Comments on: Glastherm HT: Not So Good for Insulating Hotplates http://www.neufeld.newton.ks.us/electronics/?p=957 Sun, 08 Dec 2024 17:19:24 -0600 hourly 1 http://wordpress.org/?v=3.1.3 By: Luke http://www.neufeld.newton.ks.us/electronics/?p=957&cpage=1#comment-24983 Luke Thu, 29 Apr 2010 05:15:45 +0000 http://www.neufeld.newton.ks.us/electronics/?p=957#comment-24983 I'm not sure exactly how you would implement it, maybe some sort of shallow tray or mixed with high temp epoxy, but Aerogel http://unitednuclear.com/index.php?main_page=product_info&cPath=16_17_69&products_id=89 Would be a great substance, the link above it is pretty cheap, although in granular form. I guess the solid sheets are still pretty pricey. I’m not sure exactly how you would implement it, maybe some sort of shallow tray or mixed with high temp epoxy, but Aerogel

http://unitednuclear.com/index.php?main_page=product_info&cPath=16_17_69&products_id=89

Would be a great substance, the link above it is pretty cheap, although in granular form. I guess the solid sheets are still pretty pricey.

]]> By: Leon Matthews http://www.neufeld.newton.ks.us/electronics/?p=957&cpage=1#comment-24929 Leon Matthews Tue, 20 Apr 2010 20:17:20 +0000 http://www.neufeld.newton.ks.us/electronics/?p=957#comment-24929 Oh dear, sorry to hear that... The Glasstherm sandwich was such an elegant solution -- I really wanted it to work for you! :-) Oh dear, sorry to hear that… The Glasstherm sandwich was such an elegant solution — I really wanted it to work for you! :-)

]]> By: Keith Neufeld http://www.neufeld.newton.ks.us/electronics/?p=957&cpage=1#comment-24927 Keith Neufeld Tue, 20 Apr 2010 12:18:10 +0000 http://www.neufeld.newton.ks.us/electronics/?p=957#comment-24927 I ran another test last night, with the heated platform sitting in its desired orientation on top of a loose piece of plexiglass on top of my spare Glastherm (like the acrylic mounting plate sitting on the Y stage). After running it up to target temperature, I picked up the heater "sandwich" using a pair of pliers on a corner of the plexi, and the plexi sagged significantly -- it was quite warm. Too warm, I conclude, to use with my real acrylic mounting plate in the real machine. I ran another test last night, with the heated platform sitting in its desired orientation on top of a loose piece of plexiglass on top of my spare Glastherm (like the acrylic mounting plate sitting on the Y stage).

After running it up to target temperature, I picked up the heater “sandwich” using a pair of pliers on a corner of the plexi, and the plexi sagged significantly — it was quite warm. Too warm, I conclude, to use with my real acrylic mounting plate in the real machine.

]]> By: Keith Neufeld http://www.neufeld.newton.ks.us/electronics/?p=957&cpage=1#comment-24926 Keith Neufeld Mon, 19 Apr 2010 20:50:51 +0000 http://www.neufeld.newton.ks.us/electronics/?p=957#comment-24926 Aw, Leon, there you go reminding me that I've forgotten everything I learned in my college thermodynamics class. Thanks a lot! :-) Seriously, I did consider that temperature alone doesn't tell the whole picture and it's thermal conductivity and heat transfer that matter. Your impedance analogy is elegant and excellent, and I'll remember that for future explanations! I know that getting acrylic to "sag" or warp takes much less heat than getting it to melt, because it doesn't involve a phase/state change from solid to liquid. Where my weak knowledge of thermo fails me is this: Are we basically comparing the thermal conductivity (impedance) of the Glastherm to that of the acrylic? If the acrylic is (enough) more thermally conductive, then what heat leaks through the Glastherm will dissipate out the edges of the acrylic without melting it? If the acrylic isn't conductive enough, then what heat leaks through the Glastherm will build up in the acrylic and warm it enough to sag/warp? Aw, Leon, there you go reminding me that I’ve forgotten everything I learned in my college thermodynamics class. Thanks a lot! :-)

Seriously, I did consider that temperature alone doesn’t tell the whole picture and it’s thermal conductivity and heat transfer that matter. Your impedance analogy is elegant and excellent, and I’ll remember that for future explanations!

I know that getting acrylic to “sag” or warp takes much less heat than getting it to melt, because it doesn’t involve a phase/state change from solid to liquid. Where my weak knowledge of thermo fails me is this: Are we basically comparing the thermal conductivity (impedance) of the Glastherm to that of the acrylic? If the acrylic is (enough) more thermally conductive, then what heat leaks through the Glastherm will dissipate out the edges of the acrylic without melting it? If the acrylic isn’t conductive enough, then what heat leaks through the Glastherm will build up in the acrylic and warm it enough to sag/warp?

]]> By: Leon Matthews http://www.neufeld.newton.ks.us/electronics/?p=957&cpage=1#comment-24925 Leon Matthews Mon, 19 Apr 2010 20:28:51 +0000 http://www.neufeld.newton.ks.us/electronics/?p=957#comment-24925 I'd suggest re-running your experiment with an test piece of acrylic on the 'cold' side, as per your original mounting plan, just to be sure that the measured temperature is really an indicator of a problematic amount of thermal energy. Honestly, I don't know what will happen to the acrylic, but I do know that readings from a high impedance sensor like your thermometer can be misleading when dealing with insulated heat sources -- much like using a very high impedance digital multimeter on transient voltages. Insulation is all about retarding the movement of heat energy, temperature (like voltage) by itself does not give you the full picture of how much damaging heat energy there actually is at the face of your insulation... Try touching the 'hot' Glastherm with your finger for a quick and dirty experiment (although maybe not at your heater's full operating temperature -- just to play it safe... :-) I’d suggest re-running your experiment with an test piece of acrylic on the ‘cold’ side, as per your original mounting plan, just to be sure that the measured temperature is really an indicator of a problematic amount of thermal energy.

Honestly, I don’t know what will happen to the acrylic, but I do know that readings from a high impedance sensor like your thermometer can be misleading when dealing with insulated heat sources — much like using a very high impedance digital multimeter on transient voltages.

Insulation is all about retarding the movement of heat energy, temperature (like voltage) by itself does not give you the full picture of how much damaging heat energy there actually is at the face of your insulation…

Try touching the ‘hot’ Glastherm with your finger for a quick and dirty experiment (although maybe not at your heater’s full operating temperature — just to play it safe… :-)

]]>