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 Post subject: New to plastics
PostPosted: Fri Jun 13, 2003 12:17 pm 
Hello, I've always been interested in working with plastics, and I would like to do some inexpensive experiments at home. Can I just find some old plastic stuff like packaging material and melt it, then pour it in a mold? I'm not sure about this, please help me get started.


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 Post subject: Re: New to plastics
PostPosted: Fri Jun 13, 2003 2:58 pm 
Most people here that do plastic use resins that set when you add a catalyst. This isn't cheep.

Melting plastic should work in principle, but there will be some problems. Resins are very runny, to get a thermoplastic runny enough might need a lot of heat. More heat means more distortion as the piece cools. In normal injection moulding pressure is used to force the liquid plastic into the mould. This is probably needed because the plastic starts to cool when it contacts the mould, so needs to be injected quickly. Uneven cooling would result in weak pieces even if you did get the mould to fill.

My guess is your not going to be able to do full casting with out a lot of kit.

When I say resins are expensive, you are talking about something like £20 per 2 litre kit (for the best stuff). This is expensive compared to recycling thermoplastic for free, but remember you will get something like 200 pieces from 2 litres of resin and you're not likely to burn your self!

Max


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 Post subject: Re: New to plastics
PostPosted: Fri Jun 13, 2003 8:11 pm 
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Joined: Mon Feb 03, 2003 6:54 am
Location: United States, Wisconsin
Hey all! I finally was able to play around with some polyester resin today. I wasn't making any pieces for cubes but i thought i'd try and get a feel of how to handle the stuff. One thing that kind of threw of "production" was that it had no clean up instructions, it said if it came in contact with skin i just use soap and water, but what do i do with the measuring cups and stuff. You can't just pour it down the sink plus the resin just stuck right to the measuring cup. Do you guys no what i can use to clean up the resin or is my cup foreverly resinized :)

Jake


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 Post subject: Re: New to plastics
PostPosted: Sat Jun 14, 2003 5:11 am 
I use film canisters, so they are disposable. For polyurethane I use clear ones to measure out part A and B, you can mark the quantities on the side. I then pour both parts in to a 3rd canister (a black one, so I can save clear ones for measuring). As I pour them in I get the two streams to mix, this means I don't need to stir so much.

As for cleaning, the clear ones I just give a wipe when I'm finished for the day. I just pull the resin from the black one after it has set. So even though they are disposable I get to use them lots of times.

For polyester I just use a clear canister and a syringe for the catalyst. Just before the resin has completely set I roll the canister between my hands to loosen it and pull it out.

If you want to clean up spilt resin, soap and water is good for polyurethane but you need a solvent for polyester, I use isopropanol/acetone.

For mixers, I have started using lolly pop sticks. The best ones are the sort made from rolled up paper. But wooden ones work ok. These are definitely disposable. I leave them in the resin too help pull it out when set.

If you have let polyester resin set completely in a plastic cup it is probably permanent.

Max


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 Post subject: Re: New to plastics
PostPosted: Sun Jun 15, 2003 5:11 am 
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Joined: Mon Feb 03, 2003 6:54 am
Location: United States, Wisconsin
thanks for the tips Max!


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