Gas bubble problems

Discussion in 'Castings, finishing/ repair/ and patina's' started by master53yoda, Sep 15, 2017.

  1. HT1

    HT1 Gold Banner Member

    SS needs to be heated, not specifically baked, hitting it with a torch to drive the moisture away from the casting surface will work in most cases... in a core it will only work if the core is very well vented

    V/r Ht1
     
  2. PatJ

    PatJ Silver

    I have used SS cores of 1.25" diameter, both vented and non-vented, and they both worked well, and neither were torched.
    For the vented cores, I used a 1/4" dowel rod in the center to make a hole before setting it with CO2, and then vented each end of the core up and out the mold.

    I really have not been flaming my molds, and have had pretty good luck with surface finish and lack of porosity.
    Mixing in too much SS restricts the CO2 flow through the sand, and it is pretty critical to hold the level around 3% and don't overgas.
    I use a PVC fitting about 2" in diameter for gassing, and press it to the mold in several places, 5 seconds at a time.

    I keep my molds relatively thin; actually as thin as possible, often not more than 1" thick, and sometimes 1/2" thick, and that helps with getting full gas penetration.
    I make a custom wood flask for each part, and sort of form-fit the flask around the pattern.
    Saves on sand and CO2.
    Example below.

    I really think part of the secret is to bring the AL up to temperature relatively fast, but don't superheat the melt.
    I pull the crucible as soon as it hits 1350 F, and it generally overshoots that slightly, but then cools back down to that by the time I get the pouring shank on it and pour.

    The best surface finish and least amount of porosity I have had on melts were using this method, and they did not use a degassing agent or a flux.
    I have had some gas issues with later pours, and am considering an inert gas system.
    I am hoping to use all cast iron at some point, and perhaps sidestep the issue.

    Edit:
    Several people have mentioned that the tall sprues are not necessary, and I have to agree, I could have omitted most or all of the sprue I used.
    I generally don't use much of a sprue at all these days.

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  3. master53yoda

    master53yoda Silver

    I am using a a 60 minute catalyst with my SS so I'm not gassing the mix, I also had to go to about 8% using the SS that I use as the sand is a very fine.

    I am going to try the calcium hypoclorite that HT1 mentioned I'm also going to use ingots melted in my small furnace instead of aluminum direct from the tilting furnace, it may be that remelting the ingot will remove some gas and it won't be in direct contact with the flame, the small furnace is run in a reducing atmosphere and is much easier to control temps.

    The tilting furnace does run in an oxidizing atmosphere to prevent smoke when melting oily automotive parts and the metal pool temp can be anywhere from 1100 to 1400 depending on how much un-melted scrap is in the furnace
     
  4. master53yoda

    master53yoda Silver

    I'll get some pictures Tuesday, tomorrow i have a 300 lb ingot order to get out so I won't be getting to work on it tomorrow, I really appreciate all the feedback and help as i was kind of at witts end, When it comes to combustion and making ingots etc i have that part down pat,but The scrap processing has not allowed me to spend the time on casting that I need to even git a little bit proficient.

    Art B
     
  5. PatJ

    PatJ Silver

    I use a very fine sand (OK85).
    I don't know the exact specifics of it, but I know that if I have it in a container that has a pinhole in it, the entire container will empty itself on the floor through the pinhole.
    Edit:
    Here is a cut sheet on the sand:
    http://www.ussilica.com/sites/ussil...product-data-sheets/industry/foundry/OK85.pdf

    OK85 is a manufactured round grain sand, and I assume that it is a baked product, since the moisture level is extremely low.
    If you have any moisture at all in your sand, it may cause the binder to not work correctly.

    The example above is actually uses a resin binder, but I have been converting to 3% SS and it basically works and looks about the same, such as the molds for the flywheel I cast:
    http://forums.thehomefoundry.org/index.php?threads/cretors-jumbo-flywheel.48/


    Are you not getting the strength out of the sand at lower ratios?
    What does it do at 3-5% that causes you problems?
    Broken molds I assume when you are pulling the pattern.
     
    Last edited: Sep 17, 2017
  6. master53yoda

    master53yoda Silver

    at the lower rates of SS the fine face sand remains loose also the overall mold is somewhat crumbly.
     
  7. What is pool shock?
    Thanks, Matthew
     
  8. Jason

    Jason Gold

  9. Tobho Mott

    Tobho Mott Gold Banner Member

    I don't think that's the right type of pool shock...

    Calcium hypochlorite is the chemical name for the pool shock granules that some have used for degassing aluminum. Look for that on the label. I've bought it from Walmart before here in Canada, but rarely use it.

    Careful not to boil over your crucible, and don't breathe the fumes!

    Jeff
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Build yourself a degassing lance and use Argon or Nitrogen.

    Best,
    Kelly
     
  11. nel2lar

    nel2lar Lead

    I agree with the Washing Soda but I follow it up with Lite Salt.
    Here is the directions how I do it.

    Degassing and More Fluidity
    FIRST USE:
    Sodium Carbonate better known as Washing Soda (Arm and Hammer Washing Soda)
    This removes the nitrogen bubbles.

    Then The Salt:
    (Morton Lite Salt)
    This makes the metal flow better.

    I am glad that someone mention the fine sand. I bought several hundred pounds of the finest Silicate Sand I could buy to try it on my next pour. It has been on the back burner for a while and maybe time to pull it out and see how it does.

    Be back soon.
    Nelson
     
  12. myfordboy

    myfordboy Silver

    I used salt and losalt for flux in my earlier casting days when I had no access to the proper materials and had good results with these household materials.
    I now use a drossing flux but still use the washing soda. I don't know why others have issues with it. You can see in this video for example how it bubbles. I have to pause and not push the foil wrap with the washing soda all the way down at the beginning or it will bubble out over the crucible.
     

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