Looking for Etchant to Produce Matte Finish

Try it, then, on a sample and see what happens.

I have found references for FeCl3 and would like to know if other chemistry is available before any chemical purchase.

Etching Super Invar - FinishingThis says HCL/DI water 50/50

Have you considered glass beading?

From: Etching of Metals and Thin Films - ELume, Inc

Yes, I have, but the material is sheet @ 0.008", and beading causes warpage. This is why I need chemistry, hopefully a one/two stage process.

A lot of people here complain about anonymous posts, but my pet peeve is people who ignore this rule when posting a question:

• Provide as much information as possible. The more details you provide, the better the chance that someone on the site will be able to help you find an answer.

I've long since lost count of the number of times CR4 members have responded to questions, only to get a reply that adds some critical bit of info left out of the original question, making their response a waste of effort.

I have to agree with you.

Eric Bogner, A narrative of what you need to accomplish, with details, will prevent the 20 questions that we sometimes ask to arrive at a solution.

Not knowing quantities, I can't say much, except this is starting to sound like a conveyorized spray process. There are many companies who do custom etching. (I used to be engineering manager of an equipment builder) We could etch .002 mil stainless sheets with no problem.

Tell us more.

...or not, as applicable...

FYI, Eric didn't post the original question here. He sent it in to GlobalSpec, and I shared it with the community to see if anyone could help him. He registered and joined in the discussion after I'd posted it. So, he didn't know about this rule when he initially phrased his question.

What about holding the edges down, tape or metal frame slightly smaller than the plate, and then beading at a low pressure? Can't curl that way. Air pressure can be increased to a point where you get the surface you want.

Probably easier and quicker than selecting the right etchant and other variables.

Good Luck, Old Salt

To other contributors- Thanks for making it easier for me by pulling out more information on this than the original post had.

os,

It is more complicated than that.

When the blast media hits the metal, it causes the metal on that side of the piece to expand microscopically with each impact. The other side doesn't expand.

Been there, done that.

Same with heat. Heat only one side and the metal expands away from the heat.

Not good for thin metals.

Lyn-

Thank you sir!

I wasn't aware of that. I have worked with thin "gauged" sheet metal, steel, brass, copper, stainless, aluminum, etc. but never anything as thin as 0.008". It worked with them but never tried the thin stuff. Learn something new every day.

Thanks,

Good Luck, Old Salt

I have never had the opportunity to work with Invar, but have used the EDM process to create attractive finishing options on stainless steel, copper, brass, and aluminium. EDM offers a myriad finishes and textures with consistent results. Whereas Ferric Chloride, I found, to be difficult to maintain a consistent result due to the constant breakdown of the solution.

?

Electric discharge machining (EDM)

Fully aware of EDM, I used to have injection mold cavities burned this way.

I wasn't aware that the process had evolved to the point where it was being used to texture individual metal pieces.

I'm behind the curve here, I guess.

Good day to all and thank you for the info. I had originally sent my question directly to Globalspec as you see from SavvyExacta's response, thank you sir. I have tried to reply earlier, but I'm having a problem sending.

My project is to impart a matte finish on invar alloy (36% nickel, 63% iron) sheet for aesthetic purposes only. This will be used in a microscope application in order to reduce light reflectivity. The sheets will be 8 feet long x 1 foot wide x .008" thick (thin). Right now I am using coupon material in the lab.

I used a tri acid as an immersion, (50% nitric, 25% sulfuric, 1 lb/gal. ammonium biflouride) as I am in the anodizing/electroplating industry. This produced the desired matte , however, the iron component is attacked by the nitric even @ 5%, resulting in dark streaks/"striata" which shows deep granular attack. I tried a wood's ni strike (for SS plating) to cover the dark streaks, but the exposed grain structure was not acceptable.

I also tried dichromate, sulfuric, biflouride immersions, but with the same results. As previously mentioned, beading/peening (we do this extensively) causes warpage, the lengths will be a problem along with the thickness.

All my research indicates ferric chloride as per U.S. Patent 4472236A, as a conveyor/spray process. This is also supported by the photo resist industry. As for the reply by rcdesign regarding control measures, we do know 1 mole invar consumes 2 moles ferric chloride, producing 3 moles ferrous chloride (and nickel chloride) which does not contribute to the etch.

I would think titration supported by baume and ph analysis could provide some measure of control, as the spec. is only aesthetic appearance.

Again, I was seeking an alternative and would like to thank you all in this forum for your time and input.

Regards,

Eric Bogner/lab rat

Could you laminate it with a matte PVC film? You did say it was for aesthetic purposes only. I would do just that and toss all chemistry.

Good luck, Ky.

Just for giggles, have you looked into some of the water born crossed linked spray able polymers out there to do this. Could easily be applied and safely done in a good spray booth. Little or no environmental concerns as well.

Good day from Whitby, Ontario, Canada.

I like your thinking Ky, toss the alchemy = KISS!

I did think about the spray technique Fxtrls, but I need to keep the alloy in its' "noble" state. Discolouration is an issue, (with etching) as it falls under aesthetics.

I am keeping with the etch process, as FeCl3 and/or CuSO4, HCl,H2SO4. I have a formulation for anodic Ni strip @ 70% H2SO4 + glycerine but the % troubles me as a health / safety issue.

Thanks again for all the input.

Regards,

Eric Bogner.