Titanium Grade for Aluminum Anodizing Racks

A. Hi Gangal,

Chemically pure titanium is graded by strength, with grade 1 being the least strong, and grade 4 the strongest. Some manufacturers claim their rack tip are made of Grade 4, and that seems to make sense to me for the tips and teeth. I see other manufacturers offering grades 1 and 2.

My guess is that Grade 4 will prove more durable for tips and teeth, but for the remainder of the rack it doesn't matter, and Grade 1 will be least expensive.

Further opinions and comments welcomed.

Luck & Regards,

A. Hi Mark.

Probably not. Titanium is anodized for one of two basic reasons ...

For decorative purposes like jewelry, titanium is anodized in a mild conductive solution like trisodium phosphate or Coca-Cola. A very thin, transparent, layer forms on it which comprises a partial-wavelength interference coating. It can be done in most colors of the rainbow depending on how thick it is, or it can offer oil-slick coloration if the thickness of the coating is variable. I imagine that it should be doable in a sulfuric acid aluminum anodizing solution, although I have not heard of it, but it probably requires higher voltages than your anodizing rectifiers can offer. Search the site for "anodizing of titanium" for such facts and figures.

Anodizing of titanium is also done for wear resistance and reduction of galling. The common specs for this are AMS 2487 and AMS 2488. These call for anodizing in an alkaline solution, not acid.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Several readers say they've done it in Coca Cola, but dilute phosphoric acid or trisodium phosphate is probably simpler and more repeatable. It is obviously possible in sulfuric acid anodizing solution because we sometimes see racks that are blue, but I don't recall anyone posting that they have used an aluminum anodizing solution for titanium anodizing.

Goran Budija in thread 73/08 thinks 30 volts will be enough for blue. Jeremy Wyatt says 20 volts in thread 79/26, Paul Vernon says 28 volts in thread 17/62. All say the grade of titanium and other operating parameters will affect the exact numbers. Several people called this "the first blue". I haven't checked the math, but what they are implying is that as you go to higher voltages and thicknesses, the color spectrum will repeat and there will be a 2nd blue at some greater thickness where blue wavelengths are again amplified while other wavelengths interfere.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Mark

In practice, you should be able anodize titanium using the same bath as for aluminum. You'll be limited by your rectifier with respect to the colors you can obtain. Check your specification(s) for any restrictions.