1、BRITISH STANDARD BS EN ISO 4638:1995 Polymeric materials, cellular flexible Determination of air flow permeability The European Standard EN ISO4638:1995 has the status of a BritishStandardBSENISO4638:1995 This BritishStandard, having been prepared under the directionof the Sector Board forMaterials
2、and Chemicals, waspublished under the authorityofthe Standards Boardand comesinto effect on 15July1995 BSI01-2000 The following BSI references relate to the work on this standard: Committee referencePRI/24 Draft for comment93/310383DC ISBN 0 580 23784 2 Committees responsible for this British Standa
3、rd The preparation of this BritishStandard was entrusted to Technical Committee PRI/24, Test methods for cellular plastics and rubbers, upon whichthe following bodies were represented: British Plastics Federation British Railways Board British Rigid Urethane Foam Manufacturers Association British Ru
4、bber 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 Foam Manufacturers Association RAPRA Technology Ltd. Soci
5、ety of British Aerospace Companies Limited Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date CommentsBSENISO4638:1995 BSI 01-2000 i Contents Page Committees responsible Inside front cover National foreword ii Foreword 2 0 Introduction 3 1 Scope and
6、field of application 3 2 References 3 3 Principle 3 4 Symbols and terminology 3 5 Apparatus 4 6 Test pieces 5 7 Testing conditions 5 8 Procedure 5 9 Calculation and expression of results 6 10 Test report 7 Annex ZA (normative) Normative references to international publications withtheir relevant Eur
7、opean publications 10 Bibliography 9 Figure 1 Basic principle of the test (according to Darcys laws) 7 Figure 2 Schematic diagram of an airflow permeability apparatus 8 Figure 3 Measurement cell (cylindrical section) 8 List of references Inside back coverBSENISO4638:1995 ii BSI 01-2000 National fore
8、word This BritishStandard has been prepared by Technical CommitteePRI/24 and is the English language version of EN ISO4638:1995 Polymeric materials, cellular flexible Determination of air flow permeability, published by the European Committee for Standardization (CEN) which is identical with ISO4638
9、:1984, published by the International Organization for Standardization. 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 im
10、munity from legal obligations. Cross-reference Publication referred to Corresponding British Standard ISO845:1988 BS EN20845:1995 Cellular plastics and rubbers of apparent (bulk) density Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theEN ISO title page
11、, pages2 to10, 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 the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO4638 May1995 ICS 83.100
12、Descriptors: Cellular materials, flexible cellular materials, tests, determination, permeability, air flow English version Polymeric materials, cellular flexible Determination of air flow permeability Matriaux polymres alvolaires souples Dtermination de la permabilit lair (ISO4638:1984) Weichelastis
13、che Schaumstoffe Bestimmung der Luftstromdurchlssigkeit (ISO4638:1984) This European Standard was approved by CEN on1995-05-11. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard
14、 without any alteration. Up-to-date lists and bibliographical references concerning such national standards 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 langu
15、age made by translation under the responsibility of a CEN member into its own language and notified to 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,
16、 Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland andUnitedKingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1995 Copyright reserved to CEN members Ref
17、. No. EN ISO4638:1995EENISO4638:1995 BSI 01-2000 2 Foreword The text of the International Standard from ISO/TC45, Rubber and rubber products, of the International Organization for Standardization (ISO) has been taken over as a European Standard by the Technical Committee CEN/TC249, Plastics. This Eu
18、ropean Standard shall be given the status ofa national standard, either by publication of an identical text or by endorsement, at the latest by November1995, and conflicting national standards shall be withdrawn at the latest by November1995. According to CEN/CENELEC Internal Regulations, the follow
19、ing countries are bound to implement thisEuropean Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway,Portugal, Spain, Sweden, Switzerland, UnitedKingdom. NOTENormative references to international publications are listed in
20、Annex ZA (normative).ENISO4638:1995 BSI 01-2000 3 0 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 propert
21、ies. It also enables identification of the modifications to cellular structures produced by chemical agents used in foaming, for example catalysts or surfactants. This International Standard is, therefore, useful fortwo purposes: a) in studying the structure of cellular products inconnection with th
22、eir physical properties and their method of manufacture; b) in ensuring product quality (qualityassurance). NOTEDetails 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 specif
23、ies a method for the determination of the permeability of flexible cellular polymeric materials to air flow. It is applicable to test pieces cut from products of cellular material. NOTEISO7231, Polymeric materials, cellular flexible Method of assessment of air flow value at constant pressure drop, 1
24、)specifies a simple quality 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 compare them, but merely to control the quality of a given cellular mater
25、ial. 2 References ISO471, Rubber Standard temperatures, humidities and times for the conditioning and testing of test pieces. ISO845, Cellular rubbers and plastics Determination of apparent density. 3 Principle Passing air under controlled conditions through a test piece in the form of a cylinder or
26、 parallelepiped. 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 1), which describes the air flow in a homogeneous and isotropic (see note1) porous medium under laminar flow cond
27、itions (see note2) by the equation where u is the linear air flow velocity, in metres per second, q V 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
28、metres, of the porous medium; %p is the pressure drop, in pascals, across the test piece, is the dynamic viscosity, in pascal seconds, of air; is the thickness, in metres, of the test piece. NOTE 1For anisotropic materials, it is necessary to define the direction of the flow. NOTE 2For the flow of a
29、ir to be laminar in the interior of the porous medium, it is necessary for the following conditions to be fulfilled: where Re*is the modified Reynolds number; is the kinematic viscosity, in square metres per second, of air; is a limiting value depending on the structure of the product. In the absenc
30、e of precise data on this subject, it is sufficient to use several very low air flow rates of the order of centimetres per second, on a single type of material, to verify that K does not vary or varies only slightly, with changes in u (see9.1). 4.2 specific air flow resistance, R s , is a parameter
31、derived from the permeability of a material, used particularly in the field of acoustics, and is derived from permeability by the equation It is expressed in pascal seconds per square metre(Pasm 2 ). 1) At present at the stage of draft. u q V A - K %p - = Re* uK - = R s K - =ENISO4638:1995 4 BSI 01-
32、2000 4.3 air flow resistance, R, is related to the thickness of the material , whether it is homogeneous or not (it may even consist of a skinned surface or a coating which is more or less porous, such as paint etc.). If the material is homogeneous it is proportional to the specific air flow resista
33、nce by the relationship R = R s In every case, R can be derived directly from Darcys law which is then written The inverse relationship R s= R/ can only be used to calculate R if the material is homogeneous. Air flow resistance is expressed in pascal seconds per metre (Pasm 1 ). 5 Apparatus The appa
34、ratus 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 measuring the pressure drop and for measuring the thickness of the test piece when positioned for the test. An example of a
35、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 parallelepiped or a cylinder. An example of a cylindrical measurement cell is illustrated in Figure 3. If the shape is cylindrical, an
36、internal diameter between50 and120mm is suitable (cross-section between20 and110cm 2 ). For parallelepipeds, the preferred cross-section is a square of side between45 and105mm, corresponding to the same limits of cross-sectional area as for the cylindrical shape. The total height of the cell shall b
37、e at least100mm 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 differing thicknesses, not exceeding half the total height of the measurement cell. NOTEExperience has shown that, for certain cellul
38、ar products, it is necessary to use test pieces of thicknesses of the order of100mm, and a sufficiently deep measurement cell is therefore necessary. The test piece shall rest inside the measurement cell on a perforated support positioned50mm above the base of the cell. This support shall have a min
39、imum open proportion of70% of its overall area, evenly distributed. The tapping points for the measurement of pressure and air flow shall be leak free and arranged below the level of the perforated support. NOTECalculations in8.6 are facilitated if the area of the test piece is standardized at25 or1
40、00cm 2 (56,5 or113mm diameter; square of side50 or100mm). Then u, in metres per second, is equal to400q Vor100q Vdepending on whether the small or the large test piece is used. Calculations in clause9 are facilitated if the area of the test piece is standardized at18,5cm 2 (48,5mm diameter; square o
41、f side45mm) and the thickness of the test piece is100mm. Then 5.2 Means of providing air flow 5.2.1 Source It is recommended that pressure depression systems, of the water reservoir or vacuum pump type, should be used. Alternatively, pressurization systems (air compressor, etc.) may be used. Whateve
42、r source is used, the installation shall permit fine control of the flow and shall ensure the stability of the flow in the lower part of the test cell. 5.2.2 Characteristics of the flow The source shall provide a volumetric air flow rate,q V , equal to uA cubic metres per second. The area chosen for
43、 the cell, A, shall be within the limits indicated in5.1 and the source shall permit air flow velocities up to50mms 1to be obtained. For example, for cylindrical specimens of diametersbetween50 and120mm, and with an airflow velocity of the order of10 2 ms 1 , the volumetric air flow rate through the
44、 apparatus willbe approximately between1dm 3 min 1and7dm 3 min 1 . The source shall have sufficient stability so that the instantaneous volumetric air flow rate may be estimated to better than 2,5%, and so that the change in flow rate with time does not exceed1% per minute. 5.3 Means of measuring vo
45、lumetric flow rate The instrument for measuring the volumetric air flow rate shall be placed between the source and the test piece, as close as possible to the test piece. It shall be selected from a type capable of measuring the values of flow indicated in5.2.2. The arrangement used shall permit me
46、asurement of the flow with an accuracy of2% of the full scale value. u q V A - %p R s - = K q V %p - =ENISO4638:1995 BSI 01-2000 5 The arrangement may be, for example, an assembly of flowmeters arranged in parallel, one of which can be selected to suit the required range of measurement. The flowmete
47、r used for any measurement shall allow reading of the volumetric air flow rate at a graduation between20 and100% of the full scale value of the meter. Calibrated flowmeters with a scale at least250mm long are recommended. 5.4 Means of measuring pressure drop The apparatus used for measuring differen
48、tial pressures shall permit measurements of pressure drops as small as1Pa. Inclined water or alcohol manometers or any other apparatus allowing readings with an accuracy of0,5Pa may be used. 5.5 Means of measuring test piece thickness For materials of sufficiently high density to possess well-define
49、d surfaces and which are to be measured in the uncompressed state, the thickness of the test piece shall be measured in place in the holder with an accuracy of at least1%. A suitable means of doing this is to use the thickness measurement device shown in Figure 3. This device consists of a perforated plate with a minimum open proportion of70% of its overall area evenly distributed, which may be brought progressively into contact with the test piece. This
