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topic 946

Do-it-yourself anodising




An ongoing discussion from 1997 to 2015 . . .

(1997)

Q. I commenced my internet "life" specifically to find out the pros and cons of anodising. I build and race my own drag racing vehicles and as a consequence make many brackets and parts from aluminium to keep weight to a minimum. Where I live in Queensland in the northern part of Australia puts me about 1200 kilometers from the nearest anodiser, hence my new found "love" of anodising.

Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby

I have anodised most of the aluminium bits and pieces on my car with a good deal of success, so much so, friends have asked me to do their parts, which brings me to the point of this letter.

While I have been happy to do my own bits, I need a few questions answered before I'd be confident enough to put friends parts in a bath of acid.

Currently I am using a bath with about 30 liters of electrolyte, and some sample dyes from Clariant (Australia). I anodise at about .1amp / square inch for about 40 mins. I agitate the solution with a fish tank air pump and maintain the temp at about 25 °C - 30 °C.
I mix the dyes as per manufactures instructions, and leave the work in the dye till the desired color is achieved. I then boil work in clean water for 10 mins. and at least till now, I end up with a nice piece of colored aluminium.

My concerns are:

I realise that these questions are of a somewhat basic nature, but I would be grateful if you could clear up some of my concerns. I have tried to purchase some of the references that are listed in finishing.com, but alas, no go, at least in Australia.

I must admit that since I started my foray into anodising, I never had more fun, but I am still "spooked" by the chemistry side and the dangers or problems that may exist with some of these "potions".

Regards.

Rory MClaughlin
- Australia


(1997)

A. I have 30 years experience in anodizing and will try to help answer some of your questions and you are welcome to pose other questions. I may be able to be of help or not.

Sulfuric ratio ideal is 16-18%
98% with 1.85 S.G.
electrolyte coating should not wear off
most organic dyes are not good for outdoor exposure, they will fade in sunlight
Dyes do not present a hazard to user
Chemical brightening prior to anodizing is called a bright dip
Ideal solution of 80-85% phosphoric acid and 3% nitric acid
Specific gravity should be approx. 1.710 to 1.720
Temperature range 200-220 °F
Sodium bicarb should not have any lasting effects on finish.

This should give you a very bright part.

Hope this is of some help.

Raymond Hendrix Troy, Tennessee


(1997)

A. One other consideration for you regarding anodizing parts for your friends race cars is the affect of anodizing on structural components --
-- anodizing significantly decreases fatigue strength, sometimes by up to 50%. This means that anodized structural components will be much more susceptible to fracture over time than components without anodizing. This may or may not be a factor in the components that you are anodizing, but is something to keep in mind.

larry hanke
Larry Hanke
materials testing laboratory
Minneapolis, Minnesota




(1998)

A. I am the project chemist at ACA. As to your questions:

As you treat aluminum parts, whether it is cleaning, etching, bright dipping, or anodizing, aluminum is constantly being removed from the surface. The aluminum that is removed from your part(s) stays in the bath and can affect the quality of the anodic coating, especially in the etch bath and bright dip. (BTW, premixed bright dip solutions are available [in the US, anyhow] from Albright & Wilson). Aluminum in the drag-out from the anodize bath to the dye bath can kill your dye, even if you keep the pH corrected. Also, stored organic dyes can support life (read: MOLD), so watch out.

Gerald Janssen
-coil anodizing



What is sodium bicarb?

May 19, 2014

Q. Dear All,

Can you advise what is sodium bicarb?

Best regards,
Alex

Alex Au
- Hong Kong China


probert book
Aluminum How-To

by Robert Probert
$89 New
The Chromating - Anodizing - Hardcoating Handbook

May 2014

A. Hi Alex. "Sodium bicarb" is just a slang abbreviation for sodium bicarbonate (NaHC03), aka baking soda. It is a very mild alkaline often used to neutralize acid. As you can read above, sodium bicarbonate is sometimes used for that purpose in the anodizing process.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 23, 2014

Q. Hi Raymond,

Is the ideal solution of 80-85% phosphoric acid and 3% nitric acid for brighten up? Is this a process just before anodizing?

Best regards,
Alex

Alex Au
- Hong Kong China


May 2014

A. Hi Alex. Raymond's posting was from a long time ago and he's probably not monitoring this thread but, yes, he is speaking about a chemical polishing solution there. It is used to brighten aluminum before anodizing in limited applications like the manufacture of aluminum reflectors. It is not a part of the process in most anodizing shops. This is a very nasty process, so be sure to read up on "aluminum bright dipping" and to visit at least one shop that does it before considering implementing it yourself. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



September 28, 2015

thumbs up signIt is 2015 and I am grateful for this info. I am making an acid bath, 98% Sulphuric Acid and DI water but I was unsure of the mixture. I bought a hydrometer so I will gauge adding acid until I reach the 1.7 gravity.
Thanks folks!

Rajiv Ram
- doral, florida usa


January 1, 2016

A. A final sulphuric anodising electrolyte density of 1.7 seems too high to me. I've read typical mix should be battery acid (sg of 1.265) cut 50/50 with DI water, so density is going to end up around 1.13 or am I being stupid?

John Stokes
engineering - abergavenny, Gwent, wales


February 2016

A. Hi Rajiv. Hi John. You guys need to take your time and read the page a little more slowly ... Ray's 1.7 S.G. was referring to the chemical bright dip process, not the anodizing process :-)

For anodizing he suggested 16-18% sulfuric acid (by weight), and his 16% by weight is quite widely accepted. John, I assume you are a hobbyist from your reference to battery acid. Professionals use Electronic Grade 98% sulfuric acid rather than battery acid. You can't reliably go by specific gravity because dissolved aluminum throws it off. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


February 4, 2016

thumbs up signYes sorry you are correct I should have read the post fully from the outset. 16% as you say is stated as the sulphic to water electrolyte ratio by weight. I do use Electronic grade Sulphuric Acid concentrate with a density of 98% I was referring to an article that based it's starting mix using battery acid that is already supplied with a lower density initial density.

John Stokes [returning]
skirrid engineering - abergavenny, Gwent, wales



Storage of Anodizing Acids

February 4, 2016

Q. Getting started Anodizing and I am wanting to know how to store the various chemicals. Not a fulltime hobby so leaving in the tank is not an option. I also understand that what may work for short term, may not be suitable for longer storage. Obviously the original container would be preferred, but as I will be diluting, my storage volume will not be the same.

My Battery Acid came in a plastic container. Can the diluted Sulfuric Acid anodizing bath be stored in a standard 'Home Depot' 5 Gal bucket? If not, suggestion for ~5 Gal storage.

My 67% Nitric Acid also came in plastic and instructions to transfer to glass asap. The website stated that concentrations over 30% must be stored in glass, but makes no mention for concentrations under 30%. Can 10% Nitric acid be stored in the 'Home Depot' bucket? I've searched but can find no references to Nitric Acid storage at lower concentrations. This is the one that I am most concerned about.

Frustrated because I just gave away all my 5-6 gal carboys (was beer making).

I do not foresee an issue with Dyes in the 5 gal buckets. Let me know if I am wrong on this point.

Thanx

Sterling R [last name deleted for privacy by Editor]
Getting Started with Aluminum Anodizing - Oklahoma City, Oklahoma


February 9, 2016

A. Hello Sterling, I have only used polypropylene tanks or buckets for storage of acids. With the acid concentrations that you described a white polypro with a lid should be fine.

Mark Baler
Process Engineering - Phoenix, Arizona USA


February 13, 2016

A. You would be just fine storing either or both of the chemicals you mentioned in a 5 gal Home Depo plastic bucket. If you happen to splash some on the metal handle, you'll want to rinse that off, as it will corrode.

Marc Green
Marc Green
anodizer - Boise, Idaho



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