How much insulation do I really need?
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?
Cork is bloody cheap. Why worry -- other than the fact that it's flammable. All that's needed to start a fire is having the thermistor fail or come loose. I'd use a flameproof material if you're going to insulate.
@CarlWitthoft - OK, thanks, this is the first time that I have really given thought to the flammability issues, although I had read that cork is preferable to silicon/rubbery insulation, due to less noxious fumes being given off.
@tbm0115 - :-) That really does look top notch, but is, unfortunately, a bit pricey.
@Greenonline I have to admit that you'd have the coolest looking 3D printer with some of that Classic Silica Aerogel insulating your machine!
@CarlWitthoft - As the ignition temperature of cork is 300°C, I wonder if there really is a fire risk. Do you know of any examples of burning, or scorching, of cork, when used as a heatbed insulator? Please see my question Has anyone experienced scorching or burning of cork heatbed insulation?
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.
Many thanks for the answer. I think that I see what you mean, but just to clarify a few points: By _diminishing returns_, you mean that each increase in insulation thickness gives a correspondingly reduced _increase in actual insulation_ (which, I guess, would make sense)? Are the figures of 100/75/60 W relating to the power used to maintain the heatbed at the same temperature (i.e. 70°C)? Without (necessarily) wishing to get into the mathematics too much, are those figures for the power, _guesstimates_ based on experience or did you arrive at those figures using a formula?
Yes, doubling the insulation doesn't double the power saving. The numbers are guesses, I need to work more on the maths for a real answer.