Anodizing Choices

For our LightSaga project we recently met up with Mr. Baas from Aldor BV, a company dedicated to anodizing and chromating aluminum. It’s amazing how many options and choices there are when it comes to anodizing aluminum, both in pre processing the material, the color selection and the finish. But what does anodizing do in the first place? The process of aluminum anodizing adds a layer of oxidation to aluminum extrusion products. Unlike iron or carbon steel where oxidation creates a layer of corrosion or rust, the anodizing process actually enhances the properties of aluminum. The hard, oxidized layer becomes a part of the aluminum, creating numerous beneficial properties:

  • Durability: Since anodized aluminum extrusion products have a protective layer, they are more resistant to wear from normal handling and usage.
  • Finishing: The process creates a more aesthetically pleasing finish, with either a clear or colourized appearance.
  • Corrosion resistance: The thick outer coating produced, along with proper sealing, increases the corrosion resistivity of the surface as it prevents further oxidization.
  • Lasting Color: The color finish added to anodized aluminum is more enduring due to the surface obtaining more adhesive and porous qualities during the anodizing process. The resulting anodic film coating allows for effective dyeing processes to be applied.
  • Strength:  The anodized aluminum surface is harder than pure aluminum, second only to diamonds with respect to its hard crystalline structure.

Anodized aluminum can be nearly as hard as diamond under the right anodizing process. Many modern buildings use anodized aluminum in places where the metal framework is exposed to the elements. Anodized aluminum is also a popular material for making high-end cookware such as frying pans and pots. Heat is distributed evenly across anodized aluminum, and the process of anodizing provides a naturally protective finish. It is possible to use another electroplating process to make anodized aluminum look like copper or brass or other metals. Special dyes can also be used to color the anodized aluminum for decorative uses.

Because of its strength and durability, anodized aluminum is also used in a number of other applications. Many of the satellites circling the Earth are protected from space debris by layers of anodized aluminum. The automobile industry relies heavily on anodized aluminum for trims and protective housings for exposed parts. Furniture designers often use anodized aluminum as the framework for outdoor pieces as well as the base metal for lamps and other decorative items. Modern home appliances and computer systems may utilize anodized aluminum as protective housing.

Anodized aluminum may not be appropriate for all applications because of its non-conductive nature. Unlike other metals such as iron, the oxidation process doesn’t seem to weaken aluminum. The layer of ‘aluminum rust’ is still part of the original aluminum and will not transfer to food or easily flake off under stress. This makes it especially popular for food-service applications and industrial applications where durability is crucial. The anodizing process consists on a number of steps, all adjustable to create a very big difference in outcome and virtually endless possibilities to give a product an unique and distinctive feel:

  • Pre-Treatment: Cleaning is done in a non-etching, alkaline detergent heated to approximately 60 – 65 degrees celsius. This process removes accumulated contaminants and light oils (such as oils left by skin contact).
  • Rinsing: Multiple rinses, some using strictly de-ionized water, follow each process step.
  • Etching (Chemical Milling): Etching in caustic soda (sodium hydroxide) prepares the aluminum for anodizing by chemically removing a thin layer of aluminum. This alkaline bath gives the aluminum surface a matte appearance.
  • Desmutting: Rinsing in an acidic solution removes unwanted surface alloy constituent particles not removed by the etching process.
  • Anodizing: Aluminum is immersed in a tank containing an electrolyte having a 15% sulfuric acid concentration. Electric current is passed through the electrolyte and the aluminum is made the anode in this electrolytic cell; the tank is the cathode. Voltage applied across the anode and cathode causes negatively charged anions to migrate to the anode where the oxygen in the anions combines with the aluminum to form aluminum oxide (Al2O3).
  • Coloring: Anodic films are well suited to a variety of coloring methods including absorptive dyeing, both organic and inorganic dyestuffs, and electrolytic coloring.
  • Sealing: In all the anodizing process, the proper sealing of the porous oxide coating is absolutely essential to the satisfactory performance of the coating. The pores must be rendered nonabsorbent to provide maximum resistance to corrosion and stains. This is accomplished through a hydrothermal treatment in proprietary chemical baths or by capping the pores via the precipitation of metal salts in the pore openings.

Since out product is relatively low volume but big in size we needed a place that would be able to process our 700 x 700mm ring and Aldor has this ability and does not limit us to just bare or black aluminum but also adds the possibility of color to the process. Capturing the beauty of anodized aluminum in a picture is a very hard thing to do, so the pictures in the post don’t do justice to the feel and look of the real thing but they do give some indication.

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To our prototype customers we’ll be offering a choice between etched bare aluminum (It’s like an iPod but totally different), etched black aluminum (Matte black looks very nice and was the intended color for our original clock), etched blue aluminum (This color is a chameleon in terms of appearance with light making the color look different and exciting any time of the day) and glossy black aluminum (My pick for my own clock, it looked as black glass).

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