No-Growth Anodizing?

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Posted on: 7/3/2014

Florida finisher says it has the key to limited-growth aluminum anodizing.

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AlOxidize has been successful in anodizing aluminum with almost no growth.

AlOxidize has been successful in anodizing aluminum with almost no growth.

Anodic thicknesses of 0.0008-0.0015 inch have been reached with only 0.00005 inch of dimensional growth.

Anodic thicknesses of 0.0008-0.0015 inch have been reached with only 0.00005 inch of dimensional growth.

Analytical Specialties Inc. (ASI) in Clearwater, Florida, believes it has come up with a better way to anodize aluminum that virtually eliminates growth during the coating process.
Co-owners Keith Eidschun and Joshua Cloakey say their AlOxidize process has been successful in anodizing aluminum with almost no growth. “If there is any growth, it is very limited, maybe less than 10 percent of total anodic coating thickness,” Eidschun says.

There are three primary methods of anodizing aluminum—sulfuric acid anodize (SAA), hard coat anodize (HCA) and chromic acid anodize (CAA). SAA produces a coating that will readily take dye as well as provide moderate corrosion protection. HCA creates a very dense coating that provides excellent corrosion and abrasion resistance, while CAA provides a very thin, very dense anodic coating.

With SAA and HCA, the coating formed penetrates the aluminum and grows outward from the surface at an average ratio of 50-50. Eidschun says this is a big factor. If a part is slightly over-anodized, it must be stripped and redone, and some parts simply cannot regain dimensional requirements.
SAA anodic thicknesses usually range from 0.0003 to 0.0007 inch, while HCA thicknesses range from 0.0018 to 0.0022 inch. A thickness gain of 0.2–0.4 mils can be significant, especially in shafts, holes or threaded features.

With CAA, the anodic coating is practically immeasurable and very dense. Chromic acid is a highly regulated, environmentally hazardous chemical, and the resulting coating is somewhat fragile and not rated for abrasion resistance.  

ASI’s AlOxide process is designed to offer the limited growth of CAA, the corrosion and abrasion resistance of HCA, and dying capabilities of SAA, all in one-tenth the time. Eidschun and Cloakey developed the process when they were challenged with finishing tight-tolerance customer parts at Freedom Metal Finishing, which Eidschun also owns.

Anodic thicknesses of 0.0008-0.0015 inch have been reached with only 0.00005 inch of dimensional growth, or 3-6 percent of anodic coating thickness. “Tight-tolerance products can be machined straight to dimensions they seek and not experience the customary growth of the anodize process,” Eidschun says.

Additionally, the process attains the desired coating in much less time at current, and the coating is much denser than with traditional SAA, he says. It has also proven to improve solution life as well. The average rate at which anodic thicknesses are obtained is 0.0001 inch/minute, and ASI was able to get sulfuric anodizing results in 5 minutes and meet hard coat thickness requirements in 15-20 minutes.

“It is also less susceptible to ‘burning,’ or any adverse effects that come from applying too much voltage or amperage,” Eidschun says. “Speeding up the typical process will save on power and improve profits.”

Cloakey adds, “The solution has a special ability to be unaffected by surface contaminants on parts that are anodized compared with conventional anodizing,” and perfectly clean aluminum is no longer necessary.

The anodic coating weight is roughly twice that of an SAA coating of the same thickness. Twice as dense, it gives the anodic coating the highest level of corrosion and abrasion protection that HCA offers, combined with the speed and ease of an SAA, he says.

“With only 0.0003 inch of coating, we were able to go 800 hours before showing small signs of pits,” Cloakey says. “Coatings with only 0.0008 inch of anodic thickness were able to pass back-to-back Taber abrasion testing.”

Both Eidschun and Cloakey believe their patent-pending process could be one of the biggest developments for anodizing since its discovery. “To be able to provide a faster, harder, denser and limited-growth anodize will by all means change what is known today of anodizing,” Eidschun says. 

Freedom Metal Finishing is the only shop currently providing this process, and ASI is seeking chemical distributors.

For more information, contact Keith Eidschun at keitheidschun@gmail.com, or visit asi-anodize.com or freedommetalfinishing.com 

 


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