1、BRITISH STANDARD BS 3321:1986 Method for Measurement of the equivalent pore size of fabrics (bubble pressure test) UDC 677.017.285BS3321:1986 This British Standard, having been prepared under the directionof the Textiles and Clothing Standards Committee, was published under the authorityof the Board
2、 of BSI andcomes into effect on 28 February 1986 BSI 08-1999 First published December 1960 First revision January 1969 Second revision February 1986 The following BSI references relate to the work on this standard: Committee reference TCM/24 Draft for comment 83/39262 DC ISBN 0 580 14769 9 Committee
3、s responsible for this British Standard The preparation of this British Standard was entrusted by the Textiles and Clothing Standards Committee (TCM/-) to Technical Committee TCM/24, upon which the following bodies were represented: British Textile Employers Association Confederation of British Wool
4、 Textiles Limited International Wool Secretariat Man-made Fibres Producers Committee Manchester Testing House Ministry of Defence Soap and Detergent Industry Association Society of Dyers and Colourists Society of Motor Manufacturers and Traders Limited Textile Institute Textile Research Council Amen
5、dments issued since publication Amd. No. Date of issue CommentsBS3321:1986 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definition 1 3 Principle 1 4 Apparatus 1 5 Atmosphere for conditioning and testing 1 6 Preparation of test specimens 1 7 Procedure
6、1 8 Calculation and expression of results 2 9 Test report 2 Appendix A Advice on a suitable form of apparatus and its use 3 Appendix B Derivation of equation for calculation of equivalent pore radius 3 Figure 1 Suitable apparatus 4 Publications referred to Inside back coverBS3321:1986 ii BSI 08-1999
7、 Foreword This British Standard has been prepared under the direction of the Textiles and Clothing Standards Committee. It is a revision of BS3321:1969 which is withdrawn. The principal change introduced by this revision is that details of a suitable form of apparatus have been revised. A British St
8、andard 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 immunity from legal obligations. Summary of pages This document comprises a front cove
9、r, an inside front cover, pages i and ii, pages1 to 4, 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.BS3321:1986 BSI 08-1999 1 1 Scope This B
10、ritish Standard describes a method for the measurement of the equivalent pore radius, which provides an estimate of the size of the interstices in all types of fabric which are permeable to air. The method is particularly applicable to water repellent and filter fabrics. NOTEThe titles of the public
11、ations referred to in this standard are listed on the inside back cover. 2 Definition For the purposes of this British Standard, the following definition applies. equivalent pore radius the radius of capillary of circular cross section which requires the same air pressure to force a wetting liquid f
12、rom it as from the fabric pore 3 Principle The pressure required to force air bubbles through the interstices of a fabric, wetted by a liquid and having a film of the same liquid applied to its upper surface, is observed. This pressure together with the known surface tension of the liquid is used to
13、 estimate the size of the interstices in the fabric. 4 Apparatus 4.1 Apparatus for measurement of the equivalent pore size, having the following characteristics (seeAppendix A). a) Means shall be provided for clamping the specimen of fabric in such a manner that: 1) it is horizontal; 2) a circular a
14、rea of the fabric50mm in diameter will be subjected to steadily increasing air pressure on the lower face; 3) no leakage of the test liquid occurs during the test period; 4) the specimen does not slip in the clamps. NOTE 1The clamps should be faced with resilient material (which is resistant to whit
15、e spirit). With some forms of apparatus, it has been found that the correct conditions of clamping can be attained if the clamps are faced with a suitable grade of synthetic rubber. b) The liquid in contact with the test specimen shall be white spirit which complies with BS245. c) The rate of increa
16、se in air pressure shall be200mm head of water per minute to250mm head of water per minute (2kPa/min to2.5 kPa/min 1) ). d) A pressure measuring device connected to the test head shall be calibrated in millimetres head of water (or kPa). NOTE 2It is necessary to provide a pressure measuring device o
17、f suitable range. A pressure measuring device which provides for pressures up to600mm head of water (6kPa) is suitable for most fabrics. A pressure measuring device providing pressures of up to1m head of water (10kPa) is required for measurements on close fabrics, e.g. ventiles, clean room overalls,
18、 theatre clothing and drapes. NOTE 3For details of sources of supply of a suitable apparatus contact Enquiry Section, BSI, Linford Wood, Milton Keynes MK146LE, enclosing a stamped addressed envelope for reply. 5 Atmosphere for conditioning and testing The atmosphere required for conditioning and tes
19、ting shall be the standard temperate atmosphere for testing textiles specified in BS1051. 6 Preparation of test specimens 6.1 After receipt, handle the fabric as little as possible and do not sharply fold, iron or treat it in any way other than by conditioning. Cut specimens from the fabric in a sha
20、pe convenient for handling and clamping. Take the test specimens from different places in the fabric, avoiding any creases, so that they represent the material as fully as possible. NOTEFor most types of apparatus, it is convenient to cut specimens from the fabric in the form of75mm 75mm squares. 6.
21、2 Condition the specimens to be tested in the standard atmosphere for testing specified in clause5 for at least24h. 6.3 Unless otherwise stipulated, test10 specimens from any sample of fabric submitted. 7 Procedure 7.1 Conduct the test in the standard atmosphere for testing specified in clause5. 7.2
22、 Determine the surface tension of the white spirit by any convenient method to the nearest0.5mN/m. NOTE 1Within the range of the standard atmosphere, the surface tension of white spirit usually lies between24mN/m and27mN/m, with a temperature coefficient of 0.005mN/(m C). The Wilhelmy, stalagmometer
23、, single and double capillary methods have all been found satisfactory for measuring surface tension. NOTE 2White spirit is used due to its ability to wet fabrics, particularly water repellent fabrics, without swelling the fibres. 1) 1 mm head of water = 9.80 665 Pa.BS3321:1986 2 BSI 08-1999 7.3 Soa
24、k the conditioned specimen under about15mm (depth) of white spirit in a glass dish. After soaking for a minimum period of3min remove the specimen with forceps and clamp it on the testing head. Pour a few millilitres of white spirit onto the surface of the fabric; pour just sufficient to cover the fa
25、bric completely after it has bulged slightly under the pressure exerted on the underside during the test. Note the temperature of the white spirit at this stage. NOTEVery open fabric may be more easily tested if the air pressure is allowed to increase on the underside of the specimen and bulge the s
26、pecimen before the white spirit is poured on to cover the surface of the fabric completely. 7.4 Under increasing air pressure, bubbles appear at different places over the upper surface; observe the specimen continuously whilst the pressure is increasing and record, to the nearest millimetre, the pre
27、ssure at which the first bubble appears at the third place on the upper surface. 7.5 Test further specimens until the requisite number of results is obtained. 8 Calculation and expression of results Calculate the equivalent pore radius, r, in micrometres for each specimen by means of the equation: r
28、 = 2T 10 6 / Pg or simplified r=204T/P where Calculate the mean pore radius and quote the result in micrometres to the nearest micrometre. NOTE 1The error introduced by taking =1mg/mm 3for the relative density of water at the temperature of the standard atmosphere for testing is small compared with
29、the variability of the test results. Similarly, although g is known to vary by about0.5% from place to place, the error introduced by assuming a constant value of9810mm/s 2is small compared with the variability of the test. NOTE 2The derivation of the equipment is given in Appendix B. 9 Test report
30、The test report shall include the following particulars: a) the number and date of this British Standard, i.e. BS3321:1986; b) the equivalent pore radius in micrometres for each specimen and the mean pore radius in micrometres for the sample; c) a description of the sample tested; d) details of any
31、deviation from the specified procedure. T is the surface tension of the white spirit at the temperature of the test (in mN/m); g is the acceleration due to gravity (in mm/s 2 ); is the density of water at the temperature of the test (in mg/mm 3 ); P is the bubble pressure expressed in millimetres he
32、ad of water.BS3321:1986 BSI 08-1999 3 Appendix A Advice on a suitable form of apparatus and its use A.1 A suitable form of apparatus is shown diagrammatically inFigure 1. The principal parts are as follows. A. The testing head; a brass cylindrical vessel over which the specimen “e” is clamped by a c
33、lamping ring “a” and screw “b”. It is fitted with a synthetic rubber gasket “c” of50mm internal diameter to make a seal against the specimen. B. Pressure measuring device. C. A stop-valve which serves to direct air to the testing head. D. A variable blow valve set to give the required rate of rise o
34、f pressure in A. E. A stop-valve which directs air to the pressure measuring device. F. Air reservoir of about2.5 L capacity connected to A. This ensures that the rate of flow of air necessary to maintain the required rise of pressure is so large that the loss of air through the fabric when bubbling
35、 begins will not seriously reduce the rate of rise of pressure. G. The air supply. A.2 Using the apparatus shown inFigure 1 the test is conducted as follows. Turn on the air supply. Open valve C to direct air to the test head via reservoir F, and adjust valve D to give the required rate of pressure
36、rise. Leave stop-valve E open during testing. When a bubble appears at the third place in the fabric specimen, Eis closed to allow the pressure reached to be read from the measuring device B. Appendix B Derivation of equation for calculation of equivalent pore radius For a cylindrical tube, the pres
37、sure P necessary to force liquid through it is given by the following equation: where This is the Laplace equation (see for instance ADAMSON, A.W. Physical chemistry of surfaces. New York, J. Wiley,1976). The contact angle is very difficult to measure and therefore a liquid is chosen which completel
38、y wets the material, thus cos Q =1 and the equation becomes: This equation is the same as the simplified equation given in clause8. The pressure is normally measured in millimetres head of water, because either a water manometer is used, or the pressure measuring device is calibrated in millimetres
39、head of water. Thus P = P bg where The liquid used should wet the fabric completely, have low solvent power for proofing materials, cause no swelling of the textile, have constancy of surface tension, non-toxicity, low flammability, freedom from foaming, and moderate cost. White spirit is the only l
40、iquid found that fulfils all these requirements. NOTEA background paper giving the derivation of the method and results of an interlaboratory trial was published in Textile Institute Proceedings, vol.50, no.12, p.768,1959. T is the surface tension of liquid; Q is the contact angle at liquid-solid-ai
41、r interface; r is the radius of tube. p 2T cosQ r - = P b is the head of water; is the density of water; g is the acceleration due to gravity. P 2T r - =BS3321:1986 4 BSI 08-1999 NOTEThis diagram shows one possible way of constructing the apparatus. Figure 1 Suitable apparatusBS3321:1986 BSI 08-1999
42、 Publications referred to BS 245, Specification for mineral solvents (white spirit and related hydrocarbon solvents) for paints and other purposes. BS 1051, Glossary of terms relating to the conditioning, testing and mass determination of textiles. BS 3321:1986 BSI 389 Chiswick High Road London W4 4
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