Acid etch process provides color uniformity, cost savings

More and more anodizing companies are switching to an acid etch process from the conventional alkaline etching process. Currently, there are three types of etch used for anodizing aluminum: alkaline etching, mechanical etching and acid etching.

Alkaline etching can be either a no-dump etch or a caustic recovery etch. It can produce a good matte finish and hide metal imperfections, but the process is slow and loses more aluminum than other processes. There also is a waste treatment problem, and the high viscosity of the solution makes rinsing difficult.

Mechanical etching uses almost no chemicals and works by placing extrusions on a conveyor and moving them through a blasting cabin. It can provide a uniform and matte finish, but it takes up a large amount of floor space and is not very fast.

An alternative to the conventional alkaline etching process, the acid etch process uses chemicals to remove a layer of aluminum from the extrusion or sheet, changing the bright aluminum appearance to a dull matte finish. It removes embedded impurities from the metal and smoothes out surface imperfections to produce a uniform surface. The result is a premium matte finish with low aluminum loss. Unlike alkaline etch, it also produces fluoride ions that attack the aluminum surface, producing a smooth grain edge.

Benefits of acid etch

Among the benefits of acid etching is its ability to better meet the needs of extrusion, fabrication and finishing customers in the construction industries by reducing color variation. The process also works better on aluminum with mill finish imperfections and has proven to be effective in hiding scratches and extruder flow and die lines. As a result, it allows companies to save money by anodizing aluminum that previously might have been scrapped. Using the acid-etch process, some extrusions that were difficult to anodize in the past can now be finished with good results. Storefront, curtain wall, window and door manufacturers have already noted the improved uniformity the acid etch process provides and its ability to hide metal defects that alkaline etching cannot.

The acid etch process is environmentally friendly, resulting in less waste sludge disposal. It accommodates the use of a higher percent of recycled content in extrusion billet, while still maintaining high uniformity of finish. It does not cause problems with water treatment, uses less water and has no cooling requirements. The acid etch process meets and exceeds all AAMA 611 specifications. Read more about the environmental benefits it provides on Page XX.