Ask the Expert Question-and-Answer Archive

by Ron Joseph

April, 2009

Finish Defect to Folded Metal Corners

Q. We would be grateful for a short common-sense overview on the following matter - rolling around between us, the facility owner and the relevant contractor. We here in Jacobs (Dublin - Ireland office) have a problem with finishes to folded metal Clean Room panels on a project of ours. The panels were formed from pre-coated coil - 7um primer/7um zinc/18um polyester coating - and have subsequent folds to form panel edges. The edge finish exhibits cracking (mainly microscopic but a few open up to 1mm wide)and some micro-flaking in places - not good in a controlled environment.
Contractor claims this is 'normal' tolerance for coated finish - will solve by edge touch-up exercise. We (and Owner) say this defect could not be 'normal' to the degree exhibited.

Any guidance on pre-fold coating methods or types that could avoid this problem?

A. Without seeing the problem first hand I can only give you a casual opinion. Coil coatings should be able to withstand bending without cracking. A 1 mm wide crack is far too large, but microcracks might be acceptable. Since this appears to be a coating for indoor application, I'm surprised that you found any cracks in the panels, but the word "microcracks" is relative and perhaps you are referring to ones that are really very small and within the limits of what coil coatings can withstand upon bending.

I would not expect any micro-flaking.

If you would like me to assist you further on a consulting basis please get back to me.

Regards,

Ron Joseph