From: none@none.com99   
      
   On 12/2/2025 4:02 PM, Jim Wilkins wrote:   
   > The sand has at minimum a little clay in it and when dampened can be   
   > formed like a snowball.   
      
   Preferably bentonite clay, and what you describe is called green sand.   
   In the hobby realm atleast, it seems many small foundries are   
   transitioning to petrobond where managing moisture content when not   
   engaged in the hobby for some time is not an issue.  Petrobond uses oil   
   instead of water for the same/similar affect.  To make it clump when   
   rammed.  I think Windy Hill Foundry (cast iron foundry business) also   
   uses petropond as their default casting sand.   
      
   Sodium silicate.  Its used in solution in place of just plain water.   
   CO2 causes it to harden allowing for few or no inclusions, and more   
   detailed molds made from more complex patterns.  The CO2 in air is   
   enough, but venting can help for faster mold prep, and for even faster   
   casting C02 is sometimes flushed through the mold from a gas bottle.  I   
   first ran across it when I was researching how to recycle 6061 which is   
   not a good casting alloy unmodified.  That was when I first discovered   
   the guys building the SV Seeker marine research vessel.  They were   
   casting custom porthole covers in sand molds using sodium silicate to   
   make more rigid sand molds.   
      
   FYI:  The addition of more silicon metal can improve the cast-ability of   
   6061.  I think I read 6-7% additional silicon, but one fellow I chatted   
   with claimed he got usable results with as little as 4% more silicon.  I   
   have a small gas foundry furnace on the shelf along side a couple bags   
   of silicon metal, but I have not had the time to play with it.  I also   
   have a LOT of 6061 scrap.  I've thrown away barrels of the stuff, but   
   lately I've been cutting the tops out of old Roundup(tm) barrels   
   purchased cheap and using them to store scrap.  Its why I asked a while   
   back about aftermarket barrel covers.   
      
   --   
   Bob La Londe   
   CNC Molds N Stuff   
      
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