Separate gasket
- Replaceable during service
- Material chosen freely, and changed without tool work
- Can be misplaced, stretched, or fitted crooked
Molded part guide: gaskets
Injection Molded Gaskets
A gasket seals because it is squashed. It keeps sealing because it keeps pushing back. Every molded gasket eventually stops pushing back as hard as it did on the first day, and how quickly that happens decides whether an enclosure is still dry in five years. The rest is geometry.
Squeeze
A gasket seals by pushing back
Enclosure gaskets, cover gaskets, face seals, and overmolded seal beads.
Clamping two faces onto a gasket squashes it, and the squashed material pushes outward against both faces, filling every small irregularity in them. That outward push is the seal. As long as the material keeps pushing hard enough to follow the surfaces, the joint stays closed. When the push fades below what the surfaces need, the joint leaks, even though nothing looks different.
The fading is called compression set: the fraction of the squeeze that the material never recovers. Thermoplastic elastomers take a permanent set faster than the silicone and rubber compounds used for demanding static seals, and heat speeds it up a great deal. A gasket that is fine at room temperature can lose most of its push after a summer in a hot cabinet.
Geometry decides how much squeeze there is to lose. The gasket sits in a groove, and the groove needs to be deep enough that the gasket is not squashed solid, and wide enough that the material has somewhere to bulge. A groove filled too full leaves the gasket nowhere to go, so the clamping load goes into forcing the plastic apart instead of into sealing.
There is also a choice about where the gasket lives. It can be a separate molded part dropped into a groove at assembly, or a bead of soft material overmolded directly onto the housing. The overmolded bead cannot be lost, misplaced, or fitted crooked, which removes the most common assembly errors, but it ties the seal to the part.
Features
Gasket features and what each one does
Groove and gasket are designed as one thing.
| Feature | Purpose | Design note |
|---|---|---|
| Gasket section | Provides the squeeze | Sized so it is never squashed solid |
| Groove depth | Sets the squeeze | Leaves the gasket room to recover |
| Groove width | Gives the material somewhere to go | Never filled completely by the gasket |
| Corners | Where gaskets usually leak | Generous, with even section round the turn |
| Clamping points | Apply the load | Spaced so the squeeze is even along the joint |
Compression set
A gasket stops sealing when it stops pushing back
Every squeezed elastomer keeps some of the squeeze permanently.
- The seal comes from the material pushing outward against both faces
- Part of the squeeze is never recovered, and heat speeds that up
- When the push fades below what the surfaces need, the joint leaks
- Nothing looks different from outside, which makes it hard to diagnose
Where the gasket lives
Separate gasket or overmolded bead
Assembly reliability against flexibility later.
Overmolded bead
- Always present and always in the right place
- Removes the most common assembly errors
- Needs a resin pair that bonds, and tool work to change
Drawing
What to send with a gasket
The joint, the load, and the temperature decide the material.
Housing and cover CAD showing the groove
Clamping method and how many fasteners
Service temperature, especially the high end
Fluids or gases the joint has to hold back
Service life and whether the joint is opened
Expected annual volume
Keep reading
Related guides
Seals, soft resins, and the housings they close.
Seals
Lips and interference on moving parts.
SealsEnclosures
Sealed boxes and covers.
EnclosuresGrommets
Sealed pass-through parts.
GrommetsLids
Covers that clamp onto a rim.
LidsTPE
A common gasket material.
TPESEBS
A softer sealing grade.
SEBSOvermolding
Beads shot onto a housing.
OvermoldingIndustrial and transportation
How we support industrial programs.
Industrial and transportationMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded gaskets
Why did a sealed enclosure start leaking after a hot summer?
The gasket took a permanent set and stopped pushing back hard enough. Heat is the main accelerator, so a grade rated for the peak temperature, or a deeper groove with more squeeze in reserve, is the fix. Heat aging a joint under its real clamping load, then measuring how much push is left, is the practical test.
How much should a gasket be squeezed?
Enough to follow the surface irregularities, and not so much that it is squashed solid. The groove also has to leave room for the material to bulge sideways, or the clamping load forces the joint open instead. A groove that is nearly full at room temperature leaves no room at all once the material warms and expands.
Can a molded gasket replace a rubber one?
For many enclosure joints, yes. For joints that stay hot for years or see aggressive chemicals, rubber and silicone compounds still hold their push longer, and are worth comparing against. For those joints, a molded gasket is often used for the enclosure and a rubber one for the hot section.
Is an overmolded bead better than a separate gasket?
It removes the assembly errors, which are a common source of leaks. A separate gasket is better where the joint is opened for service, or where the seal material may need to change later. Some designs use both, with an overmolded bead on the housing and a separate gasket only where service access is needed.
Next step
Quote a gasket with its groove
Upload the housing and cover with the groove shown. DFM feedback covers gasket section, groove depth and width, corners, and overmolding options.