Material Selection for TPE/steel overmolding

[ryanbrfo]

Hi, Can anyone please suggest an elastomer that will bond well to steel? and also be suitable for use in oil? (It is a steel part overmolded with an elastomer seal).

We are attempting to overmold an elastomer seal onto a small forged carbon steel part, currently we have tried Thermoplastic polyurethane with a primer, onto phosphated and un-phosphated steel.
The bond is ok, but not compatible with automotive oil (It becomes very week).

I would imagine the material used in rubber/steel bonded oil seals would be perfect, but I have yet to discover the material and processes they use.

Thanks for any suggestions.

Ryan

 

[patprimmer]

Polyurethane I think.

Regards
Pat
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[tom1953]

Was the TPU a polyether or polyester type? Polyester types will be very much less affected by oil than polyether types. A recent study I did showed 1-8% swell with polyester millable (solid, peroxide vulcanized) urethanes vs. 20-40% for polyether millable urethanes.

Also, a vulcanized, millable urethane might have a little better retention of properties after oil exposure than a thermoplastic urethane.

Hope this helps,
tom

 

[btrueblood]

You don't specify temperature, which will be a driver. Nitrile rubber might be a better choice, there are bonding primers that will achieve very high strengths when bonding to steel in a compression or transfer mold. Talk to a rubber molding shop.

 

[patprimmer]

Also try to find out what they use on steel cords used in tyres to bond the steel to the rubber. For rayon I know it's resorcinol, but I don't know for steel.

Regards
Pat
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[ryanbrfo]

Thanks everyone for the suggestions, I think we'll go with Neoprene / steel (apparently it sticks well).

Thanks

Ryan

 

[btrueblood]

They used to brass-plate the steel cords; the sulfur used for curing (crosslinking) in the rubber would corrode the zinc phase from the brass, resulting in a dendritic growth that gave very high adhesion.