1、BRITISH STANDARD BS3424-34: 1992 Testing coated fabrics Part 34: Method 37. Method for determination of water vapour permeability index (WVPI) IMPORTANT NOTEIt is recommended that this Part be read in conjunction with the information in Part 0 “Foreword and general introduction”.BS3424-34:1992 This
2、British Standard, having been prepared under the directionof the Plastics and Rubber Standards Policy Committee, was published underthe authority of the Standards Board and comes intoeffect on 28 February1992 BSI 03-1999 The following BSI references relate to the work on this standard: Committee ref
3、erence PRM/78 Draft for comment 90/42631 DC ISBN 0 580 20504 5 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical CommitteePRM/78, upon which the following bodies were repr
4、esented: British Nonwovens Manufacturers Association British Plastics Federation British Railways Board British Resin Manufacturers Association British Rubber Manufacturers Association Ltd. British Textile Confederation British Textile Technology Group Department of Health Department of the Environm
5、ent (Building Research Establishment) Electricity Industry in United Kingdom Furniture Industry Research Association Home Office Industrial Safety (Protective Equipment) Manufacturers Association London Regional Transport Made-Up Textiles Association Ministry of Defence National Union of Dyers, Blea
6、chers and Textile Workers (NUDBTW) RAPRA Technology Ltd. SATRA Footwear Technology Centre Society of Motor Manufacturers and Traders Ltd. The following body was also represented in the drafting of the standard, through subcommittees and panels: Ministry of Defence Amendments issued since publication
7、 Amd. No. Date CommentsBS3424-34:1992 BSI 03-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Principle 1 4 Apparatus 1 5 Procedure 4 6 Test report 5 Figure 1 Dish, support and cover ring 2 Figure 2 Turntable 3 Publication(s) referred to Inside b
8、ack coverBS3424-34:1992 ii BSI 03-1999 Foreword This British Standard has been prepared under the direction of the Plastics and Rubber Standards Policy Committee. The transmission of water vapour through textiles and polymer coated textiles is a feature of great significance to many end uses, additi
9、onal to apparel, such as tentage and certain types of decorative awnings for example. The present method compares the rate of water vapour transmission through the coated fabric under test with the rate of transmission through a standard woven polyester reference fabric under exactly the same circum
10、stances, thus allowing comparisons to be made between different materials. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer
11、 immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in th
12、e amendment table on theinside front cover.BS3424-34:1992 BSI 03-1999 1 1 Scope This British Standard describes a method for determining the water vapour permeability of a coated fabric relative to that of a standard woven polyester monofilament fabric. NOTEThe titles of the publications referred to
13、 in this standard are listed on the inside back page. 2 Definitions For the purposes of this British Standard the following definitions apply. 2.1 water vapour permeable the ability of a coated fabric to transmit water vapour above a minimum index level when tested in accordance with this method of
14、test prior to any previous chemical and/or physical testing NOTE 1An alternative term in common usage is breathable. NOTE 2It is recommended that neither the term water vapour permeable nor breathable be applied to any coated fabric that exhibits a water vapour permeability index less than40. 2.2 wa
15、ter vapour permeability index (WVPI) the water vapour permeability of a material expressed as a percentage of a known reference standard 3 Principle A test specimen is sealed over the open mouth of a test dish which contains water, and the assembly placed in a controlled atmosphere. Following a peri
16、od to establish equilibrium of the water vapour pressure gradient across the test specimen, successive weighings of the assembled dish are made and the rate of water vapour permeation through the specimen is determined. The water vapour permeability index is calculated by expressing the water vapour
17、 permeability of the coated fabric as a percentage of the water vapour permeability of a reference woven fabric which is tested in a similar manner, concurrently and alongside the test specimen. NOTEThe method used is based on that commonly known as the Turl dish or control dish method which is used
18、 to measure the resistance of materials to water vapour diffusion and is particularly suitable for clothing materials. 4 Apparatus 4.1 Reference fabric. A precision, high tenacity polyester woven monofilament mesh having the following characteristics: NOTEThis fabric is tightly woven and constructed
19、 from synthetic fibres of low moisture regain to avoid sagging under conditions of high relative humidity. 4.2 Test chamber. Room or cabinet controlled at the standard temperate atmosphere for testing textiles as defined in BS3424-2, i.e.a relative humidity of655% and a temperature of20 2 C. The cha
20、mber is of sufficient size to contain the turntable assembly and test dishes and to maintain them within the specified limits of temperature and humidity. 4.3 A cutting device. Capable of cutting circular specimens with a diameter not less than the outer diameter of the dish. 4.4 Burette. Conforming
21、 to class B, or better, of BS846. 4.5 Open dishes. Dishes fitted with cover rings, of the approximate dimensions shown in Figure 1 and Figure 2 manufactured from a stable, lightweight, corrosion resistant material. The interior walls of the dishes are treated to reduce their wettability to ensure a
22、uniform vertical gradient of water vapour pressure over the entire area of the dishes. NOTE 1Each dish and its corresponding covering should be numbered for identification purposes. NOTE 2To ensure accuracy in measuring water vapour loss, the dishes should be of low mass, e.g.manufactured from mater
23、ials of low specific gravity. Aluminium alloy, e.g.material designation6082 as specified in BS1474, has been found to be a satisfactory material for the dishes. NOTE 3A baked-on silicone treatment has been found satisfactory for metal dishes. 4.6 Sample support. A means of supporting the specimen in
24、 the dish, to prevent it from sagging, which would alter the depth of the air layer between the specimen and the surface of the water. NOTEOne type of support, shown in Figure 1, is constructed from stainless steel wire (0.0914mm diameter) and fits into three semi-circular depressions spaced120 apar
25、t and cut into the rim of the lid. The depth of the depressions are such that, with the support in place, the covering just fits flush onto the dish rim. 4.7 Sealing means. For securing the sample to the lip of the dish and the sealing lid in such a manner as to prevent lateral leakage of water vapo
26、ur. One such method is described in5.4 which requires the following. a) Adhesive cement. A quick-drying adhesive cement for fixing test fabrics to the rim of the test dishes. NOTEThe adhesive or its solvents should not react with or irreversibly alter any part of the test fabric. A general-purpose,
27、clear PVC/nitrile contact adhesive has been found satisfactory for this purpose. b) Adhesive tape. Pressure sensitive, adhesive-backed polymer tape with negligible water vapour transmission properties for sealing the cover rings to the test dishes. NOTEPVC electrical insulating tape approximately10m
28、m to15mm wide has been found satisfactory for this purpose. mesh aperture 18 4m; yarn diameter 32 4m; threads per cm 196.1; open area 12.5 % (approx)BS3424-34:1992 2 BSI 03-1999 Figure 1 Dish, support and cover ringBS3424-34:1992 BSI 03-1999 3 Figure 2 TurntableBS3424-34:1992 4 BSI 03-1999 4.8 Turnt
29、able. A turntable, capable of carrying at least six test dishes, which rotates uniformly to avoid formation of still air layers above the test dishes. Movement of the dishes is not to exceed6m/min. Means of accurately levelling the turntable are provided to ensure a uniform still air layer within th
30、e test dishes. The turntable is isolated from any vibration of heat generated by its motor. NOTEA turntable of the dimensions shown in Figure 2 and rotating at approximately2r/min has been found satisfactory. A turntable is more satisfactory than an electric fan for generating a slow air flow, evenl
31、y and consistently over all of the assembled dishes. Larger turntables carrying larger numbers of dishes can obviously be used. Providing the dishes are equidistant from the centre of the turntable, the air flow over each dish will be the same. 4.9 Balance. Balance capable of weighing to within0.01g
32、. NOTEThe balance is positioned close to or preferably inside the test chamber to minimize the fluctuation in atmospheric conditions on weighing the assembled test dishes. 4.10 Timer. Means for timing accurately to within 1min the intervals between weighings over a period of at least16h. 4.11 Reagen
33、ts. Water conforming with grade3 of BS3978. 5 Procedure 5.1 Take care throughout all handling operations to keep the assembled dishes level and to avoid splashing the inside surface of the test or reference fabric. 5.2 Condition the test fabric and reference fabric(4.1) for at least1h in the test ch
34、amber(4.2). 5.3 For each fabric to be tested, cut, by means of the cutting device(4.3), a minimum of5 test specimens and a minimum of2 specimens from the reference fabric, preferably without removing the specimens from the test chamber. 5.4 By means of the burette(4.4), transfer a volume of water(4.
35、11) at20 2 C to each open dish(4.5), predetermined from the dimensions of the dish to give a10 1mm deep layer of air between the surface of the water and the underside of the supported specimen. NOTE46ml of water placed in a dish constructed to the dimensions shown in Figure 2 creates an internal st
36、ill air layer of10 1mm. Position the sample support(4.6) in the dish. If an adhesive method is to be employed for securing the sample, adopt the following procedure. Apply a thin continuous layer of adhesive cement (item a) of4.7) to the rim of the dish. Carefully place the fabric specimen onto the
37、rim of the dish, avoiding contamination of the exposed test area of the fabric. Position the test fabric such that the surface which is intended to be on the outside of the clothing assembly is uppermost. Place the corresponding cover ring over the rim of the dish, now sealed by the test fabric, pre
38、ss firmly down and apply a strip of adhesive tape, (item b) of4.7) around the full circumference, sealing the joint between the cover ring and the dish. Ensure that the edge of the adhesive tape does not project above the cover ring. 5.5 Place each assembly (i.e.dish, complete with specimen), in tur
39、n, on to its corresponding position on the turntable(4.8). 5.6 Rotate the turntable with assemblies in the test chamber for a period of not less than1h to establish equilibrium of the water vapour gradient for each assembly. 5.7 At the end of the equilibration period, weigh each assembly on the bala
40、nce(4.9) to the nearest0.01g. Record the mass of each assembly and the time at which assembly was weighed. Replace the dishes on the turntable. 5.8 Rotate the turntable within the controlled atmosphere for a further period of at least16h. Reweigh the assemblies and note the mass and time of weighing
41、. NOTEIf, for internal quality control purposes, the period of controlled exposure is less than16h(e.g.8h), the balance(4.9) needs to be accurate to within0.001g. 5.9 Determine the internal diameter of the test dish as the mean of two measurements taken at right angles. 5.10 The water vapour permeab
42、ility index (WVPI) is given by means of the following equation: where (WVP) f is the mean water vapour permeability of the fabric under test, expressed ing/m 2per24h; (WVP) r is the mean water vapour permeability of the reference fabric, expressed ing/m 2per24h. WVPI WVP () f WVP () r -100 =BS3424-3
43、4:1992 BSI 03-1999 5 and (WVP can be (WVP) for (WVP) rrespectively) where where NOTEFor all practical purposes: Providing that the controlled exposure time, t, is identical for both the test specimen and the reference fabric. 6 Test report The test report shall include all the following particulars.
44、 a) a full description of the coated fabric; b) the means used of securing the test piece to the top of the dish (see4.7); c) the period of exposure within the controlled atmosphere (see5.8); d) the mean water vapour permeability index (WVPI) calculated in accordance with5.10; e) any deviations from
45、 the standard test procedure. M is the mass loss of the assembly over the time period t (in g); t is the time between successive weighings of the assembly (in h); A is the area of the exposed test fabric (equal to the internal area of the test dish) in m 2and is given by the equation: d is the inter
46、nal diameter of the test dish (inmm). WVP 24 M At - = A ; d 2 4 - 10 6 =WVPI Mean mass loss of test specimen Mean mass loss of reference fabric -100 =6 blankBS3424-34:1992 BSI 03-1999 Publication(s) referred to BS846, Specification for burettes. BS1474, Specification for wrought aluminium and alumin
47、ium alloys for general engineering purposes: bars, extruded round tubes and sections. BS3424, Testing coated fabrics. BS3424-2:Method 4, Conditioning and selection of test specimens. BS3978, Specification for water for laboratory use. BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | |
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