Press-O-Film can be used with a gauge to measure the surface roughness (“profile”) of blast-cleaned steel in the roughness range of 0.8 to 4.5 mils (or 20 to 115 micrometers). Use of Coarse Minus grade (<0.8 mil or <20 um) or X-Coarse Plus grade tape (>4.5 mil or >115 um) should be restricted primarily to checking measurements at the lower and upper ends of the primary range. 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 its range.
Press-O-Film consists of a layer of crushable plastic microfoam coated onto polyester film of highly uniform thickness. When compressed, by “burnishing” against a surface, the foam collapses to about 25% of its pre-collapse thickness. After compression, the foam acquires an impression of the surface against which it is burnished. The highest peaks on the original surface displace the fully compressed foam and come to rest against the polyester backing. The deepest valleys on the original create the highest peaks in the replica. Consequently, the thickness of the compressed tape equals the average maximum peak-to-valley profile plus the thickness of the incompressible polyester substrate.
Firmly compress tape with the smoothest surface on the rubbing tool provided, applying sufficient pressure to produce a replica with a uniform pebble-grain appearance. You should feel the roughness as you burnish. Because implicit definitions of “roughness” vary between methods, numerical profiles determined using different techniques may yield different values. Always specify the technique used.
0.5 to 1.0 mils (12 to 25 um)
0.8 to 2.5 mils (20 to 64 um)
1.5 to 4.5 mils (38 to 115 um)
4.6 to 5.0 mils (116 to 127 um)