casting over powder coated tubes

[reddwil]

I've ran into a little(BIG) problem. I started powder coating my tubes that I use to make watch parts blanks after issues with paint bleed. I read a couple threads where this was talked about but didn't really seem to get any answers. The problem I'm having is the PR separating from the tube on the ends. It first happened as I was assembling a kit. So I ruled it as possible operator error. I made 8 blanks and turned them round today. Out of 8 I had 6 that did it. A couple did it as I milled the ends the others I noticed after turning. I tried various tension while TBC. Skew, carbide all with the same results. Its only on the ends from a 1/4 to 3/8 up.

Few facts of my process. I use both type resin molds sold by members here. Silmar 41, heated resin, And so on.

I'm thinking that either something is happening to the brass tubes during the PC process with the heating and cooling of the tubes, Or the Powder coat is to hard and/or smooth for the PR to bond to it.

Please any Ideas would be great

 

[mywoodshopca]

I think I had a similar issue using a bought "white" tube. The 1/4" around each end seems to have debonded. It was a white stamp centered in the middle of the tube.

 

[ashaw]

Try using a sealer on the tubes first. I have used a spay on varnish.

 

[Brian G]

Upfront, I have zero experience with casting and I'm only speculating.

Is there truly separation, or does it just look like separating? I ask that because I've noticed when I turn and some light-colored acrylics, sometimes the ends look like the tube separated or something was causing the color to be slightly different.

I wonder if the facing of the blank when pressed against the component is reflecting light back, causing the end to look different.

Just an undeducated guess. :redface:

 

[PenMan1]

I seal the tubes after powder coating. I just use spray on Polyurathane without issue.

NOW that I've said this out loud, the next batches will likely be flawed. Painted tubes DO introduce a "new" variable into PR casting.