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Aluminum Anodizing

Aluminum anodizing is a finishing process used on aluminum to harden surfaces and to increase the wear resistance and corrosion resistance of this corrosion-prone metal. It works by engaging in electrolytic passivation and thickening the layer of oxide on the metal’s surface. This oxide layer occurs naturally on aluminum alloys, and therefore the process of anodizing is used most often on aluminum surfaces and aluminum alloy surfaces. However, anodize finishing can also be applied to metals like titanium, where it would instead be called titanium anodizing. Read More…Request for Quote

Leading Manufacturers

Toronto, ON | 1-888-741-6159

Chicago, IL | 877-409-6486

Chatham, ON | 877-556-9191

Burbank, CA | 800-497-5569

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Products Finished

In architecture, manufacturers use the process to increase the structural stability and strength of elements like roofs, exterior surface panels, and window frames. In the automotive industry, aluminum anodizing is used as protective housing for exposed aluminum parts in auto shops, and to put the finishing touches on vehicle components like trim. Next, aluminum anodizing increases the strength of the protective outer casings of electronics like satellites, mp3 players, cameras, and more.

Food and beverage applications, both commercial and domestic, benefit from the resilience of anodize finished pots, pans, and other cookware and utensils. Finally, in industrial manufacturing, manufacturers perform aluminum anodizing on plant equipment like conveyors, electrolytic capacitors, and scales.

History

Anodizing got its start in the 1920s. First, in 1923, British citizens Guy Dunstan Bengough and John Macarthur Stuart received a US patent for their anodizing method. The British government later documented this finishing method, called the Bengough-Stuart process, in their defense specifications. They used it to create corrosion resistant coating on seaplanes.

Also, in 1923, the Japanese patented oxalic acid anodizing. They, and later the Germans, used this finishing process in architecture. Four years later, Gower and O’Brien patented their sulfuric acid anodizing process.

A few decades later, between the 1960s and 1970s, builders began heavily using anodized aluminum in their architectural applications. During those years, aluminum anodizing became very popular. Since then, anodized aluminum building materials have been replaced by powder coated and plastic ones. Nevertheless, aluminum anodizing is still popular, and we are excited to see where manufacturers will take it in the future.

Materials

There are many applications for which non-aluminum anodized materials are employed. Examples of these metals include titanium, tantalum, niobium, zinc, and magnesium.

Titanium is frequently anodized for the improvement of jewelry and other decorative pieces. Anodized titanium is increasingly used with wedding bands, because it is hard and elicits a low allergic response.

Tantalum is material that, when anodized, manufacturers use to make capacitors and for decorative purposes. Manufacturers can manipulate anodized tantalum to exhibit a wide range of colors. They can also control film thicknesses by changing the anodizing voltage and temperature. Typically, anodized tantalum film thickness ranges between 18 and 23 Angstroms per volt.

Niobium is another material that manufacturers like to anodize for decorative purposes. Anodized niobium is a common element of commemorative coins and jewelry. Like tantalum, anodized niobium is available in a wide range of colors and film thicknesses.

Zinc is another metal that servicers anodize with alternative methods. Though they do not often anodize it, when they do, manufacturers use a process introduced by the International Lead Zinc Organization. This process creates an olive-green, hard, and corrosion resistant zinc.

Magnesium is a material that manufacturers anodize on a fairly regular basis. Manufacturers may seal it using oil, wax, and similar materials. Anodized magnesium is popular as a primer for paint.

Process Details

To perform aluminum anodization, manufacturers may employ a number of different methods. However, in general, the process goes something like this:

1. First, manufacturers set up an electrolytic solution bath. They may or may not enhance this with dyes.

2. Next, they take a metal like aluminum and immerse into the electrolytic solution.

3. Once the metal is immersed, manufacturers pass a direct current through the electrolytic solution, causing it to release oxygen and hydrogen.

4. When this happens, the oxygen reacts at the surface of the aluminum, acting as an anode (positive electron) while the hydrogen reacts on its surface as a cathode (negative electron). These reactions manifest as a build-up of aluminum oxide (or a different oxide, if the metal is not aluminum).

Design

When preparing to anodize a part or product, manufacturers think about a number of aspects of the application, such as desired film thickness, desired film hardness, desired film color, and desired changes to the metal. Based on these considerations, manufacturers can decide on process details, like solution/dye composition, electrolyte concentration, solution temperature, acidity, and current voltage. To create thicker or harder films, they will use weaker solutions coupled with lower temperatures and higher voltages. To produce thinner or softer films, they will do the opposite.

Machinery Used

Manufacturers use a number of different systems in order to anodize materials. While they offer customers anodize kits, they most often use themselves anodize equipment including anodizing rectifiers and anodizing rectifier controllers.

Anodizing rectifiers convert alternating current (AC) into direct current (DC). Manufacturers use this direct current to anodize parts that are corrosion resistant. That is because, when passed onto a structure, direct current stops corrosion.

Anodizing rectifier controllers are digital controls that allow manufacturers to carefully manipulate anodizing operations. They are often paired with CNC technology and computer programming. With them, manufacturers can create anodized parts and products with precise layering and colors.

Variations and Similar Processes

To perform aluminum anodizing, manufacturers employ one of three main processes: chromic acid anodization (Type I), sulfuric acid anodizing (Type II), and sulfuric acid hard coat (hardcoat) anodizing, or hard anodizing (Type III).

Type I is the oldest and most frequently utilized anodize process. To make it work, operators match a reactive metal with an electrolytic process that uses chromic acid. (Chromic acid is a corrosive, oxidizing acid that is compatible with most aluminum alloys.) They initiate anodizing by attaching an oxygen-producing anode to the metal being treated and then immersing the metal into an electrolytic solution through which a direct current passes. Throughout the process, manufacturers increase the voltage of this current. As the anode produces oxygen, it creates an oxide film.

Type I is a good option for anodizing, but it reduces the thickness of aluminum only by .02 to .4 mils, which is significantly less than the rates of reduction possible with the other two types. Also, because the EPA (Environmental Protection Agency) has marked the emissions of chromic acid as harmful to the environment, the possibility of its use is limited.

Types II and III both use another corrosive solution, a sulfuric acid solution. This solution, an acid formed from sulfur dioxide, is dense and oily. Both processes are quite similar, but they differ in terms of performance temperature and current density. One notable subtype of type II anodizing is bright dip anodizing.

Bright dip anodizing is an aluminum anodizing process during which manufacturers brighten aluminum to varying levels of luster. It works best on raw aluminum. The harder the aluminum oxide coating manufacturers allow to build up, the brighter it will be.

Type III aluminum anodizing is performed at lower temperatures and at a higher electrical current density, which yields increased anodic growth and much harder surfaces.

Anodizing Types I, II, and III are all processes that can only be applied to aluminum and aluminum alloys. For anodizing of non-aluminum metals, manufacturers may engage in a variety of similar processes. Examples include chromate conversion coating, clear anodizing, color anodizing, black anodizing, titanium anodizing, and a number of custom anodizing procedures.

Chromate conversion coating mainly differs from anodizing in that it allows the electrical conductivity of aluminum to remain intact, rather that neutralizing it.

Most often, chromate conversion coating uses either hexavalent chromium or non-hexavalent chromium. The chemical compound hexavalent chromium, which contains chromium in its +6-oxidation state, is, unfortunately, categorized by the EPA as a human carcinogen.

To avoid the issues attached to this categorization, many manufacturers use non-hexavalent chromium, an environmentally-friendly alternative coating material that meets the requirements of both the Restriction of Hazardous Substances and the European Union End-of-Life Vehicle recycling directives.

Clear anodizing, the most common type of anodize coating, uses sulfuric acid and adds a hot water seal at the end. Manufacturers most often perform clear anodizing for automotive applications.

Color anodizing is a process that manufacturers usually use for aesthetic applications. They usually perform this process after a piece’s initial anodization and sealing. To create colors like yellow, black, and white, manufacturers make use of either metallic salts or organic dyes.

Organic anodizing is an anodizing process during which manufacturers use organic acids, like malic acid, to anodize coatings. Manufacturers must be very careful and attentive when using this process. This is because these acids often cause the current to treat the aluminum with unusual aggression. Such treatment can lead to pitting or scarring.

Benefits

Aluminum anodizing and related anodizing processes offer product customers a wide range of advantages. First, the aluminum anodizing process leaves behind a strong coating that is longer lasting than something like paint or even plating. This is because paint is simply applied on top of the metal, whereas the anodized coating is made to become part of the product. Second, anodized coloring is unaffected by ultraviolet light; it will not fade. Next, aluminum anodizing is an environmentally friendly procedure. Anodized products are recyclable, and unlike organic coatings, anodized coatings do not pose a risk to the environment. Plus, the anodizing process itself is not harmful to humans. Another good thing about aluminum anodizing is the fact that it is cost-effective. Anodized products are inexpensive to make and prove to be a great investment. Finally, anodized products require very little maintenance, as they do not easily scratch and they do not show fingerprints.

Things to Consider

Get the best aluminum anodizing services available by connecting with a high-quality service provider. On this page you will find the names, profiles, and contact information of several aluminum anodizing suppliers we know and trust. Check them out by scrolling up; you will find them nestled in between these info paragraphs.

Before looking at them, we recommend you take the time to put together a list of your specifications, requirements, questions, and concerns. Do not forget to include things like your budget, your project deadline, and your delivery preferences. Also, before agreeing to work with anyone, make sure that they are familiar with and can meet the standard requirements of your products. If you are not sure what standards with which your anodized product(s) should comply, check with your industry leaders. They should be able to advise you.

Once you have got your list together, look over the manufacturers we have listed on this page. Based on which ones appear to offer services best matching your specifications, pick out three or four companies with which you would like to speak. Then, reach out to each of them to go over your application. After discussing your needs at length with each of them, compare and contrast your conversations. Consider which company not only offers the best prices, but also offers the best services for you. Finally, pick out which manufacturer is right for you, and get started on your project. Good luck!

Aluminum Anodizing Informational Video