Problems in cold sealing of anodized aluminum

A. Assuming your sealing bath parameters are maintained within limits of that particular product's specification, a remaining possibility for slow sealing time is due to bath contamination.
Try mixing a small amount of new bath in a beaker or bucket and process a test panel with it.

If the sealing is still slow/difficult even in a freshly made up bath, you should look carefully at your anodizing parameters.
Anodizing with too high temperature, too much acid, and/or too long time (too low current density) for the target thickness will result in coating with excessively large pores that are more difficult to seal.

A. Hi PNutt,
You can de-ionize the rinse water. Use the ground water in the 1st rinse, then a DI water recirculation loop on the 2nd
- or if the rinses are already counterflowed -
do a closed loop for the pair.

Luck & Regards,


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

A. Hi Bishikeshan. More words please!

Are you saying that you sometimes shut down production for a period of from 2 to 5 days? And when you try to resume production your cold-sealed parts do not seal properly as determined by a sealing test?

Are you using a proprietary cold seal? If so does the supplier have any comment?
If you are using a home-brew cold seal, what is its formulation? Do you do any analysis of the cold sealing solution? How does the problem eventually resolve itself. Luck & Regards,


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

A. Noor,

Please consider the following suggestions to solve your problem:

1. First, your free fluoride content too high 900 ppm. Normal practice 300 - 450 ppm. If free fluoride content too high it will help nickel ion precipitate into anodic pore faster resulting greenish tone.

2. Please anodize with low current density (100 - 120 A/m2). So that small anodic pore diameter can be produced resulting nickel ion difficult to precipitate into anodic pore.

3. You can add in some cobalt sulphate into your cold sealing solution to mask this greenish tone. Don't too much other wise it will harmful your sealing quality.

Hope these suggestion can help you. If you solve this problem, please let me know.

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"Chromating - Anodizing - Hardcoating"
by Robert Probert

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A. Dear Noor,

In new make-up cold sealing bath, normally we practice at concentration 3.5 - 4.0 g/l.This is mainly due to new bath less contaminant. After operating one month, try to increase to 4.5 to 5.0 g/l. You can do some sealing quality test if you seal at 4.0 g/l. Sealing process normally base on free fluoride contain instead of nickel content. Do some laboratory test. Anodize and seal at different concentration to find the best condition to suit your application. You are welcome to discuss with me further. If you don't mind, please let me know the detail of your sealing chemical composition so that we can study more.

See you bye.

Regards,

A. Noor,

I have used ALS-62. It is very powerful sealing chemical. Please reduce your sealing time. What is your sealing time for sealing 20 micron anodize material? Dye corrector may have to add in to mask this greenish tone or try to practice using some suggested operating parameters as presented to you in my last message to you. Please consult your chemical supplier for the suitable concentration to be made and correct sealing time to be used. Thank you.

Best regards,

A. DEAR NOOR MOHAMMED,

TO OVERCOME THE GREENISH FADE USING COBALT ACETATE (0.15 AND 0.30 G/L CO ) IS RECOMMENDED. USING RED OR VIOLET DYE IS RECOMMENDED ALSO. THE BEST RATIO FOR NI++/F- IS 12-14. SO PLEASE TEST RATIO. I AM NOT AGREED THE NICKEL CONSUMPTION IS HIGHER THAN FLUORIDE. FLUORIDE IS CONSUMED MORE THAN Ni. THAT IS WHY MOST PATENT HOLDERS OFFER MAKE UP FORMULATION WITH R=12-14 AND CHARGING WITH R=1 IN ORDER TO MAINTAIN FLUORIDE SHORTAGE. SO WHAT I RECOMMEND IS:
1 -IF COLOR CORRECTOR IS COBALT TYPE INCREASE TO O.3 G/L CO EQ.
2-IF COLOR CORRECTOR IS THE DYE TYPE INCREASE THE TEMPERATURE SO THAT MORE DYE CAN BE ABSORBED. MEANWHILE LESS Ni WILL BE PRECIPITATED AT 35-40 °C.

Hope my advise is tried.

A. There are 2-pack liquid cold seals available which help overcome the greenish tint that can be seen on anodising from using powder products. 2-pack product allows for better control of fluoride concentration.

A. Hi,Salam to all of you,

Mr. Noor:
Cold seal ALS-62 is a very old product; try new product for cold sealing ALS-64.
For the problem of greenish shade, I'll suggest that you must use D.I water before cold sealing rinse.
Also you have to anodize aluminum at low current density, (1.0-1.2 A/dm2).

One important thing, Mr. Noor, you can practice cold seal at even 3-3.5g/l.
If fluoride is too low then you can add Ammonium bifluoride or hydrogen fluoride.
But after putting that in, you have to stabilize pH by adding ammonia.
I'll recommend to you strongly that you never ever use caustic soda for increasing the pH.

Best regards,

A. Dear Noor,
I think you miss some points:
1- your free fluoride content is too high. 500 ppm is normal.
2- if you anodize 20 microns, cold seal duration must be 20 min.
3- (most important) you must check laboratory details, especially check fluoride promptly; it may be faulty. Check calibration solutions run normal. Also check calibration solutions. Because every time fluoride consumption is higher than nickel.

Sincerely,

A. Hi,Salam to all of you,

Mr. Haider:
You can check cold seal quality by performing a dye spot test, or one more thing that you can easily do --
take one board marker, after final finishing, make a mark on profile, then sweep it with dry cloth.
If it is removed immediately, you can think cold seal quality as good and vice versa.
I am also from Pakistan and doing my job in Karachi, in Pakistan's first aluminum extrusion company.

Best regards,

A. Peace and health to you, Muhammad.

We assume that you are doing Type 2 sulfuric acid anodizing. Are the profiles dyed? With organic dyes? What kind of seal are you using -- a cold nickel seal or hot DI water maybe? The problem is very broad and difficult to address without some specifics. Thanks.

Regards,

A. Dear Jawwad, you are using nickel based cold seal, the reason for the preparation of powder after sealing is from different things.
1. you, first of all check your pH of the bath, it may be too high or too low.
2. check your rinsing bath water, before sealing and after sealing,
3. the nickel content may be too high.
regards.

A. POWDER COMING AFTER SEALING: MAYBE THE REASON IS YOUR ANODISED COMPONENT IS OVERANODISED. CHECK TEMPERATURE OF SOLUTION, VOLTAGE AND H2SO4 CONTENT.

A. Junior, I'll admit I have no experience in working with cold seals, however, I definitely see a flaw in your rinsing technique. The rinse prior to sealing should definitely be clean, preferably DI water. Dragout of tap water (and in your case, heavily contaminated tap water) definitely isn't good for subsequent processing baths in any part of the process. Secondly, and again, I know little of cold seals, but is sodium hydroxide recommended for pH adjustments? I've worked with mid temp, and high temp seals throughout my career, and have always used ammonium hydroxide.

? Hi Adib. It would probably be helpful if you sent photos to mooney@finishing.com for posting here. I don't think we readers have much feel for this 'layer' you are mentioning. Some sort of a salt stain perhaps?

Regards,

A. You prepared too high concentration in cold sealing bath, either nickel and fluoride value. Ni+2 concentration should be 1,5-2 gr/lt and fluoride concentration should be 450-700 ppm. Also another important value is pH and it should be 6-6,5. If you ensure these values, probably you won't have any problem during production. But your bath values had became out of tolerance. So you will see powder or greenish surface if bath operates at these values. Also another piece of information: a high fluoride ion concentration requires a lower operating temperature and/or a shorter sealing time and higher pH than 7.

A. Well, thanks Mr. Kamruddin.
I have used this particular chemical for quite a time and the fact I can tell you is that it is not such an easy thing to keep the pH constant as long as production is running; however, you will always have a task to check this daily and don't allow it to over increase beyond the value of 6..