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
I’m interested to know why you used band heaters instead of flat heating elements, those are designed for flat panels like the one on your heat press so heat spreads evenly and much faster, wasting less energy
@xxxolivierxxx you’re right, this is far from optimal! We chose to try this method just because of the cost, we couldn’t find any affordable flat heating elements that fit our needs. Only with cost of 500€+. We will try to make up for that energy efficiency loss with good insulation, let’s see how that works.
Hi, i can’t download the CAD drawings of the machines. I need help on that
That would be great if you could measure the power consumption. I’m building a type of press myself that I want to make as energy efficient as possible. (So it can run from solar electric, or low-capacity power grid). The thing is, there’s really no good data to compare it with.
WE FINISHED THE MACHINE TODAY!!! we assembled everything after some intense working days with sometimes over 13 hours a day of welding, painting, screwing, buying missing parts, insulating, connecting the electronics and all that stuff.
We also gave it a test run and it worked very well up to 180°C so far! More testng will follow. Our machine “Biggie” draws a maximum of approx. 3,6kW, however it won’t draw 3,6 kWh per hour! (less) We still need proper testing for these numbers.
We installed 32 heating elements grouped into two logical groups (top side and bottom side) with 1 Temperature PID and Thermocouple per side. Due to insulation with rockwool (temperature/fireproof up to 1000°C) Biggie keeps its heat quite well, which is a big ecological advantage.
In the following days/weeks/hopefully not months we will upload step-by-step instructions on how to build this machine, so stay tuned! More facts & figures will follow too!
All the best
Precious Plastic Vienna
I’ve got a few questions:
* What are the dimensions of your mould?
* How many tons is that jack?
* If you’ve successfully produced some sheets, does the pressure from the single jack seem to be adequate (no voids, square/flush edges, etc…)?
* Is the frame rigid enough to maintain its shape, and thus a uniform thickness of the sheet?
Thanks! Our mold Inside is 516mm squared, the outside is 600mm squared. The plastic is 10mm high and the mold is 55mm. The carjack can do 5 tons.
Since we finished building yesterday, as you can imagine, we haven’t made long-term studies yet 😉 so I cannot answer the other questions just yet. The Frame should be able to handle the 5 tons with ease. I did some calculations and the beams will bend a maximum of 1.55mm when applying full load. That is totally in the elastic part of the metal bars, so that should work.
@anne-barbier I think you under-estimate the power of about 3.5kW of heating power combined wirh modern insulation. As stated before we dud tests with up to 180 Degrees Celsius and it worked even better than I expected. It climbed straight up to 180 and stayed there with a tolerance of <1%. Thats good for melting Hdpe, but the higher temperature of 200-240 degrees for PP should also be easily archievable. So as an educated guess, 250 degrees should be archievable too^^ Updates eill follow.
All the best
@flo-2 : yeah, i guess so 😉 I’d have then one more question: is there a problem with getting flat heat elements ? Seems you have those heatbands from ali-express, 6Euro the piece. I am just asking because I couldn’t really find those on ebay or tc-direct.
@anne-barbier yes exactly, we have used band heaters. There are flat heating elements available too, but the ones we found are waaay more expensive (triple or quadruple the price of the band heaters) and that was just way out of budget for us, unfortunately. 🙁
@flo-2 gotcha, thanks! so a cheap variant could be then second hand kitchen heat plates for cooking, i think they should have even some PID controllers inside … never tried but will do soon.
First of all sorry for all the not-yet-fulfilled promises, we have got very little time itm and we like to invest that time into produceing things, but we will do, just be patient 😉
Experience so far:
-Temperature of 286 Degrees Celsius archeived. (max. tested)
-Metal likes to bend when heated. A lot. So don’t weld the heated frame to the metal baseframe. It will bend.
-After heating the mould needs to stay pressed for a smooth surface.
-5 tons pressure (carjack) is waaaay too little for 0.25 Square meters. Plastic doesn’t flow out quickly.
-heating from both sides and pressing at the same time causes air bubbles inside the material.
-Every little scratch or gap in the mold lets plastic creep into it and you’ll have a hard time getting the sheet out.
As I said, as soon as I find time, i will also do the electricity draw measurement and (try to) make technical drawings so you guys can learn from our Experience & mistakes even more.
All the best,
Precious Plastic Vienna
Power consumption: Pressing a 11mm sheet PP we need approximately 1kWh per sheet.
That’s quite much. Reason is a major design issue with our machine, I’ll try to explain:
(See first picture) Below you can see our arrangement of the heating elements on the heating plate. (black circles) and they each heat the plate (obviousely). So I drew arrows to the nearest 4 corners of each heating element. Here you can see the main problem: The inner parts get heated by 4 adjacent heating elements each. On the edges there are only 2 adjacent elements, on the corners only ONE…
So we have a very unevenly spread temperature. The yellow spot is the location of our temperature sensor, so all heaters heat until that space has the right temperature, then all the heaters stop heating even though the edges are maybe only heated to half the temperature of the middle section… That leads to a situation, where we can choose to either have the mid-section inside the green circle perfect and the rest still granulate, or heat the middle too much and have a perfect outside. Ideally the outside should be at least as hot as the inside, so all redundant plastic can flow out. That is not the case with our machine, so we get 11-13mm sheets instead of perfectly flat 10-11mm ones.
Also, as mentioned in the post before this one, the 5 ton carjack is way too little pressure for this area.
Our workaround will be an additional Temperature PID for each plate and to connect the four edge heating elements together and have an additional Tempsensor on the edge, so that these heaters heat long enough.
Even with this workaround we will not be able to have an eavenly-spread temperature. So unfortunately, we cannot recommend building this exact version of a sheet press. 🙁
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. Here in Austria, used pizza ovens cost from 400€, so totally doable. (We payed more than that for the heating parts of our machine)
I hope this experience helps you, if you have any other questions about this project, I am happy to help you!
All the best
@flo-2 thanks for the follow up on this project! However, I don’t think your pictures got uploaded. Could you try again?
Yes, it seems to me that without the ability to control all of the heating elements separately with PIDs or some other controller ($$$), putting the sheets in an oven at a relatively constant temp would be best. Having a fan for convection would help things a lot.
Another approach for a heated press could be to use a hot liquid inside of pipes but you’d probably need some specialized oil for it, or high pressure. Would have to heat it in a heat exchanger too. Totally feasible, and someday I’d like to try it and heat with a rocket stove, but its a pretty big project.
As for pressure, do you think it flows poorly because of the 5 tons being insufficient, or because the plastic isn’t completely melted due to the heating issues?
Also, similarly, in your previous comment you said that heating and pressing from both sides causes air bubbles – why is this the case? Does your design allow for excess plastic to flow out the sides (flashing)? This would require filling it with extra plastic and having a depth gauge/stopper to make sure it gets to the right depth.
I would love to see a video of the process if you have time!
Thanks again for all of the information! It’s very helpful.
One other thought – I wonder what would happen if only one large heating element was used? You could make a big oven-style element using nichrome wire – I don’t actually know how to do this, but know you can buy it and other types of heating wire and bend it as necessary. For that matter, given the size of your press, I wonder if you could literally just use a couple electric oven heating elements?
The idea is that if the whole thing was heated from the same source, perhaps it would regulate/distribute heat better on its own rather than create hot spots? I have nothing to base that on other than a hunch, and can see how it would suffer the same issues as the current design.
What about adding some sort of resistors or other device into the circuits for the central heaters or just make the outer ones more powerful to compensate? Or wrapping the outside edge of the frame with some sort of heat tape/heating wire to give extra heating specifically to the edges?
Or, depending on temperature variation, you could have the probe on an edge which would allow the edges to get hotter but risk overheating the center.
As for extra PIDs, you could presumably have just 3 or 4 – 1 controls the corners, 1 the edges, 1 the center.
@flo-2 Actually I think 1kWh is not at all bad for a sheet that weighs 2.5Kg. That’s about how much it takes to pre-warm a domestic oven to plastic melting temperature.
For comparison, my small heat press machine, (http://onearmy.world/community/forums/topic/new-take-on-the-compression-machine/) uses 0.074kWh to form an item that only weighs 50g. I think there are economies of scale here, The mould halves I’m using are relatively more massive compared to the item being formed, than the amount of metal you are heating to make the plastic plate.
Building on @nickchomey‘s suggestion to reduce the power of the bandheaters in the centre, a simple way to do this is just to wire them in series which will reduce each heaters power by half, no extra components required.
Adding a thick aluminium plate to each half of the press would distribute the heat more evenly, but would also increase the energy consumption.
@andyn – would wiring in series halve the power for each one in series? Or, more accurately, 1/n ? If so, perhaps wiring in series in pairs, or whatever combination is necessary to account for the heat differential from center to edge to corner.
Aluminum plate would work well too, but likely expensive and perhaps require redesign of the press
@flo-2 another question – how long does it take to melt a sheet? Also, do you leave it to cool in the press? If so, I wonder if it would make sense to make a removable mould that, once pressed, could be secured down and removed to cool elsewhere. If on a flat surface, I don’t see how it would deform – it would simply shrink relatively predictably (which could be accounted for in advance). This would surely increase output volume tremendously.
@nickchomey @andyn @anne-barbier
Thanks a lot for all your input!
Wow I really forgot about putting them in series… now I feel stupid :’D Thanks A LOT for that hint. We will probably do a mixture: Wire all the edges parallel to pairs of center pieces and an extra PID for the corners.
anne-barbier, thanks for confirming. 🙂
Due to the uneven heating the redundant plastic doesn’t want to flow out, so after preheating for half an hour we press 1,5-2,5 hours and then let it cool inside the press. We have designed the press to be operated with swappable molds, however without clamping down, the surface won’t be flat in the end… So itm we let it cool overnight with pressure applied.
As for shrinkage we have about 2% shrinkage with pp (52->51cm)
All the best
Yes, sorry I explained it badly. You are right, the formula is 1/n, I meant wire them in series in pairs, each heater then has half the voltage and half the current across it so each pair has half the power compared to a single heater before (each individual element has 1/4 the power, P=VI, 1/2*1/2=1/4, 2*1/4=1/2).
I think wiring any more than 2 in series would reduce the power too much, 3 would be 1/3 which would be 1/9th of 3 * 1
For the ones who don’t want to use band heaters 😉
Here are a few other options:
Cartridge Heating Element (10pcs, each 650w) 65 USD
PTC heating element (200w) (5usd) ( fixed to max temperature, watts will drop automatically when the temperature is reached, can not overheat.)
ceramic heater (750w) 18.90 USD
Please know that i have not tested the heaters, and i am not a specialist 😉
My heaters dont warm . Sonda work good . I have RX C700 it s that PID good?
Heaters dont heat , helppp. Is it problem Pid REX -C700? How to set it?
I used these Tempco Strip Heaters for a sheet/panel maker that I made. These seem to make much more sense to heat flat plates. They make them in all sorts of sizes. Just be aware that the ends do not heat up so you need to account for that in the design of your press.
With all that welding for support how flat is your face plates?
What if you had those supports and then say a 25mm aluminum plate bolted to the frame, loose to allow expansion, and mount heaters to the aluminum, this should allow the heat to be much more even and cool much faster. You could even use a small fan on the end of each of your square tube supports to help it cool faster.
The aluminum should be flatter than the steel, especially if you can find some mic6.
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