Picture of the insulation material mentionned above.
Weekly update #3 (On week 4)
I didn’t update you last week. I was busy solving the overheating issues of our SSR. I think we managed it now : we added an heat sink and will have an additional fan on our electronic box.
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We didn’t melt any plastic yet, but we made slow but steady progress: The compression frame is almost built, our first mold is ready to use (a bit a dodgy setting of two stainless steel kitchen pots that should allow us to make bowls), our supply in plastic should be insured thanks to a local women association of waste pickers and the cleaning procedure is established.
We decided to work on these “thin arrowroot” biscuits and these “waiwai” noodle packagings.
Our oven has poor insulation and is degraded on top (rust and hole); so it’s not really energy efficient. I needed 25min to go from 27°C to 200°C; and the SSR heat sink was really hot after 45 min. Moreover, we never reached a temperature higher than 214°C and I saw several case studies of melting PP at 220°C.
Oven insulation is hard to find in Nepal; but I found this box containing some foam at home. I don’t really know what material it’s made of: Will it be temperature resistant? Can it start burning if I use an inappropriate one? Otherwise, do you guys have a solution for “DIY” insulation of an oven?
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Or place the oven outside before you use it.
Especially when still testing…
My outdoors is part of my workspace, just for this reason…
Having several temperature measurement locations will help you understand the oven, the temperature gradients, and what the plastic is seeing. They are not that expensive online, but I’m not sure what is easy to get in your location. You could even use a grilling/cooking thermometer if it has a remote probe sensor.
If available a fan in the oven would only help avoid burning the plastic because of uneven temperature.
For the fumes, keeping the oven near the door and a floor fan if available should help.
Thank you all for your feedback, comments and enthousiasm. We decided to start working only with the lower heating element to limit the risk of burning the top layer of films.
@s2019
: Yes, we are adding a thermocouple connected to a PID controller (temporary/testing setting on the picture down there, it seems to work pretty well!). You mentionned “several” controller. We just have one. Would you still recommend adding a fan in the oven?
@donald
True, I didn’t plan the timer. I’ll look for one or I’ll use my phone.
Sure, I know the banger of smoke. We’ll experiment gradual temperature increase, work with open doors and windows and use the good masks I have with me. Moreover, as we’re in a co-working space (next neighbors are maybe 10m from the oven, we’ll be really precautious and communicate a lot on our activities.
The fumes are not always obvious smoke. That container is a small volume.
True, I assumed this is the case as they are “now experimenting with the electronics.”, but indeed so is installing a timer….
Once it fumes: experiment failed.
But this is no news to you, right @marcvdv ?
@marcvdv , I used our kitchen oven a couple of times for experiments. Even with the windows open and a fan on, the fumes were an issue. I’ve stopped using that oven for that reason.
Hopefully you have several temperature sensors/readouts you can use during your experiments. I found oven temperatures vary significantly. Are you planning to use your own controllers? I would sill consider adding a fan of some kind.
Those range top heating elements may be useful for directly heating molds.
Or paper (with some modifications).
Or the actual answer, which is ‘bean burgers’, but hush, don’t tell anyone!
‘Extruder’ is fully metal, so would be interesting to try…
Gotta love vintage tech!
LOL 
If it doesn’t work for plastic (are you going to heat it?), then it can always be used for food…
I think you answered your own question 
Having the heating on the side would give a more even heating when looked at top to bottom.
i believe most top ‘heaters’ are actually grills, meant to put a brown colour to the top of your ‘turkey’, and as such not very usefull for even heating.
Could differ per over though (but I know mine does this).
I guess the best guess would be to experiment.
If you get even heating (using only the bottom heater) in the upside down oven, great. If it goes sideways, go sideways!
Also scored some noodle packages that might fit your description to do some testing on (like washing it in a blender). If anything usefull comes from this, I’ll let you know.
Weekly update #2
Our second week is going well!We finally got this big oven; so we won’t have to build it ourself (precious time is saved!). We just removed the circuits we didn’t need (the four electric plates) and are now experimenting with the electronics. We also got the metal and car jack for the compression frame.
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I saw in V2 compression video that the oven was flipped by 90°, having the heating elements on the side. Is that better? We planned to use the oven racks to nicely melt our plastic in molds, on grids.
Also, if we don’t rotate the oven, I considered only using the lower heating element to avoid foil burning on the top, as it occured in previous experiments of this community. Any inputs?
We are looking forward to build this oven soon, and start crazy-melting stuff!
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Yes, some of these cheap shredders already overheat just showing it a piece of paper!
Re: dvds – as the plastic is not flexable, it almost needs to be grinded to dust for simple (non-extruder) uses. Most office shredders I know are merely meant to destroy the disc, so it can no longer be used, not to shred them into small pieces, like the paper, but I would love to stand corrected on this.
I’ll try to find a second-hand blender to test cds/dvds also according to the tetrapak setup. Would be easier if the printed foil did not have to be removed…
For starters I’m going to make pave part of my garden with plastic bricks (no, not gonna pave paradise, just the pathways ).
Why is this important to mention?
Well experiments are fun, but you should always aim for a product you can actually use, instead of crap you’re just gonna melt again !
P.S. mostly in research mode this week.
This is the shredder I used on the coffee & linseed wrappers. It is quite old, and was acquired for free a long time ago from someone who had bought a better one. The rating plate says 220-250v ~0.5A 50Hz, and that it shouldn’t be run for more than 2 minutes without a 30 minute cool-down. It was made in China.
Conversely, where I work, we have a large document shredder that can also shred DVDs – so much more powerful machines do exist.
Excellent point. Washing and shredding!
I actually once build a multiple blade office paper cutter, because I had to cut a lot of same size lamminated badges out of a printed roll (with space in between them).
Did work, but if you don’t need ‘same size’ you’re way faster just chopping them up with one cutter.
I’ve also tried to cut thin foil with an office cutter (for shrink wrap packaging).
Foil just folded over the edge, along the knife (unless you close it really fast).
A build like this might work better (with some tweaks (like using razor blades)):
Could also be hand cranked…
Yep, wet blending could be an alternative and could be combined with the washing step.
I was also thinking about something as an office paper cutter with multiple blades to shred our soft plastic.
@donald
About infrared, that’s the benefit of still being a student. I’ll try to document different alternatives for optical identification. But it doesn’t seem there’s a really low cost one.
Addendum:
I was just in my shed and I saw my sledgehammer.
I think I solved the problem of shredding my old dvds
Exactly.
Motor, (magnets,) rotor, figure out the optimal container shape for the optimal flow and see what happens!
Worse case it only works with tetrapaks, but that would already be a big plus!
If you can find/make a metal fan blade and connect it with a motor on the outside, convection should help quite a bit.