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18566398802ASTM D4141 涂层室外加速暴露试验的实施方法
标准号ASTM D4141/D4141M-2014
中文名 涂层的黑箱和阳光集中暴露处理用标准操作规程
英文名 Standard Practice for Conducting Black Box and Solar Concentrating Exposures of Coatings
发布日期2014
实施日期
废止日期无
中国标准分类号A29
国际标准分类号87.040 (Paints and varnishes)
发布单位US-ASTM
5.1 As with any accelerated test, the increase in rate of weathering compared to in service exposure is material dependent. Therefore, no single acceleration factor can be used to relate two different types of outdoor weathering exposures. The weather resistance rankings of coatings provided by these two procedures may not agree when coatings differing in composition are compared. These two procedures should not be used interchangeably.
5.2 The procedures described in this practice are designed to provide greater degradation rates of coatings than those provided by fixed angle open-rack outdoor exposure racks. For many products, fixed angle exposures will produce higher degradation rates than the normal end use of the material.
5.2.1 The use of Procedure A (Black Box) instead of an open-rack direct exposure is a more realistic test for materials with higher temperature end use service conditions. For many coatings, this procedure provides greater rates of degradation than those provided by 5x00b0;, equator-facing, open-rack exposures because the black box produces higher specimen temperatures during irradiation by daylight and longer time of wetness. The black box specimen temperatures are comparable to those encountered on the hoods, roofs, and deck lids of automobiles parked in sunlight. The relative rates of gloss loss and color change produced in some automotive coatings by exposures in accordance with Procedure A are given in ASTM STP 781.4
5.2.2 The acceleration of Procedure C is produced by reflecting sunlight from ten mirrors onto an air-cooled specimen area. In the ultraviolet portion of the solar spectrum, approximately 1400 MJ/m2 of ultraviolet radiant exposure (295 to 385 nm) is received over a typical one-year period when these devices are operated in a central Arizona climate. This compares with approximately 333 MJ/m2 of ultraviolet radiant exposure from a central Arizona at-latitude exposure and 280 MJ/m2 of ultraviolet radiant exposure from a southern Florida at-latitude exposure over the same time period. However, the test described by Procedure C reflects only direct beam radiation onto test specimens. The reflected direct beam of sunlight contains a lower percentage of short wavelength ultraviolet radiation than global daylight because short wavelength ultraviolet is more easily scattered by the atmosphere, and because mirrors are typically less efficient at shorter ultraviolet wavelengths. Ultraviolet radiant exposure levels should not be used to compute acceleration factors since acceleration is material dependent.
5.3 The weather resistance of coatings in outdoor use can be very different depending on the geographic location of the exposure because of differences in ultraviolet (UV) radiation, time of wetness, temperature, pollutants, and other factors. Therefore, it cannot be assumed that results from one exposure in a single location will be useful for determining relative weather resistance in a different location. Exposures in several locations with different climates that represent a broad range of anticipated service conditions are recommended.
5.4 Because of year-to-year climatological variations, results from a single exposure test cannot be used to predict the absolute rate at which a material degrades.
Note 3x2014;Several years of repeat exposures are typically needed to get an x201c;averagex201d; test result for a g......
5.1与任何加速试验一样，与在役暴露相比，风化速率的增加取决于材料。因此，不能使用单一的加速系数来关联两种不同类型的室外风化暴露。当比较成分不同的涂层时，这两种程序提供的涂层耐候性等级可能不一致。这两种程序不应互换使用。
5.2本实施规程中描述的程序旨在提供比固定角度开放式机架户外暴露机架更高的涂层降解率。对于许多产品，固定角度曝光将产生比材料正常最终用途更高的降解率。
5.2.1使用程序A（黑匣子）代替开架直接暴露，是对具有更高温度最终使用条件的材料进行的更现实的试验。对于许多涂层，该程序比5x00b0提供的降解率更高；，面向赤道的开放式机架暴露，因为黑匣子在日光照射期间产生更高的样本温度，且潮湿时间更长。黑盒样本的温度与停放在阳光下的汽车的发动机罩、车顶和甲板盖上的温度相当。ASTM STP 781.4中给出了根据程序A暴露在某些汽车涂料中产生的光泽度损失和颜色变化的相对速率
5.2.2程序C的加速是通过将阳光从十面镜子反射到风冷试样区域而产生的。在太阳光谱的紫外线部分，当这些设备在亚利桑那州中部气候下运行时，在典型的一年时间内接收到约1400 MJ/m2的紫外线辐射暴露（295至385 nm）。与此相比，在同一时间段内，亚利桑那州中部纬度地区的紫外线辐射照射量约为333 MJ/m2，佛罗里达州南部纬度地区的紫外线辐射照射量约为280 MJ/m2。然而，程序C中描述的试验仅将直射光束辐射反射到试样上。由于短波紫外线更容易被大气散射，而且镜子在短波紫外线波长下的效率通常较低，因此反射的阳光直射光束所含短波紫外线辐射的百分比低于全球日光。紫外线辐射暴露水平不应用于计算加速度系数，因为加速度取决于材料。
5.3由于紫外线（UV）辐射、湿润时间、温度、污染物和其他因素的差异，户外使用的涂料的耐候性可能因暴露的地理位置而大不相同。因此，不能假设单一位置的一次暴露结果将有助于确定不同位置的相对天气阻力。建议在不同气候条件下的多个位置进行暴露，这代表了广泛的预期使用条件。
5.4由于年复一年的气候变化，单次暴露试验的结果不能用于预测材料降解的绝对速率。
附注3x2014；通常需要几年的重复暴露才能获得x201c；平均x201d；g……的测试结果。。。。。。