transformer bell in dishwasher - weird results

[Jeb Jeb]

Hi bottleheaders,

I just started to think about putting my kit together so thought I would start by finishing the transformer cover, which I'd like to keep natural looking with a couple of clear coats.

I started to clean it by taking a rag with a little paint-thinner and rubbed off all the grease that I could.  I was just about to run the dishwasher so thought I would pop it in with the dishes as I thought I had seen that mentioned here or on head-fi.

When it finished, I opened the dishwasher expecting to be dazzled by the gleaming metal and was quite shocked - the transformer cover was totally weird - dull, very streaky and corroded/rusted looking with lots of dirty dark grey and brownish lines and dots all over it, that no amount of cleaning would remove. (pic attached of underside) 

The only way I've been able to remove the marks is with some pretty serious sanding and it's coming up to nice finish again - so not a problem... but I'm just curious why this happened or if I did something stupid! some sort of oxidisation and accelerated corrosion?

Also, do I need to protect the underside of the cover in any way? especially now I have sanded the hell out of it.

Jeb

[smitty1110]

Soaps of all kinds are chemical bases, which can be just as corrosive as acids. The bell is probably some cheap-ish normal steel, and when the paint was removed the steel was defenseless against the corrosive effects. You should probably protect the underside, since if it's not stainless steel it might corrode over time from the moisture in the air. And yes, sanding it off is the only practical way to make it shiny again.

[Grainger49]

The corners of the underside of the end bell must be naked metal.  Grounding of the transformer goes through there.

[Jeb Jeb]

Thanks guys! - I wondered if it was the dishwasher tablet I used!  I have sanded it back to a shiny finish and given it 3 coats of rustoleum clear coat for metal - and it's come up pretty good -  you wouldn't know there was anything on there, which is what I wanted.

Grainger - thanks for the tip on that - that seems very important!  Maybe I'll just hold off on doing the underside then - I can't think it would rust like the exposed top-side would, right?  or perhaps i'll just mask off the corners with a bit of tape and spray the rest. 

Cheers,

Jeb

[Grainger49]

As long as you have good contact at the four corners for the star washers you are fine.  Nobody will see the underside of the end bell but you DO want to be safely grounded.

[mcandmar]

Mild steel like that will lightly oxidize with moisture in the air, hence they come with some form of coating on them.  Not sure what it is exactly, but its easily washed off.  The staining you seen can be nothing more than clean water, if you want the finish to stay shiny you need to seal it with something.

I would worry about the underside, if you cant see it, it dont matter.  The underside of the bell is insulated from the core so you can paint it without issue, the grounding is done via a small crush washer under one of the bolts on the top side of the bell.  Again BH did this to ensure a good earth through painted finishes.

[Jeb Jeb]

Thanks guys, much obliged to Y'all.