Sanding down Hammond transformers

Hi,

Since the quality finish on Hammonds transformers is not quite nice, I'd like to know if I can sand down the sides and top of the cores to redo the painting.

I'm asking because I do not know much in transformer design and aint sure if each core plate is isolated from one to another and if it will short circuit them if I sand down to metal.

All comments appreciated as if I should or not do it.

Thanks!
 

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My understanding is that each lamination is poorly insulated from its neighbours, but as all these weak barriers are in series the result is a higher resistance so only small eddy currents. Sanding the ends could create dead shorts so increasing eddy current losses. I would leave it as it is. If you don't like looking at it then add a perforated cover.
 

bob91343

Member
2010-03-11 10:43 pm
I don't believe you will cause a problem, especially if you use sandpaper and not emery or a file. Metal filings aren't good. Tighten the mounting screws before you proceed. Sand lightly, just enough to do the job.

Note that the mounting screws have insulating washers. Don't compromise that insulation.
 
DF96, bob91343,

Thanks for your replies gentlemen it was very helpfull and answered my question. I will sand them down beeing carefull to only remove the small impureties that built up in the original finish (not to bare metal). I would have liked to remove every thing and start from new with a nice copper finish but I dont want to take any chance and alter their performance.

Thank you!
 
Why sand it down, the usual technique to pretty up industrial hardware is to use body filler or spray putty then sand down that till it is smooth. As for the insulation between the plates, it is common practice to weld a lamination stacks together evidently with no ill effects (this is done on one side of the stack only) so I cannot see a bit of sanding causing problems.
 
I know of one MFG that does this to every exposed transformer without ill effects. has been doing it for years and even has a full time employee that does not but this! they sand the sides flat and smooth then repaint!

I have emailed Hammond today to have their expertise on that. The sales rep told me I could sand down to metal but I'll try to speak to an engineer tomorrow for approval. I want to make sure this in no way will affect the performance. The rep also proposed to have the transformers sent back to the place where I purchased them and they would take care of all the shipping expenses (mine and the store). Not bad, but I'd rather not go through that hassle and wait a week or two. I haven't mentionned either to you guys that the varnish (not paint) on the 193M choke end bells is peeling off very easy. It's supposed to be baked. If I gently touch with my fingernail, air penetrates between the metal bell and the lacquer coat. It's sad that they don't use the same finish as the OPT and PT, this one is very nice and clean. Check my picture...

Thanks!
 

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Why sand it down, the usual technique to pretty up industrial hardware is to use body filler or spray putty then sand down that till it is smooth. As for the insulation between the plates, it is common practice to weld a lamination stacks together evidently with no ill effects (this is done on one side of the stack only) so I cannot see a bit of sanding causing problems.

Thanks for the putty suggestion but here I'd rather see the laminates to keep the industrial looks. Thanks also for bringing up the welding practice. I don't know if Hammond process this way (I don't think so as I did not noticed them) but it's a good point you brought up there.
 
Dip the affected side in a very shallow tray (Don't fill it more than a couple mm's) of lacquer thinner; the varnish should be soft enough to scrape off after an hour. Just make sure you don't get any on the windings, bobbin or wires.

Cool idea! but I wont have much control over the process. Lacquer thinner is strong, it could penetrate between the laminates. I'll think over it, maybe a less volatile thinner could be more appropriate. Hmm!
 

db!

Member
2009-11-21 4:53 am
Ontario
Cool idea! but I wont have much control over the process. Lacquer thinner is strong, it could penetrate between the laminates. I'll think over it, maybe a less volatile thinner could be more appropriate. Hmm!

Lacquer thinner will not penetrate the laminations unless you leave it sitting for days; it only seems to work on open and exposed surfaces. Just be careful not to overfill the tray; 3-5mm depth is ideal.

Also, the amount of time you leave it in the thinner for isn't critical, a hour or so will soften up the varnish enough to be scraped off.
 
After you have spent some time with the lacquer thinner try using Acetone, same amount in a metal tray. Use double vinyl or other protective film gloves to avoid poisoning your self. This will melt the polyester resin that is likely the varnish used. Just wipe the core edges with a wet strength paper towel now and again until you get it as smooth as you want. Once the resin has reset, lightly sand the paper residue off and paint.

I am a transformer engineer and this is what we do in our plant to refinish or dismantle the transformer core. I would remove the endbells and bolts. keeping the isolation washers where they are on the bolts. Don't loose those, ever!!!!! Then perhaps rebolt the core with some appropriate size just to keep the pieces of I lam from dropping out.

Bud
 
No need for that high of protection from acetone. It has a relatively low toxicity (most other solvents are more toxic). More than anything without protection it may give a burning irritation to the skin, with no damage (just some dryness). Keep in mind nail polish remover is often atleast 50+% acetone (with some I have seen up to 80%).