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Exploring quality in plastics

This topic contains 12 replies, has 4 voices, and was last updated by  Matthew milner 2 days ago.

Matthew milner oxygen220

Exploring quality in plastics

10/11/2017 at 19:57

Hi so i have a project for university where i am to explore plastics and find quality in the material.

I have a number of ideas and no real end goal at the moment other than, explore plastics and produce an end product.

Week 1, (so far)

I used a tuna can as a mold and just melted hdpe and pet over a fire. results for pet were surprising as it crumbled and shattered after it cooled, however hdpe seemed very promising.

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starter
10/11/2017 at 20:09

week 1 (update)

I decided to move forwards and made a sheet metal mold for a bowl/pot shape.

I also bought a mini oven for around £30 which easily gets above 200 degrees.

The results aren’t quite what i hoped for, so far the hdpe seems to have stuck to the sides of the mold and i couldn’t get the inner part out without breaking the sides of the “bowl”. However the bottom part created a thick solid disk of hdpe which is great!

If anyone has and suggestions on how to stop this happening and how to remove the mold easily making it reusable that would be great!

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helper
11/11/2017 at 02:29

Hey @oxygen220 🙂
Try going for a low temperature, it seems like your plastic have burned a bit. HDPE melts and sticks together just fine at say 180 *c. Your mold looks great, did you fill It up with Plastic? And was IT 100% clean?
Best from Denmark!

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starter
11/11/2017 at 11:12

Hey @anris, that may have been one of the issues, I put the temperature to around 200 to get it warmed up before lowering it down to 180.

The mold was as clean as it is in the top image, however my next test I will try make a cube on Monday where I have a new mold that can be pushed through a square tube.

This time it’s been cleaned of all oils that may have been there.

Thanks 🙂

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helper
12/11/2017 at 19:24

No problem @oxygen220
I found that the plastic sticks to the molds when the temperature is to high or its been to long in the oven. You relly just have to experiment.
The precious plastic team advised to use some mold release. To prevent the stickyness.
You can also experiment with other stuf, i heard that whats in danish is called “Vaseline” (picture one) could also work. Cant say i tried it myself.

You can see a cup i have been using for some tealight holders, and that allmost no matter what you will have a little bit sticking, but it still works just fine. (picture two)

Good luck, i hope to see some updates on the topic and how your projekt goes!

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starter
13/11/2017 at 20:43

Thanks @anris, I tried out some Vaseline, im not 100% sure how much it helped but i was able to remove this next piece from the mold i will post an update with what i discovered.

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starter
13/11/2017 at 21:06

Week 2

So i went backwards a bit as i feel making a bowl at this point was a bit too ambitious and i wanted to learn a bit more about the materials. So here’s a list of things i found out.

1 – the ratio is around 4:1 of cut plastic to compressed melted plastic.
2 – Vaseline helped to remove the block from the mold but will try with more next time.
3 – burning still occurred even at 170 degrees Celsius for 20 mins.

The goal for this was to use the square steel tube as a mold to create a cube which could be pushed through the other side when removed, however when compressed i got a really small amount out of it compared to what i put in. Even so, what i got out of this was a really nice solid block of HDPE, which when sanded with glass paper and finished with 6-800 grit wet and dry holds a really nice edge.

Burning was reduced significantly compared to my first attempts, and this type of mold worked really well.

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dedicated
14/11/2017 at 07:08

Hi, @oxygen220. Not sure what happens here, but it seems that the mould of yours is not so clean to start with or may be it turns this way.

You can do a wee test and add some plastic to an aluminium coke can, place in the oven for a bit and see how it turns up.

By adding layers I made this using an aluminium can

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dedicated
14/11/2017 at 13:03

Also putting a small draft angle on your moulds instead of using parallel-sided containers will help greatly in removing the parts.

Not sure why you are getting so much burning, it could be due to hot spots. Aluminium is a much better conductor of heat than steel, so could help to avoid this by distributing the heat more evenly. HDPE is still very thick when ‘molten’ perhaps you could try a lower temperature and taking the whole process much more slowly, 20 minutes might be trying to rush it too much. Also just because your oven says 170°C, it might not actually be, and the heating might not be even throughout.

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starter
16/11/2017 at 14:24

Hi @andyn, Thanks for the advice, i did a couple more tests today with similar style mold to the one previous, and attempted some modifications to the duration and heat. unfortunately making aluminium molds id beyond my skill set.

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starter
16/11/2017 at 14:31

Week 2 (update)

This time after the success of the last block i created i attempted something larger and with a different shape (a toy car). I learnt a couple of things from this.

1 – 165 degrees at 15 mins is enough to melt the plastic without burning, however next time i would leave it a little longer as some parts did not melt 100%.

2 – I will definitely need to apply more pressure quicker if i am to create something slightly larger, especially with something as large as the attempted bowl from previous weeks.

I also attempted to make something with a small impression (similar to a lego brick). The mold was difficult to remove, however when i did it did exactly as i hoped.

This means smaller products produced in this way is a viable option, and the optimal time and temperature for this would be 20-25 mins at 165-170 degrees.

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starter
17/11/2017 at 13:52

week 2 (update 2)

Continuing on what i found, After further inspection of the car it seems the entire inside wasn’t able to melt properly and just created a shell in the shape of a car.

So i tried again, this time i put in less, i just filled the mold to the top and let it melt down, this obviously yielded less than before and therefore created a smaller car form. I also used pieces of a plastic bag to see how that would meld together, however i believe it may have been a different plastic as it didn’t bond as i would expect to the milk bottle HDPE.

I also attempted to use some acrylic in the form to create a cube with a small steel weight at the bottom.

1 – Acrylic turns to a sort of gummy bear texture when at temperatures of 165-195.
2 – once around 210 the acrylic starts to bubble and melt
3 – To allow it to fully melt it will have to be at a bubbling state for around 3-5 mins. (I heard it bubbling and attempted to press the mold together too soon, this meant the top half was a solid piece yet the lower half wasn’t able to fully melt.)
4 – It would be advised to do this outside or at least with extraction.
5 – Sanding the edges of the acrylic creates a really nice smooth surface and you can see all the bubbles that formed inside.

Over all this development was a success, The acrylic “cube” turned out really well and holds the loose steel cube well. The car will also need a little more refinement to reduce burning and hopefully create a solid object.

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starter
18/11/2017 at 14:45

Week 2 (Update 3)

I was very pleased with the results i got from acrylic, especially after touching them up with a disk sander and some wet and dry paper. So i made a couple more experiments, this time without an iron weight in the bottom so the light could shine through much easier. I will later test this with some small led’s however my phone light was enough to demonstrate this. (Looks much better in person)

I also made a “cube” with some opaque pieces in. These seemed to not melt as well as the clear acrylic which created an interesting effect.

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