Coil Anodizing Guidelines

Aluminum Coil & Coil FinishingThe following are guidelines relevant for all anodizers, including coil anodizers, regardless of anodizing specialty. Most coil anodizing applications are situational so a discussion with an SAF Anodizing Pro can be productive in setting expectations.  For information on SAF Aluminum Coil Anodizing Services visit www.saf.com/coil

  1. Always check the aluminum alloy for anodizing quality compatibility.  Mixed aluminum alloys or tempers will not produce uniform anodizing results. Die castings are difficult to anodize due to their porous nature, even if made from an anodizing quality alloy.  We recommend anodizing 5005 aluminum for sheet and 6063 aluminum for extrusions for best results.
  2. Assemblies for anodizing must have drainage holes to prevent solution entrapment.  Top holes are required for admission of air, and bottom holes for drainage.  Anodizing chemicals can leak through even the tightest welded joints, so drainage must be accommodated in the anodizing process.
  3. Two flat surfaces fastened to one another can trap anodizing solutions during processing, potentially leaking out later and damaging the aluminum finish.
  4. Aluminum assemblies for anodizing should never include non-aluminum materials.
  5. The correct aluminum alloy must also be specified if welding is involved.  For welding, 4043 aluminum is the worst choice for anodizing because it will turn a smutty black.  The preferred alloy for welding applications is 5356 aluminum.
  6. Anodizing surface quality is dependent on the furnished aluminum metal.  Anodizing does not cover up scratches or water stains.
  7. Aluminum must be kept dry and handled with gloves to prevent stains.  It is critical that aluminum be kept dry in transit.
  8. Because the aluminum must carry a certain amount of electrical current per square foot of anodized area, full size sheets must be at least 0.032″ thick.  Formed sheet should also be at least 0.032″ thick.
  9. If you have a coil or other aluminum part for anodizing specification requirement, please provide it on the front-end.  Additionally, for coil processing it is always helpful, if not critically important, for the coil anodizer to be fully informed about the end-use of the aluminum coil.
  10. Perhaps most importantly the aluminum coil, sheet, extrusion or part anodizer needs to know desired racking points on material.  The aluminum racking points carry the current needed for the anodizing process, but no anodization will occur where the rack touches the metal.  For architectural aluminum parts we often use a 3/8″ bolt for racking that has a halo of perhaps a square inch.  Racking instructions are critical!  It is also important to know which surface areas are exposed so we can inspect them for scratches, stains, etc.
  11. Aluminum fabrication should be done prior to anodizing.  An anodized surface will be subject to cracking or crazing when formed after anodizing.
  12. Make sure all aluminum is properly packaged well before shipment to the anodizer.  When possible we will re-use our customers packaging to reduce waste, but our motivation is really to ensure the professionally finished aluminum metal arrives dry and free of scratches and dents.