Question on Casting Iron

Discussion in 'Sand Casting' started by _Jason, Dec 18, 2017.

  1. _Jason

    _Jason Silver

    If this is one of you guys, I apologize. I'm not trying to call anyone out; I'm just curious about something:






    Fair Weather Foundry is one of the YouTube channels I follow because I'm curious about casting iron. In his valve body casting and machining videos, the gentleman that made the videos seems to be having hell with casting machinable cast iron and it wasn't until his friend in Mississippi cast a valve body and sent it to him that he was able to finish the task. I've been kind of mulling these over since I watched them Saturday and I'm curious what his friend might've done differently that yielded a better casting? FWF's green sand looks sort of like potting soil and I don't think he was adding ferro silicon to his iron. Could poor sand quality and low silicon levels in his cast iron be causing the issues he's having?
     
  2. ESC

    ESC Silver Banner Member

    Jason, the quick answer is carbon. It is the weakening agent in cast iron, and if enough of it is not thrown out of solution as graphite as the casting solidifies the casting will be hard. This is also a function of the cooling rate, the pouring temperature and the section thickness. Thin sections cool faster and the carbon has less time to form free graphite. The Silicon innoculants displace the carbon and so serve to improve the machineability of the casting.
    Controlling this is done with test pours into small chill wedge molds. I use them whenever I switch feedstock for my cast iron melts. I also add carbon to a melt in the form of petroleum coke granules to insure there is enough Total Carbon so the Ferro Silicon has something to displace.
    The crankshaft is an example of the soft iron. They really don't have any thin sections, but I was able to turn the ends on the lathe easily before I set it up in the grinder.
     
  3. PatJ

    PatJ Silver

    I think one of his biggest issues is not getting on a forum like this one or others where he can discuss issues with those who have the knowledge he needs to avoid the problems he is having.

    Melting and pouring aluminum is pretty easy, and almost anyone can make good parts if they pay a little attention to details.

    Melting and pouring iron is a different animal altogether, and you really must have all your ducks in a row in order to create usable machinable parts (if you are building engines).

    I asked a lot of questions online and at the local art foundry (which does a lot of iron work), and I avoided a lot (but not all) of the problems the guy in the above videos is having.

    Things that help a lot when trying to make cast iron parts is resin-bound sand (used for molds and cores), adding ferrosilicon at the right time (right before you pour), venting the mold at both the cores and at the high points in the mold, getting the iron hot enough to reach the fluidity required to fill the mold, getting a burner tuned correctly for maximum heat output, and using quality gray cast iron to begin with.

    Clarke (porosity master) has mastered all the above items, and he uses water based green sand.
    Some others here have also mastered iron (ironsides), ESC, scavenger, and a few others.

    I am on the road to getting consistent iron pours, but am not there yet.
    I have had several good iron pours, and had machinable iron with parts that were 3/4" thick and thicker (flywheels) without ferrosilicon.

    For thin parts, ferrosilicon is a must, otherwise you are basically making tool steel, and that material cannot be cut with carbide (it is not machinable using standard methods).

    I start with scrap gray cast iron, and have never added anything other than ferrosilicon, although I did buy some flux material (but have not used it yet); I think it is ground up seashells (I forget the official term).

    Making machinable parts from iron is not for the casual backyard caster; you have to pay close attention and have (or be able to achieve) a certain skill level.

    Some people make iron castings look laughably easy; don't be fooled; its not easy, it just looks easy when you finally figure out what to do (and more importantly what not to do).

    Melting iron basically pushes everything to the limits; the furnace refractory, the crucibles, the sand, cores, gloves, etc. and you need quality materials for all of it if you want things to last more than a few melts.
     
  4. Jason

    Jason Gold

    Holy cow! How did I miss his stellar fuel tank build? I can hold my own with the tig welder these days, but scratch building any pressurized vessel, you better have your act together. When that thing started popping gaskets and attachment lugs, I ducked. Not to worry, his harbor freight face shield will protect his face while his head rolls down the driveway. I don't thumbs down stuff, but I really considered it on this one! Can't blame a dude for trying, but a mig welder in the wrong hands leads to scary stuff. This is one of them. Someone tell him what a stand pipe is.:rolleyes:

     

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