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.

    If you really want to go all out for insulation, buy some aerogel!

    @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?

    Burning cork is difficult even when you WANT it to burn... Cork is the outer layer of trunks and has specifically the goal of protecting the plant from fires. I would say almost no flame risk.

  • 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.

    Also consider cork on top of the bed during heating.

    Yes, that is a good idea... I remember reading somewhere that someone suggested even corrugated cardboard helps.

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Content dated before 7/24/2021 11:53 AM