pressure difference, the amount of air per unit time through the fabric, so that air permeability of the fabric is obtained. Usually the greater the amount of ventilation, the better the permeability of the fabric; in the case of an equal amount of air permeability, the greater the pressure difference between the two ends of the fabric, the fabric air permeability worse.
Textiles according to the situation detected, the equipment meets the needs of the permeability test, no significant difference between the test results of different devices, so the standard does not require a particular instrument, as long as it can meet the standards the condition which carried out permeability testing
Air Permeability Tester, specific appearance sees Figure 3, the specific parameters in Table 4 below
Air Permeability Tester
Technical Data Sheet
Technical Specifications
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Parameter
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Test area
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5cm2、20cm2、25cm2、38cm2、50cm2、100cm2
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Test Mode
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automatic
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Test pressure
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10-3000Pa
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Airflow
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Testing time
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5-50 second
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Stop time
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3 second
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The total test time
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10-58 second
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Minimum pressure
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1Pa
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Greatest pressure
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3000Pa
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Accuracy
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±2%
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Units of measurement
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mm/s,cfm,cm3/cm2/s,l/m2/s,l/dm2/min,m3/m2/min 和m3/m2/h
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Data interface
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RS232C,Asynchronous, double acting
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Feature
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Pressure system can automatically detect pressure range and test a large area of the sample; powerful suction pump device having a silencer;
The instrument can automatically detect the area of the test head, the test is automatically selected pore size, the size of the automatic control of the fan pumping power;
Self-programming function, the customer can write a program according to their own needs;
Beginning with airflow adjustment and fine tuning switches, automatic switch, closed pipeline design, leak less than 0.1 l / m2 / s
http://www.bizbilla.com/
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