【導(dǎo)讀】Lic. ens. ed. copy. :T. he. Univ. ers. ity. of. H. ong. Kong,The. Univ. ers. ity. of. H. ong. Kong,Vers. ion. correc. tas. of. 25/. 03/. 2020. 09:. 08,BSI. Paintsandvarnishes. —Coatingmaterials. exteriorwood. ICS. Lic. ens. ed. copy. :T. he. Univ. ers. ity. of. H. ong. Kong,The. Univ. ers. ity. of. H. ong. Kong,Vers. ion. correc. tas. of. 25/. 03/. 2020. 09:. 08,(c. BSI. BSEN927-2:2020. Nationalforeword. publishedunderthe. PolicyandStrategy. 2020. ©BSI2020. ISBN9780580560149. DateComments. Lic. ens. ed. copy. :T. he. Univ. ers. ity. of. H. ong. Kong,The. Univ. ers. ity. of. H. ong. Kong,Vers. ion. correc. tas. of. 25/. 03/. 2020. 09:. 08,(c. BSI. EUROPEANSTANDARD. NORMEEUROPÉENNE. EUROPÄISCHENORM. EN927-2. April2020. BSEN927-2:2020. EnglishVersion. versions.Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuan

　　

【正文】 aximum difference39。 constraint restricts the spread of the failure distribution, which if too broad indicates unacceptable variance outside the established test capability. In this case the test is declared invalid and is repeated. EN 9272:2020 (E) 11 Licensed copy: The University of Hong Kong, The University of Hong Kong, Version correct as of 25/03/2020 09 BSI Despite the simplicity of the test, experience has shown it to be a meaningful indication of performance. Nevertheless a free panel test is very different from real building construction, and users might also need to pay regard to their own experience or that of the manufacturer of the coating material before making a final selection from qualifying systems. Some systems might meet more than one performance profile and the manufacturers? remendations should be considered. Attention is also drawn to the fact that in order to provide a mon basis for parison the weathering test piece is pine containing predominantly sapwood. Coating performance can be different on some other substrates, such as: – other soft wood species such as spruce, – pine heartwood, – hardwoods and – softwoods (including pine itself) which have been stabilized with an appropriate pretreatment. It is optional to test the coating over alternative substrates and where this information is available it will improve the reliability and relevance of the selection of coating systems for the alternative substrates. Exposure conditions As noted in EN 9271 the exterior performance of a coating will be strongly influenced by the climate and also by the construction. Within any climatic zone there will be periods of fluctuating weather, from year to year, and within a single year. Thus while a given exposure site might on average provide extreme conditions, there will be moderate or hard periods that might fortuitously coincide with the test exposure. Knowledge of the influence of meteorological conditions on performance is not sufficiently advanced to predict the effect on relative performance. Therefore the test method uses the performance of a wellcharacterized product (the ICP) on a standard substrate, as indicative of the prevailing conditions during the period of test. However because the test panel is not sheltered it can only experience medium or severe, but not mild, conditions (see Table 2 in EN 9271:1996). Coating systems should ideally be tested in a region with exposure conditions similar and representative of where they are to be used. Where this is not practicable, users will need to make an informed judgement about the likely prevailing conditions where the tested system is to be used relative to the test exposure site. In general, a coating system which performs well under severe conditions will perform even better under medium or mild conditions. If the climate prevailing during a specific exposure test turns out to be moderate, then it is not possible to predict with confidence performance of the tested systems under severe conditions. There is no alternative but to retest at a site where a hard or extreme climate can be expected. Water permeability See EN 9275 for definition of terms and test methods. Transport of water (liquid or vapour) through a coating will cause dimensional changes in a wooden substrate which might in turn lead to splitting of the wood. In constructed units such as windows the dimensional changes might cause the seizure of opening lights, or the working loose of sealants. It is largely for this reason that enduses are categorized according to the need for dimensional stability (stable, semistable and non stable). In addition to causing dimensional change a build up of water is a prerequisite to wood rot which can occur if the moisture content rises above 20 %. There are thus two factors to be considered in assessing the water transport properties in relation to coating selection: [i] rate of moisture uptake。 [ii] average moisture content over an extended period of exposure. EN 9272:2020 (E) 12 Licensed copy: The University of Hong Kong, The University of Hong Kong, Version correct as of 25/03/2020 09 BSI The permeability test provides an indication of likely moisture uptake which directly links with the required level of stability. However, moisture transport is subject to many variables including age and history of the coating and numerous design details, and at present no prediction can be made about average moisture content. Therefore maximum, but not minimum, levels of liquid water absorption are set in Table 1. Blocking Where two coated surfaces are pressed into contact, as in a window or door jamb, there is a potential risk that the coatings will adhere and cause damage on parting. This phenomenon is known as blocking. The test indicates whether this is likely to be a problem. Stackability This test relates to the blocking that might occur if coated units are stacked without protection, it applies specifically to industrial coating and gives an indication of the likelihood to damage at different mass loadings. Compatibility with glazing pounds and profiles This test evaluates patibility of coatings with both sealing pounds and sealing profiles. Testing should cover sticking, resoftening and discoloration. Blue stain in service Blue stain in service arises from colonization during or after manufacture as opposed to the growth of blue stain fungi already present in the timber. It is particularly associated with Aureobasidium pullulans and is a potential problem for transparent and semitransparent coatings, though it can also disfi