AcuraTLFan

I want to paint my brake calipers...but i don't want to spend $60 for the paint kits...just want to get s $5 can of engine paint. The problem is, i don't know if the 500 degree F engine paint will withstand the heat produce from the brakes, can anyone tell me if 500 degrees is alright...thanks

edgalang

Hey..thats what I wanted to do myself looong ago. But be forwarned! Apperantly if you do ANY visual changes what so ever, that you'll be labeled as "riced". Keep me posted.

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2002 3.2 TL Type S with Navigation
Exterior: Aegean Blue Pearl
At 3% over invoice, who can complain?

Bitium

Probably not!!!!

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bbjones

Yay! it's Physics Time!

Suppose you were to brake from 60 mph to zero, and that all of your kinetic energy went into the brakes. (Bad assumption that we will revisit later.)

60 mph = about 27 m/s. E = 1/2 m v^2, so your total energy is 560,000 J (your TL-S has a mass of around 1600 kg). Remember from physics that E = c m delta-T, where c is heat capacity, m is the mass of the thing you're heating (the brakes), and delta-T is your increase in temperature.

Assume your brakes are made entirely of aluminum. (Bad assumption, we'll revisit later). Just guessing, I'd say the calipers, pads, and rotors are about 4 kg per wheel. A Google search yields the heat capacity of aluminum: 900 J/(kg K). So, put it all together and you get:

delta-T = 560,000/(4*4*900)

(4 wheels at 4kg each)
That works out to be about 39 kelvin (=celsius) increase, or 70F.

So, if all our assumptions are true, your brakes should increase by 70F. Bad assumptions we made: All energy goes into brakes. Actually, a lot goes into the tires, as well as the other losses in the car. So that would make the 70F even smaller. Another bad assumption: it's all aluminum. Your brake pads are made out of asbestos or some equivalent that has a much higher heat capacity, thus bringing down the 70F even more. Maybe bad assumption: my guess on the brake mass. If it's a lot smaller than that, the 70F will go up. Always a possiblity: I made a math mistake. But someone will check me, I'm sure.

Bottom line: even Arizona temps of 110F + 70F is way less than 500F. Your engine paint should be fine.

Ain't physics grand?

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2002 Acura TL Type-S Dark Emerald Pearl
1986 Pontiac Fiero SE V6
1994 Ford Explorer 4x4

SoundSpeed

Very nice. (If you are right)

Bitium

bbjones is so stupid unless he was Joking!!! He is NOT RIGHT. Just one fact:
Boiling point in Fahrenheit is 212 degrees. Boiling point means water turns into gas. Do a little experiment and spray water to your rotor or caliper, you will see smoke(gas) that means is at least 212 degrees. Get it. Oh and that is just at stop. Now does this look like 170 degrees to you:


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bbjones

212F is only 40 degrees more than 170F. It wouldn't be too hard to make several runs (i.e., 0-60-0-60-0-60-0) very quickly, and get your calipers hot enough to boil water. I doubt it happens in regular driving, but I'll toss some water on mine after I drive home from work today. In any case, 212F is a far cry from 500F.

As for the picture, well, that's clearly not taken under normal driving conditions. If brakes glowed like that normally, driving at night in traffic would be quite a sight!

-the stupid guy



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2002 Acura TL Type-S Dark Emerald Pearl
1986 Pontiac Fiero SE V6
1994 Ford Explorer 4x4

TL Daddy

I painted my rusty rotors using 1500 degree Rust-O-Leum Black and my calipers with normal Rust-O-Leum in Blue - still looks new after 6 months. The rotors are what gets hot - you won't need engine paint for the calipers, but it won't hurt either.

bbjones

Here's a reference to a book that lets you calculate these things, presumably in a more careful way than I did.

The following is a quote from the link provided below:
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The "Brake Handbook" (Fred Puhn, HP Books) tells how to calculate average brake rotor temperature rise for one stop (or slow to a lower speed). A couple quick calculations, using my M5 as an example, gives a good feel for the increased brake stress from performance driving.
Average Rotor Temperature Rise for 88 M5

40mph to stop 43 F (moderate)
80mph to stop 172 F (hard)

120mph to 40mph 344 F (drivers school, e.g. Summit Point Turn 1)

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That's pretty close to my back-of-the-envelope. Note that as you drive faster and then break, the temp increase goes up a lot -- because your initial energy goes up like v^2. Ouch.

In any case, 500F paint should do the job. And you're right, the rotors will likely take most of that heat.


disclaimer: I don't think this link is selling anything: http://www.unofficialbmw.com/e28/bra...ake_temps.html

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2002 Acura TL Type-S Dark Emerald Pearl
1986 Pontiac Fiero SE V6
1994 Ford Explorer 4x4

EricL

I just love Physics, so I enjoyed that. I'll have to head back to Burbank for more auto books.

Just a thought...

While the logic is flawless, there is one point that has come up in the CLS group regarding our "under" braked cars. A number of members have experience fade from 3 100-0 stops. One of the guys now has Brembos with pads, Dot4 fluid, etc to keep from fading after 2-3 laps.

1. In the HELMS there is a temp light that will come on when the temp gets too hot. It lets the driver know that the VSA will not work! (I don't know the temp, but this might be a good place to get a temp idea)

2. The problem seems to be not in the conversion of kinetic energy to heat, but in the entire heat system. The rotors seem to be unable to unload the heat from multiple stops from 80+ to 0 MPH. So, the heat is being stored in the rotors up to point (depending on their thermal mass). Then there is radiation, convective, and conductive cooling. Since the brakes are not ducted, the heat gets a little flow across the wheels, but no real ducts. It seems that a good deal of heat flow from some quicky experiments (checking the heat of my wheels after braking) demonstrates that a lot of heat is being dissipated via conduction through the wheels (and via some radiation and convection). I think thermal inertial/bulk properties of the rotors, and combined thermal junctions (with unmodeled thermal impedances and unqualified specific heats) is doing a lot of the work. (i.e -- rotor to hub, hub to wheel, wheel to air, etc)

The problem is this -- in multiple stops, an equilibrium state is not reached, so, if you can run your math again and re-figure using 3 or 4 runs with minimal heat loss, that might be a better indicator of max temp. I know that the radiative heat is related to the difference in 4th power temps (so this may be critical), but what I'm trying to convey here is the multiple stop issue, and the lack of good heat cooling between stops.


Sorry, for the science crud...

bbjones

EricL,

Good points.

A couple of things: first of all, that calculation says that you will add 70F to your brakes *every time* you go from 60-0. As you've correctly pointed out, if you do that again and again, and the brakes can't cool in between, the temperature will keep rising. In principle, I suppose, you could get the temp high enough to start melting the aluminum, and warp your rotors.

Also, 100-0 is a lot different than 60-0, because the speed is squared. Running through that same calc, I get that 100-0 would add nearly 200F to your brakes.

Finally, you are right that we haven't tried to account for the heat dissipation. I'm sure a lot goes to the wheels and axle; the tires are also dumping heat into the wheels. Racing (with multiple braking, w/o time to cool) will heat up your brakes a lot more than driving around town.

New bottom line: AcuraTLFan, if you are going to race with your brakes, you might want to be more careful. The rotors will be the hottest part.

one more thing: I tried the water trick last night. The rotors were indeed hot enough to boil the water. They were not, in fact, glowing. The caliper assembly was warm to the touch, but not hot enough to be uncomfortable.


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2002 Acura TL Type-S Dark Emerald Pearl
1986 Pontiac Fiero SE V6
1994 Ford Explorer 4x4

dbox

i made my civic brakes glow like that once! dnt paint ur rotors man. leave it 2 the civics

Black TL

I painted one side of my car with high heat metallic silver paint and the other with some chrome car spray paint. Obviously, I am not going to leave it like this. I just wanted to see what it would look like. Anyway, I was looking at my chrome paint and you can see how hot it really gets. The paint has bubbles all over and is soft now. However, the paint I used last year (same one as the silver metallic I used again) looks the same.


Roshan

Fiddler

dont forget, your calipers dont get nearly as hot as the discs and the brake pads... the calipers dont come into direct contact with the discs... after a 30 mile trip on the highway, if u touch the brake disc, you'll probably burn your finger, but the calipers are just warm .. definitely nowhere near 500 .. not even near 212 ... so i think 500 degree paint would be just fine

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-Fiddler
ControlGenie Automation Systems
1998 Accord EX V6 Coupe (HomePage)

91M5

Good posts.

Want some practical advice? I bought black engine paint at Autozone and painted my Euro M5 4 piston calipers with about 3 coats. After three driving schools, where the brakes were sometimes hot enough to smoke when entering the pits, no flaking or blistering. This when pulling a 3800+lb car down from 115mph multiple times in 20 minutes.

I don't think you will have a problem with a mostly street driven Acura.



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91 M5
Dinan stuff
18" BBS RC's
340hp

Road Rage

Lots of ink on this topic - the calipers don't get nearly as hot as the rotors. They stay close to the temperature of the fluid, which is never going to get as hot as the temp limit of the paint - this is a no-brainer!

Just remember to change your brake fluid every two years (at least) to avoid water contamination.