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V4 Sheet-press – mould development

This topic contains 18 replies, has 7 voices, and was last updated by  Mark Bachrach 2 weeks ago.

7
Mark Bachrach markbertbach

V4 Sheet-press – mould development

11/12/2018 at 13:55

In this topic, I’d like to share all of the tests, experiments, prototypes and improvements concerning the sheet-press mould development.

I’ll be mainly working on:

*Mould release
*Structural integrity
*Simplified setup and fabrication
*Added functionality/ease of use

Please feel free to share all of your questions suggestions below.

more info about other topics within the topic of sheetpressing are found through this index topic: https://davehakkens.nl/community/forums/topic/v4-sheet-press-development/
Please keep the topic organised and put your info in the right topics.

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helper
13/12/2018 at 18:52
2

MOULD SIMPLIFICATION TEST 1.1

OBJECTIVE
Figuring out if the cut-off-edge is really necessary

SETUP

Oven: Pizza Oven (220 C) (140 min.)
Press: Small manual cold-press (50x50cm) (140min.)
Mould: See Pictures,50x50cmx 3mm sheet steel bottom with 20mm square stock frame. No cut-off edge. The lid is 50x50cm 1,5mm sheet steel
Material: PP, 4.2kg
Mould Release: Coconut Oil

Process
The oven is preheated,
The mould is cleaned and treated with the release agent,
The material is put in the mould,
The mould is put in the oven,
After 140min. the mould is put in the press,
After 140min. the sheet is retrieved.

Interesting stuff
* The lid did not release as easily as expected and parts of plastic stayed behind peeling small patches off of the sheet. — I think there was also some HDPE in the granulate —
* The bottom side did release quite easily — This is almost always the case —
* The thickness of the sheet was very consistent along the edge — The fat frame bars might have contributed to that —
* Cutting the sheet in halve revealed that there was still air trapped inside the mould — this might have to do with the simple frame bar, but maybe there is another reason —
* The thickness ended up .8 mm fatter than the frame, which is strange when you expect shrinkage — I think this was due to the press not being able to fully close the mould since too big of a surface area had to close down on the plastic that was spilling out. —

Conclusions
More tests are needed to confirm that the cut-off edge is really needed, the next test will explore a smaller thickness and subsequent tests will look explore overfilling, frame width and pressure

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helper
13/12/2018 at 20:07
1

MOULD SIMPLIFICATION TEST 1.2

OBJECTIVE
Figuring out if the cut-off-edge is really necessary for sheets with a thickness of 10mm.

SETUP
Oven: Pizza Oven (220 C) (100 min.)
Press: Small manual cold-press (50x50cm) (140min.)
Mould: See Pictures,50x50cmx 3mm sheet steel bottom with 10mm square stock frame. No cut-off edge. The lid is 50x50cm 1,5mm sheet steel
Material: PP, 2.2kg (But apparently a weird mix)
Mould Release: Coconut Oil

Process
The oven is preheated,
The mould is cleaned and treated with the release agent,
The material is put in the mould,
The mould is put in the oven,
After 100min. the mould is put in the press,
After 100min. the sheet is retrieved.

Interesting stuff
* The lid did not release as easily as expected and parts of plastic stayed behind peeling small patches off of the sheet. The lid stuck so much that I had to bend and destroy it in the process of peeling it off
I think the plastic I used was actually a mix of all kinds of weird stuff
* The bottom side would not release at all until I also decided to give up the mould and bring in the big guns, while retrieving I destroyed the entire mould, only the frame held up
I’ve never had this before, so I’ll never use weird mixes again and I’ll start looking into better release agents and solutions
* The thickness of the sheet was not very consistent throughout the sheet
this might have to do with the stiffness of the press or the weird mix of stuff
* Cutting the sheet in halve revealed that there was no air trapped inside the plastic
this might have to do with the smaller frame bar, but maybe there is another reason —
* The thickness ended up between 10 and 12 mm, which is thicker than the frame, which is strange when you expect shrinkage
I think this was due to the press not being able to fully close the mould

Conclusions
More tests are needed to confirm that the cut-off edge is really needed, the next test will explore more of the same but with extra attention to all critical variables.

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helper
17/12/2018 at 14:06
1

MOULD RELEASE SOLUTIONS TEST 2.1

 

OBJECTIVE
Figuring out what the best release agent or method is.

SETUP
Oven: Pizza Oven (200 C) (100 min.)
Press: Small manual cold-press (50x50cm) (100min.)
Mould: See Pictures,50x50cmx 3mm sheet steel bottom with 10mm square stock frame. No cut-off edge. The lid is 50x50cm 3mm sheet steel
Material: PP, 2.2kg (DVD cases, But apparently a weird with a lot of chalk additive)
Mould Release: Coconut Oil and the lid is only put on when the pressing starts, so pressing with a cold lid.

Process
The oven is preheated,
The mould is cleaned and the release agent is applied,
The material is put in the mould,
The mould is put in the oven,
After 100min. The lid is put on top and the mould is put in the press,
After 100min. the sheet is retrieved.

Interesting stuff
* Cold top pressing leaves an interesting surface finish on the cold side. The surface structure has a natural feel because of its randomness.
— I think the plastic solidifies and shrinks at the surface and starts to wrinkle and crumble up when the plastic underneath starts to flow because of the pressure, —
–the structure is not something I would like as a standard surface finish, but it could be aesthetically appreciated or useful in certain cases–
*The lid released far more easily than expected, it didn’t stick at all
— I think the plastic solidifies and shrinks at the surface contact before it has a chance to start a bond. —
* The bottom side also released with ease, but this is almost always the case
* A lot of warpage occurred
— this might have to do with the difference in cooling rates between top and bottom —
* Cutting the sheet in halve revealed that there was some air trapped inside the plastic
— This might have to do with the lack of a cut-off edge or maybe because of putting in too little material, but maybe there is another reason —
* The thickness ended up between 10 and 10.5 mm, which is nice
— I think the low viscosity of melted PP helps with spreading and closing fully—
*The sheet left a lot of rusty on the mould
–I think either the chalk has to do with that or the coconut oil contained a lot of water or the PP contained a lot of water–


Conclusions
*I’m not using coconut oil anymore it hasn’t worked for me so far and caused more trouble.
*I’ll need to find a reliable and typical batch of plastic to test multiple release solutions with, using HDPE would be good because of its habit to cause sticky trouble
*Cold top pressing doesn’t provide the results I want, but I’ll try to make it work in subsequent tests.

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starter
20/12/2018 at 23:02
0

Coconut oil might be burning off.  It starts smoking at 350f 180c and your ovens at 220c.

Refined soybean and sunflower oils have some of the highest smoke points, at around 450°F 232°C, and avocado oil’s smoke point is 520°F  270°C.

 

A fish&chip shop might be a good place to get cheap cooking oil.

 

A vacuum chamber would be great for pulling out those air pockets,  but complex to build.

helper
21/12/2018 at 04:01
0

following this one closely…. thanks for sharing

helper
07/01/2019 at 11:54
1

I still need to share 3 tests, but as a quick update, I found the ideal release agent: Silicone oil

it spreads easily, releases like never before and you only need a little bit and I think it’s available anywhere.

thx for the suggestions! would be nice to see if those organic oils render good results.

dedicated
08/01/2019 at 05:04
1

HI,  I developed a wood frame press a year ago, if you all are interested in the blueprints I have them in the Free DesignSpark Mechanical CAD program format.

 

 

 

 

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helper
08/01/2019 at 19:30
0

Great work Mark! Thanks for the great documentation.

Have you tried using aluminum sheet for the mold surface?  This is what I have been using to make smaller sheets. Sometimes I use a light film of WD-40 but have also had success with no release agent at all.  HDPE and PET came right out of the form without any sticking. PP can take a little bit of convincing but I think this is because the material I have been using is mixed and has some contamination.
You can see some examples on my IG page: https://www.instagram.com/preciousplasticusa/

Thank you for sharing your efforts!

dedicated
09/01/2019 at 05:53
0

you will just have to bite the bullet and get silicone mold release spray, or silicone spray lube.

 

Alternately some silicone car wax.

 

Here in the Philippines the mold release spray is 1usd a can and common because they use as a lube for sewing machines in the garment industry.

 

I have used silicone spray lube as well when I ran out of mold release spray.  It is greasier and more expensive than the release spray.

 

The car wax I have not tried, but I know that it makes re-painting a car very difficult without some serious work to remove the paint.

 

 

helper
19/01/2019 at 20:08
0

btw. this hydraulic press i have seen 2 months or so ago on youtube, aka ‘cold press’ is a little overkill and expensive and if not a little inefficient.

you could archive same (if not better) results by using a couple of MDF plates (5cm thick) and put a good length of a fire hose evenly between them. then you just need a standard compressor (with a beer barrel as extension, if needed) to pump all up, it gets until 8 bar and you have 99% evenly distributed pressure. works great, give it a try. bending is no problem either, nor will be a crappy build, its kinda self-adjusting.

for the release agent, bakers since use spray nowadays but i think the same stuff is good for plastic 🙂
g

helper
19/01/2019 at 20:35
0

@cgoflyn,

If I understand correctly, that is an extremely good and creative idea with effectively creating a large air bag/pneumatic press… As you say, it would result in an even distribution of pressure which would surely significantly lessen the required frame rigidity and thus weight and cost.

Or would it? You’d still more or less have a box frame to hold the panel/hose in place, and you’d have the same pressure requirements – the only difference would be that the pressure would be evenly distributed along the beam vs concentrated at the hydraulic jacks. Both would span the same distance and be secured at the ends in the same manner. I’ll have to look into beam deflection calculations for uniform vs point distribution of force…

I know nothing about compressors, so how would you size the compressor? Surely the total surface area/volume matters in some way…? What would differ between a 20cm x 20cm and a 2m x 2m press? With the same pressure requirements for the plastic, is it just a difference in the time required to fill it up?

I suppose that’s the case – pressure is pressure .. It’s easy to pump a road bike tire to 120psi with a floor pump, but getting a truck tire to 40psi with the same pump takes a long time (ive done it out of curiosity despite having a small compressor…)
On that note – and I’m just brainstorming – could you perhaps use a few truck tire inner tubes all connected to the same compressor? Maybe its necessary to be inside of a tire to keep it from exploding?

Any thoughts you have would be appreciated. And if you can find a link to the video you mentioned, that would be great as well.

helper
19/01/2019 at 21:50
0

hi, i’ve no pics or video anymore but it’s quite simple :
– cut the fire hose in equal parts to cover the desired area
– seal the ends (epoxy & wood discs is fine)
– connect each segment to each other (takes some while) with standard pneumatic pipes
– the final pipe goes to compressor

some other notes:
– you could go also with 25 mm MDF plates, if it bends you always can flatten it in many ways by heating it up again (hand blower)
– if consistent thickness is an issue, you can also build up solid barrels and roll it like pasta  through it 🙂
– compressor size: the smallest do about 8 bar for 60x80cm. 150L will probably do ok for 1.5 meter x 2m, you will have to try… no idea, just make sure it’s not running non-stop. if your deposit tank is big enough, pressure will be good enough for about the 20 minutes.
hope this helps 🙂

helper
19/01/2019 at 21:53
0

@cgoflyn, thanks!

I found a slew of articles/forums about building a press like this for making skis and snowboards, which is a much more difficult process, given the shape etc… They are heated presses and seem to use more pressure too.
One example: http://www.happymonkeysnowboards.com/MonkeyWiki/index.php?title=Monkey_Press_Construction

You’ve definitely got me thinking a bunch! Thanks again!

helper
20/01/2019 at 20:39
0

@nickchomey, my pleasure.

for anyone interested in material development (PP) aftermath, please have a look at this : https://www.youtube.com/watch?v=6XNvNH6Z_6w&ab_channel=HLNSupplies, would be nice to know this can be done with recycled plastic sheets. guess the sheets have to be done with the same material just and some finger crossing 🙂

dedicated
23/01/2019 at 07:37
0

I have been looking at tee shirt transfer presses here in the Philippines.

 

It looks as if one would be able to use a standard tee shirt press to melt plastic in a mold, then transfer it to a secondary press for pressing and cooling.

 

the secondary press could even be made from wood.

 

 

dedicated
24/01/2019 at 08:51
0

Hey guys.  I was in the area of Manila where they sell all the heat presses for tee shirts.  Its a huge arcade that basically sells all that kind of stuff for the entire country.

 

I stopped by a shop along the way to buy some hex bar for the shredder shafting and I saw they were selling these heat presses, kinda big 15×15 inches and sales guy said it could do over 250c. the Price was 8000 pesos which is 150USD.  Actually cheaper than Ali express prices.

 

So I got my hex shaft (ill do a different post on that one next week)  and coming back I was wondering if they had a teflon iron on release film.

 

Sure enough they did and I got a half square meter of it for 4 USD.

 

I took it home, fired up my iron (checking the temperature with the laser thermometer) and proceded to replicate the ironing bags demonstration.

 

To my surpise the teflon sheet worked even better than the silicone sheet.

 

I still used plywood with silicone as the base, but the top was the sheet of teflon.

 

It works the best out of all the things I have tried so far.

 

Super pumped here for out planned Precious Plastic Plastic Bag Working Group meetup on the 3rd of Feb.

 

I have a crazy idea of fabricating boats from shitty used plastic bags.

 

First experiment will be documentation, and trying to iron a sheet of plastic over a wood mold.

 

After we get our technique down, We will build a wooden form, and make a canoe from plastic bags.  Then test it in the neighborhood swimming pool.

helper
28/01/2019 at 10:41
0

Guys, I like your enthusiasm, but this topic is intended to discuss mould development for the cold press sheet-press, so please post all this other stuff in the right topic, I’d suggest here

helper
28/01/2019 at 11:05
2

thx @justinc

I did try aluminium moulds, however, aluminium sheets are more expensive and harder to come by. Also After a while, some scraping is required for cleaning and the aluminium will scratch quite easily. All of these inconveniences might not appear on a smaller scale but when pressing 4 sheets a day of 1.22m x 1.22m, these problems need to be handled. In my experience, steel is better suited since it is cheap, easily available, common to process and more wear and tear resistant.

Also, the sticking problems are only becoming an issue on a larger scale since the total sticking force will grow with sheet size.

for sure mixed materials cause the biggest problems, with 100% pure materials, sticking is not a problem, but with big batches of ‘bottom-up’ recycled plastics, there is always some contamination.

Just 2 weeks ago, I pressed a sheet with PP material that was sorted with a special magnetic density separation system to a 95% pure PP mix from Urban Mining, and the sticking problems were completely eliminated. Of course, the silicone oil also did its job, but comparing the sheet to sheets with the same process variables to other sheets with less well-sorted material mixes, the difference was apparent.

Btw, your work on Instagram looks awesome, very professional! did you make the sheets with a compression oven? what size are you working on?

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