Polyester Lacquer Crack Mitigation

[AutoWoodEng]

Hi All,

I have this problem that has arrived just lately and largely with cracks in the "A" surface of our polyester lacquered parts. I have tried many things to eliminate this problem by changing the order that cut outs are made thinking that the residual stresses from the shrinkage in the polyester may be slightly relieved from the "pre-cuts". The problem was not able to be fixed by that, I am curious if instead of making 4 coats raising the value to five smaller coats would help to prevent cracks during the routing process?

Thanks

AutoWoodEng

 

[patprimmer]

Is Polyester the substrate or the coating. If substrate, what type of polyester. What manufacturing process.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

You imply you did this successfully in the past and the problem only recently started. What has changed about the time the problem emerged.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[AutoWoodEng]

Patprimmer

The substrate is Aluminum and there is a polyester lacquer coating (Which is 4 coats) on the surface. What has changed would be reducing the number of coats (keeping the thickness the same).

Regards

 

[Compositepro]

Thicker coating layers certainly have a greater tendency to crack during drying/curing than thinner layers.

 

[patprimmer]

Lets see if I have this correct, or if there is a major language problem here as I see some contradictions between your first and second posts.

You applied 5 thin coats of polyester paint to aluminium, then form or punch holes. No problem.

You changed to 4 thicker coats then had problems with the paint cracking.

You tried changing the forming and punching process, but still have problems.

If I have accurately interpreted your real question:-

Go back to 5 coats. Problem solved. End of story.

Otherwise:-

Improve primer coat or aluminium surface treatment to improve bond.

Use modified paint with slightly tougher surface or produces a film with higher elongation at break.

Modify curing process to give tougher final film.

Adjust timing of forming punching re degree of cure of paint. ie form/punch while film still a bit soft.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.