On cleaning transformers

[rsumperl]

Greeting everyone,
     Got some potted transformer on eBay that were brand new, however they have some surface rust. Any issues anyone can think of if I have them glassbeaded?

Thanks,
 Ray

[WA1GFZ]

mask off the insulators and you will be fine

[Mike/W8BAC]

mask off the insulators and you will be fine

To expand on what Frank said, The insulators have to be masked so NO glass bead hits them.

If the glass bead has been used even once to blast off paint or corrosion on other metals it (the glass bead media) has metal mixed in it. If you blast that used media on your transformer insulators the metal particles stripped off the previous work will be imbedded in the porcelain of your transformer inviting a short. Be very careful.

[W2XR]

For xfmrs and chokes with accumulated surface rust, I have them glassbeaded first. Be sure they use a relatively fine abrasive; I can't recall what the guy uses where I bring my parts, but it's not the same material used for blasting car chassis.  Tell them what you need and they can usually make the right media selection relative to your specific requirements and application.

I mask the porcelain feedthrus or insulators with duct tape before giving them to the glassbeading shop, with instructions for them to be careful of the fragile porcelain parts. The duct tape can easily withstand the pressure of the bead media hitting it, if the guy doing the glassbeading does'nt get carried away. So far, I have never had a problem, but I have used the same shop for years, and he knows what I want.

Just be careful in the event that you elect to have the xfmrs refinished with an oven-bake paint, the oven temperature is high enough to correctly bake the finish, but not so high that you melt the tar or potting material. Oven-bake paints typically require around 180 to 200 degrees F to properly cure and harden. I have had numerous tar-filled power xfmrs and filter chokes repainted over the years using this process and at this temperature range with no ill effects.

With powdercoating this is even more of a problem, due to the application temperature of around 400 degrees, F. That temperature is completely unacceptable for transformers and other magnetics; it will not only ruin the potting material, but will probably damage the windings and internal insulative materials as well.

73,

Bruce

[The Slab Bacon]

just FWIW youse guys may want to look up someone in youe area that does "sodablasting" It is a process very similar to sandblasting, but uses common baking soda.

this process is now the hot lick for automotive restoration and paint stripping as it removes the old paint and rust, but does not damage the base metal like sandblasting.

It has become the in thing and is somewhat more environment friendly than some of the abrasives used in sandblasting.

                                                              The Slab Bacon

[WA1GFZ]

walnut shells work great in a blaster. We used them to blow coating off pc boards. They are ground up into a fine powder.

[The Slab Bacon]

walnut shells work great in a blaster. We used them to blow coating off pc boards. They are ground up into a fine powder.

I have heard of this before, they also have fine ground plastic powder ans plastic chips as well. A lot of this stuff is used in car restoration. It is becoming a science unto itself.

[W2XR]

Frank & Frank,

I think you can purchase some of this more esoteric blast media from the Eastwood Company if you have your own blasting capability. Eastwood sells lots of supplies for auto restoration work.

There is a shop here on Long Island that does blast with walnut shells and sodablast, but I have never used them. For the kind of parts that I get blasted, such as potted transformers and chokes, old chassis and rack cabinets, and other sheetmetal aluminum and steel parts for various restoration and homebrewing projects, the glassbead media when shot at the correct (i.e. not excessive) pressure has always yielded excellent results for me. The blasted surface is invariably ready for prime and paint, with little to no other prep work required, other than blowing the work clean with compressed air and making sure every last trace of media has been removed. And you have to literally go right to the paint shop or paint the parts yourself if the material that was blasted is of a ferrous material. It will immediately start rusting otherwise.

So much of the final result also depends upon the skill and care of the guy shooting the media. I recall one situation where I was involved in a project to get three CY-979A/URR cabinets for the R-390A glassbeaded and then painted. Another shop that I did not normally use did a test blast on the inside of one of the cabinets, and he used too much pressure, with the result that the metallic screening began to distort. Good thing we were watching and stopped the test immediately. I had another shop (the one I normally use) do the blasting, and there was literally no deformation to the screening or any other part of the cabinets whatsoever, and they came out looking great. As with anything else, sometimes you have to be a real PITA with these guys to make sure it is done right.

When the weather starts warming up, I am getting the cabinet for my GPT-750 glassbeaded. I have the TMC blue paint mixed and ready to go. The damn cabinet is big and weighs probably 300 lbs; a fellow I know is getting the cabinet blasted for me with fine media in a large chamber at an aeronautical glassbeading facility not open to the general public, so that is a big help, and he is picking it up at my QTH as well and then delivering the completed cabinet to the paint shop. He's a good guy!

As with anything else, your mileage may vary. The only problem is, there is frequently no opportunity for a second chance when media blasting if you or the technician doing the work are not careful.

73,

Bruce

[The Slab Bacon]

Bruce,
         One of the BIG advantages of sodablasting is that it DOESNT cause the base metal to start oxidizing immediately. (Something in the baking soda blast media actually retards the oxidation of the base metal.) You have plenty of time to prep, prime, and paint it more at your leisure. This is a big advantage when doing large jobs. It might be well worth considering for anyone getting ready to do a large broadcast transmitter cabinet restoration, or something of equal size and difficulty.

[N3DRB The Derb]

when I worked at th heart pacemaker joint, they had to blast the ceramic feed throughs (basically platinum thru-holes in ceramic beads with 4 holes) and they used dolomite for the media. I used to take radio parts in there and blast em, an extremely fine powder form that wouldnt take out the sputtered platinum  surface. they hadnt figured out a way to mask it yet (late  80's)

I don't know if dolomite is  more or less = to soda or not but I think it's somewhat similar.

[k4kyv]

If the transformer has surface rust, just scrape off any loose scaly stuff with sandpaper or steel wool, then give it a coat of rusty metal primer.  This paint uses a fish-oil base, and is designed to soak in and impregnate the rust, then harden.  That seals the rust and prevents it from further accumulating moisture from the air, while the rust serves as an adherent that makes the paint almost impossible to scrape off.  Then top coat it with a good satin or semi-gloss finish.  No need for exotic sandblasting to restore the transformer, plus, the finish will be more durable.

This summer I accidentally spilt some rusty metal primer on a piece of wood. After it dried I couldn't scrape it off; it seemed to have migrated a few thousandths of an inch into the surface.  With ordinary oil primer designed for wood, after it dries it can be easily peeled off with a blade.  So why wouldn't the RMP hold paint even better than regular oil primer? I did a web search and found several sites that said it was ok to use rusty metal primer on wood.  One of the companies that makes this primer is Rustoleum. I  called their customer service and asked about this, and the rep said that yes, Rustoleum rusty metal primer was perfectly good for priming wood and would take acrylic latex top coat just fine.  A gallon of RMP is actually a little cheaper than a gallon of good grade oil base wood primer.  I finished up a painting project using RMP primer on  the wood.  It will be interesting to see in a few years if the paint on the wall that is primed with RMP deteriorates any sooner or later than the rest of the building that is primed with regular oil base primer.

The cast-iron end bells of transformers I have treated with RMP and then applied semi-gloss black paint look like they just came from the factory.

[WBear2GCR]

Don, I wonder if they still have fish oil in Rustoleum anymore. All the paints today have changed formulas to get rid of the VOCs... there ought to be something somewhere online with the contents/ingredients, if not the company will likely tell you.

Harbor Freight sells walnut shells...

Where can you buy enough baking soda for blasting without spending too much??

                 _-_-bear

[W2XR]

Bruce,
         One of the BIG advantages of sodablasting is that it DOESNT cause the base metal to start oxidizing immediately. (Something in the baking soda blast media actually retards the oxidation of the base metal.) You have plenty of time to prep, prime, and paint it more at your leisure. This is a big advantage when doing large jobs. It might be well worth considering for anyone getting ready to do a large broadcast transmitter cabinet restoration, or something of equal size and difficulty.

Hi Frank,

I did not know that. Thanks for sharing this information about sodablasting. I'll have to do some looking into this process, and maybe visit the guy here on Long Island that uses this media.

It can be a real PITA to schedule everything so that the glassbeaded (ferrous) work gets painted immediately, especially if the weather is not cooperative, such as during rainy or very humid condx. The sodablasting would solve this problem.

73,

Bruce

[KM1H]

Fish oil based is ancient history.

For working with rusty metal as well as protecting freshly blasted or stripped ferrous items Ive found the Zero Rust products to be far superior to box store stuff. Their Red Oxide or Black coatings are the best performers for long term measured in 5+ years outdoors and other colors are available.

I buy rattle cans as well as quarts and gallons and mix my own for grays and browns which I use as a top coat even over wrinkle paint to renew or recolor.

The Prep Step solution will retard flash rust of cleaned metal for up to 6 months and is also a mild etchant to enhance paint adhesion.

Do a Google to read the info and locate a distributor.

Carl
KM1H