Raised plastic/resin pattern on my transformer. Faulty or removable? [resolved]

[NearlySentient]

Hi Folks, excitedly unboxing my crack kit and have noticed the transformer has a highly visible raised pattern on it like it got sat on a patterned piece while the resin was still wet. Is this a manufacturing fault or is it removable? If removable please guide me how so I can remove it without causing any damage.  See the pic:

[caffeinator]

Shh! It means you got the 'textured finish' for free!

Just kidding. You're right, probably from sitting on a rack to dry or something like that. I've seen similar patterns on various transformers before. I have lightly sanded and painted over with good results.

[Paul Birkeland]

I would paint over it and leave it alone.  If you remove too much varnish, that can be a bigger problem than cosmetics are.

[NearlySentient]

I would paint over it and leave it alone.  If you remove too much varnish, that can be a bigger problem than cosmetics are.

Thanks Paul, I think I'll ask customer support for a replacement as I wasn't intending to paint the transformer and as is that defect will bug me forever looking at it. Cheers.

[Paul Birkeland]

It's not a defect, they all sit on an open chicken wire shelf when they are varnished, so all of them will look like that.

If you have to remove that pattern, I would get some adhesive backed 220 grit sand paper and stick it down to something very hard and flat (a spare piece of glass would be ideal) and gently rub the transformer against that until the lines are barely visible.

[dstarr3]

I would paint over it and leave it alone.  If you remove too much varnish, that can be a bigger problem than cosmetics are.

Could you go into more detail about that? What would happen if too much varnish was removed?

[Doc B.]

The primary issue would be rust where the varnish has been sanded off. Another potential issue is sanding into the metal and leaving metal filings that can fall into the coil area. Also, in theory, if one removes too much varnish there might be some issue with laminations coming loose. But you would really have to douse the thing with acetone to do that kind of damage. I suspect careful sanding with some 320 to 400 grit sandpaper to just smooth off the grid marks would be OK. I'm considering doing a video on this in the future.

[NearlySentient]

From what I've read if you sand too much varnish off and expose the bare metal then coat it with something conductive (metallic paint??) then you can cause inductive currents inside the metal.

[NearlySentient]

As an FYI to anyone reading this thread, I tried the flat sanding method that Paul mentioned but the surface created by all those metal shims in the transformer is surprisingly uneven so that didn't work. Doc B also responded to my query to customer service and confirmed this isn't a manufacturing fault and suggested gently sanding it down. I tried that with 600 grit but found that to get the pattern fully out meant I had to be pretty aggressive which left that side of the transformer looking different to the other sides so I ended up giving it a couple of coats of some matt black high temperature silicone based paint I had lying around.  Will post some pics once my build is complete.

[Doc B.]

Sounds like you got to the result you wanted. My suggestion does assume understanding that the side you lightly sand will look different than the others and thus the lams will require a coating all over to even out the look, whether clear or opaque. The suggestion not to use conductive paint is a good one. Typically lam stacks are painted black because it downplays the slightly uneven surfaces of the lam stack. I have seen lam stacks painted with black wrinkle finish paint to good effect.

A contrasting finish on the bell end can draw the eye away from the stack too, even to the point where painting is not necessary. It's easy to get wrapped up in the appearance of one part that will not be noticed in the finished project. I learned this years ago when I was restoring antique radios. My mantra when building  project - whether it be an amp or a motorcycle - is "it's the sum of the parts you look at, not just this part".

[dstarr3]

As I'm looking for paints, what kinds of temperatures should I expect this component to reach? For instance, I'm looking at a wrinkle paint that's good for up to 350'F, which I'm sure is plenty, but it also requires curing at 200'F for twenty minutes, which I don't know if the transformer would like

[Doc B.]

200F is probably OK. IIRC the transformers have a 105C rating, which is about 220F. You can always use a little lower temp for a bit longer too. Maybe try 175F for 30 - 45 minutes.

And it would probably cure OK over time just with normal operation. But the paint needs to be handled very carefully before it has fully cured.

[Paul Birkeland]

There are ample spray paint options that don't require putting your power transformer into an oven and crossing your fingers that nothing bad happens.  While the wire insulation and varnish used to put these together carry very high temperature ratings, the plastic bobbin inside the transformer may not be as happy about what you plan to do. 

[dstarr3]

I actually remembered that I have both a food dehydrator and toaster oven in the attic that have already been spoiled for food use from previous maker projects, so I'm just going to chuck it in whichever one of those will best keep a temp of about 150-175'F for a few hours.

[dstarr3]

Another option I'm considering is just some spray-on truck bed liner. Looks like the Rustoleum stuff is good for up 200'F, doesn't need to cure, and is designed to be applied to bare metal.

These are the two paints I'm currently deciding between:
https://www.oreillyauto.com/detail/c/wrinkle-plus/vht-wrinkle-plus-11-ounce-black-spray-paint/vht5/sp201
https://www.homedepot.com/p/Rust-Oleum-Automotive-15-oz-Black-Truck-Bed-Coating-Spray-248914/202097787

EDIT - Skip the Rustoleum, if you want to use bed liner spray, get Herculiner brand. Rated for up to 250'F.