Anodized finishes provide outstanding surface properties including excellent resistance to abrasion, erosion, and ultraviolet light degradation. These finishes are highly durable, have an exceptionally long life expectancy, and require only minimum maintenance.
Some basic guidelines to consider when preparing metal for an anodize finish are:
No mixing. Mixed aluminum alloys or even tempers will not produce uniform results. For best results use 6063 alloys for extrusions and 5005 for sheet stock.
Bend and form before finishing. Anodic films are very hard. As a result most post-production bending will lead to the film “crazing,” which will give the appearance of a spider web. Crazing produces a series of small cracks in the finish.
Store properly. Store aluminum in a dry and controlled environment. Do not allow moisture to build-up between the pieces as this will cause severe corrosion, known as white rust, which will not be removed in the finishing process. This is important not just to the customer; the finisher should also ensure proper climate control where aluminum is stored.
Avoid adhesives. Tape or adhesive on the aluminum may leave a residue that may not be removed in the anodize process.
Agree on specification and expectations. In the architectural industry, the most recognized specification is AAMA-611. If specific parameters are required, it is important to furnish the finisher with the desired requirements to ensure the job is completed to the customer’s expectation.
Watch for welds. Welded parts will show a color difference on the weld versus the remainder of the part. The heat developed from the welding process can disturb the metallurgy on nearby metal and cause a localized discoloration after anodizing. Ensure the proper 5356 alloy welding wire is used, and the lowest heat possible.
Prevent solution entrapment. Proper drainage holes are essential for drainage of solution allowing entrapped gas to escape from the parts. Even the tightest of welded joints will cause anodize chemicals to weep out.
Talk racking. The finisher needs to know where parts can be racked. There are a variety of ways anodizers can rack parts, from welding material to spline bars, to a screw down bolt system. In any case, contact marks are visible on the aluminum. It is important to define what is acceptable and what is unacceptable with regard to exposed surfaces and rack marks.
Handle with care. Good shipping practices are essential to a quality job. Prior to shipment to the finisher, package metal carefully to ensure the metal arrives dry and free of scratches and dents.
Quality in, quality out. Metal free from defects will produce a higher quality finish. Avoid sending the finisher metal with scratches, dings, heavy die lines, die pick-up, etc. These metal quality defects will show through the anodize process.