Hey everyone, it’s Jake from the thermal spray crew here. Let’s cut to the chase—when you’re relying on thermal spray coatings to keep your parts from corroding, wearing out, or overheating, cutting corners on quality inspection is like skipping a oil change on your work truck: it’ll fail way sooner than it should, and cost you way more in the long run. As someone who’s been in this game for 8 years, sending out coatings that don’t hold up is the last thing I want on my watch. That’s why today I’m breaking down exactly how we (and you) inspect thermal spray coating quality—no fancy jargon, just real-world stuff that actually works. Thermal Spray
First off, let’s get one thing straight: thermal spray isn’t a one-and-done process. The coating’s quality starts way before we even fire up the spray gun. Like, surface prep is 90% of the battle, right? If the part’s got grease, rust, or even a tiny bit of leftover machining oil, that coating’s gonna bubble up or peel off in 6 months max. So the first inspection step here is post-prep check. We use a quick solvent wipe first—we swipe a lint-free cloth with isopropyl alcohol over the base metal, and if the cloth doesn’t have any gunk on it, we’re good. Then we do the roughness test, because the spray particles need something to grab onto. If the surface’s too smooth, the coating won’t anchor right. We use a surface profilometer—super cheap, handheld tool that gives a Ra number (average roughness) in like 2 seconds. For most of our clients, we target Ra 3-6 microns, and we’ll log that number right on the job sheet so you can see it. No guesswork here.
Once we spray the coating, we jump right into non-destructive testing (NDT) because we don’t wanna ruin the part we just worked on. The first quick check is visual, but not just a glance—we get up close with a 10x magnifier and good LED light. We’re looking for things like bare spots, cracks that are super small, or weird discoloration that might mean the spray heat was off. If you see a spot where the coating’s missing, that’s a red flag. And weird gray or black streaks? That usually means the powder was contaminated or the gas mix was wrong—we toss that batch immediately, no exceptions. We used to miss a few tiny bare spots early on, so now we do a full sweep of every part, not just the high-stress areas.
Next up is thickness measurement, and this is non-negotiable. Too thin, and it won’t protect the part. Too thick, and it’ll crack from thermal expansion or add unnecessary weight (which matters a lot for things like aerospace components). We use two main tools here, depending on the coating type. For magnetic materials (like steel parts), we use a magnetic induction gauge—we just touch the probe to the coating, and it gives us a readout in seconds. For non-magnetic stuff, like aluminum or stainless steel, we use an eddy current gauge. Both are accurate to within 0.001 mm, so we can hit exactly the thickness you ordered. We mark 5-10 key spots on every part (high stress, edges, corners) and log all those numbers, so you can audit them anytime. If you order a 250 micron coating, we’re not sending you 100 microns—period.
Now, adhesion is probably the most important thing, because if the coating peels off, all that thickness and roughness checks are useless. Adhesion testing sounds scary, but there’s a standard way to do it that’s not destructive (or at least only destructive on test coupons, which we include with every job). We use a pull-off adhesion test, per ASTM D4541 (don’t panic, it’s a standard). For test coupons that are sprayed at the same time as your parts, we glue a metal stub to the coating, then pull it straight off with a calibrated tester. The force needed to pull the coating off tells us how strong the bond is. For most industrial applications, we need at least 70 MPa, and we usually get 80-100 MPa if we did the surface prep right. We keep that test report on file for every order—no hidden results, you can ask for it anytime. We also do a quick impact test on the shop floor sometimes: we take a hammer and lightly tap a 1-inch square of coating. If it cracks or pops off, we redo that part. It’s rough, but it catches stuff the lab tests miss because it mimics real-world impacts.
Wait, I should mention porosity too—this is a big one that a lot of people sleep on. Porosity is tiny little gaps in the coating, and if there’s too much of it, corrosive fluids or air can get through to the base metal, making it rust from the inside. For things like hydraulic pistons or pump components, we need super low porosity. We use a few methods here. First, we do a water break test: spray water on the coating, and if it beads up evenly, no pores. If there’s a spot where water sheets out, that’s a pore. Second, we use a digital microscope to count porosity spots on a small sample area, and we aim for less than 1% porosity for corrosive applications. For things that need lubricity, like bearings, we actually want a tiny bit of porosity (1-3%) to hold oil, which is why we tailor the spray parameters based on what you need.
Oh, and let’s not forget about post-treatment checks. Sometimes we seal the coating, right? For things that are exposed to chemicals or moisture, a sealant fills in the pores so nothing gets through. We check the sealant coverage by wiping a chemical indicator (like copper sulfate) on the coated part. If the coating doesn’t react, that means the sealant is covering all the pores. If it does, we go back and re-seal that spot. Simple, fast, and it works.
Let me give you a real example of why this matters. Last year, a construction client came to us saying their excavator bucket edges’ thermal spray coating peeled off in 3 months. We looked at their old inspection records—they had a thickness test that said 200 microns, but no adhesion or porosity. Turns out, their old prep team missed a little bit of rust on the bucket edges, so the bond was garbage. We redid the whole job, did full adhesion testing, and now those buckets have lasted 18 months so far, no issues. That’s why we don’t cut corners on inspection—we know it’s gonna save our clients money, and keep our reputation intact.
A lot of people ask us, “Do you just test your own work?” Heck no—we also send random samples to a third-party lab every month to verify our tests. We don’t wanna be biased, so having a neutral set of eyes check our numbers makes us way more confident. And if you’re inspecting parts on your end, just remember: don’t skip the basic stuff. Thickness is easy to check with a cheap gauge, adhesion tests can be done in-house with a pull-off kit now, and visual plus porosity checks will catch 90% of the problems before the part goes into service.
Wait, quick note: every coating is different, so the inspection steps change a little. For ceramic coatings on turbine parts, we do more thermal cycling tests to make sure they don’t crack from heat changes. For polymer coatings on food equipment, we check for chemical resistance and make sure there’s no lead or other contaminants. We tailor our inspection plan to your specific application, not a one-size-fits-all.
If you’re out there dealing with parts that wear out too fast, or coatings that don’t hold up, hit us up to chat. We can walk you through our full inspection process, send over test reports for any past jobs, or even come out to your shop to train your team on basic thermal spray quality checks. No pressure, just good info. We’ve worked with small fabricators and big industrial plants, so we know what different clients need, and we’re here to make sure you get a coating that actually works for your needs.
Resistance Welding Electrode At the end of the day, thermal spray coating quality isn’t about passing a single test—it’s about checking every step, from prep to post-treatment, to make sure the final product is gonna do what you need it to do. Skip the quick checks, don’t trust vague “it looks good” claims, and get hard numbers. That’s how you avoid the headaches of part failure, downtime, and extra costs.
References
- ASTM International. Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers (ASTM D4541).
- Davis, J.R. (Ed.). Handbook of Thermal Spray Technology. ASM International.
- Sauer, B. (2018). Non-Destructive Testing of Thermal Spray Coatings. Journal of Thermal Spray Technology.
- ISO 14922:2018. Thermal Spraying — Qualification and Testing of Thermal Spray Coaters.
- Karthikeyan, J. (2020). Quality Assurance in Thermal Spray Coatings: A Practical Guide. Surface Engineering.
Foshan Jiafengrui New Materials Technology Co., Ltd.
We are one of the most professional thermal spray manufacturers and suppliers in China, also support customized service. Please feel free to wholesale high quality thermal spray in stock here from our factory. Welcome to view our website for more information.
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