Why do flashlight get anodized?

[NoNotAgain]

Anodizing done in batch processing is extremely cheap to perform.

The military process Mil-A- 8625 type III is typically a natural color finish which varies from tan to olive green. Black anodizing is a dye added to the sealing operation.

Type III anodizing is a minimum of .002" thick and is done for abrasion resistance first, then corrosion resistance secondly. .002" doesn't sound like a lot of thickness, but that's per surface, so threads aren't the best thing for type III.

As for Ceracote, i'd do KG Coatings Gunkote instead. Can be performed at home and if you select the 1000 series material, it's room temperature cured.

Lauer Firearms offers a coating called Duracote. Duracote is Sherwin Williams Polane repackaged at five times the cost.

 

[MeMeMe]

No blanket on the outside. The anodize coating could act as a thin layer of insulation. I say could because some desingers build their ideas around the properties of the annodize layer to achive a more efficient conduit.

Black anodized aluminum has significantly better emissivity than bare aluminum and better than oxidized aluminum hence it will run cooler ... It dissipates more heat.

 

[Kestrel]

The issue with that reasoning is that while heat loss by radiation is to the fourth power of delta-T (compared to the third power of delta-T for heat conduction or convection) the radiative coefficient is far far smaller, so that aspect is relatively insignificant until delta-T is in the ~500+ Kelvin region.

Short version: for 'normal' temps relatively close to ambient, thermal radiation can be ignored for calculating overall thermal transport.

And for those admiring the 270W/mK thermal conductivity cited for single-crystal alumina compared to the high-300's for polycrystalline aluminum metal, please keep in mind the two following issues:
1) Thermal transport between adjacent grains of Al2O3 is very low due to poor phonon coupling.
2) Thermal transport between Al2O3 and aluminum metal is also very low due to inefficient coupling between electrical and phonon heat transfer.

And yes, this is my field of study

 

[Skaaphaas]

The issue with that reasoning is that while heat loss by radiation is to the fourth power of delta-T (compared to the third power of delta-T for heat conduction or convection) the radiative coefficient is far far smaller, so that aspect is relatively insignificant until delta-T is in the ~500+ Kelvin region.

Short version: for 'normal' temps relatively close to ambient, thermal radiation can be ignored for calculating overall thermal transport.

And for those admiring the 270W/mK thermal conductivity cited for single-crystal alumina compared to the high-300's for polycrystalline aluminum metal, please keep in mind the two following issues:
1) Thermal transport between adjacent grains of Al2O3 is very low due to poor phonon coupling.
2) Thermal transport between Al2O3 and aluminum metal is also very low due to inefficient coupling between electrical and phonon heat transfer.

And yes, this is my field of study

Woosh

Thanks for the answer, gave me a lot of stuff to go Google!

 

[MeMeMe]

The issue with that reasoning is that while heat loss by radiation is to the fourth power of delta-T (compared to the third power of delta-T for heat conduction or convection) the radiative coefficient is far far smaller, so that aspect is relatively insignificant until delta-T is in the ~500+ Kelvin region.

Short version: for 'normal' temps relatively close to ambient, thermal radiation can be ignored for calculating overall thermal transport.

While your analysis sounds impressive and you are correct that conductive heat loss, especially if hand held is dominant, heat-loss due to radiation while low, is not necessarily insignificant, when one considers the use case and the failure mechanisms for both LEDs and the electronics associated with them. True, for a handheld light that is use maybe a few 100 hours, it won't matter, but even for flashlight users, there are usage models where the difference is substantial ....

q = ε σ (Th​4​ - Tc​4​) Ah
​
Plug some real numbers ....

σ = 5.6703 10-8​
ε = 0.8
Th = 333.15 (60C - cause you tail standed on a table to light a room)
​Tc = 288.15 (15C - rooms a bit cool, but maybe you are outdoors and that number becomes lower)
​Ah = 0.015 = 3cm diameter, 15cm length -- It's a bit of a bigger flashlight, but still quite reasonable for a higher powered unit.

Total Radiative Heat loss = approx 3.5 watt

​Assuming that flashlight is sitting is tail-standing on a table, the heat loss due to convection is going to be pretty poor. The heat loss due to convection and radiation are going to be pretty similar, i.e. +/-50%. Since this is your area of study ... I am sure you can do the math yourself.

Now, with the emissivity of oxidized aluminum from 0.1 - 0.2, and the emissivity of anodized aluminum being 0.7-0.8, one can see quite clearly for this larger flashlight, the heat loss difference between anodized and non-anodized would be almost 3 watts. THAT is not insignificant.

For a 7W total heat loss (10 watt flashlight, LED efficiency low due to high drive, optic and electrical losses), the difference in operating temperature between 0.2 and 0.8 emissivity for our tail stander is going to be 10-20 celsius different. That is not insubstantial.

And for those admiring the 270W/mK thermal conductivity cited for single-crystal alumina compared to the high-300's for polycrystalline aluminum metal, please keep in mind the two following issues:
1) Thermal transport between adjacent grains of Al2O3 is very low due to poor phonon coupling.
2) Thermal transport between Al2O3 and aluminum metal is also very low due to inefficient coupling between electrical and phonon heat transfer.

And yes, this is my field of study

Not sure what relevant point you are trying to make? A higher number, i.e. high 300's versus 270, would mean that the polycrystalline aluminum would be a better conductor than single crystal alumina, but both these numbers are wrong. Aluminum is typically about 237, not high 300's, and single crystal alumina, i.e. sapphire for the less informed, is about 35-40.

https://www.azom.com/properties.aspx?ArticleID=1721

 

[Kestrel]

Ok, yes it is easier to get accurate numbers when looking up references; I happened to recall the TC for Aluminum Nitride rather than for Aluminum Oxide.

I did note your analysis stopped short of calculating heat flux - '10/20 deg cooler' doesn't appear to be a complete answer to the original query. Comparing heat radiation to convection during tailstanding is less relevant than holding the flashlight in the hand - i.e. conduction - which is closer to common configs, and helps keep flashlights significally cooler than from the contribution of heat radiation.

Not sure what relevant point you are trying to make?

If you were to bother with reading prior posts, you would see that component of my reply was to content from another poster rather than yourself - sorry to let you know that this thread isn't about you in it's entirety.

I'm just too busy to dig into the weeds with technical pissing contests, which is why I try to avoid posting in these threads. Please feel free to continue using 'The Google' for informing others here.

Best regards,

 

[thermal guy]

Lots of numbers folks. Lots of numbers. Anodizing makes the light pretty. Let's leave it at that😂😂😂

 

[bykfixer]

Way over my head.

I surmize that some anodize for a thermal benefits?

 

[archimedes]

Photons, phonons ... let's not get over-excited, they're all just wavicles to me :huh2:

 

[MeMeMe]

... or you could admit you were inaccurate and that yes I deed anodizing makes a difference. The 10-20c was from a quick simulation I ran. Too many variables to nail down a number so 10-20 felt honest. 20 is very realistic for the scenario given. It's my line of work too.

I provided a reference in case their was a question of my accuracy. It's best when telling someone else they are wrong and it is their area of study.

 

[thermal guy]

And it makes the lights look pretty 😂😂😂😂

 

[bykfixer]

And in the red corner wearing green and blue...it's the op.

And in the blue corner it's an administrator... wearing a ban hammer

:touche:...

 

[thermal guy]

And the rest of us are googling the crap out of whatever the hell it is there saying 🤔😃

 

[focusworks]

While your analysis sounds impressive and you are correct that conductive heat loss, especially if hand held is dominant, heat-loss due to radiation while low, is not necessarily insignificant, when one considers the use case and the failure mechanisms for both LEDs and the electronics associated with them. True, for a handheld light that is use maybe a few 100 hours, it won't matter, but even for flashlight users, there are usage models where the difference is substantial ....

q = ε σ (Th​4​ - Tc​4​) Ah
​
Plug some real numbers ....

σ = 5.6703 10-8​
ε = 0.8
Th = 333.15 (60C - cause you tail standed on a table to light a room)
​Tc = 288.15 (15C - rooms a bit cool, but maybe you are outdoors and that number becomes lower)
​Ah = 0.015 = 3cm diameter, 15cm length -- It's a bit of a bigger flashlight, but still quite reasonable for a higher powered unit.

Total Radiative Heat loss = approx 3.5 watt

​Assuming that flashlight is sitting is tail-standing on a table, the heat loss due to convection is going to be pretty poor. The heat loss due to convection and radiation are going to be pretty similar, i.e. +/-50%. Since this is your area of study ... I am sure you can do the math yourself.

Now, with the emissivity of oxidized aluminum from 0.1 - 0.2, and the emissivity of anodized aluminum being 0.7-0.8, one can see quite clearly for this larger flashlight, the heat loss difference between anodized and non-anodized would be almost 3 watts. THAT is not insignificant.

For a 7W total heat loss (10 watt flashlight, LED efficiency low due to high drive, optic and electrical losses), the difference in operating temperature between 0.2 and 0.8 emissivity for our tail stander is going to be 10-20 celsius different. That is not insubstantial.




Not sure what relevant point you are trying to make? A higher number, i.e. high 300's versus 270, would mean that the polycrystalline aluminum would be a better conductor than single crystal alumina, but both these numbers are wrong. Aluminum is typically about 237, not high 300's, and single crystal alumina, i.e. sapphire for the less informed, is about 35-40.

https://www.azom.com/properties.aspx?ArticleID=1721

That's really interesting. I've been toying with the idea of going cerakote on my next light design but I'm thinking the thermal properties of the anodizing are going to outweigh the irritation of its electrical properties.
Jordy

 

[lunas]

aluminum in the raw reacts quickly to form an oxide layer if raw aluminum is exposed to water it will react to form hydrogen and aluminum oxide. Aluminum oxide is largely unreactive and non conductive and harder than raw aluminum... So as a finish to give aluminum durability it gets anodized.
http://www.elementalmatter.info/aluminum-reaction.htm

IMHO aluminum is an inferior material to use Stainless Steel, copper, and titanium are far superior.

 

[thermal guy]

Lol I'm sorry I had to.

 

[Fireclaw18]

Why anodize a flashlight?

- It looks "tactical" (tactical flashlights must be black... at least that's how they're marketed)
- Anodizing makes a light good, especially when brand new.
- it helps protect from scratches. Of course the downside is while bare aluminum scratches more easily, the scratches are the same color as the aluminum so generally are much less visible than on dark-colored anodize.
- Dark colored anodizing radiates heat better than polished bare aluminum.

 

[MeMeMe]

That's really interesting. I've been toying with the idea of going cerakote on my next light design but I'm thinking the thermal properties of the anodizing are going to outweigh the irritation of its electrical properties.
Jordy

Not that familiar with Carakote, but in general, thin layers of paint while an insulator are thin so the thermal resistance is small. You need to balance that against the area of contact with your hand when handheld. The rough math is easy. Normal everyday paint has high emissivity and when stand mounted would run even cooler than anodized assuming a typical thin layer on a typical light. Handheld would need to work out.

 

[MeMeMe]

aluminum in the raw reacts quickly to form an oxide layer if raw aluminum is exposed to water it will react to form hydrogen and aluminum oxide. Aluminum oxide is largely unreactive and non conductive and harder than raw aluminum... So as a finish to give aluminum durability it gets anodized.
http://www.elementalmatter.info/aluminum-reaction.htm

IMHO aluminum is an inferior material to use Stainless Steel, copper, and titanium are far superior.

For lower power lights stainless makes sense but it is a poor thermal conductor and if polished has very low emissivity. It will run hotter than anything ... well except titanium.