The authoritative public forum
  for Metal Finishing 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 [affil links] 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 Epstein
OSE - San Jose, California
2002

---

"The Surface Treatment & Finishing of Aluminium and Its Alloys" by Wernick, Pinner & Sheasby (note: this book is two volumes) on eBay or AbeBooks or Amazon (affil links) 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

---

---

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

---

---

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?

Josh Alexander
Hobbyist - Santa Clara, California, USA
January 10, 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?

Josh Alexander [returning]
- Santa Clara, California, USA
January 11, 2016