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  • scraping masters

    Ductile iron can be bought in bar stock, has any one out there used the stuff for scraping masters or parallels. When I looked it up in the machinist handbook, it fell somewhere between grey iron and low carbon steel. Does the grain structure lend itself to scraping? Is it stable enough like properly treated grey iron?
    Thanks for now

    Tim

  • #2
    Sure. Sawn ductile works good for scraped reference tooling but the solid stock will be heavy. If you feel ambitious, mill out some tasteful cavities in places that reduces weight without sacrificing stiffness.

    I suggest you place your roughed out work in a cheap foam picnic carrier and haul it to the local welding supply house and have the man dump in a little liquid argon. Close the lid and leave it sit for a few days until the argon is all gone. Caution!!! haul the carrier in an open pick-up bed. Liquid argon in a closed vehicle poses a suffocation hazard.

    This ensures all the unconverted metallurgical mysteries get converted enhancing the stability of your finished scraped reference.

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    • #3
      Forrest,

      Liquid Argon is going to be more expensve than illegal drugs. Liquid Nitrogen is pretty cheap and less of a waste of material and the energy to liquify it.

      Both present suffocation dangers.

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      • #4
        Interesting regarding liquid argon and or nitrogen, is this a concern with all cast products, ie certain scraping masters available as rough cast from Morgan, or is the process limited to ductile iron? Is there any literature out there regarding the process of stabilizing of these metals, other than throwing them in a steel pile out back for a few years?

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        • #5
          Yeah argon is expensive but only a few pints are required. You don't have to fill the picnic cooler, only chill the work and add an inch or so to keep it at temp for a while. I threw in an old wool blanket to soak up the liquid gas so it didn't slosh in transit.

          My nearest air reduction plant is many miles away making lN2 'spensive, besides they'd bill me minimum charge.

          The local welding supply outfit doesn't carry lN2 so the few times I've needed cro gas I got lAr for freebies by tipping a few exhausted cryo flasks around until I could draw the dregs from the liquid tap.

          Guess I shoulda said, huh.

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          • #6
            I would like to echo T wise's second post,
            in reference to stabilizing these metals.
            Morgan's basic casting is $ 150 unmachined but heat stress relieved once.
            His second level of "Value added" is the same casting rough machined and stress relieved again or maybee stress relieved two more times. For this he requests $495 . . . DUH am I missing somthing ? In any case seems to me like he is making a large selling point of seemingly stabilizing the casting. . . .
            \
            heck rough machining a raw 26" X 3" or 4" casting wouldn't warrent that kind of price increase . . . To anyone with access to a mill or planer.
            Is that heat stabilization somthing like 260 degrees F for 12 hours or somthing ?

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            • #7
              I have a dumb question I've been pondering.

              Old time method for aging cast iron to make it stable was to throw it outside for a season or so. I've known of cast iron for straight edges to be also subjected to a heat soak in the shop stove, then left out in the winter.

              What I've read about cold treating is that the process of leaving cast iron outside worked because of the drop in temperature in severe climate did the actually stabilization. Today they are using gas and really getting things really cold, and they also do it at a controlled rate of cooling and reheating back up to normal temperature. They are even treating plastics.

              So what I am pondering is. Soaking at elevated temperature as in the barrel stove in shop in a bed of hedge coals. Then later after a time putting in deep freeze for a while. Should be as good or better as letting sit outside for a winter. Gets cold around here but not as cold as a deep freezer. Doubt that it will ever get any colder.

              I do recall CI as being stable till it gets as cold as it has been, if its been down to -20f it will be stable at -10f, but if temp drops to -40 it might warp. I try to keep shop above freezing since I added some insulation.

              Just dumping in liquid nitrogen seems like it would cool metal too fast, maybe slower would be better, blanket idea would help. Wrap part in blanket in cooler, slash a bit of liquid gas on it, close lid, wait a while and wet it down good.

              Poor mans sub zero treatment?

              [This message has been edited by halfnut (edited 12-03-2002).]

              [This message has been edited by halfnut (edited 12-03-2002).]

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              • #8
                You can use any cold producing method. I've used dry ice, liquid propane (non smoking operation), any handy cryogenic gas, and freezers.

                Cooling rate is always a consideration. You don't want to thermal shock the piece but on the other hand most liquid gases have about 10% the latent heat of evaporation. For all the seeming violence of the reaction a dunk in liquid gas is about as drastic as a dunk of cold work in hot water.

                I don't just dump liquid gas in into the foam picnic cooler on a warm part. For one there might be a small explosion that spattered liquid gas on me. My method for using liquified gas is to trickle it in here and there over the part and let it sizzle in rising puddles until it gets to equalibrium temp. It takes a few minutes.

                If you really want a slow ramp to temp. Place a coffee can containing a pint or two of liquified gas in the cooler with the work, cover the cooler, and let equalibrium make its slow magic over a few days. You may have to top up the gas at first.

                Dry ice is probably the easiest to handle and it gets you to 70 below.

                One last thing, don't pull the work out when its cold, condensation will cause it to rust.

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                • #9
                  Wow ! Thats a wealth of Practical information ! THANKS !
                  Just today got a Book via ebay Doall' "Quality Control" Here's a quote from chapter 5

                  Chapter 5 Stability
                  -Metallurgical changes
                  While seasoning over a period of years is possible by exposing the work to seasonal changes, this is prohibitive in cost and time. Therefore it became necessary to develop a more rapid method of accomplishing complete dimensional stability. There appear to be three main factors involved in stabilizing gage blocks and other precision devices. First , the block must be uniformly hardened by proper heating and quenching; second complete transformation of the austenite in steel is necessary; and third, the martensite must be throughly tempered. Deep freezing plays an important part in the complete transformation of austenite, for as it is well known all of the A is not transformed into M after heating and quenching. It is this untransformed portion which causes the change in demension over a perod of time. It has been found that by subjecting gage blocks to temperaturee of 120 degrees F. below zero and then allowing the blocks to reach room temperature that a large part of the remaining A is transformed to M. Repeated cycles of freezing and drawing will eventually give 100 percent transformation to M and , therfore complete stabilization.
                  As the temperature of the piece is reduced to 120 deg F below zero only about 3 percent A remains By repeatedly tempering the piece and cooling to minus 120 degree F 100 percent transformation can be attained.

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