7/29/2019 CoatingPro May2010 - Dry Film Thickness vs Profile

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COATINGS EXPERTS

Dry Film Thickness vs. ProfileBy L.D. "Lou" i t ~ c Ph.D., Teclwiarl Editor

T his mon th we: will explore astbject requested b y < ' ~ re

7/29/2019 CoatingPro May2010 - Dry Film Thickness vs Profile

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'Figure 1.PI>Jomended p ro file rega rd less of the DFTof the coating system applied ove r thezinc p rimer. (( 40 IJ m of zinc is to be wetapplied over '1 l ; ~ s su rf.-ace. i t would bealmost impossible to achieve"'nonl inaUy .40 1-11n ove r a SO Ilm anchor pattern, o rprofile he;ght. Nom ina l 10 J.Un is th eaccepk d standard 20%. That suggests32 to 48 1-un is the acceptab le OFT range.But is tha t above the peaks. th eavcrngc peak he ight, or from the bo ttomof the peak valley? IJl proctical terms. thedesired OFT will be one that has a reasonab le coverage over the pea ks to add resstheservice. Since thezinc is solventbased.it also m ust be applied in s uch a wa)' asto 01llow jt to shrink back as the solventfla shes o ff. Extending the su bsequentcoats in t his case to com plete lhe coatingsyste1n, whether the applkation OFT ofthe subse-quent coats is 120 j.lm o r 210 j.lmmatters little. sjncc the jntim:ue relation ship between the zinc and the substrnte isforemost.Is there on applicable Interno tional standard that coversmeasuring profile vs. OFT?Pro m l hc point of 'icw of coating th ickness measurement. ISO 198101 describestwo m ethods for d ~ ! - a l i n g wi th the profi leresu lting fro m a brasive dc an ing of asubstrate. Acc-arding to the main bod)' of

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the text. the gauge is adj usted to measureon a smooth surfaceand then a correctionvalue is sub tracte d from the thicknessmeasurement depend ing o n the pro file asdefined by ISO 8503- 12, the ISO SurfaceCompa rator.

'f his method was selected becatse itis often the case tha t the coating has beena pplied before the ins pector a rr ive s tomeasure the film thjckness and it is no tpossible to adjust th e gauge to the sudaccthat has been c o ; ~ ; t e d

T he correct ion va lues con tai nedin t he doc u me n t a r c fine blasJ ;: IO

medium blas t=25 a nd coa rseblast::;40

' l"his me thod meO'lsures the thickness of the coatlng over the peaks of theprofile. In the ca.."c where the actua l blas tprofile }s not known. the defat t ' '