DIY Sheet press
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
So a couple observations.
Instead of heating the press, if it was pre baked it in a oven and then pressing with a non heated press ala the latest press should work better?
About to commit funds to this project but I dont want to go down the wrong path.
20 ton hydraulic jack will be fine? looking to press 1200x600mm sheets.
Also have you looked at silicone heaters? they claim operating temperature up to 250c with built in thermistor or k type thermocouple.
@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.
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…
@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.
@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.
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.
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.
I did some numerical approximations with the two-dimensional heat-equation and the results were somehow surprising to me (even though they are somewhat trivial).
Disclaimer: The following results are just qualitative approximations, do not rely on them. The values you can see in the pictures have no real meaning.
So basically I took a template for computing the 2D-heat equation in excel and modified it to my needs. On the first picture I set the conductive parameter to 1 everywhere, also on the edges. Also I set the temperature on the edges fixed to 0, which approximates the ambient temperature, so the edges are cooled by the constant temperature of the surrounding air. I also added the 16 heat sources, spread out similar to the real design. Then I played around with some parameters and after 140 iterations: Boom: Pic1. This is about the temperature distribution that we could see with our tests. a big hot circle in the middle, too hot in the center core and too cold on the edges and especially in the corners.
So for Pic 2: (looks promising, doesn’t it?) I kept everything as it is, except for the conductivity of the edges, which I divided by 10. So basically I mathematically insulated the heatpress on the edges. After the same 140 Iterations, the results are amazing!
However, as written before, the results should not be taken too seriousely, at least not the quantitative results.
I will try to improve the approximation by punching in realistic numbers for temperatures, conductivities, lengths etc. if I find the time in the near future!
all the best
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.
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:
I’m still faffing with my shredder, so just mulling things over at this point.
Just some ideas!
Ok, so I just read this:
Really nice thesis.
Those rams are a better starting point than the small jacks for a big set up I guess.
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.
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.
I’ve been looking into economical heated press solutions, and I was wondering how viable it would be to just combine two domestic electric griddles into a redneck press. The issue is that I can’t seem to find an affordable electric griddle capable of melting PET, which is the kind that I have an abundance of. They all seem to go to about 200-230°C, whereas the temperature needed to melt PET is around 260°C.
I also discovered something called an “oil core skillet” which intrigues me when thinking of its application as a reduced-cost, even heating solution for a heat press. I can’t seem to find any information on the manufacturing process, though. All I see it that it uses a double-lined bottom with a heating source suspended in silicate oil which distributes the heat throughout the metal without creating a hot spot.
Just thinking out loud.
PET is 230-240c
You will get a hard brittle plastic output.
Try a Tee shirt transfer press instead.
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