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How to Anodize Aluminum

How to Anodize Aluminum

We are often asked for a general description of the process steps to define how to anodize aluminum.   Here is an overview of what a typical industrial aluminum anodizing line would involve.  Note that we are assuming the parts have already been thoroughly cleaned, masked and rack-mounted prior to the chemical processing done here.  Here is an overview of  how to anodize aluminum using the Type II sulfuric or clear anodizing process:

How to Anodize Aluminum Type II Class I, Overview

Looking at these steps more closely:

How to Anodize Aluminum

Step 1:  Place in the cleaner tank for 5 to 10 minutes to remove dust and light oils and then rinse.  We like to have the parts dipped into and out of the cleaner tank a number of times while processing to be sure they are completely clean and free of water break.  It is best to use a cleaner tank designed with an inside weir and a pump so any oils removed from the parts will be skimmed off the surface of the cleaner solution.

 How to Anodize Aluminum steps 1 & 2, Type II Class I

How to Anodize Aluminum

Step 2:  Place in the etch tank for 30 seconds to 2 minutes, depending upon the aggressiveness of the etch solution, then rinse thoroughly.

 How to Anodize Aluminum steps 3 & 4, Type II Class I

How to Anodize Aluminum

Step 3:  Swish the parts around in the Deox tank, then place into the Deox tank to remove any oxidation (or smut) and then leave parts there for 5 to 15 minutes.  Rinse completely.

 How to Anodize Aluminum steps 5 & 6, Type II Class I

How to Anodize Aluminum

Step 4:  Dip two or three times to work any air bubbles out of the parts, then place in the aluminum anodize tank.  Start the rectifier and let it ramp up to the required voltage or amperage.  Note that most specifications call out for a ramp time of 3 to 5 volts per minute.  Vigorous air and solution agitation (if not mechanical agitation too) is required for full, consistent coverage.  After the 30 to 45 minute process time, pull the parts and rinse them very well.  Note that relatively high voltages and certainly high amperage capabilities are present when anodizing, so extreme care should be taken and electrical contacts should not be touched while the power supply is turned on.

How to Anodize Aluminum steps 7 & 8, Type II Class I

How to Anodize Aluminum

Step 5:  Put parts into the Hot Sealer tank (usually just boiling deionized water) for the 15 to 30 minute process time.  Once parts come out of the sealer tank, they should be blown off with clean, dry air until they are dry.

      How to Anodize Aluminum step 9, Type II Class I

How to Anodize Aluminum

How to anodize aluminum as per Mil-A-8625 or Type II Class I is specific to clear sulfuric acid anodizing, but is also a general overview of a “typical” anodizing procedure.  Type II Class II (dyed or colored aluminum anodizing) is the same process as above, but with color dyes right after the anodize step, and to maintain colorfastness in the dyed anodic film, a nickel acetate or dichromate seal is usually used instead of a hot DI seal.

Note that different chemical suppliers will probably call out different process times, and many customers (especially aerospace or aircraft manufacturers) may have different process parameters and / or preferred chemicals and vendors, so if you are considering having an aluminum anodizing line designed for your specific needs, the types of parts and your key customers may be an important factor to consider.  How to anodize aluminum may vary slightly based upon these considerations, but not substantially.

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