51035

Alodine? Chromating Alum tubes.  

January 23, 2009

Not being that familiar with all of this, I am looking for some answers. We have some alum. tubing that is anodized. We machine the ends (face & thread) and then assemble the complete product. We are finding that while in the field these parts are beginning to deteriorate where the anodizing was cut. I am looking for an in house way to coat these. I can have them sent out to our platers to be anodized or chromate dipped but that adds to our lead time. I have tried the alodine 1132 pen and that does not work as well as I would like. I see that we can dip these ourselves but am worried about disposing of the waste and the rinse water. Do they have to be rinsed at all or can they just be left to dry. Is there a process to coat these that will give me a good finish for a harsh enviroment, that will not produce waste that needs to disposed of by a service?

Any help or suggestions would be greatly appreciated.

Thanks,

Dan Cibulskis
product manufacturer - Aurora, IL, U.S.A.

There is no good way to do a "cheap" good job.
Ideally, You would do all of the machine work, then alodine or irridite the whole tube, mask the threads and anodize the whole unit. The prep steps for the anodize will remove the unmasked chromate conversion coating. The masking/demasking is the expensive step.
There is no good way to "hold" the part for the mechanical steps after anodize. It may look OK, but it damages the anodize. Since those steps should be done with cutting fluid, now you have a problem of getting the part clean enough to chromate. Also, a proper chromate will use prep steps that will damage the anodize. You will have a problem with most companies certifying the product if you do not do the complete process. Also, the chromate will be inferior if you do not.

James Watts
- FL

Dan,

You mentioned the Alodine 1132 pen. Was the touchup area exposed to air for any length of time prior to your touchup attempt? If so, clean the surface to be chromated with a scotchbrite pad to remove oxidation, then touchup with the 1132 pen. The chromate coating should form a bit quicker than direct application to the unclean/oxidized surface.

Terry Lycans
Aerospace - Dayton, OH, USA

Actually it is common to chromate areas that are machined after anodizing. I have seen several examples of this. Also there is such a thing as a no-rinse chromate. Talk to the chromate suppliers about the suitability of their product.

Leo Herringon
- Grand Rapids, MI, USA