湿热试验与盐雾试验的主要区别是湿热试验的雾滴没有盐分是蒸馏水,虽然盐滴因其导电率高、叉含氯离子而腐蚀作用剧烈,但对渗透压而言,蒸馏水的活度高,涂层是半透膜,蒸馏水渗入漆膜的能力比盐液强。水分透入漆膜,在两层漆膜之间积聚,会降低层间附着力,而起泡。随后再向深入一步发展,到达漆膜与底板之间,降低附着力,导致漆膜起泡,同时水分与金属底板接触,产生电化学腐蚀作用。在漆膜内吸收水分,会引起漆膜膨胀而产生内应力,降低附着力而起泡,漆膜吸水率在蒸馏水中比盐水中高,就对涂膜的破坏力来说,湿热试验是很苛刻的。
总体概况
湿热试验是将涂有漆膜的样板或实物置于温度和湿度受控制的密闭试验箱内,一定时间后观察起泡、腐蚀及附着力下降等变化,评定涂膜抵抗湿热水汽(有时包含有凝露)能力的试验。考核涂层对湿热带气候的环境适应性和耐蚀能力。湿热试验时,涂层的耐水性和水汽渗透性比一般常温浸水试验失效要快。湿热试验引起的腐蚀不及盐雾试验剧烈。
涂层耐湿热性能检测相关技术标准
标准名称:Standard Practice for Testing Water Resistance of Coatings in 100% Relative Humidity
标准编号:ASTM D2247 - 11
标准概述:Water can cause the degradation of coatings, so knowledge of how a coating resists water is helpful for assessing how it will perform in actual service. Failure in tests at 100 % relative humidity may be caused by a number of factors including a deficiency in the coating itself, contamination of the substrate, or inadequate surface preparation. This practice is therefore useful for evaluating coatings alone or complete coating systems.Tests at 100 % relative humidity are used for specification acceptance, quality control, and research and development for coatings and substrate treatments. Some tests are used for a pass or fail determination at an arbitrary time. A coating system is considered to pass if there is no evidence of water-related failure after a period of time. Other tests are used to monitor degree of failure as a function of exposure time.
标准名称:漆膜耐湿热测定法
标准编号:GB/T 1740-2007
发布日期:2007-09-11
实施日期:2008-04-01
标准概述:本标准规定了色漆、清漆或相关产品的涂层抗高温、高湿环境能力的试验方法。本标准适用于漆膜耐湿热性能的测定。
标准名称:Standard Practice for Testing Water Resistance of Coatings Using Water Fog Apparatus
标准编号:ASTM D1735 - 08
标准概述:This practice covers the basic principles and operating procedures for testing water resistance of coatings in an apparatus similar to that used for salt spray testing.This practice is limited to the methods of obtaining, measuring, and controlling the conditions and procedures of water fog tests. It does not specify specimen preparation, specific test conditions, or evaluation of results.
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