Replica Tape: Unlocking Hidden Information

From JPCL, July 2015

by David Beamish, DeFelsko Corporation

A surface profile is composed of a complex pattern of peaks and valleys. This article explains a developing technology that allows for extraction of useful information from replica tape, beyond just peak height....
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Tagged categories: Quality control; Replica tape; Surface preparation; Surface Preparation; Surface preparation equipment; Surface profile

Comment from Kevin Schweikhart, (8/2/2015, 10:23 AM)

Thanks Dave for continuing to improve our industry with your research, your writings and your products.

Comment from Mark Puckett, (9/1/2015, 12:01 PM)

interesting but Im curious what happens when you blast over existing profiled steel from previous profiled areas painted over...creating specifications for additional testing is nice but even better to know if those specifications are even achievable in the most dominate use area

Comment from David Beamish, (9/3/2015, 3:49 PM)

Our testing did not include surfaces that had been blasted twice, say, to reduce a too-high profile or to remove coatings from surfaces that had been blasted before. We hope that formulators, specifiers and blast media producers will use this field instrument to conduct research into these very issues, and others.

Comment from Harry Wilke, (9/9/2015, 12:33 PM)

Similar question - Abrasive Blasting with recycled LG 50 Steel Grit. One would expect the resulting profile to be in the 2.1 mil range. Yet we are seeing 3.9 - 4.4 mils. This can only be attributed to pre-existing surface profile. I tend to use the KTA-Surface Profile Comaparator and photograph these one the actual surface along with my replica tape measurements. This way I report the profile height as measured and evaluated visually. The high definition photographs reveal a remarkable amount of information when zoomed.

Comment from Marius Hamza, (10/23/2015, 10:08 PM)

The article is very interesting extremely well documented. I really enjoy reading it while having my morning coffee.

Comment from William Guan, (10/25/2015, 11:04 PM)

It is a very interesting idea of using replica tape and 3D image for peak density. I myself contributed to Mr. Roper's study by providing him the polyurethane coated samples on steel panels with different peak counts and also conducting some tests for his program. In general, my experience of using replica tape was not very great for 3 reasons: 1) the tape measured maximum peak depth rather than average; 2) the error % of the tape is so significant that the measured number might not be a true reflection of the actual profile depth (if one reads the fine printing of the tape manufacturer's instruction on the error of the tape, one could understand what I meant); and 3) the result depends on how hard the tape was pressed while doing the measurement. Quite be honest, I trusted what my finger's feel after touching a blasted steel more than what the replica tape would tell me. Therefore I was supporting Roper's idea of using stylus rather than tape in his study. I will be interested in seeing more data to support the accuracy and correlation of peak height/peak counts from the 3D tape measurements.

Comment from David Beamish, (11/8/2015, 1:26 AM)

Replica tape does indeed measure the max profile depth. More accurately stated, it measures the average of the maximum peak-to-valley distances. This relates closely to the values given by surface roughness instruments (drag stylus) and ensures protective coatings cover the maximum peaks. The % error in the tape is well known now and can be reduced by averaging 2 readings, 1 for each grade of tape. This error can be fully corrected with the use of digital micrometers that linearize the result. Burnishing pressure concerns can be alleviated by pressing lightly and ensuring both and x-y motion an a circular motion for 30 – 40 seconds.

Comment from Adrian Grace, (12/22/2015, 5:00 PM)

I come from down under in Australia. I value this quality publication for helping me keep up to date with our industry. I fully endorse their choice of Defelskos replica tape reader as top feature in 2015; it is an innovative product that will help us improve coating life in the future; thank you David Beamish & Paint Square for supporting our industry.

Comment from michael misiaszek, (2/1/2017, 2:15 PM)

This is a well written article. Have you looked at surfaces beyond blasted metal to where this may be useful?

Comment from Andreas Momber, (2/2/2017, 4:00 AM)

You can find many answers to your questions, including effects of overblasting and of recycled abrasives, in the comprehensive book "Blast Cleaning Technology", Springer, 2008

Comment from Tony Rangus, (2/3/2017, 12:22 PM)

My employer starting using acetate replica tape back in the early 1980"s to perform in-situ metallography to look for creep damage in high temperature steam lines. The metallic surface is polished with successively finer grits down to one micron diamond paste. The surface is etched to remove disturbed metal & re-polished with the diamond paste and again etched to show microstructure. A solvent is put over the area and the replica tape is pressed firmly over the area and allowed to dry. The tape shows the reverse image of the microstructure & is viewed at about 500X with a light microscope to look for creep damage. The tape can be sputtered with a few molecular layers of gold and then viewed with an SEM. Did a bunch of boiler piping life assessments in the mid-1980's.

Comment from David Beamish, (2/11/2017, 1:19 PM)

In response to your earlier question Michael, I believe there are a number of other applications for replica tape. The American Galvanizing Assoc. has a trial underway to examine its ability to characterize zinc surfaces prior to coating. An SSPC committee is studying its value in measuring textured concrete coatings. The Powder Coating industry has conducted some trials whereby the textured surface of cured powder is analyzed. And finally, our company is extracting drag stylus roughness info from replica tape including Ra, Rz and other important parameters. We hope to publish papers on several of these endeavors later this year.

Comment from Russell Draper, (6/7/2017, 12:11 PM)

Thanks Dave for this thought provoking paper. When I look at Roper's data I do not see the same relationship that you found of increasing pull-off strength with increasing peak density before he exposed his samples. It was only after he had exposed his panels (to salt water/ spray) that he found a meaningful relationship between peak density and pull-off strength. All of his coatings failed cohesively before exposure, it was only after exposure that failure at the coating/substrate interface happened. Where you measuring adhesion before or after exposure to water?

Comment from David Beamish, (6/8/2017, 2:22 PM)

Our adhesion tests were performed after the coating had cured and did not include any testing after environmental exposure, either salt spray or immersion. In the Roper paper, I believe Coating A tests had only 9 non-exposure pulls. I think that’s why a conclusive trend is not apparent in his non-exposed data. We, on the other hand, had many more non-exposed data points (failures at the substrate) with which to establish trends.

Comment from trevor neale, (6/9/2017, 10:03 AM)

I also consulted with Mr Roper during his work, one point that has not been mentioned in measuring profiles is the huge variance in profiles when measuring over different steel grades and relative to steel hardness which is rarely factored into specifications.

Comment from Simon Hope, (6/12/2017, 4:23 AM)

Thought provoking discussion, as has been said, Testex tape can lead to so many variables, doing in house training with a small blasted sample, it is amazing the variation in readings we get and how many errors occur taking readings. The usual human error factor can never be mitigated for! I guess the most useful thing with a Testex tape is that you have a tangible piece of evidence that can be re-analysed at a later date if needed. Also a very good indicator of surface cleanliness when you look at all the rubbish that gets picked up, amazing the effect of a particle of grit on the readings! Great article and discussions!!

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