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Thread: more questions

  1. #1
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    Default more questions

    OK I have now more questions to ask....well 2 really. Can you make your own green sand for casting or is it better to buy it? I'm a little way off from that but will be needing it sooner or later.
    Next what size flasks are best to make? The largest I can envisage for now would be a 300mm square but how deep? Is there a formula to use?
    Cheers
    Pete
    Boycott Shampoo!!
    Demand Real Poo!

  2. #2
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    casting sand / green sand is easy enough to make

    i use pertrobond , mix 20:1 with sharp super fine high purity silica sand , then add oil

    with green sand , solid plasterers sand ( sharp sand ) is mixed with powdered bentonite clay ( kitty litter ( not all kitty litter read the label )) in a ratio of 10:1 , then water is added to get a good green strength

    mixing by hand hand can be done in small batches , but is a time consuming exercise
    you have to coat the sand grains in clay by rubbing squashing mixing and ramming
    you will soon wish you owned a " muller " to do it for you

    you want just enough water so the sand sticks together when squeezed , if it sticks to your hand its way too wet and will vent too much steam when molten metal hits it , too dry and it wont stay together in the flask

    flask sizes are pretty much what you need , a 300x400x75mm deep x 2 , can get quite heavy so you want to keep them small if you can

    you want atleast 50mm all the way around the part , if the part is tall you want the same distance in height around the part , to help seal the flasks

    large flat surfaces will also be a problem , so you want about 5:1 width to height minimum ratio so the sand dosnt fall out when you move them

    large flat surfaces are also a problem when the metal is denser than the sand , and the cope ( top flask) "floats" away from the drag ( bottom flask)
    large weights on top will help

    also a higher poring pressure helps , so some large tin cans full of green sand with a hole pressed into it , sitting ontop of the cope ( top flask ) will help when pouring
    how come a 10mm peg dont fit in a 10mm hole

  3. #3
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    another form of "sand " is bonded sand
    sodium silicate , is mixed with water and sand , rammed into shape , then hardened with the use of co2 , then oven dried

    mainly used as a "core " material when you want to cast some thing with a hole in it
    can also be used for very fine detailed castings , a lot finer than petrobond or greensand ( using fine sand of course )

    have a look at some of the vacuum assisted castings by mullernick http://www.woodworkforums.com/f267/v...moulds-160866/

    sodium silicate , can be made from "caustic soda" ( drain"o") and silica gel ( "dont eat" packet ) , look it up on the net ,
    how come a 10mm peg dont fit in a 10mm hole

  4. #4
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    Thanks for the answers I can see what is needed and you explained it well. I'll look around and see what I can find
    Pete
    Boycott Shampoo!!
    Demand Real Poo!

  5. #5
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    before you mix your sand , test some
    copper at 1100c will over heat some sands , causing them to foam up and turn to crap
    silica sand will turn too glass , and fully melt at 1600c

    quartz is silica sand , freshly crushed and screened is expensive , but look around
    99% silica sand , graded too 100um ( a bit fine for green sand ) is what i use and got it from a cement products seller , its a thickener / anti slip additive for epoxy floor coatings , < dam expensive sand
    but my local darwin " river sand " foams at 900c and would have to truck in sand anyway
    after looking for 3 weeks i bit the bullet and bought 5 x 15kg bags at $25 a bag , the bee's knee's of silica sand , pertobond cost me $160 to make 2x that , then the 4lt of synthetic 2 stroke oil , the sand aint cheep , but you reuse it over and over again

    i couldn't find an old bath tub to mount under my work bench ( with 3 lids ) so installed old laundry trough's under my work bench to hold the sand with hinged lids , spoons ,rammers , hole cutting pipes , chalk dusting sock all have a place to live under the lids

    beach / sand blasting / filter sand has been tumbled to stop it packing down and clogging
    all the sharp corners have been knocked off
    we want it to pack down and clog so avoid those sands

    brickys like the sand 1/2 round, with a bit of clay , so they can tap there bricks into place , solid plasterers prefer sharp sand with no clay , if its all one colour it should be fine too use , if there are brown , cream , white graines , it will probably foam up with heat ( river sand )
    how come a 10mm peg dont fit in a 10mm hole

  6. #6
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    Thanks for the info on sand. I will be starting with ali first and maybe look at the hotter metals later....
    Pete
    Boycott Shampoo!!
    Demand Real Poo!

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