1. Think clearly before painting: What do you want? — The flue environment determines the life of paint
Don't rush to buy paint yet, you have to figure out where the hell your flue expansion joint is staying.Flue Expansion Joint Painting RequirementsIt's not just a paint and it's done. Think about it, what's running in the flue? High temperature smoke? Acid condensate? Or dirty wind with particles? Is the temperature 200℃ or 600℃? Is there sulfide or chloride corrosion? These environmental factors directly determine which kind of paint you should use. Using it wrong is equivalent to putting a paper vest on the expansion joint, which will rot when touched.
A few days ago, a customer called and said thatMetal rectangular expansion jointIt peeled off less than three months after spraying the paint. I asked them what paint they used, and the answer was "ordinary anti-rust paint". Good guy, there are more than 300 degrees in the flue all the year round, so it's weird that ordinary rust-proof paint can hold up. So the first step is to take a piece of paper and write down the temperature, composition, whether there is condensed water, and whether it is open (ultraviolet) of the flue medium. If you are unsure yourself, go to your technical department for a working condition table, or ask our customer service directly, and we will help you judge.
Second, don't fool the surface treatment: the rust removal is not clean, and the patent leather falls off faster than your hair
This step is the hardest hit. Many workers want to save trouble. Take a wire brush and "swish" twice. Believe it or not, 90% of the adhesion of paint depends on surface treatment. There is oil, rust, oxide scale on the surface, and the paint won't stick at all, like building a house on sand-it collapses sooner or later.
How to do it specifically?
- Degreasing:Use solvents (such as acetone, industrial alcohol) to wipe the surface oil clean. Don't use gasoline, it's a big safety hazard.
- Rust removal:Sandblasting or shot blasting is the preferred treatment, which meets the standard of Sa2.5 (the surface exposes a metallic luster without visible rust). If conditions do not allow, at least use an electric sander with grinding wheel plate to grind to St3 level. Handmade wire brushes? That's a fool. Don't use it.
- Clean up dust:There is a layer of fine dust on the surface after sandblasting, blow it clean with compressed air, or vacuum it. It can't feel like sand.
Tips:Primer should be sprayed within 4 hours after treatment, otherwise the metal surface will re-oxidize and rust, and the front will be completely dry. Especially on days when the humidity exceeds 70%, don't work and wait until the weather is good.
Third, paint selection is a technical job: temperature resistance, anti-corrosion and adhesion, all of which can't be missed
There are thousands of brands of paint, but if you pick it wrong, you will kill yourself chronically. According to our distribution for power stations and cement industriesCorrugated expansion joint for power station industryAndMetal Corrugated Expansion Joints in Cement IndustryExperience, I will directly give you a few reliable choice directions:
- Temperature ≤200℃:Epoxy zinc rich primer + epoxy cloud iron intermediate paint + polyurethane top coat. This combination has good weather resistance and moderate cost.
- Temperature 200℃ ~400℃:Use silicone high temperature resistant paint, divide primer and top coat. Pay attention to buying something that can withstand 400℃ for a long time. Don't buy a bargain that is labeled "temperature resistant 400℃" but can only carry it for a short time.
- Temperature 400℃ ~600℃:Only inorganic zinc-rich paint or ceramic paint should be used. This occasion expansion joint body is usually stainless steel, but painting is still necessary for corrosion protection and aesthetic appearance. However, it should be noted that the corrugated area of the expansion joint should not be too thick, otherwise it will affect the flexibility.
- Acid flue gas (e.g. desulfurization flue):Paint with vinyl ester resin or glass flakes. This kind of paint can resist strong acid corrosion, but the construction requirements are high, so it is recommended to find a professional manufacturer to do it.
By the way, if you useNon-metallic expansion joint (fabric fiber expansion joint)Don't spray paint! The body of non-metal expansion joint is fabric + rubber, and ordinary paint will corrode the fabric as soon as it is sprayed. This occasion can only use special silicone rubber coating or not spray, directly rely on the corrosion-resistant layer of the material itself.
4. Start spraying! Environment, technique, thickness-there are pits in every step
The paint is selected, the surface is also treated clean, and the painting is started. There are the most pits here, so I'll give you a smooth through.
1. Environment:The temperature is 5 DEG C to 35 DEG C, the relative humidity is less than 75%, and the substrate temperature is more than 3 DEG C higher than the dew point. Can't reach it? Turn on the hot air blower or stop work. Don't be quick, it will be too late if the paint film bubbles.
2. Spraying technique:The spray gun is 20~30cm away from the workpiece, moves vertically and has an even speed. Each coat of paint should be sprayed "wet and wet" (the last coat is not completely dry before the next coat is sprayed), but don't spray it too thick at once, which is easy to hang. When spraying the bellows, the gun head should be aimed at the side of the corrugation. Don't just spray at the peak, which is easy to leak in the trough.
3. Thickness:Use a wet film card to measure the thickness just after spraying. The total dry film thickness of the primer is 60-80 μ m, the intermediate coat is 60-80 μ m, and the top coat is 40-60 μ m. Touch it with gloves, and then proceed to the next step if it is no longer sticky.
Note:sprayUniversal corrugated expansion jointWhen the corrugated part, the paint film should not be too thick, otherwise the corrugation will lose its elasticity and the expansion joint will be wasted. Don't ask me why I know-last year, there was a construction site that sprayed too thick, and as a result, the ripples cracked, so it was reworked directly.
5. Don't rush to finish the work after spraying: cure, inspect, repair, and rework if you miss one step
Finished paint does not mean finished. Under natural curing conditions, wait at least 24 hours for slight contact and 7 days for full hardness. In a hurry to use? It can be heated and cured (baking at 60℃ ~80℃ for 2~4 hours), but pay attention to the temperature gradient, and don't deform the expansion joint by baking.
Check with the naked eye for hanging, leaking spray, orange peel and pinholes. Take a flashlight and shine it obliquely, and mark it if there are any defects. Use a thickness gauge to measure the thickness of each layer, and polish off the unqualified places and spray them again. The adhesion test is made by crossing method (100-grid knife). After cross-scribing, adhesive tape is applied to tear. Only when the shedding area is
Small area defects are polished with sandpaper and then partially repainted, and large area excess tolerance must be re-sprayed. Don't make do with it. Once the flue expansion joint leaks after running, you can't fix it.
Six, last two sentences: These common mistakes, you probably also made
I write this article because I see my friends making low-level mistakes every day, and I feel distressed for those white money. Summarize a few of the most common ones:
- Myth#1:"The expansion joint is made of iron. Just apply ordinary iron red primer." — Wrong! The temperature resistance of ordinary iron red paint is only about 100℃, and it bubbles in the flue in minutes.
- Myth 2:"It is better to spray it thicker to preserve corrosion." — Wrong! If the paint film is too thick, it will become worse and easy to crack. Especially the corrugated joint, thicker affects the compensation amount.
- Myth#3:"Non-metallic expansion joints can also be painted."-Wrong! Non-metallic expansion joints should be coated with silicone rubber or not sprayed at all, and painting without authorization will only accelerate aging.
- Myth 4:"Put it into operation as soon as you spray it." — Wrong! It is necessary to wait until the paint film is completely cured, otherwise the solvent will volatilize and form bubbles at high temperature, and the whole paint skin will peel off.
At the end of the day,Flue Expansion Joint Painting RequirementsThe core is three words: working conditions, cleaning the surface and controlling the thickness. When it is in place, it will take three to five years for expansion and energy saving. If you are still worried, just take a picture and send it to our technology, and we will follow your product model (such asHigh temperature axial expansion joint、Desulfurization flue gas baffle dooretc.).