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
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.
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.
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. 😐
PET is 230-240c
You will get a hard brittle plastic output.
Try a Tee shirt transfer press instead.
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.
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.
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.
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!
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.
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.
@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.
@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.
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 , ’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 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.
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
@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
@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.
@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.
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.
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.
@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 : 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.
Hi, i can’t download the CAD drawings of the machines. I need help on that
@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.
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