A 7-mil wet film coating will yield a dry film thickness of 4 mils, which is the minimum thickness required to attain the necessary corrosion and electrical values referenced in XXXX ’ Technical Bulletin 30. The coating thickness plays and corrosion properties. Thinner coatings of 1-3 mils do not exhibit the corrosion resistance of 4-5 mil coatings.
7 mil 的湿膜厚度可形成 4 mil 的干膜厚度，这是要达到 XXXX 技术公告 30 中的规定耐腐蚀和导电性所需的最小干膜厚度。涂层厚度是影响导电和防腐蚀性能的重要因素。较薄（1-3 mil）涂层所体现出的防腐蚀性要低于 4-5 mil 的涂层。
The coating will be smooth to the touch when cured. It is recommended that the coating be cured at room temperature for 2 hours followed by 250°F +/-10°F for one-half hour whenever possible. Alternate cure cycles are available, but with significant differences in corrosion and electrical properties. Two alternate cure schedules are two hours at room temperature followed by 150°F for two hours, or 7 days at room temperature.
涂层固化后应摸起来光滑。建议涂层在室温下固化 2 小时，然后如可能，在 250°F +/-10°F 的温度下固化半个小时。还有其他可用的替代固化步骤，但产生的防腐蚀和导电特性会有很大差异。两种替代固化方法是在室温下固化两个小时，然后在 150°F 下固化两个小时，或在室温下固化 7 天。
Full electrical properties are achieved at room temperature after 7 days. It should be noted that the 250°F cure cycle reflects the ultimate in corrosion resistance properties. The 150°F/2 hour and room temperature/7 day cures will provide less corrosion resistance than the 250°F cure, but are well within the specification noted in Technical Bulletin 30.
在室温下固化 7 天后，可以达到完整的导电特性。需要说明的是，250°F 的固化循环可以达到最佳的防腐蚀特性。150°F下两小时固化和 7 天室温固化方法所能达到的防腐蚀能力要低于 250°F 固化处理，但可达到技术公告 30 中规定的参数值。
1091 Primer
1091 底漆
Because of the sensitivity of surface preparation on certain substrates and the availability of equipment to perform the etching of aluminum prior to the conversion coating, XXXX has introduced 1091 primer, which is an adhesion promoter for CHO-SHIELD 2000 series coatings. When used in conjunction with an alkaline etch or chemical conversion coating per MIL-DTL5541F, Type I, Class 3, the 1091 primer will provide maximum adhesion when correctly applied. (See Technical Bulletin 31.) This primer is recommended only for the 2000 series coatings on properly treated aluminum and is not recommended for composites.
考虑到涂装铬酸盐涂层前特定基材表面制备的敏感性及铝材清洁设备的可用性，XXXX 推出了 1091 底漆，该产品可作为 CHO-SHIELD 2000 系列涂层的增粘剂。当与碱性蚀刻或化学转化层（按 MIL-DTL5541F I 型 3 类）一起使用时，如能正确使用，1091 将提供最高的粘合性。（见技术公告 31）仅经过正确处理的铝材在涂装 2000 系列涂层时建议使用此底漆，不建议用作复合涂层。
For further assistance on the application of CHO-SHIELD 2000 series coatings on other metallic and non-metallic substrates, contact XXXX ’Applications Engineering Department.
有关 CHO-SHIELD 2000 系列涂层在其他金属和非金属底材上的涂装方法，请联系 XXXX 公司的应用工程部门。
Galvanic Corrosion
电化腐蚀
The most common corrosion concern related to EMI gaskets is galvanic corrosion. For galvanic corrosion to occur, a unique set of conditions must exist: two metals capable of generating a voltage between them (any two unlike metals will do), electrically joined by a current path, and immersed in a fluid capable of dissolving the less noble of the two (an electrolyte). In summary, the conditions of a battery must exist. When these conditions do exist, current will flow and the extent of corrosion which will occur will be directly related to the total amount of current the galvanic cell produces.
EMI 垫片最常见腐蚀问题就是电化腐蚀。要发生电化腐蚀，必须存在一套特殊的条件：两种金属可在二者之间形成电压（任何相异金属均满足此条件），二者通过电流通道电气连接，且浸于能够溶解二者中次贵金属的液体中（电解液）。总起来说，必须存在电池条件。当存在上述条件时，将会形成电流，而腐蚀程度将直接与原电池形成的总电流量相关。
When an EMI gasket is placed between two metal flanges, the first condition is generally satisfied because the flanges will probably not be made of the same metal as the gasket (most flanges are aluminum or steel, and most EMI gaskets contain Monel, silver, tin, etc.). The second condition is satisfied by the inherent conductivity of the EMI gasket. The last condition could be realized when the electronic package is placed in service, where salt spray or atmospheric humidity, if allowed to collect at the flange/ gasket interface, can provide the electrolyte for the solution of ions.
当 EMI 垫片安装于两个金属凸缘之间时，因为两个凸缘可能是由两种不同的金属制成，因此，一般会满足第一个条件（大多数凸缘为铝或钢材制成，大多数的 EMI 垫片含蒙耐合金、银、锡等）。由于 EMI 垫片固有的导电性，第二个条件也满足。当电子仪器组件的使用环境具有盐雾或湿气，如盐雾或湿气会在凸缘和垫片之间的界面处汇集，则可提供用于离子融解的电解液，进而满足第三个条件。
Many users of EMI gaskets select Monel mesh or Monel wire-filled materials because they are often described as “corrosion-resistant.” Actually, they are only corrosion- resistant in the sense that they do not readily oxidize over time, even in the presence of moisture. However, in terms of electrochemical compatibility with aluminum flanges, Monel is extremely active and its use requires extensive edge sealing and flange finish treatment to prevent galvanic corrosion. Most galvanic tables do not include Monel, because it is not a commonly used structural metal. The galvanic table given in MIL-STD-1250 does include Monel, and shows it to have a 0.6 volt potential difference with respect to aluminum – or almost the same as silver.
许多 EMI 垫片的用户选择蒙耐金属网或填有蒙耐金属网的材料，因为这些材料经常被称作“耐腐蚀”材料。实际上，这些材料的耐腐蚀性仅是长时间不易于发生氧化，即使在潮湿位置。然而，就与铝凸缘之间的电化学兼容性而言，蒙耐合金极具活性；当使用蒙耐合金时，需要对其大量的边缘进行密封，同时，应对凸缘进行表面处理，以防止发生电化腐蚀。大多数的电化腐蚀表不包括蒙耐合金，因为，这种它不是常用的结构金属。MIL-STD-1250 中的电化腐蚀表包含了蒙耐合金，表中显示，其与铝之间的电压差为 0.6，或是与银基本相同。
A common misconception is that all silver-bearing conductive elastomers behave galvanically as silver. Experiments designed to show the galvanic effects of silver-filled elastomer gaskets in aluminum flanges have shown less corrosion than predicted. Silver-plated-aluminum filled elastomers exhibit the least traces of galvanic corrosion and silver-plated-copper filled elastomers exhibit more. (See Table 3).
我们有一个常见的误区是许多人认为所有含银导电橡胶的电化腐蚀性能与银相同。但试验表明，安装于铝凸缘内的含银橡胶垫片因电化反应产生的腐蚀低于预计值。含有镀银铝的橡胶电化腐蚀迹象最小，含有镀银铜表现出更高的橡胶电化腐蚀迹象。(请参阅 表 3)。
Tables of galvanic potential do not accurately predict the corrosivity of metal-filled conductive elastomers because of the composite nature of these materials. Also, these tables do not measure directly two important aspects of conductive elastomer “corrosion resistance”: 1) the corrosion of the mating metal flange and 2) the retention of conductivity by the elastomer after exposure to a corrosive environment.
因为含金属导电橡胶材料的组合特性，电化腐蚀表无法精确地预测含金属橡胶材料的电化腐蚀性。同时，这些表格未直接测量导电橡胶“耐腐蚀性”的以下两个重要方面：1) 配合金属凸缘的腐蚀性和 2) 在暴露于腐蚀性环境中后，橡胶能够保持的导电性。
Instead of using a table of galvanic potentials, the corrosion caused by different conductive elastomers was determined directly by measuring the weight loss of an aluminum coupon in contact with the conductive elastomer (after exposure to a salt fog environment). The electrical stability of the elastomer was determined by measuring its resistance before and after exposure. Figure 5a describes the test fixture that was used. Figure 5b shows the aluminum weight loss results for several different silver-filled conductive elastomers. The aluminum weight loss shows a two order of magnitude difference between the least corrosive (1298 silver-platedaluminum) and most corrosive (1215 silver-plated- copper) filled elastomers. For silver-containing elastomers, the filler substrate that the silver is plated on is the single most important factor in determining the corrosion caused by the conductive elastomer
在确定各种导电橡胶造成的腐蚀性时，不要使用电化腐蚀表，而是直接测量与导电橡胶相接触的铝试样的重量损失（在接触盐雾环境后）。通过测量接触盐雾环境后的电阻，确定橡胶的电气稳定性。图 5a 所示为使用的测试夹具。图 5b 所示为不同的含银导电橡胶导致铝材发生的重量损失。铝的重量损失显示了最不易腐蚀（1298 镀银铝）和最易腐蚀（1215 镀银铜）橡胶之间的差值。对于含银橡胶，镀银的填料基材类型是确定导电橡胶腐蚀性的最重要因素。
Figure 5c shows the weight loss results for nickel and carbon-filled elastomers compared to 1298. The nickel-filled materials are actually more corrosive than the silver-plated-aluminum filled elastomers. The carbon-filled materials are extremely corrosive.
图 5c 显示了含镍和含碳橡胶所造成的重量损失与 1298 之间的比较。含镍材料的腐蚀能力实际上要高于含镀银铝的橡胶。含碳材料最具腐蚀性。 |
