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  1. #1
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    Default Paint prep question

    I have several ancient sets of cast change gears,all prickly rust. Top half of the stack the gears are dished,then the rest are spoked. The rust is very stable,so I feel that if I emery the worst off and the bright metal begins to show,that should be good enough and the paint will stay put. I use red oxide primer.

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    Run the gears through a bead blast cabinet and you'll be amazed at the bright finish left behind. The metal surface will also be in perfect condition to immediately paint. We use this process on all machinery handles, misc parts during our restoration projects

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    Bead blasting is tough to beat. Rust has to be gone.

    If you are really anal, following up with a phosphoric acid rinse or some etching primer is pretty good.

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    Pressure wash to blow the flake crap off.
    Soak in 5% Phosphoric in water for a few hours to convert rust to Iron Phosphate.
    Phosphoric acid treatment is worthless unless all rust is thoroughly wetted!
    Dry completely.
    Brush off any loose iron phosphate.
    Paint.
    There is NO NEED to prime. Iron phosphate provides the bonding layer between iron and enamel.

    Any form of hard media blasting only seals rust seeds into the micro pores of the iron. They will find water and come back to spall the paint.

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    Can't disagree with bead blasting surfaces you intend to paint. But I don't care for bead blasting surfaces that will remained exposed metal, I just don't like the white look it leaves. Not sure if you're painting gear teeth or not. I use emery and wd-40 or areas that would remain exposed metal.

    I generally wash, or wipe down with mineral spirits. Then wipe down again with paint thinner. Then prime and paint. Paint generally sticks very well for me this way.

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    Interesting,thanks for your replies. Have got them rubbed down smooth.

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    Personally I wouldn’t even paint them, I’d just clean them up, oil them and leave them bare, an oily wire wheel preferably at not too high a speed will work well for this. That’s just my opinion on it, if your dead set on painting them then the advice that others have given is good. Don’t go painting the teeth though!

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    Quote Originally Posted by Franz[emoji767
    ;3174610]Pressure wash to blow the flake crap off.
    Soak in 5% Phosphoric in water for a few hours to convert rust to Iron Phosphate.
    Phosphoric acid treatment is worthless unless all rust is thoroughly wetted!
    Dry completely.
    Brush off any loose iron phosphate.
    Paint.
    There is NO NEED to prime. Iron phosphate provides the bonding layer between iron and enamel.

    Any form of hard media blasting only seals rust seeds into the micro pores of the iron. They will find water and come back to spall the paint.
    Not try to start anything here but I have to say my personal experience tells me that blasting and painting seals the "rust seeds". I've never heard the term "rust seed" btw. Then again I'm always willing to learn.
    I agree completely about using phosphoric acid for rust. It works for sure. Personally I like a large spoon tank (electrolytic rust removal) or blasting and paint ting but phosphoric does work well also.

    Sent from my Pixel 2 using Tapatalk

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    Quote Originally Posted by challenger View Post
    Not try to start anything here but I have to say my personal experience tells me that blasting and painting seals the "rust seeds". I've never heard the term "rust seed" btw. Then again I'm always willing to learn.
    I agree completely about using phosphoric acid for rust. It works for sure. Personally I like a large spoon tank (electrolytic rust removal) or blasting and paint ting but phosphoric does work well also.

    Sent from my Pixel 2 using Tapatalk
    First, there is NO ELECTROLYTIC rust removal. It is a misnomer for the process of electroplating rust off one object and onto another, or attracting the rust to a carbon based electrode it will not stick to and filtering the rust out of the electrolyte once you figure the filtration out. Only been doing it for 30 years now and my tank runs 24/7 with clear electrolyte, no scum on top, and does the job. The electrolysis occurring in the solution is less than occurs charging a wet cell battery.

    Second, All metal is porous, more so with rusty metal, and no blast media gets all the rust out of the porosity. Metal is normally blasted to the gray iron standard, meaning the inspector can see no brown rust on visual inspection within 1 hour of blast.
    Solid media, of the sand nature, regardless of media, be it sand, aluminum oxide, black beauty, glass or any other hard media peens the micropores shut with rust still in them. 20-30kpsi water does a better removal leaving less rust behind and doing less peening. Believe me, water is very hard and hits dam hard at 20kpsi.

    Microscopic bits of rust peened into craters and pores sit there waiting for water and the game is back on. Old saying rust never stops is absolutely true. Once the rust seed finds water it will grow and exert force. That combination will spall any coating over the rust, and the blister will grow.

    The only way to prevent recurring rust is to soak the iron in Phosphoric acid solution to thorough wetting. That will convert the rust to Iron Phosphate.

    Phosphated iron offers two benefits, the first being rust killing. The second benefit is Iron Phosphate is a coating enamel will adhere to, so the primer layer and priming process can be eliminated from the job.

    Phosphating works so well I often let objects from my electroplating tank flash rust so I can then phosphate and coat. I have many objects that now have a 30 year life on the paint.

    I've also run molasses chelation on rusty objects when time was available to do it.

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    Like the electrolytic approach-it seems the old oil drum or whatever is sacrificial,whereas it would seem carbons go on and on...

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    Once the metal gets coated with layers of rust from the parts being spooged the process slows down. I can see the amp meter show fewer and fewer amps running through the circuit after several parts. I use a plastic 55 gallon drum with the upper 1/3 cut off and I line it with sheet steel. I remove this and wire brush it and reinstall. My parts hang from a large copper rod that goes across the top. I clip the negative to the end of the rod and off we go. Positive goes to the metal lining. This process is great for me. It's nearly free and works within hours for the average part.
    Fwiw I will be looking for a cheap source of phosphoric acid to add to the arsenal.

    Sent from my Pixel 2 using Tapatalk

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    Thanks to government do gooders 85% Phosphoric is hard to come by, unless you have friends at CocaCola or live near a farm supplier in lettuce country. You can find a good substitute in the paint department of Homer Desperate called concrete cleaner. The dilution ratio will need to be adjusted.

    Tanks are nice, once you compensate for mineral content in the water and accept that there is no point to running high amperage to accomplish nothing but heat generation in your electrolyte. Tanks are even nicer when you create a filtration system that pulls the dissolved iron from the solution and use carbon electrodes that do not require cleaning. The beauty of carbon is the rust you plated off just sinks to the bottom of the tank.

    This tank is running 10 amps @ 24 volts employing about 1 square foot of carbon electrode.
    Anything above 10 amps only generates heat. Heat accomplishes nothing.
    Attached Thumbnails Attached Thumbnails alm-ge-4.jpg   alm-ge-5.jpg  

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    I agree. Mine runs at about ten amps and the parts emit a nice array of bubbles when it is running well.
    Where are you getting the carbon rods. That is the deluxe version. Steel is OK but carbon is the cats ass for doing good sponge operation.

    Sent from my Pixel 2 using Tapatalk

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    Quote Originally Posted by challenger View Post
    I agree. Mine runs at about ten amps and the parts emit a nice array of bubbles when it is running well.
    Where are you getting the carbon rods. That is the deluxe version. Steel is OK but carbon is the cats ass for doing good sponge operation.

    Sent from my Pixel 2 using Tapatalk
    Not rods, carbon impregnated fiberglass sheets about 3/16 thick.

    Surface area is key to the process. Ideally match electrode to the object being derusted in surface area.

    The big tank is 250 gallons.
    Neighbor won't let me near his pool.


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