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  • de-smuting zinc die-cast

    Spent more time then usual in the shop last weekend. That left me with more than a few questions.

    I have found the removing the rust from pot metal can be done very easily with electrolytic reduction, which is often referred to as 'electrocleaning' or 'electrolysis.' Goggling for either term will direct you to many informative articles. Electrolysis is the amateur term and the 'pros' talk about electrocleaning.

    After a few hours (or few days depend on the amount of rust to be removed) all of the rust is gone leaving a fine black/grey powder on the surface. The most amazing thing is how steel bolts that hold cast pieces to pot metal pieces are freed.

    I am finding that typical acid base desmutters attack the substrate too quickly to be useful. Anyone have any suggestion on how to get rid or the smut?

  • #2
    Re: de-smuting zinc die-cast

    Probly the easiest would be sand blast if you have that but I don't know of another way......but if you had the blaster then you wouldn't go through all that electrocleaning....so I really don't know..
    www.chrome-plater.blogspot.com

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    • #3
      Re: de-smuting zinc die-cast

      Actually, I have pretty much stopped bead blasting on zinc die-cast parts. It is much less time consuming to electroclean the parts

      It was taking me 45 min. to an hour to blast and disassemble an old carb. Then another 30 min to reblast after disassembly. Then they had to soak in boiling degreaser for another 30 minutes to get out the bead that became embedded in the castings.

      For electrocleaning, I have 3 X 20 gallon tanks set up. I just hang the carbs by 10 ga. copper hooks until they look pretty clean. Then they get disassembled and rehung. The bigger pieces each get their own hook and the little pieces all go in a mesh plastic basket with a piece of screen at the bottom of the basket. I run the current very low, about 1 to 1.5 amps per carb and let them soak as long as needed.

      Once I got the tanks set up, it works pretty slick. Labor time is down from 75 min to about 5 mins. Now, If I can just get that smut removed with a quick dip, rinse, rinse. I'll be in good shape.

      If anyone is interested I can write up a more complete description of my setup and processes.


      Dave

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      • #4
        Re: de-smuting zinc die-cast

        Hi Dave:

        I'd be interested in your electroclean process. What chemical(s) are you using in the bath?

        I tried my first carb body a couple of days ago. After degreasing, I soda blasted it, which worked well, but takes more time and media than bead blast. Nice part is the baking soda doesn't etch the surface or embed at all, and just dissolves in a water rinse.

        However, after blasting and acid activating, it would not chromate at all, so I'm working on the assumption that this particular carb body is not zinc die-cast at all, or contains too little zinc to be receptive to chromate.

        Sean
        Seans Zinc Plating page

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        • #5
          Re: de-smuting zinc die-cast

          Hey Sean,

          Right now I am using Washing Soda as a source of Sodium Carbonate 1/2 cups per 5 gallons water and Dawn detergent at 1/4 cups per 5 gallons.

          I have tried lye but it seems to etch the die-cast if you are not careful.

          I degrease in a hot tank before deoxing.

          I have a proprietary product on order that has some special inhibitors to prevent zinc die-cast etching. I'll let you know how it works.

          For electrodes I have tried sheet metal which wears out quickly and rebar which does not seem to have enough surface area. I have settled on stainless steel sheet which works really well. I lined 3 X 20 gallon tanks with one 4x6 ft sheet of 16 ga ss sheet. The sheet was a bit pricey at $120

          If you go with the stainless steel you will need to be careful with the bath solution. Wear gloves and take your sludge to the local transfer station.

          I have started using distilled water (via RO) to make up the bath, my local tap water has a lot of calcium the seems to coat the electrodes.

          Dave

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          • #6
            Re: de-smuting zinc die-cast

            Thanks Dave!

            That's essentially what I've been using for electro-rust removal, washing soda, w/rebar electrodes. Works great on ferrous rust, but I had never considered trying it on other metals. Will have to do so now.

            I've been using lye in a home-brew hot tank for super cleaning ferrous metals, but it's definitely a no-no for anything with aluminum. It will dissolve it rapidly! Been using carb-cleaner in-a-can from the auto parts store for non-ferrous stuff.

            Sean
            Seans Zinc Plating page

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            • #7
              Re: de-smuting zinc die-cast

              Sean,

              I have been derusting at room temp. The tempature of the bath seems to have no effect on the rate of derusting.

              There are two schools of thought on the current used to derust. The restorers like to use low current flows (1A per sq ft)for long periods of time. Some of the derusting shops recommend high current flow (50A to 70A per sq ft) for just a few minutes.

              Using high currents has the effect of rapidly forming hydrogen bubbles which can loosen and lift off big flakes of rust. On the other hand it doesn't seem to throw as well into the bowls and throats of carbs.

              I like the lower currents because it seems to clean out the insides of parts better.

              I've got several 2X1X1 ft tanks going. I line the tanks with stainless steel sheet and then run a 3/4 inch copper pipe lengthwise down the tanks to hang the parts from. I hang the parts from hooks made from 8 ga solid wire.

              About three times a day I check the carbs to see how they are doing. Rust chunks get a light scraping and then I rehang the part differently. There are many holes and protrusions to hangs carb in different ways.

              To keep track of how the parts are coming along I move the cleaner parts to the front and right most tanks. I add new carbs to the back left tank. They are pretty much arranged rusty to clean.

              Depending on the size of the carbs I fit about 4 per tank.

              If you try to derust electrically would you mind trying to soda bast the smut off? The price of ultrasonic tanks is making my toes curl. I have not looked into soda blasting very much. What does the price of a small unit cost?

              Thanks
              Dave

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              • #8
                Re: de-smuting zinc die-cast

                Hi Dave:
                I have been derusting at room temp. The tempature of the bath seems to have no effect on the rate of derusting.
                I've never considered temperature for the electro-derusting. Just whatever the ambient temp happens to be (as long as the bucket's not frozen).

                The lye based hot-tank, being purely chemical, is temp sensitive. Hot (140-160) cleans better & faster than cold, but I only use it for ferrous materials.

                Interesting observation on current density for cleaning. Will have to experiment with that on some smaller parts. Up to now, I've only been derusting large, heavily rusted steel parts, simply hooking them up to a battery charger and lettin 'er rip!

                If you try to derust electrically would you mind trying to soda bast the smut off?
                Will do, but I don't forsee trying it for a while.

                I have not looked into soda blasting very much. What does the price of a small unit cost?
                I haven't invested much of anything at this point, wanting to see how well it worked first.

                I got one of those cheap spot blasters w/about 14-oz hopper, and a 50lb bag of medium grit soda from an abrasives supplier. Fill up the hopper and blast outdoors. I don't have many parts to do this way, so the media is lost.

                It works well, but since it's not as aggressive as glass bead, it takes more time and media. On the positive side, it doesn't peen the surface or erase any detail, and washes away in water. No glass embedding problem.

                I pre-cleaned this 1946 carb body in Berrymans carb cleaner, then soda blasted it. Remnants of the original irridescent chromate are clearly evident in the before photo, and it's all gone in the after photo (photos link to larger images):

                __ ___

                Unfortunately, this particular carb body would appear to have little to none zinc content. I got NO reaction whatever out of it in the acid pickle, and it would not take any chromate. So I'll be plating it one day (hopefully thiss weekend).

                Sean
                Seans Zinc Plating page

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