Powder coating should provide metal surfaces and parts with a durable, protective outer shell, but sometimes things don't quite work out as planned.
More often than not, this is due to powder coating mistakes during preparation and application.
Here are six mistakes that cause powder coating to fail.
To ensure the best possible powder coating finish, you need to make sure your pre-treatment processes are thorough.
These processes can include vapour degreasing, aqueous and immersion washing.
Poor cleaning and pre-treatment can cause things like poor adhesion of powder coatings. It can also impair effective resistance to corrosion or chemicals once the coating process is complete.
Where degreasing is not powerful enough this can impact other pre-treatment processes such as chromating and phosphating.
If degreasing is insufficient then fabricating oils may remain on the surface. These can liquefy at high temperatures.
Where cleaning fails to remove oxides, this may cause the conversion layer applied during chromating to appear uneven or spotty. Alternatively, the layer may not bond at all if the pre-treatment has the wrong formulation or the timings are off.
Another pre-treatment mistake is applying a conversion layer treatment for too long. This causes the layer to be too thick to apply an even powder coating layer over it.
If the powder spray pattern appears uneven or weak then this is normally due to poorly maintained equipment. It shows up as an inconsistency in the build-up of film and the pigmentation of the powder.
You get poor spray patterns where parts of the spray gun, feeding hose or pumps aren’t functioning the way they should be.
It can be that this equipment has simply come to the end of its working life. But what you may need to do is make sure it's cleaned thoroughly to remedy the problem.
In other instances, a poor flow can be down to a broken or worn pump.
If the gun is spitting or having sudden surges, then shows that the powder feed is inconsistent.
The usual culprit for this is excess fluidisation. The fluidisation process involves the use of air to turn the powder into a liquid state. This makes the powder easier to apply.
But if there's too much fluidisation, air bubbles form in the powder feed. When this happens, there’s an inconsistent mix of air and powder coming out of the gun.
Another thing that can cause the gun to spit powder is residue collecting on its tip or electrodes that then breaks off in one go.
Sometimes the hose is the cause if it's worn or has kinks.
The overall finish of a powder coating depends on the thickness and coverage of the film.
If it's too thick, you can get issues such as orange peel or sagging.
The orange peel effect is an uneven texture resembling the skin of an orange. Sagging is where the film shifts in the curing oven and actually starts to sag.
Problems with powder coating not being thick enough are that you start to see surface blemishes through the coating or even the surface itself. The coverage is insufficient to coat the surface evenly and effectively.
This may be due to having the wrong settings on the powder gun, but frequently it’s down to not having good grounding of the surface to create the necessary charge for the powder to stick to it.
When you ground a part or surface for powder coating, you’re creating a path for the charged powder to flow along. Without this path, the coating won’t adhere evenly.
If the powder coating goes lumpy in its box, you're not going to find it easy to work with.
Storage conditions are critical for powder coatings, because, ultimately, they can affect performance.
Where you get lumpy powder, this may be because it's been stored at too high or low a temperature.
You can also get lumps in powder when feeding it, caused by continuous vibrating during the operation.
To ensure your powder coatings are lump-free, store them according to the manufacturer’s recommendations and check your feed processes.
You can always filter lumpy powder to get it fine and even again.
One of the advantages of powder coating is that you can apply it to sharp edges or tricky corners and still come out with an even finish.
However, sometimes powder coating fails to penetrate these recesses properly. When this happens, you can see that the coating thickness is uneven in some areas compared to others.
You should check the powder flow, to see whether it's too high or too low. Also, check the nozzle of the spray gun for its suitability for this particular task. There may be not enough charge to the gun or the voltage is too high.
The failure to penetrate recesses can also be down to operational errors. The distance from the gun to the surface being sprayed may be too near or far.
The obvious solution to eliminating mistakes in powder coating is to use a professional powder coating service.
For more information about this, please contact us.