Anodizing Racks: Titanium vs. Aluminum

A. Hi Poul, 2024 is the best material but the racks can be made out of the same material as you are anodizing. They must not rob the current by being of a material that anodizes at lower voltage than the parts. A 6000 series aluminum is "uh, okay", especially for a short-lived prototyping experiment as long as you are not anodizing 2000 series aluminum. Obviously, titanium is a better idea though.

But since you say you are new to the process and just starting, I should note that most shops don't build their own racks. They usually buy them from suppliers familiar with the needs of anodizing racks. Sometimes for small parts you can purchase a 'standard' titanium rack and save the expense of custom design.

Luck & Regards,

A. Many of our anodize racks are made out of titanium.

Titanium conducts the electricity to the part which is necessary but the titanium does not anodize, like an aluminum rack would, and thus you don't have to strip it in between uses ... it lasts forever.

A. For anodise jigging you are limited to aluminium or titanium if you are going to use metal or a non-conductive material that will withstand acid and heat.

Titanium would be best (also costs a lot).

Other options to try which may or may not work:

Thick (0.75 inch) polypropylene

Etch prime / prime the aluminium rings (try some old ones to allow for the paint thickness - also use up your waste).

Ask your finisher if the rack can be redesigned.

Redesign the part with a tag to hold when finishing which can be removed after.

A. Although it's expensive, I would recommend Titanium, as it won't have to be stripped after coating, like your Al rings.

A. Are you using 2024 aluminum, which is the best alloy for this purpose? If so, and it's still not good enough, try titanium.

A. Your analysis of the situation is a good start, Ken. One situation which would favor aluminum racks is when they don't actually need to be stripped. For example, for architectural extrusions the parts can sometimes be attached to the racks with aluminum sheet metal screws which go into tapped holes in the rack. The current is conducted from the rack, through the screws, to the parts -- so anodizing can build up on the rack without causing a problem. And because the tapped holes in the rack have a screw in them, they don't anodize. Of course, sometimes the anodizing on the rack won't survive the pretreatment (especially if etching is involved).

Both aluminum and titanium are widely used because neither is superior for all situations.

A. Jigs: the best results are always obtained using alloy jigs. Titanium by its nature is hard, leaving marks against work pieces, and does not pass current well.

A. With aluminum racking, yes, you have to account for the additional surface area of the rack. With titanium racking, you do not.

A. Hi Klay. The ideal material of construction is 2024 Aluminum because it requires the highest voltage and builds the thinnest film. But I would expect 7075 aluminum to be okay when the parts are 6061.

Regards,

A. Hello Samrat,
Aluminium jigs are fine as long as you wire brush the points of contact with the components before jigging.
They will get thinner with time, from repeated anodising, so you will need to replace them periodically.
If the titanium is leaving marks then that rules it out.
One other point I will make is, try not to mix alloys in the tank, as they all have different electrical conductivities. So that when anodising you can not be sure that you have the current density range on the components that you think you have. This being important to ensure consistent anodic films. This applies to the jigs as well.
Best regards