EMI o rings. Those seal ring gaskets are made of silicone compounds, combining environmental sealing with electromagnetic interference protection.
Consisting of metal or metal-coated particles, silicone o rings are filled with silver, silver aluminium, or nickel graphite.
Experienced o ring suppliers UK will be able to advise you on the best type of o ring for your specific application, with EMI o rings, in particular, being highly effective for the automotive, aerospace, industrial, medical, and military sectors.
O ring adhesive
Manufactured from EMI elastomers and solid cords, bonded o rings are designed to provide EMI shielding and environmental sealing capabilities to a range of industries.
The benefits of using EMI shielded o rings are that they provide reliable protection against electromagnetic interference, radio frequency interference, and environmental sealing and electrical conductivity.
Cut by gasket manufacturers, silicone o ring cord ends are bonded together to form a tight seal. This bonding process is carried out via cold bonding or vulcanisation.
Of course, like with anything, there are both pros and cons to each process which we will explore in a little more detail below.
Cold bonding
As the bonding name suggests, cold bonding doesn’t use any heat. Instead, a non-conductive adhesive is placed on the cord ends. Due to not using a compression moulding technique, customers wanting these o rings will experience shorter lead times, and due to the production volume of these rings, cold bonding also helps limit your cost per part.
However, it is important to be aware and note that during the o ring splicing process, if the o ring is spliced incorrectly, the non-conductive adhesive will no longer be effective when the two ends are bonded together.
Providing a reliable shielding for most applications, for you to get the maximum benefit from these o rings, they must be bonded together by experienced gasket fabricators to ensure speed and precision.
Vulcanisation
The vulcanisation process uses heat to join the cut lengths’ ends, using conductive adhesives, creating single, solid o rings from EMI cords or extrusions.
Applied to the ends, the adhesives are then pressed together in a vulcanising press or hot mould.
These o rings can also match the reliability of conductive shielding elastomers, i.e., vulcanised EMI o rings provide reliability and typically meet or exceed the strength of the material it is used alongside.
Vulcanised o rings offer consistency and dependability and should be used in static, non-pressurised environments.
However, compared to cold bonding, lead times are longer, and sometimes costs are slightly higher as this particular process requires compression moulding techniques.
Ultimately you need to select the most appropriate o ring glue and joining method for your application.
Binding agents
We know that EMI o rings are more economical compared to moulded o rings, and they do not compromise performance.
And when a vulcanised o ring uses an EMI bonding agent with the same characteristic as the extruded cord, then EMI penetration or leakage can be prevented.
This is why EMI o rings should be bonded using silicone-based adhesives containing EMI filler as non-silicone glues without EMI filler can create a weaker seal which makes the application more susceptible to leaks.
(Finding the right gasket seal for your application is vital. To support your decision-making you might also be interested in o ring shrinkage and the shrink rate calculation, which you can find more about in our latest post, “O ring squeeze.”)
It’s also important to note that acrylics and other non-silicone glues tend to dry much harder than EMI silicone cord. This means you will often find a `hard spot` in the finished gasket as the acrylic adhesives can’t match the temperature range of the EMI cord material, making them easily breakable.
To prevent these issues and risks of leaks, the vulcanised o ring should use the same EMI bonding agent as the extruded cord, with the bond strength and elongation checked against standard o rings to ensure the highest of standards.
At Specialist Sealing Products, we supply o ring stock to cut and bond using the various methods mentioned above. With a range of options available call us today on xxx to find out more and to see how we can help you.
