Anodizing and powder coating aluminum longitudinal materials: 'Proper pre-treatment is becoming increasingly important'

Not surprising, according to Philip Hilven, Sales & Commercial Manager at Alural, because increasing air pollution is putting increasing strain on aluminum profiles. Moreover, recycled aluminum is being used more often. "A positive development, but one that creates new challenges. For example, better pretreatment is necessary to prevent corrosion and to enjoy high-quality coated exterior joinery for a very long time."

Alural is a specialized and independent finishing company, operating in Belgium for the European market. "We anodize and powder-coat aluminum longitudinal materials," Hilven said. "For example, profiles for windows, doors and blinds, which processors cut to size and assemble into a high-quality finished product." 

For pretreatment, Alural has an automatic treatment line, in which the profiles are successively degreased, rinsed, pickled, rinsed again, pickled again and dried. "Then a high-quality conversion coat (primer) is applied," he says. 

"At the end of this process, the profiles are automatically routed to the spray booths, where they are coated in the desired powder quality. The powder coating, in combination with the selected pretreatment, provides the best possible protection against weathering and UV radiation and has excellent temperature and corrosion resistance."

Various choices

Processors, facade builders and architects can choose from an extensive range of colors and gloss levels, as well as many surface textures, at Alural. For pretreatment, they have three options. "First, we offer a standard pretreatment, with a total stain removal of at least 1 gram/m²," Hilven says. "This means that all oxidizing surface particles are removed from the profiles using a special pickling process, before the conversion layer and powder coating are applied." 

The standard treatment is still in limited use anno 2021, he says. "To ensure the quality and durability of the products, processors are increasingly scaling up to a Seaside or Qualité Marine (2 gram/m²) pretreatment, which gets us right down to the pure aluminum."

Pre-anodizing as the new standard

Hilven also sees growing demand for the "Rolls Royce" of pretreatment: pre-anodizing. "In pre-anodizing, 2 to 5 g/m² of the longitudinal material is pickled off, after which a very thin layer of the base material is oxidized in a controlled manner. This treatment ensures perfect corrosion resistance and excellent adhesion of the powder coating." 

A disadvantage of the technique, however, is the additional treatment passage, which requires a longer lead time. "As of June 1, we will be able to reduce this lead time considerably by integrating pre-anodizing and powder coating into one processing line. This will allow us to deliver five (!) days faster," said a proud Hilven, who expects pre-anodizing to become the new standard.