Every sealed device has a silicone part doing the quiet work: the gasket that keeps water out of a housing, the membrane that opens under a finger's pressure and closes when it is removed, the valve that passes air one way and not the other. These are the least visible parts in any programme and the first to be blamed when a device fails an ingress test, because the failure is never the housing; it is always the seal.
We mould silicone gaskets, valve membranes and diaphragms in platinum-cure LSR for device, appliance and equipment programmes.
Why silicone for functional seals
Silicone holds a compression set better than TPE across the temperature range a device sees, it survives steam and peroxide sterilisation where TPE does not, and platinum-cure LSR carries no peroxide residue that migrates into a sealed cavity over the life of the device. For parts that open and close thousands of times, the material choice is between LSR and a mechanical spring, and the membrane wins on cost at every volume below ten thousand units.
Gaskets: the groove is the specification
A gasket is specified by its groove, not its drawing. The groove depth sets the compression, the compression sets the seal force, and the seal force has to be low enough that the housing closes by hand and high enough that the ingress rating holds after thermal cycling. We mould to the buyer's groove and verify compression set per lot, because a gasket that seals on the first closure and leaks after a hundred thermal cycles has taken a set that the drawing never described.
Valves and diaphragms: the crack pressure
A valve membrane has one number that matters: the pressure at which it opens. Too low and the device leaks through its own valve; too high and the user cannot actuate it. The crack pressure is set by the membrane thickness, the slit geometry and the durometer together, and all three are tool decisions. We verify the crack pressure on a sample basis per lot with a rising-pressure test and report the open and close values, because a valve that opens at the right pressure but closes at the wrong one is a flap, not a valve.
Specification
| Gasket | LSR 30 to 60 shore A, per groove drawing |
|---|---|
| Diaphragm | LSR, thickness 0.3 to 1.5 mm, slit or flat |
| Valve membrane | Crack pressure per programme, verified per lot |
| Compression set | Reported per lot, 22 h at programme temperature |
| Sterilisation | Steam, peroxide and gamma compatible grades |
| Packing | Lot cards, dust-controlled bagging |
| MOQ | 10,000 pieces per part number |
Tooling for seal parts
Seal parts are a cavitation business. A gasket tool at 32 cavities pays for itself in the first production lot and locks the programme to a part number for the life of the device, which is why the specification review before the tool is cut is the most valuable step in the programme. Cold-runner LSR tools with a vacuum vent are standard, because a seal part with a short shot at the parting line is scrap at any price. Tool build runs four to five weeks and repeat lots run 20 to 22 days after approval.
Compliance for device seals
LSR compounds declare to FDA 21 CFR 177.2600 and EU 10/2011 as the destination requires, and programmes that sterilise add the post-sterilisation extractables file, which is a compound-level test run once per material lot rather than per production lot. The compound declaration covers the pigment system, which matters more on seal parts than anywhere else: a gasket in a dark colour carries a higher pigment load than the same gasket in natural, and the migration result follows the pigment.
Related reading
Our platinum silicone component programme covers the moulded-part family, and the silicone products category lists the full range.
