For this technical lesson we will deal strictly with aluminum and its anodizing properties. Anodizing involves the immersion of aluminum into a suitable electrochemical solution which is subjected to a current flow. The electrochemical reaction between the solution and the aluminum forms an oxide film on the surface of the aluminum. The amount of oxide produced can be controlled with great accuracy.
Hard Anodizing is also called HARDCOATING. Hard anodizing is a term used to describe the production of anodic coatings with film hardness or abrasion resistance as their primary characteristic. They are usually thick by normal anodizing standards and they are produced using special conditions. This type of anodizing is often used in applications where components require a very wear resistant surface such as pistons, cylinders, and hydraulic gears. They are usually left unsealed but can be impregnated with materials such as waxes or silicone fluids to give particular surface properties.
Since hard anodizing is a process which adds a coating to the surface of the aluminum, it is necessary to understand how this process works.
Hard anodizing is an anodic process which will penetrate 50% and build-up 50%. Therefore, your part dimensions will change by .002" on a .002" hardcoat or finish thickness. The finish thickness (penetration and build-up) of hard anodizing can vary allowing a finish thickness from a few tenths to .003". Your particular requirements depend on a number of factors such as engineering requirements or. Therefore, it is essential to allow for the hardcoat build-up changes on blueprints and/or purchase orders. Our STANDARD finish is .002".
Our process conforms to a number of standards and specifications. Please check with us to see if your needs can be met. The most common standards which we conform to are Mil-A-8625 Type III Class 1 and 2, Mil Std-171 Finish 7.5, AMS 2468, and AMS 2469. Other corporate standards can be met as well.
Working with various aluminum alloys can pose a number of problems. Hard anodizing some alloys is not recommended. The list below briefly describes each alloy along with their hard anodizing properties.
Please remember that the coating thickness of hard anodizing is 50% build-up and 50% penetration. In other words a .002" coating will only build-up .002" per side, not .004" as in plating or painting which is 100% build-up. Hard anodizing coatings may vary a few tenths to as much as .008" depending upon engineering requirements. Remember, the STANDARD coating is .002".
Since all alloys can be hard anodized, however, some are more difficult than others . In addition, problems can arise while hard anodizing different alloys at the same time. If the lot of parts are made up of different alloys the finish thickness will vary from part to part. Each alloy anodizes at a different rate, therefore, the amount of anodizing can vary from alloy to alloy.
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