Shot blasting aluminium profiles before anodizing

Shot blasting is an impact surface treatment: the shot, thrown by centrifugal blast wheels, strikes the profile and, in a single pass, cleans it and gives it an even finish. It is a closed-circuit process, economical and free of environmental contamination. On aluminium profiles, stainless steel shot is used so the material is not contaminated with carbon residue and later oxidation is avoided. The final roughness can be adjusted by varying the impact speed, according to the result the user wants.

Chemical pickling with caustic soda and sulfuric acid does the job, but it carries costs: it consumes large volumes of product, generates effluents that must be treated, produces vapors that damage facilities, poses a risk to staff handling hazardous chemicals, and requires long bath times. These are exactly the points where mechanical shot blasting makes the difference.

Profile recovery and quality
• Recovers off-spec profiles and second-selection material.
• Removes water stains, die scratches and defects caused during handling.
• Homogenizes the surface without causing structural damage to the profile.
• Lets you control the final roughness to the desired result.

Savings in chemicals, time and sustainability
• Reduces alkaline bath time by up to 85 %, depending on bath temperature and soda concentration.
• Lowers caustic soda and sulfuric acid consumption, and effluent treatment cost.
• Reduces chemical risk to staff and vapor damage to facilities.
• Low operating cost (about 1.5 kg of stainless steel shot per ton of anodized profile), longer extrusion die life and a return on investment of 1 to 3 years.

Shot blasting before anodizing is especially worthwhile for aluminium extruders and anodizing plants that want to recover off-spec material, cut chemical and effluent use, or add process capacity at low operating cost. It is an automatic process, simple to operate and requiring no specialized personnel.