Getting some coating problems. I’ve done a couple of tumbler style cups with no cratering or fisheyes. An the other hand I’ve done these small ornaments for my wife and have gotten fisheyes and craters on some of them, not all of them. Some of the items I’ve pre-baked at a higher temperature to get any contaminates out. Some I haven’t. I’m just not sure what causing them.
I have a three stage air dryer at the compressor. A water/oil filter at the gun and an automatic drain at the compressor that surges every ten minutes.
My process for powder coating is this…
Cut the metal
Grind the slag off
Die-grind the whole piece
Acetone with paper towel (while wearing latex gloves)
Burn any lint, etc off with torch
Pre-bake the metal (not always)
Spray the piece in the booth
Cook/cure the piece for desired time
Let cool outside the oven
Just not sure what has caused the issues on only maybe 4 out of 15 pieces coated.
1 Like
I would recommend not wiping the part with a towel. Instead spray the part with acetone, then blow it off, the shoot it
1 Like
Hey Andy do you think that die grinding it is putting any contaminants into the metal? Sometimes the die grinder spits some oil onto the parts I’m grinding.
And I’ll definitely get a spray bottle and start spraying the acetone on.
1 Like
That is a huge possibility. I would recommend sand blasting instead of grinding. I also understand that some people don’t have a sand blaster, so it you don’t then I would use a new piece of sand paper or scotch Brite, then spray then shoot
1 Like
I’d pre-bake all the time. I’m never sure what’s been soaked into my metal parts before I got them. Are you seeing any correlation between when you don’t bake & then get cratering/fisheyes?
Andy - yeah I don’t have a sandblaster, so I grind the parts to get the dross off, I think sandpaper would take forever, especially on some of the more intricate pieces. I did a piece tonight, split letter monogram, and used the grinder to get the dross off and then I used the die-grinder with scotch bright pad - new. I then sprayed with alcohol, and then placed the part in the oven at 450 for 30 minutes.
I will re-pre-bake tomorrow before I PowderCoat.
Jim - is there a set temperature to pre-bake? after 30 minutes at 450 the part was brassy looking. kinda cool looking, but hoping I didn’t do anything to the metal.
Thanks again and repeatedly,
Bill
I usually take the powder coat temp and add 25 degrees. Anything that would off-gas while baking the powder will be volatized. The change in color of your raw part shouldn’t affect anything - unless you’re doing critical heat-treated parts. In that case you have to be careful to keep the temps within the range the treater will give you so as not to affect the temper. But that’s not likely to be an issue with something you’re going to powder coat. 
You don’t want to go overboard because it may warp the piece so that’s why I use the +25 degree value.
1 Like
Thanks brother. I’m gonna bake everything out. I like using the die grinder hooked to the air compressor but maybe that’s the culprit. This weekend I will test two small pieces of scrap. My metal is cold rolled steel and I know the place I get it from coats it.