Replenishing Bentonite in Green Sand? When? How much?

Discussion in 'Sand Casting' started by Melterskelter, May 14, 2018.

  1. Melterskelter

    Melterskelter Gold Banner Member

    What method or guidelines do casters use to determine when to replenish bentonite in green sand? I am casting iron and iron is reputedly wearing on green sand due to relatively high casting temperatures. How to know when and how much bentonite to add back?
     
  2. dennis

    dennis Silver

    Green strength starts to go?
     
  3. Melterskelter

    Melterskelter Gold Banner Member

    Yah, I posted that when I was really green at green sand. Now I am just sort of green. But, that seems to be the answer. I have campaigned my green sand pretty hard with iron and it has actually held up remarkably well. A few months ago I added some western bentonite to my original mix which had only southern bentonite. The western seemed to significantly improve green strength better than it ever was new with only southern. In the future I will only be using equal parts southern and western bentonite as I believe is commonly recommended. But, I've been using the same sand 500 to 600 pounds for 3 years and probably a ton of cast iron or so in it. It still works fine.

    Denis
     
  4. HT1

    HT1 Gold Banner Member


    I remember using a 60 / 40 ratio western on the High side


    V/r Ht1
     
  5. Billy Elmore

    Billy Elmore Silver

    The mystery mix...gives you perfect green strength and superior hot strength. Everyone in the industry is still seeking it.
    Adding to above comments on when sand should be replaced. We never actually do a dump here. We dont reuse sand that has been in contact with the floor so it gets dumped or if we get any kind of contaminant in it we dump it. We lose a lot in shakeout processes and cleaning machines. Our fines get sucked out by the dust collectors over various parts of shakeout and the mulling system. We only have to add new sand and clay and that is based upon our lab results. We are using a fine synthetic sand for better surface finish within our process. It creates a lot of fines and we can start seeing some signs of gas build up if they get too high. We simply cut back on the bond and add more new sand to get the fines back down. When you consider how often our sand gets turned around and how many molds we produce each day it is hard for me to imagine sand ever becoming unusable. I would think it can just be reconditioned by adding new sand and mulling to help distribute the fines to get the perm to where it needs to be. I only have experience with yellow velvet sand and synthetic sand so some of you guys may feel differently about it but I have never seen the need to just dump sand because it was burnt out. As I stated though... we do remove a lot of our fines with our process.
     
  6. HT1

    HT1 Gold Banner Member

    I dont think there is a way for the hobbiest to remove fines,
    that is the biggest contamination I have seen, that would require a dump
    in the Navy we added sand to dilute fines out also, but eventually you get more sand then you can store, so we would shovel it all out riddle it , put as much back in storage as the bin would hold, then shovel the rest over the side

    QED

    V/r HT1

    P.S. I would think hobbiest would never get to the point of building up fines, but alot of guys are only working with a few hundred pounds of sand, cast Bronze of Cast Fe regularly, you will get fines building up
     
  7. Billy Elmore

    Billy Elmore Silver

    Due to regulations on silica dust we probably suck more than fines out of our sand. Some of the sand in our landfill still looks like good sand but if it gets sucked into a baghouse it is dumped. I will be taking some of our landfill sand home to make some molds...got the good stuff stashed in the back.LOL
     

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