Hey Jim, I'm happy to help if I can but I have no experience with the low-temp powders used to coat plastic.
I won't come out and say that Eastwood's powders are junk but it's pretty widely known in the restoration industry that everything they sell can be found under its real manufacturer at 40-60% less than they sell it for. Watch out for really cheap pricing (it's probably recycled), and try not to buy anything from overseas. I use a few different suppliers -- Prismatic is my favorite due to the amazing selection (over 6,500 colors, textures and finishes), and IFS has the best gloss black I've ever shot.
Tiger Drylac, Sherwin Williams and Azco Nobel have also been around for a long time and have devoted followings.
Prep is 97% of a job done right. It's basically the same for all metals but some coaters rely on phosphate treatments or powder primer for rust / corrosion protection on steel or stuff that will be living outside all the time (such as cast iron lawn furniture).
I typically do the majority of the needed bodywork first because it's easier to see then than after it's been blasted. Post-blasting bodywork touch ups are common too -- but I try to get the metal as close to perfect as possible before any powder starts flying.
If the part is bare metal, I will then outgas it at 500 degrees for anywhere from 3-8 hours depending on the composition (steel / aluminum), the level of grunge and metal thickness. Any part subjected to oil, fuel or silicone (Armor All or tire wet) can surprise you with bubbling (the noun version of outgassing addressed next), an uneven powder finish or adhesion issues so the cleaner it is the better.
Outgassing can be either a noun or a verb depending on the context. Its purpose is to heat the part to a higher temperature and cook it for longer than you would to cure the powder so it pulls any trapped impurities and air pockets in the metal when it was formed to the surface where it can be blasted away. This is absolutely CRUCIAL when working with aluminum which is a very porous metal -- especially brand new CNC stuff that may have machine oil on bosses and old used aluminum like an intake manifold. Keep in mind a V8 intake will require at least an hour to get to 500 degrees and the longer you let it stay at that temp, the better the overall results will be.
I outgas stuff at night after 7:00 p.m. when the electric rates go down. What I don't spend running the shop can be passed down to customers and lets me stay at $40 an hour instead of the $175+ for single color work some shops charge.
The only time I outgas
after blasting is when the part is already painted (some paints get harder to remove after they've been heated). Some are so thick from the factory that I use chemical stripper first to avoid hours at the blast cabinet later.
After outgassing it goes into my blast cabinet and gets a total white blast.
Every part is then lovingly hand washed (truly! lol) with an industrial etching cleaner and completely rinsed. That is the last time I will be touching the metal with my skin rather than by a hook, wire or a glove. It is sprayed with denatured alcohol to remove any lingering oils / fingerprints and Total Dissolved Solids in your water, blown dry with compressed air and either hung up on my spray rack or placed on a jig.
To make sure it's completely dry, I let it sit and clean my gun and spray area (about 24 mins.), gather any silicone plugs for threaded holes and, on jobs with several parts to coat, mock up my oven hanging layout while it's still cold to assure myself I can get the stuff in it without touching anything or rubbing against other coated parts nearby. If you want a bunch of parts to match it's best to coat and cure them at the same time due to differences in barometric pressure and humidity which can make a bigger impact than you might realize. Some powders love it humid and others do not so you'll have to play with that some and keep notes.
Pull your masking tape and remove any silicone plugs before you put parts in the oven with a little twisting/pull motion. The opening will turn out cleaner and you won't have a big funky ridge of cured powder to shave off with a razor blade later.
Most powders like a hot oven at the outset but some others (wrinkles, textures, veins, rivers, etc.) like to ramp up slowly.
Recommended mil thicknesses, cure times, UV stability and particulars about that powder will vary (check the MSDS). Do not start your timer until the PART reaches the optimum temperature, not the oven. Get an infrared temp gun if you don't have one yet -- without it you will merely be guessing and hoping for the best.
I'm not keen on getting into how to do multi-color custom work here because it's how I'm able to keep food on my table. I hope you understand. There are places that can do a decent job on two colors but very few like me who venture way beyond that. Maybe when I get closer to retirement I'll write a technical guide because the ones out there now are more of "The Blind Leading The Blind" from what I've seen of them. Even though I've been at this for 20 years this year, I will STILL never call myself an expert because there is always something new to learn. Keep an open mind and don't be afraid to think outside the box.
If anything comes up in your coating efforts that you have a question about, just call me. I work really late into the night and don't get up early but you can catch me pretty much every day after 10:00 a.m. Central time, even on weekends.
I hope this helps! I hadn't intended to write a novel today but there's no such thing as too much info about a subject that interests you.