|Grade (descriptive)||Range When Used With Gage (mils) / (um)|
|Fine / Medium||not applicable|
|Coarse Minus||0.5 to 1.0 / 12 to 25|
|Coarse||0.8 to 2.5 / 20 to 64|
|X-Coarse||1.5 to 4.5 / 38 to 115|
|X-Coarse Plus||4.6 to 5.0 / 116 to 127|
Testex replica tape can be used with a gauge to measure the surface roughness (“profile”) of blast-cleaned steel in the roughness range 0.8 to 4.5 mils (or 20 to 115 micrometers). Because inspectors, as a rule, have a target profile in mind. it is always best to start measurements with the grade of tape that has the target profile closest to the center of it’s range.
Testex’ lowest grade (thinnest) tape, Coarse Minus, should be used only to check measurements at the lower end of the next higher grade, Coarse, while our highest grade tape, X-Coarse Plus, should only be used to check measurements at the high end of the X-Coarse grade range.
Firmly compress tape with the smoothest surface on the rubbing tool provided, applying sufficient pressure to produce a replica with a uniform pebblegrain appearance. You should feel the roughness as you burnish.
Fine/Medium grade material is commonly used in applications in which the replica is analyzed using precision laboratory techniques. This grade is not suitable for use with a “dial thickness gage.” Fine grade tape (rarely used) has a thin Gold coating to facilitate electron microscopy. Medium grade (“metallized”) tape has a thin Indium coating to facilitate optical interferometric measurement. Fine and Medium grades have the same foam thickness. Only the vapor-deposited metallic coatings differ.
All grades are coated onto a tough polyester substrate 2.0 mils (50 um) in thickness.
Because implicit definitions of “roughness” vary between methods, numerical profiles determined using different techniques (replica tape, interferometer, confocal microscope, analog stylus, digital stylus) may yield different values. Always specify the technique used.
In July 2010 Testex introduced a new “high temperature” version of its Coarse and X-Coarse grades of Press-O-Film replica tape. Press-O-Film HT is formulated for better performance at the elevated temperatures encountered in the most challenging environments. While stable at 140 °F (60 °C), earlier formulation Press-O-Film gradually softened at higher temperatures. The new Press-O-Film HT adds a 12 °F (6 °C) safety margin.
Other physical properties remain nearly identical except for some loss of agreement where different grades overlap. The effect is most noticable between Coarse and X-Coarse grades. The new instructions will recommend that where these two grades give different profiles and both profiles are in the range 1.5 to 2.5 mils (38 to 64 µm) those differing values be averaged.
The new version will replace the existing product.