It would be very useful to know how much pressure (PSI, kPa, etc…) is needed to make a quality sheet in a sheet press.
I’ve seen estimates from 5psi to 100psi. Some presses use small springs or concrete blocks and others use 4 hydraulic jacks.
Does anyone know what is actually needed?
Hey, there are mixed infos about but I know from the v4 Sheetpress developer, Jason that 5T is a good start. The size of flakes and sheet thickness will have their play too. I’ve seen also good results on smaller sheet presses such as Cassandra-Light, using a 3T jack.
Thanks! Though this just adds to the confusion… The Cassandra has up to 18psi (5 tons on 560sq in).
Meanwhile, this official machine uses 10kpa or 1.5psi, or 0.75 tons Start a Sheetpress Workspace to Recycle Plastic
And, again, ive seen some that say enormous amounts are needed…
I think I really just need to do some experiments myself… 4 years ago when I first started thinking about this stuff I did some small testing melting shredded plastic in a roasting pan in my oven, then quickly brought it outside, put a thick hardwood sheet and jack stand on top and put it under the rear axle of my truck that was jacked up. I figure it was about 1.5 tons of weight on 192 sq inches (12x16), so 15.5 psi… The sheets were pretty good, though the surface was a bit rough and shards weren’t quite as fused as I’d have liked.
Yet, given that some PP presses use considerably less pressure, I suspect that it just wasn’t hot/melted enough rather than not being enough pressure.
Moreover, I intend to make a hot press which will surely result in better melting and fusion.
Ideally I’ll be able to find a minimum necessary pressure and be able to build the frame in a way that minimizes steel costs while maintaining flat/uniform sheets without deflection of the press frame/platform.
Hey,
yes, we’re apparently still in the dark about the real numbers, mix, etc… granted 
We’re finishing another hydraulic-based sheetpress end of this month (here the progress) . There is a gauge to read out the pressure. I am using a bit more efficient and denser heat grid (penetrating the plate by half the cartridge heater diameter).
For what thickness and material are you aiming? Perhaps I can re-produce something here …
Fancy stuff! I will be building something considerably more… rustic…
I’m looking to use PP, PE and maybe PS. Probably up to 3/4" or 19mm. Ultimately I would want to make full sheets of plywood - 4x8 feet or 1.2x2.4 metres.
But, I figure that the thickness and dimensions don’t really matter all that much.
It would be cool if you were able to do a few tests with different melting temps and pressures to see what is truly the minimum required pressure. I figure that higher temps will result in lower pressures as it will be less viscous.
If you have a spare press, it could even be interesting to see what would happen if you melted it under minimal pressure and then pressed it in the spare/cold press. I suspect that pressure while heating/melting would be both faster and need less pressure to produce quality sheets.
Perhaps all the testing isn’t all that necessary for you to do, but it would be valuable information for people in general - future designs with less steel might be possible.
1.2x2.4 meters is quite a challenge but has been often requested. With the current method, thats about 30kW.
Thickness actually matters, as far I understood. It’s slowing down the cooking when increasing. On the injector, it was about 20-40% longer, going from 25 to 30mm barrel diameter.
However, I am curious how far we can go with temperature. I need a bit more data as well, also to go for blow moulding as next : Blow moulding 1800mmØ acrylic dome. 900mm high hemisphere - YouTube
Okeey, will update the other thread and the library as soon I’ve got finally something going. Oil heating next (used on industrial presses)
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Yes, the thickness would affect how much energy is needed and probably the speed of processing, but shouldn’t affect the pressure requirement.
Have you done any work with oil heating yet? It’s something I’ve been considering and seems to be the best solution. Could even use a waste oil burner rather than LPG or electricity.
oil heating, not yet - just started digging, doesn’t look too hard and the heat-loss could be minimized as well.
and yep, gas heating could do as well, it’s just a boiler after all. there have been a couple of ideas to make a PID for.