Author Topic: Black Body Thermal References and Fraser's new Black Body project :)  (Read 1589 times)

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Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #25 on: February 05, 2018, 03:00:14 am »
NASA's plot if the four best performing paints. Krylon Ultra Matte Black (1602) is in the top 4 and thankfully easily purchased, unlike most specialist high Emissivity coatings.

Fraser
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #26 on: February 05, 2018, 03:14:19 am »
The Nextel paint is a suede paint, as found in cameras. It has a soft plush finish ! This explains why the Matte finish works so well. Not quite what I want on a thermal emission plate though.

Fraser
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #27 on: February 05, 2018, 03:44:53 am »
FLIR's comment on enhancing Emissivity........

http://www.flir.com/science/blog/details/?ID=71556

Who would hav thought that 'white out' correction fluid was useful in thermography eh ?  :D As the article says, the visible colour is not that important, more important is the finish. Matte is best.

Fraser
« Last Edit: February 05, 2018, 03:46:56 am by Fraser »
 

Offline SeanB

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #28 on: February 05, 2018, 03:49:50 am »
Looking at your scratches you probably will have to remove the plate, strip it down to bare metal and repaint it Fraser, those scratches reveal corrosion under the paint, which will flake off the rest with time as it progresses. Probably came from condensed water containing salts, that went through the existing porous paint and attacked the underlying casting. You will be best off ( unless you are happy with the small difference in temperature in spots) stripping off all, applying a decent thin layer of chromate primer to the well sanded metal and then putting a few even coats of the matt over the primer, probably around 6 thin even coats.
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #29 on: February 05, 2018, 04:12:04 am »
More comment on Krylon Ultra Matt Black

(2006)
A. The emissivity of Krylon Ultra Flat Black Paint is listed in the web site below as 0.97 at 5 um. I have recently used a 3-5 um InSb radiometric thermal imager to measure the emissivity. I sprayed the paint on a copper plate and mounted it on a cold finger of a variable temperature dewar with a calcium fluoride window. I rotated the dewar window so as to not back reflect. I measured an emissivity of 0.89 for the setup. If we exclude the reflection from the window (~0.04 x 2), this would give an emissivity for the black paint of ~0.97 in agreement with the web site.

http://www.infrared-thermography.com/training.htm

From this site.....

https://www.finishing.com/1600-1799/1670.shtml

Fraser
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #30 on: February 05, 2018, 04:23:32 am »
SeanB,

Many thanks for the helpful comments.

Indeed, I was expecting to recoat the whole emission plate.

Note however that the damage was caused by rough, uncaring, handling during the disposal process 😔

The unit had not been well protected in transit to MoD auction, and to me. It had a badly deformed base plate and radiator fin as a result of being dropped. Something entered the emission aperture and scratched the paint off. I did complain to the seller that none of this was mentioned in the auction listing but he was an awkward person to deal with at the best of times. Nil response, as expected. He is an MoD auction buyer who cares not a jot about what he sells, its condition, or serviceability. He just covers himself with 'sold as seen, untested'. Not someone I would normally do business with but these thermal source heads are uncommon so 'beggars cannot be choosers'.

Fraser
« Last Edit: February 05, 2018, 04:34:56 am by Fraser »
 
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Offline SeanB

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #31 on: February 05, 2018, 05:01:45 am »
I would suggest for the stripping of the existing paint is to contact somebody local who can do CO2 bead blasting, as that will safely strip the existing coating off the unit, and not leave any residue either. I would also mask off the plate as well before taking it there, after stripping off all parts, and make sure to put sacrificial screws in all tapped holes, and mask off the entire area other than the areas to be blasted with some painters tape and card, using a firm grip tape so that the beads will not peel it, and at least 2 layers on the edge where it will be exposed to the beads, and probably not on the front face at all, but around the sides. A clean front with a coat of paint, hidden by the bezel is not going to be a concern.

I did the same for having heater plates recoated with a non stick coating by a local ship repair company years ago, helped though that the one guy was living next door to me in the flats at the time, and we got on well. Got a nice well blasted frosty plate back with a nice green non slip PTFE coat on it, emissivity definitely changes as you go from the oxidised rough matt aluminium extrusion to the PTFE, and it normally runs around 140C with 5 200W cylindrical heating elements in the body. Did have to do a lot of helicoil inserts though, but the existing holes were in any case well worn, the bead blasting with fine grit just finished off most of them rather well, but I was planning on doing the inserts anyway, had already ordered the inserts for the lot, simply as the stainless inserts survive heating cycles better.

Might take a spare one, with a PT100 pocket adaptor instead of the Fenwal thermoswitch, put in a PID controller and run it off 40VAC instead of mains ( slow down the ramp) and see about giving the flat face a coat of mystery emissivity Aerolac matt black as a poor man's black body, seeing as I do have a couple of them spare. Not going to win any beauty contests though for looks.
« Last Edit: February 05, 2018, 05:07:35 am by SeanB »
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #32 on: February 05, 2018, 05:37:46 am »
Thanks SeanB :)

Beyond camera accuracy checks, a thermal reference can be a very useful tool to have around if experimenting with lenses, attenuators and windows :)

Fraser

« Last Edit: February 05, 2018, 09:31:28 am by Fraser »
 

Offline mahony

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #33 on: May 03, 2018, 08:32:16 pm »
Hi Fraser,
I am searching for high emissivity paint too. Seems like the nice Nextel 3101 c10 is available from a swiss company:
https://www.ibzagshop.ch/de_CH/e-shop/nextel-lackiersystem/lack/3101-nextel-suede-coating

Unfortunately the price tag is significant... 186 CHF per litre.  |O

Do you, or someone else have any experience with paint from those guys:
http://paints.labir.eu/

I think for my purpose this might be sufficient:
http://paints.labir.eu/paint/thermographic-paint-for-high-temperature-applications

Emissivity is claimed to be ~95+% except a small dip at 13µm. My current cheap rattle can flat black seems to be around 93 to 94% using a simple reflexion test with a hot soldering iron.
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #34 on: May 03, 2018, 11:17:36 pm »
Hi,

The 'official' high Emissivity coatings are expensive and hard to source, as you have found. The Nextel product is a surface coating rather than a paint. It is what you find in SLR bodies and is more of a flock coating. That is to say, it is furry ! This coating is VERY fragile and easily damaged if not protected from fingers or contact with other objects. Great for a lab, but not too practical elsewhere.

As detailed in this thread, I opted for the very Matt Krylon paint for my Black Bodies. Some other paints have very variable Emissivity characteristics across the LW thermal spectrum and at differing temperatures.

The paint you referenced looked interesting. It is the first I have seen that is easily available and claims to be specifically for high Emissivity thermal imaging applications. If you get that paint I would be interested to hear of your experiences with it.

Fraser
« Last Edit: May 03, 2018, 11:19:28 pm by Fraser »
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #35 on: May 04, 2018, 12:11:30 am »
I am in the process of ordering the LabIR high Emissivity paint for testing purposes.

Fraser
 

Offline mahony

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #36 on: May 04, 2018, 03:18:44 am »
So am I.
Just finish testing initial testing with my Arduino/Peltier based cheapo-DIY-Blackbody. Temperature control and stability looks good now I need some black paint ... hopefully a bit better than some std. flat black.
 

Offline Fraser

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #37 on: May 05, 2018, 06:53:00 am »
Nil response from the company today...... disappointing start.

Fraser
 

Offline mahony

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Re: Black Body Thermal References and Fraser's new Black Body project :)
« Reply #38 on: May 08, 2018, 04:58:51 am »
The same for me - maybe they are not interested in single can sales?
Do you have any reliable source in europe for some similar product? Otherwise I might just go with a can of Krylon Camouflage Ultra Flat Black - at least there is a German guy selling some of them on eBay...
 

Offline Spirit532

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It would be interesting to do a group buy of the Nextel 3101 C10 paint. The $187/l price is a bit painful, but think about it - how many liters of paint do you need to cover a dozen blackbody sources? It would probably end up costing ~$5-10 to cover a single emission plate of acceptable diameter.

However, it should be noted that, as per the datasheet, this is a 2-part coating that requires a thinner to make the right consistency, and a hardener to activate it.
The article numbers for those are "NEXTEL-Härter 6018"(hardener), mixed in 8 parts paint, 1 part hardener by weight, and the thinner is "NEXTEL-Verdünner 8061", of which an additional 10-15% are required for air spraying.

The coating itself is available here: https://www.ibzagshop.ch/de_CH/3101-nextel-suede-coating-14068-0015/7751
The hardener is also not very affordable: https://www.ibzagshop.ch/de_CH/e-shop/nextel-lackiersystem/haerter-verduenner/6018-nextel-haerter
The thinner has an acceptable price: https://www.ibzagshop.ch/de_CH/e-shop/nextel-lackiersystem/haerter-verduenner/8061-nextel-verduenner
 

Offline Fraser

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It is worth noting that I have yet to see a commercial blackbody thermal reference covered in the Nextel 3101 C10 coating. There is likely a very good reason for that as Such references are definitely not cheap so coating cost is unlikely the reason. All the reference sources I have seen or used looked to have a dark grey flat paint coating simikar in appearance to normal matte black chalkboard paint. I know it is more than likely the unobtainium 3M high emission paint coating though.

It would be possible to become the equivalent of a 'Voltnut' with high Emissivity coatings, but such is not necessary in thee real world. Even my most expensive industrial thermal cameras are still stated as +-2C accuracy under perfect conditions. The important factor in a reference plate is knowledge of its emission characteristics over a range of temperatures. The NASA testing has kindly provided that information for a number of paints. I am fortunate to own some very accurate spot temperature measurement and plotting equipment so I can check the temperature/emission characteristics of my references.

The classic accuracy check fir thermal cameras used at home is the 100C boiling water and 0C melting ice in water test. These provide some measure of confidence check without the need for expensive or exotic reference equipment. A PT100 RTD can be used as a water temperature check and the Emissivity of water is a known value.

Then there is the cheap and simple "Ambient temperature thermal reference" I previously detailed in this sub forum. With a decent PT100 RTD thermometer fitted, such would be a very useful test source. The Emissivity plate would beef to be tested though.

Fraser
« Last Edit: Yesterday at 11:39:15 pm by Fraser »
 


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