Basically, the electric current forces the positive ions to attract to the negatively charged plates while the negative ions are attracted to the aluminum part, which the positive anode. From here, the electrochemical reaction forces pores to open up on the surface of the aluminum so that the positive ions can escape.
In a uniformly geometric pattern, these pores dig down into the substrate of the part. The combination of the aluminum surface and negatively charged ions create a barrier layer, which is known in the anodizing aluminum process as the surface layer the makes parts resistant to corrosion.
Anodized Type I: This is the most basic type, using chromic acid to produce a thin and ductile anodized layer on an aluminum part. Anodized Type II: Instead of using chromic acid, Type II utilizes sulfuric acid in order produce a thicker anodized layer on a part, making it more suitable for coloration. Anodized Type III: Similarly to Type II, this method also uses sulfuric acid, but produces a thicker anodized layer that is also suitable for coloration. Anodizing aluminum parts also presents an array of options when it comes to adding color.
The coloration process works by injecting a pigment into the empty pores of the part. You might not realize it, but you probably interact with products and parts that have been anodized on a daily basis. There are a number of benefit you can leverage when anodizing aluminum parts, both visually and mechanically. The most common way to specify different types of anodizing is by the military specification for anodic coatings for aluminum and aluminum alloys MIL-A Type I anodizing, the oldest known method, is performed in a bath of chromic acid.
Type II anodizing, being the most commonly applied, has a layer with a thickness ranging between 1. Type III anodizing, also known as hard anodizing and used where increased wear and corrosion resistance is desired, consists of oxide layers thicker than 25 nanometers. Choosing whether or not to anodize your aluminum extrusions depends on the intended applications for the products. As this article has highlighted, there are both benefits and drawbacks to anodizing.
In that case, anodizing could be ideal for finishing your extruded products. However, anodizing might not be the best option if electrical conductivity is essential or if further forming processes are to be performed on the piece. These might cause the oxide layer to crack. Anodizing also slightly increases the dimensions of the piece. Therefore it is not recommended if you are working with very tight size tolerances. If you are looking for alternatives to anodizing, you might consider using powder coating as a way to finish your aluminum items , giving them a bright colored finish.
If a matte finish works for your application, and you need more extended durability and protection against UV fading, you might consider PVDF coating your aluminum products. Aluminum extrusions can be designed to fit a wide range of products used in various industries. But product designers often have difficulty achieving optimal extrusion profile design and reducing manufacturing costs.
In this guide, we provide 11 tips to help you optimize your designs for the extrusion process. For typical non-hard coatings, the depth can be up to 10 microns. Once this level is reached, and if no color is needed, the process is stopped and the surface can be sealed simply by rinsing in water.
That will leave you with a hard, natural aluminum oxide coating, able to withstand chemical attack and very scratch resistant. Aluminum oxide is rated 9 out of 10 on the Mohs hardness scale, meaning second only to diamond. Hard anodizing, sometimes called Type III, offers greater corrosion protection and resistance to wear in extreme environments or with moving mechanical parts subject to a lot of friction.
This is produced by continuing the electrical current until the depth of the pores exceeds 10 microns, all the way to 25 microns or even more. This takes more time and is more expensive but produces a superior result. What is oxidation? It simply means to react with oxygen. And oxygen is very reactive, readily forming compounds with most other elements.
When aluminum is exposed to the atmosphere it quickly forms a layer of aluminum oxide on the surface, and this layer provides a degree of protection against further corrosion. But aluminum must withstand more than just pure air and water. Acid rain, salt water and other contaminants can still exploit weaknesses in the surface passivation. Even modern alloys will vary in response to this environmental exposure, ranging from mere surface discoloration all the way to mechanical failure.
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