When aluminum is anodized, it receives a thin-film coating of aluminum oxide that protects the aluminum against further oxidation and corrosion. The anodizing process, however, occurs in several stages, and although it is regarded by many as an environmentally-friendly process already, new innovations have led to the further “greening” of aluminum anodizing. Several companies follow unique steps to keep anodizing safe and green.
The first stage in almost any basic anodizing process involves cleaning the substrate. Cleaning serves several purposes, but its main function is to remove and eliminate surface contamination that arises as a result of various forming processes (such as extrusion), manufacturing dust and lubricants, and additional workplace grease. After cleaning, the substrate is then rinsed to ensure previous reactions are completed and to further reduce the likelihood of cross-contamination.
After cleaning and rinsing, etching can begin. Successful etching reduces the substrate surface in order to produce a smooth, matte finish and eliminate any surface flaws generated by forming processes. Once the surface is sufficiently etched, it is then deoxidized and any additional metal oxides that may still remain after cleaning and etching are also removed. The surface is then deemed “active” and ready to undergo anodizing.
To create a thin-film anodic coating on the aluminum substrate, electricity is applied to the substrate to induce oxidation. The result should be a thin-film anodic coating comprised of aluminum and oxygen that will serve to protect the integrity of the component. If a colored coating is desired, an additional metal can be electrodeposited. Once anodizing is complete, the coating is sealed with a metal-based compound.
The anodizing process described above is already a relatively eco-friendly process. Toxic metals are not generally used, and very few toxins are released as a result. Additionally, byproducts are typically recyclable, and the aluminum end-product is also non-toxic and safe for a wide array of consumer uses, including those that designed for cosmetic and food and beverage applications.
To make anodizing even cleaner, companies such as Anomatic, Lintec, and DAC take several measures to make anodizing a sustainable, green manufacturing process.
For many companies, this process begins with the selection of aluminum—a metal that when recycled is already in a metallic state—which requires no additional purification and reduction, merely melting. Any leftover aluminum scrap that accumulates during the manufacturing process can be recycled. Additionally, recycled aluminum alloys (such as 3004) can be used, but care must be taken to ensure that the alloys meet regulations because some recycled alloys can contain higher amounts of heavy metals.
In the drawing process, when aluminum is formed and pressed into the desired shape, several kinds of oil and grease are used. Oil can typically be removed and reused, while scrap aluminum with oil residue can be subjected to a special oil removal process before being recycled. The aluminum substrate itself is degreased to recapture oils for reuse. The entire process doesn’t create any toxic byproducts or emissions.
During anodizing several inorganic acids are used to dissolve aluminum. To prevent contamination and pollution, the aluminum component is rinsed between stages and the excess acids are treated before being sent to a wastewater treatment plant.
Through applying these processes at various stages in anodizing, companies are making responsible strides toward an even cleaner kind of anodizing. The careful monitoring of waste, proper material selection and handling, and attention to ways in which all byproducts can be re-used or recycled has played an integral role in the greening of anodizing, and companies that abide by these practices and lead by example have been increasingly recognized for their commitment to greener anodizing.