Metal + silicone parts
Metal is stiff and conducts heat, so two things go wrong: thermal expansion pulls the interface apart, and disinfection fluid or wash water creeps in from the edge.
Interface and structure
Surface preparation comes first. Stainless steel is degreased, blasted or passivated; aluminium is judged by anodising thickness and sealing state; copper and galvanised parts need a transition primer because plating adhesion is inconsistent. Silicone does not bond to metal by itself, and self-bonding grades only work on specific metals in a specific cleanliness window.
Mechanical locking is the more reliable route: through-holes, flanges or undercut grooves let silicone flow through and lock, with primer added on top. Long metal inserts also need the expansion difference handled - shortening the continuous overmold and leaving a buffer section beats thickening the rubber.
Five points for silicone over metal
- Fix the surface state: blast grit, passivation or anodising thickness sets the ceiling for bond strength.
- Prefer mechanical locking: holes, flanges and grooves combined with primer survive cycling and re-assembly.
- Thermal expansion: shorten continuous coverage on long inserts instead of adding rubber.
- Media resistance: disinfection fluids, dishwasher detergent and sweat all affect the primer.
- Insulation versus heat path: keep coverage continuous where insulation matters, leave metal exposed where heat must escape.
Parts in this group
Metal + silicone parts
Five parts, each pairing a different metal substrate with a different duty cycle.
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Hemostat grip sleeve
Silicone over a stainless steel instrument body: non-slip, insulating, resistant to disinfection fluid, no delamination after repeated cycles.
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Electric screwdriver grip handle
Silicone over an aluminium frame: damping and grip, no delamination after long-term hand pressure.
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Fascia gun massage head
Silicone over a zinc-plated steel insert: high rebound, no delamination under percussion.
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Outdoor searchlight tail grip sleeve
Silicone over copper terminals and an aluminium housing: grip in rain and gloves, lip and spigot sealing, no cold hardening.
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Cookware pan handle
Silicone over cast iron or stainless steel: heat insulation and grip, no delamination after repeated dishwasher cycles.
Dimensions, hardness and tolerances follow the project drawing. The remaining pages in this group are being published one at a time.
Failure modes
The three failures we see most
The location of the failure usually points back to the cause.
- Edge lift: missing primer at the edge or poor venting; check whether lift clusters near the parting line.
- Local delamination: appears after thermal cycling, usually uneven rubber thickness or oil residue on the metal.
- Rubber cracking: hardness and wall thickness mismatch, so impact stress concentrates; change the structure before changing the compound.
FAQ
Questions on this group
Is blasting always required on stainless steel?
Blasting raises roughness and removes residue, so it is required in most cases. Chemical treatment or a dedicated primer can replace it if sampling proves the bond, but oil and polishing residue still have to go first.
Can a metal + silicone part go through a dishwasher?
It depends on detergent concentration, water temperature, cycle count and the hydrolysis resistance of the primer. Run the real wash programme in a cycle test instead of relying on the material temperature table.
Why are copper and galvanised parts harder to bond?
Plating adhesion is inconsistent and copper oxidises quickly. Confirm plating adhesion first, then choose a transition primer; if that is not stable, make mechanical locking the primary joint.
Other composite groups
Changing the substrate changes the interface route.
Send the substrate and the structure
Tell us the metal grade, surface condition, disinfection or wash method and annual volume; we answer with an interface route and a sampling plan.