Gasketing done the right way

Synthetic rubber gaskets and cushioning pads are readily die or water-jet cut.

Notches should be designed into the gasket if hole(s) must be near the edge.

Thermoset molded elastomers do not lend themselves to the same level of tolerancing of rigid machined materials. It’s handy to use tolerance designations from the Rubber Manufacturers Association (RMA) for those parts. Dimensional tolerance designations are referred to as RMA A2 “Precision” and RMA A3 “Commercial.”

Compared to die-cut gaskets, those that are water-jet cut have less concavity. This is true even for cellular materials up to 2-in. thick. The compartment-housing gasket is an ideal gasket design for water-jet cutting. The holes are small and placed close to the edge of the gasket.

Geometrically, gasket design is a simple task. But for a gasket to perform properly and stand the test of time, material selection is key, even more so than the geometry of the part itself. Here’s a list of material properties that should be taken into account when designing gaskets and cushioning pads. There are also a few die-cutting tips that will help ensure gaskets meet spec:

Durometer is the hardness of a material. The Shore A scale is typically used for solid elastomer compounds. Materials with a very low number are jelly soft while those with high values are hard like the sole of a shoe.

Force deflection is the “firmness” of a material. It represents the amount of force (in psi) needed to compress a square-inch section of material 25%. Force deflection instead of Durometer rating is generally used for specifying sponge materials. Typically a “soft” sponge has a deflection force of between 2 and 7 psi; “medium” ranges from 6 to 14 psi; and a 12 to 20-psi deflection force gives a “firm” rating.

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