How do geet rid of corrosion on my 3rd Eico 720?

[kg8lb]

 I repeat , just in case it was unclear:

" You may "lead" in the deeper pits with solder then sand to finish for a painted surface but not so with commercial copper electroplating ."

  The "lead"  comment was meant as a suggestion for painted finishes only. I had hoped that part was clear . Brazing , or copper buffing are the preferred fillers for plating. As a filler, Copper buffing is usually preferred over brazing. Brazing is usually saved for major flaws.  

  Zinc castings , often called "potmetal" are a different animal . The filler is zinc welding rod for major fixes followed by good old copper plating, finishing and buffing, repeatedly until the desired surfaces are generated.

  "Potmetal" however has varying results since there is quite a variety of alloys . Decades of Concept car building and high value restorations have seen literally tons of plated parts both old and new.

[W2WDX]

Hi,

My 2c

I don't like the paint method for several reasons. I have used that Krylon stuff in experiments and it does not last. Most of those chassis are either zinc plated steel copper plated. The problem with the rust is it occurs underneath the copper and the copper flakes away as the oxides "grow". Now if you paint you should strip away all the copper and zinc (preferably chemically) and get down to pure steel and chemically treat it before painting. That is alot of work. Also the paint overtime will peel and crack due to heating and cooling from the tubes. Plus it can stink in the process.

Bear has it right. The best solution, if you really want the copper, is stripping the entire chassis of components and pay to have it re-plated professionally. If the copper look is not important to you, just go with the bare steel.

What I have found for switches is to use the 100% formulation of DeOxit liquid. Not the diluted spray type, but the thick liquid type that comes in a squeeze bottle. Apply it to the contacts and let it sit awhile. Then use a very soft small plastic brush and carefully rub the contacts. Rinse with a high purity alcohol (92% pure minimum), let dry & repeat several times. After you have finished cleaning, dry thoroughly (use a hair dryer on low if your impatient) and then apply tiny amounts of DeOxit to the contacts and dab any excess up with a clean dust free cloth (I use an eyeglass cloth.) I do not recommend a Q-tip for this, otherwise you will be sitting there with a magnifying glass pulling little pieces of cotton fibers out of the switch, which is just as bad as dust for intermittent switch problems. Use a small chemically inert very fine and very soft plastic brush. The makers of DeOxit make a nice little brush, but they are not cheap. A baby's toothbrush is a good choice. The contacts come out like new with no loss of silver plating, except where there is mechanical wear. The black stuff is silver oxide, at first, which is as conductive as silver. But its course molecular surface tends to bind to particles particularly sulfur and it then converts into silver sulfide which is not conductive. Both compounds are black once "fixed" or oxidized, so its best to remove it. DeOxit slows this chemical process, acting as a "molecular buffer" in non-technical terms. Its not really a "buffer" so-to-speak, but that gives you idea what is going on at the molecular level. I suspect it works at not allowing oxygen from bonding to metals, much like why pure sodium is stored in oil. Its the fact that it functions at the molecular level is why it can & should be used sparingly, its expensive and you do not need much for it to do its job. (Side note: After rinsing with alcohol don't forget to re-lubricate the switch detents and shafts with synthetic lubricants.)

Deoxit gets a bad rap because people use it in the diluted form, and use it indiscriminately. It is only meant for metal contacts and it should be applied very very sparingly. Its bad reputation comes from when it is used, incorrectly, in carbon pots. It is not designed for this use. It will loosen the carbon substrate as if it is oxidation and the pot WILL fail very soon afterward. Caig makes an entirely different formula for carbon and plastic pots which was called MCL (I think they call it Fader Lube now.) But if you want to believe the "spray away on everything" guys, take it from whence it comes. Deoxit works on the molecular level, and massive bombardment like its a flux cleaner or tetrachloride is just a bonehead approach. I keep a 2.5oz. bottle of the 100% solution which I use daily at my shop, and it lasts about six months. That's how little you need.

John, W2WDX

[kg8lb]

The oxides growing under copper plating are the main reason for using zinc under the copper. Not often done that way on mass produced gear. The Krylon copper is quite different from other Krylon paints it has real copper in the pigment and holds up quite well as do good , polyurethane and epoxy finishes . Properly applied, paint can last very well . For the most part I resist using anything in a rattle can but the Krylon copper works well. Rust Oleum brand has copper in pint cans that can be applied with a brush or thinned and sprayed.I have quite a few pieces of gear that are over 40 years old and the painted chassis often look better than plated chassis of the same vintage. All finishes are dependent on the care taken in application.
  The paint is just one of many options but it can work surprisingly well.

 A prime cause of corrosion on any metal surface is simple dust. The dust catches and holds moisture . The moisture and dust decompose releasing corrosive acids that etch into the metal. Zinc provides a sacrificial layer that limits the corrosive effects. A periodic dusting , cleaning and waxing can go a long ways towards preserving plated parts. Parts painted with good paints are also quite durable.

  The Q Tip suggestion is well taken . Not only the stray fibres but the cotton swabs can easily snag and distort the contact fingers not a lot of fun to repair.

[KM1H]

A fairly easy way to harness rust is to first lightly sand the chassis to remove the loose rust. Then brush on a coat of Zero Rust Prep Step to provide a good adherance for a coat of Zero Rust Red Oxide. Then spray a finish coat of whatever you want. This is guaranteed to prevent rust blisters from reforming which will happen with other paints that do not chemically bond with the rust and seal it.

The nice thing for many that dont have a spray paint setup is that the paints come in rattle cans and a little goes a long way.

Around here Zero Rust is used on many snow plow trucks and bridges by local, county and state highway departments as well as individuals. Ive been using it for almost 20 years and used to be a distributor before selling my speciality hot rod, customs and antiques autobody and restoration shop. Ive tried all the others and all were left lacking.

Carl

[kg8lb]

 Zero Rust is one brand of many  coatings.A very good process at that ! Many rust tuff-conversion coatings  are Alkyd or Phenolic based . Some of the preps for these paints rely on phosphates and conversions. They are very effective at preventing rust and improving bond by etching.

Many of today's better paints protect from corrosion extremely well. Corrosion can start below the paint but usually initiated from poor preparation or from porosity in the paint or flaws in the paint surface allowing ingress of moisture and air. Generally,  clear coatings afford the best top surface protection . Plain old Rust-Oleum is a good , Alkyd based air dry enamel that can provide a real tough finish. It takes a LONG time to fully cure but works very well. Most paint shops can put up paints into rattle cans on a custom basis reasonably. No problem with that .
  Luckily most of our radios do not live in environments as severe as snow removal equipment . A good, painted finish can last for decades upon decades without lifting or peeling if done well.

 Hardened clear coatings can protect bare metals and bare plating very well, lasting for years on end. Copper plating, like chrome is very porous and provides for easy penetration of corrosive elements. That is why zinc below and/or clear on top can help protect the finish .

 This Retro 75 is brushed brass sheet with a hardened urethane coating. I have power supplies that were painted with hand rubbed , mirror finished black laquer over steel that still look great at 30 years old.:

[WBear2GCR]

What's the gold colored box?? Did you finish that? How, with what??

Btw, it doesn't open into a larger image - link seems bad.


Someone gave me credit where it was not due - I did not suggest a complete chassis strip, just the method used for old bumpers of heavy copper plate then taking it down to fill the pits... I suggested that it may be possible to do that trick with brush plating, although building a thick coat that way may be impossible.

                     _-_-bear

[kg8lb]

The gold colored brass box is my third Retro 75 transceiver. For some reason it seems the pic that I posted  in the Retro 75 threads will open much larger.

http://inlinethumb50.webshots.com/26033/2424665320032728487S600x600Q85.jpg


  The brass case was home - made from brass sheet stock and the knobs from brass bars. The case was hand sanded in a straight line after the brass was planished flat and filed to make a flat surface. The sanding was stopped at 400 grit , again all one direction sanding for a "brush" finish . It was then clear coated with a hardened urethane clear coat. The knobs were turned with carbide tools and clear coated with no further finishing aside from light de-burring.
  The case is not yet complete . I still need to disassemble the front and rear plates for final engraving. The rig works great.
Over Steel, Zinc etc:
http://www.caswellplating.com/kits/flashcopper.html

Other metals:
http://www.caswellplating.com/kits/copper.htm
  BTW: If you are doing copper plating at home, you can easily plate over solder. Use the right solder however.