Spira Gaskets are made from spring temper tin plated beryllium copper or stainless steel. The advantage of using these materials is that the gasket acts as a spring and the ratio of force to deflection is linear. So if it takes one pound to deflect the gasket 1% of its diameter, it will take 25 pounds to deflect the gasket 25% of its diameter, provided that the sides of the gasket are not constrained during compression. This advantage allows fastener spacing to be calculated to fairly close tolerances. During deflection, to avoid damaging the gasket as well as to take advantage of linearity, it is important that the sides of the gasket not be constrained. To achieve this, all but one of the following groove designs allows lateral freedom of movement for the gasket. Optimal deflection is 25% of the gasket’s diameter which minimizes compression set.
With proper design, significant savings can be realized in the reduction of fasteners and fastener maintenance costs. These savings can in turn more than pay for the cost of the gasket as well as improving performance and reliability over the life of the system. For more information see How to Calculate Fastener Spacing.
The width of the groove should
be a minimum of 35% larger than the diameter of the gasket. The depth
of the groove should be 75% of the diameter of the gasket. See below for
recommended groove dimensions.
If using a groove in a square configuration, it is important
to choose a groove radius that will not damage the spiral, nor inhibit
its performance. Generally speaking, we recommend an optimal corner radius
of 1.5 times the diameter of the gasket or greater. The recommended radius
for the “D” Multi-Seal is 1.5 times the width
This groove can either be extruded, or machined using a special dovetail cutter which is available from Spira. When machining this groove, a standard o-ring groove must be machined first. See Dovetail Groove Cutters for more information.
Use the same groove dimensions as the standard o-ring groove discussed previously. Use very small (1/16”) dots of glue every 3-4” along the groove. Since the glue may degrade the shielding, use as little as possible to hold the gasket in place. You can also minimize shielding degradation by placing the glue dots at fastener locations. We recommend using either super glue, epoxy, or RTV. We do not recommend the use of conductive adhesives since their conductivity tends to degrade over time, thus degrading the shielding and giving you a false indication of the long-term shielding you will achieve. See below for recommended groove dimensions.
This is a standard o-ring groove with narrower sections every 2 to 4 inches that
“pinch” the spiral in place. Since this groove can be die-cast or molded into an enclosure, it is ideal for use in high-volume cost-sensitive applications.
The figure illustrates suggested dimensions according to the diameter (D) of the gasket. The undercut directly under the pinched area is critical in the design and use of the groove. Contact us for any additional information.
This groove is only recommended in
Traditionally, only our spiral type gaskets are recommended for groove mounting. However, almost any type of gasket can be designed into a groove if desired. The important thing to remember is to allow 25% of the diameter of the spiral to protrude above the top of the groove. Also, be sure to choose a groove wide enough to allow the spiral lateral expansion for optimal performance.
The table below shows the recommended mounting dimensions for commonly used sizes of spiral gaskets. The chart applies to Spira-Shield, Ultra Quick-Shield, Quick-Shield, Flexi-Shield, Endur-o-Shield, and “D” Multi-Seal gaskets. The dash numbers shown can be matched with those in the part number charts of the applicable gasket. We have not included dimensions for the narrow o-ring groove. Generally speaking, a narrow groove is defined as any groove that is narrower than the recommended width of our other o-ring grooves.
The chart applies to the following gaskets:
* D = Diameter of spiral
** E = Width of "D" Multi-Seal