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Thread: How to make a permanent mold?

  1. #1

    How to make a permanent mold?

    Hello again!

    Is it possible to make a iron mold to cast aluminium?

    Maybe I can make a two part mold out of iron?
    is it possible to mold the mold without any high cost machines?
    Last edited by reefeer; 12-15-2013 at 04:38 AM.

  2. #2
    Cast iron is a commonly used material for an aluminum permanent or semi-permanent mold. Pre-heating a mold is very important and also using a mold coat. The casting shape and material property specifications are what drive the casting process for me.

  3. #3
    What do you mean with a "mold coat"? Do you mean like a mold release? When the aluminum cools it also shrinks and it just falls out when you hold if upside down, so I'm not sure what you mean.

  4. #4
    Administrator Site Admin Anon's Avatar
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    Commercial permanent molds for aluminum have a coating (some sort of ceramic product) that's reapplied every couple hundred castings. This prevents the aluminum dissolving iron from the mold surface--alloying concerns aside, it greatly extends mold life.
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  5. #5
    These mold-coats (mold-realeasers) are very expensive. Thanks for the info.

  6. #6
    From my understanding it's a graphite material, and it's applied before every pour to help release and prevent erosion of the mold.

    You can cast the rough shape of your mold in iron but generally they are machined and then polished/finished to final shape

  7. #7
    Okey. Is it possible to make a mold in any other material to cast aluminium? it doesnīt need to be permanent mold. A casting method that gives nice and great surface. Lost wax casting seems to be hard and take time but it gives nice and smooth surface. Is there any other method. Maybe easier than lost wax casting?

  8. #8
    There is a tremendous amount of experience on this forum, but more information would really make it easier to help you. If you tell us what you want to make and an idea of how many, we will have a much better idea what process will be most economical, both in time and money for you.

    Having a very smooth surface straight from the casting process, especially with a metal as easy to finish as aluminum, will run up both your time and money costs. In most cases a permanent pattern and sand casting in a good fine grained sand will give you a casting that cleans up very quickly.

    If the shape makes sand casting less economical, then a silicone mold for wax patterns to do lost wax would be the next most economical. Your costs and needed equipment materials will be more that for sand casting so it is the next step up the ladder in terms of costs.

    In sand casting and lost wax, you also have the option of making your pattern in multiples. That way you get many parts for each poured mold.

    As Anon pointed out, iron and steel are soluble in liquid aluminum. A permanent mold in these materials requires a protective coating, so in addition to your much higher costs to produce the mold, you have the ongoing costs for the mold protection. On top of that, any failure in your mold protection and you have then damaged your expensive mold and have the replacement cost. This one is a big step up the ladder in terms of cost. In addition, you have almost zero flexibility in terms of changes.
    Where are the donuts?

  9. #9
    Yes thatīs a good idea. I have different things I want to cast. In this case I want to cast animal ornaments. For example a rein-deer with itīs horns. How to cast these shapes. I understand That I have to use cores. Right?
    I just want to cast maybe 10 casts of every object.
    (Like you said small potatoes) maybe the cheapest alternative is sand casting. To get a great surface finnish I can make some snding with a sand-papering machine and/or some blasting.

    Another method Iīve read about was plaster mold casting. Very similar to sand casting.
    Yes itīs expensive with plaster, and it take time to dry the plaster.
    Anyone used this method?
    Last edited by reefeer; 12-18-2013 at 03:08 PM.

  10. #10
    Here's a member's thread on building some dies out of steel for diecasting/gravity casting:

    If you only need 10pcs each, then investment casting with wax models will be the way to go. Plaster should work, it's my understanding that the molds need to be reinforced a bit to prevent cracking and that the mold must be fired thoroughly to drive off chemically bound water

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