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rurwin
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 2:55 pm

I have a plan. That's a dangerous thing.

Around our house we have vast numbers of milk-bottle tops. For some reason we don't put them in the recycling bin. In fact it seems that very few places recycle them, so maybe I have to step up to the mark.

These things are HDPE -- high density polyethylene -- AKA recycling number 2.

Now from reading the Wikipedia page, and a few others, I find that the melting point is somewhere between 130C and 180C, and I can find no reference to any hazardous gases that may be given off.

That's too hot for a double saucepan, or is it... Water boils at 100C of course, but oil doesn't. In fact 180C is the bottom end of a deep-fat fryer's range.

So I plan to make a positive mould out of modelling plastic, or maybe balsa. Then use either sand or salt as a negative mould, as I learned a long time ago in metalwork classes. I'll melt the bottle-tops in a tin can in the chip-pan, with a thermometer to make sure it stays around 150C-ish. When it's all melted, with great care, I'll pour the plastic into the mould, wait for it to set, and then remove the finished case. If I used salt for the mould, any bits stuck to the case will dissolve off in warm water.

Now the reason I'm posting this now, rather than when I can gleefully post pictures of my finished (green) case, is that someone here may know something I don't. So if this plan is horribly dangerous above and beyond playing with super-heated fluids, please tell me.

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RaTTuS
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 3:03 pm

How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

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meltwater
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 3:26 pm

Sounds a little dodgy to me...at least video it so that if it goes Pete Tong, it'll at least it'll be entertaining (just make sure it is not yourself you risk damaging).

Good luck though...it may well be a stroke of genius.
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timgiles
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 7:20 pm

Yes - please youtube it for us Either way you will get a super case or it will be a valuable lesson for all the kids at school learning with the RPi on how not to melt your fingers.

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rurwin
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 7:52 pm

Thanks for the link RaTTus. That does not look too hopeful, but I may make a few experiments anyway.

The trouble with videoing it is that the only person who can hold the camera is SWMBO and, of necessity, she wont be in the house

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abishur
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 7:57 pm

I really like the idea of this!  Does it help that the milk jugs themselves are HDPE (not just their little blue caps)?
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tufty
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 8:10 pm

Take the milk out first

MarkA
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 8:32 pm

Does it make any difference that a domestic oven should get to over 200C with ease? Melting in an oven should be much less hazardous than the hot oil....

When I did chemistry at uni, hot oil baths were common and not really a concern. Amazing how our attitude to safety has changed. Nowadays its pat checks and electric mantles.

So think what could go wrong, either burnt down house or just lost eyebrows, and if you are still happy with your plan then go for it. Sensible precautions like having a fire blanket to hand may be worthwhile, just in case!

Have fun, 'cos this is what it's all about!

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grumpyoldgit
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 9:00 pm

rurwin said:


I have a plan. That's a dangerous thing.

Around our house we have vast numbers of milk-bottle tops. For some reason we don't put them in the recycling bin. In fact it seems that very few places recycle them, so maybe I have to step up to the mark.

These things are HDPE -- high density polyethylene -- AKA recycling number 2.

Now from reading the Wikipedia page, and a few others, I find that the melting point is somewhere between 130C and 180C, and I can find no reference to any hazardous gases that may be given off.

That's too hot for a double saucepan, or is it... Water boils at 100C of course, but oil doesn't. In fact 180C is the bottom end of a deep-fat fryer's range.

So I plan to make a positive mould out of modelling plastic, or maybe balsa. Then use either sand or salt as a negative mould, as I learned a long time ago in metalwork classes. I'll melt the bottle-tops in a tin can in the chip-pan, with a thermometer to make sure it stays around 150C-ish. When it's all melted, with great care, I'll pour the plastic into the mould, wait for it to set, and then remove the finished case. If I used salt for the mould, any bits stuck to the case will dissolve off in warm water.

Now the reason I'm posting this now, rather than when I can gleefully post pictures of my finished (green) case, is that someone here may know something I don't. So if this plan is horribly dangerous above and beyond playing with super-heated fluids, please tell me.


At least by typing this up the paramedics will have a record of what exactly it is fused to your skin, which may also prove useful to the coroner.

hvc123
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 9:47 pm

i also have been looknig at creating my own cases, have a look here at http://www.directplasticsonlin.....ral/1.5mm/ they have it in sheets for less than a couple of quid, makes it a lot easy in a sheet form (apparantly) but i too am stuck at the actual melting and moulding part

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meltwater
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 10:06 pm

Just had visions of some freak accident and a RPi based superhero is born...
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hvc123
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 10:57 pm

lol PiMan, a bit like spiderman when peter parker was bitten by that spider, except 90% burns from moulten plastic....

from now on call me Pi Man !!

Prometheus
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Re: Case made from milk-bottle tops

Thu Feb 09, 2012 11:28 pm

hvc123 said:


i also have been looknig at creating my own cases, have a look here at http://www.directplasticsonlin.....ral/1.5mm/ they have it in sheets for less than a couple of quid, makes it a lot easy in a sheet form (apparantly) but i too am stuck at the actual melting and moulding part



If your RPi isn't going to be in a hot environment but you want to make a plastic case, then you might want to take a look at materials like Wonderflex or Friendly Plastic. They're both often used in costuming, and thus are meant to be easily mouldable by hobbyists.

Wonderflex is sheet plastic with fabric embedded in it, that can be moulded into shape by heating it up, and Friendly Plastic comes in the form of low-melting-point plastic pellets that can be melted in hot water and then shaped however you like.

Benedict White
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 12:28 am

Grumpyoldgit said:


At least by typing this up the paramedics will have a record of what exactly it is fused to your skin, which may also prove useful to the coroner.


Ah... the power of positive thinking!

Joules
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 1:32 am

Please be very cautious about putting plastics in a domestic oven. It"s actually quite easy to over cook them leading to chemical decomposition with a good chance of liberating something nasty. Your oven maybe at 200c, but the radiant element is alot higher. We have an injection moulder here in the workshop and it is good for moulding with plastic milk bottles (if thourghly cleaned) and best of all pop bottles.

The point being it has a very small heating chamber that is precisely temperature controlled with fume extraction. Please look very carefully at what happens to your choice in plastic if overheated, you may not get a second chance to get it wrong.

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meltwater
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 9:42 am

Joules said:


Please be very cautious about putting plastics in a domestic oven. It"s actually quite easy to over cook them leading to chemical decomposition with a good chance of liberating something nasty. Your oven maybe at 200c, but the radiant element is alot higher. We have an injection moulder here in the workshop and it is good for moulding with plastic milk bottles (if thourghly cleaned) and best of all pop bottles.

The point being it has a very small heating chamber that is precisely temperature controlled with fume extraction. Please look very carefully at what happens to your choice in plastic if overheated, you may not get a second chance to get it wrong.


Probably make the sunday roast taste a little off too...
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rurwin
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 11:28 am

That's one reason I favour the oil bath -- it's easier to limit the temperature. The other reason being that is seems not to melt properly in an oven. I'm hoping that a little agitation may help.

On the friendly-plastic thing, I know about that stuff, but it melts at temperatures that the RPi case may come across, like being left in a hot car for example.

Joules
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 12:25 pm

I think you would be better vac forming a case, be it plastic milk bottle or pop bottle. Plastic just won"t run like resin into a mould. You need to force it and hold it till it cools otherwise it will just creep and distort.

Vac forming can be as simple as a heat gun and a vacuum cleaner. The mould carved from wood or plaster of paris. A frame would be required to hold the plastic to stop it shrinking into a lump. The sheet can just be stapled to the frame, then play the heat over the plastic till it sags. Plenty of guides on the net for vac forming, and some good guides for plastic injection.

Asmodeus
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 1:30 pm

You could cast two-component polyurethane (Resin):

 http://www.panzer-modell.de/tipps/resin/resin.htm (german)

Google.translate

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panik
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 2:33 pm

Everything from hand moldable plastic to soft gel magnets, conductive fabrics, rubber glass, aluminum foam and other mind-blowing materials:

https://www.inventables.com

Not exactly on topic, but you might want to have a look.
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mole125
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Re: Case made from milk-bottle tops

Fri Feb 10, 2012 4:50 pm

panik said:


Everything from hand moldable plastic to soft gel magnets, conductive fabrics, rubber glass, aluminum foam and other mind-blowing materials:

https://www.inventables.com

Not exactly on topic, but you might want to have a look.


A uk site that has much of the same is http://www.mindsetsonline.co.uk/, it's actually run with Middlesex university and aimed at Science and DT teachers but anyone can order.

linwiz
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Re: Case made from milk-bottle tops

Tue Dec 02, 2014 5:58 pm

Did you ever do this? I was wondering if HDPE would produce unsafe amounts of static and damage the pi. I plan on experimenting with multiple types of plastic melted together, whatever is in my recycle bin at the time. I am not sure if this will work or if I should stick to one type of plastic, but I will find out at some point.

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rurwin
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Re: Case made from milk-bottle tops

Wed Dec 03, 2014 5:57 pm

No, I never did it.

I still think it is worth trying, but one would have to know exactly what they were doing and be very careful. It is not a matter of sticking it in something hot. It is a matter of heating it to a specific temperature and taking all due precautions.

Eye protection, skin protection, adequate ventilation, precise temperature control, stable equipment... at least.

It may still be necessary to mold it under pressure, which would be a whole new level of complexity.

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Re: Case made from milk-bottle tops

Wed Dec 03, 2014 6:03 pm

This is a great old thread! First time I've seen it. Plastic recycling.

I guess industry would shred/granularise the plastic with some sort of rotating toothed things, not unlike a paper shredder? Then if you could get fine granules or powder, it could be fed into some sort of adapted 3D printer head thing... (Not the usual plastic rod they use.) Perhaps dropped into a cylinder and a plunger used to feed the powder into the head. It could then be played into a mould.

Maybe :)

linwiz
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Re: Case made from milk-bottle tops

Wed Dec 03, 2014 6:16 pm

This is where I got the idea from, and his method seems to work great. I would need to have a different mold than the one he used, one that creates a hollow box the pi can fit into and one to make the lid.
http://www.instructables.com/id/How-To- ... -Easy-Way/

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