Why Choose High-Performance Vulcanized EMI O-Rings?

EMI-Shielded o-rings (or EMI o-rings) are designed to provide reliable protection against electromagnetic interference (EMI), radio frequency interference (RFI), as well as ensure environmental sealing and electrical conductivity. EMI o-rings are commonly utilized within the medical, automotive, aerospace, and military industries.

The purpose of this article is to demonstrate why the selection of high-performance vulcanized EMI o-rings is most often the best economic decision vs. molded o-rings. This, while also not compromising critical performance requirements.

Below, is a high-level view of the advantages and disadvantages of vulcanizing and molding EMI o-rings.

EMI O-Ring Shielding Performance Environmental Resistance Cost Lead Time

Inside Diameter <3 Inches

Mil-Spec Applications
Vulcanized O-Ring Excellent Excellent $$$ 0 – 2 Weeks No No
Molded O-Ring Excellent Excellent $$$$$ 6 – 10 Weeks Yes Yes

Vulcanization with EMI-Based Bonding Agents

To prevent EMI penetration or leakage, the vulcanized o-ring must use an EMI bonding agent with the same characteristic as the extruded cord. Global O-Ring and Seal ensures EMI o-rings are bonded using silicone-based adhesive containing EMI filler to stop interference from entering or leaving the seal.

Other manufacturers may use non-silicone glues without EMI filler, which can cause EMI leakage and make for a weaker seal. Jump to differences in bonding agents.

Costs of Molded EMI-Shielded O-Rings

EMI/RFI o-ring compounds can be costly, and the molding process generates wasted uncured compound. The cost of the wasted compound is built into the overall price of the o-ring.

Vulcanized EMI o-rings eliminate this wasted compound expense entirely. Lead times are improved significantly because the extruded cord is inventoried and ready to be vulcanized on

Non-Silicone glues, such as acrylics, dry to a much harder durometer than the EMI silicone cord itself. This leaves a “hard spot” in the finished gasket where acrylic adhesives cannot match the temperature range of the EMI cord material, making them susceptible to breaking.

To prevent EMI penetration or leakage, the vulcanized o-ring must use an EMI bonding agent with the same characteristic as the extruded cord. Global O-Ring and Seal ensures vulcanized EMI o-rings are bonded with silicone-based adhesive containing EMI filler to stop interference from entering or leaving the seal.

Validation of High-Performance in Vulcanized EMI O-Rings

To demonstrate the advantages of our vulcanized EMI o-rings, a series of trials were performed using various profile shapes and sizes of EMI cord. Silicone EMI adhesive was utilized in the bonding of the cord. During each trial, we visually inspected the bonded EMI o-rings for defects. We also measured bond strength and elongation when comparing the data to standards.

Statistical analysis validated the consistency in the production of the vulcanized o-rings to protect against electromagnetic interference (EMI) and radio frequency interference (RFI). Further, these electrically conductive EMI/RFI o-rings served as dependable environmental sealing as their molded counterparts.

When to Use Molded EMI O-Rings

The primary driver of molded o-rings is when they must meet a military specification that explicitly calls out molded rings (MIL-DTL-83528C).

Another instance includes EMI o-rings that are too small cannot be vulcanized and would require molding. The minimum size that can be vulcanized is dependent on the cross-section and the size of the tool. You can always call our experienced Sales Team at 832-448-5550 to determine the appropriate size if you know the cross-section.

In all other applications, we recommend vulcanized EMI o-rings as they are typically utilized in static, non-pressurized environments. For more information, check out our dedicated page for EMI-Shielded O-Rings.

Not All Bonding Agents Are the Same

Currently, many manufacturers vulcanize EMI o-rings with a non-conductive RTV silicone adhesive lacking EMI filler. This makes it possible for radio waves to penetrate the joint and make way for EMI interference within the product. Manufacturers using a non-conductive, non-silicone adhesive also risk EMI leakage.

Non-Silicone glues, such as acrylics, dry to a much harder durometer than the EMI silicone cord itself. This leaves a “hard spot” in the finished gasket where acrylic adhesives cannot match the temperature range of the EMI cord material, making them susceptible to breaking.

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