Summary for alochrome primer flaking Discussion
Flake off alochrome with primer is the central problem in this thread: Khair Shishani reported that parts treated with Alochrome 1200s and then room-temperature cured primer were flaking, with the primer coming off together with the Alochrome and exposing bare metal. He noted that monthly salt spray and adhesion tests had not failed. Shazli Rani later described a similar paint-peel issue on clad aluminum after alkali clean, rinse, de-ox, Alodine, rinse, and dry, and said trials showed that de-ox times longer than 4 minutes caused paint-adhesion failures; reducing de-ox to 1-3 minutes helped. Larry Brayden added a related concern on high-strength steel landing gear parts primed with BMS 10-11 type 1 and asked whether a primer batch issue might be developing. The thread suggests process timing and material-specific sensitivity may matter, but it does not give a single confirmed root cause.
2004
Q. Hello,
This is our first experience having this problem. We treated the part with Alochrome 1200s process and followed by priming. The primer is cured at room temperature. We found out that the primer flakes off together with Alochrome . (The Alochorome sticks to the primer after flaking ).This exposed the bare metal on the part. We conducted 3 monthly test for salt spray test and paint adhesion. So far we never failed.
We have conducted some experiment. We treated one test piece with Alochrome process and bend it. We found out the Alochrome still attached to the plate. Then we treated Alochrome and primer on the second test piece. After we bend it, the primer flake off at certain area together with the Alochrome. The primer that we are using is mixing of primer and activator. Any info is much appreciated.
Thanks,
Zuraida Mohamed
Plating shop at aircraft manufacturing company – Sungai Buloh, Selangor, Malaysia
A. Zuraida,
Having seen this problem first hand in the past it is clear that the chromate conversion is not adhering correctly to the substrate. There are a few possible causes to this problem. Firstly the pretreatment of the material prior to the Alocrom 1200 process could be the root cause. In most cases the material should be vapour degreased using trichloroethylene, cleaned aqueously and de-oxidised prior to Alocrom. I find that if I degrease until condensation stops, aqueous clean for 5 mins, and de-oxidise to remove 10 microns/surface/hour, the alocrom coating adheres perfectly. following alocrom 1200, dry the material at 30 degrees C for 10 – 20 mins. It is also prominent to leave the material untouched after alocrom 1200 process for up to 2 hours, as the coating is very fragile, and can be easily damaged. A final though on this matter would be the curing of the paint, which could require curing at a higher temperature. This you will have to find out from your paint supplier. I suggest trying this sequence of processes and re-testing, and hopefully things should work out correctly for you.
Best Regards,
Stuart Haynes
– Manchester, England
2004
A. May be you have water contamination, before primer, shop air filter, part not properly dried and etc.
Good luck
Khair Shishani
aircraft maintenance – Al Ain, UAE
2004
Q. I am taking on where Mdm Zuraida left off. Trials were done using test pieces and actual parts (which were scrapped). The paint peel we faced were confined to clad aluminium. The processing step were, alk clean, double rinse, de-ox,double rinse, Alodine, double rinse and dry.
We played around with the de-ox immersion times, spec allows
1-10 minutes. We found that anything de-ox’d for more than 4 minutes will fail paint adhesion (paint with Alodine). paint used were both normal cured and oven cured to manuf requirements. Now the de-ox is limited to 1-3 minutes. Can’t really understand what happened. Can anyone shed some light?
Shazli Rani
Plating Shop -Aerospace Manufacturing – Sungai Buloh, Selangor, MALAYSIA
February 28, 2008
Q. We have recently started seeing the same problem with primisg of high strength steel landing gear parts using BMS 10-11 type 1. Is it possible that a primer batch issue is emerging?
Larry
Larry Brayden
– Dublin, Ireland
April 25, 2008