Fabricating After Finishing – Not Recommended

Bending and forming of high-performance PVDF coated aluminum – often referred to as post forming- is a common practice by many in the industry. However, the three largest architectural paint manufacturers, Akzo Nobel, PPG and Valspar do not recommend  this practice. They caution that great care should be taken if the aluminum is formed after painting.

All three paint manufacturer warranties state that the warranty is void if any fabricating operation damages the coating, or damages the substrate to an extent that the coating film is compromised, delaminated or degradated.

Akzo Nobel, PPG and Valspar offer several warnings against post forming finished aluminum:

  • Post forming the coated aluminum substrate will open small micro cracks in the
    paint and pretreatment, which will leave the bare substrate at risk for failure. While PVDF coatings are  flexible, they are not super flexible; as a result, when forming  the substrate, stress is put on the coating either at the surface (adhesion failure) or within the coating (cracking) and corrosion can set in.
  • Warming the aluminum prior to bending, with a purpose to increase flexibility of the

    Fracturing of mil aluminum

    aluminum and its coating, can cause the surface to soften and make it much more susceptible to scratching and marring.

  • Bending of heavy extrusions that have been heat-treated can result in cracking the aluminum and paint film.
  • Improper set-up of press/brake or forming die can damage the paint film.
  • Fracturing or cracking is not necessarily related to the paint coating, but can, and often is, related to the aluminum alloy and the flexibility of the aluminum in post-forming. The aluminum has a tendency to fracture and crack underneath the paint film.
  • Severe bending on a small radius can cause cracking of the aluminum substrate, which will result in cracking of the paint film.   .

Here is an example of brake metal that was post formed. A series of AAMA 2605 tests
were conducted including cross hatch, direct impact and pencil hardness. These test results indicate no issues with the paint, its application, or performance. Although the paint was compromised on the bend, all testing passed – even that done right next to the bend area.

It is always best practice to form the aluminum prior to painting.

2 thoughts on “Fabricating After Finishing – Not Recommended

  1. I can appreciate the warning for post bending heavy extrusions, however there should also be some type of guide line stating up to what gauge aluminum could be post bent without having crazing, as we all know the curtain wall industry and metal panel both post bend metal, and if we are ordering aluminum 0.50 you would think that before your priced these flats sheet you would ask what the customer is using it for so that you could provide an explanation stating that you cannot post bend your product that is post painted in lieu of having an un happy customer like Massey Glass, we also work with other manufacturers that coil paint and I guess this unhappy customer will have to review every project and coil paint in lieu of psot painting.

    • Good afternoon JR,

      Thank you for your post and I can certainly understand your position and concern. The challenge is there is no definitive thickness of sheet where crazing will necessarily become an issue. Various factors like alloy, temper, paint type, solid color versus mica/metallic, tooling, degree of bend, and material thickness, as well as many other conditions can all be factors. These many variables are one reason why manufacturers don’t warrant post formed materials, and Linetec has always communicated finishing after forming as best practice. As you state post forming is common practice in our industry and there are many companies like Linetec providing finished flat sheet or prefinished coil. While we don’t often hear of people having issues with post forming, there will always be occurrences where there is failure and discontent as a result. It is for this reason Linetec tries to communicate to the industry as we did in the blog you referenced to make people aware of the inherent dangers with processing materials in specific ways. We certainly appreciate Massey Glass’s business and don’t want you to be an unhappy customer. We welcome you to contact us at any time if you have questions regarding any of the services we provide. While we will not be able to tell you if a paint finish will craze on a specific thickness of sheet, we may be able to identify a different solution we feel will provide a better end result.

      Thanks again for your post.
      Jon Close

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