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IndustryArena Forum > MetalWorking > Casting Metals > Understanding metal castings
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  1. #1
    Join Date
    Dec 2016
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    2

    Understanding metal castings

    Hi
    I'm starting new in the metal casting and just more of a hobby then anything else. I have built a home made foundry using the instructions available on internet with PoP and sand. I'm planning using styrofoam to carve some designs and pour molten aluminium on it over this weekend to make it sturdy.
    My question is - What benefits does aluminium metal casting have over say papier mache or just using plaster of paris to create designs on its own. Apologies if the questions comes across as a layman question but as said earlier - Im pretty new to this .if someone can let me know what are the advantages of this - that will be awesome .

    john.

  2. #2
    Join Date
    Feb 2006
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    210
    Really? You are comparing aluminum and paper mache? I wouldn't even know how to start.

  3. #3
    Join Date
    Apr 2004
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    5728

    Re: Understanding metal castings

    I'd say stick to the paper mache and plaster. You can get seriously hurt by melting aluminum and pouring it on things. No matter what you might have seen on YouTube, this is not something you should attempt without knowing what you're doing, or at least having someone who does know what they're doing standing by - physically present - with both of you wearing the proper safety equipment, like full leathers, gloves, cap, gaiters, goggles, and mesh face shield. The least little bit of water residue in your mold or equipment will cause a steam explosion when that molten metal hits it, that will send 1000-degree metal bits flying everywhere. Trust me - I've been there; you don't want to be...
    Andrew Werby
    Website

  4. #4
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    Dec 2016
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    Re: Understanding metal castings

    Quote Originally Posted by awerby View Post
    I'd say stick to the paper mache and plaster. You can get seriously hurt by melting aluminum and pouring it on things. No matter what you might have seen on YouTube, this is not something you should attempt without knowing what you're doing, or at least having someone who does know what they're doing standing by - physically present - with both of you wearing the proper safety equipment, like full leathers, gloves, cap, gaiters, goggles, and mesh face shield. The least little bit of water residue in your mold or equipment will cause a steam explosion when that molten metal hits it, that will send 1000-degree metal bits flying everywhere. Trust me - I've been there; you don't want to be...
    Thanks . I am trying to order stuff online as I write this down . I have heard about the water residual and the fact that blows up in the face. I wanted to get an idea if I should invest that kind of money in this . The more I read about this the more it appeals me ..... When I looked at this for the first time - I was like I can do paper machie but then I see people building car parts using all of this and I do have a thing for kinetic models and this will help me to realise that.

  5. #5
    Join Date
    Dec 2013
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    5717

    Re: Understanding metal castings

    Quote Originally Posted by johndow View Post
    ...........I have heard about the water residual and the fact that blows up in the face. I wanted to get an idea if I should invest that kind of money in this . ...........
    In a word...NO. At least not until you understand the process and all of the safety issues involved. First, what you are talking about is lost foam casting, similar to lost wax casting. You are not coating the foam with aluminum, you are replacing the foam with the aluminum in the mold. Aluminum pours at around 1200° F, the foam melts at around 400° F or a bit less

  6. #6
    Join Date
    Jan 2017
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    24

    Re: Understanding metal castings

    I am new to this just as you. So far I've done 2 pours, not very successful.
    I did research the whole thing thoroughly. I've read that steam explosion is highly unlikely when it comes down to aluminum (zinc, lead, tin too).
    As it proved with my first two pours, water can only ruin your casting but it wouldn't do any damage to you or the surroundings. There is always a risk, but the way I see it, you have to do something extremely stupid to cause steam explosion with molten aluminum (like pouring molten aluminum in a small diameter steel cylinder that has water in the bottom).

    As for your question, the benefits of aluminum over plaster shapes or papier mache.... Well it depends what you goal is. If it is just for presenting the shape, then stay away from aluminum. Plaster and papier mache would be great for you (as well as resin casting, or zinc/lead casting). If you have some money to spare, get an entry level FDM 3D Printer, and you have it all solved.

    Casting aluminum is for when you need certain qualities in your model. Most of all strength, rigidity and thermal conductivity (as in my case).

    If lost foam is your method of choice, then you must consider how will you be shaping your foam. For simple shapes you might get away with a simple DIY foam cutter, made with a resistive heater wire (or Kanthal as it is called here. This is the name of the most well known manufacturer of such wire). For complex shapes, you have to consider CNC machining of styrofoam, or possibly 3D printing a PLA shape and attempting lost PLA method (similar to lost foam method).

    All in all, whichever approach you choose, if you need complex shapes, you will need access to either a 3d printer or a CNC mill/router (unless you are very skilled in manual shaping). And let's not forget that if you have access to a CNC mill/router, you might be able to cut your shape directly out of aluminum, bypassing the casting process.

  7. #7
    Join Date
    Apr 2004
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    5728

    Re: Understanding metal castings

    zeox wrote:

    "As it proved with my first two pours, water can only ruin your casting but it wouldn't do any damage to you or the surroundings. There is always a risk, but the way I see it, you have to do something extremely stupid to cause steam explosion with molten aluminum (like pouring molten aluminum in a small diameter steel cylinder that has water in the bottom)."

    Sorry, but you didn't prove anything; you just got lucky. You don't need visible liquid water to cause a steam event that will shoot hot metal all over the place; just invisible residual water, like in a steel ingot mold that hasn't been properly pre-heated, is enough to trigger something like that. The internet is full of people who have survived doing foolish things, who then feel impelled to tell others that it's okay to do things that are unsafe without really knowing what they're doing or taking the necessary precautions. It's great that nothing bad happened to you in the course of your two attempts to cast metal, but despite what you may have read (or watched on YouTube) foundry work is inherently dangerous, and things you don't know about it can hurt you - badly.
    Andrew Werby
    Website

  8. #8
    Join Date
    Jan 2017
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    Re: Understanding metal castings

    Quote Originally Posted by awerby View Post
    Sorry, but you didn't prove anything; you just got lucky. You don't need visible liquid water to cause a steam event that will shoot hot metal all over the place; just invisible residual water, like in a steel ingot mold that hasn't been properly pre-heated, is enough to trigger something like that. The internet is full of people who have survived doing foolish things, who then feel impelled to tell others that it's okay to do things that are unsafe without really knowing what they're doing or taking the necessary precautions. It's great that nothing bad happened to you in the course of your two attempts to cast metal, but despite what you may have read (or watched on YouTube) foundry work is inherently dangerous, and things you don't know about it can hurt you - badly.
    You are right of course. I forgot to mention that this applies to sand castings. When it comes down to permanent molds, it is a completely different story.

    It is important to understand the mechanics of an explosion. In most cases that is the rapid expansion of gases, which if trapped within a shell/boundary will cause an explosion (usually bursting the shell). If there are no obstructions for the expanding gas there won't be any explosion, just some gas exhaust that will mess up the solidifying metal.

    In the case of a permanent mold, you might get the water residue trapped between solid and molten metal. One has to give, and that is of course the molten metal shooting in a random direction.
    I don't wish that to anyone.

    But I do believe, that while sticking to sand casting, it is indeed very unlikely to achieve a steam explosion.
    I used a totally wrong formulation for greensand, containing over 20% of water in it. So if this didn't cause any explosion, I don't see what else could do so in a sand casting process.
    I have even thrown beer cans with some leftover beer in them into the melt. No problem whatsoever.
    Now that I think of it, if you are using muffin pans for casting shapes, you might get a steam explosion, so... Be careful with the muffin pans

  9. #9
    Join Date
    Dec 2007
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    2134

    Re: Understanding metal castings

    I've done quite a bit of smelting and really can't emphasis enough the risk of moisture causing a blow out.

    I think you've been incredibly lucky as others have pointed out, and reading your posts, to a newbie it would sound like water and smelting mix just fine, but they don't.

    For any person new to smelting, absolutely MAKE SURE there is no water around!

    cheers, Ian
    It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!

  10. #10
    Join Date
    Jan 2017
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    24

    Re: Understanding metal castings

    Quote Originally Posted by aarggh View Post
    I've done quite a bit of smelting and really can't emphasis enough the risk of moisture causing a blow out.

    I think you've been incredibly lucky as others have pointed out, and reading your posts, to a newbie it would sound like water and smelting mix just fine, but they don't.

    For any person new to smelting, absolutely MAKE SURE there is no water around!

    cheers, Ian
    I do agree, Ian. I do not wish to argue, first because I am a total noob at this, secondly because whenever I brag, karma punishes me
    So if I continue explaining how highly unlikely the steam explosion is, next time I pour I might end up in a hospital

    I do however want to learn from your experience. If you have the time to elaborate, I would be glad to hear about the incidents that you've had (and hopefuly survived uninjured), and most of all the ones that involve casting aluminum in sand (greensand as being the one with the most water content).

  11. #11
    mangaliron Guest

    Re: Understanding metal castings

    Aluminium metal casting have a lots of benefits like it is easily customized casting for production needs. it is a higher and faster casting rather than other materials. it is a lightweight, versatile, and used for different purpose.

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