White spotty haze after sealing and dry

[blackcote]

As long as the parts are wet they look prestine... but after they dry... there is this white spotty haze or film (neither word is a good description.. it's more of a haze with white spots in it). Searching around I found maybe a possibility that I need to increase the Current Density? I was thinking that it was some particulate matter in the dye... but I have not experimented with drying the parts before sealing to see if it shows up at that stage yet. Sealing process is through the boiling water method. To remedy this for now we have been applying a very mild aluminum polish (used on automotive wheels) and it seems to work... or maybe it is just covering the spots up. I don't know but they look very nice afterward. But on the brushed finish parts, our client is not satisfied with some parts as we think the polish might be building up in the brushed grooves and causeing more of a buffed look than desired.

Has anyone else run into this haze that might point me in the right direction??

[sswee]

Re: White spotty haze after sealing and dry

I've seen it caused from dissolution, old sealer, tap water being used in a step, and letting the part dry coming out of sealer before the rinse. Since you said you boil to seal, we can rule out the sealer related causes. Most probable would be dissolution or something in the water. What CD and run time are you using? Are you using RO water to boil?

[kickn]

Re: White spotty haze after sealing and dry

You should also check the acidity of the boiling water - I always neutralise first before sealing so that there is no acid left on the part - this has all but eliminated the streaks we used to get.

[Sid03]

Re: White spotty haze after sealing and dry

I've seen it caused from dissolution, old sealer, tap water being used in a step, and letting the part dry coming out of sealer before the rinse. Since you said you boil to seal, we can rule out the sealer related causes. Most probable would be dissolution or something in the water. What CD and run time are you using? Are you using RO water to boil?

what he said ^

[blackcote]

Re: White spotty haze after sealing and dry

We use distilled water in the boiling operation. Letting the part dry after boil seems to exaggerate the haze. We now rinse in cold water immediately after boiling... and it seems to reduce the haze somewhat. Rinses are via a tap water. All other steps are distilled. CD is around 10 ASF using CV for now. It takes a good 90 minutes to get a good deep black color. Temps around 70. I'm getting very consistant results, but I'd like to reduce the time, but haven't had time/courage to experiment with changing parameters.

So your ruling out sealer (both old and drying after?) as I'm not using a chemical to seal. I'm leaning toward tap water for rinse rather than dissolution... based on that I've seen less color absorbtion when I use less time to anodize. I got some more parts coming today and will try the distilled rinse this weekend and see if it helps.

Thanks.

[sswee]

Re: White spotty haze after sealing and dry

Changing the rinse to distilled is the first thing I would try. According to the 720 rule a 10A CD should only have to run 72 minutes for a one mil coating with a peak voltage of 25V. I use CC power which has given me more consistant results. On the dissolution possibility, what tank temp. do you run and what kind of agitation is used? Both can increase dissolution even if the rest of your parameters are in range to give a good coating.
SS

[blackcote]

Re: White spotty haze after sealing and dry

Tank temps are around 70 very, very rarely getting above 72. Agitation is via air pumped to the bottom of the tank in a loop around edge the air directed to center of tank.

I'd like to use CC, but have not had much luck/consistency with it other than the LCD use (which takes too long to do when more volume is needed) and we do a fair amount of random size parts and figuring area gets to be a tedious task that takes too much time for the number of parts being done. I've always wondered if I could just hook the parts up and turn on CV and get a rough amp reading and then switch to CC... seems a little naive to me though.

[sswee]

Re: White spotty haze after sealing and dry

The agitation makes a huge difference. If you do enough to warrant the expense, you may want to look into a pump to circulate the electrolyte. It was worth it on my setup in better results and no acid mist.

I am not familiar with procedure on anodizing parts CV with unknown SA. I have always calculated SA. The difference for me running CC instead of CV is I did not have to watch for PAR. On LCD run times, using an 8A CD on CC runs 90 min for a 1 mil coating. If you can tell approx. SA by current draw in CV, I would be curious if you couldn't take a reading then switch to CC.

[M_D]

Re: White spotty haze after sealing and dry

It could be the tap water rinse you are using; I have seen that cause a haze during the sealing process. It would be a simple test to use RO or distilled water before the sealing. Another way to test is to blow a part dry before sealing, and leave one wet with tap water.

We use 8-12 amps CD, depending on the parts and can get a good black (or other color) in 50-70 minutes anodize time.

Dye will get weak after a period of time, which might be one explanation why you have to anodize longer to get the color acceptable. Another might be that the parts aren?t getting as much current as you calculate.

When you push the anodizing time far enough to get mild dissolution it softens the anodizing so it will dye easier. At higher current densities like 10-12 amps I believe a higher concentration of acid works better (for dying) with a shorter anodize time. Otherwise the anodize layer is harder (less porous) and doesn't dye as well. It's something to think about if you don't eventually find the problem.

I don't think 72? electrolyte is the problem, but as sswee said if the circulation isn't enough to keep the part surface cooled it can easily get to warm without the tank temp getting to warm. It depends on tank volume to current ratio. If you swish a part (which cools the part surface and boundary layer of electrolyte) and watch the volts (CC mode), they will usually go up. The higher the volts go, the more likely increasing the agitation will help. The volts will fall to normal after a few seconds of leaving the part stationary, assuming they went up to begin with. The warmer the temperature, the less volts needed to maintain X amps.

We use CC all the time at 12 amps CD, but we do mostly parts we machine and know the surface area to a high accuracy.

There are so many different types of haze and smut, but if you can wash it off with soap and water or wipe it with a dry towel and end up with a clean part, then it probably isn?t dissolution.

I have found when everything is in balance that the parts will never look cleaner or nicer than when they are first dried off after the sealer step. It's easier said than done, but it is nice when you achieve that.