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I have an old contactor, which was humming. I ignored it until the coil burned out. When replacing the coil, I noticed the iron core was rusty, so I sanded it with 600grit to remove all rust in the core and contactor's core contact, and then covered it with a thin film of PB Blaster "MultiMax" since it said it handled high temperatures. This worked like a charm, and contactor ran completely silent (but more importantly, the current draw while closed was near the datasheet's specs). However, about two weeks have gone by and now I can hear the humming start again--so I can only assume some rust is building up again. Is there some rust protection specifically for these types of electromagnetic cores? Essentially, thin-film rust protection for use in continuous hot temperatures?

Esteban
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  • For long term, you probably need something that bonds to the surface instead of coating the surface. Imagine clearance values are quite tight. – crip659 Oct 22 '22 at 15:20
  • Rather than rust building up, it may just be the PB Blaster wearing away or evaporating. In any case, why not just replace the contactor? – Armand Oct 22 '22 at 20:24
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    @Armand, I suspect it's rust because this is actually the second time I clean the core surfaces. But first time I used transmission oil with rust protection. But yes, the PB Blaster is definitely just wearing away or becoming ineffective. A replacement runs about $550.. if I just leave it humming the coil lasted me about 2 years and a replacement runs for $70. So I don't mind a little elbow grease to avoid paying $550 out of pocket. – Esteban Oct 23 '22 at 17:29
  • @crip659, yep, the clearance are very tight, mirror finish when I finish polishing them. – Esteban Oct 23 '22 at 17:29

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Remove all traces of oil from the core that you wish to protect from rust. Apply a gun blue product to the clean, shiny metal according to the product directions. I recommend Birchwood Casey Perma Blue or Super Blue, available in sporting goods stores or the sporting section of department stores, and also online. The gun blue will lightly etch the metal and change the chemical composition of the surface. When the process is complete according to label directions, wipe the blackened surface with a full synthetic motor oil, then clean away any excess oil with a clean cloth.

The surface will now be highly resistant to rust due to the blackened surface retaining a permanent layer of heat resistant oil. This works well on steel gun barrels that get sizzling hot.

The initial cleaning before bluing is necessary because any oil on the metal surface will prevent the chemical from working.

MTA
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