What did we do wrong?

[Z]

To avoid any problems you should get a Reverse Osmosis system. Well water/city water contain metals, city water can have up to 500 ppm in the water and well water like mine at home as about 110ppm in it. Just go with pure water to avoid any problems all together. Regular tap water is alright for your cleaning stages but Id use pure water for rinsing before you go into the anodize tank and all tanks afterwards.

[fourkbmx]

well water have about 6 up to 250 or more mg/L chlorides you should make a test on the water, because the un-treated water of the wells have also other stuff that can react on the process, i use demineralized water with out any problem.

[blackcote]

Thanks for all the info. We've been using our tap water for strictly rinse steps all else is distilled mixes. So I could see how chlorides if present could get to the other solutions over time. We've only ever had one customer complain of such pitting, but then not everyone is of the same particular mindset... and I guess we've just never noticed it on any other parts. What bothers me about this possible solution (chlorides) is that the parts are not evenly pitted, just certain areas or spots on the part and not every part in the batch gets pitted, just a select few... which would logically point me to something outside the solutions. I would have to guess my logic is flawed from inexperience I guess I'll see if I can find a test kit for chlorides.

[sumo]

looks to me like someone dropped those parts prior to process. You need to check all parts and make phone calls prior to process otherwise, you get stuck in situations like this.

[acidrain]

Originally Posted by sumo

looks to me like someone dropped those parts prior to process. You need to check all parts and make phone calls prior to process otherwise, you get stuck in situations like this.

Huh? How do you arive at dropped parts from pitting?

[destroyer125]

In the second picture, it looks like a ding, the first looks like pitting.

[blackcote]

We got a fairly large batch of parts in today to ano, and I want to use them as my test run for pitting problems before I change anything. My question is since this is 7075 mat'l, If nothing else has changed, should I still get pitting on the parts, no matter the material? We were using 6xxx before.

[blackcote]

We think we have it figured out. Upon processing larger orders there tends to be a bit of a wait in the rinse tanks after the desmut (before ano), becuase the ano process is so much longer than the cleaning steps. The first rinse tank after the desmut gets a fair bit of gunk in it from the rinsing process, and parts were being kept in it for the duration of anodizing another batch. While in there something was causing a reaction to occur with the surface of the aluminum and causing many little spots to be developed, which turns out to be the pitting observed. When the parts were pulled out ready for the next ano run it was fairly obvious that the spots shouldn't be there as all the parts remaining to be run were very non-spotted. What exactly was causing the pitting remains a mystery, but we now know how to avoid it.

[blackcote]

Some pics of the recently discovered evidence. This is on 7075 material.

[blackcote]

And for comparison... One of the customer's pieces with pits that the ano has been stripped.