Picture framing effect?

[callmej75]

Anyone got any good advice for that? I tried powder coating several samples last night and after I would bring the chrome out of the oven for a transparent, I would wait until the part cooled to maybe 175* and shoot the transparent. Everytime it was coming out with a nice fat outline on the sample chips and be good coverage in the middle. I adjusted KV's up and down several times in small increments, increased gun distance, decreased air pressure, all of that stuff and still ran into the same problem. I just recently grounded my rack to a 36" copper tube and my gun is also grounded to the rack at a separate point. I get excellent powder coverage to the part but that framing effect is a killer. Anyone got any helpful advice on maybe gun settings and air pressure to get rid of this framing effect stuff?

[coleman5]

why are you grounding to a coper pipe ?

[Popeye]

You mean it's heavier around the edges... that would make it darker around the edges..
Are you spraying both sides?
If you are, spray the back first and the do the front. It's always thicker around the edges.

[callmej75]

Originally Posted by coleman5

why are you grounding to a coper pipe ?

I thought it was a better conductor for a ground? Am I wrong? If so please let me know and I'll use a regular grounding rod.

[callmej75]

Originally Posted by Popeye

You mean it's heavier around the edges... that would make it darker around the edges..
Are you spraying both sides?
If you are, spray the back first and the do the front. It's always thicker around the edges.

Well when I did my first samples when I set everything up, they all turned out great. But I think I found my problem. My samples were suspended too far down....so i shortened the hooks and it cured it a little. I don't have a powder flow setting on my gun so I just adjust the air down to maybe 10psi.

[pickleboy]

Originally Posted by callmej75

Well when I did my first samples when I set everything up, they all turned out great. But I think I found my problem. My samples were suspended too far down....so i shortened the hooks and it cured it a little. I don't have a powder flow setting on my gun so I just adjust the air down to maybe 10psi.

that would make sense. if it was to close to the heat element then the edges would overcure. edges normally get warmer than the middle of a part. that is partly the reason that powder will pull away from the edges if they are sharp.

[pickleboy]

Originally Posted by callmej75

I thought it was a better conductor for a ground? Am I wrong? If so please let me know and I'll use a regular grounding rod.

typically speaking there is no need for earth ground in powder coating. the circuit is only needed to run from the control box to the part on the groound side, and from the box to the gun. static charge takes care of the rest. if you are grounding the clamp and parts to earth ground this could possibly be causing you to not get full charge on the powder transfer to part. just a thought.

[callmej75]

Originally Posted by pickleboy

typically speaking there is no need for earth ground in powder coating. the circuit is only needed to run from the control box to the part on the groound side, and from the box to the gun. static charge takes care of the rest. if you are grounding the clamp and parts to earth ground this could possibly be causing you to not get full charge on the powder transfer to part. just a thought.

Well I was grounding my gun to the top of the rack, and the bottom of the rack is grounded to the earth ground. How could I use a multimeter or something to test if I have good ground? I remember reading a method but I can't remember where it was...but I always make sure my hooks and rack are ground down enough to expose bare metal for good ground....not to mention at my clamp is ground too.

[callmej75]

Originally Posted by pickleboy

that would make sense. if it was to close to the heat element then the edges would overcure. edges normally get warmer than the middle of a part. that is partly the reason that powder will pull away from the edges if they are sharp.

I guess what I'm saying is I see my powder gather around the edges when I spray the powder on....and I read on a website on the troubleshooting that it says to suspend your parts closer to your rack to minimize this. On my sample pieces I always file down the edges to reduce the faraday on the edges and to eliminate any sharp places.

I always spray the front, then look at the back and I notice there is maybe 1/2" wrap around so I try to hit the middle but it still builds up on the edges.