blasting surface roughness 1

[Amirrul]

Hi all,

is there any tolerance for blasting surface roughness?. in this case the acceptance criteria is 50 - 100 micron, but what we achieved on site is 180 micron. is it still acceptable or any problem that may be occurred if there is excessive lasting surface roughness?. appreciate the advice.

 

[Interpreter888]

I can't think off the top of my head if there is an acceptance criteria but I know that if 180 microns is at or above the coating thickness required for the first coat, you will have peaks of metal exposed through the first coat. The protruding metal exposed to the environment will rust which can cause adherence issues with an overcoat.

 

[BenMacier]

Of course there must be a bloody tolerance on surface blasting and it should even differentiate between shot, grit, and mix of both blasting cycles.
High peak, mean of 10 peak, etc over a small surface should be measured if you can't afford scanning the entire blasted surface to check its quality before applying coating.
If the surface preparation is crap, your coating won't last.
Remember: garbage in(side), garbage out(side).

* Finding a solution is great * Knowing how to implement it is fantastic * Believing it is the only one and best is naive ?

 

[IRstuff]

You're 80% over the upper acceptance limit, so it failed, period. There's no amount of reasonable tolerance that would bring you into compliance

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[WKTaylor]

FYI... There are surface roughness comparators available for various roughness conditions.

Years ago I almost got in fist-fights with machinists that couldn't PROVE that surface roughness requirements for their work was or wasn't being met. I purchased a set of surface 'scratch' comparators from the following company. There are comparators for machined surfaces [of many types]… of course... for shot-blasted and grit-blasted surfaces. This set of comparators was a come-to-Jesus moment for these guys... and displays various aspects/conditions of 'surface roughness, waviness and lay'. Many young engineers borrow them for shop floor use and also their own personal education.

NOTE. This is NOT a product/company endorsement... simply my experience/usage.

Surface Roughness Comparators [made to comply with ASME B46.1] shown are available from GAR Electroforming Division, Electroformers Inc, P.O. Box
340, Danbury, CT 06813.

NOTE. I'm pretty certain that these comparators are available in metric [SI] units-of-measurement, also. They aren't cheap... but they can be priceless in arguments!

a. Use the S-22 Conventional Machining Microfinish Comparator to evaluate machined surface finish quality (general
purpose).
b. Use the G-63 Cylindrical Turned Microfinish Comparator to evaluate lathe-turned and hole surface finish quality (general purpose).
c. Use the G-6 Grit-Blast Microfinish Comparator to evaluate grit-blasted surface finish quality (general purpose).
d. Use the SH-6 Shot-Blast Microfinish Comparator to evaluate shot or bead-blasted surface finish quality (general purpose).
e. Use the M-15 Master Visual-Tactual Set to evaluate and compare machined surfaces produced by various machining
methods (precision evaluation of surfaces falling within a narrow-range of fine finishes).

Regards, Wil Taylor
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