Q&As on Teflon (PTFE) impregnated Hard Anodizing of Aluminum

Robert is right as usual, the smallest particle of Teflon is many times bigger than the largest pore of the anodized oxide. So they mix it in a water-borne coating (adhesive) to get it to stick. Also since the Teflon is inert and non-conductive it will not/can not co-deposit with the oxide. In my opinion, a REAL hardcoat will give you all the protection you need.

A. You have to give all details of the application, Temperature/Service conditions and base substrate
regards,

I agree that posted questions are more interesting, and help is easier to give, when details are included, Jayesh; I request the same frequently. Still, Elangovan has revealed that he is with a shop that does hard anodizing of aluminum, and is asking generally how the Teflon impregnation process process for hard anodizing is performed.

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

Also available in Spanish

You'll love this book. Finishing.com has sold almost a thousand copies without a single return request :-)

Q. For example, is it a dip process after anodizing? If so, does the hard anodizing require sealing, which is unusual for hard anodize, or does it demand that there is no sealing. Can it be done after parts have been put on the shelf, or must it be done immediately in-line? Maybe it must be sprayed on rather than dipped? Is any kind of baking for curing or for diffusion required? I too would like a general introduction to the technology. Thanks!

A. Juan,

PTFE is applied after anodizing. Because of porous structure of anodic coating on aluminum surface, PTFE partially permeates into the micro-pores and also partially bonds the anodic coatings on surface. There are several proprietary PTFE formulations and processes available commercially in the market. To get more information, you may contact Chris Jurey at Luke Engineering & Mfg. Co., Inc [a finishing.com supporting advertiser] .

A. Information on PTFE impregnated Hardcoat will be very difficult to obtain. These processes are proprietary and closely guarded. As you discovered, even the U.S. Military was unable to obtain process information to include in MIL-A-63576. Some of the earliest work was done in the late 1950's by Luke Engineering's founder, W.P.Hayduk, in developing the Lukon 24 process. Others have developed their own procedures or tried to reverse engineer this process with varying degrees of success.. These different approaches have resulted in a number of branded products with a wide variety of application techniques, performance, and costs.

A. We do teflon Hardcoat at my shop.

A lot of companies have there own in-house proprietary processes for this finish.

My finish, as well as these proprietary named processes all meet the same specs, thus leading me to believe they are all similar and just the name is different i.e., TUFFRAM, LUKON, SINTEF, POLYLUBE, etc. You can contact the mfgr. of the teflon product we use. It is: RO-59 [Stoughton, MA]

Q. I would like to hear from some other finishers re: are their proprietary teflon hardcoat processes really special or is it all just in the name?

"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)

!! I would be very interested in hearing from someone with a documented, scientific study or proof of an anodic coating which has had the pores impregnated with PTFE. The largest pore diameter obtainable from anodizing is phosphoric acid anodize and it is an order of magnitude smaller than the smallest particle size of PTFE.

There are processes which have the PTFE contained in the anodize solution, however, typically a dip immersion is performed or a spray application is performed after anodize.

There is an article available from Lubrication Engineering, Volume 38,8 pages 497-498, 507-509 -- which is the only documented study I have seen.

Dupont has been the best technical help to me in the past concerning PTFE coatings, they make both a solvent and a water based dispersion PTFE product used in Teflon hardcoating processes. Sizes of various anodic pore diameters are readily available in The Surface Treatment and Finishing of Aluminum and its Alloys, an oft quoted reference in the industry.

Q. I agree with Ward that scientific studies are needed to understand the teflon impregnation process. Of course, if the companies claiming to have knowledge of this process decide to enlighten us, then we do not need to waste time or money. As David Kraft suggested, almost all the processes seem to be similar in nature. For the past few years we have been trying to understand the pore development process on pure aluminum and its alloys, and made considerable progress on that too. Yet, it is hard to understand how teflon can be impregnated in the porous oxide layer whose diameter is less than teflon. Currently phosphoric acid is known to provide the largest pore diameter. So, unlike electrocoloring process in which the metal ions (like Cu or Ni) actually deposit within the pore walls and fill the pore, I wonder if Teflon fills up from the bottom of the pore too. Anyone willing to collaborate/fund/share knowledge on the research?

A. Are you looking for "Vydax" (with an A not E)? It is a mixture of CFC 113 or isopropyl alcohol (at one time there were six grades available) and white wavy particles of polytetrafloroethylene (PTFE). It is a Dupont product and I'm sure you can still reach them about it.

Tom

A. Some time ago, I had helped solve this problem for an electronic fabricator. If no one has a better/cheaper suggestion, I would get a
1) 1st choice- PVD Chromium Nitride coating,
2) second try- PVD other nitrides, carbo-nitrides. Considering the cost of molds, PVD cost becomes acceptable in many cases.

In my project, Chromium Nitride minimized "flash" related sticking problems.

A. Hi Kevin. We appended your inquiry to an existing thread on that topic. As you can see, you can use specification MIL-A-63576. As you can also see though, it will take a small miracle to "avoid any problems due to lack of proper documentation".

Regards,

A. Hi Frank, we linked your inquiry to one source for the spec. I visited Sanford Process in Natick, MA decades ago. When I last checked, Sanford Process was is Woonsocket, RI, and is now a division of Katahdin Industries. You can contact them about that Sanford Hard Lube -- but there are several suppliers of teflon hard coat, not just one, and some suppliers of it like Luke Engineering & Mfg. Co., Inc [a finishing.com supporting advertiser] are making this forum possible for you.

A. I can't say if TIA exists. However as to testing for it ...

With an SEM it wouldn't be difficult, looking face on (not a section as you were suggesting) to focus on a pore. A simple attachment on an SEM is an EDXA (energy dispersive x-ray analysis), it gives readings of elements present. Scanning outside a pore would give readings for Aluminum, whatever it is alloyed with and oxygen (from the oxide layer), and any residue from other surface treatments. Scanning into a pore will give readings for fluorine and carbon, if the Teflon (PTFE, polytetrafluoroethylene) is present there. If there was more Teflon in the pores than on the general surface then the readings for fluorine and carbon would be that much higher there. Ian

A. Sir, my research yielded the statement that Teflon can NOT impregnate anodize because the smallest Teflon particle is still bigger than the largest anodize / hardcoat pore.

You may want to look at site - they CLAIM to do Teflon impregnation.

Ed. note: When this reply was printed, it could be read as either a sincere recommendation, or as sarcasm. However, after the additional replies, it seems to be a 'slam'. It is the long-standing policy of finishing.com that we do not print 'slams', so we have removed the reference.

A. My understanding is that the Teflon particle is bigger than the anodize pore and will not fit in or "impregnate". I have interrogated several company reps at trade shows over the years who claim Teflon impregnation and received no more evidence than a smile and the assurance "oh yeah it impregnates into the pore". Maybe after we locate the Loch Ness monster and bigfoot we can put more effort into looking for evidence of Teflon impregnated anodizing.

Well... maybe, perhaps a representative from will pipe up in this forum, and offer us some proof that their coating does indeed impregnate the pores in the anodic coating...or does this indeed resemble the "sky hook" racking technique that leaves no rack marks? Marc Green anodizer - Boise, Idaho 2000 My follow up reply, although a little sarcastic, was in no way meant as a "slam", towards a company whose work I have seen, and liked. However, I do believe this is a good forum, and opportunity, for a company who makes claims that appear to be impossible to share proof, that this is, indeed, possible. I'm not asking for any proprietary processes here, as a matter of fact, this could turn into a good business opportunity for a company that's willing to offer some kind of evidence to back up any claim that they are able to impregnate a PTFE coating into an anodic pore. Marc Green anodizer - Boise, Idaho 2000 Agreed, Marc! Thanks! If the company that was mentioned (or any other company) wants to claim they do TIA, and defend it here, they are certainly welcome to ... and we'll be happy to put their name back on the page, and everyone is very welcome to challenge the claim. But those words were put in their mouth by someone else and we can't put their name up in lights, throw down the gauntlet, and demand that they drop everything to come running over to this forum to defend someone else's interpretation of their claims on pain of being considered 'fraidy cats. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey 2000

A. This topic came up as a side discussion at the recent Technical Symposium of the International Hard Anodizing Association (IHAA). Two PhD scientists with metal finishing backgrounds argued opposite sides of this issue. Both offered "proof" to support their positions.

However, unlike the scientists, most of the hardcoaters present did not much care how "PTFE Impregnation" works but rather if it works and how well.

Anodizers have developed proprietary "impregnation" processes based on a variety of techniques. Little information is publicly available and there is no standardized testing to compare results. Field testing is the only foolproof method to verify the friction and wear reducing properties of each method. So it is buyer beware.

A. Size of particles of PTFE doesn't matter when the process of impregnation is done at temperature over the melt temperature of PTFE. Over this temperature particles don't exist anymore and PTFE, depending on its molecular weight, can be liquid. But a process which does not use pressure and high temperature together cannot impregnate pores.
We apply impregnation to porous material (not aluminium) with PTFE and it really gives impervious properties to this material. Application of powder and sintering it is not an impregnation, only a superficial coating which cannot prevent pitting corrosion. Some porosities remain. When only friction properties are required, it is acceptable. When corrosion matters, it can be an issue.