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topic 46180

Anodizing Racks: Titanium vs. Aluminum



A discussion started in 2000 & continuing through 2017

(2000)

Q. We send out one of our components for anodizing & bright dip finish. This component is round and quite thin (.014"). We have found through experience that we must supply a ring to put around part of the OD of the component to keep it from becoming distorted by the pressure of the racking device. The problem is that we make the ring out of aluminum and after about 3 or 4 uses the ID of the rings become too large and are no longer useable and must be replaced.

The question is: Can these rings be made out of some other material that would not be affected by the anodize process (they must also be able to withstand the heat of the process)?

Thanks for any input.

Stan Kmiecik
- Addison, Illinois, USA


 

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.

David A. Kraft
- Long Island City, New York


 

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.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


 

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

Marc Green
Marc Green
anodizer - Boise, Idaho


 

A. Are you using 2021 ^2024 aluminum, which is the best alloy for this purpose? If so, and it's still not good enough, try titanium.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

sidebar
 

Ted,

Please take a minute to explain what the advantages of using 2021 Al would be? I'm just curious.

Thanks,

Marc Green
Marc Green
anodizer - Boise, Idaho


 

Sorry, that was a typo. Should be 2024. Quoting from AESF's Intensive Training Course: "2024 alloy ... requires the highest voltage to produce the desired current density but forms the thinnest film." For these reasons it steals the least current, is most easily stripped because of its thinness, and lasts the longest because the amount that has to be stripped on each cycle is the least.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



(2007)

Q. In the anodizing industry, some people are using titanium racks and some are using aluminum racks. Why? What is the main difference? On the surface, Ti racks cost more, (5-9x) but last a lot longer. Aluminum racks have to be stripped after each use.

How do anodizers decide which kind of rack to use?

Ken Kuang
supplier - San Diego, California


(2007)

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.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


July 17, 2014

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.

humphrey sylvanus-peek
anodizing - fleet hants uk



Must rack area be considered in calculating anodizing current?

April 12, 2014

Q. I'm so happy I found threads like this.
I'm new to anodizing and I'm using an LCD (low current density anodizing) kit from a hobby plating supplier.

Regarding Paul's post on letter 30512 (which is very helpful), he mentioned something about surface area related to racking as follows:
"This assumes no voltage drops due to bad connections, and you haven't increased the actual surface area with racking."

My question here is does the racking area affect the calculation?
If the answer is yes, does this change with the material type of rack titanium/aluminum.

Thanks again for all this great information.

Mohamed A. Moniem
- Cairo , Egypt


July 20, 2014

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

Marc Green
Marc Green
anodizer - Boise, Idaho



Why Not Copper Racks for Anodizing?

October 13, 2017

Q. Do you think copper jigs are fit for anodising and electrocolouring as they are very good conductors of electricity? Why are people are not using copper as material for jigs?

Sachin Jindal
Jindal exports - Mandi gobindgarh, India


simultaneous October 15, 2017

Hi Jindal
If you make copper anodic in an anodising solution it well dissolve, the parts will be ruined and the solution will become unusable. You can use copper for the frame of a jig but the exposed contact points should be aluminium or titanium and the rest well insulated from the solution.

geoff smith
Geoff Smith
Hampshire,
       England



October 15, 2017

Because copper and sulfuric acid anodizing are not very compatible. The copper rack, or rack tips, would burn and dissolve into the anodizing solution once the current is applied to the work.

The same reasoning is behind why 2xxx series (high Cu content) Al can be challenging to anodize.

Marc Green Marc Green
anodizer - Boise, Idaho



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