1、BRITISH STANDARD Polymeric materials, cellular flexible - Determination of air flow permeability I The European Standard EN IS0 4638 : 1995 has the status of a British Standard BS EN IS0 $638 : 1995 COPYRIGHT European Committee for StandardizationLicensed by Information Handling ServicesBS EN IS0 46
2、38 : 1995 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PRI/24, Test methods for cellular plastics and rubbers, upon which the following bodies were represented: British Plastics Federation British Railways Board Britis
3、h Rigid Urethane Foam Manufacturers Association British Rubber Manufacturers Association Ltd. Department of the Environment (Building Research Establishment) Furniture Industry Research Association Furniture, Timber and Allied Trades Union Ministry of Defence National Bed Federation Limited Phenolic
4、 Foam Manufacturers Association RAPRA Technology Ltd. Society of British Aerospace Companies Limited Society of Motor Manufacturers and Traders Limited This British Standard, having been prepared under the direction of the Sector Board for Materials and Chemicals, was published under the authority o
5、f the Standards Board and comes into effect on 15 July 1995 O BSI 1995 The following BSI references relate to the work on this standard: Committee reference PR1124 Draft for comment 931310383 DC ISBN O 680 23784 2 Amendments issued since publication Amd. No. Text affected Date COPYRIGHT European Com
6、mittee for StandardizationLicensed by Information Handling ServicesBS EN IS0 4638 : 1995 Contents Committees responsible National foreword Foreword Method O Introduction 1 Scope and field of application 2 References 3 Principle 4 Symbols and terminology 5 Apparatus 6 Test pieces 7 Rsting conditions
7、8 Procedure 9 Calculation and expression of results 10 Test report fige Inside front cover 11 2 3 3 3 3 3 3 4 5 5 5 6 7 Figures 1 Basic principle of the test (according to Darcys laws) 7 2 Schematic diagram of an airflow permeability apparatus 8 3 Measurement cell (cylindrical section) 8 Annex ZA (n
8、ormative) Nonnative references to international publications with their relevant European publications 10 i COPYRIGHT European Committee for StandardizationLicensed by Information Handling ServicesCEN EN*ISO*463B 95 m 3404589 0076057 bTb m BS EN IS0 4-638 : 1995 National foreword This British Standa
9、rd has been prepared by Technical Committee PR1124 and is the English language version of EN IS0 4638 : 1995 Polymeric materials, cellularjlexible - Determination of airflow permeability, published by the European Committee for Standardization (CEN) which is identical with IS0 4638 : 1984, published
10、 by the International Organization for Standardization. Cross-reference Publication referred to Corresponding British Standard IS0 845 : 1988 BS EN 20845 : 1995 Cellulurplastics and rubbers of apparent (bulk) density Compliance with a British Standard does not of itself confer immunity from legal ob
11、ligations. ii COPYRIGHT European Committee for StandardizationLicensed by Information Handling ServicesEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN IS0 4638 May 1995 ICs 83.100 Descriptors: Cellular materials, flexible cellular materials, tests, determination, permeability, air flow English
12、version Polymeric materials, cellular flexible - Determination of air flow permeability Matriaux polymres alvolaires souples - Weichelastische Schaumstoffe - Bestimmung Dtermination de la permabilit lair der Luftstromdurchlssigkeit (IS0 4638 : 1984) (IS0 4638 : 1984) This European Standard was appro
13、ved by CEN on 1995-05-11. CEN members are bound to comply with the CENKENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national stand
14、ards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to
15、the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN E
16、uropean Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels O 1995 Copyright reserved to CEN members Ref. No. EN IS0 4638 : 1995 E COPYRIGHT European Committee for StandardizationLicensed by Information
17、Handling ServicesCEN EN*IS0*4b38 95 W 3404589 0096059 479 W Page 2 EN IS0 4638 : 1995 Foreword The text of the international standard from ISO/lY 45, Rubber and rubber products, of the International Organization for Standardization (ISO) has been taken over as a European Standard by the Rchnical Com
18、mittee CEN/TC 249, Plastics. This European Standard shaIl be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 1995, and conflicting national standards shall be withdrawn at the latest by November 1995. According to CENKE
19、NELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom. NOTE. Normative references t
20、o international publications are listed in annex ZA (normative). COPYRIGHT European Committee for StandardizationLicensed by Information Handling ServicesCEN EN*IS0*4638 95 m 3404589 0096060 L90 m Page 3 EN IS0 4638 : 1995 Polymeric materials, cellular flexible - Determination of air flow permeabili
21、ty O Introduction The air flow permeability of cellular materials indicates, in an indirect manner, some of their structural properties. It may be used to establish correlations between the structure of these materials and some of their physical properties. It also enables identification of the modi
22、fications to cellular structures pro- duced by chemical agents used in foaming, for example catalysts or surfactants. This International Standard is, therefore, useful for two pur- Poses: a) in studying the structure of cellular products in connec- tion with their physical properties and their metho
23、d of manufacture; b) in ensuring product quality (quality assurance). NOTE - Details of publications relating to flow behaviour in both laminar and turbulent conditions are given in a bibliography. 1 Scope and field of application This International Standard specifies a method for the deter- minatio
24、n of the permeability of flexible cellular polymeric materials to air flow. It is applicable to test pieces cut from products of cellular material. NOTE - IS0 7231, po/vmericr meterias, Cellular flexible - Method of assessment of air flow velue at constant pressure drop,11 specifies a simple quality
25、 control method which is also based on the flow of air through cellular materials. This can be used when it is not the intention to calculate the intrinsic properties of various materials in order to com- pare them, but merely to control the quality of a given cellular material. 2 References IS0 471
26、, Rubber - Standard temperatures, humidities and times for the conditioning and testing of test pieces. IS0 845, Cellular rubbers and plastics - Determination of ap- parent density. 3 Principle Passing air under controlled conditions through a test piece in the form of a cylinder or parallelepiped.
27、Measurement of the pressure drop between the two free faces of the test piece. 4 Symbols and terminology 4.1 Air flow permeability, K. is given by Darcys law (see figure I), which describes the air flow in a homogeneous and isotropic (see note 1) porous medium under laminar flow condi- tions (see no
28、te 2) by the equation where u is the linear air flow velocity, in metres per second ; qv is the volumetric air flow rate, in cubic metres per second, crossing the test piece; A is the right cross-sectional area, in square metres, of the test piece; K is the flow permeability. in square metres, of th
29、e porous medium; Ap is the pressure drop, in pascals, across the test piece; is the dynamic viscosity, in pascal seconds, of air; 6 is the thickness, in metres, of the test piece. NOTES 1 For anisotropic materials, it is necessary to define the direction of the flow. 2 For the flow of air to be lami
30、nar in the interior of the porous medium, it is necessary for the following conditions to be fulfilled : V where Re is the modified Reynolds number; v is the kinematic viscosity, in square metres per second, of air ; 1) At present at the stage of draft. COPYRIGHT European Committee for Standardizati
31、onLicensed by Information Handling ServicesCEN ENmISOa4638 95 M 3404589 009bObL O27 m Page 4 EN IS0 4638 : 1995 q is a limiting value depending on the structure of the product. In the absence of precise data on this subject, it is sufficient to use several very low air flow rates of the order of cen
32、timetres per second, on a single type of material, to verify that K does not vary or varies only slightly, with changes in u (see 9.1). 4.2 Specific air flow resistance, R, is a parameter derived from the permeability of a material, used particularly in the field of acoustics, and is derived from pe
33、rmeability by the equation R, =- rl K It is expressed in pascal seconds per square metre (Pa.s-m-*). 4.3 Air flow resistance, R, is related to the thickness of the material 6, whether it is homogeneous or not (it may even con- sist of a skinned surface or a coating which is more or less porous, such
34、 as paint etc.). If the material is homogeneous it is proportional to the specific air flow resistance by the relation- ship R = B-R, In every case, R can be derived directly from Darcys law which is then written 4v Lp I R, u =- =- The inverse relationship R, = R/6 can only be used to calcu- late R
35、if the material is homogeneous. Air flow resistance is expressed in pascal seconds per metre (Pa-s.m-1). 5 Apparatus The apparatus consists of a measurement cell into which the test piece may be placed, and means for production of a steady flow of air, for measuring the volumetric air flow rate, for
36、 measuring the pressure drop and for measuring the thickness of the test piece when positioned for the test. An example of a suitable apparatus is shown schematically in figure 2. It shall include the following elements. 5.1 Measurement cell The measurement cell shall be in the shape of a parallelep
37、iped or a cylinder. An example of a cylindrical measurement cell is illustrated in fQure 3. If the shape is cylindrical, an internal diameter between 50 and 120 mm is suitable (cross-section between 20 and 110 cd). For parallelepipeds, the preferred cross-section is a square of side between 45 and 1
38、)5 mm, corresponding to the same limits of cross-sectional area as for the cylindrical shape. The total height of the cell shall be at least 100 mm greater than the thickness of the test piece. For tests other than for quality assurance, it is useful to make allowance for the use of test pieces of d
39、iffering thicknesses, not exceeding half the total height of the measurement cell. NOTE - Experience has shown that, for certain cellular products, it is necessary to use test pieces of thicknesses of the order of 100 mm, and a sufficiently deep measurement cell is therefore necessary. The test piec
40、e shall rest inside the measurement cell on a per- forated support positioned 50 mm above the base of the cell. This support shall have a minimum open proportion of 70 % of its overall area, evenly distributed. The tapping points for the measurement of pressure and air flow shall be leak free and ar
41、ranged below the level of the per- forated support. NOTE - Calculations in 8.6 are facilitated if the area of the test piece is standardized at 25 or 100 cm2 156.5 or 113 mm diameter; square of side 50 or 100 mm). Then u, in metres per second, is equal to 400 4“or 100 qydepending on whether the smal
42、l or the large test piece is used. Calculations in .clause 9 are facilitated if the area of the test piece is standardized at 18,5 cd 148.5 mm diameter ; square of side 45 mm) and the thickness of the test piece is 100 mm. Then 5.2 Means of providing air flow 5.2.1 Source It is recommended that pres
43、sure depression systems, of the water reservoir or vacuum pump type, should be. used. Alter- natively, pressurization systems fair compressor, etc.) may be used. Whatever source is used, the installation shall permit fine control of the flow and shall ensure the stability of the flow in the lower pa
44、rt of the test cell. 5.2.2 Characteristics of the flow The source shall provide a volumetric air flow rate, qv , equal to UA cubic metres per second. The area chosen for the cell,.A, shall be within the limits in- dicated in 5.1 and the source shall permit air flow velocitik up to 50 mm-s“ to be obt
45、ained. For example, for cylindrical specimens of diameters between 50 and 120 mm, and with an air flow velocity of the order of m-s- l, the volumetric air flow rate through the apparatus will be approximately between 1 dr b) if studying a new material, or for particular applications, kshould be exam
46、ined for the maintenance of a substantially constant value within any part of the field of variation of u, and this value used as representative of the material. In both cases, the result shall be given in the form of a mean value R, to two significant figures. For the former purpose, the arithmetic
47、 mean value K obtained on the group of test pieces, together with the mean value of the apparent density, u = 0,010 mms-; a = 35 kg-m-3. For the latter purpose, the arithmetic mean value of K obtained on the group of test pieces within a given range of velocities shall be quoted together with the me
48、an value of the apparent density, B. Example: R = 2,5 x IO-* m2; for 0,005 u 0.02 m-s“; 6, = 40 kg-m-3. The results can equally well be- expressed in terms of the specific resistance R, instead of K. If is being determined for acoustic purposes, the value of Ror R, extrapolated graphically to a velo
49、city of 0,W mms“ shall be shown if a significant variation of is observed within the range of velocities under consideration. 9.2 For non-homogeneous test pieces In this case, the calculation of Kor R, is meaningless and the air flow resistance R shall be calculated for each test piece from the equation 4 COPYRIGHT European Committee for StandardizationLicensed by Information Handling ServicesPage 7 EN IS0 4638 : 1995 See 4.3 for an explanation of the symbols and units. The requirements of 9.1 shall be observed when considering R instead of R, (or KI. 9.3 Precisi
