Summary for hard anodised parts painting Discussion
Hard anodised parts that are subsequently painted was the core issue in Simon Ossage’s question about 6082 aluminium parts with some anodised areas left exposed. He asked whether a 24-hour limit before the first paint stage was truly necessary, noting that his samples showed no adhesion problems even when painted later. He also asked whether hot-water sealing after painting was pointless if self-sealing had already occurred, and how much sealing improves corrosion resistance for parts exposed to seawater and freshwater rinsing. Finally, he questioned whether etch primer has any value on anodised surfaces. The excerpt provided does not include any answers, so no consensus or named advice is available from the thread text shown. The practical takeaway from the question itself is that the process sequence was causing handling damage and rework, and the key technical uncertainties were the validity of the timing limit, the benefit of later sealing, and the usefulness of etch primer on anodic film.
April 17, 2013
Q. Hi, we are producing parts from 6082 aluminium that are hard anodised then painted leaving some areas of the anodising exposed.
We have a restriction in that the parts must have their first paint stage complete within 24 hours of anodising after which final painting takes place in normal time. We then completely immerse the part to hot water seal the remaining areas. As well as being a logistical nightmare with parts shuttling between anodisers to painters then back to anodisers the extra handling is resulting in damage and a lot of rework.
I have a couple of questions:
1. Can anyone tell me if the 24 hour time frame is valid? We have looked through all the literature we can find and the only reference available is a Boeing specification stating 16 hours. We have done many samples that are way beyond 24 hours with no observable effect on adhesion
2. If the answer to 1. is affirmative and self sealing will occur at > 24 hours are we wasting our time subsequently hot water sealing? This is typically occurring at 1 to 2 weeks after anodising when paint is complete
3. We believe hot water sealing increases corrosion resistance compared to self sealing but by how much? These parts will be subject to multiple immersions in sea water followed by fresh water flushing but small amounts of sea water may be trapped in the anodised areas.
4. The paint scheme is etch prime, prime and top coat. It is my belief that the etch prime is useless on an anodised surface – am I correct?
Thanks in advance
Simon Ossage
Product Assurance Engineer – Portsmouth, England