Where theworld gathers for metal finishing
Q&As since 1989
-----
What's the cheapest best way to clean dirty (organic stained) anodized aluminum?
Q. Looking for a cleaning agent which will clean heavily used anodized aluminum carriers. Crud comes from hand prints, Permanent marking pen, and evaporated epoxy. Following is a list of attempts to clean up the carriers trying to make them look new again. No.(2) below works great except for cost and danger. Also if left in too long will actually remove the anodized layer. I've yet to try (3) below. Numbers (2) and (3) are used in the Semiconductor Wafer Fabrication processing in cleaning silicon wafers (slices). Need suggestions on other chemicals that might work. After all is solved, I'll push introducing mandatory cleaning prior to carrier usage to maintain acceptable appearance of carrier.
The following is my present program. Need suggestions!
1. Using 15% NaOH (lye) heated to 45 deg. C removes not only the dirt/scum on the carriers but also removes the anodized hard protective layer which takes 5 to 10 minutes plus rinse time because the permanent pen markings are difficult to remove. This chemical attacks the anodized layer faster than the scum. Soft aluminum becomes exposed which will cause faster wearing/abrasion of the lead holding slots. This in turn will eventually cause misalignment when attempting to load lead frames from these etched carriers into automatic processing equipment. The lead frame sliding action into slots will not be smooth nor will the end slide doors. This technique I do not recommended for the two reasons mentioned.
2. Using 75% concentrated Sulfuric Acid plus 50% Hydrogen Peroxide heats (exothermic reaction) up quickly and removes all scum within less than 20 seconds. If left too long, will also remove the protective hard anodized layer. Timing during dipping is critical. Also, concentration mixture is critical. The effervescence is excessive and overflows the top of the beaker [beakers on eBay or Amazon] which can be dangerous. This is not a procedure inexperienced operators can handle. Process is expensive because 3000 ml of sulfuric acid plus 1000 ml to 2000 ml of Hydrogen peroxide will only clean about 3 or 4 carriers. Process if fast and needs a very experienced person. Protective equipment is essential and demanding. Special forceps (Stainless steel or Teflon coated metal forceps) are required (which we don't have) along with rubber gloves which extend up to the elbow or higher plus sleeve protectors and face mask. The hot concentrated sulfuric will attack anything organic. This acid must be washed off immediately from any contact with wearing apparel or person.....etc. This process removes all scum/markings in short time. Carriers look as original appearance if process is controlled. Possible control is possible if etching beaker is placed in an ice bath. My record is 2/5 carriers retained their anodized layer.
3. To be tried: 50% Sulfuric Acid + 50% Ammonium Hydroxide. This may be less violent and more controllable than (2) above. Need to order the Ammonium Hydroxide.
Aaron EpsteinOSE - San Jose, California
2002
|
"The Surface A. Hi Aaron, The removal of permanent marker stains from metal surfaces is difficult to accomplish using highly alkaline or highly acidic products, as you have mentioned or tried yourself. If these approaches work at all, it is primarily because the product dissolves some of the substrate and the soils are removed right along. I suggest using a solvent-based cleaner. This will give you the best chance of removing the marker stains. It will probably do a good job on the other soils as well. You could also modify your current attempts by using alkaline or acid cleaners that have some detergency. In both cases, it would be advisable to contact a chemical supplier for these products. A formulated product will have a better chance of providing consistent cleaning performance than the "tankside chemistry" you're currently doing. George Gorecki- Naperville, Illinois 2002 A. What do you have against using specially formulated aluminum soak cleaner for dirt? Acid is a terrible cleaner of organic dirt. NaOH is not a good cleaner as it dissolves aluminum. Todd Osmolski- Charlotte, North Carolina, USA 2002 |
A. We thank you for a "model letter", Mr. Epstein--it is well detailed and offers the readers a chance to learn something. I wish I had a good answer for you. But have you considered testing the kinds of cleaners that the medical and dental industries use for sterilizing aluminum instruments? There are a number of them, some are enzyme based, and maybe something can be easily accomplished with enzymes that is impossible to achieve with raw acids and bases.
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002
A. The problem is the seal or lack thereof. Hardcoat anodize, unless otherwise specified, is left unsealed as sealing it lowers the abrasion resistance. Unsealed, it has a gazillion pores waiting to absorb anything that touches it... finger oil, Magic Marker, coffee, etc. Removing it is like trying to take the dye out of a black anodized part (not happening!).
My suggestion would be to seal the anodize initially with either nickel acetate, DI water, or even PTFE. The PTFE will retard staining materials. If the loss of abrasion resistance, minimal as it may be, is really a concern, there are several room temperature seals that accomplish the same thing without degradation of the wear characteristics of hardcoat.
The idea of a peracetic acid [on eBay or Amazon] sterilizer as used in the medical industry (i.e. one mfg is Steris) is a good thought. Certainly they attack organics such as germs and bacteria. These sterilizers also go after dyes, however, so be careful if color anodized.
Best of luck...
Milt Stevenson, Jr.
Syracuse, New York
2002
Q. Thanks for all your responses. In the future, we'll order carriers that are sealed with some sort of media. Suggestions were: High Phosphouous Electroless Nickel, Anodize in Sodium dichromate, use Nickel acetate, or Teflon coat. Thanks for these suggestions.
What I need right now is a cleaner that will remove the baked in hand-oil and permanent marking ink stains. The carriers have turned sort of a dark yellowish brown.
Thanks again to you all and Best regards,
Aaron Epstein- San Jose, California
2002
A. Hi again. Unfortunately, as Milt said, it's probable that it's "not happening!" . . .
Anodizing creates a structure with millions of microscopic "drill holes" extending almost all the way through the anodizing layer. This is why anodized surfaces can be so effectively dyed: the "drill holes" / "honeycomb" suck in the dyes, and then they are usually sealed (the top end of the drill hole / honeycomb swelled up to lock the dye in place.
Hard anodized parts are not sealed, so stains are sucked deep into those drill holes. And what's worse, over time the pores may partially close themselves, locking those stains in place. Again, I would investigate whether an enzyme stain remover can "eat" those stains; but even that is a slim hope. But if the dimensions allow, you can strip, re-anodize, and seal the parts.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Hard anodizing discoloration/stain from grease
Q. I bought a product that is 6061-T6 aluminum and Type III hard coat anodized. Upon removal of a part from the assembly I noticed that the anodizing was discolored underneath and had created an outline of the removed part. I've tried using acetone in attempt to remove the discoloration but yielded no results.
The object removed is comprised of steel and parkerized with an unknown grease between the two bearing surfaces (steel and aluminum).
I'm curious as to what is the cause of this discoloration and outlining of the part?
Is it removable without stripping and re-anodizing?
Hobbyist - Santa Clara, California, USA
January 10, 2016
A. Hi Josh. We appended your inquiry to a previous thread on a similar subject. Hard anodizing is usually not sealed, leaving millions of "drill hole" pores that suck in the stains. Chances are very slim of removing the stain, although a vapor degreaser might reduce it somewhat if you know someone with access to one. If not, you could soak the part overnight in a caustic-free solvent like kerosene (outside!) and hope for some improvement, but "some" is the keyword.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 2016
Q. I've found that the anodizing was done to MIL-A-8625 / MIL-PRF-8625
[on DLA]E, Type III.
In the possibility that it was sealed I would wager that it would be impossible to remove. Is this correct?
- Santa Clara, California, USA
January 11, 2016
A. Hi Josh. I'm not sure if there is a misunderstanding in your posting or just a typo. If the anodizing is sealed, it's hard for stains to get into those drill-hole pores, so the aluminum is less likely to stain. If the anodizing is unsealed, dirt and stains will go down into those pores and prove impossible to get out.
Type III anodizing is not sealed because sealing softens it, which explains why you have those stains that you're not able to get out.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 2016
Q, A, or Comment on THIS thread -or- Start a NEW Thread