disappearing powder?

[bldgengineer]

Hey guys been lurking for quite some time now and been powdering for a little bit with some success. Lately, I've been having some problem with what seems like "disappearing powder" or I think it might shrink to the middle. For example: when I do a valve cover, it sits on one of the grates from my over in my booth. I coat it from top to bottom and then move it to the oven. 20-25 mins later when I take it out, the sides of the valve cover look like they barely got covered. It kinda fades from the bottom to the top!

Any ideas what might be going on here?

[SCOTTRODS]

Hey guys been lurking for quite some time now and been powdering for a little bit with some success. Lately, I've been having some problem with what seems like "disappearing powder" or I think it might shrink to the middle. For example: when I do a valve cover, it sits on one of the grates from my over in my booth. I coat it from top to bottom and then move it to the oven. 20-25 mins later when I take it out, the sides of the valve cover look like they barely got covered. It kinda fades from the bottom to the top!

Any ideas what might be going on here?

I thought Surely by now someone would give some help.....

The powder being thin or light is obviously not disappearing, but is too thin on the part. The way to insure a good coverage is to use an LED flashlight or worklight to look for the substrate indicating thin spots.... LED's seem to really make the thin spots visible,... you should see no signs of substrate coloring or shiny spots from previous coatings.

Hope this helps....

[peter61]

Also make sure you have a good ground without that the powder will bounce right off.

[bldgengineer]

I thought Surely by now someone would give some help.....

The powder being thin or light is obviously not disappearing, but is too thin on the part. The way to insure a good coverage is to use an LED flashlight or worklight to look for the substrate indicating thin spots.... LED's seem to really make the thin spots visible,... you should see no signs of substrate coloring or shiny spots from previous coatings.

Hope this helps....

Ok Thanks a lot Scott I'll give this a try next time. I've learned a lot from reading your posts. Looks like I got another use for the big D cell mag lite I bought besides protection for night work in DC

[Harleydad]

The VC sitting directly on the oven rack "may" also be causing a faraday effect. Along with LED light suggestion to check coverage, try setting the part on something that will raise it off the rack a bit. That something would obviously have to withstand a cure cycle.

[SCOTTRODS]

The VC sitting directly on the oven rack "may" also be causing a faraday effect. Along with LED light suggestion to check coverage, try setting the part on something that will raise it off the rack a bit. That something would obviously have to withstand a cure cycle.

Good Point Jeff..... I recommend wadding up large balls of Aluminum foil, so the ground will transfer through to the cover too..... Just big enough wads to get the VC off the rack at the edges.