Liquid masking for anodizing
adv.
Q. Any suggestions on using liquid masking? We are black anodizing 4" x 8" x .063 aluminum plates and need to mask parts on both sides.
Doug Pickerd- Blairsville, Pennsylvania, USA
A. OK, I will bite. If you are masking off BOTH sides, what are you anodizing?
I have yet to see the perfect liquid maskant. Most have to be solvent soaked to remove the maskant after anodizing. This is a costly process as well as a time consuming one. The peelable ones required several coats and some would not peel. A vinyl, superXP 2000 would peel off of smooth surfaces, but would not come off of rough surfaces. Wax does not seem to be a good choice either.
I have used stick on cabinet paper for some flat plates. Just burnish the edges with a flat stick so that it does not leak.
- Navarre, Florida
February 27, 2012
A. My company looked into several types of masking products for anodize about 4 months ago. We didn't have much luck with anything. Tapes usually could not withstand the processes involved and the liquid would adhere to the parts but the edges would come up and trap chemicals during the process. I would recommended contacting a couple of places and just asking for samples. I hope you can find something that works.
Aimee Longacre- Savannah, Georgia, USA
February 27, 2012
A. Doug
If the surface is flat, consider using 2-mil polyester tape. For difficult surfaces we use Microshield, and as James advised, a solvent like acetone is required to remove it. For best results, let it air dry overnight before processing.
- Colorado Springs, Colorado
February 28, 2012
A. UHMW (thick) tape with one (I forget which one) will hold and not lift in many cases. If you burnish the edges, it works better.
If you can stay out of the caustic for long periods, aluminum tape can be used.
We used to buy tape by the log and have it cut to our sizes.
There are a few companies that will do this with little markup, just a bit of lead time.
- Navarre, Florida
February 29, 2012
A. The key to any liquid mask is to insure a very clean surface prior to applying. A conversion coating will also help the masking adhere.
We've had very good results with the aforementioned Microshield, including the edges.
I've also noted that it helps to apply the liquid masking to a lightly buffed finish (if not using a conversion coating), not an "as machined" finish.
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Marc Green anodizer - Boise, Idaho |
February 29, 2012
A. OK. I'll bite off a chunk also. Masking is a problematic process. It is time consuming,costly and sometimes produces a mess.
If you indeed MUST mask, as I often do, DO IT RIGHT! The effort to mask requires proper pre-clean and I have found the curing process to be detrimental to final results.
I bake my parts (where possible) in warm/hot air after masking. This could be in a hot air dryer or an oven.Too thin/thick of a mask also is detrimental.
Hope this helps.
Regards
Eric Bogner/Lab Tech.
- Toronto, Ont., Canada
February 29, 2012
A. One thing many people don't realize about the adhesives on tapes is that they are not a simple as "slap it on and go." The adhesives for industrial tapes used for anodizing are pressure-sensitive. That means you must push down HARD on them to activate the adhesive. And beyond that, the adhesive takes time to "flow," which it will do, on a microscopic level, over the next 24 hours. This creates a better and more complete stop-off bond for masking of the anodizing process.
Although I am not an anodizer, having worked with them on many masking projects, I can tell you that they are amazed at the improved results of simply pushing down hard and waiting overnight for the adhesive to flow. Don't discount tape; it may take more time to wait for it to work, but it's a lot easier and less labor-intensive to remove than the liquid masks. Of course, this assumes the surface is flat/smooth enough that tape is an option. 2 mil green polyester tape with a silicone adhesive (like the one used in powder coating) is a good choice.
- Monee, Illinois
I had forgotten about that. We used a pizza roller, about 5 inches to press down sheets on parts.
There was a difference between the adhesives one acrylic and the other was silicone. One worked far better than the other.
Also tape can be bought with different thicknesses of the adhesive on some tapes.
- Navarre, Florida
March 2, 2012
A. If you are paying attention while pressing the tape, you can tell visually when it is adhering. Best tape for non-chromated surfaces is 3M #420 lead foil with a natural rubber adhesive; doesn't stand up well to nitric based deoxidizers though. Not suitable for hard anodize unless you're really careful; boss the foil over onto the aluminum and you'll get a pretty nasty current flow. It works well on contours as the lead doesn't have a memory like the polyester tapes.
The 3M aluminum foil tape (I forget the #) works well except the acrylic adhesive sticks to your part when you remove the tape, and if it hard anodizes, the tape comes off in pieces.
- Colorado Springs, Colorado
March 30, 2013
A. I work in the aerospace industry,and can probably shed a little light on this one. Step 1: A good solvent clean, I would use MEK (Methyl Ethyl Ketone). It will take off any dirt and other oils or substances that would effect your area to be masked. Step 2: If you have the capabilities, apply MIL-DTL-5541 Class 1A Conversion coating by brush or immersion process, masking sticks to this a lot better than it does to bare metals. Step 3: Use green polyester tape to mask the parts. CAUTION: Any bubbles or peeled edges will leak anodize under the tape. Use an X-acto knife around the edges and then use a popsicle stick to "iron out" the tape using a good deal of pressure
Robby Harris- Steelville, Missouri, USA
