DIY Sheet press

Precious Plastic Machine Development
#1

Hi there!
We (preciousplasticvienna) are experimenting quite some time now making 300x300x2mm sheets (you can check our instagram for pictures) and now we want to produce bigger plates. (500x500x10mm)
Since that size doesn’t fit our bought 38x38cm sheet press, we will build one ourselves!

The press should:
– produce ~520x520x10mm sheets so that cou can cut off the edges to get 500x500mm output
– have both sides heated so we won’t have to turn it around
– have an exchangeable mold so we don’t have to wait hours inbetween producing plates
– be time efficient (30 mins per sheet at max. would be great!)
– consume at max. 3kW so we don’t need an extra plug (not the most important thing but would be great)
– not cost more than 500€ to build

my drawings: On the first you can see the rough overall design. There will be a carjack mounted on the bottom to build up the desired pressure. It presses together the two heated sides of the press.

On the upper right of the second picture you can see my idea of the heating. the small circles are short rings of a metal tube that are welded onto the base plate. Onto these rings wwe want to mount the heating coils that are used for injection and extrusion too. We are well aware this is not the most energy-efficient design, however it is the most doable and budget-friendly one we could find. We will compensate that with using good insulation.

On the third picture on top you can see the guiding of the heated moveable plate, we are not so sure whether we really want to include this since it is a big source of problems because of the small tolerance.
On the bottom right of picture #3 you can see the cross section of the mold for the sheet and on the bottom left holes in the base of the mold in order to get the sheet out after molding.

We will begin shopping for parts shortly and are happy about any feedback/ideas/suggestions etc.!

All the best
Flo

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#2

That’s awesome @flo-2
I have wanted to build a heat press using flat ceramic heaters for a while but have not had the time or money to work on it.

Hope your press give you great results.

#3

Updates on my research here.

 

We broke several car jacks.

 

Abandoning the screw type car jack for now.

 

Purchased a 3 ton airbag jack to get more pressure.

 

1750 kg rated car jack was not enough.

 

Using the c channel frame as the linear guide to keep the press straight.

 

Results by  mid November at latest.  Lots of projects in progress here.

#4

It seems that an Arduino or two, a few thermocouples and normally closed relays would solve your problems.

I’d have 1 thermocouple for the center along with a relay that could kill power to the center 4 heating elements.  Then I’d monitor and control those along with the ring outside in pairs.  So you’d have a front left thermocouple and corresponding relay to kill power to those 2 heating elements, the same for “front center”, “front right”, “right center”, “right rear”, etc.  Light up an LED when the whole thing is at your desired temperature.

You could even press automatically with a linear actuator to pump the jacks handle and a load cell underneath to know when to quit.

I could draw it up if my description isn’t clear?

#5

Dear flo2 .   “We will maybe go for a used pizza oven in the future, where we heat our plastic and then press it in a press that is just a press. ”
As you said , hope this could be the best way to solve many of your problems  . May use some heater elements to warm the press  plate .Heat it else where -some fumes may generate and  to take  care of your health .  pore it on the press tray with oil paper on both side  , use trolley for shifting to press     . I am not expert just a thought in my mind . Have a good day

#6

Great experiment. I think the turbo cooker is what they are selling as air fryer in the states. Same features, heater, temperature control and a fan. I think, a larger version could be made using a metal bladed fan and some of the typical heater/PID/TC hardware.
Great results.

I was surprised that the generic Chinese 12 ton or 20 ton hydraulic shop press isn’t available cheaply in the Philippines. It would make the build almost off the shelf.

Great work

#7

I’ve done some research after this suggestion and it seems the biggest complaint among affordable shirt transfer presses is that they don’t maintain a very high amount of pressure and are limited to around 15 minutes of use at a time.  Plus most sources I have found state that the melting temperature of PET is 500 degrees Fahrenheit (Wikipedia says >482) whereas the shirt presses generally only go up to 480 Fahrenheit. 🤷‍♂️
I think the biggest issue is that I really don’t know where to look for things. 😐

#8

PET is 230-240c

 

You will get a hard brittle plastic output.

 

Try a Tee shirt transfer press instead.

#9

regarding pressing pressure.  At the moment I do not have a proper press in the shop.  However I was pressing sheets of HDPE between 2 sheets of 3/4 inch phenolic plywood and standing on it.

 

2 ton car jack and a big hand wheel in a press?

 

I really need to experiment more with this.

 

My local motor supplier sells 12v motorized scissor jacks.  It may be something to check.

#10

after a lot of experimenting last week, We came up with some usable results.

 

Compared to the oven press which is just soo slow in my experience.

 

1, Melting HDPE in a turbo cooker, then pressing worked surprisingly faster than using a oven.  The air movement really made the difference.

2.  Melted HDPE sticks to teflon, and the cheap silicone baking trays.  yet did not stick to silicone spatulas.  It did stick to baking sheets but released when cool and released from teflon baking trays when cool but not when hot.

 

3 Extrusion and then pressing was the fastest and most energy efficient of all the methods we tried, although moisture will make bubbles much more this method than with the turbo cooker allowing the vapor to escape.

4 heat gun does work as well, but it is wasteful on power.  best to use it for heating up the end of the extrusion machine and bending beams/sheets.  We made several sheets from shredded HDPE.  It was kinda slow and using unshredded bottle caps resulted in a better weld.

5 mixing LDPE and HDPE resulted in a better product if we was going to make boats.  the added LDPE gave it a bit of flex and made it much harder to break.

6 Using unsorted HDPE color material, the end result is a greyish material with a slight red tinge.  Not exactly a pleasant color.  However with the addition of graphite powder.  I got a matte black color that also had a nice smooth feel,  It also adds in UV resistance.  It did not take much to change the color.  one hopper with 1table spoon. mixed directly in the hopper so as to avoid making extra messes.

#11

Ok, so I just read this:
https://repository.tudelft.nl/islandora/object/uuid%3A6a751140-cbcb-4830-89cc-21f418fdfa42?collection=education
Really nice thesis.

Those rams are a better starting point than the small jacks for a big set up I guess.

#12

Great discussion, and good to see some practical tests. A couple of thoughts that crossed my mind:

  1. How about using multiple cheap car jacks distributed beneath the press which are modified to be connected to a single hydraulic pump. Then you’d get even pressure at multiple lift points which should mean more even pressure. It may just require a single hole drilling and tapping to take a fitting to intercept the high pressure line to the ram. It seems to be possible to buy a 2 tonne jack for ~£20
  2. Have you considered using silicon heater mats? Some of them will hope with up to 300C. RS (never cheap!) have these 500W ones, but I suspect that they could be found elsewhere:
    https://uk.rs-online.com/web/p/silicone-heater-mats/0245685/
    I’m still faffing with my shredder, so just mulling things over at this point.

Just some ideas!

#13

Looks like a fun analysis. If your design is still similar to the sketches from last year, the heat transfer assumption at the plate perimeter probably won’t drive the temperature distribution when in use. If your Excel template can handle a control TC location(s) and use it for your heater zones, that and the assumption for heat transfer into the plastic should dominate.

Commercial thermal analysis software is pricey but you may find a free PCB analysis tool that can do a bit more than the Excel solver.

Thanks for sharing, it is nice to see analysis being done.

#14

Hi, new to this topic, but LOTS of fabrication experience.  I got no money so I can’t try this myself, but why not use combustables for your heat source?  It would have waaay more energy density per $.  People throw out barbques everyday.  The design of a barbeque is meant to distribute heat over a large flat surface as uniformly as possible.  Gas heat the plates, then press with a jack or a screw.  If you want to go the extra mile, you can use a thermocouple and some solenoids to control the flow rate to make it that much more accurate.  There should be a faster heat up/ cool down process, since you dont have heating elements that heat up/ cool off.

#15

great, if you have all this ‘engineering data’ and you’ve made it work, then good. can your share it or not ?

our thermaforming guy said there is no real good low-cost way to apply pressure equally over such size than pneumatics. but possible he’s wrong like me 🙂

#16

its quite easy to maintain even thickness.  just use  pins as spacers and some decent linear guides to keep it straight.

Again, I need valid engineering data here.

 

I cant spend $$ on research based on your words.

#17

@btmetz, btw. not sure it was your team but there was low-tech sheet press on Facebook. Would be nice if you could share back the files/drawings you have. That would go into a public PP machine publicly extendable/translatable library. Thanks a lot, awesome piece.

#18

@btmetz, I don’t need to apply math. The point was rather about the quality of your sheets (regular thickness, consistency, etc…). I have it really hard to figure a single way to maintain this properties with a single 20T tonne press. not even with 4.

#19

I really would like to see your numbers on this one.

 

I have seen presses doing entire truck frames in 3mm steel plate with 50 tons.  So unsure where your math comes from?

 

Plus the plastic is soft like bubble gum when hot, so as long as it is compressed in a timely manner before it freezes, we should be good…

 

 

#20

@btmetz , ’20 ton hydraulic jack will be fine? looking to press 1200x600mm sheets’, i don’t think so, as often hydraulic is brute force. you won’t get anything regular, that 20T jack will just cover a small portion, except you’re rich and you can effort steel plates with at least 4 cm thickness of that size, even though, it’s going to bend after 50 cm. possibly you have better results with 2 large rolls.