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Exploring quality in plastics


This topic contains 19 replies, has 7 voices, and was last updated by  Matthew milner 7 months 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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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!

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!

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 🙂

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!

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.

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.

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

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.

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.

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.

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.

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.

23/11/2017 at 00:57

Week 3

After seeing some great results with acrylic, especially as i passed light through them i decided to try create a cylinder.

This would then hopefully become a light shade at a later date. After much struggle i did finally manage to get it out of the mold. a couple of things i found out whilst doing this.

1 – to remove 1 cylindrical mold requires A LOT of force, too much for it to be safe to do again without risking damaging the plastic.

2 – Acrylic when cooled does not shrink! making it harder to get out of a mold.

To compensate for this i have cut the mold into thirds and will try again by attaching jubilee clips to the outside and a disk of some sort on the inner mold to retain its shape.

I also considered making cone shaped molds, however i wouldn’t be able to compress the mold the same way i have been doing as the shape of the mold wouldn’t allow me to create a ring that would fit.

23/11/2017 at 20:30

@oxygen220 I’m not sure I am following.. did you mix HDPE with acrylic plastic ?
If so, good idea for reasearching but very bad for the production of more plastic mixes 🙂
The cube looks really cool by the way 😉

28/11/2017 at 02:45

@armbouhali Im not mixing them no, i started with HDPE as it was readily available then i moved onto acrylic as my experiments developed. I also have a fair amount of the stuff as scrap i have been collecting from work as i have been looking for a way to make good use of it.

28/11/2017 at 03:07

Week 4

This week i changed the mold as it was incredibly difficult to get out. I cut it into thirds and held it together using jubilee clips. The mold worked and i was able to remove it straight after it had cooled. However it would be easier if i could bolt it together instead of having to rely on balancing the pieces in place.

I also used a different colour combination the second time around to experiment with what effects and control i can get out of this process.To some degree i am able to control where the colour ends up and how much there is, However i still had difficulty filling in all the gaps but this could be down to how tricky the mold was to put together.

Light shade-
To give the cylinder some life i decided to turn it into a pendant light shade. Of course this isn’t the only product the material could be good for but its a good example of using its translucency. Acrylic has some very nice solid properties about it, Such as holding an edge and polishing, which is similar to polystyrene.

28/11/2017 at 18:04

The lampshade looks so great! I hope that I will be able to make those someday too 🙂

02/12/2017 at 04:55

These videos might be helpful.

14/12/2017 at 17:11

Week 5

This is a post to conclude my research and development of exploring qualities in plastics.

Through this project i worked mainly with HDPE and Acrylic. I found that whilst experimenting with HDPE it was much harder to create something consistent and so i moved away from that and put my focus on the acrylic.

1. I took scrap pieces of acrylic from my work that i had been saving up as they would otherwise been thrown away and cut them into smaller pieces with a pair of pliers. I found that when melting HDPE it shrunk a lot and i would only get around 1/4 the amount i put in (volume wise). However with acrylic, this shrunk less and i was able to consistently create something much stronger with much greater structural integrity.

2. I tried several different methods of creating molds, The first “bowl” shape got stuck and i was unable to remove it without damaging the mold and the plastic inside.

I then moved onto using a square tube to create the form. This was to try create a block that would be easily removed by just pushing it out the other side. This worked much easier and i continued to use this method. (I also used Vaseline as mold release which helped a lot.)

My next take on creating a cylindrical mold led to a similar thing happening with the first, I used 2 circular tubes and a ring to create the first light form. This got stuck inside the tubes as it cooled and took a lot of force to remove. In the end i was forced to cut the inner tube out. I then cut both tubes into 3 pieces and welded pieces onto them to fix together with jubilee clips.

3. I decided with the forms i created to make a pot and a pendant light shade. Of course these are not the only products that could have been made with this method, there is a multitude of simplistic house hold products that could be created in this fashion and with relative ease.

I added a place of brass / copper to the top and a ring on the outside to hide the edge and grip the sides. This was a minimal, clean solution to creating these products that didn’t require over manufacturing them. It also highlights the fact that 95% of these products are made from recycled materials that would otherwise become waste that we can not dispose of properly.

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