Metal finishing Q&As since 1989

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Etching Nylon 6/6

I need to etch some small machined nylon 6/6 parts so they can be bonded to aluminum with adhesive. Can anyone help me with this. I need a process that I can use in my shop. Is there a chemical dipping solution that I can use and then water rinse. Help!

Terry Nash
aerospace technologies - Lilburn, Georgia, USA
2006

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Terry,

I use an etch at my company, but only on a lab scale because it is particularly nasty.

The formula is: 75 parts potassium dichromate, 120 parts water, 1250 parts sulfuric acid.

Add the sulfuric acid very slowly and with plenty of stirring in the beginning, until the potassium dichromate has dissolved before fully adding the sulfuric. Allow the solution to cool to room temperature before use.
Immerse the parts for 5-15 seconds. The parts should go a milky colour. Immediately rinse well with water.

This produces a good bonding surface with reasonable bond durability.

Brian Terry
aerospace - Yeovil, Somerset, UK
2006

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2006

Brian,

Thanks so much for your help. As I am ignorant of chemicals and such, I need to know at what point do I introduce the water? Do I mix the potassium dichromate & water and then add the sulfuric acid? Also, are there any issues regarding the fumes produced other than using normal care in trying not to breathe any vapors.

Best Regards,

Terry Nash
- Lilburn, Georgia, USA

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2006

Brian has described this solution is "particularly nasty". I'd say it is definitely not for use by someone who claims to be ignorant of chemicals. There must be a lab tech at your facility, or a visiting tech service rep from a chemical company who can guide you in this in "hands on" fashion?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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First of two simultaneous responses -- 2006

Caution, other than safety, it produces a regulated waste and quite probably is not RoHS compliant, if that is a factor.
The best option is to talk to tech services of the original manufacturer of the nylon to get their opinion on the best way to do it.
Abrasive blasting with a very course media may give it enough tooth for the adhesive.
Choice of adhesive may be critical.

James Watts
- Navarre, Florida

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Second of two simultaneous responses -- 2006

I understand there are similarities between the chemistry of nylon and the chemistry of proteins, and pretty-well anything that will etch or otherwise damage human skin will attack nylon. That gives a wide range of substances!

You'd need to experiment to distinguish between smoothing or polishing which I guess you wouldn't want, and etching or roughening which I guess is what you're after.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

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2006

Terry,

Sorry, been away on holiday for a couple of weeks. Never even went near a website for that period!

Anyway, the order should be potassium dichromate and water first. Dissolve as much of the dichromate as possible and then add the sulfuric acid.

Take note of what Ted said, if you are inexperienced with chemicals do not play with this stuff, it is dangerous and should really only be handled by trained personnel who know their way around chemicals of this nature.

As for fumes, this mixing should only be done under fume extraction (we use a standard laboratory fume cabinet). You should also wear full personal protective equipment (acid resistant rubber gloves [on eBay or Amazon], chemical resistant overalls, safety glasses/(goggles [on eBay or Amazon])/face shield).

Once cooled there is no problem with fumes so the actual process of etching does not need to be carried out under active extraction. Full personal protective equipment is required throughout the process though.

There should be no worry about RoHS compliance, this is a surface etch reaction and the dichromate is not incorporated into the surface (although you must rinse thoroughly to prevent any residues remaining).

Hope this helps.

Brian Terry
aerospace - Yeovil, Somerset, UK