Tips, tricks, traps and reality of Surface Profile measurement
Inspection— tips, tricks, traps and reality of a surface profile
This is not about what you’ve already been taught about surface profile. Its additional information that you may like or need to know.
Surface preparation is broken up into two areas:
● surface cleanliness, class of blast
● surface profile, roughness.
Surface profile also known as surface texture, anchor pattern, surface roughness; expressed as an average peek to valley height. It’s about expanding and increasing the surface area to gain adhesion for the coating system.
The blast medium should be viewed to see if it’s suitable to give the profile required. Also that the style of surface profile is suitable for the coating that’s being applied.
What creates a varied surface profile shape and height?
● Size of the medium
● Shape of the medium
● Weight of the medium
● Hardness of the medium
● Speed of the medium
● Angle of impact
For measurement you need an area where the surface shape will have no effect on the profile reading. An area that is free of pitting and rogue peaks.
An area that best represents the profile that’s being created. Not the texture of the surface shape that pre-existed on the surface.
You cannot measure the profile with testex tape or a needle gauge in this area. Best to use a visual profile comparator.
You can see here the natural surface of the corroded steel.
You may be able to use testex tape and needle profile gauge in this area although the pits and the hollows becomes part of the measurable profile. Best to use
a visual profile comparator.
Best to use a visual comparator as the surface waviness can become part of the measurement.
Although that’s called profile depth there that would be better called a stray rogue peak.
That as a reading would not represent the area as a surface profile reading. Readings like that needed to be excluded from the set of readings taken.
A scattering of stray rogue peaks / surface hackles can be detrimental to the coating system. This can be caused by foreign larger particles in the blast
A smaller gauge foot / measurement area gives a more accurate test result.
Peak to valley, peak to valley you would think was a peak B to valley C to give a profile height. Instead it maybe peak B to valley A where you get a higher
reading. There is no relationship between B and A as an anchor path. Area D could be taken as part of the profile readings although it’s a natural pit.
Testex tape, odd isn’t it? That are you not measuring the peaks but instead measuring the hollows. Should you rub the peaks far too hard you can reduce the
height of the profile reading result.
Needle profile gauge the finer the needle on finer textures the higher the profile reading result. Although it may not have a large impact on heavy profiles
and shop peening results.
Needle profile gauge, random placing of the gauge on the surface would not always place the needle in the lowest part of the profile. By locating the needle
in the lowest part of the profile then placing the gauge down would give you a higher profile reading.
Just because you have measured the profile at the start of a project you still need to take new readings daily. Each blast nozzle should have the profile it
produces checked. Far too many unwanted variables can creep into the process to reduce the profile height.
Diminishing profile causes:
● Dropping grit pressure
● New nozzle versus an old nozzle
● Grit worn out / reused / used too often
● A finer grit being used
● Too much medium coming through the nozzle
● Low angle of impact
● Blasting into a corner
● Nozzle too close to the surface being blasted
Extreme profiles how to reduce their impact on a coating system
You can re-blast the surface with a finer medium, this will take the profile height down.
On a shop primer / coating system you may need additional thickness as the peaks may spot rust.
A scattering of distinguishable profile peaks abrasive blasted surface: Reason, a small amount of newer grit mixed in with the older grit this should not be
considered as part of the surface profile as it is scattered. An older blasted surface that’s been brush blasted over to reinvigorate, heighten the profile.
Looks good but may well have a detrimental effect on the coating system.
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