Rick Watson

Re: Small Part Problems

Hello,

I would like to get some feedback on a problem that I have been fighting for the last couple of weeks.

We are trying to black anodize small parts in high volume (cheap price) on titanium racks. The material is 6061 and there are various machined sizes, but all are small. They will all easily fit on every station of a 144 station pin rack.

The problem is that when we run these parts on titanium they "burn" on the edges. I have tried various coating thickness from .0004 (blue) to .0014 (black but burned). In order for me to get the parts black, they burn.

The interesting thing about this whole situation is that I can run these parts on aluminum racks up to .0015 thickness with no burn whatsoever and black as the ace of spades!

Now for what I have tried on the titanium:

Less amperage for longer time
More amperage for less time
Cooler acid temperature (68 F)
Increased acid tank agitation
Brand new titanium racks
Decreased quantity of parts on rack
Added anti-burn chemical to acid tank

My acid concentration is good, as is the aluminum content. I am having no problems with anything else burning, just this one job. Additionally, we use these titanium racks almost exclusively in our operation with no burning.

At this point, I would like to hear any thoughts you guys may have on this matter. I am out of things to try. Thanks in advance for your help!

Regards,

Rick Watson

Chris Snyder

Re: Small Part Problems

Rick
For me most burning of anodizing is caused by some type of localized overheating. As I am guessing that you are talking about Type 2, CL2;
(If you are taling about Type3 Cl2; It is a different set of problems)

1.If your are anodizing by amp (not volts) and resistance can cause an overvoltage problem and then cause a overheating problem then in turn cause a burn.

2.When you load your tank with parts you can change your aggitation flow and then in turn change the agitation around a area of a part that could cause overheating

3. Do not go over 20 volts (18 normal) on 6061

Chris Snyder

Re: Small Part Problems

Are you sure that it is 6061 material

David B. Hunt

Re: Small Part Problems

Rick: 

I think your first idea of using aluminum racks is the easiest answer.

Ryan Cook

Re: Small Part Problems

I do not think the alloy is 6061 I have this question..   what color are the parts after they come out of the etch? Grey dark grey, black???

Sounds to me like you have a serious voltage issue OR the rectifiers may be acting up...(post how many volts/amps you were reading during the plating cycle...)

I routinely plate 200+ parts  at a time on titanium racks..  i plate by voltage and let the rectifiers do the rest..

I plate at 16.5 volts for 30 minutes and apply commonly 4-6 tenths..  no burning at all ever..   No additives, etc... My parts come out of the black Dye black.   

I have this question..   how well do you rinse the parts before they go into your plating tank?  Possible contamination out of the deox????    Copper and zinc have a bad effect on plating baths and can sometime simulate a burn..

let me know how it turned out...

Labrat

Re: Small Part Problems

Titanium racks used anodically forms a very hard titanium oxide layer, especially on the tips of the racks, being closest to the cathodes. If your rectifier is set on constant amperage instead of constant voltage, this oxide layer may be causing electrical resistance, which causes the voltage to increase to overcome the resistance, causing burning. To see if this is a possibility, try sanding the rack tips agressively, then process again.

Hope this helps.