Figure 15. Shielding Effectiveness vs. Applied Pressure
图 15. 屏蔽效果与所施加压力之间的关系图
Thus, in determining the performance to be expected from a junction, find the value for an applied pressure which is 10 percent less (for βd = 2) than the value exerted by the bolts directly adjacent to the gasket. For example, examine a portion of a typical gasket performance curve as shown in Figure 16.
因此，在确定接合处可能达到的性能时，首先确定较垫片邻近螺栓所施加压力小 10% 的压力值（ βd = 2），然后找到该压力值对应的电气性能。例如，按图 16 所示，检查垫片某一部分的性能曲线。
The average shielding effectiveness of the gasketed seam is a function of the mean applied pressure, pm.
对于使用了垫片的接缝，其平均屏蔽效果是平均压力 pm的函数。
For spacings which approach or are equal to one-half wavelength, the shielding effectiveness is a function of the minimum pressure, p1. Therefore, the applied pressure must be 20 percent higher to achieve the required performance. For this condition, the space between the fasteners can be considered to be a slot antenna loaded with a lossy dielectric. If the slot is completely filled, then the applied pressure must be 20 percent higher as cited. Conversely, if the slot is not completely filled (as shown in Figure 17), the open area will be free to radiate energy through the slot.
对于接近或等于波长一半的间距，屏蔽效果应由最小压力 p1 确定。因此，所施加的压力必须高出 20%，以达到所需的性能。在这种情况下，紧固件之间的间距可被视为一个带有损耗介质的狭缝天线。如果该狭缝被完全填实，则所施加的压力必须高 20％。相反，如果该狭缝未被完全填实（如图 17 所示），则该敞开区域将会被辐射能自由穿过狭缝。
Figure 16. Typical Gasket Performance Curve
图 16. 垫片典型性能曲线
Figure 17. Unfilled Slot is Free to Radiate When Spacing is Equal to 1/2 Wavelength
图 17.当间距等于 1/2 波长时，辐射可自由穿过未填实的狭缝
The cut-off frequency for polarizations parallel to the long dimension of the slot will be determined by the gap height, h. The cut-off frequency for the polarization vector perpendicular to the slot will be determined by the width of the slot, w. The attenuation through the slot is determined by the approximate formula
对于平行于狭缝较长方向的极化矢量，其截止频率将由空隙的高度 h 确定。对于垂直于该方向的极化矢量，其截止频率将由空隙的宽度 w 确定。通过狭缝的衰减由下面的近似公式确定
where
其中
d = the depth of the slot,
d = 狭缝深度，
and
和
λc is equal to 2w or 2h, depending upon the polarization being considered.
λc 等于 2w 或 2h，具体值取决于所考虑的极化分量。
This example also illustrates why leakage is apt to be more for polarizations which are perpendicular to the seam.
本例还说明了为什么垂直接缝的极化分量更易于发生泄漏。
For large values of βd, the percentage adjustments must be even greater. For example, the percentage increase required to satisfy βd = 3 is 64 percent. It is desirable, therefore, that βd should be kept as small as possible. This can be achieved by using stiff flanges or spacing bolts closer together.
对于较大的 βd 值，调节百分比必须越大。例如，要满足 βd = 3 时的情况，百分比增加必须为 64 ％。因此，应 βd 应尽可能地保持较小的值。我们可以通过使用刚性凸缘或减小螺栓之间的间距，还实现该目的。
华译网上海翻译公司曾经翻译过大量有关凸缘设计资料文件，Beijing Chinese Subtitling Translation Service Agency has translated many technical documents about Flange design.
Designing a Solid-O Conductive elastomer Gasket-in-a-Groove
设计安装于开槽内的实心 O 型导电橡胶垫片
The “solid-O profile” is the most often specified conductive elastomer EMI gasket for several key reasons. Compared to other solid cross sections, it offers the widest deflection range to compensate for poorly toleranced mating surfaces and to provide reliable EMI shielding and pressure sealing. It can be installed in a relatively small space, and is the most easily installed and manufactured. It also tends to be less prone to damage, due to the absence of angles, corners or other cross section appendages.
因为多种重要原因，导电橡胶 EMI 垫片通常规定采用实心 O 型垫片。与其他实心截面相比较，O 型垫片可以提供最大的变形范围，以补偿配合表面之间的公差和提供可靠的 EMI 屏蔽和压力密封作用。其可安装于相对较小的位置，也是最易于安装和加工的垫片类型。同时， O 型垫片还因为不存在夹角或其它特殊截面，不易于发生损坏。
The “gasket-in-a-groove” design offers five significant advantages over surface-mounted EMI gaskets:
“槽内安装垫圈”较平面安装的 EMI 垫圈具有五个重要优点：
1. Superior shielding, due to substantial metal-to-metal contact achieved when the mating surfaces are bolted together and “bottom out”. (Flat die-cut gaskets prevent metal-to-metal contact between mating flange members, which reduces EMI shielding performance – especially in low frequency magnetic fields.)
1. 极佳的屏蔽性，因为当配合表面由螺栓固定在一起的时候，可实现真正的金属之间的接触。（模切平垫圈使凸缘构件的配合表面无法实现金属间接触，降低了 EMI 屏蔽性能，特别在低频磁场中。）
2. Positive control over sealing performance. Controlling the size of the gasket and groove can ensure that required shielding and sealing are achieved with less careful assembly than is required for flat gaskets. In other words, the gasket-in-a-groove is more foolproof.
2. 可有效地控制密封性能通过控制垫片和开槽尺寸，可保证达到所需的屏蔽和密封性能，而不需要像平垫片一样，装配时需要特别小心。换言之，槽内安装垫片使用起来更加安全、简单。
3. Built-in compression stop provided by the groove eliminates the risk of gasket damage due to excessive compression.
3. 开槽提供的 内置压紧挡块 可防止垫片因过度受压而发生损坏。
4. A gasket retention mechanism can be provided by the groove, eliminating the need for adhesives or mounting frames.
4. 开槽可提供垫片固位机制，不需要使用粘合剂或安装框。
5. high current-handling characteristics of the metal-to-metal flange design improves the EMP and lightning protection offered by an enclosure.
5. 金属之间相接触的凸缘设计具有高电流处理能力，可提高外壳的 EMP 和防雷击保护能力。
This section presents the method for calculating groove and gasket dimensions which will permit the shielding system to function under worst-case tolerance conditions. Adherence to these general guidelines will result in optimum shielding and sealing for typical electronics “boxes”. It should be understood that they may not be suitable for designing shielding for sheet metal cabinets, doors, rooms or other large, unconventional enclosures.
本章将介绍开槽和垫片尺寸的计算方法，以使屏蔽系统在最恶劣的公差情况下也可实现屏蔽效果。通过遵守这些一般准则，您的电子器件外壳将能够实现最佳的屏蔽和密封效果。需要说明的是，这些方法不适用于板金机柜、门、房间或其他大型非常见外壳的的屏蔽设计。
Important Notes: The guidelines presented here are intended to consider only “solid O” gasket cross sections. The calculations for hollow O, solid and hollow D, and custom gasket cross sections differ from these guidelines in several key areas.
重要提示：此处所述的指导原则仅针对“实心 O 型”垫片。对于空心 O 型垫片、实心和空心 D 型垫片及其他定制的垫片截面，与此处所述的指导原则在几个重要方面存在差异。
XXXX generally does not recommend bonding solid O gaskets in grooves. If for some reason your design requires gasket retention, contact XXXX ’ Applications Engineering Department for specific recommendations, since the use of adhesives, dove-tailed grooves or “friction-fit” techniques require special design considerations not covered here.
XXXX 建议一般不要在槽内粘接 O 型垫片。如果特定原因，您需要对垫片固位，请联系 XXXX 公司的应用工程部，获取相应的建议，因为使用粘合剂时，燕尾形开槽或“摩擦配合”技术需要特殊的设计注意事项，本指南中未包含此类内容。
Extreme design requirements or unusually demanding specifications are also beyond the scope of the guidelines presented here. Examples would include critical specifications for pressure sealing, exceptionally high levels of EMI shielding, exceptional resistance to corrosion, harsh chemicals, high temperatures, heavy vibration, or unusual mounting and assembly considerations.
同时，在此处所述的指导原则中，也未考虑一些极端的设计要求或要求特别严格的规范。这些情况包括对压力密封具有较重要的规定、要求特别高的 EIM 屏蔽水平、需要特别高的防腐蚀性能、需要在腐蚀性极强的化学环境、高温、高振动下工作及异常的安装和装配注意事项。
Mechanical Considerations Causes of Seal Failure
导致密封失效的机械原因 |
