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Natural Rubber Metal bonding issues

Natural Rubber Metal bonding issues

Natural Rubber Metal bonding issues

Hello dear friends!

The company I work for is facing some problems with the bonding between rubber and metal.

Please forgive the upcoming long post!

The issue appears only on some of the products, mainly the spherical bearings, mostly in the middle area of the product.
The products are vulcanized by transfer process and the rubber is natural rubber.
We've tried many approaches, mainly:
- we've heated the metal parts;
- we've changed the adhesives;
- we've tried that the adhesive reaction and rubber vulcanization to take place in same time;
- we've increased the work temperature;
- and others...(we're facing this issue for a long time now).

Our latest observation, in the lab, is that when we try to bond the rubber already vulcanized on the metal parts the bonding is very, very good. But if we apply small movement the bonding is weak.
We think that maybe because in the middle of the part the temperature isn't as high as it is in the extremes of the part the rubber doesn't get vulcanized uniformly in the entire mass in the same time and although it gets vulcanized the bonding there is weak.

What do you think? Has anyone encountered this problem? Are there any solutions? Are there any good practices to follow?

Regarding the thermal expansion of the rubber, what is the influence of the rubber's condition on it?(vulcanized vs unvulcanized)

Thank you all!

RE: Natural Rubber Metal bonding issues

I suggest you contact the supplier/manufacturer of your bonding agent and ask it's technical team for their thoughts.

Dow has published a technical guide on-line at: http://msdssearch.dow.com/PublishedLiteratureDOWCO... This could have pertinent information in it.

RE: Natural Rubber Metal bonding issues

Dear GrahamBennett,

Thank you for your suggestion but we contacted the supplier, we even changed the supplier, we tested many bonding agents as suggested by different suppliers an still no resolution.

For other geometries there are no problems.

RE: Natural Rubber Metal bonding issues

Steel is often plated with brass in order to improve adhesion to rubber.

RE: Natural Rubber Metal bonding issues

Thank you Compositepro but that it's not a solution for us...

Any other ideas or experiences?

Thank you all!

RE: Natural Rubber Metal bonding issues


Is the metal properly cleaned before applying bonding agent?

RE: Natural Rubber Metal bonding issues

In my experience natural rubber itself has the best adhesion to metal surfaces from all the rubbers. I suggest you try following:
- clean the metal surface with sandblasting if it`s steel, or burn it if it`s brass. Allow the metal to cool down before applying adhesive.
- the vulcanisation can be at lower temperatures with extended time depending of the size of the product.

Please inform if this is helpful.

RE: Natural Rubber Metal bonding issues

If you can brass plate the steel then you can about 1phr cobalt naphthenate to your formulation, increase the sulfur content to around 8 or 10phr, and change the accelerator to DCBS (e.g. Santocure DZ). Note: this is a modified tyre breaker skim adhesion formulation.

RE: Natural Rubber Metal bonding issues

Hello all,

First of all thank you for your interest in helping!

An expert came to us and he told us that the problem seem to be caused by air or gasses.

We're going to investigate this possibility.

Thanks again

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