Conductive Elastomer Gasket Design
导电橡胶垫片设计
Gasket Design
垫片设计
Gasket Junction Design
垫片接头设计
The ideal gasketing surface is rigid and recessed to completely house the gasket. Moreover it should be as conductive as possible. Metal surfaces mating with the gasket ideally should be non-corrosive. Where reaction with the environment is inevitable, the reaction products should be electrically conductive or easily penetrable by mechanical abrasion. It is here that many gasket designs fail. The designer could not, or did not treat the mating surface with the same care as that given to the selection of the gasketing material.
理想的垫片安装表面应为刚性且为内嵌结构，以能够完全容纳垫片。此外，其应尽可能导电。与垫片相接触的金属表面理想状态下应不具有腐蚀性。如其无法避免与环境发生反应，则反应产品应具有导电性，或易于通过机械磨蚀穿透。许多垫片未能达到此要求。设计人员无法，或未能像选择垫片安装材料一样，细心地对配合表面进行处理。
By definition, a gasket is necessary only where an imperfect surface exists. If the junction were perfect, which includes either a solidly welded closure, or one with mating surfaces infinitely stiff, perfectly flat, or with infinite conductivity across the junction, no gasket would be necessary. The more imperfect the mating surfaces, the more critical the function of the gasket. Perfect surfaces are expensive. The final solution is generally a compromise between economics and performance, but it should not be at the expense of neglecting the design of the flange surfaces.
根据定义，仅当存在缺陷表面时才需要使用垫片。如果连接完好，其中包括焊接可靠的外壳或配合表面极坚硬、平整或在连接处具有无限导电性时，则将不需要使用垫片。配合表面越不完好，则垫片的功能越重要。完好的表面需要高昂的成本。因此，最终的解决方法一般是综合地考虑经济性和性能，但不得以忽略凸缘表面的设计为代价。
The important property that makes a conductive elastomer gasket a good EMI/EMP seal is its ability to provide good electrical conductivity across the gasket-flange interface. Generally, the better the conform-ability and conductivity, the higher the shielding effectiveness of the gasket. In practice, it has been found that surface conductivity of both the gasket and the mating surfaces is the single most important property that makes the gasketed seam effective; i.e., the resistance between the flange and gasket should be as low as possible.
导电性橡胶垫片能够成为良好的 EMI/EMP 密封件的一个重要特性是其能够在垫片凸缘之间的交界面上提供良好的导电性。一般而言，配合能力和导电性越强，则垫片的屏蔽有效性越高。在使用中已经发现，垫片和配合表面的表面导电性是保证垫片安装接缝有效的唯一最重要属性，即应保证凸缘和垫片之间的电阻尽可能的低。
At this stage of the design every effort should be given to choosing a flange that will be as stiff as possible consistent with the construction used and within the other design constraints.
在此设计阶段，在保证与所使用结构相符和符合其他设计条件的前提下，应尽最大努力地选择刚性最大凸缘。
1. Flange Materials
1. 凸缘材料

华译网上海翻译公司曾经翻译过大量有关导电橡胶垫片设计资料文件，Beijing Chinese Subtitling Translation Service Agency has translated many technical documents about Conductive Elastomer Gasket Design.
Flanges are generally made of the same material as the basic enclosure for reasons of economy, weldability, strength and resistance to corrosion. Wherever possible, the flanges should be made of materials with the highest possible conductivity. It is advisable to add caution notes on drawings not to paint the flange mating surfaces. If paint is to be applied to outside surfaces, be sure that the contact surfaces are well masked before paint is applied, and then cleaned after the masking tape is removed. If the assembled units are subject to painting or repainting in the field, add a autionary note in a conspicuous location adjacent to the seal that the seal areas are to be masked before painting.
考虑到经济性、可焊接性、刚度和耐腐蚀性，凸缘材料一般与外壳主体材料相同。。在可能处，应采用具有最高导电性的材料加工凸缘。建议在图纸上使用警告注明，不要在凸缘配合表面刷漆。如果要在外表面上刷漆，应确保在刷漆前使用胶带将接触表面盖好，然后拆下遮盖胶带后，对其进行清洁。如果组合单元需要在现场刷漆或再次刷漆，则应在靠近密封的显眼位置添加警示说明，注明将密封区域遮盖好后再刷漆。
Ordinarily, the higher the conductivity of a material, the more readily it oxidizes – except for noble metals such as gold and silver. Gold is impervious to oxidation, and silver, although it oxidizes, forms oxides that are soft and relatively conductive.
一般而言，除金银等贵金属外，材料的导电性越强，则其越易于发生氧化作用。金不会发生氧化，而银即使会发生氧化，但其形成的氧化层非常软且导电性较好。
Most oxides, however, are hard. Some of the oxide layers remain thin while others build up to substantial thickness in relatively short time. These oxides form insulating, or semi-conducting films at the boundary between the gasket and the flanges. This effect can be overcome to a degree by using materials that do not oxidize readily, or by coating the surface with a conductive material that is less subject to oxidation. Nickel plating is generally recommended for aluminum parts, although tin has become widely accepted. Zinc is primarily used with steel. Consult the applicable specifications before selecting a finish. A good guide to finishing EMI shielded flanges for aerospace applications has been published by SAE Committee AE-4 (Electromagnetic Compatibility) under the designation ARP 1481. A discussion of corrosion control follows later in this guide.
不过，大多数的氧化物都非常坚硬。有些氧化层会保持较薄，但有些氧化层会在较短的时间内形成较大的厚度。这些氧化物会在垫片和凸缘之间的界面上形成绝缘或半绝缘膜。我们可以通过采用不易于发生氧化的材料，或在配合表面上涂装一层不易于发生气体的导电性材料，在一定程度上克服此问题。对于铝件而言，一般建议采用镀镍处理，尽管镀锡处理已被广泛接受。钢铁件一般采用镀锌处理。在选择表面处理前，请查看适用的规范。SAE 委员会 AE-4 （电磁兼容性）在 ARP 1481 中针对航天应用，对 EMI 屏蔽凸缘的表面处理方式提供了良好的指导原则。在该指南中的后面内容中，讨论了有关腐蚀控制的问题。
2. Advantages of Grooved Designs
2. 开槽设计的优点
All elastomer materials are subject to “Compression Set,” especially if over compressed. Because flange surfaces cannot be held uniformly flat when the bolts are tightened (unless the flanges are infinitely stiff), gaskets tend to over compress in the areas of the bolts. Proper groove design is required to avoid this problem of over compression. A groove also provides metal-to-metal contact between the flange members, thereby reducing contact resistance across the junction.
所有的橡胶材料均易于发生“压缩形变”，特别是在过度压紧时。因为在螺栓拧紧时，凸缘表面无法保持平整（除非凸缘具有无限的刚性），螺栓区域的垫片易于发生过压紧现象。因此，需要采用开槽设计，以避免过压紧问题。同时，开槽还可在凸缘构件之间提供金属接触，因此，可降低连接处的接触电阻。
A single groove will suffice for most designs. Adding a second groove parallel to the first adds approximately 6 dB to the overall performance of a single-groove design. Adding more grooves beyond the second does not increase the gasketing effectiveness significantly.
对于大多数设计而言，单槽结构即足够。如果再添加一条与第一条槽口相平行的开槽，则可较单槽口设计的总体性能再提高约 6dB 左右。当超过两条开槽后，再添加开槽也无法再明显地提高垫片有效性。