Direction to previous posts

[larryp]

I am having a problem with a sooty deposit on 6061. The dye color is black, the deposit will buff off with some effort. If some one could direct me to previous posts dealing with this it would save reinventing the wheel. My anodize bath is appx 50/50 water/battery acid, I have no chiller so it runs at outside air temp (90-100*f). It does have aeration. Power supply is regulated bench supply. Using cleaner,etch,desmut,anodize,dye,acetate sealer, all have aeration. Clear water rinse after each step. Is the excel based 720 calculator still available, I tried accessing it yesterday but could not get to it. I would like to cross check my manual calculations in case I am way off and that is causing my problem. Thanks, Larry

[cameraman]

Inneresting, gramslam seems to have removed it. You can use the browser based calculator in message #8 of the same thread.

Your acid concentration should be 3:1 water to acid, and temp of 60-75° F.

[acidrain]

Not sure what "prvious post" you are refering to, but here is some help:
The 720 calculator is the 8th post down in this thread: Anodizing calculations (720 Rule)
Your acid is too strong, and the temp too high. Go with 1:3 acid/water, and no more than 70F.
If you are having smut before the ano step, use Caswells de-smut.
If you are having smut during the ano run, it's because of the temp and acid concentration.
Also, be sure to calculate and adjust your amps per 720 rule.

[larryp]

cameraman, acidrain Thanks for replies. The previous posts I referred to were ones that it seems every new guy (me) asks and have been asked time and time again, I didn't have any specific posts in mind. I thought if some all time classics came to mind you could steer me to them. The smut is not apparent until the part comes out of sealer. They have been looking good in all steps prior to that, at least to my inexperienced eye. I'll figure something out to chill the bath. Following is a link to the power supply I use. http://www.bkprecision.com/www/np_specs.asp?m=1689 Could somebody tell me if it is appropriate for the job? About the max amps I can get out of it occasionally is 9-10 before it nears the voltage limit of 15. Most times it runs about 3-5 before running out of steam, sometimes it won't get over 1 to 2 amps. My method of operation is to figure the surface area, get the parts in bath and under power, turn the power supply up until it peaks amps, then figure time in bath using 720 rule. I got the calculator application on my my machine without incident, thanks. For my enlightenment, what effect is the high acid ratio likely to cause? Larry

[acidrain]

Ahhh... makes sense.
The effects of acid too strong is desolution. Same with temp too high.
Desolution is when the acid is eating the ano layer as fast as it's being formed. The result is a soft, chalky ano layer that is not durable, and will not hold dye well. Usually it's evident after sealing.

[cameraman]

I don't think anyone minds re-answering questions, although you can sure learn a lot from perusing old threads.

To chill, I've used bags of ice (left in bag - don't contaminate your acid) and have siphoned acid into bottles and stuck in refrigerator overnight.

The power supply at your link isn't constant current. A constant current supply has a knob with which you set the current output, and the power supply varies the voltage as the part's resistance increases. You'll have much better results with CC, and you may not need it to be as big as you might think. Try plugging numbers into the calculator - at 3 amps you can anodize up to 96 in² (4.5 amps/ft² CD). Caswell's 3 amp rectifier is a little over $100. Their next one up, 5 amps, would anodize 160 in². You can also usually find good deals on eBay. If you plan to do much anodizing, it's a worthwhile investment.

[larryp]

cameraman,acidrain, Thanks for the consideration/time given to my questions. Back on the acid deal, I am using battery acid (35% sulphuric if memory serves). Should I still use 3:1 ratio when using battery acid rather than pure acid? As an additional thought, the sooty deposit seems to occur when I attempt to run the power supply output higher. I'll work on getting a more suitable power supply. Thanks again guys. Larry

[cameraman]

Sorry, you're right, that's misleading - I tend to take it for granted that we're talking battery acid and not concentrated acid. It should be stated 3 parts water to 1 part battery acid.

[larryp]

Results of 7/20 efforts. Got anodize bath in an ice bath kinda like salad bar, was able to stabilize temp at 68-70*f. Changed bath concentration to 3 parts distilled water/ 1 part battery acid. Ran parts at 1.5-2 amps for 4 hrs. which according to calcs was just right for 1/2 thousandth thick film. Lance Caswell gave me guidance on proper calcs. Result was once more a sooty deposit after sealing. This deposit may have wiped off easier than the previous sooty deposits. I'm keeping all other baths at proper temps, plenty of rinsing, doing ju-ju rituals. I've done some things when just starting to run stuff that came out of sealer all shiny and beautiful. Since then things have gone astray. Anybody got any ideas? Larry.

[cameraman]

Working backward, it looks like you were anodizing around 220 in² at a CD of 1 amp/ft²?

According to the information I've seen, 3 amps/ft² is about the minimum CD for good dye results. I would think that 1 amp/ft² would be low enough that the anodic layer wouldn't grow fast enough to stay ahead of the acid - meaning dissolution (the sooty deposit).

Could there have been some sort of miscommunication? Using a CD of 3, I calculate 4.6 amps for 120 minutes to get .5 mil.

I'll be interested in seeing what some of the others have to say. It seems to me that you should up the amperage and lower the run time.

The only other thing I can think of is contaminated part - did it pass the water break test?