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Heating cast iron to make it grow

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  • #31
    The results are in. The piston which was heated to bright orange and then allowed to air dry did not change in any way. The heating and air cooling had no effect whatsoever.---BUT---The piston that was heated to bright orange and then tipped into a can of oil has grown, and uniformly measures 0.876" , measured at multiple spots around the piston. So, yes, about 0.001" of growth on the 0.875" diameter. I will set the "grown' piston up in my lathe and turn some off the diameter to see if the machineability has been altered by this test.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #32
      The third test has just been completed. I burned up two drill bits trying to enlarge the center hole in that "grown" piston, to mount it on an arbor. So--not only does the heat and quench make the piston marginally larger, it makes it harder than the devil's horn. Test is over. I conclude that "growing" a cast iron piston is possible, but not advisable because the iron becomes super hard and can no longer be machined with conventional tooling.---Brian
      Brian Rupnow
      Design engineer
      Barrie, Ontario, Canada

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      • #33
        Originally posted by brian Rupnow View Post
        The third test has just been completed. I burned up two drill bits trying to enlarge the center hole in that "grown" piston, to mount it on an arbor. So--not only does the heat and quench make the piston marginally larger, it makes it harder than the devil's horn. Test is over. I conclude that "growing" a cast iron piston is possible, but not advisable because the iron becomes super hard and can no longer be machined with conventional tooling.---Brian
        The hardening result should have been expected...but the experiment could be prolonged by reheating and cooling slowly to see if the part maintains its larger size, or reverts to its original dimensions. I would probably do the heating with it surrounded by powdered charcoal inside an aluminum foil wrapper, and in-turn inside a charcoal packed container, both to provide a reducing atmosphere and to greatly slow the heating/cooling cycle.
        That is, I would if I could get to my Lindberg 1200*C heat treating furnace.

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        • #34
          Originally posted by brian Rupnow View Post
          The third test has just been completed. I burned up two drill bits trying to enlarge the center hole in that "grown" piston, to mount it on an arbor. So--not only does the heat and quench make the piston marginally larger, it makes it harder than the devil's horn. Test is over. I conclude that "growing" a cast iron piston is possible, but not advisable because the iron becomes super hard and can no longer be machined with conventional tooling.---Brian
          Looks like you got the martensitic transformation. Now heat it to about 800-900 F to get to a hardness you can machine. You know the term quench and temper. You quenched, now do the temper. You won't lose the size in the temper.

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          • #35
            Interesting, because the usual instructions specify a slow cooling. The mechanism is supposedly carbon agglomerating, which is supposed to happen with slow cooling and not with fast. But hardening is known to cause a size change in steels.

            How sure are you of the cast iron grade and carbon percentage?
            CNC machines only go through the motions

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            • #36
              I think you ended up with chilled cast iron. This is some times done to get a hard surface. A piece of metal is inbeded in the sand mold to remove the heat quicker making it harder. For more than you want to know about it try here.

              http://yvasanwala.tripod.com/Materials/ (may have to copy & past not sure the link will work)

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              • #37
                When we were casting steels with a higher carbon you had to be careful due to a peritectic transformation as the steel cooled in the mound of the caster, it would suddenly shrink away from the mound leaving a gap, often causing a bleed of the cast slab, sometimes a breakout, then the entire contents of the mound just disappeared into the spray chamber below, usually with a hell of a bang.
                The reason for the shrinkage was a change of phase as the metal cooled from a fcc structure to a bcc structure, when the carbon moves to the centre of the Crystal there is a shrinkage of the Crystal.
                It would seem that the same applies to the iron in the pistons, it’s going from bcc to fcc, the opposite, sudden cooling is locking the structure resulting in larger crystals.
                Just a thought
                Mark

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