Green Sand Molds

Discussion in 'Sand Casting' started by oldironfarmer, May 25, 2018.

  1. oldironfarmer

    oldironfarmer Silver Banner Member

    In the warm weather I'm trying to cast early in the day. Should I expect to be able to make a mold late in the day and then have it perform well the next morning? So far I've been making up molds just before I heat the metal, or while the furnace is running.

    Another question, while I think I'm getting acceptable results, I have no way of knowing whether I'm ramming the sand too hard. It is right that if you don't have gas pockets the sand has adequate porosity? I try to get it pretty firm against the pattern.
    Last edited: May 25, 2018
  2. Melterskelter

    Melterskelter Silver Banner Member

    One person's experience: I have waited 2 days to pour a green sand mold and it did fine. I have commonly rammed one up the evening before casting without problems. I do cover them with foil or plastic to prevent drying.

    And I put something over the sprue hole to prevent me and a curious mouse from having a bad day on the day I pour. I have heard stories of mice finding a cozy spot in a mold left over night.

    On the sand ramming question: be sure not to ram it too hard. Then again not too soft either.
  3. HT1

    HT1 Silver Banner Member

    alright.. umm it's a bad practice , but will in your case probably give acceptable results. there is the potential for the moisture from the sand to move into the mold cavity ... I believe this would happen if the mold warmed rather then cooled overnight ... one of the science experts here can probably help. but since best practice is to face warm a mold just before closing, which should be immediately before pouring... still bad practice, if moisture condenses in your mold, you will know, your sprue and risers will boil over like a volcano and shoot molten metal into the air... Seen it first hand, from the end of a pouring shank on bronze, very scary several burns on the pouring team, myself included... destroyed all the light fixtures in the shop... Plastic and molten metal you figure what won.

    V/r HT1
  4. Melterskelter

    Melterskelter Silver Banner Member

    How do you know condensation caused the blowout? Just trying to wrap my head around that condensation risk given that common binders are hygroscopic and bentonite clays are very strongly hygroscopic. Now a mouse is not hygroscopic ;-). When I have stored overnight molds covered with foil or plastic, I have noted some condensation on the cover material, but the sand was very dry, in fact I patted it in at the basin at the sprue opening as I was worried about washing sand into the mold.
    Last edited: May 26, 2018
  5. oldironfarmer

    oldironfarmer Silver Banner Member

    If you ram up cold sand on a cold day, warm humid air moving in could wet the mold. We've all seen the days when the concrete in the shop sweats because of warm air moving in. Doesn't seem like it would penetrate too far, but certainly in the openings if they weren't sealed. In my case I make the mold inside then carry it outside just before pouring so if i had to do it, the mold would be overnight in a steady atmosphere.

    Didn't know best practice was to warm the face before closing (of course there's so much I don't know). That tells me the dry green strength is heavily relied upon. Now i'm thinking I should be in no hurry to close flasks to retain moisture.
  6. HT1

    HT1 Silver Banner Member

    it was not a blowout . if the mold had not had 3 large 2.5 inch risers it probably would have exploded. metal boiled out of the mold continuously while we poured shooting all the way to the ceiling of the space. the sand had too much moisture, and we closed the mold without face heating the mold. because we treated the mold like it was petrobond rather then green sand.. because it was a bronze plaque... but it was about 2 ft X 4 Ft so it had to be greensand as Petrobond does not have enough green strength to make molds that big ... now how much moisture is too much, where we at 7% rather then 5%???

    look there are a thousand variables when you make a mold everything you do to control those variables helps you make consistent successful castings...

    I remember having a hell of a time in Japan and the Philippines because the humidity was so high sand would gain moisture setting rather then loose it, so we would over-mull sand, under a Supply vent to let friction and moving air move moisture out of the sand rather then adding it, we would face heat the folds just before closing and pouring with a HUGH rosebud we would double our degasser for each heat we went from 50 /50 to about 90% successful castings ... It required a really sharp team, litterally the first mold would be getting poured as the last mold was getting closed and clamped.. but that is what we had to do.

    Lastly trust me I feel your pain, I'm in Florida. I get up and ram molds from 5-8, light off and pour, take a break open molds and mull sand all before noon, then go inside and carve new patterns in the AC... I put molds down the night before once... and a stray dog seemed to think they where his personal stepping stoned, crushed 2 of 7 molds

    V/r HT1
  7. Melterskelter

    Melterskelter Silver Banner Member

    I have a pic here of what I found in the sand this morning as I was shaking out a CI casting—- couldn’t believe it and couldn’t stop laughing. 389C3817-95EB-49F8-A57A-279DE75A51A5.jpeg
    I guess that proves mice often sneak into molds overnight—- indeed, I had rammed this one up the day before casting. Otherwise the casting process was uneventful.
    Last edited: May 29, 2018
    Jason and oldironfarmer like this.
  8. Petee716

    Petee716 Silver Banner Member

    Lost mouse casting. Genius!
    Melterskelter likes this.
  9. Tobho Mott

    Tobho Mott Silver Banner Member

    Wow. I remember an old post (90% sure it was on AA) where someone using a cereal additive in their sand kept finding dead mice that had been snacking on his sand then dying when the bentonite swelled up to many times its original size.

    That pic right there is one really good reason to cover up your sprues and risers if you're gonna store your molds overnight! I cover mine even when I'm just going inside to grab a drink or something, but I've been doing so for fear of earwigs and spiders getting in there, not mammals! Of course, we have so many stray cats hanging around, I haven't seen a live mouse on my property in a couple years... Can you imagine the fountain of molten metal that would cause?!

  10. Melterskelter

    Melterskelter Silver Banner Member

    I could not dribble a "slop" of molten iron like that in another thousand pours even if I tried to replicate it every time. It was uncannily similar to its furry counterpart! Oh, well. Good for a laugh. But, yes, on advice of others, I have made it a practice to make sure sprues are plugged on any stored molds. There is a "pet" salamander that I have seen in the molding area on several occasions that I suspect would find an unattended sprue inviting. I suspect that such a critter would cause quite a (dangerous) burp of metal as he turned instantly to vapor.
    Last edited: May 31, 2018
  11. Tobho Mott

    Tobho Mott Silver Banner Member

    Wow, I just noticed that isn't an actual mouse, lol. Darn tiny phone screens... :oops:

  12. oldironfarmer

    oldironfarmer Silver Banner Member

    We all believe it wasn't just you being gullible.:rolleyes:
  13. Tobho Mott

    Tobho Mott Silver Banner Member

    I believe that without any doubts at all.

  14. Jason

    Jason Silver Banner Member

    I'm glad jeff stepped in that one before I did. :p It does look like mickey.

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