El Toro;n78770 said:
I feel the same as you jlcustomz.............my two car trailers 4 years old the are a rusted mess both were power coated. My brothers trailer was a factory painted trailer 6 years old looks great. Also some of the other projects just don't seam to hold up and when chiped go right to rust and then creeps under the coating. Reminds me of por-15. Looks very nice when new. Hell I painted a rusty metal metal brace for oudoor use with SPI epoxy and acrylic enamel a few years ago and still looks great even when I bent a section.
Just my opinion
Just like with liquid coatings, prep is everything.
Manufacturers have the advantage of being able to specify substrate and or treat the substrate prior to the coating efforts. Sadly it doesn't occur to many of them that they have this type of control. In most cases where you see failures like the trailers you mentioned it is simply lack of knowledge on the manufacturing side.
There are certain metals that lend themselves more friendly to cleaning and conversion coating processes. CRS is usually very nice to work with where structural tubings with carbon scale are less awesome for a professional coater to work with, structural shapes like flat bar, angles, channels etc suck even worse.
An awesome coating on a steel framed trailer made up of structural mild steel tube and shapes (bar/angle/channel) will start with a blast spec. Shot blast is currently fairly popular because you can maintain the shot size in your reclaim cycle. A shot blast profile will typically be specified, for me as a coater what I like to see is all of the blue/black mill scale to be gone and for the blast profile to not be too damn rough.
You can also acid pickle these types of parts for removal of the scale film, acid pickles are typically submersion processes which takes a huge amount of space and forces special efforts to get the acid bath solution back out of open tubes or other pocket areas that will scoop solutions from a process tank.
The reason to remove the scale from these types of steel parts is because that layer is a weak link between your coating and the underlying substrate. A coater will likely use a spray cleaner stage to remove oils and soils from the parts, then a rinse, often times a second rinse. In the old days we would then shoot for an iron phos stage, this will most often be a heated chemical spray stage where the acidity of the stage itself leaches off a microscopic amount of iron as it in turn deposits iron phosphate molecules at the surface of the substrate. It's sort of like a plating process on a very mild scale. This will be followed by multiple rinse stages with the stages becoming increasingly cleaner until the final rinse where the TDS will hopefully be under 20 parts per million on solids.
I personally prefer the newer "nano coatings" like henkel's NT1 over old fashioned iron phos but I'm just giving a process example for the sake of showing how involved the prep can be for a truly long lasting coating.
Next is powder selection, if it's a single coat process then hopefully they are choosing something like a "supreme weathering" or "super durable" variety of a TGIC polyester. They will have film thickness standards and they will have pre tested the cure cycle with temp recorder probes attached all over a bare steel part to insure the proper temp induced cross linking of the coating.
But here's how things sometimes go rather than the above.
Bubba wipes the trailer frame down with some paint thinner until the rags aren't too black, there is no blast process. Roll it into a batch booth, blow some powder on (black powder, we really don't know anything else other than it's black) then we roll it in an oven and bake it for a while.
All the scale removal and cleaning, conversion coating and rinse processes, they remove hyper corrosives from your steel and replace them with an inert layer that promotes adhesion and prevents corrosive creeping under the paint film when chips and scratches occur. The cure is also crucial as the powder has dry blended A and B components that need to melt in order to blend and actually cross link right on the part itself as it's being cooked. The powder manufacturer will spec "time at temp". You need the powder to reach the target temp and hold for X-minutes or the cross linking will fail to occur. This is where you get a paint film that flakes off like potato chips, under cured powder. You can and will have cured and under cured powder on the same part due to heat sink areas. Thicker heavier areas will take longer to get up to temp.
It costs money to do it right. And typically you will only see it done right in big name brand manufacturers that have been in business for many years and care to continue in business for many more.
I would not be bringing a hot rod frame or other parts to a custom powder coater with the idea in my head that they are going to do do a better coating job than I can do in my liquid spray booth in my shop.
Now If I was forced to bring a hot rod frame to a powder coater because my customer was irreversibly mesmerized by the word "powder", then I would be there with the powder coater observing the cleaning and prep process as well as insisting on a dry cure test or two with heat probes attached to record substrate temp/time for the bake cycle.
I would do all that to help protect my customer from expensive paint failures, I'd also say a prayer or two and cross my fingers.
"OK smarty pants, what would you do instead of powder coating then?"
I'd prep the parts, likely with a blast profile, I would clean the parts per prep instructions that can be found here at SPI and coat them with SPI epoxy followed by a high solids single stage 2k urethane, formulated in the gloss level and color that the customer requires.
And now I offer apologies. lol
I'm too new a guy here to be posting a lengthy tech type rant.