recommend a dark temporary coating

Discussion in 'Off-Topic' started by strantor, Apr 28, 2014.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    I've used my thermal imager only a couple of times now in the line of duty and already encountered the "emissivity" problem. Doesn't accurately measure shiny objects. I was thinking "if I had an acetylene torch, I could just turn off the oxy and coat this bad boy with black carbon, that would wipe right off." But I didn't have a torch and even if I did, I don't think my customer would get a warm fuzzy feeling watching someone who they undoubtedly presume to be a mechanically incompetent wire biter aiming a flame axe at their megadollar extruder barrel. Plus I wouldn't like to carry around heavy bombs in my car all over town either when they would be rarely used.

    So I want something less crazy; I'm imagining an aerosol can full of some magic substance like the carbon that a torch would deposit, or a jar of dust thats brushed on like how they dust for fingerprints in the movies. Something that wipes right off (or blows off with compressed air would be better) and won't cause problems for mechanical devices (ex: a gritty powder that would damage gears) and wont cause problems for electronics (nonconductive). Maybe a colored tape, but preferably not; I foresee issues with it not conforming to changing surfaces (anything that's not flat) and not sticking well to oily surfaces or melting to hot surfaces.

    I this sort of a preemptive request. I haven't dedicated much time to researching yet, thought this oost might save me some time if anyone here knows what I'm talking about and where to get it. I looked briefly and everything I saw was high emissivity permanent coatings.
     
  2. strantor

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    Something like a machinist's blueing that has high emissivity
     
  3. alfacliff

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    Dec 13, 2013
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    there is a product called "sight black" available at gun shops, used to blacken the sights of guns. it wipes off easily, just like the carbon black it replaces. I think the mfgr is "Birchwood Casey" but might be wrong.
     
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  4. strantor

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    Hey, that looks perfect! Thank you!
     
  5. shortbus

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    The flame of an ordinary candle will also put soot/carbon on a surface. Gunsmiths use it when fitting parts.
     
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  6. ErnieHorning

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    Apr 17, 2014
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    Simple, just use a black dry erase marker. It wipes right off.
     
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  7. THE_RB

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    Doesn't need to be black.

    I use white stickers and liquid paper (which rubs off metals easily).

    Liquid paper has the convenience of coming in a little bottle complete with paintbrush. It depends how big you need to make the spot?
     
  8. Duane P Wetick

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    Apr 23, 2009
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    Gaffer's Tape available at many AV stores is used by Cameramen to secure cables and props and carrys a very low emissivity rating. It looks like black duct tape.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  9. Biff383

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    Jun 6, 2012
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    Spray on dry film graphite lube would work. And has other uses in the field.
     
  10. atferrari

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    Is it easy to eliminate later?

    My experience with graphite is more than limited but I learnt that it is a pervasive thing.
     
  11. shortbus

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    Something else that might work but isn't black, milk of magnesia. When still working, we put it on cartridge heaters that were used in plastic and rubber injection molds. They make a commercial product that's pretty expensive, but the chemical in it was, magnesium hydroxide, milk of magnesia. This was used to make the heaters easy to remove when they burned out. It also helped with heat transfer as a secondary use. It wipes off easy when dried out.
     
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  12. GopherT

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    Nov 23, 2012
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    Baby powder, talc, corn starch, gypsum, chalk, dry erase markers, hair spray, carbon black (lamp black), tempra paint powder, ...

    almost any fine powder will work. Depends on temperature (corn starch will ignite in a dust cloud, for example) and not all powders will stick to smooth surfaces - especially if they are vibrating with motors.
     
  13. ErnieHorning

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    Apr 17, 2014
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    Not sure how accurate the temperature measurement is going to be with something that you can just blow off. Have you actually tried these and know that they’re within a degree or two?
     
  14. GopherT

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    I didn't mean to make plaster casts with the stuff. You just need a very thin layer to tame the reflection. Essentially the same question as, "do women who wear a thin layer of makeup record lower body temperature than non-makeup wearing people if measured with an ir thermometer? ". I assume the thickness is negligible (especially if there is no oil carrier in the powders suggested above.
     
  15. Wendy

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    Mar 24, 2008
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    Something I've wondered. Black, flat black, would seem to be an important component for emissivity. Anything else would through the readings off, seems to me.
     
  16. THE_RB

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    Assuming it reads IR the same way a non-contact thermometer does, the colour is not that critical. It's more about the reflectivity and makeup of the surface, if it is shiny metal or not.

    I use paper stickers, matte or gloss does not matter and white is fine. I discovered that after testing stepper motors that the metal body of the motor would not give a good reading but the little specs sticker on the motor body read just fine.

    Any paint should work fine, and any colour. But anodised metal won't, even black anodised which is a bit counter-intuitive since it is a matte black and you would expect it to be ok.

    And a solid aluminium surface won't read, but if it has a tiny aluminium foil sticker on it, that reads fine! Go figure. :)
     
  17. ErnieHorning

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    Apr 17, 2014
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    The visible color doesn’t matter; it’s what’s emitted at the IR range. Most automobile windows now, don’t pass IR or UV but they used to. Cars used to get to almost 200°F with the windows up on a sunny day; might get up to a little over 100 now. I’ve used black project cases that passed IR just fine too.

    Black anodizing doesn’t pass IR but simply wiping it with black magic marker or dry erase and it would work just fine. I’ve seen where some of the round stickers that we used to place over an EPROM window would pass IR while some wouldn’t.

    Try measuring a dark colored ceramic resistor sometime. I’ve seen it measure around 100°F, while touching it will burn a reverse image of the manufacturer’s logo on your finger. So you know it's over 140.

    Close enough isn’t going to do it when a transistor measures 120°F when it’s over 150.
     
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  18. THE_RB

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    Do you have a contact thermometer too? I have both types at hand (contact/non contact), as it's important to know your measurements are correct.

    You can contact thermometers from ebay quite cheap, and you can order lab grade glass thermometers from the Pharmacy to check the calibrations. :)
     
  19. GopherT

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    If a 5 degree error (or there about) is not acceptable from a thin piece of tape, or less from a dusting of powder, then the user needs a better thermometer - one with an on board emissivity control.

    Shielding possible emissions from hotter objects that are nearby also help.
     
  20. ErnieHorning

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    Apr 17, 2014
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    I work a large company and have access to a variety of high and low end equipment.


    I believe we still have a National Standard glass thermometer around somewhere. It’s a calibrated one that about two feet long, marked at .1°F increments.

    Typically, I just use thermal couples that are accurate to 1°F. You can attach them with Cyanoacrylate (Super Glue) and press id down so you get a good contact. It’s good to 180°F, it works well with electronics. For higher temperatures (HALT testing), JB Weld is good 500°F but its permanent unless you want to grind it off.

    I find that most infra-red thermometers give inaccurate temperatures. They also differ in whether they work with a particular object. So placing a particular piece of tape or powder may or may not work with two different models or brands.


    Most of the time, I can tell if a silicon part is in normal range by just using my sense of smell and a finger touch. 140°F is where you’re not going to get burned but you feel you feel uncomfortable in holding it there for more than a few seconds.
     
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