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ABRASIVE CONTAMINANTS LEFT ON BLASTED SURFACE

TRANSCRIPTION:

Today I’m going to reveal one thing you should definitely add to your job spec to guarantee the integrity of your project and to maximize your ROI.

Hello, I’m Pete Mitchell with the GMA Garnet Group. I’m the Vice President of Technical Management.

So, what we’re going to talk about today is the classifications of blasting and what a true clean surface is.

There are standards in this industry that they set for near white regular white metal, and it’s always been curious to me why you can have a 30-page long specification and 29 pages of that are to the actual coating and there’s this little snip at the end about how to blast it.

You read in any class that 80 to 85% of the failures on a coating job are due to improper surface prep so in your guidelines they give you the standard SP10 or which is NACE2 near white and you got your SP5 which is which is your white metal that’s not a get out of jail free card.

That is a standard, but that’s a guide. That does not set just because an inspector walked in the door and said yep that looks like white metal.

You can’t say oh my surface is perfect and that’s exactly what I need for putting the coating on.

What we’ve done is we’ve gone in and done some further research into the blasting.

We’ve done some magnification pictures here and what you have is this is a true white metal.

This is a surface that was blasted with our tough blast and it looks spotless.

I went in and did some further investigation… that surface right there actually has about three to four percent embedment.

Every surface every abrasive leaves something on the surface but not much.

But what what’s really critical is when you start looking at some of the other abrasives on the market, you start seeing two different things.

You see actual embedment, you see angular crystals, or very friable crystals that tend to shatter and they embed into the surface.  They stick into the metal.

You’ll also see some that almost look like they splattered onto the surface. it looks like you shot a paintball at the steel surface and it cakes on the metal like a clay.

I’ve seen contaminant as high as 50/60 percent on the surface but with the naked eye you looked at the plate and you said that has a little bit of a shade to it but yeah that’s white metal.

Well fifty percent of a surface being covered with an embedment is not white metal and it’s not just one particular product or a few different types of products. You see it in both your byproducts – your slags, your glass, anything that anything that was a derivative from another product.

Or you even see it in your natural minerals.

In your by-products like your slags very angular but they do tend to shatter and that’s where you get heavy embedment.

you see it’s almost like knives thrown into the steel and I’ve seen on average about 40 percent of the surface is covered in embedment.

Some of the other slags tend to have some miscellaneous by-products in the material as well and that’s where you see the caking.

The one in the middle there was actually a green blast abrasive but you see the white and blue spots on it and I’ll show you a slide in a minute and show you actually what that is but that was a byproduct in there that was caked on.

Here we’re looking at three natural abrasives and usually this particular these particular products you would look at it and say this is your go-to for white metal.

But look at the actual surface that’s just that picture is just 25 times and so it looks like there’s paint on the surface.  it almost looks like somebody splattered paint. Well, what that is when you have natural minerals coming out of the ground there’s other by-products in it.

If I’m going to sell garnet I want to put as close to 100 garnet in the bag as I can. other natural softer minerals tend to hit the surface and cake and cause contamination.

when you look at by-products  – slags you have one there on the left is a cold slag  – you see the chunks actually in the surface.

Well, if were you trying to read a profile on that one it misleads you on what your profile is because it’s sticking out and that’s what you’re trying to get the coating to stick to.

The one on the right is actually a nickel slag and remember a minute ago I was talking about the blue and white spots, that material in your hand looks like it’s green. It’s just looks like a natural green sand but on the surface, it leaves those little white and blue caked areas.

And I wondered what it came from until I zoomed in and took a magnification.

I took a 25 times picture of the actual mineral and I see the other trash particles that are in there that cake to the surface.  All of that is going to impede getting your coding adhesion and it’s going to cause problems down the line.

We then took it to another level and did backscatter microscope pictures and you see the top which is one of the other garnets and you see a few spots. the yellow is the actual steel and then you see the blue the greens.

It’s interesting when they do this they can even tell what mineral it is by the scan that they take. The one on the bottom had 40 percent embedment and again when the inspector looked at it he said it’s white metal.

Remember the definition for white metal says no contaminants.

The definition for near white says no more than five percent.

Well, if you’re 40% embedded on the surface you’re not even near white.

Here’s another interesting one.  This particular product – one of its marketing tools is that it cleans the surface so clean the steel sparkles.  Well anybody that’s really looked in with a magnified picture of a good blasted white metal clean surface knows metal doesn’t sparkle like that.

So there has to be something else on there.  So, I went and did 25 times and 75 times pictures of it and it’s obvious to see what the issue is.  There it is.  It actually left a cake.  It’s actually physically caked on the surface and the sunlight is catching it and making it sparkle.

So instead of it actually being clean, they’ve actually put a film on the surface, and the coating is not going to be able to get to the metal.

Here is a comparison. This is our tough blast product at 25 times and 175 times. Look at the difference in the white metal.

You don’t see all the other contaminates on there.

Here’s the two side by side.

So I then took it down and did a backscatter analysis of it.

You can see the different portion on there and it specifies that it’s calcium silicate.

This particular material is an abrasive that’s made with tempered glass and having calcium silicate on the surface just made sense.  It’s the contaminant from the abrasive.

An interesting twist that we took from this, when we were really looking at the embedment level, I took a device that does a 3d peak density test because I was curious why some, that looked heavy with embedment, we noticed that some would have very strong pulls, and some would have very light pulls. And we’re trying to figure out why.

Why when they have the exact same profile is the pull different?

Well, we went in and noticed the peak densities. One product had up to twenty-four thousand peaks, the other only has six thousand.

Well then, when you go back and look at the magnified picture – the product on the right that only has the 6000 (all those red peaks) – that’s also the same one that had the embedment.

So, it leads to believe that what you’re reading… you’re reading those tops of the embedment.

So realistically that abrasive only gave you maybe a one and a half mil. let’s say you were getting a three and a half mil with Testex Tape.  You’re only getting a one and a half mil and you wonder why your coating is not sticking to the substrate.

So, wrapping this up … you have your specifications. you have your SP10…you have your SP5… even by definition near white blast says there should be no more than five percent, but then you go down to the acceptable variations, and they offer you variations of shading and discoloring and it lists the blast abrasives.

But again, it says it must be less than five percent.

You go to white metal and it says it should be clean, so it does lead to wonder – both of those say by the naked eye, but if you look at one surface next to each other, and one is a nice clean gray surface, and one has a brown tinge to it…or one has a green tinge to it you can’t say that’s a minor shade.

Realistically if there’s 40-50% embedment on the surface that’s not white metal.

So with all of that information what that tells you is you can’t just put into your spec surface must be SP5 surface must be SP10.  If you’re a facility owner… if you’re a coating manufacturer that’s putting a warranty on your product… if you’re someone out there that the actual final outcome of that asset is critical to your role, you need to go further than just throwing up an okay spec to get by the job.

You need to look further into it and see is that surface truly clean good white metal?

There are certain abrasives that leave contaminants… and there’s some that just leave nice white metal so when you’re writing a spec, when you’re putting together the scope and the plan… this is where you should look into spec’ing abrasives that do not change the surface – that do give you true white metal and give you the outcome that you would want.

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