Multishield Oriented Wire Gaskets, or embedded wire elastomer materials come in three main types. The basic principle in each case is based on moulding (encapsulating), either, individual wires, woven wire mesh or expanded mesh into an elastomer sheet. The resultant gasket material in each case has the combined properties of excellent low contact resistance and a high level of environmental sealing afforded by the elastomer carrier.
In Multishield (formerly Duroseal), individual wires are moulded into a silicone sheet so that they are orientated at right angles to the sealing faces of the gasket. When compressed each wire acts as a point contact electrically connecting the two sealing faces whilst the silicone provides a very effective hermetic seal. One advantage of this gasket type is that there is no conductivity possible across the width of the gasket which can be useful in some applications.
The three main elastomer types are:
Silicone ZZ-R-765 2B 40 – a 40 shore A hard silicone elastomer with excellent high temperature performance
Silicone sponge AMS 3195 – a sponge elastomer carrier where lower compression force is required
Fluorosilicone Mil-R-25988 50 – a fuel and oil resistant elastomer with a wide temperature operating range and excellent ageing characteristics
In combination with the above the two main wire types normally used are
Monel (copper/nickel) alloy – a corrosion resistant alloy that provides reliable long term shielding performance
Aluminium – where improved galvanic compatibility with aluminium enclosures is required
This material is available in strips, fabricated sheets or lengths. Small gaskets can be supplied die cut as a single piece whilst larger gaskets must be assembled from strips (frame style). We would normally recommend that we supply gaskets pre-fabricated to your drawing.
Multishield sheets come in either 100mm or 152mm widths with a length of 900mm and can have self adhesive backing if required.
Each material is available in thicknesses up to 10mm and is available with self adhesive backing if required.
Design considerations
It is recommended that where possible these gaskets are designed in with some form of compression limitation. To this end compression stops in the form of collars or studs may be incorporated into the gasket itself. Ideally compression should be controlled within 5 – 25% depending on gasket cross-section and enclosure construction.
This material type can require relatively high closure forces, therefore it is important to ensure that covers/flanges are sufficiently rigid and that fastener spacing is not so large as to cause poor sealing due to ‘quilting’ or distortion of the sealing faces.
We recommend Electromagnetic Testing Services Ltd to test EMI shielding products in your application.
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