I have been looking at cork sheet insulation for my 200 mm x 300 mm aluminium PCB heatbed, by I am not entirely sure how thick it should be. There seems to be a trade off between losing a few millimeters of print height, and providing adequate installation.
I have seen 10 mm thick table mats, and then 5/3/2 mm thick cork insulation tiles. On some forums people say they use two 2 mm sheets beneath the aluminium heater and then another 1.5 mm aluminium plate under those, to hold it altogether (source: Re: Is a cork board necessary under the heated bed?).
Hopefully this does not come across as a how-long-is-a-piece-of-string type question. I am just trying to get the right amount in the first place whilst spending as little as possible, and keeping the mass/volume and height down. If someone else has already gone through the empirical adjustments themselves, then it might save me the time and expense of having to test various configurations.
- Would just 2 mm thick cork backing be sufficient?
- Is 10 mm overkill?
- Does silver foil backing help considerably, thereby enabling one to reduce the thickness of the cork?
Since 50% of the bed is uninsulated, you're definately into diminishing returns as soon as you start adding any insulation.
With that area, I think you are looking at 1.2W per kelvin for a 2mm thickness.
I'm guessing a bit with these powers, but roughly, maybe from 100 W un-insulated, 75 with 2mm, 60W with 4mm. You can get a reasonably accurate measure of the power by looking at the duty cycle of the heating element.
Actually, its not clear if your primary goal is to reduce energy/maintain a very high temperature, or speed the initial heating. You can place a temporary sheet of cork on top of the bed (preferably extending over the edges to prevent convection) and this will significantly improve heat-up times.