How long can green sand molds sit prior to casting?

Discussion in 'Sand Casting' started by Melterskelter, Apr 9, 2021.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I have heard that green sand molds should be cast more or less immediately after they are made. But the circumstances of my setup is such that I routinely wait a day or two following molding to fill the molds with iron. And yesterday I poured a mold that had been sitting for 6 days since it had been made. I do leave some sort of cover on the top of the mold---either a plywood cover or, in some cases, aluminum foil to prevent them from druying out. And I should say that I am not at all sure they need to be covered. I do it just because... I have never had a mold partially collapse due to storage.

    Anyway, I just opened the poured mold this morning. The 36" casting filled just fine and there were no sand defects seen. The total weight of the casting with runners and pouring basini was 38 pounds and the mold itself was 400 pounds.

    I wonder what other folks' experience in this regard might be.

    Denis
     
  2. I try to pour the same day or overnight. I have had to wait four days due to blowing rain and like yours poured just fine. I don't cover them.

    Total weight of pouring basin and runners was 3.8 pounds.:D

    We may be in a different league.:cool:
     
  3. rocco

    rocco Silver

    There's probably not a one size fits all answer to that question, I think we can reasonably assume there are multiple factors that affect the longevity of molds. Off the top of my head, weather matters, molds will likely last longer in cold or damp weather than they would during hot and dry weather, size matters, heavier molds will dry out more slowly, surface area matters, with molds of equal weight, the ones with the less surface area exposed to the air will dry out more slowly. Also, the green sand itself probably has an impact as well, things like sand grain size, clay and moisture content may all come into play.
     
    Last edited: Apr 9, 2021
  4. I have one that's a week old now, it's sitting on an aluminium matchplate and covered in plastic sheet, I've been checking it occasionally and spritzing it with water. Another one was a 4" round ingot mould in a stainless steel bucket that was 6 months old and dried out before I used it, I gave it a spritz too on the day of use.
     
  5. Peedee

    Peedee Silver

    Watch out for critters getting into the sprue, that could make for a bad day. I had a mold I didn't pour and it just got left for a month while I was busy. When I came to break it up it was like soft concrete!

    My green sand was a little heavy on the clay and I didn't bother pouring it so not sure what the result would have been.
     
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  6. Melterskelter

    Melterskelter Gold Banner Member

    The reason I mentioned the size of the mold is that I recognized that its mass may affect drying. But, I am wondering if drying necessarily results in weakness. I have made a green sand open mold to use in the event of having extra metal at the end of a pour. It has sat open for a couple weeks or more and gotten very dry. But it did not get crumbly.

    I agree with the fact that each of our experiences could differ due to differences in sand formulation, weather, and and mold size. What I am interested in mostly is to see if there are failure stories related to pour delays. So far, no such stories.

    Indeed, mice hang out at the barn. I do not fail to cover sprues and open risers. I have heard stories of small animals taking up residence in molds and resulting in totally unexpected eruptions. We can all do without that.

    Denis
     
  7. Although larger might dry out slower, HT1 recommends drying the face., matching your ingot mold experience. My green sand does dry out pretty firm. No reason it shouldn't handle hot metal.

    If I catch a mouse in my mold I'll kill him.
     
  8. MoltenDave

    MoltenDave Copper

    I think the mouse may end up having a worse day than you. I have left molds for a week before casting. I cover them with paper, partly so they don't dry out, and partly to keep bugs out.
     
  9. Tobho Mott

    Tobho Mott Gold Banner Member

    I worry about spiders infiltrating my molds and causing them to steam-explode, but I never even considered a mouse!

    Doesn't take much effort to lay a scrap of cardboard or sheet metal over sprues and risers if you have to let a mold sit...

    Jeff
     
  10. KDM

    KDM Copper

    I'm not sure a few days makes a great deal of difference. We were in a slate mine recently and traditionally, they had made their own iron cogs and stuff. They'd spend several weeks making the positives from wood, then several weeks making a whole batch of greensand moulds, then one big melt, where they poured them all in one go.
     
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  11. Billy Elmore

    Billy Elmore Silver

    I have never had an issue with hand molds. We can not let our production molds sit for too long or they will get to crumbly to use in our process. We could most likely pour them and they would...maybe... be ok but we could not transport them on our machines with iron in them or they would fall apart and create a huge mess. If they have been sitting for more than a few hours we will skip them and make new ones. This happens a lot at the beginning of first shift Monday morning...the weekend guy gets the machine setup and makes a few molds ahead of first shifts arrival. Sometimes he does this too soon and the molds collapse during transit. We have started just pouring a few half full molds to get weight on the mold stack...to get fresh hot iron into nozzle..and to keep the mold stack from crumbling. I have noticed the sides dry out but do not seem as crumbly as the bottom and this could possibly be from slight rust developing where the mold contacts the steel on the bottom and the rust is dragging the bottom apart. I kept a 3D printed mold for a few weeks...maybe months and poured it with no issues.
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    Do you use green sand or air set or something else? It seems like my green sand actually gets harder as it dries.

    Denis
     
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  13. Billy Elmore

    Billy Elmore Silver

    We use synthetic silica sand...probably much drier than would be used in hand molding. Having a much drier mold to start with may be a factor. We have to blow around 700 lbs in the chamber every 6 seconds and the sand has to have a lot of flowability to get a good even fill in the chamber before squeezing. The combination of the weight of the molds and the rust created by the mold sitting on the steel rails may be the biggest factors...it is definitely worse on the bottom of the mold. We also use a blend of different clays because we need the hot strength and green strength but if the green strength gets too high our molds will look like black beach balls rolling backwards down the incline shaker.LOL So it may be a combination of all those factors. Ceramic/carbosand will turn into cement if left to dry too long. Nearly tore our system apart trying to run molds left on line for couple days.LOL
     
  14. Billy Elmore

    Billy Elmore Silver

    Adding to this post... I almost took pics of molds left on line over weekend...barely made it to shaker pan as just being delivered on belt was causing them to fall apart.
     

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