Very often, the design of the equipment enclosure will dramatically limit the choice of gasket materials. Some enclosures are lightweight aluminium or even plastic with very little potential for withstanding distortion during compression of the shielding gasket. Normally, the more robust the enclosure is the wider the range of materials that can be employed for gasketing. Similarly, wide and well reinforced flanges permit higher compressive forces particularly where limit stops are fitted.

Possibly the most difficult configuration for conventional shielding exists where a 'knife-edge' return on a door or cover is to mate with a conductive gasket, in addition to providing an environmental seal to IP55 [PDF] or higher. If the enclosure can be modified to feature an additional return edge or flat where the knifeedge originally finished, the problem is easily solved but this is not always possible and is usually costly.  Also remember:

¡ñ Mating surfaces must be clean, flat, smooth and conductive (no paint, preservative, oil or grease should be visible).

¡ñ Ideal fixings are outside the shielded envelope and particular attention should be paid to screws/bolts passing through the enclosure to secure coverplates in position.  

¡ñ Avoid gasket materials that are too hard for the type of enclosure.  

¡ñ Avoid knife-edges wherever possible.

¡ñ Consider the environment and select gasket materials that are suitable and will not degrade, e.g. fluorosilicone rubber instead of plain silicone where hydrocarbon contamination is likely.    

¡ñ Consider the operating temperature range. 

¡ñ Do not over-engineer the design. The most expensive materials are not always the right ones for the job.

¡ñ  Do not under-engineer to save money, this does not work in the long-term.   

¡ñ Do not over specify. 100dB may be comfortable but will 60dB solve the problem?

¡ñ Use standard or 'catalogue' products wherever possible.   

¡ñ Consider the possibility of Galvanic Corrosion.