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experiments with household goods casting

 Post subject: Re: experiments with household goods casting
PostPosted: Wed Aug 31, 2011 5:29 am 
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right - dissembled the glue gun and found the problem - there's a ball valve at the end designed to let only liquid glue through (so you can't accidentally jam the nozzle with an unheated stick.)

clearly the PE sticks didn't get hot enough / gooey enough to pass through. but at least i've a working glue gun again.

testing will continue


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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Sep 08, 2011 3:43 am 
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bad news comrades - transparent silicone caulk has a lower ignition tempreture then the black stuff i started with.

new moulds required. again.


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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Sep 08, 2011 8:42 am 
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Does that mean you got the plastic bags hot enough then?

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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Sep 08, 2011 10:38 am 
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nah - went back to the 'set them on fire' method.

it was an unusally deep mold - about 1.4 cm deep and big with it. I wanted to see how well the plastic coped as it cooled re shrinkage and distortion.

as it happened the entire thing went up in flames. yay. fortunately, I had my novelty blue watering can next to me full of water.


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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Sep 08, 2011 11:37 am 
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madd0ct0r wrote:
fortunately, I had my novelty blue watering can next to me full of water.
See, you ARE learning something.

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 Post subject: Re: experiments with household goods casting
PostPosted: Thu Sep 08, 2011 12:19 pm 
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this is a highly entertaining thread, your ghetto setups are awesome, although I really liked the HDPE trowel

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Sep 16, 2011 12:09 pm 
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So, been a bit slow on the experimental front recently – real life has been picking up a bit.

But not enough to stop me!

Wife decided the stash of carrier bags was getting excessive, we weren’t using them up fast enough. Half of it was destined for the bin. What a terrible waste. Surely I could condense that huge stuffed bag into something smaller?

Step 1: choose crap, never used pan.
Step 2: bring 1cm of water to the boil
Step 3. stuff bags in, close lid.
Step 4: as bags soften (but not melt) keep stacking plates upon them to compress the mass down.
Step 5. don’t tell wife about the dinnerplates
Image

Step 6. when reasonably squished, flip the bags and cook the other side



Results:

Image

The outside edge of the cake is well fused – a layer about 2mm thick. Plastic still reasonably soft and flexible compared to the flambed version.
Inside the crust, nothing changed. Bags pretty much identical.
Before cutting open, would have made a good seat cushion.
Still smaller then it was at least.

Since I was in the mood I also tried the oil frying method:

Image

Compared to the careful heating of before, this was a joy to do – get oil hot, add bag, watch bag shrivel into blob of plastic, stir in next bag.

But the final material was even worse then I feared. I thought it’d be waxy, but it positively leaked oil. Stank like the time you woke up with your face in some very badly cooked chips. I’ve heard of it being used to make an ad hoc washing machine bearing and I can believe it. But that’s about all I’d use this for.

So, maybe an oil bath heating an inner bowl?

Heating will have to be done very slowly – the plastic really doesn’t conduct heat well and it’d be raw inside while burning outside – like cooking a turkey from frozen.

Interesting though.

The most amazing result? The cheap crap pan that’s never been used was part of an electronic hotpot set. It was a wedding gift that we have never, ever used.

Guess what a friend brought around that night as her contribution to the party? Mushroom hotpot.
Guess who opened his big mouth and said ‘ hey, we’ve got a electronic hotpot plate – should we use that?’
Guess who then had to explain to the assorted guests why there were traces of molten plastic stuck inside the pan…


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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Sep 16, 2011 2:57 pm 
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Step 5 in the above can be very dangerous and I would not recommend it ;)

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Sep 16, 2011 3:38 pm 
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mmm ... cake

Results of the oil frying look like they might lend themselves to some interesting photography.

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 Post subject: Re: experiments with household goods casting
PostPosted: Tue Sep 27, 2011 5:57 am 
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So, rainy season has started so I find myself reluctant to sit outside hunched over burning silicone.

Tme to try the oil bath. Heating was kept as slow as possible, done ove maybe 30 min.

had to cut the result in half with a hacksaw : result:

Image

However, the plastic was barely gooey - far to thick for what I had in mind. The monumental headache doing it indoors gave me (even though no fire involved) means I doubt I will take this particular idea further.

experiments however, will continue.


as a freebie, here's a shot of the rainchain I set up when the noise of the water on the roof got too damn annoying. Wanted to try one of therse out ever since I heard of them. Works reasonably well, espcially at the low levels of water inbetween ranstorms.

Image


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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Oct 24, 2011 7:24 am 
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OK. plastic bag mountain getting excessive again, so tried stuffing as many as I could into a beer can, heating it, stuffing more and so on. In theory the high heat won't matter, because there's no air inside the can.
I'm not really sure what happens to polymer molecules at high temp - possibly branching with a resultant tougher, brittle material. Half of the fun is waiting to find out!

current project is investigating whether mixing aluminim flakes into the silicon will give me something that gets nicely hot in the microwave., plan then being to pack mold with plastic powder, microwave, let cool and pull out a plastic mini (or at least a mini with 2mm thick walls and a soft heart of unchanged white powder.)
getting that through customs will be fun ;)

I also found a place that sells resin. yay.

So now I need pressure pot thing to keep the air bubbles small. Since my marinade for the pork last night underwent a minor chemical reaction, i'm looking into what happens when coke and MSG meet (ala the menthos fountain) or possibly MSG and acid (ala It Burns!)
In theory, place mould in strong tupperware box. Pour liquid into box. pour resin into mold. add powder on a piece of paper. Secure lid. shake powder off paper. Watch Tupperware box carefully.

Can anyone tell me why ensuring air bubbles in your miniture are extremely high pressure is a good thing? Will it not just rip the resin apart when I open the mold?


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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Oct 24, 2011 7:40 am 
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madd0ct0r wrote:
Secure lid. shake powder off paper. Watch Tupperware box carefully.

That's pretty ingenious. Well, if it works ;)

I dunno about coke and MSG, but if it froths up won't there be a risk of it geting inside the mould? seem to remember that you don't really want water (or water-based coke) touching the uncured resin.

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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Oct 24, 2011 9:51 am 
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I'd probably clingfilm it first to make sure the resin gets pushed down and not just air pushing into it.


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 Post subject: Re: experiments with household goods casting
PostPosted: Mon Oct 24, 2011 12:17 pm 
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madd0ct0r wrote:
Can anyone tell me why ensuring air bubbles in your miniture are extremely high pressure is a good thing? Will it not just rip the resin apart when I open the mold?


Probably not, though it probably depends on the tensile strength of the resin. The main reason to put the bubbles under pressure is to decrease their size. Bubble diameter varies with the cube root of the volume, so doubling the pressure (to around 8 psi) reduces bubble diameter by about 20%. 50psi reduces diameter by around 57%. 100 psi rediuces diameter by a factor of three. Since most air bubbles are submillimeter diameter to begin with, you end up with very small bubbles that will probably pop if too close to the surface, leaving very easily fixed imperfections, but are usually buried deep enough to ignore.

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 Post subject: Re: experiments with household goods casting
PostPosted: Fri Oct 28, 2011 12:19 pm 
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ok. tupperware boxes, while excellent for vacumn or a packed lunch, don't seal high pressure very well.

Used a combination of coke (cos seriously, who drinks that stuff?) and ground up berroca (fizzy vit c) tablet. Reasonably satisfactory hiss, but observing the plastic bag I had inside no serious development of pressure - possibly 2 atmos temporarily.

RE the can of plastic - there was sufficient air trapped in the bags or between them to allow oxidation breakdown of parts of the plastic.
Very little melted, the plastic just dosen't transfer heat well.

But most of it is reusable and considerably more compact, so it all helps.

Microwavable silicone is the next step i think.


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