Posted by VINNY (68.78.140.238) on August 07, 2008 at 18:42:31:
In Reply to: POLISHING ALUMINUM BEFORE HARDCOAT posted by TIM BYRNES on July 29, 2008 at 13:35:03:
: ONE OF THE SURFACES ON A 6061-T6 SQUARE BLOCK GETS POLISHED TO A MIRROR FINISH BEFORE HARDCOATING. WE DO NOT GET THE SAME HARDCOAT THICKNESS ON THE POLISHED SURFACE THAT WE GET ON THE REST OF THE PART. FIVE SIDES WILL HAVE .002 THICKNESS AND THE POLISHED SURFACE WILL ONLY HAVE .0012 THICKNESS. IS THIS COMMON OR IS THIS THE FAULT FAULT OF THE ANODIZER?
Anodizing is a process that dissolves the aluminum of the part being anodized and replaces that aluminum with the anodic coating. It is polished so I would assume your anodizer is limited to the pretreatment he can do to the part without removing the work of the polishing. There are probably compounds that are used in the polishing that are starting to dissolve as the part starts to anodize so it can start anodizing later in the process. You are also removing all the porosity of the aluminum on that surface which makes it take longer to dissolve.
Otherwise, anodize is not selective. It is not the anodizers fault. Maybe you can change compounds for the polishing or just machine the surface flat instead of buffing.