Summary for anodized part absorbs grease Discussion
Anodized part absorbs grease into oxide layer near edges is the core concern in this thread, where Sam from Kedah, Malaysia asks why clear anodized aluminum assembly parts show an oily surface near edges and screw holes after grease was applied to the threads at the customer’s request. He also asks whether anodizing builds up at edges and whether the oxide layer can crack near threaded holes or edges. Robert H Probert says the grease question is not clearly related to the anodizing issue and asks for the alloy, coating thickness, and free acid before drawing conclusions. He answers the cracking question directly: yes, anodic films are brittle, and the risk is worse with thicker films, low free acid, low temperature, high current, and work-hardened areas such as drilled/tapped holes and edges. He adds that the problem can be reduced, at some cost to hardness, by using higher free acid, higher temperature, lower current, and less work hardening from better tooling.
February 22, 2021
Q. Hi everybody,
My name is Sam from Kedah, Malaysia. I’m a QA engineer.
I’m having some issues with non-official feedback by our customer on some clear anodized aluminium assembly parts with oily surface near to edges and screw holes. We had applied some grease for the screw holes as per customer request.
Below are my questions:
1) Normally, anodizing layer will build up around edges of part? How many µm will it build up as the oxidize layer surface is limited?
2) Will the surface of the oxidize layer crack under external processes especially near to threaded holes or within the threaded hole itself? … or around the edges?
Please advise for the issue above.
Regards,
Sam Tew
– Sg, Petani Kedah, Malaysia
A. When you come back, tell us the alloy, thickness, and free acid. We do not understand the relation between the grease and the questions.
Question 2 is YES. all anodic films are brittle worse with thickness, low free acid, low temp, high current, and near work hardened areas like drilled/tapped holes and edges. At the expense of hardness we can help this problem with higher free acid, higher temp, lower current, and less work hardening by using shaper tools.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
February 23, 2021
Q. Hi Robert,
The aluminium using was 6061/ 6082, using anodizing type II sulfuric acid, thickness around 10~18 µm.
The part we assembled had to put medical grease (Klubersynth UH-14-1600) on screw and screw hole that lock the parts as per customer request.
regards,
Sam
Sam Tew
– Sg. Petani Kedah
February 23, 2021