Powdertech Corby explains how to get that effortless coating for metal finishes

Metal finishing, be it painting, anodising or powder coating, is usually the last process a fabrication will undergo before installation, yet the performance of metal finishing and the effect it can have on the construction process and programme is greatly influenced by early design decisions. Richard Besant, Director at Powdertech Corby, outlines some simple but often overlooked considerations that should be made at the very start of a project.

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As designs become ever more intricate, it is particularly important to clearly identify the parts in a manner that won’t be obscured by the powder coating or paint. Marker pen will not do – it will be removed by the pre-treatment process, and it could show through the final coating. Engraving a part number using a simple pen or more sophisticated automatic machine ensures that the finished components are easily installed in the correct location. Design drawings must clearly identify, using standard notation, the extent of seen (primary) faces, coated but not seen (secondary) faces and unseen faces. Using this information in conjunction with suitable jigging points, your powder coater will suspend the parts to ensure that the surfaces are coated correctly and to the required aesthetic standard.

Design for a perfect finish

Metal finishing is greatly influenced by seemingly small details in the design of the fabrication. For instance, venting and draining holes for galvanising in the correct position and of the correct size ensure that the metal sinks fully into the zinc bath and drains completely on removal. If any part of the fabrication floats, it will form a ‘burned’ surface with incomplete protection and poor surface finish.

Components are generally suspended for powder coating, so suitable hanging points in the correct location on an unseen face, once installed, need to be identified in the design drawings. Sharp edges, commonly caused by laser, water and plasma cutting, must be rounded off as they can cause fracturing of galvanising and localised thinning of painting and powder coating. The material must be strong enough to avoid distortion during the powder coating process with temperatures up to 200ºC. Blind holes that trap air and prevent the complete coverage of pre-treatment chemicals must be avoided, and rivets and welds checked to ensure that the chemicals will not become trapped and ‘boil out’ during curing thus ruining the final coat.

The final destination

The installed location of the metal, both its environment and ease of access, need consideration. Narrow gaps, overlapping joints and deep recesses should be avoided for a marine location as free draining, and easy cleaning is important to limit corrosive activity. This is also true for parts that are difficult to access for regular cleaning in any environment.

Designing for the best outcome

Metal finishers want their coatings to be successful and design elements, overlooked in the design process which they have been unable to influence, are frustrating. Compromises have to be made; certain elements may need re-doing and delays in final construction can occur. These issues can be avoided if the design is optimised for coating application. A high-performance, attractive and durable coating will be the result.

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