Dec, 07 2016

Bonded O-Rings for EMI Shielding

Bonded O-Rings for EMI Shielding

Specialty Silicone Products (SSP) extrudes EMI elastomers into solid cords that come in various stock sizes. Die cutters and other gasket fabricators can convert these cords into bonded O-rings that provide EMI shielding and environmental sealing. To join the ends of cords together, fabricators can use either cold bonding or vulcanization. Each method has advantages and disadvantages, so it’s important to select the technique that best suits your requirements. Here’s what you need to know.

Cold Spliced EMI O-Rings

Cold splicing involves applying a non-conductive adhesive to the cord ends. This joining technique is considered to be “cold” because, unlike vulcanization, there’s no heat involved. With cold spliced O-rings, the absence of compression molding means shorter lead times for your customers. As many as 200 to 400 EMI O-rings can be cold bonded in a single shift, which helps to limit per-part costs. For most applications, cold spliced O-rings provide reliable EMI shielding.  

There are disadvantages to cold bonding, however. For example, because a non-conductive adhesive is used, a cord that’s been spliced incorrectly may permit the passage of certain frequencies. In addition, cold-splicing EMI fluorosilicones can be challenging because of the chemical resistance of the base material. Die cutters and other gasket fabricators may also discover that some customer part drawings require vulcanization even when cold splicing may be a better choice.

Vulcanized EMI O-Rings

Vulcanization is a joining process that uses heat and pressure to create a single, solid O-ring from EMI cords or extrusions. Engineers like that vulcanized EMI O-rings are made from a single electrically-conductive material, and that a non-conductive adhesive isn’t used. They also like that vulcanized O-rings can match the reliability of conductive shielding elastomers that are supplied in other forms (such as die cut gaskets). Plus, vulcanized bonds typically meet or exceed the strength of the material itself.   

Vulcanized EMI O-rings have some disadvantages, however. Lead times are longer than with cold splicing. Tooling costs are higher, too. Ultimately, the part costs of vulcanized EMI O-rings are higher because molding labor is required. For more information about vulcanized O-rings and cold-spliced O-rings for EMI shielding, or to order EMI cordstock from SSP, email Dominic Testo or contact SSP on-line