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I want to create a mold, so that when I want to make for example, planet Earth in plastic in 3D, then I can pour the molten plastic into mold. So that I can give a form. Not only this, but… when I buy Pepsi, or something with hard plastic, I can use that hard plastic to melt it and then create something with it. I want to be creative.

Questions:

  1. What do I need to make a mold so that I can pour any molten plastic in it?
  2. It is even possible to make a mold so that you can pour in it any molten plastic?
  3. It is possible to make the mold in the you want?

CLARIFICATION

What I’m trying to tell is, that I have found out that you can melt at home any plastic, and then you only need is a mold so that you can give a form to it.

Problem

The only thing is that I don’t know what type of material I need to use so that I can create a special mold for this. From clay I can create mold so that I can pour a molten plastic? Don’t know.

NOTE: I have put “material/s” because, I’m don’t know what kind of materials I need so that I can put with plural or singular. Got me?

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    I think your understanding of how plastic moulding works is lacking; you can't generally just pour plastic, you need to injection mould at high temperatures and pressures - this isn't generally something you can do it home. – walrus Oct 12 '18 at 13:27
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    Check out the Precious Plastics series on Dave Hakkens you tube channel. He has serious mechanical engineering expertise and is working specifically on reusing plastics. Pay attention to all the solid steel hardware involved in his process. Yes, he created it all diy-style, but it is still very serious hardware. – Henry Taylor Oct 13 '18 at 4:51
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Injection molding can in fact be done at home. But judging from the OP this method would be far and above beyond the scope of his current knowledge on these types of things.

The easiest way to cast plastic parts at home or in your workspace if that’s the case would be with the use of a commercially available product such as SmoothOn.

Simple. Sold on amazon as well as most other online retailers.

I suggest doing at the very least some cursory research into the process’ used when casting/molding with SmoothOn products, as they offer a variety of materials such as polyurethanes, rubbers, silicones etc. a quick google search will lead you in the right direction. YouTube aswell.

Also, just as a quick tip to lead you in the right direction, try finding some videos of sculptors and character designers using this stuff for they’re own casting/molding needs and you’ll have a good point of reference to start from. Good luck :)

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  • I only wanted to know how to create a mold in the way you want, and how can you create it in the way that holds the molten plastics in it safely. – Alex A Oct 13 '18 at 6:14
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    @AlexA well, tbh I understand your looking to utilize any old plastic to “be creative” but perhaps there are safer/cleaner means to accomplish whatever exactly it is that your trying to have as a final product. Most plastics are known to release hazardous and downright dangerous compounds when heated up or burnt. – R00tD00m Oct 13 '18 at 12:46
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Most plastics can;t be cast easily in this way as they don't have a distinct liquid phase and even when 'melted' have very high viscosity. Generally thermo-softening plastics are formed under considerable pressure eg by injection moulding, extrusion of blow-moulding, or are formed from softened sheets as in vacuum forming.

If you want to cast plastic parts the best solution is a resin. Typically made by mixing two liquid parts which have low enough viscosity to be poured into a mould and then set hard in the mould by a room temperature reaction between the constituent parts.

Polyester, Polyurethane and Epoxy are commonly used for small and medium scale casting. You can also add granular pr powder fillers to improve strength, simulate other materials etc etc.

For hobby use PU resin provides a good mix of properties, it casts well has reasonable strength and is fairly convenient and safe to handle with reasonable precautions.

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  • Can you name what type of hard and safe plastic to melt easily and then give any shape or form? – Alex A Oct 16 '18 at 14:01
  • What kind of metal I need to use for pouring any molten plastic? – Alex A Oct 16 '18 at 14:02
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    @AlexA if you re-read the answer you'll notice that the point is that there aren't any hard, safe, easily meltable and pourable plastics. This has been explained several times. With regard to what kind of metal, steel and other metals are normally used to create mould for injection moulding. – walrus Oct 16 '18 at 20:44
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Before going farther, there are some plastics that can be safely melted at home with good ventilation as long as you use the right procedure (warm it slowly and don't exceed the temperature needed to melt it), and some plastics that give off toxic fumes when they melt, so you should never try to melt those indoors. Do your research.

The question asks about the mold material. High-temperature silicone rubber will handle most kinds of melted plastic. You can also use materials like clay (fired) and plaster. So that part's easy.

Most common thermoplastics melt at temperatures a household oven can reach. So yes, you can melt almost any thermoplastic at home. That part is also easy.

The hard part is how to do the molding. As the other answers point out, you can't simply pour most kinds of melted plastic into a mold. Most thermoplastics don't become a thin liquid that will flow into nooks and crannies of a complex mold by gravity. They become like sticky putty. That's why they are generally forced into a mold under pressure.

But that isn't the end of the story. For some applications, you can still mold those plastics at home without special equipment, and there are a few plastics that do become a liquid that you can pour into a mold.

  1. The plastics that become very viscous are commonly pressed into sheets or blocks that can be cut and machined to make stuff. People do it at home with no special equipment; there are lots of online links to that. But these plastics can also be molded into simple shapes, and even pressed into simple open molds. Molds with deep fine detail, or complex two-part molds, require equipment you aren't likely to have at home. But I've molded simple items out of HDPE.

    The mold has to be strong enough to not distort under pressure. For simple shapes, you can make the mold out of wood (I've made things like brackets that way). To copy an item and capture detail, you can make a mold out of silicone rubber that is contained inside a wooden frame.

    You scoop the melted plastic into the mold and slightly over-fill it. Then cover it with baking parchment and a board (and a board under the mold if the bottom isn't solid). Clamp the top board against the mold. The plastic can flow slowly, so tighten the clamps after a few minutes. If the board bottoms out against the mold, open it up and add a little more plastic. If it is a small mold and the plastic has cooled, remove the plastic, remelt it, and start over using more plastic. Repeat the clamping process. When the plastic is cool, remove the clamps and it's ready (you will probably need to trim off some flash).

  2. Some plastics do melt into a pourable liquid that you can cast. Here are a few common ones.

    • Embossing powder. There's a whole craft industry built around the hobby of casting small items with this. The powders are proprietary, but a chemist who dabbles in stuff like this guessed that they are primarily acrylic powder and posted videos on making your own by precipitating it from acrylic floor polish. (Couldn't locate the original, but here's a summary).

      The DIY powder works for embossing, but I've never tested it for melt and pour. The powder would be expensive though; the floor polish isn't cheap, and the acrylic is just a small portion of it. If the commercial embossing powder is mostly acrylic, it might be possible to break up acrylic plastic sheets from the hardware store and melt that (never tried it).

    • Hot melt glue. It shrinks a little when it cools, but you can minimize that by coating the mold with a layer. Let it cool a little. While it is still very warm, add another layer. Repeat until the mold is full. It's probably softer than you tend to think of as plastic, but it's a handy material for quickly turning out items that don't need to stand up to abuse.
    • PETE is the plastic usually used for water, soda, and juice bottles. It melts to a liquid phase that can be poured into molds. I've also used molds made by forming or embossing aluminum sheets or soda cans, then melting the plastic right in the mold. You'd never guess it from the soft bottles, but when you melt PETE into a molded block, it is very hard, extremely tough stuff.
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