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  1. #1
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    Default Molasses and antique cast iron parts

    I noticed that there have been a few posts on the various homemade brews to clean rusty steel and cast iron.

    I think it prudent to give folk particularly those cleaning antique: ie irreplaceable, parts to provide a heads up on what happened to me some years back.

    I was asked to cast iron weld repair an exhaust manifold for a big old Dodge fire engine that the rural fire brigade had acquired.

    The manifold passages were chockers with black carbon soot and would be almost unweldable at all, with all the excess carbon.

    The manifold was duly inserted into a bath 9:1 water to molasses mixture.

    As happens sometimes due to work pressures I did not get back to it for 3 weeks or so. Upon retrieval from the foul mix, the manifold had been chewed out and looked like a sponge.

    I am surmising that the immersion time was too long and the mix after consuming the carbon coated inside the exhaust passages kept on motoring and ate its way through the interstitial carbon of the cast iron metal.

    Guys image a sponge structure in cast iron. This manifold was far beyond welding.

    Fortunately, the RFB boys were able to source another manifold for the Dodge.

    Grahame

  2. #2
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    Default

    Grahame,
    So what you are saying is, you made a special low back pressure manifold.


    Peter

  3. #3
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    Default

    Hi Bollie
    What I made is not repeatable in these Forums. We had success previously with steel items but had not seen the effect on Cast Iron.
    It was so porous it would have been a fire hazard. A fire in the fire engine is not a good look.

    I can't say what really did it, the extra carbon or the length of time of immersion. The Old Dodge was hardly vintage and replacement parts were available so no real harm done. File it under lessons learn't the hard way.

    Maybe not so for any restoration blokes with some rare Cast Iron component. If using the molasses with Cast Iron my caution would be check and check often.

    Hate to see it happen to someone else.

    Grahame

  4. #4
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    Got any scrap cast iron and molasses Grahame? I'd like to see what this cast iron sponge looks like

  5. #5
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    Default

    No plans in the near future to do so. I have a few issues to overcome after my prostate operation.

    Perhaps you can try yourself?

    If it makes a difference we got the molasses from the Sugar School which was attached to Mackay Tafe in those days. I have no idea if the raw molasses is different from the stuff out of the supermarket

    Grahame

  6. #6
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    I do enjoy a good scientific experiment, I'll grab some molasses out of the drum at my parents stables and do some "Scientific testing"

  7. #7
    BobL is offline Member: Blue and white apron brigade
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    If you want to do the experiment properly you will need a good balance.

    Weigh the part before you start and then every time you pull the part out to check on progress wash off all the molasses and blow it dry with compressed air and weigh it again.
    The amount of weight that is lost over time will will allow you to plot a graph and then give you a quantitative measure of the dissolution rate - I am in the middle of the same experiment for steel in acetic, oxalic and citric acids.

  8. #8
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    It just so happens that I am about to use this method to clean some CI parts. I have been gifted a Gilbro table saw/planer combination which is in very good condition other than surface rust. I have used molasses/water before to clean milling machine parts with excellent results. I used a roughly 10:1 ratio and I too let work/life get in the way and did not remove the parts for about 3 weeks. Seemingly no ill effects, the parts came out immaculate. I wonder if the type of CI determines what effect the mollases has on the metal or perhaps the exhaust manifold was full of porosity and the mollases just made it worse?

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  9. #9
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by simonl View Post
    I wonder if the type of CI determines what effect the mollases has on the metal or perhaps the exhaust manifold was full of porosity and the mollases just made it worse?
    The purity of the metal itself is important. I spent many years dissolving up small amounts of ultra pure (99.995+% purity) metals in various acids. Some metals when highly purified are very difficult to dissolve even in very strong acids while others that at lower purity don't normally dissolve easily will.

    However I suspect the molasses is more likely to blame. Molasses is not just sugar but a wide range of sugars and other chemicals including about a dozen different weak organic acids including formic acid (same as what is found in ants and red wine) aconitic acid, lactic acid (a waste product generated by muscles that causes cramps) malic acid (made by all living things and the sour bit in "salt n' vinegar" chips), tartaric, succinic (an important acid in all living things and part of the energy production cycle in all cells) and citric acids.
    Aconitc and malic are closely related to citric acid.

    The concentrations of the acids depends on many things like the starting stock, natural bacterial content, temperature, and degree of fermentation and exposure to air. These will convert more or less sugar to these weak acids. The amounts vary from none to small or more. Seeding molasses with certain bacteria is a known way to generate industrial amounts of lactic acid.

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