Teflon Impregnated Anodizing

Question:

From what I have read, Teflon® impregnated anodizing does not really have Teflon impregnated in the coating, but it is actually only adhered on the aluminum oxide surface. Would you please explain this. Also, what is the hardness of a hardcoat anodized surface? P.B.

Answer:

It can be both ways. If a waterborne Teflon emulsion is introduced into the anodizing bath, some of the Teflon particles will be trapped in the anodic coating during coating formation. This may be done with both Type II and Type III anodic coatings. Teflon may also be “applied” to the surface of the coating after the part is anodized and sealed. This can be done by either dipping the part in a water-borne Teflon emulsion, or by spraying the part with the emulsion or with a solvent-based emulsion such as Vydax and gives very good lubricity to the surface. Doing this before the parts are sealed is of no advantage because the Teflon molecules are too large to enter the anodic pores. I think the “applied” method will give more lubricity, but the “trapped” method may last a little longer. I have never seen any testing that proved this one way or the other.

The hardness of the hardcoat anodized surface may typically be anywhere from 40 to 70 Rockwell C. That’s roughly equivalent to Vickers 350 to 600, or so. I wish I had a table that compared the two scales, but I don’t. This is an issue that is continually coming up. In the end I believe that whatever the “hardness” value, it has to be acceptable for the particular application. Remember that the real “hardness” of these anodic coatings is measured in terms of wear resistance measured parallel to the anodic surface. It is not an impact hardness that is applied more or less perpendicular to the surface.