EN ISO 4638:1995

SLOVENSKI STANDARD
01-maj-1999
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Polymeric materials, cellular flexible - Determination of air flow permeability (ISO
4638:1984)
Weichelastische Schaumstoffe - Bestimmung der Luftstromdurchlässigkeit (ISO
4638:1984)
Matériaux polymeres alvéolaires souples - Détermination de la perméabilité a l'air (ISO
4638:1984)
Ta slovenski standard je istoveten z: EN ISO 4638:1995
ICS:
83.100 Penjeni polimeri Cellular materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

International Standard
i
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.ME)I(flYHAPO~HAfl OPTAHM3ALWlFl l-IO CTAH~APTM3A~MM.ORGANlSATiON INTERNATIONALE DE NORMALISATION
Polymeric materials, cellular flexible - Determination
of air flow permeability
Mathriaux polym&es alvholaires soup/es - Dbtermina tion de la perm6abilit6 9 /‘air
First edition - 1984-05-15
UDC 678.4-405.8 : 620.193.29 Ref. No. IS0 4638-1984 (E)
cellular materials, flexible cellular materials, tests, determination, permeability, air flow.
Descriptors :
Price based on 7 pages
Foreword
lS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work of developing International
Standards is carried out through IS0 technical committees. Every member body
interested in a subject for which a technical committee has been authorized has the
right to be represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the IS0 Council.
lnternationai Standard IS0 4638 was developed by Technical Committee ISO/TC 45,
Rubber and rubber products, and was circulated to the member bodies in
February 1982.
It has been approved by the member bodies of the following countries:
Austria Romania
Germany, F. R.
Belgium India South Africa, Rep. of
Brazil
Indonesia Spain
Canada Ireland Sri Lanka
China Mexico Thailand
Czechoslovakia Netherlands Turkey
Denmark Nigeria USA
Egypt, Arab Rep. of Poland USSR
France Portugal
on
The member body of the following country expressed disapproval of the document
technical grounds:
United Kingdom
0 International Organization for Standardization, 1984
Printed in Switzerland
IS0 4638-1984 (E)
INTERNATIONAL STANDARD
Polymeric materials, cellular flexible - Determination
of air flow permeability
3 Principle
0 Introduction
Passing air under controlled conditions through a test piece in
The air flow permeability of cellular materials indicates, in an
the form of a cylinder or parallelepiped. Measurement of the
indirect manner, some of their structural properties. It may be
pressure drop between the two free faces of the test piece.
used to establish correlations between the structure of these
materials and some of their physical properties. It also enables
identification of the modifications to cellular structures pro-
duced by chemical agents used in foaming, for example
4 Symbols and terminology
catalysts or surfactants.
4.1 Air flow permeability, K, is given by Darcy’s law (see
This International Standard is, therefore, useful for two pur-
figure 11, which describes the air flow in a homogeneous and
poses :
isotropic (see note 1) porous medium under laminar flow condi-
a) in studying the structure of cellular products in connec-
tions (see note 2) by the equation
tion with their physical properties and their method of
manufacture ;
qv K AP
=-=-
U
b) in ensuring product quality (quality assurance).
A
where
NOTE - Details of publications relating to flow behaviour in both
laminar and turbulent conditions are given in a bibliography.
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;
1 Scope and field of application
A is the right cross-sectional area, in square metres, of the
This International Standard specifies a method for the deter-
test piece; _
mination of the permeability of flexible cellular polymeric
K is the flow permeability, in square metres, of the porous
materials to air flow.
medium ;
It is applicable to test pieces cut from products of cellular
Ap is the pressure drop, in pascals, across the test piece;
material.
q is the dynamic viscosity, in Pascal seconds, of air;
NOTE - I SO 7231, Potymeric materials, Cellular flexible - Method of 6 is the thickness, in metres, of the test piece.
assessment of air flow value at constant pressure drop,l) specifies a
simple quality control method which is also based on the flow of air
NOTES
through cellular materials. This can be used when it is not the intention
1 For anisotropic materials, it is necessary to define the direction of
to calculate the intrinsic properties of various materials in order to com-
the flow.
pare them, but merely to control the quality of a given cellular material.
2 For the flow of air to be laminar in the interior of the porous
medium, it is necessary for the following conditions to be fulfilled :
2 References
Re” = % < n
V
IS0 471, Rubber - Standard temperatures, humidities and
times for the conditioning and testing of test pieces.
where
Re” is the modified Reynolds number;
I SO 845, Cellular rubbers and plastics - Determination of ap-
parent density. v is the kinematic viscosity, in square metres per second, of air;
1) At present at the stage of draft.

is0 46384984 (El
q is a limiting value depending on the structure of the product. In The total height of the cell shall be at least 100 mm greater than
the absence of precise data on this subject, it is sufficient to use
the thickness of the test piece. For tests other than for quality
several very low air flow rates of the order of centimetres per
assurance, it is useful to make allowance for the use of test
second, on a single type of material, to verify that K does not vary
pieces of differing thicknesses, not exceeding half the total
or varies only slightly, with changes in u (see 9.1).
height of the measurement cell.
NOTE - Experience has shown that, for certain cellular products, it is
4.2 Specific air flow resistance, R,, is a parameter derived
necessary to use test pieces of thicknesses of the order of 100 mm, and
from the permeability of a material, used particularly in the field
a sufficiently deep measurement cell is therefore necessary.
of acoustics, and is derived from permeability by the equation
The test piece shall rest inside the measurement cell on a per-
R, =A
forated support positioned 50 mm above the base of the cell.
K
This support shall have a minimum open proportion of 70 % of
its overall area, evenly distributed.
It is expressed in Pascal seconds per square metre (Pa l s m -2).
The tapping points for the measurement of pressure and air
4.3 Air flow resistance, R, is related to the thickness of the
flow shall be leak free and arranged below the level of the per-
material 6, whether it is homogeneous or not (it may even con-
forated support.
sist of a skinned surface or a coating which is more or less
porous, such as paint etc.). If the material is homogeneous it is
NOTE - Calculations in 8.6 are facilitated if the area of the test piece is
proportional to the specific air flow resistance by the relation-
standardized at 25 or 100 cm2 (56,5 or 113 mm diameter; square of
side 50 or 100 mm). Then u, in metres per second, is equal to 400 qvoor
ship
100 qVdepending on whether the small or the large test piece is used.
Calculations in clause 9 are facilitated if the area of the test piece is
R = &R,
standardized at 18,5 cm2 (48,5 mm diameter; square of side 45 mm)
and the thickness of the test piece is 100 mm. Then
In every case, R can be derived directly from Darcy’s law which
\
is then written
qv
K=-
AP
4v AP
=-=-
u
* Rs
5.2 Means of providing air flow
The inverse relationship R, = R/6 can only be used to calcu-
late R if the material is homogeneous.
52.1 Source
Air flow resistance is expressed in Pascal seconds per metre
It is recommended that pressure depression systems, of the
(Pasm-l).
water reservoir or vacuum pump type, should be used. Alter-
natively, pressurization systems (air 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
5 Apparatus
the lower part of the test cell.
The apparatus consists of a measurement cell into which the
test piece may be placed, and means for production of a steady 5.2.2 Characteristics of the flow
flow of air, for measuring the volumetric air flow rate, for
measuring the pressure drop and for measuring the thickness The source shall provide a volumetric air flow rate, qv, equal to
of the test piece when positioned for the test. uA cubic metres per second.
An example of a suitable apparatus is shown schematically in The area chosen for the cell, A, shall be within the limits in-
figure 2.
dicated in 5.1 and the source shall permit air flow velocities up
to 50 mm+ to be obtained.
It shall include the following elements.
For example, for cylindrical specimens of diameters between 50
and 120 mm, and with an air flow velocity of the order of
5.1 Measurement cell
10s2 ms-I, th e volumetric air flow rate through the apparatus
will be approximately between 1 dm3mminB1 and 7 dm3~minV1.
The measurement cell shall be in the shape of a parallelepiped
The source shall have sufficient stability so that the instan-
or a cylinder.
taneous volumetric air flow rate may be estimated to better
than f2,5 %, and so that the change in flow rate with time
An example of a cylindrical measurement cell is illustrated in
does not exceed 1 % per minute.
figure 3.
If the shape is cylindrical, an internal diameter between 50 and 53 .
Means of measuring volumetric flow rate
120 mm is suitable (cross-section between 20 and 110 cm2).
The instrument for measuring the volumetric air flow rate shall
For parallelepipeds, the preferred cross-section is a square of be placed between the source and the test piece, as close as
possible to the test piece. It shall be selected from a type
side between 45 and 105 mm, corresponding to the same limits
of cross-sectional area as for the cylindrical shape. capable of measuring the values of flow indicated in 5.2.2.
...