3-D surface profile rendering can be an improved alternative for the classical tape based Testex. With this tape based approach, a visual comparator or spring micrometer is required.
Surface profile is probably the most critical part of a coating system, it determines for a large part the adhesive bond between the surface and the coating. Within standardization committees like (ISO and AMPP) it has been a subject for several years that the measurement of just the the height of the profile is insufficient as indicator to proper adhesion. Besides peak height. the number of peaks per square inch or cm is a second critical determinator for good adhesion. The number of peaks per square surface area is also referred to as peak density.
An important reason that up to today, it has not been intergrated into relevant coating and surface preparation standards, is that field equipment was not capable to measure other parameters than peak height. The standard way to measure peak density in the past was a surf test. This is an instrument with a diamond stylus that is pulled over the surface and counts the peaks and valleys. The limitation is it only measures in a straight line and only for 1 cm distance. It is best used on a flat horizontal surface and is more suited for the lab than the field.
The American brand Defelsko introduced a detector (Positector 6000 RTR3D) with a surface profile probe than can properly measure peak density in the field. We have used the equipment for several years and have the following obeservations.
Get a better bond
The bond between paint and the steel surface is largely mechanical. The goal of surface profiling is to increase the bonding area and measuring peak height and peak density can help determine whether or not a coating will bond sufficiently. While having sufficient peak height is well understood, the effect of peak density has been hard to determine since there is not a lot of real would data on how the peak density affects the adhesive bonding of the coating to the substrate. By using the Positector 6000 RTRP probe, we can gain a better understanding of the relationship between peak density and how it effects the bonding of the coating to the substrate.
In the future, specifications may start showing up that require measuring both peak height and peak density. Currently, the DeFelsko RTR3D probe is the easiest way to do both.
Posisoft software automatically can generate 3D graphs and supplies most of the information you need. There are also 3rd party programs that can provide additional data and ways to manipulate the graphs. With the abilities of a 3-D imaging tool such as Gwyddion, which is open-source software, you can verify that a surface has the profile right depth as well as the proper peak density to maximize the bonding of the coating to the surface.
Integration with other devices
You can use 3-D surface profile technologies like for instance a Positector 6000, to transmit data to a mobile device for easy access with most of the probes. Doing this can help keep inspectors on the move and allow them to save time. Having information from the device so close at hand can also give you a better look at valuable information. By using the memory feature of the Smartlink or the Positector Advanced body, you can collect data from several different probes and send the batched data to your computer.It should be noted that due to the file size, the RTRP probe only works with the Advanced body, and you can only store one image at a time which must be downloaded before you can take another image. The software of choice, which is free, is Gwyddion.
The RTR3D probe will work with the standard body but works best with the Positector advanced body which is $680.00 for the body and probe is $1895.00. The Positector body combines surface profile gauge functions with several other gauge types such as ultrasonic thickness, dry film thickness, dew point meter, coating thickness on concrete and other nonmetallic substrates, and the New Shore A & D Durometers, This can also save you the hassle of having to download from other meters since you can store all the readings from the different probes in one body and all you have to do to get the data is download one meter.
This article is written by Tom Swan from M-Test. M-Test is a specialized firm that supports inspector and coating companies to choose the optimal technologies for inspection and coating testing. You can find more information at their website: http://www.m-testco.com/